Maximum Cr Removal Research Articles

Chromium (VI) adsorption onto activated sulfate lignin

Activated lignin having surface area of 1023 m2.g-1 has been prepared from sulfate lignin that was treated by 30 % H2O2 and carbonized at 300 °C in order to test the chromium (VI) adsorption from aqueous solution. The influence of contact time, pH, initial concentration of adsorbent and adsorbate and temperature on the adsorption capacity were investigated. The maximum removal of Cr(VI) was found to be 92,36 % at pH=2 and contact time of 80 min. Optimal concentration of lignin and Cr(VI) were found to be 3.8 g.l-1 and 180 mg.l-1, respectively. The adsorption kinetics was tested pseudo-first-order and pseudo-second-order equation. The analytical data were fitted well in a pseudo-second-order equation and the rate of removal of chromium was found to speed up with increasing temperature. Activation energy for the adsorption process was found to be 18.19 Kj.mol-1. The Langmuir and Freundlich adsorption isotherm models were applied to describe the isotherm and isotherm constants for the adsorption of Cr (VI) on lignin. These constants and correlation coefficients of the isotherm models were calculated and compared. Results indicated that Cr (VI) uptake could be described by the Langmuir adsorption model. The maximum adsorption capacity (qm) of Cr (VI) on lignin was 75.75 mg.g-1 at temperature of 40°C. The dimensionless equilibrium parameter (RL) signified a favorable adsorption of Cr (VI) on lignin and was found between 0.0601 and 0.818 (0<RL<1). The thermodynamic parameters like ΔG°, ΔS° and ΔH° were calculated and it has been found that the reaction was spontaneous and endothermic in nature. This study indicates that lignin has the potential to become an effective and economical adsorbent for removal Cr (VI) from the waste water.

Chromium (VI) adsorption onto activated kraft lignin produced from alfa grass (Stipa tenacissima)

Activated lignin having a surface area of 1023 m2 g-1 has been prepared from sulfate lignin that was treated by 30% H2O2 and carbonized at 300 °C in order to test the chromium (VI) adsorption from aqueous solution. The influence of contact time, pH, initial concentrations of adsorbent and adsorbate, and temperature on the adsorption capacity were investigated. The maximum removal of Cr(VI) was found to be 92.36 % at pH=2 and a contact time of 80 min. Optimal concentration of lignin and Cr(VI) were found to be 3.8 g L-1 and 180 mg L-1, respectively. The adsorption kinetics data fitted well with a pseudo-second-order equation, and the rate of removal of chromium was found to speed up with increasing temperature. Activation energy for the adsorption process was found to be 18.19 kJ mol-1. The Langmuir and Freundlich adsorption isotherm models were applied to describe the isotherm and isotherm constants for the adsorption of Cr (VI) on lignin. These constants and correlation coefficients of the isotherm models were calculated and compared. Results indicated that Cr (VI) uptake could be described by the Langmuir adsorption model. The maximum adsorption capacity (qm) of Cr (VI) on lignin was 75.75 mg g-1 at 40°C. The dimensionless equilibrium parameter (RL) signified a favorable adsorption of Cr (VI) on lignin and was found to be between 0.0601 and 0.818 (0<RL<1). The thermodynamic parameters such as ΔG°, ΔS°, and ΔH° were calculated, and it was found that the reaction was spontaneous and endothermic in nature. This study indicates that lignin has the potential to become an effective and economical adsorbent for removal Cr (VI) from waste water.

Biosorption of Cr(VI) from Water Using Biomass of Aeromonas hydrophila: Central Composite Design for Optimization of Process Variables

The potential use of biomass of Aeromonas hydrophila for biosorption of chromium from aqueous solution was investigated. The variables (pH, initial Cr(VI) concentration, biomass dose, and temperature) affecting process were optimized by performing minimum number of experimental runs with the help of central composite design. The results predicted by design were found to be in good agreement (R2 = 99.1%) with those obtained by performing experiments. Multiple regression analysis shows that uptake decreases with increase in pH and biomass dose, whereas it increases with increase in temperature and concentration. The maximum removal of Cr(VI) predicted by contour and optimization plots was 184.943 mg/g at pH 1.5, initial Cr(VI) concentration 311.97 mg/L, temperature 60 degrees C, and biomass dose 1.0 g. The removal of Cr(VI) was governed by adsorption of Cr(VI) as well as its reduction into Cr(III), which further gets adsorbed. The sorption capacity of biomass was calculated from experimental data using Langmuir sorption model and was found to be 151.50 mg/g at 40 degrees C and pH 1.5, which is comparable to other biosorbents. In addition to this, Dubinin-Radushkevich model was applied, and it was found that nature of sorption was chemisorption.

