Search

Abstract: The adsorptive removal of toxic para-chlorophenol using activated carbon adsorption columns is a proven effective engineering process. This paper examined the possibility to stratify an adsorbent bed into layers, in order to enhance the adsorption process performance in terms of increased column service time and adsorbent bed saturation. Four different types of fixed-bed adsorption columns are used and compared under the same operating conditions, but with the variation of column geometry and activated carbon particle size stratification. The Type 3 column – a cylindrical column with particle stratification packing, is found to be the most efficient choice, as the extent of column service time and adsorbent bed saturation are the largest. This could eventually decrease the frequency of adsorbent replacement/regeneration and hence reduce the operating cost of the fixed-bed adsorption process. The Homogeneous Surface Diffusion Model (HSDM) was applied successfully to describe the dynamic adsorption of para-chlorophenol onto Filtrasorb 400 (F400) activated carbon in different types of columns. The Redlich-Peterson isotherm model equation, an experimentally derived external mass transfer correlation and a constant surface diffusivity are used in the HSDM. The optimised surface diffusivity of para-chlorophenol is found to be 1.20E-8 cm2/s, which is in good agreement with other phenolics/F400 carbon diffusing systems in literature. [Copyright &y& Elsevier]

In recent years, there has been growing awareness that by 2050, many countries will experience critical issues related to water scarcity. The need to recycle/reuse wastewater after pollution treatment is a major concern worldwide for ensuring water security at the national level. Treatment technologies to remove major pollutants, namely, heavy metals, anionic impurities and the vast range of organic compounds, have received substantial attention from the scientific community. Water resource pollution is increasing due to an increasing world population and its corresponding activities. Amongst the different technologies used to decrease pollutant levels in water, adsorption technology is highly effective even at low pollutant concentrations. Carbonaceous materials and their composites have been widely used due to their unique surface properties and high adsorption capacities, but better adsorbents with higher pollutant adsorption capacities and faster uptake are still needed. Recently, the development of graphene-based adsorbents, with their highly active surfaces and large surface areas, has created much excitement. Therefore, an updated review is needed to summarize this graphene research. This review provides a summary of the literature in the field of adsorptive removal of organics from water, with a focus on phenols and dyestuffs. The synthesis methods, characterization techniques, adsorption behaviors, experimental parameters, mechanisms, thermodynamics, the effect of coexisting ions and regeneration–desorption processes are considered. Finally, research challenges and knowledge gaps – limited regeneration and solute recovery studies, the behavior of mixed pollutants effluents, designing graphenic adsorbents for specific pollutants, treatment system economic analyses - in the field are discussed. [Display omitted] • Modified graphene oxide, MGO, reviewed for phenols and dye removal. • Equilibrium isotherm analyses and adsorption kinetic models are reviewed. • MGO adsorption showed rapid kinetics reaching 90% capacity under 5 min. • The MGO capacities compared very favorably with alternative adsorbent capacities. • Gaps in the literature studies and the direction of future studies are presented. [ABSTRACT FROM AUTHOR]

Abstract: The rates of adsorption of cadmium, copper and zinc ions onto bone char have been studied in three single component systems using an agitated batch adsorber. The effects of initial metal ion solution concentration and bone char mass have been studied. The capacities of the three metals on bone char are 0.477, 0.709 and 0.505 mmolg−1 for cadmium, copper and zinc respectively which are much higher than most other adsorbents reported in the literature for these three metals. In order to model the experimental concentration decay curves, a film-surface diffusion equation proposed by Crank (1979) has been solved. The model results correlate the experimental better than a previously applied film-pore diffusion model. However, the results indicate that the surface diffusion coefficient was a variable function of initial metal ion concentration. The surface diffusivities vary from 3.00×10−9 to 8.80×10−9 cm2 s−1, 2.11×10−9 cm2 s−1 to 5.4×10−9 cm2 s−1 and 3.10×10−9 to 8.49×10−9 cm2 s−1 for cadmium, copper and zinc respectively, for metal ion solution concentrations of 2.10–5.40 mmoldm−3. [Copyright &y& Elsevier]

