Removal of Cr(V1) from aqueous solutions by adsorption on fly ash-wollastonite

The ability of a homogeneous mixture of fly ash and wollastonite (1:1) to remove Cr(V1) from aqueous solutions by adsorption has been investigated. The extent of removal is dependent on concentration, pH and temperature of the solution. The applicability of the Langmuir isotherm for the present system has been tested and the surface mass transfer coefficient at 30°C and pH 2.0 determined. Maximum removal was observed at pH 2.0 and 30°C. The adsorption is first governed by diffusion followed by surface compound formation. The thermodynamic parameters, desorption results and infrared studies indicated that the surface compounds, formed by interaction of adsorbate ions and different constituents of mixed adsorbent, were stable in nature.     

Removal of congo red from aqueous solutions by biogas waste slurry

Removal of Congo Red was carried out using biogas waste slurry as adsorbent at different concentrations of dye, adsorbent dosage, agitation time and pH. The process follows the first-order rate expression. The equilibrium data fit well in the Freundlich model of adsorption. Maximum removal of dye, 95%, was observed in the pH range 2.3–9.4. Desorption of Congo Red showed that it is solubilised in 50% acetic acid to the extent of 6% and the remainder appears to be chemically complexed irreversibly to the adsorbent. Low desorption of dye from the adsorbent surface in water indicates that the process may not be, essentially, a reversible one.     

Removal of Cu(II) from aqueous solutions by recycled tire rubber

A batch adsorption system was applied to study the adsorption of Cu(II) ions from aqueous solutions by crumb rubber. The effects of pH ranging from 1.5 to 7.0, contact time ranging from 6 to 96 h and initial metal concentration ranging from 1 mg L^− 1 to 50 mg L^− 1 on the removal of Cu(II) were studied. Results show that adsorption of Cu(II) is pH-dependent and the best results are obtained at pH = 6.0. Results also show that copper uptake is accompanied by displacement of zinc and therefore probably involves an ion exchange type mechanism. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. Results clearly show that crumb rubber is an effective adsorbent for the removal of Cu(II) from aqueous solutions.     

Removal of Cu(II) from aqueous solutions by chelating starch derivatives

Two chemically modified starch derivatives, crosslinked amino starch (CAS) and dithiocarbamates modified starch (DTCS), were prepared and used for the removal of Cu(II) from aqueous solutions. CAS was found to be effective for the adsorption of Cu(II), which tended to form a stable amine complex. Adsorption of Cu(II) onto DTCS was higher than that onto CAS. Experiments showed that the adsorption processes of Cu(II) on both CAS and DTCS were endothermic, and followed Freundlich isothermal adsorption. For both adsorbents, dynamic modeling of their adsorption showed that the first‐order reversible kinetic model described the adsorption process. The adsorption rate constants of CAS and DTCS were 1.578 and 10.32 h^?1, respectively. From the results of the thermodynamic analysis, free energy ΔG, enthalpy ΔH, and entropy ΔS of the adsorption process were calculated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3881–3885, 2004     

Removal of As(V) species from extremely contaminated mining water

The effective removal of arsenic compounds from strongly contaminated mining water with a high content of As (about 50 mg/l) and other metals, especially iron (about 5000 mg/l) has been studied. The process ran in two steps. At first, the raw acid mining water containing predominantly Fe²⁺ ions was partially precipitated with a small amount of an alkaline agent. On a small portion of the precipitated iron (about 30–40%), more then 90% of the arsenic was adsorbed forming a toxic precipitate, which was then stirred under an inert agent (Ar) and further in air for 1 h. Secondly, the precipitation of the first step liquid residue (using the same or a different alkaline agent) enabled the final treatment of the mining water at pH 8.5. While arsenic was substantially removed by the first precipitation, the other components including residual iron, manganese, zinc and sulfates were precipitated quantitatively during the second step. The mass of the second precipitate depended strongly on the alkaline agent used in the second step.The mechanism and kinetics of arsenic sorption onto iron species, and phase changes of the sorbent during the sorption process were investigated. The composition of the precipitates was verified by XRD and XRF analyses, as well as by infrared and Raman spectroscopy. The precipitation of a raw mining water resulted in formation of a complex inorganic system where amorphous phases dominated. Various crystalline phases, predominantly concerning Fe(II)–Fe(III), As, Zn and sulfates also appeared, depending on the actual oxidizing state of the whole system and on redistribution of its components.The two-step precipitation of arsenic contaminated mining water results in a significant ecological and economical improvement due to the decrease in the amount of waste toxic mass.     