Sorption of Cr(VI) ions on two Lewatit-anion exchange resins and their quantitative determination using UV–visible spectrophotometer

The sorption of Cr(VI) from aqueous solutions with macroporous resins which contain quarternary amine groups (Lewatit MP 64 and Lewatit MP 500) was studied at varying Cr(VI) concentration, adsorbent dose, pH, contact time and temperature. Batch shaking sorption experiments were carried out to evaluate the performance of Lewatit MP 64 and Lewatit MP 500 anion exchange resins in the removal of Cr(VI) from aqueous solutions. The concentration of Cr(VI) in aqueous solution was determined by UV–visible spectrophotometer. The ion exchange process, which is dependent on pH, showed maximum removal of Cr(VI) in the pH range 3–7 for an initial Cr(VI) concentration of 1 × 10 −3 M. The optimum pH for Cr(VI) adsorption was found as 5.0 for Lewatit MP 64 and 6.0 for Lewatit MP 500. The maximum Cr(VI) adsorption at pH 5.0 is 0.40 and 0.41 mmol/g resin for Lewatit MP 64 and Lewatit MP 500 anion exchangers, respectively. The maximum chromium sorption occurred at approximately 60 min for Lewatit MP 64 and 75 min for Lewatit MP 500. The suitability of the Freundlich and Langmuir adsorption models was also investigated for each chromium–sorbent system. The uptake of Cr(VI) by the anion exchange resins was reversible and so it has good potential for the removal of Cr(VI) from aqueous solutions. Both ion exchangers had high bonding constants but Lewatit MP 500 showed stronger binding. The rise in the temperature caused a slight decrease in the value of the equilibrium constant ( K c) for the sorption of Cr(VI) ion.

Removal of hexavalent chromium from aqueous solutions by D301, D314 and D354 anion-exchange resins

Removal of hexavalent chromium from electroplating industry wastewater is obligatory in order to avoid pollution. Batch shaking experiments were carried out to evaluate the adsorption capacity of resins (D301, D314 and D354) in the removal of chromium from aqueous solutions. Varying experimental conditions were studied, including Cr 6+ concentrations, resin amounts, initial pH, contact time and temperatures. The ion-exchange process, which is pH-dependent, indicated the maximum removal of Cr 6+ in the pH range of 1–5 for an initial concentration 100 ppm of Cr 6+. It was found that more than 99.4% of the removal was achieved under optimal conditions. High adsorption rates of chromium for the three resins were observed at the onset, and then plateau values were gradually reached within 30 min. The experimental results obtained at various concentrations (27 ± 1 °C) showed that the adsorption pattern on the resins have followed Langmuir isotherms and the calculated maximum sorption capacities of D301, D314 and D354 were 152.52, 120.48 and 156.25 mg/g, respectively. The thermodynamic parameters (free energy change Δ G, enthalpy change Δ S and entropy change Δ H) for the sorption have been evaluated. It was also found that the adsorption of chromium on these anion-exchange resins follows first-order reversible kinetics.

Adsorption behavior of Cr(VI) on modified natural zeolite by a new bolaform N, N, N, N′, N′, N′-hexamethyl-1,9-nonanediammonium dibromide reagent

The demand for effective adsorbents is to increase in response to the widespread recognition of the deleterious health effects of Cr(VI)–oxyanions exposure through drinking water. In this study, Cr(VI)–oxyanions uptake from aqueous solutions by a new bolaform N, N, N, N′, N′, N′-hexamethyl-1,9-nonanediammonium dibromide reagent-modified natural zeolitic materials from Zahedan, Iran, was investigated using batch technique. Spectrophotometry method was used for Cr determination. The Cr(VI)-solution concentration varied between 2 and 104 mg L −1. It was shown that the Cr(VI) uptake strongly depended on pH. The maximum removal of Cr(VI) occurred in acidic media at pH < 1.5. The amounts of Cr(VI) adsorbed increased with increase in dose of both adsorbents and their contact time. Based on results an adsorption mechanism has been suggested. The adsorption data for modified zeolite using the amine was consistent with Langmuir isotherm equation and the equilibrium data was analyzed using the Langmuir isotherm.