Three solutions to the film surface diffusion mass transport model are discussed. The solutions are based on the homogenous surface diffusion model (HSDM) and are compared using three different adsorption systems. The mass transport solutions include a Crank–Nicholson implicit finite difference method, a semi-analytical solution method and a Cartesian collocation method. The three solutions are compared for accuracy, stability, convergence and computation CPU time.The experimental systems used two adsorbents, activated carbon, a mainly microporous material, and sorbsil silica, a mainly macroporous material. Two categories of adsorbates were selected for the study, phenol, a relatively small organic molecule, which does not ionise, and basic dyes, larger organic structures, which exist as ionisable salts. A range of initial adsorbate concentrations were studied. The range of material types and experimental conditions selected should be sufficient to test and compare the three models under a variety of conditions. [Copyright &y& Elsevier]

In this opinion paper, the current scenario and the main challenges in adsorption for water treatment are presented shortly. It is expected that this discussion paper will serve as a fast literature directive to support new ideas and novel investigations in the field. A general background about the topic is first presented. Subsequently, some important aspects that are well developed in literature are discussed, including adsorbent materials, adsorption operation mode, modeling, regeneration, and process operation with real samples. In the last section, it has been pointed out what should likely be the next steps required to advance in this knowledge. [ABSTRACT FROM AUTHOR]

• Graphene oxide was used for adsorption of diesel from oil-water emulsion. • A high capacity of 1335 mg/g was achieved. • Adsorption capacity increased under increasing salinity, tested up to 100 g/L NaCl. • Adsorption showed extremely rapid kinetics reaching 90% of capacity within 4 min. • Fixed-bed column tests demonstrate compact adsorption system with good regeneration. Large quantities of oily wastewaters are produced globally from oil extraction and refining industries containing low concentrations of dissolved and finely emulsified oils. These waters are difficult to treat within a small footprint as often necessary, especially on offshore sites, and often contain high salinity making many treatment methods ineffective. In this study the use of graphene oxide (GO) as an adsorbent is investigated using diesel as a representative oil. GO demonstrated a high adsorption capacity of 1335 mg/g according to the Freundlich isotherm and based on theoretical surface area was likely due to limited multi-layer adsorption. Increasing salinity to 1% increased adsorption capacity by 75%, remaining constant thereafter, confirming the suitability for the material for saline produced water remediation. Adsorption was extremely rapid, reaching more than 90% of the equilibrium capacity within 4 min, and was represented best by a pseudo-second order kinetic model. Fixed bed column tests confirmed the ability for excellent removal capacities under a short contact time and good regeneration, indicating the potential of GO for industrial oil-water emulsion separation applications. Based on careful analysis of isotherm and kinetic data, in conjunction with theoretical considerations, a rapid multi-layer physisorption mechanism, influenced by GO agglomeration, is proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel method was introduced by integrating magnetic field exposure with adsorption technique. [•] Combined magnetic field and adsorption process has a vital role in treating POME. [•] Adsorption performance and adsorption rate could be enhanced by magnetic field. [•] Magnetization process accelerated the removal of colour, TSS and COD in adsorption process. [•] The new method increased the percentage removal of colour, TSS and COD by 39%, 61% and 46% respectively. [Copyright &y& Elsevier]

Abstract: A number of chars from waste tyre rubber were prepared by carbonisation at 673–1173K. The effects of holding time, heating rate and particle size on the textural characteristics and elemental composition of the resultant chars were investigated. It was demonstrated that temperatures over 773K did not have a significant improvement on the total surface area but resulted in lower char yields following increased aromatisation. Modelling of dye adsorption isotherms showed that the Redlich–Peterson expression yields the best-fit between experimental and predicted data. Furthermore, for a larger sized dye like Acid Yellow 117 (MW=848g/mol), the amount adsorbed by the tyre char is not directly proportional to the total surface area when compared with a commercial carbon, revealing that factors other than total surface area are involved in the adsorption potential of the tyre chars. [Copyright &y& Elsevier]