Removal of basic and acid dyes from aqueous solutions by a waste containing boron impurity

In this study, batch experiments were carried out for the sorption of basic blue 41 (BB 41), and acid blue 225 (AB 225) onto boron waste (BW) from boron enrichment plant. The operating variables studied are the initial dye concentration, contact time, solution pH, and adsorbent dosage. The experimental equilibrium data were analyzed by using various adsorption isotherm models and the results have shown that the adsorption behavior of AB 225 and BB 41 could be described well reasonably by Langmuir and Temkin isotherms, respectively. Kinetics studies indicated that the adsorption of both dyes follow pseudo-second-order kinetics. The sorption of basic dye increased at high pH values, whereas the opposite was true for acidic dye. The results indicate that BW could be employed as low-cost alternatives to the commercially available adsorbents in wastewater treatment for the removal of acid and basic dyes.     

Removal of Pb(II) from aqueous solution by adsorption using activated tea waste

A basic investigation on the removal of Pb(II) ions from aqueous solutions by using activated tea waste was conducted in batch conditions. An inexpensive and effective adsorbent was developed from waste tea leaves for the uptake of Pb(II) from aqueous solution. The influence of different experimental parameters—shaking time, particle size, adsorbent dose, initial pH, temperature, etc.—on lead uptake was evaluated. Lead is adsorbed by the developed adsorbent up to maximum of 99.7%. The initial Pb(II) concentrations were 5, 10, 15 and 20 mg/l in the experiment. The adsorption was found to be exothermic in nature. The Langmuir, Freundlich and Tempkin isotherm models were tried to represent the equilibrium data of Pb(II) adsorption. The adsorption data was fitted very well to the Langmuir isotherm model in the studied concentration range of Pb(II) adsorption. Isotherms have been used to determine thermodynamic parameters of the process: free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°). Column experiments were performed to study the practical applicability of the system. The kinetics and the factors controlling the adsorption process were also discussed. Activated tea waste is a better adsorbent compared to other adsorbents available in literature.     

Removal of cadmium(II) from aqueous solution by agricultural waste cashew nut shell

Cashew nut shell (CNS) is a low cost adsorbent that has been used for the removal of cadmium(II) from an aqueous solution. The effects of various parameters such as solution pH, CNS concentration, contact time, initial cadmium(II) concentration and temperature were examined. The CNS was effective for the quantitative removal of cadmium(II) ions in acidic conditions and equilibrium was achieved in 30 min. The experimental data were analyzed by two-parameter (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich) and three-parameter models (Redlich- Peterson, Koble-Corrigan, Toth and Sips) by nonlinear regression analysis. The characteristic parameters for each isotherms and related correlation coefficients have been determined by using MATLAB 7.1. Thermodynamic parameters such as ??G ^o , ??H ^o and ??S ^o have also been evaluated, and it was found that the sorption process was feasible, spontaneous and exothermic. Pseudo-first-order, pseudo-second-order, Elovich kinetic and intraparticle diffusion models were selected to follow the adsorption process. The results of the kinetic study show that the adsorption of cadmium(II) could be described by the pseudo-second order equation, suggesting that the adsorption process is presumably chemisorption. A single-stage batch adsorber was designed for different adsorbent dose-to-effluent volume ratios using the Freundlich equation. The results indicate that the cashew nut shell could be used to effectively adsorb cadmium(II) from an aqueous solution.     

Enhanced Removal of As(V) from Water with Iron-Coated Spent Catalyst

Abstract

The effectiveness of pretreating a spent catalyst with an iron-salt solution to improve its As(V) removal capacity was studied. Various factors, such as types and concentrations of iron salt, pH. and initial As(V) concentration were investigated for their effects on the improvement of As(V) removal capacity. A significant increase in As(V) removal capacity can be achieved by iron-coated spent catalyst. Adsorption density of As(V) decreased with increasing pH. Langmuir adsorption isotherm was utilized to describe the adsorption reaction. Results from IR analysis and zeta potential measurement indicate that As(Y) is specifically adsorbed onto iron-coated spent catalyst. This study shows that spent catalyst can be converted to a useful adsorbent for As(V) removal.     

