Chromium(VI) removal from aqueous system using Helianthus annuus (sunflower) stem waste

The objective of this study was to investigate the Cr(VI) removal efficiency of sunflower waste from aqueous system under different process conditions. Two adsorbents were prepared by pre-treating the sunflower stem waste. One adsorbent was prepared by boiling it and second adsorbent was prepared by treating it with formaldehyde. Batch mode experiments were carried out as a function of solution pH, adsorbent dosage, Cr(VI) concentration and contact time. FT-IR spectra and SEMs of the adsorbents were recorded to explore the number and position of functional groups available for the binding of Cr(VI) ions and morphology of the studied adsorbents. 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 sunflower stem absorbent and formaldehyde-treated sunflower stem absorbent for the removal of Cr(VI) were 81.7 and 76.5%, respectively for dilute solutions at 4.0g/L adsorbent dose. The applicability of Langmuir, Freundlich and Dubinin-Radushkevich isotherms was also tested. The results revealed that the hexavalent chromium is considerably adsorbed on sunflower stem and it could be an economical method for the removal of hexavalent chromium from aqueous systems.     

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.     

The use of sulphuric acid-carbonization products of sugar beet pulp in Cr(VI) removal

A carbon rich adsorbent prepared from the reaction of sugar beet pulp with sulphuric acid and gas formed during carbonization process have been studied for Cr(VI) removal from aqueous solutions. The SO(2) rich gas was shown to be an excellent Cr(VI) reductant. The equilibrium and kinetic studies were conducted by using the carbonaceous adsorbent derived from sugar beet pulp. The lower pH favoured Cr(VI) adsorption but substantial Cr(VI) reduction was observed. The Langmuir and Freundlich isotherm models were applied and the Langmuir model best fit the equilibrium isotherm data. The maximum adsorption capacity of chromium calculated from Langmuir isotherm is about 24 mgg(-1) for 25 degrees C. The adsorption of Cr(VI) is an endothermic process and follows the pseudo-second-order rate kinetics. The sulphuric acid-carbonization is an economical method for particularly chromium removal because the gas generated during carbonization exhibits good Cr(VI) reduction properties and carbonaceous material obtained is an efficient Cr(VI) adsorbent.     

Hexavalent chromium removal from wastewater using aniline formaldehyde condensate coated silica gel

A resinous polymer, aniline formaldehyde condensate (AFC) coated on silica gel was used as an adsorbent in batch system for removal of hexavalent chromium from aqueous solution by considering the effects of various parameters like reaction pH, dose of AFC coated silica gel, initial Cr(VI) concentration and aniline to formaldehyde ratio in AFC synthesis. The optimum pH for total chromium [Cr(VI) and Cr(III)] adsorption was observed as 3. Total chromium adsorption was second order and equilibrium was achieved within 90-120 min. Aniline to formaldehyde ratio of 1.6:1 during AFC synthesis was ideal for chromium removal. Total chromium adsorption followed Freundlich's isotherm with adsorption capacity of 65 mg/g at initial Cr(VI) 200mg/L. Total chromium removal was explained as combinations of electrostatic attraction of acid chromate ion by protonated AFC, reduction of Cr(VI) to Cr(III) and bond formation of Cr(III) with nitrogen atom of AFC. Almost 40-84% of adsorbed chromium was recovered during desorption by NaOH, EDTA and mineral acids. AFC coated silica gel can be effectively used for treatment of chromium containing wastewaters as an alternative.     

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.     

