Removal of Cr(VI) from aqueous solutions using modified red pine sawdust

The adsorption of Cr(VI) from aqueous solutions on sawdust (SD), base extracted sawdust (BESD) and tartaric acid modified sawdust (TASD) of Turkish red pine tree (Pinus nigra), a timber industry waste, was studied at varying Cr(VI) concentrations, adsorbent dose, modifier concentration and pH. Batch adsorption studies have been carried out. Sawdust was collected from waste timber industry and modified with various amount of tartaric acid (TA) (0.1-1.5M). The batch sorption kinetics has been tested and the applicability of the Langmuir and Freundlich adsorption isotherms for the present system has been tested at 25+/-2 degrees C. Under observed test conditions, the equilibrium adsorption data fits the linear Freundlich isotherms. An initial pH of 3.0 was most favorable for Cr(VI) removal by all adsorbents. Maximum Cr(VI) was sequestered from the solution within 120 min after the beginning for every experiment. The experimental result inferred that chelation and ion exchange is one of the major adsorption mechanisms for binding metal ions to the SD. Percentage removal of Cr(VI) was maximum at the initial pH of 3.0 (87.7, 70.6 and 55.2% by TASD, BESD, and SD, respectively). Adsorption capacities range from 8.3 to 22.6 mg/g for SD samples.     

Adsorption of Cr(VI) from aqueous solutions by spent activated clay

Adsorption of Cr(VI) onto spent activated clay (SAC), a waste produced from an edible oil refinery company, was investigated for its beneficial use in wastewater treatment. After pressure steam treatment, SAC was used as an adsorbent. The adsorption kinetic data were analyzed and fitted well in a pseudo-first-order equation and the rate of removal was found to speed up with decreasing pH and increasing temperature. Activation energy for the adsorption process was found to be 4.01–5.47 kcal/K mol. The Langmuir adsorption isotherm was used to fit the equilibrium data and the effect of pH, temperature and ionic strength were studied. The maximum adsorption capacities for Cr(VI) ranged from 0.743 to 1.422 mg/g for temperature between 4 and 40 °C under a condition of pH 2.0. The studies conducted show the process of Cr(VI) removal to be spontaneous at high temperature and endothermic in nature. From the waste utilization and environment point of view, the work carried out is important and useful. Results obtained can serve as baseline data for designing a treatment process using this low-cost adsorbent for the treatment of wastewater rich in Cr(VI).     

Low cost removal of reactive dyes using wheat bran

In this study, the adsorption of Reactive Blue 19 (RB 19), Reactive Red 195 (RR 195) and Reactive Yellow 145 (RY 145) onto wheat bran, generated as a by-product material from flour factory, was studied with respect to initial pH, temperature, initial dye concentration, adsorbent concentration and adsorbent size. The adsorption of RB 19, RR 195 and RY 145 onto wheat bran increased with increasing temperature and initial dye concentration while the adsorbed RB 19, RR 195 and RY 145 amounts decreased with increasing initial pH and adsorbent concentration. The Langmuir and Freundlich isotherm models were applied to the experimental equilibrium data depending on temperature and the isotherm constants were determined by using linear regression analysis. The monolayer covarage capacities of wheat bran for RB 19, RR 195 and RY 145 dyes were obtained as 117.6, 119.1 and 196.1 mg/g at 60 degrees C, respectively. It was observed that the reactive dye adsorption capacity of wheat bran decreased in the order of RY 145>RB 19>RR 195. The pseudo-second order kinetic and Weber-Morris models were applied to the experimental data and it was found that both the surface adsorption as well as intraparticle diffusion contributed to the actual adsorption processes of RB 19, RR 195 and RY 145. Regression coefficients (R2) for the pseudo-second order kinetic model were higher than 0.99. Thermodynamic studies showed that the adsorption of RB 19, RR 195 and RY 145 dyes onto wheat bran was endothermic in nature.     

