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A series of cationic tamarind seed polysaccharides (CTSPs) with different degrees of substitution were synthesized by etherification of tamarind seed polysaccharides (TSP) with 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTAC). By elemental analysis, zeta potential and FTIR, the successful linking of cationic groups on the chain of TSPs were confirmed, and the substitution degrees were determined as 0.143, 0.197 and 0.346, respectively. NMR data indicated that the quaternary ammonium groups were linked to C6 of T-Gal. Subsequently, the flocculation behaviors of CTSPs in kaolin solution were investigated, and the results showed that both the degree of substitution and pH affected their flocculation properties. Charge neutralization and positional blocking effects caused flocculation to show an increasing and then decreasing trend with increasing substitution of CTSPs, whereas the lower the pH, the less flocculant was required to achieve the same flocculation effect. The presence of positive charges allowed CTSPs to effectively remove negatively charged waste water such as kaolin suspensions. [Display omitted] • A novel cationic tamarind seed polysaccharide-based flocculant (CTSP) was designed and prepared. • The surface of CTSPs was more rough and uneven than that of TSP. • CTSP showed excellent flocculation ability in neutral and acidic range. • Charge neutralization plays a leading role in the process of flocculation. [ABSTRACT FROM AUTHOR]

Passive daytime radiative cooling (PDRC) is a cooling technology with no energy consumption and no pollution generation. It emits self-generated heat to outer space using thermal radiation, thus reducing its temperature. Radiative cooling technology aims to the energy consumption problem of buildings and environmental pollution caused by the use of Freon in compressor air conditioners. Many kinds of radiative cooling coatings have been attempted, but the cost and large-scale practical application have been challenging. This work prepared a composite coating with a radiative cooling function using calcined kaolin (CK) powder and waterborne fluorocarbon (WF). The inexpensive CK has a wide particle size distribution and exhibits high solar reflectivity (RS) and infrared emissivity (EIR). The excellent adhesion and chemical stability of waterborne fluorocarbon (WF) provides a good guarantee for the practical use of the coating. As a result, the CK/WF coating achieves an RS of 91% and an EIR of 95% in the transparent atmospheric window (ATW) of 8–13 µm. The coating demonstrated a temperature decline of 3.8 °C under direct sunlight in the field. The coating meets the conditions for large-scale applications. When used as a roofing material for simulation, it can save up to 30% of energy consumption throughout the year. Overall, the CK/WF coating has outstanding energy saving and pollution reduction performance, which will further advance the radiant cooling material into real-world applications. [Display omitted] • The RS and EIR of Calcined kaolin/ water-based fluoro olefin vinyl ether copolymer (CK/WF) coating reached 91% and 95%. • The low powder content of the CK/WF coating provides high adhesion force. • Cheap CK powder provides a new idea to reduce the cost of radiation-cooling coating. • Under direct sunlight, the CK/WF coating can achieve a cooling effect of − 3.8 °C. • EnergyPlus simulations show that the coating could save 10% of energy consumption in most areas of China. [ABSTRACT FROM AUTHOR]

Passive daytime radiative cooling (PDRC) coatings for building exteriors are important for building energy efficiency. The development of inexpensive and environmentally friendly radiative cooling (RC) coatings with high adhesion, waterproofing and UV-ageing resistance for building facades remains a highly challenging task. In this work, kaolin/polyacrylate (K/P) paints with excellent overall performance were prepared by spraying method using green waterborne acrylate as binder, cheap and easily available K as filler, and polymethylhydrosiloxane (PMHS) as hydrophobic modifier. The K/P coating has excellent optical properties with a solar reflectivity (SR) of 86.6% and an infrared thermal emissivity (ITE) of 96.8%. RC temperatures of 13.2 °C (under shielded condition) and 3.1 °C (under open condition) were achieved under direct outdoor daylight with an average irradiance of 778 W/m2. In addition, building energy simulations show that the K/P coating improves heating energy consumption while reducing building cooling energy consumption. However, for most cities in China, the energy savings of the K/P coating on annual building energy consumption is still as high as 6.6%. In particular, the K/P paint used as an exterior wall coating has high adhesion, excellent water resistance, and strong UV ageing resistance, and its optical properties (solar reflectance and infrared thermal emittance) remain unchanged after 10 accelerated ageing cycles. Therefore, the K/P coatings have excellent comprehensive performance and have a wide range of application prospects in the field of green and energy-saving buildings. [Display omitted] • The kaolin/polyacrylate (K/P) coatings can be produced on a large scale. • The K/P coating uses water as a solvent and do not pollute the environment. • The K/P coating achieved a sub-ambient temperature drop of 13.2 °C under direct sunlight. • The K/P coating exhibits high adhesion strength, excellent water resistance and strong ageing resistance. • Building energy consumption simulation shows that the CK/P coating can save about 6.6% of energy. [ABSTRACT FROM AUTHOR]

Aggregation is an economical and widely existing method to in fine particles dewatering, but the mechanism of composite applications of inorganic coagulants/flocculants remains unclear. In this work, the aggregation process of kaolin particles using Fe(III) and xanthan gum (XG) was investigated by settling testing. The results shows that the combination XG and Fe(III) was effective in the flocculation of kaolin, which due to the self-assembly multilayers built onto the surface of kaolin. Further, density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) analyses were performed to detect the flocculation mechanism. It was found that [Fe(Ⅲ)(OH)]2+, [Fe(Ⅲ)(H 2 O) 6 ]3+ and [Fe(Ⅲ)(OH) 2 ]+ were the dominant species, which could complex with the XG on kaolin surface by the Fe-O adsorption site. However, the precipitate Fe(OH) 3(s) covered on the kaolin surface is difficult to combine XG by coordination reaction under alkaline conditions. The research elucidated a new insight into of composite applications of inorganic coagulants and flocculants which could expand our knowledge of aggregation process, further define the relationship between coagulation and flocculation for enhancing colloidal particle settling in practical application. [Display omitted] [ABSTRACT FROM AUTHOR]