• Development of novel multimechanistic adsorption model. • Application of extended Freundlich isotherm model. • Dual chelation and surface complexation mechanistic model. • Application to cadmium adsorption on nanochitosan. This study involves the development of a novel model encompassing two distinct mechanisms for the adsorption of cadmium ions onto nanochitosan to predict the composite equilibrium isotherm. The application of the multistage Freundlich isotherm analysis demonstrates that two regions are involved in the equilibrium process. This can be attributed to two types of adsorption mechanism, namely, chelation of the cadmium ions with the lone electron pairs on the free amino groups of chitosan and the second phase mechanism involves the surface complexation of the cadmium ions forming complexes of which more than one option is possible. Analysis of the high uptake loading enables the amount of cadmium adsorbed by each mechanism to be determined from the two regions of the Freundlich isotherm; the amino-chitosan-cadmium chelation capacity is 1.749 mmol Cd and the surface complexation capacity is 0.184 mmol/g. From these data the two individual isotherms for each mechanism are evaluated using a selection of different isotherm combinations to develop a better and more detailed representation of the multimechanism adsorption process. Based on the lowest SSE value, the best combination was Sips-Sips followed by the Sips-Langmuir for the chelation and surface complexation mechanisms respectively. Finally, a second optimisation modelling process has been applied using two generic isotherm equations to determine the isotherm constants without any Freundlich interstage loading capacities. The differences between the two approaches are significant, confirming that experimental adsorption data are required for each mechanistic stage independently. [ABSTRACT FROM AUTHOR]

Abstract: NH2–MCM-41 and COONa–MCM-41 were prepared by grafting aminopropyls and propionates on the pore wall of the mesoporous silica MCM-41 for the separation of and Cu2+. Single and binary component adsorptions show that has a 100% selectivity for adsorption at low pH (<3.5 i.e., point of zero charge, p.z.c.), while COO−Na+–MCM-41 adsorbs only Cu2+ over the entire pH range of the study (i.e., pH 1.5–5.5). Adsorption uptakes were rapid on both adsorbents reaching equilibrium in less than 3h and in most cases less than 10min. The adsorption capacity of for is high, approaching the theoretical values of two aminopropyls for one , the Cu2+ adsorption on COO−Na+–MCM-41 was less efficient requiring five propionates to adsorb one Cu2+. High purity hydrogen dichromate and copper chloride solutions were respectively recovered by a simple acid wash and the regenerated adsorbents were reused without a loss of performance. [Copyright &y& Elsevier]

Abstract: A feasibility study has been carried out on the preliminary process design of the production of activated carbon from the bamboo scaffolding waste based on 30tonnes of bamboo waste per day throughput. A comparison of the process economics of the stand-alone bamboo carbonization plant with a plant that is integrated into another major processing facility has been studied. The preliminary process design was based on various literature sources and an economic evaluation, in which the total capital investment (TCI), the production cost, the return on investment (ROI), the cash flow and the internal rate of return (IRR) of the stand-alone plant and integrated plant were estimated. The TCI of the stand-alone plant and integrated plant are HK$ 7,430,000 and HK$ 6,430,000, respectively. Net present values of two plants at various discount factors have been determined and the IRR have been estimated as 13.0 and 20.1% for the stand-alone plant and integrated plant, respectively. Sensitivity analysis reveals that the cash flow of the project would be increased or decreased up to 40, 65 and 120% by varying production factors of cost of chemical activation agent, production capacity and selling price of activated carbon, respectively, in the extent of ±25%. [Copyright &y& Elsevier]

The adsorption of three acid dyes onto activated carbon has been studied. Three single, three binary and one ternary systems have been investigated and both equilibrium and kinetic studies have been determined. The equilibrium capacities based on the Langmuir analysis are 0.253, 0.125 and 0.219 mmol g-1 carbon for Acid Blue 80, Acid Red 114 and Acid Yellow 117, respectively. The batch adsorber rate data for the seven systems have been analysed based on an intraparticle diffusion rate parameter derived from the plots of dye adsorbed versus the square root of time. The data indicate the adsorption mechanism is predominantly intraparticle diffusion. The multicomponent system rate parameters have been correlated with the single component rate parameters by the use of the Langmuir equilibrium parameters. [Copyright &y& Elsevier]

