Removal of hexavalent chromium from aqueous solutions by micellar compounds

The recovery of toxic metal compounds is a deep concern in all industries. Hexavalent chromium is particularly worrying because of its toxic influence on human health [1], [2] and [3]. Actually the wastewater norm (0.1 mg/l) is very strict and will become more severe in the near future. We present in this paper the experimental results of the metal ion which is bound on micellar compounds and then retained by ultrafiltration membrane. A well known surfactant cetyltrimethylammonium bromide (CTABr) is used as an adsorbent to remove hexavalent chromium from wastewaters. The effects of various experimental parameters on equilibrium adsorption of Cr(VI) on the surfactant have been investigated using batch adsorption experiments. It was found that the capacity of chromium adsorption on CTABr increases with initial metal concentration and in a lesser extent with pH solution. Total chromium adsorption decreased slightly with a rise in temperature suggesting an exothermic adsorption of chromium, thermodynamic parameters are evaluated. It has also been observed that the capacity of chromium adsorption decreases with the mass of adsorbent and concentration of other ions present in the solution. The metal ion adsorption on surfactant is well represented by the Freundlich isotherm.     

Sulfamic acid functionalized slag for effective removal of organic dye and toxic metal from the aqueous samples

Surface functionalization of blast furnace slag with sulfamic acid(a zwitterion) was performed for the removal of Cr~(3+) and methylene blue dye(MB) from water samples. The slag functionalization process was optimized using Response Surface Methodology Design. Statistical analysis of the parameters that include the sulfamic acid amount(A), reaction time(B), and temperature(C) revealed that(A) increase had a negative effect on the adsorption of both pollutants by the zwitterion slag, whereas(B) and(C)increase presented a positive impact. At the optimum condition of 2 g sulfamic acid amount, 50 min reaction time and 37 °C temperature, the prepared slag showed a removal efficiency of more than 90% for both Cr~(3+) and MB. Surface characterization by SEM/EDS, FTIR, XPS and surface area analyser, showed an improvement in surface properties and the incorporation of zwitterionic NH_2~+ and S@O groups of sulfamic acid. Adsorption isotherm and kinetic studies conducted with the zwitterion slag showed the adsorption process was suited to Freundlich isotherm model and pseudo-second-order kinetic model.The thermodynamic study conducted revealed the spontaneity of the process based on the calculated negative DG(Gibb's free energy) values. The prepared zwitterion slag offered easy regeneration with dilute HCl solution and showed a considerable removal(Cr3+: 65% and MB: 80%) for both pollutants even after 3 cycles of usage.     

铬酸铬渣生产铬鞣剂过程除铁技术研究进展

铬鞣剂被认为是目前制造轻革的重要材料,以铬酸铬渣为原料生产铬鞣剂是低成本的生产方法之一,但是以含铁的铬酸铬渣作原料生产铬鞣剂会影响铬鞣剂产品的质量。详细介绍了有机络合法、萃取法等在铬鞣剂生产中除铁的应用,从反应原理、工艺流程和除铁效果等几个方面对各种方法进行了对比,评价使用不同生产方法的技术优劣,并对低含铁铬鞣剂的应用前景做了展望。     

Effective removal of Cr(VI) and methyl orange from the aqueous environment using two-dimensional (2D) Ti3C2Tx MXene nanosheets

Industrial use of heavy metals and dyes critically depends on the effective handling of industrial effluents. Effective remediation of industrial effluents using various adsorbent materials has thus become critical. In this paper, we study two-dimensional MXenes as an adsorbent for removing Cr(VI) and methyl orange (MO) in waters. The physico-chemical performance of MXenes was studied using X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer?Emmett?Teller, scanning electron microscopy, high resolution-transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy techniques. The adsorption system, including influence of contact time, pH of solutions, co-ions, and desorption experiments were performed for effective Cr(VI) and MO removal. The Cr(VI) and MO removal rate of the MXenes was very fast, and the kinetic system was driven by pseudo-second-order kinetics. The sorption isotherm closely well-tailored with the Langmuir isotherm, and the maximum removal efficiencies were 104 and 94.8 mg/g for Cr(VI) and MO, respectively. The MXenes was successfully regenerated by 0.1 M NaOH aqueous solution and can be repeatedly recycled. The uptake of Cr(VI) and MO by the MXenes was mainly due to chemical adsorption, namely electrostatic adsorption, complexation, surface interactions, and ion exchange mechanisms. This investigation demonstrates the selectivity and feasibility of the MXenes as a real adsorbent for eliminating Cr(VI) and MO from the aqueous environment.     

Production of carbonaceous material from avocado peel for its application as alternative adsorbent for dyes removal

Adsorption processes have received special attention for contaminants removal thanks to their capability to generate effluents with high quality as well as their simple design. In the current work, the agro-waste residue avocado peel is proposed to be used as alternative to conventional activated carbons whose use is sometimes restricted to high costs, upgraded by their exhausting after long term operations. The carbonization procedure was optimized and analyzed through factorial design and response surface methodology by evaluating temperature(400–900 °C) and time(30–90 min) effects: optimal conditions were found at 900 °C and 65 min, generating an adsorbent with 87.52 m2·g-1of BET surface area, a mesopore volume of 74% and a zero point charge at 8.6. The feasibility of the carbonaceous material was proved for the removal of a variety of dyes by investigating substrate(10–50 mg·L-1) and solid(0.5–20 g·L-1) concentration effects and statistical significance: complete removal of Naphthol Blue Black and Reactive Black 5 was reached under optimal conditions(10 mg·L-1and20 g·L-1of dye and solid, respectively), while Basic Blue 41 was eliminated by using 13.4 g·L-1of the adsorbent.Overall, dyes removal by adsorption on carbonized avocado peel is presented as a promising technology due to the low cost and easy availability of the precursor, as well as the straightforward generation, the satisfactory characteristics and the proved adsorption capacity of the adsorbent.     

