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This first part of the work is devoted to development of high-performance cement composites (HPCCs) with aim to elaborate a mix design methodology for obtaining defined properties of HPCC with industrial by-products such as fly ash, silica fume, and colloidal silica. The research employs innovative methods of experimental design and response surface optimization to find a compromise between the set compressive strength and mix workability. Stage 1 consists in selecting appropriate raw materials and designing an initial mix. Stage 2 involves finding an optimal dosage of superplasticizer. Stage 3 is the response surface optimization, which includes experiment planning with variable parameters x1 (fly ash) and x2 (nanosilica), conducting practical experiments, results of analysis and approximation, using mathematical models of 1st, 2nd, and 3rd order polynomials. The final Stage 4 implies finding the optimal compromise solution between strength and mix flowability, as well as experimental validation of the results obtained. The approach developed can be used for the design of similar multi-component mixes. [ABSTRACT FROM AUTHOR]

Colloidal silica-bonded castables offer several advantages compared to traditional calcium aluminate cement (CAC)-bonded castables, including lower torque values during mixing, superior drying properties, and a lower CaO content. Nevertheless, information on the combination of CAC and colloidal silica is limited, and the effect of CAC additions on the drying properties of colloidal silica-bonded castables remains unknown. In this study, these drying properties were measured by rapidly heating 400 kg samples to 500 °C and assessing the resulting damage to each sample. Additionally, the physical and chemical properties of small-scale samples were analyzed to evaluate the impact of CAC addition. The analyzed properties included cold crushing strength (CCS), density, permanent linear change (PLC) and weight loss. The microstructure of the samples was investigated by FESEM and EDS. The results indicate that adding 1.5 wt.% increased the cold crushing strength at 20 °C, while lower CAC amounts had no noticeable effect. A mullite phase was observed in the sample without CAC, and correspondingly, anorthite was found in those with CAC additions. The samples exhibited significant differences in the drying tests, with the degrees of damage increasing with the CAC addition. [ABSTRACT FROM AUTHOR]

Fabricating large-scale porous bioactive glass bone scaffolds presents significant challenges. This study aims to develop formable, in situ setting scaffolds with a practical gelation time of about 10 min by mixing 45S5 bioactive glass with sodium silicate (waterglass) and an acid initiator. The effects of pH (2–11), waterglass concentration (15–50 wt.%), and acid initiator type (phosphoric or boric acid) were examined to optimize gelation kinetics and microstructure. A 10 min gelation time was achieved with boric acid and phosphoric acid at various pH levels by adjusting the waterglass concentration. Exponential and polynomial models were proposed to predict gelation times in basic and acidic environments, respectively. The optical properties of the gels were studied qualitatively and quantitatively, providing insights into gelation kinetics and structure. Acidic gels formed smaller particles in a dense network (pores < 550 nm) with higher light transmittance, while basic gels had larger aggregates (pores ~5 µm) and lower transmittance. As the waterglass concentration decreased, pore size and transmittance converged in both groups. The onset of gelation was detected around 8 min using the derivative of light transmittance. This work identifies the key factors controlling waterglass gelation and their impact on gel structure, enabling the tailored creation of formable, in situ setting bioactive glass bone scaffolds. [ABSTRACT FROM AUTHOR]

The nature of serpentinite interaction with low-concentration sulfuric acid solutions is studied. Using IR-Fourier spectroscopy, X-ray, and serpentinite leaching with sulfuric acid solutions containing 10–60% of stoichiometrically required amount (SRA) of H2SO4 (taken relative to the molar magnesium content in serpentinite), it is shown that the appearance and influence of silica on the course of serpentinite dissolution is detected at concentrations of 30–40% of SRA of H2SO4. On the basis of the obtained results, this article points out the technological, economic, and ecological advantages of use of sulfuric acid solutions of low concentrations in the process of acid processing with the aim of producing magnesium salts.