Removal of chromium from aqueous solution by using oxidized multiwalled carbon nanotubes

The batch removal of hexavalent chromium (Cr(VI)) from aqueous solution by using oxidized multiwalled carbon nanotubes (MWCNTs) was studied under ambient conditions. The effect of pH, initial concentration of Cr(VI), MWCNT content, contact time and ionic strength on the removal of Cr(VI) was also investigated. The removal was favored at low pH with maximum removal at pH <2. The adsorption kinetics was modeled by first-order reversible kinetics, pseudo-first-order kinetics, pseudo-second-order kinetics, and intraparticle diffusion models, respectively. The rate constants for all these kinetic models were calculated, and the results indicate that pseudo-second-order kinetics model was well suitable to model the kinetic adsorption of Cr(VI). The removal of chromium mainly depends on the occurrence of redox reaction of adsorbed Cr(VI) on the surface of oxidized MWCNTs to the formation of Cr(III), and subsequent the sorption of Cr(III) on MWCNTs appears as the leading mechanism for chromium uptake to MWCNTs. The presence of Cr(III) and Cr(VI) on oxidized MWCNTs was confirmed by the X-ray photoelectron spectroscopic analysis. The application of Langmuir and Freundlich isotherms are applied to fit the adsorption data of Cr(VI). Equilibrium data were well described by the typical Langmuir adsorption isotherm. Overall, the study demonstrated that MWCNTs can effectively remove Cr(VI) from aqueous solution under a wide range of experimental conditions, without significant Cr(III) release.     

Removal of chromium and toxic ions present in mine drainage by Ectodermis of Opuntia

This work presents conditions for hexavalent and trivalent chromium removal from aqueous solutions using natural, protonated and thermally treated Ectodermis of Opuntia. A removal of 77% of Cr(VI) and 99% of Cr(III) can be achieved. The sorbent material is characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, infrared spectroscopy, thermogravimetric analysis, before and after the contact with the chromium containing aqueous media. The results obtained from the characterization techniques indicate that the metal ion remains on the surface of the sorbent material. The percentage removal is found to depend on the initial chromium concentration and pH. The Cr(VI) and Cr(III) uptake process is maximum at pH 4, using 0.1g of sorbent per liter of aqueous solution. The natural Ectodermis of Opuntia showed a chromium adsorption capacity that was adequately described by the Langmuir adsorption isotherm. Finally, an actual mine drainage sample that contained Cd, Cr, Cu, Fe Zn, Ni and Pb was tested under optimal conditions for chromium removal and Ectodermis of Opuntia was found to be a suitable sorbent material. The use of this waste material for the treatment of metal-containing aqueous solutions as well as mine drainage is effective and economical.     

Removal of hexavalent chromium from aqueous solution by agricultural waste biomass

In the present study adsorption of Cr(VI) from aqueous solutions onto different agricultural wastes, viz., sugarcane bagasse, maize corn cob and Jatropha oil cake under various experimental conditions has been studied. Effects of adsorbent dosage, Cr(VI) concentration, pH and contact time on the adsorption of hexavalent chromium were investigated. The concentration of chromium in the test solution was determined spectrophotometrically. FT-IR spectra of the adsorbents (before use and after exhaustion) were recorded to explore number and position of the functional groups available for the binding of chromium ions on to studied adsorbents. SEMs of the adsorbents were recorded to explore the morphology of the studied adsorbents. Maximum adsorption was observed in the acidic medium at pH 2 with a contact time of 60min at 250rpm stirring speed. Jatropha oil cake had better adsorption capacity than sugarcane bagasse and maize corn cob under identical experimental conditions. The applicability of the Langmuir and Freundlich adsorption isotherms was tested. The results showed that studied adsorbents can be an attractive low cost alternative for the treatment of wastewaters in batched or stirred mode reactors containing lower concentrations of chromium.     

Adsorption of Cr(VI) on 1,2-ethylenediamine-aminated macroporous polystyrene particles

An adsorbent, 1,2-ethylenediamine-aminated macroporous polystyrene (EDA-PSt) particles was used to adsorb Cr(VI) from aqueous solution. Effect of pH value, contact time, temperature, adsorbent dosage and initial Cr(VI) concentration on adsorption amount of Cr(VI) on EDA-PSt were investigated. The results showed that the adsorption isotherm can be well described by the Langmuir equation and the adsorption kinetics fitted to the pseudo-second-order model. According to Langmuir equation, Q_m was calculated to be 175.75 mg g⁻¹. The breakthrough curve experiment showed that the dynamic adsorption capacity for Cr(VI) on EDA-PSt was 100.06 mg g⁻¹. The adsorbed Cr(VI) could be desorbed by 0.1 mol L⁻¹ NaOH and the desorption ratio was 67.28%.     