A simple and effective preparation method of the powder surface coating was found. Namely, spraying hydroxyl-silicone oil (HSO) ethanol solution on the surface of calcined kaolin and nano-TiO 2 composite (CKT) powder and formed the HSO layer due to the volatilization of ethanol. Subsequently, the samples were heated at 250 ℃ to form the HSO cure coating. The FT-IR, MAS NMR, XPS and SEM measure results indicate that the surface modification reaction occur between the OH groups in HSO molecules and HO-AlVI in the calcined kaolin. No any chemical reaction carry out on the Si, Ti sites on the surface of CKT composites. The performance testings show the HSO modification reaction dramatically improve the hydrophobicity of the CKT composites. The modification coating has no any negative effect on the whiteness, but the oil absorption values slightly reduce. Interestingly, it increases again after curing because the HSO layer releases a large great of lipophilic groups such as CH 3 and CH 2 during the curing process. The comparison of performances with nano-TiO 2 and calcined kaolin shows that the CKT composites are expected to replace nano-TiO 2 in many fields. A simple and effective manufacture method of the powder surface coating was found. Namely, spraying hydroxyl-silicone oil (HSO) ethanol solution on the surface of the calcined kaolin and nano-TiO 2 (CKT) composite powders, then heat cured, finally formed a HSO cured coating on the powder surface.The analysis on the measure results of a series of characterization sucha as FT-IR, MAS NMR, XPS and SEM indicated that the surface modification reaction occurred between the OH groups in HSO molecules and HO-AlVI in the calcined kaolin. No any chemical reaction carried out on the Si, Ti sites on the surface of CKT composites. The curing process made the HSO coating removal a larger amount of CH 3 and CH 2 groups, meanwhile formed a cured coating on the surface, which coated the CKT mixture powder outside itself and formed a modified powder particles. The whole modification reaction included three steps: ① hydration reaction between HSO and HO groups on the surface of the CKT composites; ② autopolycondensation betwee HSO molecules; ③ oxygen gas oxidized and formed new network consisted Si-O-Si on the surface of particles. The CH 3 and CH 2 groups removed and formed of Si-O bonds during the curing process. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, raw kaolin clay was activated with a strong base solution in order to improve its surface characteristics and adsorption performance. The alkali activation evidently caused etching process and ion exchanges of both Al3+ and Si4+ with Na+ on the silica and gibbsite basal surfaces, enhancing the surface area of the kaolinite particles. Adsorption of rifampicin (RIF) on the raw and alkali-activated kaolin was well described by the Langmuir isotherm and the pseudo-second-order kinetics models. The maximum adsorption capacity of RIF on the alkali-activated kaolin was 8.295 mg g−1, enhanced compared with the raw kaolin (5.931 mg g−1). The adsorption was due to weak electrostatic and hydrogen bonding interactions between RIF and the kaolinite surfaces. Adsorption mechanism, kinetics, rate limiting-step, and thermodynamics were described in detail by fitting mathematical functions of the established semiempirical models to the experimental data. The recyclability of the kaolin-based adsorbents was demonstrated by their effective regeneration. Overall, the alkali activation improves the adsorption performance of kaolin to be practically applicable as environmentally friendly and sustainable absorbents for the removal of RIF and probably other pharmaceutical compounds from hospital wastewater. [Display omitted] ● Alkali activation has improved the surface characteristics of raw kaolin. ● Adsorption capacity of rifampicin (RIF) on the alkali-activated kaolin was enhanced. ● Adsorption of RIF was well described by the Langmuir and pseudo-second-order models. ● Adsorption mechanism of the removal of RIF on the kaolin-based adsorbents was proposed. ● Recyclability of the kaolin-based adsorbents was demonstrated by their effective regeneration. [ABSTRACT FROM AUTHOR]

Aggregation is an economical and widely existing method to in fine particles dewatering, but the mechanism of composite applications of inorganic coagulants/flocculants remains unclear. In this work, the aggregation process of kaolin particles using Fe(III) and xanthan gum (XG) was investigated by settling testing. The results shows that the combination XG and Fe(III) was effective in the flocculation of kaolin, which due to the self-assembly multilayers built onto the surface of kaolin. Further, density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) analyses were performed to detect the flocculation mechanism. It was found that [Fe(Ⅲ)(OH)]2+, [Fe(Ⅲ)(H 2 O) 6 ]3+ and [Fe(Ⅲ)(OH) 2 ]+ were the dominant species, which could complex with the XG on kaolin surface by the Fe-O adsorption site. However, the precipitate Fe(OH) 3(s) covered on the kaolin surface is difficult to combine XG by coordination reaction under alkaline conditions. The research elucidated a new insight into of composite applications of inorganic coagulants and flocculants which could expand our knowledge of aggregation process, further define the relationship between coagulation and flocculation for enhancing colloidal particle settling in practical application. [Display omitted] [ABSTRACT FROM AUTHOR]

A simple and effective preparation method of the powder surface coating was found. Namely, spraying hydroxyl-silicone oil (HSO) ethanol solution on the surface of calcined kaolin and nano-TiO 2 composite (CKT) powder and formed the HSO layer due to the volatilization of ethanol. Subsequently, the samples were heated at 250 ℃ to form the HSO cure coating. The FT-IR, MAS NMR, XPS and SEM measure results indicate that the surface modification reaction occur between the OH groups in HSO molecules and HO-AlVI in the calcined kaolin. No any chemical reaction carry out on the Si, Ti sites on the surface of CKT composites. The performance testings show the HSO modification reaction dramatically improve the hydrophobicity of the CKT composites. The modification coating has no any negative effect on the whiteness, but the oil absorption values slightly reduce. Interestingly, it increases again after curing because the HSO layer releases a large great of lipophilic groups such as CH 3 and CH 2 during the curing process. The comparison of performances with nano-TiO 2 and calcined kaolin shows that the CKT composites are expected to replace nano-TiO 2 in many fields. A simple and effective manufacture method of the powder surface coating was found. Namely, spraying hydroxyl-silicone oil (HSO) ethanol solution on the surface of the calcined kaolin and nano-TiO 2 (CKT) composite powders, then heat cured, finally formed a HSO cured coating on the powder surface.The analysis on the measure results of a series of characterization sucha as FT-IR, MAS NMR, XPS and SEM indicated that the surface modification reaction occurred between the OH groups in HSO molecules and HO-AlVI in the calcined kaolin. No any chemical reaction carried out on the Si, Ti sites on the surface of CKT composites. The curing process made the HSO coating removal a larger amount of CH 3 and CH 2 groups, meanwhile formed a cured coating on the surface, which coated the CKT mixture powder outside itself and formed a modified powder particles. The whole modification reaction included three steps: ① hydration reaction between HSO and HO groups on the surface of the CKT composites; ② autopolycondensation betwee HSO molecules; ③ oxygen gas oxidized and formed new network consisted Si-O-Si on the surface of particles. The CH 3 and CH 2 groups removed and formed of Si-O bonds during the curing process. [Display omitted] [ABSTRACT FROM AUTHOR]

Wastewater containing polluting nanoparticles during purification is an emerging concern that has created the need to develop more efficient methodologies of wastewater treatment. Therefore, this contribution provides a study regarding the removal of gold and silver nanoparticles stabilized with poly(vinylpyrrolidone) (AuNP-PVP and AgNP-PVP) using flocculation at concentrations of 1.5 and 7.5–8 mg/L in kaolin aqueous dispersions. With this goal in mind, chitosan was grafted with poly(N -vinylcaprolactam)(PNVCL) and poly(acrylic acid)(PAAc) (CS- g -PNVCL, CS- g -PNVCL-PAAc), which was verified by characterization using NMR-spectroscopy, thermogravimetric analysis, dynamic light scattering, and zeta potential measurements. At pH 7, the graft copolymers presented a lower zeta potential than chitosan (close to zero), and the PVP-stabilized nanoparticles exhibited a negative surface charge (around −20 mV). The bridging mechanism during the flocculation process was discovered to be responsible for improving the performance of chitosan using chitosan-based graft polymers with low concentration (0.5 mg/L). CS- g -PNVCL-PAAc allowed higher turbidity reduction (82%), while CS- g -PNVCL was the best flocculant in nanoparticle removal (94% from 7.5 mg/L), at room temperature. The flocculants showed higher ability towards the removal of AgNP-PVP, as compared to AuNP-PVP. By increasing the temperature to 45 °C, the turbidity removal increased, while the nanoparticle removal only improved when the CS- g -PNVCL-PAAc flocculant was used. The effectiveness of chitosan-based flocculants for the removal of metallic nanoparticles as emerging contaminants is reported for the first time. Besides, the removal efficiency of metallic nanoparticles by flocculation is superior as compared to adsorption methods. [Display omitted] • Flocculation performance of chitosan was surpassed by chitosan-based graft copolymers. • A low flocculant dosage of 0.5 mg/L was enough for removal of AuNP and AgNP. • The bridging mechanism was identified as being responsible for nanoparticles removal. • Flocculant CS- g -PNVCL allowed high AgNP-PVP removal: 94% from 7.5 mg/L in 60 min [ABSTRACT FROM AUTHOR]

To generate effective dispersants for kaolin suspensions, it is important to study how the properties of dispersants affect their performance in suspensions. In this work, kraft lignin was modified via oxidation with nitric acid under varied conditions to produce oxidized lignin (OL) with different charge densities and molecular weights. The effects of anionic charge density and molecular weight of the lignin based products on the dispersion and sedimentation of kaolin particles were studied fundamentally. The adsorption of OLs on particles as well as the changes in the zeta potential, relative turbidity, hydrodynamic diameter and sedimentation of particles under static (non-stirring) and dynamic (stirring) conditions were systematically investigated. Dispersion studies suggested that both charge density and molecular weight had great impacts on the stability of kaolin particles. Sample OL8 with the charge density of −3.6 meq/g and molecular weight (Mw) of 30,243 g/mol was the most effective dispersant for kaolin suspension. The hydrophilicity of OLs were similar and thus did not affect the dispersion analysis. [ABSTRACT FROM AUTHOR]