The coexistence of different foulant compositions in the feed water of reverse osmosis (RO) systems causes serious complications in the fouling process of the membranes. Hence, in this technical research, the phenomenon of combined inorganic (gypsum)-colloidal (silica particles) fouling (inorganic-colloidal fouling) of brackish water RO (BWRO) process was studied in the lab-scale experiments. Moreover, the effect of the presence of air micro–nano bubbles (AMNBs) in the feed water; as a new practical method for control of membrane fouling, was investigated on this phenomenon. For this purpose, a suspension with the potential of inorganic scaling [calcium sulfate, Saturation index (SI)=0.96 ] and colloidal fouling (colloidal silica, 50 mg/L) was used to form the inorganic and colloidal foulings (simultaneously) on the membrane surface during the inorganic-colloidal fouling process. All experiments were performed twice, once in the absence and once in the presence of AMNBs. Finally, the results of this research were compared with the results of the inorganic and colloidal fouling studies. Based on the results, the inorganic-colloidal fouling formed a dense and compact fouling layer on the membrane surface, which severely reduced the permeate flux (76.3%) and salt rejection (4%). The amount of decrease of these two parameters in inorganic-colloidal fouling was much higher than each of individual inorganic and colloidal foulings. In the presence of AMNBs, both types of inorganic and colloidal foulings greatly reduced and the major portion of inorganic-colloidal fouling was related to the colloidal fouling. Thus, a significant decline was observed in adverse effects of inorganic-colloidal fouling on the membrane performance and the permeate flux and salt rejection decreased by 18.5% and about 1%, respectively. The results of this study could introduce the micro–nano bubbles (MNBs) technology as an effective method to inhibit the inorganic-colloidal fouling in RO systems. Practical Applications: Today, reverse osmosis processes are known as efficient technologies for supplying drinking water from brackish and sea water resources due to their high ability to remove various compounds. The separated compounds from the water accumulate near the membrane surface and consequently deposit on it and/or inside its pores. This phenomenon is called membrane fouling and has adverse effects on the performance of reverse osmosis processes. Water resources usually have different types of pollutants that simultaneous presence of them can intensify the membrane fouling process. Gypsum scaling and colloidal silica fouling are two major common types of reverse osmosis membrane fouling. Therefore, in this research, the effects of the inorganic-colloidal fouling were studied on the performance of a commercial brackish water reverse osmosis membrane, in presence and absence of air micro–nano bubbles. The results showed that the combined fouling formed a complex fouling layer on the membrane surface in absence of air micro–nano bubbles. In real-scale reverse osmosis process, this layer can severely reduce the membrane permeate flux and salt rejection which result to increase in the operational and maintenance costs. Alternatively, the presence of air micro–nano bubbles in the reverse osmosis feed flow could limit both inorganic and colloidal foulings and their synergetic effects on each other. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to perform the surface treatment of synthetic α-Fe2O3 red iron oxide pigment with hydrolysate 3-aminopropyl silane (A) and colloidal silica (CS) and investigate the effects of surface-treated pigment on the styrene acrylic (SA) emulsion and polyurethane (PU) dispersion. Design/methodology/approach: For this purpose, firstly red iron oxide particles were modified with A and CS separately in an aqueous medium. After isolation of the modified iron oxide were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). Moreover, the degree of the dispersion stability of the modified pigment in coatings with SA emulsion and PU dispersion was investigated by using an oscillation rheometer. Loss (G''), storage (G') modulus, loss factor [tan(δ)] and yield stress (τ0) values were determined by performing amplitude and frequency sweep tests. Findings: The τ0 in SA coatings decreases with the amount of used A and increases with the amount of used CS. The τ0 decreases as the amount of used A and CS in PU coatings increases. The use of CS on red iron oxide pigments causes storage modulus to increase in SA coatings at low angular frequencies, while it causes a decrease in PU coatings. Originality/value: To the best of the authors' knowledge, for the first time, the suspended state of the iron oxide hybrid pigment formed with CS in the coating was investigated rheologically in this study. [ABSTRACT FROM AUTHOR]