Biosorption of hexavalent chromium by chemically modified seaweed, Cystoseira indica

Abstract The sorption of hexavalent chromium by marine brown algae Cystoseira indica , which was chemically-modified by cross-linking with epichlorohydrin (CB1, CB2), or oxidized by potassium permanganate (CB3), or only washed by distilled water (RB) was studied with variation in the parameters of contact time, pH, initial metal ion concentration and solid/liquid ratio. They were used for equilibrium sorption uptake studies with Cr(VI). The results indicate that biosorption equilibriums were rapidly established in about 2 h. The Cr(VI) adsorption was strictly pH dependent, and maximum removal of Cr(VI) on biosorbents were observed at pH 3.0. The maximum Chromium uptakes were 22.7, 24.2, 20.1 and 17.8 mg g −1 , respectively, for CB1, CB2, CB3 and RB. The order of maximum Cr(VI) uptakes for various biomasses was CB2 > CB1 > CB3 > RB. A comparison of different isotherm models revealed that the Dubinin–Radushkevich (D–R) isotherm model fitted the experimental data best based on R 2 , q max and standard error (S.E.) values and the mean energy of the sorption values indicated that biosorption of Cr(VI) by C. indica may be an ion exchange reaction.

Hexavalent chromium removal from aqueous solution by adsorption on treated sawdust

The studies on adsorption of hexavalent chromium were conducted by varying various parameters such as contact time, pH, amount of adsorbent, concentration of adsorbate and temperature. The kinetics of adsorption of Cr(VI) ion followed pseudo second order. Langmuir adsorption isotherm was employed in order to evaluate the optimum adsorption capacity of the adsorbent. The adsorption capacity was found to be pH dependant. Sawdust was found to be very effective and reached equilibrium in 3 h (adsorbate concentration 30 mg l −1). The rate constant has been calculated at 303, 308, 313 and 318 K and the activation energy ( E a) was calculated using the Arrhenius equation. Thermodynamic parameters such as standard Gibbs energy (Δ G°) and heat of adsorption (Δ H r) were calculated. The Δ G° and Δ H r values for Cr(VI) adsorption on the sawdust showed the process to be exothermic in nature. The percentage of adsorption increased with decrease in pH and showed maximum removal of Cr(VI) in the pH range 4.5–6.5 for an initial concentration of 5 mg l −1.

Removal of chromium(III) from aqueous solutions using Lewatit S 100: The effect of pH, time, metal concentration and temperature

The removal of the Cr(III) ion from aqueous solutions with the Lewatit S 100 ion-exchange resin is described; and the performance of this resin was compared with Chelex-100 resin. The effect of adsorbent dose, initial metal concentration, contact time, pH and temperature on the removal of Cr(III) was investigated. Lewatit S 100 shows a remarkable increase in sorption capacity for Cr(III). The Batch ion-exchange process was relatively fast; and it reached equilibrium after about 150 min of contact. The ion-exchange process, which is pH dependent show maximum removal of Cr(III) in the pH range 2.8–4.0 for an initial Cr(III) concentration of 1.0 × 10 −3 M. The equilibrium constants were 36.67 at pH value 3.5 for Lewatit S 100 and 6.64 at pH value 4.5 for Chelex-100 resin. Both of the resins had high-bonding constants. The equilibrium related to their ion-exchange capacity and the amount of the ion exchange was obtained by using the plots of the Langmuir adsorption isotherm. It was observed that the maximum ion-exchange capacity of 0.39 mmol of Cr(III)/g for Lewatit S 100 and 0.29 mmol of Cr(III)/g for Chelex-100 was achieved at optimum pH values of 3.5 and 4.5, respectively. The thermodynamic equilibrium constant and the Gibbs free energy flow were calculated for each system. The ion exchange of Cr(III) on these cation-exchange resins followed first-order reversible kinetics. The intra-particle diffusion of Cr(III) on ion-exchange resin represented the rate-limiting step. The rise in temperature caused a slight increase in the value of the equilibrium constant ( K c) for the sorption of Cr(III) ion for both resins.

Adsorption behavior of Cr(VI) on activated hazelnut shell ash and activated bentonite

The possible use of activated hazelnut shell ash and activated bentonite as the adsorbents of Cr(VI) from synthetic solutions and the effect of operating parameters were investigated. The activated hazelnut shell ash was prepared thermally in two sizes 0.5 and 1.0 mm. The maximum removal of Cr(VI) occurred at pH 3 by activated hazelnut shell ash and at pH 5 by activated bentonite. The amounts of Cr(VI) adsorbed increased with increase in dose of both adsorbents and their contact time. The equilibrium data was analysed using the Langmuir and Freundlich isotherms. The characteristics parameters for each isotherm were determined. The Freundlich adsorption model was applied to describe the equilibrium isotherms and the isotherm constants were determined. The Freundlich model agrees very well with experimental data.