Novel fixed-bed adsorption investigations applying carbon nanotube (CNT) coated poly-amidoamine dendrimer (PAMAM) as an adsorbent have been studied for the adsorption of As(III) as arsenous acid, Co 2+ , and Zn 2+ from aqueous solution. FTIR, SEM, 1 H NMR, TGA, TEM, Raman Spectra and zeta potential measurements have been employed for characterizing the synthetic nanocomposite and these techniques indicated that the dendrimer functionalized CNTs have been favorably synthesized. The effects of process parameters including flow rate, initial concentration and bed height on the duration of the breakthrough time, mass transfer zone, adsorption capacity and exhaustion time at breakthrough were investigated. Decreasing initial concentration and flow rate, and increasing bed height, increased the exhaustion and breakthrough times. In addition, the removal capacity at breakthrough was enhanced with decreasing flow rate, initial ion concentration and increasing bed height. The notably high maximum adsorption capacities at fixed bed breakthrough of the studied ions were 432 mg/g for As(III) as arsenous acid, 494 mg/g for Co 2+ , and 470 mg/g for Zn 2+ at bed height of 12.0 cm, influent concentration of 100 mg/L and flow rate of 0.5 mL/min. Almost no previous fixed bed data for PAMAMS exist. Adsorption results were correlated using the Thomas, Yoon-Nelson, and Bohart-Adams models. Empirical breakthrough curves were found to be best fitted with the predicted curves produced by the Thomas and Yoon-Nelson equations. This study illustrates the efficiency of PAMAM/CNT nanocomposite for the adsorption of As(III), Co 2+ , and Zn 2+ from aqueous solution. [ABSTRACT FROM AUTHOR]

In the present study, hydroxyiron-modified montmorillonite (HyFe-MMT) nanoclay was prepared using a simple wet chemical synthesis method. Arsenite (As (III)) removal using raw montmorillonite and HyFe-MMT was compared and evaluated by adsorption experiments conducted under various conditions (adsorbent dosage, iron loading, contact time, pH, and initial As (III) concentration). The nanoclays were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectrometry (FTIR), BET surface area analysis, thermogravimetric analysis, scanning electron (SEM) microscopy, and transmission electron microscopy (TEM). Fast adsorption kinetics were observed in which more than 55% of As (III) was removed using HyFe-MMT within the first 30 s of the adsorption process. The kinetics were most accurately modeled using the pseudo-second-order equation (R 2  = 1). Optimum As (III) adsorption was obtained between a pH of 6 to 7. The Freundlich model properly described the adsorption process (R 2  > 0.99). It was determined that the adsorption capacity of raw MMT was increased to more than five times after iron modification. The HyFe-MMT adsorbent presented could be used for arsenic contaminated groundwater, drinking water, or wastewater. [ABSTRACT FROM AUTHOR]