Rapid face of urbanization has lead to increase in concrete production, rising concerns about its implications for climate change, depletion of resource materials and environmental degradation. Concrete is prone to attacks by various aggressive environment effects. Depending upon the requirements, different types of concrete have been developed using nano based materials. One of the most used materials at nano scale is nano silica. The effect of use of nano silica in the form of colloidal silica is used in the present study as replacement and addition to cement to study the sulphuric acid attack on concrete. Colloidal silica with 30% of nano solids of SYCOL-TX is replaced and added to cement in different proportions i.e., 0, 0.5, 1, 1.5, 2, 2.5 and 3% respectively. Optimum mix is found out by conducting compressive strength test to concrete specimens after 28 days of curing. The test samples prepared with optimum content of colloidal silica are immersed in different concentrations of 1.5, 3, 4.5 and 6% sulphuric acid solution for a time period of 28, 56, 90 and 180 days, after 28 days of water curing. Visual appearance, weight loss and compressive strength lossare determined in the study to study the effect of sulphuric acid attackon concrete specimens. From the results it is observed that incorporation of colloidal silica in concrete enhances its compressive strength and resistance to acidic environments in terms of durability. [ABSTRACT FROM AUTHOR]

Water seepage flow can dissolve soluble minerals that exist in rock formations. With the development of the excavated area due to dissolution, the water seepage velocity (discharge) into the dissolved rock will also increase. Therefore, water seepage and dissolution propagation are two interrelated processes. Mosul Dam foundation has experienced these processes since its construction, resulting in karstification in the reservoir and foundation of the dam. The present seepage-dissolution measure to minimize this phenomenon relies on traditional cementitious grouts. However, this measure has not been able to address the issue effectively. Currently, there are a few studies on the chemical remediation of soluble rocks under the influence of high-velocity water flow and water pressure. Therefore, the first part of the current study focuses on the impact of high-velocity water flow and water pressure on the dissolution acceleration of gypsum/anhydrite rocks. In the second part, the waterproof capacity of silica colloidal and its impact on the solubility reduction of the rocks is evaluated. Two distinct laboratory models were designed to simulate rock dissolution in the dam abutments and under the dam. Two sets of experiments were conducted on untreated and silica-treated samples. The experiments were executed on the samples extracted from Fatha Formation outcrop and problematic layers of brecciated gypsum situated at varying depths of the Mosul Dam foundation. The obtained findings reveal that the colloidal silica grout markedly prevents the water seepage impact on the soluble rock and that it can be very useful as an alternative to cement-based grouts. [ABSTRACT FROM AUTHOR]

Colloidal silica is a relatively new grouting low-carbon material used in soil improvement projects. A series of mechanical tests on a sand with different solid contents of the binder, i.e. 40, 30 and 20% solid content have been performed. Unconfined compressive strength at 7, 28 and 56 days, shear tests and permeability tests at 7 days were assessed. A statistical interpretation of these data has been performed and values were interpreted. A mathematical prediction model was suggested to estimate the mechanical strength of the grouted sand as the dilution grade varies. Furthermore, some considerations useful for geotechnical design on the evolution over time of the mechanical characteristics of the grouted sands have been carried out. Results show, from a statistical and mathematical view, that colloidal silica is a promising binder for ground improvement applications. [ABSTRACT FROM AUTHOR]

The waterglass or St o¨ ber method is commonly used to synthesize spherical colloidal silica; however, these methods have some disadvantages, such as complicated processes for the removal of sodium ions and expensive and energy-consuming raw materials such as tetraethoxysilane (TEOS). In this study, size-controlled spherical colloidal silica was synthesized from silicon metal at room temperature using an ultrasound process with hydrazine monohydrate as the solvent. Silicon metal dissolves easily in hydrazine monohydrate under ultrasound irradiation, and spherical colloidal silica can be synthesized by adding alcohol to this precursor solution. By changing the concentration or type of alcohol, size-controlled colloidal silica 20–200 nm in size could be easily obtained. In addition, finer and more monodisperse particles were produced by low-frequency ultrasound irradiation, which had a higher stirring effect at the particle formation stage. The present method is effective because size-controlled colloidal silica can be synthesized at room temperature using only silicon metal, hydrazine, and alcohol as raw materials, without complicated processes or expensive and energy-consuming raw materials such as TEOS or tetramethoxysilane (TMOS).