Silkworm exuviae--a new non-conventional and low-cost adsorbent for removal of methylene blue from aqueous solutions

In this paper, silkworm exuviae (SE) waste, an agricultural waste available in large quantity in China, was utilized as low-cost adsorbent to remove basic dye (methylene blue, MB) from aqueous solution by adsorption. Kinetic data and sorption equilibrium isotherms were carried out in batch process. The adsorption kinetic experiments revealed that MB adsorption onto SE for different initial dye concentrations all followed pseudo-second order kinetics and were mainly controlled by the film diffusion mechanism. Batch equilibrium results at different temperatures suggest that MB adsorption onto SE can be described perfectly with Freundlich isotherm model compared with Langmuir and D-R isotherm models, and the characteristic parameters for each adsorption isotherm were also determined. Thermodynamic parameters calculated show the adsorption process has been found to be endothermic in nature. The analysis for the values of the mean free energies of adsorption (E(a)), the Gibbs free energy (ΔG(0)) and the effect of ionic strength all demonstrate that the whole adsorption process is mainly dominated by ion-exchange mechanism, which has also been verified by variations in FT-IR spectra and pH value before and after adsorption and desorption studies. The results reveal that SE can be employed as a low-cost alternative to other adsorbents for MB adsorption.     

Removal of Cr(VI) from aqueous solutions using pre-consumer processing agricultural waste: a case study of rice husk

This paper reports the feasibility of using pre-consumer processing agricultural waste to remove Cr(VI) from synthetic wastewater under different experimental conditions. For this, rice husk, has been used after pre-treatments (boiling and formaldehyde treatment). Effect of various process parameters, namely, pH, adsorbent dose, initial chromium concentration and contact time has been studied in batch systems. The removal of chromium was dependent on the physico-chemical characteristics of the adsorbent, adsorbate concentration and other studied process parameters. Maximum metal removal was observed at pH 2.0. The efficiencies of boiled and formaldehyde treated rice husk for Cr(VI) removal were 71.0% and 76.5% respectively for dilute solutions at 20gl(-1) adsorbent dose. The experimental data were analyzed using Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherm models. It was found that Freundlich and D-R models fitted well. The results revealed that the hexavalent chromium is considerably adsorbed on rice husk and it could be an economical method for the removal of hexavalent chromium from aqueous systems. FTIR and SEM were recorded, before and after adsorption, to explore number and position of the functional groups available for Cr(VI) binding on to studied adsorbents and changes in adsorbent surface morphology.     

Synthesis of ordered large-pore mesoporous carbon for Cr(VI) adsorption

Highly ordered mesoporous carbon with large accessible pores (OMC-P) was prepared by using laboratory-made poly(ethylene oxide)-b-polystyrene diblock copolymer as template via the evaporation-induced self-assembly method. The OMC-P was first used as adsorbent for removal of Cr(VI) ion from aqueous solution. Adsorption behavior was studied as a function of time, concentration of adsorbate, temperature, and pH. The kinetics of adsorption of Cr(VI) ion onto OMC-P is well fit to the pseudo-second order model. The Cr(VI) ion adsorption is favored at lower temperatures and at initial acid pH values in the equilibrium. The Freundlich and the Langmuir isotherm fit the equilibrium data satisfactorily. The influence of porosity on equilibrium adsorption capacity was investigated on three types of carbon materials, namely, OMC-P, ordered mesoporous carbon templated from amphiphilic triblock copolymer F127 (OMC-F) and commercial activated carbon (AC). The prepared OMC-P exhibits much higher adsorption performance than the other two carbons.     

Carbonate effects and pH-dependence of uranium sorption onto bacteriogenic iron oxides: kinetic and equilibrium studies

The removal of U(VI) from groundwaters by adsorption onto bacteriogenic iron oxides (BIOS) has been investigated under batch mode. The adsorbent dosage, the uranium concentration, the concentration of carbonate and the use of a real groundwater spiked with uranium comprised the examined parameters. In addition, the effect of pH was examined in two different water matrixes, i.e., in distilled water and in real groundwater. Equilibrium studies were carried out to determine the maximum adsorption capacity of BIOS and the data correlated well with the Langmuir and Freundlich models. The presence of carbonate affected adversely the adsorption of U(VI) onto BIOS. The maximum adsorption capacity of BIOS was 9.25 mg g(-1) at 0.1mM carbonate concentration and decreased to 6.93 mg g(-1) at 0.5mM carbonate concentration, whereas at carbonate concentration of 2mM practically no adsorption occurred. The data were further analyzed using the pseudo-second order kinetic equation, which fitted best the experimental results. The initial adsorption rate (h) was found to increase with decreasing the concentration of carbonate in all cases. When experiments were accomplished in the absence of carbonate, the pH values did not have an effect on the adsorption of U(VI). However, the extent of U(VI) adsorption was strongly pH-dependent when the experiments were carried out in the real groundwater. The maximum adsorption capacity increased sharply as the pH decreased and optimum removal was obtained in the pH range 3.2-4.0, thus bacteriogenic iron oxides can found application in the removal of U(VI) by adsorption from low pH or low carbonate waters.     