Removal of chromium (III) and cadmium (II) from aqueous solutions

Chromium and cadmium are toxic heavy metals present in wastewaters from a variety of industries. A strong cationexchange resin, Amberlite IR 120, was used for the removal of chromium and cadmium. The resin was prepared in two different cationic forms, as Na⁺ and H⁺. The optimum conditions were concentration, pH, stirring time and resin amount. The concentration range was between 2–50 mg/L, pH range between 2–10, stirring time between 5–60 min, and the amount of resin was from 50–1000 mg. Exchange capacities, moisture content and optimum conditions of this resin were determined in a batch system. The stirring speed was 2000 rpm during all of the batch experiments. The initial and final chromium and cadmium amounts were determined by atomic absorption spectrophotometry. The optimum conditions were found to be a concentration of 20 mg/L, pH of 5.5, stirring time of 20 min and 100 mg of resin. The results obtained show that the Amberlite IR 120 strong cation-exchange resin performed well for the removal and recovery of chromium and cadmium.     

活性炭负载Fe(III)吸附剂去除饮用水中的As(V)

利用活性炭负载水合铁氧化物制备了复合吸附剂,并用于饮用水中As(V)的去除. 研究了活性炭种类、粒度、溶液pH值、Fe(III)盐浓度和干扰离子等对As(V)去除的影响. 结果表明,煤质活性炭作为基质负载水合铁氧化物比椰壳炭和果壳炭具有更好的除砷效果. 随着炭粒度降低,除砷效率显著增加. 在pH 3~9范围内,活性炭负载水合铁氧化物可有效吸附As(V). F-, Cl-, SO42-的加入对As(V)的去除效率基本无影响,而SiO32-和PO43-则明显抑制As(V)的去除. Langmuir模型比Freundlich模型能更好地描述复合吸附剂对As(V)的吸附平衡. 动力学研究表明,As(V)吸附反应可用二级速率方程描述.     

Removal of phosphate from aqueous solutions by iron nano-particle resin Lewatit (FO36)

Lewatit FO36 resin was covered with Fe (III) nano-particles, and it was used as a new way to eliminate phosphate. Column experiments were carried out in 11 stages in fixed bed columns with constant flow rate of 9 ml/min and the empty bed contact time (EBCT) of 2.1 min. The adsorption capacity was calculated for different concentration of phosphate solutions. After resin was regenerated by using NaOH and NaCl solutions, the adsorption capacity of resin was computed for 6mg/L of phosphate, typically. The adsorption capacity of resin was checked again a typical concentration of phosphate. The adsorption capacity measurements of regenerated resin show that the concentration of phosphate reached to 1.6mg/g after an 8.5% decrease when the initial concentration of phosphate is 6 mg/L. Competition of anions with phosphate was analyzed using chloride, sulfate, bicarbonate and a combination of these anions. Finally the effect of resin in phosphate removal was studied for a typical real sample, and the data was analyzed using statistical software (SPSS 13). The statistical results indicated that Cl⁻, SO₄³⁻, HCO₃⁻ and combined competing anions did not have a strong influence on the phosphate removal efficiency.     

Removal of phenol from aqueous solutions by continuous RF-pertraction

Water dephenolation was studied using a multistage Rotating Film Pertractor (RFP). This relatively new liquid membrane technique allows the use of almost water-insoluble liquids as intermediate organic ‘membranes’. The effects of the main processing parameters such as disc rotation velocity, temperature and phase flowrate, on removal efficiency were studied. A mathematical model describing the process of dephenolation in a counter-current multistage cascade of n-RFP contactors was proposed for the prediction of phenol removal.     

花生壳制活性炭及其脱六价铬研究

本文研究了用花生壳制备活性炭和用此活性炭去除水溶液中的Cr（Ⅵ）。采用化学活化法,即用H2SO4、H3PO4、ZnCl2、KOH活化花生壳中的炭。同时研究了这些活化剂的浓度和用量、热解时间和温度对活性炭性能的影响。采用亚甲基蓝吸附实验评价活性炭的性能。结果表明H3PO4和ZnCl2是良好的活化剂,KOH和H2SO4效果较差。溶液的pH值对活性炭吸附Cr（Ⅵ）的能力有很大影响。活性炭的吸附能力随着pH值的降低而升高,同时在不同的pH值下,炭的吸附速率也不同。pH值越低,Cr（Ⅵ）被吸附的越快。等温实验结果表明,在pH值等于2时,用H3PO4和ZnCl2活化的活性炭对Cr（Ⅵ）的吸附能力分别达到125．0和83．3mg·g^-1。花生壳活性炭吸附Cr（Ⅵ）的机理比较复杂,与溶液的pH值有关。在pH值等于2时,等温吸附可以用Langmuir模型模拟;在pH值等于2～7时,可以用Freundlich模型模拟。     

Removal of As(V) and Cr(VI) in aqueous solution by sand media simultaneously coated with Fe and Mn oxides