Application of dolochar in the removal of cadmium and hexavalent chromium ions from aqueous solutions

Dolochar, a waste material generated in sponge iron industry, is processed and put to test as an adsorbent for removal of Cd(II) and Cr(VI) ions from aqueous solutions. The dolochar samples were characterised to determine the different phases and their distribution by reflection microscopy. The analysis indicated that the sample consists of metallic iron, fused carbon, and Ca-Mg bearing phases (Ca-Mg-silicate-oxide) along with lots of voids and pores. The fixed carbon (FC) content of the material is 13.8% with a Langmuir surface area of 81.6 m²/g and micropore area of 34.1 m²/g. Batch adsorption experiments have been conducted to study the sorption behaviour of Cd(II) and Cr(VI) ions on dolochar as a function of particle size, contact time, adsorbent dosages, pH and temperature. It is observed that higher pH and temperature enhances sorption of Cd(II) ions. In contrast, the adsorption for Cr(VI) is found to be better in acidic pH in comparison to alkaline media. The equilibrium adsorption isotherm data are tested by applying both Langmuir and Freundlich isotherm models. It is observed that Langmuir isotherm model fitted better compared to the Freundlich model indicating monolayer adsorption. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° indicate the effectiveness of dolochar to remove Cd(II) and Cr(VI) ions from aqueous solution. The kinetics of adsorption is found to better fit to pseudo second order reaction.     

Error analysis of equilibrium studies for the almond shell activated carbon adsorption of Cr(VI) from aqueous solutions

In this study, the preparation of activated carbon from almond shell with H2SO4 activation and its ability to remove toxic hexavalent chromium from aqueous solutions are reported. The influences of several operating parameters such as pH, particle size and temperature on the adsorption capacity were investigated. Adsorption of Cr(VI) is found to be highly pH, particle size and temperature dependent. Four adsorption isotherm models namely, Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich were used to analyze the equilibrium data. The Langmuir isotherm provided the best correlation for Cr(VI) onto the almond shell activated carbon (ASC). Adsorption capacity was calculated from the Langmuir isotherm as 190.3 mg/g at 323 K. Thermodynamic parameters were evaluated and the adsorption was endothermic showing monolayer adsorption of Cr(VI). Five error functions were used to treat the equilibrium data using non-linear optimization techniques for evaluating the fit of the isotherm equations. The highest correlation for the isotherm equations in this system was obtained for the Freundlich isotherm. ASC is found to be inexpensive and effective adsorbent for removal of Cr(VI) from aqueous solutions.     

Chromium removal from electroplating wastewater by coir pith

Coir pith is a by-product from padding used in mattress factories. It contains a high amount of lignin. Therefore, this study investigated the use of coir pith in the removal of hexavalent chromium from electroplating wastewater by varying the parameters, such as the system pH, contact time, adsorbent dosage, and temperature. The maximum removal (99.99%) was obtained at 2% (w/v) dosage, particle size <75microm, at initial Cr(VI) 1647mgl(-1), system pH 2, and an equilibrium time of 18h. The adsorption isotherm of coir pith fitted reasonably well with the Langmuir model. The maximum Cr(VI) adsorption capacity of coir pith at 15, 30, 45 and 60 degrees C was 138.04, 197.23, 262.89 and 317.65mgCr(VI)g(-1) coir pith, respectively. Thermodynamic parameters indicated an endothermic process and the adsorption process was favored at high temperature. Desorption studies of Cr(VI) on coir pith and X-ray absorption near edge structure (XANES) suggested that most of the chromium bound on the coir pith was in Cr(III) form due to the fact that the toxic Cr(VI) adsorbed on the coir pith by electrostatic attraction was easily reduced to less toxic Cr(III). Fourier transform infrared (FT-IR) spectrometry analysis indicated that the carbonyl (CO) groups and methoxy (O-CH(3)) groups from the lignin structure in coir pith may be involved in the mechanism of chromium adsorption. The reduced Cr(III) on the coir pith surface may be bound with CO groups and O-CH(3) groups through coordinate covalent bonding in which a lone pair of electrons in the oxygen atoms of the methoxy and carbonyl groups can be donated to form a shared bond with Cr(III).     