Sludge, a byproduct produced from numerous industrial activities, has been recognized as an ecological burden for the society. However, viewing the sludge, as a carbon-rich material, has stimulated new gateways for the production of porous activated carbons for water treatment applications. Herein, various textural properties of the sludge-based activated carbons have been compiled and critically reviewed with the focus on surface area, pore size and pore size distribution for both physically and chemically activated carbons. It has been found that chemical activation using various activating agents yields more superior adsorbents with high specific surface areas than physical activation methods. Moreover, the potential of sludge-derived activated carbons for the sequestration of metals and dyes from aqueous media has been discussed. Furthermore, the adsorption mechanism in several adsorbent–adsorbate systems and the effect of various parameters on the adsorption behavior of different dyes and metals on sludge-based activated carbons have been reviewed. It has been shown that the pollutant uptake capacities of the adsorbents derived from sewage sludge are not only governed by the textural properties of the adsorbents, but also by their surface properties, such as the functional groups and the surface charge and thus it is proposed that both of these crucial factors be considered concurrently. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the recovery of base oils from waste lubricants was investigated using a novel combination of solvent extraction and adsorption on solids. The performance of six extracting solvents (n-hexane, 1-butanol, petroleum ether, 1-hexanol, carbon tetra chloride, and acetone) was evaluated experimentally. Solvent to oil ratios from 1:1 to 4:1 were also examined. This research has studied the effect of the use of KOH to enhance flocculation. The results show that 1-butanol achieved the best performance with the maximum percent sludge removal, followed by n-hexane, petroleum ether, 1-hexanol, carbon tetrachloride, and acetone. The percentage of oil sludge was found to increase with the increase of solvent to oil ratio until it reached the maximum at the ratio of 3:1. The application of an adsorption process using different adsorbent materials was investigated. Adsorbent materials such as almond shell, walnut shell, eggshell, and acid activated clay which were prepared locally were used. It was found that the acid activated clay was able to give the best conditions for treating the waste oil followed by the almond shell powder. The results from the test showed that, viscosity increased from 38.3cst for used lube oil to 85cst for acid/clay treatment and the flash point increase from 178°C to 238°C, while the density decreased from 912 to 896kg/m3, the pour point from −6 to −13.2°C and colour from 0.53 to 0.12. Other results from the different tests showed varying degrees of improvement with the best results obtained using the acid/clay treatment. [Copyright &y& Elsevier]

Abstract: Novel Fe loaded activated carbons have been prepared from sugar beet pulp (BP) agricultural residues by direct steam activation followed by iron impregnation with or without previous oxidation. The corresponding activated carbons were: BP–H2O, BP–H2O–Fe, BP–H2O–H2O2–Fe and BP–H2O–MnO2–Fe. The textural characterization of these tailored activated carbons was based on nitrogen adsorption/desorption isotherms leading to BET surface area values between 741 and 821m2/g and total porous volumes between 0.58 and 0.79cm3/g. Elemental analysis and ash content showed that carbon content reached 78% for BP–H2O with 13.6% of ash and decreased to 50% in iron-based materials. BP–H2O and BP–H2O–Fe revealed a basic nature with pHPZC values of 9.8 and 9 respectively while BP–H2O–H2O2–Fe and BP–H2O–MnO2–Fe had acid pHPZC (5.1 and 3.6). Their surface chemistry has been investigated by XPS analysis and by the quantification of the surface chemical moieties based on Boehm’s approach. A clear relationship was found between the surface iron content and the strong acidic groups. Arsenic (As(V)) adsorption isotherms were performed and Langmuir, Freundlich, Redlich–Peterson models were used to describe the experimental data by non-linear regression. It was found that Redlich–Peterson isotherm provided the best fit and the Langmuir adsorption capacities confirmed that the iron-based activated carbons were highly attractive for As(V) removal with capacities up to 17mgg−1. Finally, it has been shown that the surface iron content determined by XPS analysis is very well correlated with Langmuir qm values (r 2 =0.982) and with the strong acidic moieties deduced from the Boehm’s method. [Copyright &y& Elsevier]

Abstract: A series of activated carbons were prepared from bamboo by chemical activation with HCl, HNO3 and H2SO4. Unlike phosphoric acid, these three acids are not commonly used as an activating agent for lignocellulosic materials. The effect of operating variables such as activation temperature, impregnation ratio (the mass ratio between bamboo/acid) and holding time were investigated. The resultant carbons were evaluated for the yield, surface area, pore size distribution, pH, elemental composition and ash. At an impregnation ratio (the mass ratio between bamboo/acid) of 1, activated carbon with BET surface area and micropore volume as high as 553m2/g and 0.239cc/g was obtained at 1173K using H2SO4 as an activating agent. Lower impregnation ratio and shorter holding time were favourable to the yield and surface area while increasing impregnation ratio enhanced mesoporosity of the carbons. This can be attributed to the transformation of micro- to mesopores in the presence of higher ‘basic’ element contents such as nitrogen and sulphur. [ABSTRACT FROM AUTHOR]