Removal of copper from aqueous solution using Ulva fasciata sp.--a marine green algae

Batch adsorption experiments were carried out for the removal of copper from its aqueous solution using Ulva fasciata sp. a marine green algae as adsorbent. The adsorption of Cu(II) by Ulva fasciata sp. was investigated as a function of pH, contact time, initial Cu(II) and adsorbent concentrations and adsorbent size. About 0.1 g of Ulva fasciata sp. was found to be enough to remove 95% of 20 mg/L copper from 30 mL aqueous solution in 20 min. The optimum pH value was found to be 5. The dynamic data fitted to the pseudo-second order kinetic model. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were determined. The experimental adsorption data were fitted to the Langmuir adsorption model. The maximum adsorption capacity was 26.88 mg/g. The applicability of Lagergren kinetic model was also investigated.     

Potential Malaysia agricultural waste materials for the biosorption of cadmium(II) from aqueous solution

Biosorption of cadmium(II) ions (Cd²⁺) onto Ananas comosus (AC) peel, Parkia speciosa (PS) pods and Psidium guajava (PG) peel were investigated in this study. Batch sorption experiments were performed by investigating the effect of initial pH. It was found that Cd²⁺ uptake was highly dependent on the initial pH and Cd²⁺ removal efficiency was highest for PG peel, followed by AC peel and PS pods. Biosorption experiments were carried out using different initial Cd²⁺ concentration and the experimental data obtained was fitted to both Langmuir and Freundlich isotherms. The experimental data was found to best fit the Langmuir isotherm, and adsorption capacities of 18.21 mg/g (AC peel), 25.64 mg/g (PS pods) and 39.68 mg/g (PG peel) were obtained. Comparison with published adsorption capacities for other low-cost biosorbents indicates that PS pods and PG peel have potential as low-cost biosorbent materials for the removal of Cd²⁺ from aqueous solution.     

Characterization of chromium (III) removal from aqueous solutions by an immature coal (leonardite). Toward a better understanding of the phenomena involved

Removal of chromium (III) from aqueous solutions by leonardite (a low-cost adsorbent) was studied in a series of batch experiments. Stabilization of the adsorbent material with alginate beads was also investigated. The extent of adsorption was evaluated as a function of the solution pH, contact time, and the adsorbate concentration. Cr(III) removal was pH dependent, reaching a maximum at a pH range of 4–5. Kinetic studies allowed gives relevant information regarding mass transfer processes involved during the sorption process. Equilibrium data fitted well to both the Langmuir and Freundlich isotherm models and the maximum adsorption capacity turned out to be 75.2 mg Cr(III) g^?1. Encapsulation of leonardite in alginate beads resulted in a slightly lower adsorption capacity.     

Removal of Cr(VI) from industrial wastewaters by adsorption Part I: determination of optimum conditions

Aim of this study is the determination of the Cr(VI) removal efficiency of treated pine sawdust and also to find out the thermodynamic and kinetic parameters of Cr(VI) removal process in batch systems. Sawdust has been treated with 1,5-disodium hydrogen phosphate before the adsorption experiments. The effects of initial concentration of Cr(VI) ion, temperature, amount of adsorbent and pH of the solution on adsorption have been investigated. Optimum conditions for adsorption were determined as T=40 degrees C, sawdust dose=4 g, pH 2, by using the results of these experiments and an additional set of experiments was performed under these optimum conditions in order to see the change in the adsorption efficiency. Removal of chromium ion was found as highly dependent on pH and initial Cr(VI) concentration of the solution. In order to find out thermodynamic and kinetic parameters equilibrium adsorption models were applied. Although experimental data confirm with both Langmuir and Freundlich isotherm models, they suit most on Langmuir isotherms. Adsorption rate constant was determined from Lagergren equation. Equilibrium constants, adsorption free energy, enthalpy and entropy change values were also determined. It was found that adsorption process follows first order kinetic and adsorption of Cr(VI) on sawdust has the spontaneous nature.     