Grape waste as a biosorbent for removing Cr(VI) from aqueous solution

Grape waste generated in wine production is a cellulosic material rich in polyphenolic compounds which exhibits a high affinity for heavy metal ions. An adsorption gel was prepared from grape waste by cross-linking with concentrated sulfuric acid. It was characterized and utilized for the removal of Cr(VI) from synthetic aqueous solution. Adsorption tests were conducted in batch mode to study the effects of pH, contact time and adsorption isotherm of Cr(VI), which followed the Langmuir type adsorption and exhibited a maximum loading capacity of 1.91 mol/kg at pH 4. The adsorption of different metal ions like Cr(VI), Cr(III), Fe(III), Zn(II), Cd(II) and Pb(II) from aqueous solution at different pH values 1-5 has also been investigated. The cross-linked grape waste gel was found to selectively adsorb Cr(VI) over other metal ions tested. The results suggest that cross-linked grape waste gel has high possibility to be used as effective adsorbent for Cr(VI) removal.     

Adsorption characteristics of trivalent chromium on palm oil fuel ash

The metal uptake characteristics of ash particles obtained from the combustion of oil palm solid waste (referred to as palm oil fuel ash) are evaluated using trivalent chromium as a model adsorbate. The equilibrium and kinetic properties of Cr(III) are studied in batch stirred-tank experiments. The extent of Cr(III) removal increases with an increase in solution pH. The maximum equilibrium uptake capacity at pH 6 is 0.31 mmol/g of sorbent. A Langmuir isotherm model with pH-dependent parameters accounts very well for the measured equilibrium data. Modeling studies using a second order irreversible reaction model and a pseudo-first order kinetic model indicate that transient profiles obtained experimentally for a range of initial metal concentrations and sorbent dosages are in good agreement with calculated curves of both models. The two kinetic models can be employed for a useful summary of the experimental data so long as their rate coefficients are empirically correlated with the two system variables: initial metal concentration and sorbent dosage. Electronic Publication     

Sorption and desorption studies of chromium(VI) from nonviable cyanobacterium Nostoc muscorum biomass

This communication presents results pertaining to the sorptive and desorptive studies carried out on chromium(VI) removal onto nonviable freshwater cyanobacterium (Nostoc muscorum) biomass. Influence of varying the conditions for removal of chromium(VI), such as the pH of aqueous solution, the dosage of biosorbent, the contact time with the biosorbent, the temperature for the removal of chromium, the effect of light metal ions and the adsorption-desorption studies were investigated. Sorption interaction of chromium on to cyanobacterial species obeyed both the first and the second-order rate equation and the experimental data showed good fit with both the Langmuir and freundlich adsorption isotherm models. The maximum adsorption capacity was 22.92 mg/g at 25 degrees C and pH 3.0. The adsorption process was endothermic and the values of thermodynamic parameters of the process were calculated. Various properties of the cyanobacterium, as adsorbent, explored in the characterization part were chemical composition of the adsorbent, surface area calculation by BET method and surface functionality by FTIR. Sorption-desorption of chromium into inorganic solutions and distilled water were observed and this indicated the biosorbent could be regenerated using 0.1 M HNO3 and EDTA with upto 80% recovery. The biosorbents were reused in five biosorption-desorption cycles without a significant loss in biosorption capacity. Thus, this study demonstrated that the cyanobacterial biomass N. muscorum could be used as an efficient biosorbent for the treatment of chromium(VI) bearing wastewater.     