Fabricating large-scale porous bioactive glass bone scaffolds presents significant challenges. This study aims to develop formable, in situ setting scaffolds with a practical gelation time of about 10 min by mixing 45S5 bioactive glass with sodium silicate (waterglass) and an acid initiator. The effects of pH (2–11), waterglass concentration (15–50 wt.%), and acid initiator type (phosphoric or boric acid) were examined to optimize gelation kinetics and microstructure. A 10 min gelation time was achieved with boric acid and phosphoric acid at various pH levels by adjusting the waterglass concentration. Exponential and polynomial models were proposed to predict gelation times in basic and acidic environments, respectively. The optical properties of the gels were studied qualitatively and quantitatively, providing insights into gelation kinetics and structure. Acidic gels formed smaller particles in a dense network (pores < 550 nm) with higher light transmittance, while basic gels had larger aggregates (pores ~5 µm) and lower transmittance. As the waterglass concentration decreased, pore size and transmittance converged in both groups. The onset of gelation was detected around 8 min using the derivative of light transmittance. This work identifies the key factors controlling waterglass gelation and their impact on gel structure, enabling the tailored creation of formable, in situ setting bioactive glass bone scaffolds.

Improving the green mechanical strength of colloidal silica‐bonded corundum castables is essential to their widespread utility. The effects of varying contents (0–2 wt%) of La2O3 on the green mechanical strength of colloidal silica‐bonded corundum castables were investigated. The findings demonstrate that La2O3 has a positive impact on the green mechanical strength of colloidal silica‐bonded castables. The colloidal silica‐bonded corundum castable containing 2 wt% La2O3 exhibits higher green mechanical strength than the cement‐bonded corundum castable. Additionally, the castable shows excellent construction performance. The basic properties of La2O3 and La(OH)3 facilitate the absorption of H+ from the surface of colloidal silica to form more siloxane bonds and speed up gelation. Fourier transform infrared spectroscopy and X‐ray fluorescence spectroscopy analyses indicate that La3+ ions participate in the condensation of –Si–OH and bond the broken Si–O bonds to create Si–O–La chemical bonds. La3+ ions bridge the colloidal silica particles, leading to stable three‐dimensional network structures that result in an increased green mechanical strength of the castables. The water consumption during the hydration reaction expedites gelation, further contributing to the enhancement of the green mechanical strength of the corundum castables. Given its wide sources and stable performance, La2O3 can be considered an efficient setting agent with the potential for extensive industrial application. [ABSTRACT FROM AUTHOR]

PNIPAAm‐grafted thermoresponsive hollow nano‐holed polymeric‐shell (HHPS) particles were fabricated from surface‐modified colloidal silica (CS) with poly(ethylene glycol) methyl ether‐3‐(triethoxysilyl)propyl isocyanate (PEGME‐IPTES) and 3‐(trimethoxysilyl) propyl methacrylate (MPS) as templates. The polymeric shells were then synthesized through a "grafting‐through" approach via surface‐initiated polymerization of N‐isopropyl acrylamide (PNIPAAm) using potassium persulfate (KPS) as an initiator, followed by the etching of CS with hydrofluoric acid to remove the CS core templates. CS nanoparticles and PEGME‐IPTES were presynthesized using tetraethoxysilane (TEOS) and distilled water in methanol with ammonia solution as a catalyst by the sol–gel method and using 3‐(triethoxysilyl) propyl isocyanate (IPTES) with poly(ethylene glycol) methyl ether (PEGME) in the presence of dibutyltin dilaurate. The chemical structures of bare and modified CS, PNIPAAm, PNIPAAm‐CS, and HHPS particles were characterized by FT‐IR and NMR spectroscopies. SEM and TEM images confirmed that the resulting HHPS particles had a significant number of interconnected nanoholes. To evaluate the LCST behaviors of HHPS particles, the transition of transmittance and the changes in particle diameter according to the temperature change were measured through UV‐vis spectroscopy, DLS, and microscopy. [ABSTRACT FROM AUTHOR]