With the development of industries, copper nanoparticles (Cu NPs) have been abundantly discharged into natural water and may threaten the safety of aquatic environments. The stability (such as homoaggregation and heteroaggregation) of Cu NPs in aqueous phase may affect their toxicity. Turbiscan, including three kinds of data processing methods (transmitted intensity (T), variation of average transmitted intensity (ΔT) and Turbiscan stability index (TSI), were used to investigate the homoaggregation and heteroaggregation of Cu NPs with humic acid (HA) and kaolin in aqueous phase. T and TSI were used to analyze Cu NPs-kaolin and Cu NPs-HA-kaolin systems, respectively, whereas T and ΔT were used to analyze Cu NPs and Cu NPs-HA systems. Results showed that the stability of the system is influenced by the dissolution and sedimentation of Cu NPs, and the aggregation and sedimentation of Cu NPs, HA and kaolin. When pH is 4, the dissolution of Cu NPs is the main factor affecting the system stability. Kaolin may reduce the stability of system by sedimentation or impeding the dissolution of Cu NPs. When pH is 8, the aggregation and sedimentation of Cu NPs mainly affect the system stability. Kaolin renders the system unstable by promoting the aggregation of Cu NPs. In addition, HA improves the stability of the system by inhibiting the aggregation of Cu NPs and kaolin when pH = 4 and 8. Ionic strength reduces the stability of system by condensing electric double layer. Therefore, Turbiscan can be used to study both homoaggregation and heteroaggregation in a relatively long period (12 h), and three kinds of data processing methods can be applied based on the properties of the samples. [ABSTRACT FROM AUTHOR]

Influence of sensor surface quality on apparent wall slip (AWS) effects in aqueous kaolin suspensions was studied using AWS rotational viscometry with four unconventional cone-cone (KK) sensors of different materials and surface finishing. The fluidity φ [ σ ] and slip χ [ σ ] material functions were obtained for three concentrations of kaolin (30, 35, and 40 wt.%) applying several gap thicknesses (between 0.6 and 1.6 mm). Positive slip coefficients were found in the sensors made from titanium or stainless steel with smooth or sand-blasted surfaces. A negative AWS effect was detected for the sensor made of aluminum alloy with eloxal coated surfaces. This negative AWS effect is interpreted as a consequence of possible formation of a stagnant layer at the walls. [ABSTRACT FROM AUTHOR]

In this work, the influence of pH and ionic strength on the flocculation performance of cationic xylan copolymer in kaolin and bentonite suspensions was systematically investigated. The cationic xylan was produced via copolymerizing xylan with 2-(methacryloyloxy ethyl) trimethylammonium chloride (METAC), and the cationic xylan copolymer (CMX) showed a maximum adsorption of 4.6 and 1.8 mg/g on kaolin and bentonite particles at the CMX dosage of 8 mg/g, pH 10, 30 °C and 1 h, respectively. The reduction in charge density of CMX from 2.66 to 2.48 meq/g was observed, with an increase in pH of CMX solution to from 2 to 10. The maximum increase in the zeta potential of kaolin (+54 mV) and bentonite (−3 mV) suspensions and the highest removal of kaolin (75%) and bentonite (96%) from the suspensions were obtained at 8 mg/g CMX and pH 7. Stability studies revealed that pH had a noticeable influence on the sedimentation of kaolin and bentonite particles. CMX increased the destabilization index of kaolin (0.4–45) and bentonite (0.2–51) suspensions by increasing the floc size of kaolin and bentonite particles to 9.5 μm and 12.7 μm, respectively. CMX removed more of bentonite than kaolin at any pH under static and dynamic conditions. The impact of inorganic salts on the removal of kaolin particles was also studied. CMX exhibited better performance than a commercial flocculant (PDADMAC) in flocculating the commercially produced effluent. [ABSTRACT FROM AUTHOR]

Breakage and regrowth of flocs has been studied for several years, however little attention was paid to the regrowth ability of broken micro-flocs which are mainly formed during the initial flocculation stage. In this paper, a continuous optical monitoring method was employed to investigate the kinetics of flocs formation, and especially more evident flocs properties (strength and recovery factor) were also explored. The results showed that breakage at the beginning of flocculation stage can improve flocs regrowth to greater sizes when the coagulation was initially dominated by charge neutralization at a predetermined dosage. Furthermore, second dose of different coagulants during this breakage process improved kaolin particles removal efficiency to varying degrees. Separately, the second dose of Al 2 (SO 4 ) 3 continuously enlarged the floc size with the increasing dosage, contrarily that of PACl reduced the floc size. Based on the analysis of flocs properties, this phenomenon can be well explained by the difference between coagulation mechanisms under the second dose of Al 2 (SO 4 ) 3 and PACl respectively: newly formed hydroxides of Al 2 (SO 4 ) 3 enhanced broken flocs regrowth to larger sizes and entrapped more particles (lower residual turbidity) by sweep flocculation; that of PACl formed compact flocs due to stronger electric density of Al hydroxides. It was worth noting that turbidity removal performance was even better when the overall dosage by second dose only counted for ∼70% of one-time dose. Importantly, this study aimed at providing a feasible economic dose strategy for the real coagulation-flocculation application. [ABSTRACT FROM AUTHOR]

The flocculation by compositions, based on synthetic poly-1,2-dimethyl-5-vinylpyridinium methyl sulfate (K1),poly-trimethyl(methacryloyloxyethyl)-ammonium methyl sulfate (K2) and natural polyelectrolyte (chitosan, Cs) using an aqueous kaolin dispersion was studied. Floccule formation parameters and sedimentation rates were determined by optical microscopy, turbidimetry and microelectrophoresis. The synergistic effect is observed using the polyelectrolyte compositions, it appears in 40% increase of the floccule sedimentation rates and promotes the formation of two times more dense floccules compared to using individual flocculants. The synergistic effect of two cationic polyelectrolytes was confirmed by the flocculation research results in aqueous-salt solutions at various NaCl salt concentrations. A study of the behavior of the two polyelectrolytes macromolecules in solution was performed to explain the observed synergistic effect. The decrease of macromolecules hydrodynamic radius in the joint presence of two like-charged polyelectrolytes was revealed by the capillary viscometry, dynamic and static light scattering. It was determined, that the behavior of two cationic polyelectrolytes in the common solution determines the character of their behavior on the dispersed phase surface in the flocculation process. [ABSTRACT FROM AUTHOR]

We perform an experimental study of the rheology of a foamed non-reactive particulate paste. The paste is a concentrated suspension of metakaolin, a material commonly used in the production of ceramics and in the construction industry. Most manufacturing processes of porous ceramics or foamed building materials require the preparation and handling of a foamed slurry. The slurry is a concentrated particulate paste, which has a non-Newtonian rheology. In particular, a minimum stress is necessary to make it flow: it is a yield stress fluid. We systematically investigate the influence of bubble addition on the workability of our metakaolin slurry by dispersing bubbles of known radius at a chosen volume fraction in the surfactant-laden metakaolin paste. We perform rheometry measurements to characterize the minimum stress required for the foamed materials to flow (yield stress), and the dissipation occurring during flow. We show that the yield stress of the foamed samples is equal to that of the metakaolin paste, and that dissipation during flow increases quadratically with the bubble volume fraction. We show that this behaviour can be well understood from the recent results of Ducloué et al. [7] . This agreement suggests that the results we present here on foamed metakaolin samples may apply to a broader class of foamed particulate pastes. [ABSTRACT FROM AUTHOR]