Removal of Cr(VI) from wastewater using rice bran

The novel biosorbent rice bran has been successfully utilized for the removal of Cr(VI) from wastewater. The maximum removal of Cr(VI) was found to be 99.4% at pH 2.0, initial Cr(VI) concentration of 200 mg l −1, and temperature 20 °C. The effect of different parameters such as contact time, adsorbate concentration, pH of the medium, and temperature was investigated. The adsorption kinetics was tested for first-order reversible, pseudo-first-order, and pseudo-second-order; reaction and the rate constants of kinetic models were calculated. Mass transfer of Cr(VI) from the bulk to the solid phase (rice bran) was studied at different temperatures. Different thermodynamic parameters, viz., changes in standard free energy, enthalpy, and entropy, have also been evaluated and it has been found that the reaction was spontaneous and endothermic in nature. The Langmuir and Freundlich equations for describing adsorption equilibrium were applied to data. The constants and correlation coefficients of these isotherm models were calculated and compared. Desorption studies was also carried out and found that complete desorption of Cr(VI) took place at pH of 9.5. The data were also subjected to multiple regression analysis and a model was developed to predict the removal of Cr(VI) from wastewater.

Removal of chromium from industrial waste by using eucalyptus bark

Several low cost biomaterials such as baggase, charred rice husk, activated charcoal and eucalyptus bark (EB) were tested for removal of chromium. All the experiments were carried out in batch process with laboratory prepared samples and wastewater obtained from metal finishing section of auto ancillary unit. The adsorbent, which had highest chromium(VI) removal was EB. Influences of chromium concentration, pH, contact time on removal of chromium from effluent was investigated. The adsorption data were fitted well by Freundlich isotherm. The kinetic data were analyzed by using a first order Lagergren kinetic. The Gibbs free energy was obtained for each system and was found to be −1.879 kJ mol −1 for Cr(VI) and −3.885 kJ mol −1 for Cr(III) for removal from industrial effluent. The negative value of Δ G 0 indicates the feasibility and spontaneous nature of adsorption. The maximum removal of Cr(VI) was observed at pH 2. Adsorption capacity was found to be 45 mg/g of adsorbent, at Cr(VI) concentration in the effluent being 250 mg/l. A waste water sample containing Cr(VI), Cr(III), Mg, and Ca obtained from industrial unit showed satisfactory removal of chromium. The results indicate that eucalyptus bark can be used for the removal of chromium.

Removal of Cr(VI) from aqueous solution by two Lewatit-anion exchange resins

The sorption of hexavalent chromium, Cr(VI), from aqueous solutions on macroporous resins containing tertiary amine groups (Lewatit MP 62 and Lewatit M 610) was studied at varying Cr(VI) concentrations, adsorbent dose, pH, contact time and temperatures. The concentration of chromium in aqueous solution was determined by inductively coupled plasma spectrometry (ICP–AES). Batch shaking sorption experiments were carried out to evaluate the performance of Lewatit MP 62 and Lewatit M 610 anion exchange resins in the removal of Cr(VI) from aqueous solutions. The ion-exchange process, which is pH dependent, shows maximum removal of Cr(VI) in the pH range 2–6 for an initial Cr(VI) concentration of 100 ppm. The sorption increases with the decrease in pH and slightly decreases with the increase in temperature. Both ion exchangers had high bonding constants with Lewatit M 610 showing stronger binding. It was observed that the maximum adsorption capacity of 0.40 mmol of Cr(VI)/g for Lewatit MP 62 and 0.41 mmol of Cr(VI)/g for Lewatit M 610 was achieved at pH of 5.0. The thermodynamic parameters (free energy change, Δ G°; enthalpy change, Δ S°; and entropy change, Δ H°) for the sorption have been evaluated. The rise in temperature caused a slight decrease in the value of the equilibrium constant ( K c) for the sorption of Cr(VI) ion. The sorption of Cr(VI) on the resin was rapid during the first 15 min and equilibrium was found to be attained within 30 min. The sorption of Cr(VI) onto the resins followed reversible first-order rate kinetics. Such ion exchange resins can be used for the efficient removal of chromium from water and wastewater.