Colorless and transparent semi‐alicyclic fluoro‐containing polyimide (PI) nanocomposite films with enhanced high‐temperature dimensional stability and sustained optical transparency were designed and prepared via incorporation of nano‐sized colloidal silica (SiO2) fillers into the PI matrix derived from hydrogenated pyromellitic dianhydride (HPMDA) and 2,2′‐bis[(4‐aminophenoxy)phenyl]hexafluoropropane (BDAF). The derived PI composite films, abbreviated as 6FCPI‐X in which X stands for the weight percent of the SiO2 in the composite films, exhibited superior thermal and comparable optical properties to the pristine 6FCPI‐0 (6FDA‐BDAF) matrix film. For example, as for the thermal properties, 6FCPI‐35 composite film showed a glass transition temperature (Tg) of 279.1°C and a residual weight ratio at 750°C (Rw750) of 66.1%, which were apparently higher than those of 6FCPI‐0 matrix (Tg = 272.2°C; Rw750 = 47.1%). More importantly, the 6FCPI/SiO2 nanocomposite films showed obviously lower linear coefficients of thermal expansion (CTE) values as compared with that of the 6FCPI‐0 matrix. 6FCPI‐35 composite film showed a CTE value of 36.1 × 10−6/K in the temperature range of 50–250°C, which was lower than half of that of the 6FCPI‐0 matrix (CTE = 77.9 × 10−6/K) in the same range of temperature. In addition, incorporation of nano‐sized colloidal SiO2 particles basically maintained the intrinsically good optical properties of the pristine 6FCPI‐0 matrix film. 6FCPI‐35 composite film showed the optical transmittances of 81.7%, 85.3%, and 87.2% at the wavelength of 400 nm (T400), 450 nm (T450), and 500 nm (T500), respectively, which were in the same level with those of the 6FCPI‐0 film (T400 = 84.0%; T450 = 86.3%; T500 = 87.6%). The 6FCPI series of nanocomposite films also exhibited similar CIE Lab color parameters, including the yellow indices (b*) lower than 2.0 and haze values lower than 1.0%. [ABSTRACT FROM AUTHOR]

Improving the green mechanical strength of colloidal silica‐bonded corundum castables is essential to their widespread utility. The effects of varying contents (0–2 wt%) of La2O3 on the green mechanical strength of colloidal silica‐bonded corundum castables were investigated. The findings demonstrate that La2O3 has a positive impact on the green mechanical strength of colloidal silica‐bonded castables. The colloidal silica‐bonded corundum castable containing 2 wt% La2O3 exhibits higher green mechanical strength than the cement‐bonded corundum castable. Additionally, the castable shows excellent construction performance. The basic properties of La2O3 and La(OH)3 facilitate the absorption of H+ from the surface of colloidal silica to form more siloxane bonds and speed up gelation. Fourier transform infrared spectroscopy and X‐ray fluorescence spectroscopy analyses indicate that La3+ ions participate in the condensation of –Si–OH and bond the broken Si–O bonds to create Si–O–La chemical bonds. La3+ ions bridge the colloidal silica particles, leading to stable three‐dimensional network structures that result in an increased green mechanical strength of the castables. The water consumption during the hydration reaction expedites gelation, further contributing to the enhancement of the green mechanical strength of the corundum castables. Given its wide sources and stable performance, La2O3 can be considered an efficient setting agent with the potential for extensive industrial application. [ABSTRACT FROM AUTHOR]

This study aims to synthesize stable colloidal silica via the peptization method as a green and low-cost route. It is crucial to adopt a proper synthesis procedure and choose an appropriate raw material. To achieve this purpose, kaolin was employed as a silica rich source that occurs abundantly in nature. The process involves synthesis of the wet gel through the succession of calcination, acid leaching, alkaline treatment, sodium silicate precipitation, and then peptization of the wet gel. Effect of the acid type on acid leaching was evaluated. Effective factors affecting the gel purity such ad acid concentration, pH of gelation, and temperature of alkaline treatment, were studied and optimized via a statistical design of the experiments. Subsequently, the influential parameters on stability and particle size of the obtained colloidal silica, including the temperature of the gel formation, pH of sol medium, concentration of silica gel, and type of stabilizing base, were investigated via one-facto-at-a-time. The samples were characterized by X-ray fluorescence analysis (XRF), dynamic laser light scattering analysis (DLS), X-ray Diffraction (XRD), Fourier transform infrared (FTIR), Brunauer–Emmett–Teller (BET), and Field emission scanning electron microscopy (FESEM) analyses. Results showed that under optimum conditions, ultra-pure silica gel with a silica content of 99.34 % was obtained. The colloidal sample with the highest stability (zeta potential of −75.6 mV), had nanoparticles showing sizes in the range of 21–66 nm.