Geopolymers are innovative mineral binders. These materials are still under research development in order to better understand the formation mechanism, the local structure and the final working properties. The aim of this study is to provide predictive tools permitting to control the geopolymerisation reaction. At first, it is important to determine the parameters responsible of raw materials reactivity. For alkaline solutions, the siliceous species distribution and connectivity control the reactivity. Concerning metakaolins, the Si/Al molar ratio, the wettability value, the amorphous phase content and the amount of reactive tetrahedral aluminum are responsible of metakaolin reactivity. Moreover, the reactivity of raw materials was proven to determine the geopolymer existence domains in the Si–Al–M/O ternary diagram. Thermal analysis during and after curing give informations about the amount of water consumed during the reaction and trapped in the final structure as well as the energy required for oligomer formation which seem to be directly related to raw materials reactivity. The pores distribution and size are also influenced by raw materials reactivity. Reactive precursors, especially reactive alkaline solutions, induce higher densification rate and, therefore, lower porosity and larger pore size. Furthermore, reactive precursors favor the formation of geopolymer network. This fact was evident by 29 Si NMR. As a consequence, the increase of geopolymer phase in the structure improves the mechanical strength while the competition of different networks is source of weakness. [ABSTRACT FROM AUTHOR]

Aluminosilicate mineral Kaolin-loaded nanocomposite beads containing cationic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and thermoresponsive N-isopropylacrylamide (NIPA) have been successfully synthesized by combined method of dropwise freezing into cryogenic liquid and sedimentation cryogelation. Hertzian elasticity, thermal stability, and responsive-swelling properties were investigated. The nanocomposite gels exhibited better mechanical properties and thermal stability than neat copolymer gels. The stress and displacement distribution on surface of Kaolin-loaded nanocomposite beads were evaluated with classical Hertz theory, and the results were compared with the results obtained from Rubber elasticity theory. The scaling relationship for contact stress and surface displacement was obtained assuming Hertz's small contact area, and the compression force was scaled with displacement with an exponent of 1.34 ± 0.08. The elastic properties directly attributed to effective potential showed that Hertz potential is valid for small deformations and the elastic modulus decreased with the swollen bead diameter. Addition of Kaolin and NIPA to PDMAEMA-based network has opposite effect on the mechanical properties. The elastic modulus increased, but the swelling ratio decreased with addition of Kaolin. The opposite behavior was observed when NIPA was added, the swelling increased and the mechanical properties weakened. All gels showed significant temperature sensitivity as a result of combination of PDMAEMA and PNIPA, while the swelling was higher at acidic pH than alkaline pH. An overshooting effect attributed to the dynamic conformational changes of tertiary amine of DMAEMA was observed during swelling in pH 3.6. The increase in network density of nanocomposite gel with addition of Kaolin leads to slower relaxation of molecules, and water absorption tends to become relaxation-controlled. An increase in diffusion exponent is observed as diffusion changes from Fickian to non-Fickian. Influence of single salts; NaCl, KCl and K 2 CO 3 on swelling of nanocomposites was investigated. The swelling of Kaolin-loaded nanocomposites decreased with increasing ionic strength, and a "salting-out" effect was observed. The use of naturally occurring nanoscale particles in such structural material design is an important method for biomedical applications and separation technology. [Display omitted] • Design of Kaolin-containing nanocomposite beads of DMAEMA and NIPA. • Combination of dropwise freezing into cryogenic liquid with sedimentation cryogelation. • Evaluation of stress and displacement distribution with classical Hertz theory. • Hertz modulus decreased monotonically with the swollen bead diameter. • Excellent temperature, pH and salt-responsive swelling of nanocomposite beads. [ABSTRACT FROM AUTHOR]

Composite NaMnt (SWy-2)-kaolin (KGa-2) gels at more than 10 wt% solids with the NaMnt fraction ≥ 20% formed an open cellular microstructure. The flexible, nanosized NaMnt platelets formed the continuous structure with kaolin particles dispersed within it bonding with the NaMnt platelets. The morphology adopted by the single layer NaMnt platelets is varied and complex producing a wide range of unique particle interaction configurations. Many acquired a curved shape surface with curled edges. Some of the platelets developed elongated string-like features made by the curling of edges and may have 3–5 of these strings for bonding. Kaolin particles are rigid and multilayered, and most have a platelet morphology. A common NaMnt-kaolin bonding configuration observed was the face at the curled-edge of NaMnt platelet resting on the face of the kaolin particle. A 15.5 wt% gel with a 1:2 mass ratio of NaMnt to kaolin was demonstrated to display both thixotropic and rheopectic behavior. A stepdown shear rate method was used to evaluate the structural development kinetics at 10 s−1 of this gel commencing with the structural state sheared to equilibrium at 1000 s−1. The Leong model described this kinetics well and found that the structural development characteristic time to be very fast, in seconds. The ageing behavior was also evaluated without the imposition of a constant shear. The yield stress increase continued for weeks and months for the 2:1 kaolin to NaMnt composite gels at 15.5 and 10.7 wt% solids. The characteristic time of the structural development process was much longer, in days. Upon reducing the NaMnt content from 33.3% to 20%, the 10.8% wt% gel became weakly time-dependent with a marginal yield stress. A continuous structure cannot be formed immediately upon the cessation of shear due to an inadequate NaMnt platelet concentration. [Display omitted] [ABSTRACT FROM AUTHOR]

Aluminosilicate mineral Kaolin-loaded nanocomposite beads containing cationic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and thermoresponsive N-isopropylacrylamide (NIPA) have been successfully synthesized by combined method of dropwise freezing into cryogenic liquid and sedimentation cryogelation. Hertzian elasticity, thermal stability, and responsive-swelling properties were investigated. The nanocomposite gels exhibited better mechanical properties and thermal stability than neat copolymer gels. The stress and displacement distribution on surface of Kaolin-loaded nanocomposite beads were evaluated with classical Hertz theory, and the results were compared with the results obtained from Rubber elasticity theory. The scaling relationship for contact stress and surface displacement was obtained assuming Hertz's small contact area, and the compression force was scaled with displacement with an exponent of 1.34 ± 0.08. The elastic properties directly attributed to effective potential showed that Hertz potential is valid for small deformations and the elastic modulus decreased with the swollen bead diameter. Addition of Kaolin and NIPA to PDMAEMA-based network has opposite effect on the mechanical properties. The elastic modulus increased, but the swelling ratio decreased with addition of Kaolin. The opposite behavior was observed when NIPA was added, the swelling increased and the mechanical properties weakened. All gels showed significant temperature sensitivity as a result of combination of PDMAEMA and PNIPA, while the swelling was higher at acidic pH than alkaline pH. An overshooting effect attributed to the dynamic conformational changes of tertiary amine of DMAEMA was observed during swelling in pH 3.6. The increase in network density of nanocomposite gel with addition of Kaolin leads to slower relaxation of molecules, and water absorption tends to become relaxation-controlled. An increase in diffusion exponent is observed as diffusion changes from Fickian to non-Fickian. Influence of single salts; NaCl, KCl and K 2 CO 3 on swelling of nanocomposites was investigated. The swelling of Kaolin-loaded nanocomposites decreased with increasing ionic strength, and a "salting-out" effect was observed. The use of naturally occurring nanoscale particles in such structural material design is an important method for biomedical applications and separation technology. [Display omitted] • Design of Kaolin-containing nanocomposite beads of DMAEMA and NIPA. • Combination of dropwise freezing into cryogenic liquid with sedimentation cryogelation. • Evaluation of stress and displacement distribution with classical Hertz theory. • Hertz modulus decreased monotonically with the swollen bead diameter. • Excellent temperature, pH and salt-responsive swelling of nanocomposite beads. [ABSTRACT FROM AUTHOR]