Studies on adsorptive removal of Co(II), Cr(III) and Ni(II) by IRN77 cation-exchange resin

The adsorption of cobalt, chromium and nickel from aqueous solutions on IRN77 cation-exchange resin has been studied comparatively. The percentage removal of cobalt, chromium and nickel was examined by varying experimental conditions, viz. dosage of adsorbent, pH of the solution and contact time. It was found that more than 95% removal was achieved under optimal conditions. The adsorption capacity (k) for cobalt, chromium and nickel were calculated from the Freundlich adsorption isotherm. The adsorption of cobalt, chromium and nickel on this cation-exchange resin followed the Lagergren kinetic model. Also the competitive adsorption of multi-metals onto the IRN77 resin was studied. The studies showed that this cation-exchange resin can be used as an efficient adsorbent material for the removal of cobalt, chromium and nickel from water and nuclear power plant coolant water.     

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 1x10(-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 chromium from water and wastewater by ion exchange resins

Removal of chromium from water and wastewater is obligatory in order to avoid water pollution. Batch shaking adsorption experiments were carried out to evaluate the performance of IRN77 and SKN1 cation exchange resins in the removal of chromium from aqueous solutions. The percentage removal of chromium was examined by varying experimental conditions viz., dosage of adsorbent, pH of the solution and contact time. It was found that more than 95% removal was achieved under optimal conditions. The adsorption capacity (k) for chromium calculated from the Freundlich adsorption isotherm was found to be 35.38 and 46.34 mg/g for IRN77 and SKN1 resins, respectively. The adsorption of chromium on these cation exchange resins follows the first-order reversible kinetics. The ion exchange resins investigated in this study showed reversible uptake of chromium and, thus, have good application potential for the removal/recovery of chromium from aqueous solutions.     

Adsorption of copper (II), chromium (III), nickel (II) and lead (II) ions from aqueous solutions by meranti sawdust

The present study proposed the use of meranti sawdust in the removal of Cu(II), Cr(III), Ni(II) and Pb(II) ions from synthetic aqueous solutions. Batch adsorption studies showed that meranti sawdust was able to adsorb Cu(II), Cr(III), Ni(II) and Pb(II) ions from aqueous solutions in the concentration range 1–200 mg/L. The adsorption was favoured with maximum adsorption at pH 6, whereas the adsorption starts at pH 1 for all metal ions. The effects of contact time, initial concentration of metal ions, adsorbent dosage and temperature have been reported. The applicability of Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm was tried for the system to completely understand the adsorption isotherm processes. The adsorption kinetics tested with pseudo-first-order and pseudo-second-order models yielded high R² values from 0.850 to 0.932 and from 0.991 to 0.999, respectively. The meranti sawdust was found to be cost effective and has good efficiency to remove these toxic metal ions from aqueous solution.     

Mechanisms of the removal of hexavalent chromium by biomaterials or biomaterial-based activated carbons

Three papers published during recent 2 years in Journal of Hazardous Materials made a mistake in analyzing chromium species in aqueous solution, resulting in incorrect elucidation of Cr(VI) biosorption; the Cr(VI) was removed from aqueous solution systems by 'anionic adsorption'. However, it has been proved that Cr(VI) is easily reduced to Cr(III) by contact with organic materials under acidic conditions because of its high redox potential value (above +1.3 V at standard condition). Therefore, it is strongly possible that the mechanism of Cr(VI) removal by biomaterials or biomaterial-based activated carbons is not "anionic adsorption" but "adsorption-coupled reduction". Thus, for researches of Cr(VI) biosorption, researchers have to analyze not only Cr(VI) but also total Cr in aqueous solution and to check the oxidation state of chromium bound on the biomaterials or activated carbons.