Adsorption of Cr(VI) on activated rice husk carbon and activated alumina

The possible use of activated rice husk and activated alumina as the adsorbents of Cr(VI) from synthetic solutions and the effect of operating parameters were investigated. The activated rice husk carbon was prepared thermally in two sizes 0.3 and 1.0 mm. The maximum removal of Cr(VI) occurred at pH 2 by activated rice husk and at pH 4 by activated alumina. The amounts of Cr(VI) adsorbed increased with increase in dose of both adsorbents and their contact time. The Freundlich isotherm was applied.

Comparison of bioleaching of heavy metals from sewage sludge using iron- and sulfur-oxidizing bacteria

The aim of the present study was to compare the bioleaching efficiency of Cu, Zn and Cr from anaerobically digested sewage sludge using iron- and sulfur-oxidizing bacteria. Bioleaching was performed on sewage sludge collected from the Yuen Long wastewater treatment plant. A 15% (v/v) inoculation of either iron- or sulfur-oxidizing bacteria with 4 g FeSO 4 l −1 and 0.75% elemental sulfur, respectively, was added to sewage sludge with or without autoclaving in the bioleaching experiment. The mixtures were shaken continuously in an incubator at 30 °C for 16 days and samples were tested at 2-day intervals for pH, ORP and metal determination. The results showed that the iron-oxidizing system required only 2 days as compared to 4 days for the sulfur-oxidizing system to reduce the sludge pH from 7 to 2. Both systems achieved a maximum Cr removal of 52–58% after 12 days of bioleaching, but for iron-oxidizing bacteria with iron-sulfate as an energy source it was 20% higher at the beginning of leaching process. Although it took only 2 days to solubilize Cu by iron-oxidizing bacteria as compared to 8 days for sulfur oxidizing bacteria, the iron-oxidizing system removed only 80% of the total Cu, which was 20% lower than that of the sulfur-oxidizing system. Both iron- and sulfur-oxidizing bacteria achieved 95% Zn removals after 4 days of bioleaching. The results demonstrated that the iron-oxidizing system had a faster removal rate than the sulfur-oxidizing bacteria. Nevertheless, further work should be done to improve the bioleaching efficiency of iron-oxidizing bacteria, especially for Cu and Cr.

Biosorption of Chromium(VI) From Aqueous solutions by green algae spirogyra species

Biosorption of heavy metals is an effective technology for the treatment of industrial wastewaters. Results are presented showing the sorption of Cr(VI) from solutions by biomass of filamentous algae Spirogyra species. Batch experiments were conducted to determine the adsorption properties of the biomass and it was observed that the adsorption capacity of the biomass strongly depends on equilibrium pH. Equilibrium isotherms were also obtained and maximum removal of Cr(VI) was around 14.7×10 3 mg metal/kg of dry weight biomass at a pH of 2.0 in 120 min with 5 mg/l of initial concentration. The results indicated that the biomass of Spirogyra species is suitable for the development of efficient biosorbent for the removal and recovery of Cr(VI) from wastewater.

Removal of chromium ions by agar immobilized cells of the cyanobacterium Anacystis nidulans in a continuous flow bioreactor

Anacystis nidulans, an isolate from the polluted waters, was able to grow in Chu-10 medium with Cr up to 100 μM concentration. Free and agar immobilized cells of the organism having 1 mg of protein removed 35 and 43 nmol of Cr, respectively, from the medium in 6 h. At pH 7.0, the rate of Cr removal by free and immobilized cells increased by 54% and 56%, respectively, over uptake by cells in medium. At a fixed concentration of 30 μM Cr, in terms of unit biomass, a cell density equal to 200 μg of protein/ml was found to be optimum for maximum Cr removal. The efficiency of the continuous flow bioreactor (12.5 × 2 cm) loaded with agar immobilized cells at a fixed concentration of Cr (30 μM) and fixed biomass load (10 mg protein) was compared at different flow rates. The metal removal efficiency of the bioreactor depended on the flow rate. The reactor functioned with 86% efficiency of Cr removal for 6 h at a flow rate of 0.05 ml/min. With increased flow rate, the efficiency of the reactor decreased. The operative time of the reactor at a flow rate of 0.05 ml per min was 48 h, and it decreased to 5 h at a flow rate of 0.5 ml/min. The significance of these results in Cr removal from the industrial effluents is discussed.