Kaolin based suspensions have wide range of applications such as slurry wall, drilling fluids, adhesives, cosmetics, refractories and pharmaceuticals, due to their abundance in nature, low cost and non-swelling nature. On the other hand, the unique properties (i.e., biodegradability) of biopolymers make them suitable candidate for variety of applications including modification of clay suspensions. In this study, the rheological properties of kaolin suspensions modified with different biopolymers (xanthan gum (XG), sodium carboxymethyl cellulose (CMC), potato starch (PS), chitosan (Ch) and apple fibre (AF)) have been investigated by varying the biopolymer type, content and clay content. The main objective of the present study is to propose a substitute for the natural mud sample. Frequency sweep tests, stress ramp-up tests and time-dependent tests were performed by using the Couette geometry (coaxial cylinders) for the prepared suspensions. The rheological results showed that both viscosity and moduli were significantly influenced by adding different biopolymers into the kaolin suspensions. For instance, an increase in viscosity of modified suspensions was observed: 3 – 4 orders of magnitude by adding xanthan gum (1 wt%) or sodium carboxymethyl cellulose (5 wt%) and 6 orders of magnitude by adding apple fibre (5 wt%). Likewise, the incorporation of different biopolymers significantly affected the complex modulus of modified clay suspensions. For example, similar or higher values of complex modulus than the pure kaolin suspension were observed at low xanthan gum or sodium carboxymethyl cellulose content (0.1 wt%). In case of chitosan, the complex modulus of the modified suspensions was higher than the complex modulus of pure kaolin suspension, even at very low polymer content (1 wt%). In the case of potato starch, a decrease in complex modulus by increasing polymer content till 10 wt% was observed followed by an increase in complex modulus with polymer content. The shear rate ramp-up and ramp-down experiments showed that the time-dependent behaviour of kaolin suspensions was not strongly influenced by adding different biopolymers. This knowledge will provide a base to choose a suitable substitute for the natural mud sample. [Display omitted] [ABSTRACT FROM AUTHOR]

A method for preparing hydrophobic silica aerogel with kaolin as raw material and dried at ambient pressure is proposed. The process of preparing the aerogel consists of three stages including activation of kaolin, preparation of wet silica gel and hydrophobic modification. The effects of hydrochloric acid concentration on the physical properties and structures of the silica aerogel are investigated. Effects of removing Na + from the solvent solution on the structure and properties of aerogel are discussed. The aerogel obtained with kaolin has comparable structure and property to those prepared with other more expensive silica sources. The newly proposed method is expected to simplify the manufacturing technique, to shorten the production time and to reduce the costs of silica aerogel. [ABSTRACT FROM AUTHOR]

Application of magnesium hydroxide as a coagulant for treating reactive dyes wastewater assisted with kaolin was studied. The coagulation performance and floc properties were investigated under different dosages and initial turbidity. The relationship between Flocculation Index (FI) and reactive dyes removal was then discussed with controlled experiments using intelligent Particle Dispersion Analyzer (iPDA). Kaolin clay had significantly influence on floc formation and reactive dyes removal. The suitable magnesium ion dose of 144 mg/L was obtained under initial turbidity of 45 NTU and pH value of 12. The results showed that final turbidity decreased with increasing coagulant dose. Reactive dyes removal efficiency tended to increase with the increase of initial turbidity of kaolin. The experiments showed that the higher FI value of the system, the higher reactive dyes removal efficiency was obtained. Floc image showed that average floc size of reactive red (X-3B) is smaller than that of reactive yellow (X-R). Based on the changes of zeta potential and floc properties, charge neutralization and precipitate enmeshment were proposed to the main coagulation mechanisms. [ABSTRACT FROM AUTHOR]

This study investigated the surface chemistry–microstructure–rheology relationship of two very well characterised, low impurity CMS source kaolinites; low defect KGa-1b and high defect KGa-2. The knowledge gained will improve the overall understanding by acting as a reference material for comparison with other studies. The trend of the yield stress–pH result was adopted to investigate kaolinite properties or factors that affect this trend. Both the KGa-1b and KGa-2 kaolinite slurries displayed similar zeta potential–pH and yield stress–pH behaviour. Crystallinity and particle size therefore did not affect the trend of the yield stress–pH and zeta potential–pH behaviour. The larger yield stress of the finer KGa-2 slurries is due to a higher particle concentration. Both kaolinite slurries exhibited a maximum yield stress at zero zeta potential. Their yield stress–solid volume fraction data were found to obey a power law model with the same exponent value of 3 accounting for a fractal dimension of 2.3 unaffected by pH. Cryo-SEM images of the vitrified microstructure of 35 wt% KGa-1b and 15 wt% KGa-2 suspensions at the maximum yield stress showed a 3-D microstructure formed by compacted clay aggregates which themselves are formed by a mixture of particle interaction configurations – face–face with stair–step feature and edge–face. Particle interaction modelling was discussed. [ABSTRACT FROM AUTHOR]

In this study, novel cationic polyamidine (Pa) was synthesized and used as coagulant aid with aluminum sulfate (AS) for kaolin-humic acid simulated water treatment. The effects of Pa on coagulation performance and floc properties were investigated. Results showed that Pa addition significantly enhanced the removal of turbidity, ultraviolet absorbance at 254 nm wavelength (UV 254 ) and dissolved organic carbon (DOC). AS–Pa exhibited high coagulation efficiency at border pH range and increased floc size and growth rate significantly. Floc recovery ability was also improved, while floc fractal dimension was lower with Pa addition. This would be attributed to high cationic charge density and long chain of Pa, which could enhance the effect of charge neutralization and adsorption bridging. [ABSTRACT FROM AUTHOR]

Numerous studies on the surface charge-pH and yield stress-pH behaviors of kaolin slurries with respect to the pH-dependency of alumina (Al) sheets, silica (Si) sheets and edges in kaolin particles have been carried out. There is, however, still a paucity of studies that explain if the alumina sheets or the silica sheets in kaolin particles contribute in greater extents to the surface charges of kaolin particles that will consequently affect the kaolin particle interactions and yield stresses. In this study, the contributions of the alumina and the silica sheets to the zeta potential-pH and yield stress-pH behaviors of Riedel kaolin particles, which display no isoelectric points (IEPs), are analyzed by comparing these behaviors of Riedel kaolin slurries to that of alumina and silica slurries with and without Mg 2+ and Ca 2+ cations. With and without cations, the behaviors of Riedel kaolin slurries were more similar to the behaviors of silica compared to alumina slurries. The principal reason for this similarity is due to the high concentrations of negative charges on both silica and Riedel kaolin particles at all pH compared to the lower concentrations of negative charges on alumina particles. This explains that the permanently negatively charged silica sheets contribute in greater extents to the surface charge-pH and yield stress-pH behaviors of Riedel kaolin slurries compared to the alumina sheets. [ABSTRACT FROM AUTHOR]

The hybrid coagulation–microfiltration process has been used for water treatment plants. However, membrane fouling is still the major barrier for its application. In this study, the impact of interactions between natural organic matter and particles on fouling has been investigated. The model substances were kaolin, humic acid and aluminum as the coagulant. The results demonstrated that flux was almost kept constant for humic acid due to its linear structure. However, the flux of the synthetic solution decline was substantial. More interesting, the addition of aluminum with different dosages played a significant role in membrane filtration. With the low dosage of AlCl 3 as 0.06 mmol/L, there were no visible flocs, but the flux of the synthetic solution showed a noticeable decreasing due to the complexation of humic acid and aluminum. With the increase of aluminum, the flux was apparently improved for the flocs formed. It indicated that the dosage of coagulant was a key parameter to decide the effect of filtration since coagulation had both positive and negative effects on membrane fouling. Additionally, the experimental results also revealed that the floc structure and pore blocking might take the major responsibility for the flux decline. [ABSTRACT FROM AUTHOR]