Removal of chromium (VI) from aqueous solution using treated oil palm fibre

This study proposed an oil palm by-product as a low-cost adsorbent for the removal of hexavalent chromium [Cr (VI)] from aqueous solution. Adsorption of Cr (VI) by sulphuric acid and heat-treated oil palm fibre was conducted using batch tests. The influence of pH, contact time, initial chromium concentration and adsorbent dosage on the removal of Cr (VI) from the solutions was investigated. The optimum initial pH for maximum uptake of Cr (VI) from aqueous solution was found to be 1.5. The removal efficiency was found to correlate with the initial Cr (VI) concentration, adsorbent dosage as well as the contact time between Cr (VI) and the adsorbent. The adsorption kinetics tested with pseudo first order and pseudo second order models yielded high R(2) values from 0.9254 to 0.9870 and from 0.9936 to 0.9998, respectively. The analysis of variance (ANOVA) showed significant difference between the R(2) values of the two models at 99% confidence level. The Freundlich isotherm (R(2)=0.8778) described Cr (VI) adsorption slightly better than the Langmuir isotherm (R(2)=0.8715). Difficulty in desorption of Cr (VI) suggests the suitability of treated oil palm fibre as a single-use adsorbent for Cr (VI) removal from aqueous solution.     

Removal of methylene blue from aqueous solution by dehydrated wheat bran carbon

Dyes are usually presents in the effluent water of many industries, such as textiles, leather, paper, printing and cosmetics. The effectiveness of dye adsorption from wastewater has made to get alternative different low cost adsorbent to other expensive treatment methods. The adsorption of methylene blue onto dehydrated wheat bran (DWB) was investigated at temperatures (25-45 degrees C), initial methylene blue (MB) concentrations (100-500 mg L(-1)) and adsorbent dosage at the given contact time for the removal of dye. The optimum adsorption conditions were found to be as medium pH of 2.5 and at the temperature of 45 degrees C for the varying adsorbent dosage. Equilibrium isotherms were analysed by Freundlich, Langmuir and Redlich-Peterson isotherm equations using correlation coefficients. Adsorption data were well described by the Langmuir model, although they could be modelled by the Freundlich and Redlich-Peterson model as well. The pseudo-first order and pseudo-second order kinetic models were applied to test the experimental data. It was concluded that the pseudo-second order kinetic model provided better correlation of the experimental data rather than the pseudo-first order model. The mass transfer model as intraparticle diffusion was applied to the experimental data to examine the mechanisms of rate controlling step. It was found that at the higher initial MB concentration, intraparticle diffusion is becoming significant controlling step. The thermodynamic constants of the adsorption process were also evaluated by using the Langmuir constants related to the equilibrium of adsorption at temperatures varied in the range 25-55 degrees C.     

Removal of lead from aqueous solution using Syzygium cumini L.: equilibrium and kinetic studies

The biosorption of lead ions from aqueous solution by Syzygium cumini L. was studied in a batch adsorption system as a function of pH, contact time, lead ion concentration, adsorbent concentration and adsorbent size. The biosorption capacities and rates of lead ions onto S. cumini L. were evaluated. The Langmuir, Freundlich, Redlich-Peterson and Temkin adsorption models were applied to describe the isotherms and isotherm constants. Biosorption isothermal data could be well interpreted by the Langmuir model followed by Temkin model with maximum adsorption capacity of 32.47 mg/g of lead ion on S. cumini L. leaves biomass. The kinetic experimental data were properly correlated with the second-order kinetic model.     

Adsorption of p-nitrophenol from aqueous solutions onto activated carbon fiber

The adsorption of p-nitrophenol (PNP) onto activated carbon fiber (ACF) was investigated in simulated wastewater in a batch system to evaluate the effects of solution pH, presence of sodium chloride, adsorbent doses and temperature. It was found that PNP adsorption amount depended on pH, sodium chloride content, adsorbent doses and temperature. Langmuir and Freundlich models were applied to describe the adsorption isotherms. Freundlich model agreed with experimental data well, indicating the possibility of more than just one monomolecular layer of coverage. SEM photographs of ACF before and after adsorption revealed that it was in part with multimolecular layers of coverage on ACF surfaces. The change of free energy, enthalpy, and entropy of adsorption were also evaluated for the adsorption process. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data. The experimental data fitted very well the pseudo-second-order kinetic model. Attempts were made to desorb PNP from ACF using dilute NaOH solution and water, and desorption efficiency was obtained to the extent of 92.7% with 0.025 M NaOH and water at 368 K.     