The investigation focused on the rheological impact of sodium chloride and calcium chloride on PEO silica water mixtures, specifically studying their gelation/shear thickening behaviour referred to as "shake gels". Monitoring viscosity over time at a constant shear rate revealed a significant increase in viscosity by several orders of magnitude at a specific time point. Interestingly, higher concentrations of sodium chloride and calcium chloride correlated with shorter times required for gel formation. Following gel formation, dropping the shear rate facilitated the observation of the gel's relaxation back into a liquid state. Notably, higher concentrations of sodium chloride or calcium chloride resulted in slower relaxation processes. Furthermore, a notable difference emerged: at a consistent shear rate, calcium chloride exhibited faster gelation compared to sodium chloride, while during relaxation, calcium chloride relaxed at a slower pace than sodium chloride. This behaviour can be attributed to the effect of salt on polymer molecules. The presence of salt results in reduction in Debye length and polymer gets contracted. Consequently, shearing becomes more easier even though at lower shear rate as salt concentration increases. In contrast, during the relaxation process, polymer restructuring is hindered due to electrostatic repulsion and Debye length decreases, resulting in slower relaxation as salt concentration increases. The variations in gelation and relaxation behaviour between different salts can primarily be attributed to the differing ionic strengths exhibited by these salts. [Display omitted] [ABSTRACT FROM AUTHOR]

Shake-gels are aqueous mixtures of silica and Poly(ethylene-oxide) (PEO) that form reversible gels when subjected to an applied force, such as shaking. This shear-thickening effect can be observed using a rheometer, which shows discrete, sudden changes in the material's viscosity. Preliminary qualitative investigations have shown that the gelation time varies depending on the conditions used. We also measure the time required for the gel to relax and revert to its liquid state. To quantify the relationships between these variables and better understand the process and kinetics, a systematic investigation was conducted, focusing on the effects of polymer concentration and temperature on gelation and relaxation times. Experiments were carried out using a rheometer with double-gap concentric cylinder geometry, applying a constant shear rate to samples with varying polymer concentrations and temperatures. The results showed that, at a fixed shear rate, gelation and relaxation times varied significantly, ranging from a few seconds to over an hour. Both gelation and relaxation occurred more rapidly as polymer concentration increased. Additionally, higher temperatures led to faster gelation and relaxation times and vice versa. [Display omitted] [ABSTRACT FROM AUTHOR]

Magnesium hydroxide (Mg(OH) 2) suspensions are encountered in the nuclear industry as legacy waste that is to be packaged for long-term storage. It is desirable to increase the solids content of the waste to minimize the total volume, yet this would produce high yield stress fluids that are difficult to process. However, high solids content suspensions of low yield strength are desired. Blending nano-silica (nano-SiO 2) into a high yield stress suspension of 27 vol% Mg(OH) 2 , the suspension yield stress was reduced from 86 Pa to 47 Pa. X-ray CT imaging revealed that approximately two-thirds of the 3 vol% nano-SiO 2 added to the Mg(OH) 2 suspension was well-dispersed, with the rest forming large clusters that had minimal interaction with the Mg(OH) 2 network. SEM images showed small aggregates/individual particles of nano-SiO 2 dispersed between Mg(OH) 2 particles. We conclude that the finely dispersed nano-SiO 2 act like ball bearings to lubricate contacts between the irregularly shaped Mg(OH) 2 particles, thus decreasing yield stress. When aging the samples for several days, the yield stress of the binary suspension increased, reversing the yield stress reduction that was observed within the first day. The network stiffening is attributed to the formation of magnesium silicate hydrate (MSH) due to a reaction between soluble Mg2+ and Si(OH) 4. The MSH precipitates onto the nano-SiO 2 to fuse particles together, thus reducing their effectiveness as flow modifiers. While this is a side effect of this particular binary suspension, the initial yield stress drop remains encouraging to provide the desired fluid conditions to process legacy wastes. [Display omitted] [ABSTRACT FROM AUTHOR]