Owing to their anisotropic surface charge and anisometric shape aqueous clay slurries are known to exhibit rich rheological behavior with the existence of yield stress at very low solids concentrations which can be modulated using different pH modifiers. The impact of particle-particle association on the rheological behaviour of two different clays, a swelling 2:1 (bentonite) and a non-swelling 1:1 clay (kaolin) was investigated. Effect of factors such as pH, pH modifiers, and solids concentration on the rheological behaviour was studied using Small Amplitude Oscillatory Shear (SAOS) and shear rheology. For kaolin, the microstructural strength as measured using storage modulus (G′) was reflected directly in the high shear response. However, for bentonite the high shear viscosity evolved non- monotonically as a function of G′ which was connected to its swelling behaviour. Cohesive energy density increased sharply as a function of volume fraction for bentonite compared to kaolin and may provide a basis for the stark contrast in industrial unit operation response of the two clays. The results highlight the importance of using several rheological material functions to understand the true microstructure of clay dispersions. [Display omitted] [ABSTRACT FROM AUTHOR]

The variations in rheological-pH behaviors between suspensions of low and high calcium (Ca) kaolin were evaluated via zeta potential, yield stress and sedimentation methods. Elemental analysis via x-ray fluorescence (XRF) showed that Riedel kaolin (0.028%) carries ∼18.0 times lesser Ca concentrations than Unimin kaolin where Riedel slurries displayed a maximum yield stress at ∼pH 2.0 when Riedel particles carried low negative zeta potential magnitudes while Unimin slurries exhibited a maximum yield stress at pH 8.6 when Unimin particles were highly negatively charged. With Ca 2+ cations added to Riedel slurries at sufficiently high concentrations, Riedel's negative zeta potential magnitudes decreased especially along high pH, maximum yield stress peaks shifted to high pH and solids content obtained during consolidation increased by ∼14.0 weight percentages (wt%) at pH 8.0 to be similar to Unimin. These changes in Riedel's behaviors and the reasons for Unimin's behaviors is due to the adsorption of hydrolyzed Ca(OH) + hydroxy complexes onto these particles, which reduced particle negativity and induced unlike charge attractions between these particles to improve consolidation and increase slurry network strengths, and the presence of hydrolyzed Ca(OH) 2 precipitates, which increased yield stresses of these kaolin slurries at high pH. The hydrolysis-pH behaviors of Ca 2+ cations varied via acid and base titration paths to correspondingly affect and cause the rheological-pH behaviors of Unimin slurries to be varied via acid and base titration paths. Overall, this study explains the effect of elemental variations between kaolin particles that affects the rheological-pH behaviors between the respective kaolin slurries. [ABSTRACT FROM AUTHOR]

Highlights: [•] Flocculation by Al-PAM and Fe-PAM in comparison with partially hydrolyzed H-PAM. [•] Adsorption kinetics of Al-PAM, Fe-PAM and H-PAM on silica and alumina surfaces. [•] Role of electrostatic attraction and hydrogen bonding in polymer adsorption and flocculation. [ABSTRACT FROM AUTHOR]

Highlights: [•] There was full re-growth for monomeric Al or in situ polymeric Al13. [•] The break-up process displayed irreversibility for unstable small polymeric Al. [•] There was a significant increase of D f when the pH changed from 5.2 to 6.0. [•] The number of small flocs after breakage and re-growth decreased at acidic pH. [•] The strength of flocs is strongly correlated with D f of flocs. [Copyright &y& Elsevier]

Highlights: [•] 0, 10, 20 and 30wt% loading of CO (NH2)2, KCl, NaCl, and Na2SO4 utilized. [•] Concentration of A-PAM system fixed (0.5% w/v) according to industry requirement. [•] Ion dissociation affected dissolution rate, viscosity and turbidity reduction. [ABSTRACT FROM AUTHOR]

In the present work, a type of amphiphilic alkyl quaternary ammonium salt, dimethyl distearylammonium chloride (DAC), was introduced and used as a selective flocculant in kaolin and bentonite suspensions. The selective flocculation property was evaluated by turbidity tests, floc size measurements, zeta potential variation, contact angle measurements and scanning electron microscopy (SEM) observation. The results indicated that an appropriate amount of DAC could achieve selective flocculation at alkaline condition. Based on the experimental facts from size, zeta potential and contact angle measurements, the different flocculation mechanisms of kaolin and bentonite were also investigated. For kaolin suspension, charge neutralization was quite predominant. At different pH level, a low dosage (45 mg/L) of DAC always caused excellent flocculation while high dosage (> 45 mg/L) gradually leaded to restabilization owing to the electrostatic exclusion. For bentonite suspension, bridging effect played the key role. Under acidic condition, bentonite particle always performed good flocculation phenomena at different DAC dosages. But it would gradually lead to enhanced flocculation efficiency from poor to good with increasing the dosage of DAC under alkaline condition. As a result, DAC showed the selective flocculation performance by controlling the dosage of DAC and pH, which provided us the guidance on designing more effective selective flocculant in complex clay mixture system. Flocculation effect of DAC in kaolin and bentonite dispersions at pH 9 [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] Kaolin determines the location of the pH of maximum yield stress. [•] Bentonite content determines the magnitude of the yield stress. [•] The τ ymax (mixed clay)/τ ymax (kaolin) is the same for both low and high Ca(II) kaolins. [•] The yield stress–DLVO model is obeyed by low Ca(II) clay. [•] This model is not obeyed by high Ca(II) clays. [ABSTRACT FROM AUTHOR]

Highlights: [•] Colloidal stability of latex dispersions was tested in cement pore solution. [•] Carboxylated styrene–butadiene (SB) latex is unstable and coagulates. [•] Latex reconstituted from SB powder is more stable than its liquid precursor. [•] Reason is shielding effect of polyvinylalcohol/kaolin coating on SB powder surface. [•] Nonionic EVA latex (liquid or powder) is stable in cement pore solution. [Copyright &y& Elsevier]

Abstract: Starch ampholytes (AmS) – cationic starch succinates – with the degree of substitution according to cationic groups of 0.29 or 0.36 and the degree of substitution according to anionic groups from 0.11 to 0.34 were prepared by succinylation of precationized starch. FT-IR spectra confirmed the incorporation of carboxylic groups into the backbone of cationic starch. Scanning electron microscopy was used for evaluation of the granular structure and surface morphology of modified polysaccharides. The decrease in accessibility of cationic quaternary ammonium groups in AmS was detected by means of polyelectrolyte titration. Colloidal dispersions of AmS were verified in the flocculation of kaolin suspensions and the sedimentation of wastewater sludge. Their flocculation performance was studied in connection with ξ-potential measurements and compared with that of cationic starch. The main advantage of AmS application is broadening of the flocculation window. The mechanism of flocculation by starch ampholytes has been proposed. [Copyright &y& Elsevier]

Highlights: [•] Interfacial reduction rates of 2-nitrophenol affected by Fe(II)/Cu(II) interaction. [•] Fe(II)/Cu(II) interaction affect peak oxidation potential of active species. [•] Fe(II)/Cu(II) molar ratio affect mineral-sorbed Fe(II) density. [•] A lower peak oxidation potential indicates a higher reduction rates. [•] A higher normalized sorbed Fe(II) density indicates a higher reduction rates. [Copyright &y& Elsevier]