Abstract: Experiments have been carried out to prepare char from waste bamboo scaffolding for wastewater treatment. Carbonisation parameters such as temperature, holding time, heating rate and particle size were investigated. When the material was heated to 1173K for 2h, surface area and total pore volume (V total) were 327m2/g and 0.185cm3/g, respectively. Particle size and heating rate appear less influential to the yield and textural characteristics of the resultant chars. Bamboo char obtained in this study did not show very high adsorption capacities for two acid dyes (Acid Blue 25 and Acid Yellow 117) but exhibited significant uptake of Methylene Blue. The equilibrium data were modelled by three different isotherms, namely, Langmuir, Freundlich and Redlich–Peterson model. Comparing the predicted data using optimised parameters from each model based on the SSE error function, the Redlich–Peterson isotherm appears the ‘best’ model to correlate experimental data. [Copyright &y& Elsevier]

Abstract: Selective gold adsorption was investigated for the NH2-MCM-41 and SH-MCM-41 adsorbents prepared by grafting aminopropyl and thiolpropyl groups on the surface of the MCM-41 mesoporous silica. The single component adsorption of gold, copper and nickel from salt solutions, and the binary adsorption studies of Au3+/Cu2+ and Au3+/Ni2+ solutions were carried out for the two adsorbents. Gold adsorption from simulated gold mining solution and gold electroplating wastewater were also reported. The NH2-MCM-41 and SH-MCM-41 displayed strong affinity for gold in the solution and both exhibited 100% selectivity for the gold in the binary Au3+/Cu2+ and Au3+/Ni2+ solutions. The NH2-MCM-41 is more suitable for the gold mining solution, while SH-MCM-41 is efficient for gold adsorption from the electroplating waste containing high amount of organics. The gold was recovered as high purity salt solution by elution with mineral acid for NH2-MCM-41 and thiolsulfate for SH-MCM-41. The regenerated adsorbent remained selective to gold and exhibited the same adsorption capacity as the fresh adsorbent. Also, the regenerated adsorbent performed well even after several reuses. [Copyright &y& Elsevier]

Minimum total amount of microwave treated date stone carbon (S S1 + S S2) for removal of Malachite Green using Langmuir-Freundlich model for different discharge concentrations, C2. [Display omitted] • High surface area carbon from microwaved waste date stone • High adsorption capacity of 98 mg/g for Malachite Green • Optimised two-stage batch adsorber design for minimum adsorbent use Microwave and thermal treatment methods have been applied in order to produce two derived active carbons using waste date pits/stones from a date syrup processing plant. The adsorption properties of the two products have been tested for the adsorption of the toxic Malachite Green dye, which is commonly applied in the textile and plastics industry. Equilibrium isotherms were determined by experiment and evaluated using six isotherm correlations. The optimum fitting correlation for the thermally treated product was the Langmuir-Freundlich isotherm and for the microwave product was the Redlich-Peterson. The surface areas of the thermal product and the microwave product were 669.3 m2/g and 1123 m2/g respectively; and maximum malachite green adsorption capacities were 58 mg/g and 98 mg/g respectively. A two-stage batch adsorber model has been developed to optimize the two-step adsorption process to adsorb malachite green and minimize the amount of adsorbent, and therefore adsorbent cost, used for both thermal treated and microwave treated date stones. The output applications include the minimum total adsorbent for designing various percentages dye removal based on various effluent discharge concentrations and various initial dye concentrations. [ABSTRACT FROM AUTHOR]

The ability of bone char to adsorb three metal ions, namely, copper(II), zinc(II) and cadmium(II) ions from wastewater has been studied. Three single-component equilibrium systems and three binary equilibrium systems have been measured experimentally. The three single-component equilibrium data were analyzed using the Langmuir and the Sips equilibrium isotherm equations. The Sips isotherm gave a better fit of the experimental data than the Langmuir isotherm based on the sum of squares errors (SSE) analysis. The Cu–Zn, Cu–Cd and Cd–Zn binary equilibrium experimental data were examined by incorporating the Langmuir and the Sips isotherm equations into the ideal adsorbed solution theory (IAST). The solution methods and the predicted results for the three binary systems at different metal ion compositions have been evaluated. In addition, the application of the IAST to the model prediction for the fixed bed system is presented. [Copyright &y& Elsevier]