Significant challenges remain for the remediation of chlorinated-solvent plumes in groundwater, such as trichloroethene (TCE) and tetrachloroethene (PCE). A novel slow-release permanganate gel (SRP-G) technique may show promise for the in-situ treatment (remediation) of chlorinated contaminant plumes in groundwater. A series of laboratory experiments were conducted to characterize the primary physical factors that influence SRP-G gelation processes to optimize SRP-G performance for plume treatment. Specifically, experiments were conducted to quantify gel zeta potential, particle size distribution, and viscosity to determine SRP-G gelation characteristics and processes. These experiments tested various concentrations of two SRP-G amendment solutions (NaMnO 4 and KMnO 4) prepared with 30-wt.% and 50-wt.% colloidal silica to determine such influences on zeta potential, particle size distribution, and viscosity. The results of this study show that SRP-G solutions with low zeta potential and relatively high pH favor more rapid SRP-G gelation. The concomitant interaction of the predominantly negatively charged colloidal silica particles and the positively charged dissociated cations (Na+ and K+) in the SRP-G solution had the effect of stabilizing charge imbalance via attraction of particles and thereby inducing a greater influence on the gelation process. Gel particle size distribution and changes in viscosity had a significant influence on SRP-G solution gelation. The addition of permanganate (NaMnO 4 or KMnO 4) increased the average particle size distribution and the viscosity of the SRP-G solution and decreased the overall gelation time. SRP-G amendments (NaMnO 4 or KMnO 4) prepared with 50-wt.% colloidal silica showed more effective gelation (and reduced gelation time) compared to SRP-G amendments prepared with 30-wt.% colloidal silica. Under the conditions of these experiments, it was determined that both the 7-wt.% NaMnO 4 solution and 90 mg/L KMnO 4 solution using 50-wt.% colloidal silica would be the optimal injection SRP-G solution concentrations for this in-situ treatment technique. [Display omitted] • Slow-release permanganate gel (SRP-G) solution was unstable at low zeta potential and relatively high pH. • Increase in permanganate concentration caused decreasing gelation time for the SRP-G solution. • Gelation time decreased with increases in SRP-G solution viscosity. • SRP-G solution is a promising technique for in-situ chlorinated plume treatment in aquifers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Colloidal silica was synthesized from silicon metal at room temperature. • Ultrasound significantly promoted dissolution of silicon into hydrazine monohydrate. • Colloidal silica was obtained by simply adding alcohol into precursor solution. • Ultrasound stirring and dispersion effects contributed to particle monodispersity. • This is simple, energy-saving, and cost-effective way of colloidal silica synthesis. The waterglass or St o ¨ ber method is commonly used to synthesize spherical colloidal silica; however, these methods have some disadvantages, such as complicated processes for the removal of sodium ions and expensive and energy-consuming raw materials such as tetraethoxysilane (TEOS). In this study, size-controlled spherical colloidal silica was synthesized from silicon metal at room temperature using an ultrasound process with hydrazine monohydrate as the solvent. Silicon metal dissolves easily in hydrazine monohydrate under ultrasound irradiation, and spherical colloidal silica can be synthesized by adding alcohol to this precursor solution. By changing the concentration or type of alcohol, size-controlled colloidal silica 20–200 nm in size could be easily obtained. In addition, finer and more monodisperse particles were produced by low-frequency ultrasound irradiation, which had a higher stirring effect at the particle formation stage. The present method is effective because size-controlled colloidal silica can be synthesized at room temperature using only silicon metal, hydrazine, and alcohol as raw materials, without complicated processes or expensive and energy-consuming raw materials such as TEOS or tetramethoxysilane (TMOS). [ABSTRACT FROM AUTHOR]