Abstract: Although many studies have investigated the removal of fluoride by aluminum (Al) coagulation, few studies focus on the effects of fluoride on the coagulation behaviors towards colloids such as kaolin suspensions. In this study the effects of fluoride at different molar ratios of fluoride to Al (R F:Al) on turbidity removal, zeta potential, flocs growth, and residual Al levels were investigated by a series of batch experiments, and the Visual MINTEQ software was also used to illustrate the species distribution of Al and fluoride at different R F:Al levels. In insufficient Al dose ranges, fluoride showed adverse effects at R F:Al above 10:10, whereas fluoride exhibited little effect on coagulation at R F:Al below 2:10 at pH<8. At pH>8, little effect was observed over wide R F:Al ranges, from 1:10 to 30:30. The adverse effects of fluoride were related to decreased zeta potential, smaller flocs, and elevated levels of residual Al. At pH 6, the fluoride at R F:Al of 10:10 contributed to the decrease of the zeta potential from −1.7 to −6.7mV, decrease of floc size from 119.7 to 29.0μm, and increase of residual Al of 0.22mg/L as Al. For the overdosed dose of 20mg/L as Al, the presence of fluoride decreased residual turbidity from 22.7 to 20.6NTU, owing to the lowered zeta potential and the inhibited re-stabilization of particles. Moreover, this study indicates that after adsorbing fluoride, the spent freshly-prepared aluminum hydroxides (in-situ Al2O3·xH2O) may be reclaimed as coagulants for colloid removal after being dissolved by acid solution. This strategy is valuable to minimize the reagent cost for the removal of fluoride by in-situ Al2O3·xH2O. [Copyright &y& Elsevier]

Abstract: A new coagulant aid, Enteromorpha extract (Ee), was studied to enhance the coagulation performance when it was used together with aluminum sulfate (AS). The dual-coagulant, aluminum sulfate–Enteromorpha extract (AS–Ee), was achieved by dosing Ee 30s after AS was dosed. AS–Ee and AS were comparatively evaluated regarding their coagulation performance. The results showed that Ee played an important assistant part in the coagulation process. The coagulation effect of AS–Ee was about 10% higher than that of AS with respect to the removal of turbidity, UV254 and DOC. Floc characteristics were also investigated in terms of floc size, strength and recovery ability, with the results indicating that the strength of flocs produced by two coagulants were both enhanced with Al dosage increasing, while the floc recoverability was decreased. Floc produced by AS–Ee had bigger size and faster growth rate than that by AS. Meanwhile, the former was also stronger and had a better recoverability than the latter. The charge neutralization was the dominant mechanism of AS, and Ee had good adsorption bridging effect. Due to the combination of two advantages, coagulation efficiency of the dual-coagulant could be enhanced significantly. [Copyright &y& Elsevier]

Abstract: Nanoparticle with higher aspect ratio and greater surface area renders higher micro-bridging ability in flocculating paper furnishes adsorbed with cationic polymers. Sodium titanate nanobelt is a typical one-dimensional nano-material with extremely high aspect ratios. In this paper, the nanobelt was synthesized hydrothermally and successfully peeled with tetramethylammonium hydroxide (TMAOH). The peeled nanobelt was characterized by XRD, TEM, BET surface area and surface charge measurement, and employed as a microparticle component partnered with cationic polyacrylamide (CPAM) to constitute a retention system. The flocculation behavior of kaolin clay by CPAM/nanobelt system was investigated using a photometric dispersion analyzer connected with a dynamic drainage jar. The morphology of flocculated kaolin was characterized by TEM and optical microscope. The results showed that the peeling treatment reduced both the length and the width of nanobelt, increased the charge density and sorption capacity to CPAM but did not significantly alter its structure and zeta potential in aqueous dispersion. The peeled nanobelts partnered with CPAM offered the biggest synergistic flocculating effect at a very low dosage, especially the ones that were peeled for 6–10 days. The kaolin flocs induced by CPAM/peeled nanobelt were larger and denser than those induced by CPAM alone, and become even denser but smaller with increased peeling time. [Copyright &y& Elsevier]

Abstract: In this study, we systematically investigated the effects of sulfuric acid treatment on the physico-chemical and pore characteristics of halloysite. XRD results indicate that sulfuric acid will destroy the crystal structure of halloysite and finally turn it into amorphous silica. The acid will react with halloysite nanotubes from both inner and outer surfaces, dissolve the [AlO6] octahedral layers and led to the rupture and collapse of [SiO4] tetrahedral layers. The BET surface area and total pore volume of halloysite increase firstly with treatment times from 1 to 13h, and then start to decrease due to disaggregation of silica layers. The acid treated halloysites exhibit fixed micropore and controllable mesopore size distributions and are effective low-cost adsorbents. The maximum adsorption capacity of acid treated halloysite for methylene blue is more than 60mgg−1 and can be controlled by pH values. Furthermore, the acid treated halloysite are potential supporters for enzyme, drug, sensors, and so on. [Copyright &y& Elsevier]

Abstract: The effect of binary mixtures of cationic and anionic electrolytes on the kinetics of aggregation, size and strength of flocs formed from kaolin and bentonite particles as a function of the polymer dose, mixture composition, sequence of the components addition and intensity of stirring the system has been studied. A synergism in the flocculation capacity in mixtures of moderate and weakly charged polyelectrolytes was observed; the biggest aggregates have been found at condition of adding first the cationic polymer then the anionic one. An initial intensive short stirring the suspension accelerates the aggregation process and increases the size of flocs independently of the sequence of polymers addition. In mixtures of cationic and anionic polyelectrolytes, the ζ-potential of particles is determined by the adsorbed anionic polymer independently of the charge density of polyelectrolytes and sequence of addition of the mixture components to the suspension. The laws observed were explained by features of polyelectrolytes conformation in adsorbed mixed polymer layers. [Copyright &y& Elsevier]

Abstract: The floc formation, structure and strength remain a problematic topic to be addressed clearly to guide the flocculator design. To study the relationship among floc structure, strength, size distribution, and fractal dimensions, the alum–kaolin flocs formed under different coagulation stages and mechanisms were investigated at various agitation rates. A new method based on the fractal theory was employed to analyze the strength of flocs. The relationship between fractal dimensions and floc size distribution was then discussed with controlled experiments, providing comparison between calculation results of the new method and the strength factor as well. The results show that both size and fractal dimension of flocs decrease with increasing shear rate. The floc strength follows the hierarchy: gradually increased shear rate from 40rpm to 60rpm>stable 60rpm shear rate>gradually decreased shear rate from 60rpm to 40rpm>stable 40rpm shear rate. Flocs formed under gradual shear increasing could easily re-flocculate and recover their strength after breakage. [Copyright &y& Elsevier]

Abstract: The interaction between strong polycations, which possess the ammonium quaternary centers attached to an acrylic macromolecular chain derived from poly(N,N-dimethylaminoethyl methacrylate) (polycations Q x ), and divalent counterions was investigated by viscometry and turbidimetry. Conformational changes of polycations were influenced by the polycation charge density, counterion nature (SO4 2− or S2O8 2−) and concentration. The morphology of the polycation layers deposited onto silicon wafers has been studied by tapping mode atomic force microscopy, a strong influence of the polycation and ammonium persulfate concentration on the surface topography being observed. The optimum flocculation concentration of polycation decreased and the flocculation window increased in the presence of S2O8 2−, in the destabilization of kaolin model dispersion. Removal of Congo Red from aqueous solution by the complex system formed between polycations and divalent counterions was also investigated. The behavior of polycations Q x in separation processes was compared with that of one polycation containing 95mol% N,N-dimethyl-2-hydroxypropyleneammonium chloride units in the backbone (PCA5). [Copyright &y& Elsevier]