In this research, sand media simultaneously coated with iron and manganese (iron and manganese coated sand, IMCS) were applied to treat synthetic wastewater contaminated with both Cr(VI) and As(V). Scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) were used to characterize the surface properties of the coated layer of IMCS. Adsorption of Cr(VI) and As(V) onto IMCS followed a typical anionic type, showing a gradual decrease of adsorption as the solution pH increased. In a single system, IMCS showed a greater adsorption capacity for As(V) than that for Cr(VI) over the entire solution pH range. In a binary system, As(V) preferentially occupied the limited adsorption sites on IMCS and therefore Cr(VI) adsorption was suppressed. This result indicates that As(V) adsorption onto the surface of IMCS occurs through a strong chemical bonding such as an inner-sphere complex. As(V) adsorption onto the IMCS was well described by second-order kinetics. From the adsorption isotherm experiments at pH 4, the maximum adsorbed amount of Cr(VI) and As(V) onto IMCS in a single system was 102 mg/kg and 455 mg/kg, respectively.     

Removal of chromium (VI) from aqueous solutions using quaternized chitosan microspheres

In this study, quaternized chitosan microspheres (QCMS) were prepared and its Cr(VI) removal potential was investigated. Batch experiments were conducted to examine kinetics, adsorption isotherm, pH effect, and thermodynamic parameters. Equilibrium was attained within 50 min and maximum removal of 97.34% was achieved under the optimum conditions at pH 5. Adsorption data for Cr (VI) uptake by the QCMS were analyzed according to Langmuir, Freundlich, and Temkin adsorption models. The maximum uptake of Cr(VI) was 39.1 mg·g^-1. Thermodynamic parameters for the adsorption system were determinated at 293 K, 303 K, 313 K and 323 K. (ΔH°=16.08 kJ·mol^-1;ΔG°=-5.84 to -8.08 kJ·mol^-1 and ΔS°=74.81 J·K^-1·mol^-1). So the positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption.ΔG° values obtainedwere negative indicating a spontaneous adsorption process. The kinetic process was described by a pseudo-second-order rate equation very well. The results of the present study indicated that the QCMS could be considered as a potential adsorbent for Cr (VI) in aqueous solutions.     

Removal of chromium(VI) from aqueous solutions using polypyrrole-based magnetic composites

PPy/Fe₃O₄/AgCl composites were prepared via in situ polymerization for the removal of highly toxic Cr(VI). The structure and morphology of the prepared composites were characterized by the XRD, SEM, TEM, and VSM examinations. Up to 100 % removal was found with 1000 mg/L Cr(VI) aqueous solution at pH 2.0. The process of Cr(VI) ions’ adsorption was easy to reach equilibrium at higher temperatures. Adsorption results showed that Cr(VI) removal efficiency by the composites decreased with an increase in pH. Adsorption kinetics was described by the pseudo-second-order rate model. Isotherm data fitted well to the Langmuir isotherm model. Desorption experiment showed that the regenerated adsorption of PPy/Fe₃O₄/AgCl can be reused successfully for three times successive adsorption–desorption cycles without appreciable loss of its original capacity.     

Removal of Pb(II) from aqueous solutions by using clinoptilolite and bentonite as adsorbents

In the present study, the ability of natural zeolite clinoptilolite and bentonite (clay) to remove Pb(II) from aqueous solutions has been investigated in batch reactors with a maximum contact time of 120 min. Adsorption tests of Pb(II) were carried out using a solution concentration of 1,036 ppm at initial pH = 4, and solid to liquid ratio of 2 g/100 mL. The effects of agitation speed (0, 100, 200, 500 rpm), temperature (28°C, 45°C, 60°C) and particle size (2.5–5.0 mm, dust) of the minerals were examined. The effect of acidity of the aqueous solution was also examined. Bentonite was found to be more effective for the removal of Pb(II) than clinoptilolite, under the experimental conditions used. The removal of Pb(II) using bentonite reached 100% at ambient temperature and mild agitation (100 rpm), while it was approximately 90% at 60°C without agitation. On the other hand, the highest removal level reached by clinoptilolite was 55%. Clinoptilolite dust is found to be more efficient than granular clinoptilolite. Agitation and temperature affected the uptake of Pb(II), especially in the case of granular clinoptilolite (2.5–5.0 mm). Finally, it can be seen that acidity of the aqueous solution influences the removal of lead by the minerals. The adsorption of lead increases with an increase in pH of the solution from 1 to 4.