Hydrated cement: a promising adsorbent for the removal of fluoride from aqueous solution

The present study was carried out to investigate the potential of cement hydrated at various time intervals for the removal of excess F- from aqueous solution by using batch adsorption studies. The influence of different adsorption parameters, viz. effect of adsorbent dose, initial concentration, pH, interfering ions and contact time were studied for their optimization. It was observed that the adsorbent exhibited reasonably significant F- removal over a wide range of pH. The presence of carbonate and bicarbonate ions in aqueous solution were found to affect the F- removal indicating that these anions compete with the sorption of F- on adsorbent. The equilibrium adsorption data were fitted well for both the Freundlich and Langmuir isotherms and the adsorption capacities were calculated. Comparative studies for F- removal in simulated and field water show relatively higher F- removal in simulated water. XRD and SEM patterns of the hydrated cement were recorded to get better insight into the mechanism of adsorption process. From the experimental results, it may be concluded that HC was an efficient and economical adsorbent for F- removal.     

Spent tea leaves: a new non-conventional and low-cost adsorbent for removal of basic dye from aqueous solutions

In the present study, spent tea leaves (STL) were used as a new non-conventional and low-cost adsorbent for the cationic dye (methylene blue) adsorption in a batch process at 30 degrees C. Equilibrium sorption isotherms and kinetics were investigated. The experimental data were analyzed by the Langmuir, Freundlich and Temkin models of adsorption. The adsorption isotherm data were fitted well to the Langmuir isotherm and the monolayer adsorption capacity was found to be 300.052mg/g at 30 degrees C. The kinetic data obtained at different initial concentrations were analyzed using pseudo-first-order, pseudo-second-order and intraparticle diffusion equations. The results revealed that the spent tea leaves, being waste, have the potential to be used as a low-cost adsorbent for the removal of methylene blue from aqueous solutions.     

Kinetics and equilibrium studies for the adsorption of Acid Red 57 from aqueous solutions onto calcined-alunite

The adsorption of Acid Red 57 (AR57) onto calcined-alunite was examined in aqueous solution in a batch system with respect to contact time, pH and temperature. The first-order, pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intraparticle diffusion model up to 90 min. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The equilibrium data are successfully fitted to the Langmuir adsorption isotherm. The Langmuir isotherm constant, K(L), was used to evaluate the changes of free energy, enthalpy and entropy of adsorption for the adsorption of AR57 onto calcined-alunite. The results indicate that calcined-alunite could be employed as low-cost material for the removal of acid dyes from textile effluents.     

活性炭负载Fe(Ⅲ)氧化物去除水中的磷酸根

利用活性炭负载铁氧化物制备了复合吸附剂,并用于水中磷酸根的去除.采用BET,SEM及XRD等手段对复合吸附剂的物理化学特性进行了表征,用静态吸附实验方法比较研究了复合吸附剂和活性炭从水溶液中吸附磷酸根的性质.结果表明:复合吸附剂具有快的吸附速度和高的吸附容量,其吸附磷酸根的性质受溶液pH值、铁含量及阴离子浓度的影响.在pH=3.0时,复合吸附剂对磷酸根的吸附容量为98.39 mg/g,而活性炭为78.90 mg/g.相比之下,Freundlich模型比Langmuir模型能更好地描述复合吸附剂和活性炭对磷酸根的吸附过程;而Lagergren二级方程却能很好地描述复合吸附剂对磷酸根的吸附动力学.水合氧化铁/活性炭复合吸附剂吸附磷酸根为吸热过程.     

Chromium (VI) adsorption on boehmite

Boehmite was synthesized and characterized in order to study the adsorption behavior and the removal of Cr(VI) ions from aqueous solutions as a function of contact time, initial pH solution, amount of adsorbent and initial metal ion concentration, using batch technique. Adsorption data of Cr(VI) on the boehmite were analyzed according to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) adsorption models. Thermodynamic parameters for the adsorption system were determinated at 293, 303, 313 and 323K temperatures. The kinetic values and thermodynamic parameters from the adsorption process show that the Cr(VI) ions adsorption on boehmite is an endothermic and spontaneous process. These results show that the boehmite could be considered as a potential adsorbent for chromium ions in aqueous solutions.