Abstract: A laboratory batch study has been performed to study the effect of various physic-chemical factors such as initial metal ion concentration, solution pH, and amount of adsorbent, contact time and temperature on the adsorption characteristics of zinc (Zn2+) metal ions onto kaolin. It has been found that the amount of adsorption of zinc metal ion increases with initial metal ion concentration, contact time, solution pH but decreases with the amount of adsorbent and temperature of the system. Kinetic experiments clearly indicate that adsorption of zinc metal ion (Zn2+) on kaolin is a two steps process: a very rapid adsorption of zinc metal ion to the external surface is followed by possible slow decreasing intra-particle diffusion in the interior of the adsorbent which has also been confirmed by intra-particle diffusion model. The equilibrium time is found to be in the order of 60min. Overall the kinetic studies showed that the zinc adsorption process followed pseudo-second-order kinetics among pseudo-first-order and intra-particle diffusion model. The different kinetic parameters including rate constant are determined at different initial metal ion concentration, solution pH, amount of adsorbent and temperature respectively. The equilibrium adsorption results are analyzed by both Langmuir and Freundlich models to determine the mechanistic parameters associated with the adsorption process. The value of separation factor, R L from Langmuir equation also gives an indication of favorable adsorption. Finally thermodynamic parameters are determined at three different temperatures and it has been found that the adsorption process is exothermic due to negative ΔH° accompanied by decrease in entropy change and Gibbs free energy change (ΔG°). [Copyright &y& Elsevier]

Abstract: The aim of this work was to evaluate the flocculation of kaolin by using positively charged nonstoichiometric interpolyelectrolyte complex (N-PEC) nanoparticles formed by the interaction of chitosan with poly(sodium 2-acrylamido-2-methylpropanesulfonate) (NaPAMPS) and two random copolymers of AMPS with t-butyl acrylamide, comparative with chitosan. The flocculation efficiency was evaluated by optical density at 500nm. The N-PEC nanoparticles were more effective than chitosan in the kaolin separation, especially at low molar ratios between charges, when the flocculation window was more then double at an optimum dose lower than that of chitosan. The main advantage of N-PECs is the increase of critical concentration for kaolin re-stabilization, the N-PEC particles adsorbed on the kaolin surface protecting them more efficient against re-dispersion. The influence of low molar mass electrolytes on the flocculation with N-PECs was also investigated. [Copyright &y& Elsevier]

To extend the application of kaolin in solar-light induced water splitting, MnS-CdS solid solution modified S-doped kaolin (Mn x Cd 1−x S/S-kaolin) composites were in-situ prepared via the high-temperature sulfurization. Compared with kaolin and S-doped kaolin, MnS and CdS greatly enhanced H 2 evolution rate, especially Mn x Cd 1−x S. H 2 evolution rate was affected by Mn/Cd molar ratio, Mn 0.5 Cd 0.5 S content, and sulfurized temperature. The optimal 4-Mn 0.5 Cd 0.5 S/S-kaolin with a Mn/Cd molar ratio of 1:1 and a nominal Mn 0.5 Cd 0.5 S content of 28% treated at 823 K could obtain the highest H 2 evolution rate (4955.27 μmol g−1 h−1), which was 49.33 and 25.28 folds higher than kaolin and S-doped kaolin, respectively. H 2 evolution capacity of 4-Mn 0.5 Cd 0.5 S/S-kaolin decreased from 24,476.79 to 24,262.35 μmol g−1 after five cycles. It's ascribed to the tight interface among S-doped kaolin, MnS and CdS for the efficient transfer and migration of photo-excited charges, and the sufficient active sites formed in S-doped kaolin and S-defected Mn 0.5 Cd 0.5 S were suitable for the efficient photon utilization and visible-light harvesting. [Display omitted] • Mn x Cd 1−x S/kaolin was prepared via high-temperature sulfurization. • H 2 evolution rate of optimal Mn 0.5 Cd 0.5 S/kaolin was 4955.27 μmol g−1 h−1. • The tight junction interface favored the transfer and separation of charge carriers. [ABSTRACT FROM AUTHOR]

Nitrogen fertilizer is one of the most vital major nutrients that plants need. However, its utilization rate was only 30~35%, and most of nitrogen was lost due to volatilization and leaching, which not only led to environmental pollution but also wasting of resources. Therefore, developing cost-effective, eco-friendly and multifunctional slow-release fertilizer (SRF) is still great challenging in agricultural production, and its carriers are very important. In this paper, a novel SRF was successfully prepared by eco-friendly inorganic/organic composites containing porous geopolymer and biocompatible polymers including starch (Sta) and polyvinyl alcohol (PVA). Firstly, the loess particle (Lo), a kind of widely distributed and eco-friendly cheap natural silicate, was used to synthesize porous loess-based geopolymer (Lo-GP). Secondly, using Lo-GP as carrier, Sta and PVA as gel coatings, and boric acid as a crosslinking agent, a novel multifunctional SRF (NF@Lo-GP/Gel) including nutrition elements of N, P and K fertilizer was prepared. Its structure and micromorphology were characterized by FT-IR, XRD, TG-DTG, BET, SEM, and EDS. NF@Lo-GP/Gel in the soil environment exhibited well water retention capacity, water absorbency in salt solutions, remediation of soil pH value, partly degradation in soil and promoting the growth of maize plants because of the organic-inorganic composites in NF@Lo-GP/Gel. The N nutrient slow-release longevity of NF@Lo-GP/Gel was more than 90 days and the cumulative release rate could be kept in 51.4%. It indicated that three-dimensional network and eco-friendly geopolymer with high porosity represent capacity for N fertilizer, as well as persistent slow-release performance. These results showed that geopolymer could be used as a carrier to load nutrients and the obtained NF@Lo-GP/Gel was a slow-release fertilizer with multifunctional performances. [Display omitted] • The porous loess-based geopolymer (Lo-GP) was prepared by loess particles. • Using Lo-GP as carrier, a novel multifunctional SRF was prepared with simple method. • The obtained SRF presented multifunctional properties including slow releasing. • NF@Lo-GP/Gel could loosen the soil just like earthworms while releasing nutrients. • The prepared NF@Lo-GP/Gel has the advantages of eco-friendly. [ABSTRACT FROM AUTHOR]

The flocculation performance of two cationic starches with different charge densities with kaolin clay was investigated by a statistically designed set of small angle light scattering experiments. The analysis of variance of the results showed that shear and starch concentration were important factors affecting the floc size for both starches. The temperature was found to be a significant factor only for the higher charge density cationic starch S880. The combination effect of NaCl and starch concentration and that of temperature and starch were found to be significant for the floc size of the S880 system. The combination effect of shear rate and NaCl was found to be significant for the floc size induced by the low charge density S858. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: This work discusses fluidity of highly concentrated kaolin suspensions prepared by filtration technique in the presence of a dispersant (sodium salt of polyacrylic acid). Two types of rheological tests were carried out on the kaolin aqueous suspensions at different concentrations of kaolin C (12–75wt.%) and dispersant C d (0–1wt.% of dispersant/wt. of solid). A classical coaxial viscosimeter was used to measure viscosity of suspension when it was fluid-like. A texture analyser was used for rheological analysis of the thicker kaolin suspensions. A sol–gel (percolation) transition, starting from the kaolin volume fraction φ c =0.05, was observed in the absence of a dispersant. The addition of a dispersant shifted this percolation transition to higher volume fractions. The rheological data showed that the platelet particles can align in a hydrodynamic flow. A dispersant or kaolin load suppresses the interaction forces between basal and edge faces of the kaolin particles, which bear different charges. As a result, a face-to-face arrangement arises, which is supported by the electron microscopy images. Hence, the loosely packed card-house structure, which is typical for the aqueous kaolin suspensions, undergoes a gradual conversion into an oriented structure under the load of solid particles or dispersant. A maximum of the percolation threshold was reached for a certain optimum dosage of the dispersant (C d ≈0.5wt.%). The higher filtration efficiency was observed for a loosely packed card-house structure in dispersant-free suspensions at low pH. A dispersant improves fluidity and dryness of the filter cakes, however, produces an oriented face-to-face structure of particles, which causes a rise in resistance to liquid flow during filtration. [Copyright &y& Elsevier]