含碱性表面基团活性炭去除Cr(Ⅵ)的研究

介绍了用氧化剂和高温处理制取含碱性表面基团活性炭的方法，测定了它们的离子交换空量。研究了溶液pH和Cr(Ⅵ）的初始浓度对Cr（Ⅵ）去除率的影响。讨论了含碱性表面基团活性炭对溶液中Cr(Ⅵ）的去除机理。     

Characteristics of unburned carbons and their application for humic acid removal from water

Two unburned carbons (UCs) were separated from coal fly ash and their physicochemical properties were characterised using N₂ adsorption, XRD, SEM, XPS, FT-IR and potentiometric mass titration. Chemical treatments using HNO₃ and KOH were also conducted on one of the unburned carbons. The adsorption of humic acid from aqueous solution was performed on these untreated and chemically treated UCs. It was found that the UCs showed different porous structure and surface chemical properties, which influenced their adsorption behaviour. UCs exhibited high adsorption capacity for humic acid. After chemical treatment, the textural structure and surface functional groups of the unburned carbon were changed and the adsorption behaviour showed significant difference. Acid treatment did not change the surface area but reduced the functional groups while basic treatment significantly enhanced the surface area in microporous section but still reduced the surface functional groups. Particle size and pH solution will also influence the adsorption capacity. The adsorption will increase with decreasing particle size for humic acid. Higher pH solution will reduce humic acid adsorption on unburned carbon. Ionic strength will also affect humic acid adsorption showing positive effect on adsorption capacity.     

Tannin-based adsorbents from green tea for removal of monoaromatic hydrocarbons in water: Preliminary investigations

In this study, we report the adsorption of benzene and toluene from water using rarely reported tannin adsorbents. Tannin gel and tannin powder were synthesized by adding formaldehyde to green tea extract, while iron nanoparticles were synthesized by the addition of FeSO₄?·?7H₂O. The surface morphology of the synthesized adsorbents was determined using SEM and FTIR prior to application to contaminated water. The results show up to 88% removal of benzene and toluene in a batch system after 30?min of reaction time, with a higher rate of removal of toluene compared to benzene. A low pH value of 2 had an adverse effect on the tannin gel, reducing the total adsorption of benzene to approx. 37.5%. On the other hand, iron nanoparticles were least affected by the pH with an adsorption of 62.9% for benzene and 83.3% for toluene.     

The use of fly ash from the combustion of poultry litter for the adsorption of chromium(III) from aqueous solution

Fly ash, from the combustion of poultry litter, was assessed as an adsorbent for chromium(III) from aqueous solution. The adsorption process was studied as a function of temperature and time. Adsorption was best described by the Langmuir model. The adsorption of chromium(III) on the fly ash was endothermic and kinetic studies suggest that the overall rate of adsorption was pseudo‐second order. At low initial concentrations film diffusion effects contribute to limiting the overall rate of adsorption while at higher initial chromium(III) concentrations pore diffusion becomes more important. An adsorption capacity of 53 mg dm^?3 was reached at 20 °C. © 2002 Society of Chemical Industry     

Comparing the efficacy of a novel waste-based adsorbent with PAC for the simultaneous removal of chromium (VI) and cyanide from electroplating wastewater

The potential of powdered pistachio hull (PHP) for the co-adsorption of Cr(VI) and cyanide from electroplating wastewater was compared to that of powdered activated carbon (PAC). The results of dynamic adsorption experiments indicated that the complete and simultaneous removal of Cr(VI) and cyanide from wastewater was achieved with 2 g/L of PHP after 60 min of contact. Alternatively, with PAC, 69.2 and 77.8% of Cr(VI) and cyanide, respectively, were removed under the same conditions. Adsorption of Cr(VI) and cyanide by PHP and PAC followed pseudo-second order kinetics, and the equilibrium adsorption data best fit the Langmuir isotherm. The maximum capacity of PHP for the co-adsorption of Cr(VI) and cyanide was 117.6 and 151.5 mg/g, respectively, and the maximum capacity of PAC for the adsorption of Cr(VI) and cyanide was 47.6 and 39.4 mg/g, respectively. It was found that which intraparticle diffusion controlled the adsorption of Cr(VI) and cyanide onto PHP and PAC under the selected conditions. Overall, PHP efficiently adsorbed Cr(VI) and cyanide from industrial effluents; thus, PHP is an affordable and cost-effective system for the treatment of wastewater.     

Tailoring activated carbons for enhanced removal of natural organic matter from natural waters

Several pathways have been employed to systematically modify two granular activated carbons (GACs), F400 (coal-based) and Macro (wood-based), for examining adsorption of dissolved natural organic matter (DOM) from natural waters. A total of 24 activated carbons with different physical and chemical characteristics was produced. The impact of carbon treatment on the DOM adsorption was examined by conducting isotherm experiments at a neutral pH using the modified carbons and a DOM isolated from the influent to Myrtle Beach drinking water treatment plant in South Carolina (USA). Adsorption of the DOM by two activated carbon fibers, with relatively uniform pore size distributions, showed that only pores with widths larger than 1 nm were accessible to the DOM macromolecules. Increases in the carbon supermicropore and mesopore volume (i.e., >1 nm) increased the DOM uptake, if the surface chemistry was favorable. The isotherms normalized on a surface area basis showed the significance of carbon surface chemistry on the DOM uptake. At neutral pH, adsorption of negatively charged DOM molecules was favored by basic and positively charged surfaces, while the DOM uptake was minimized when the surface had acidic characteristics. High temperature ammonia treatment of oxidized carbons considerably enhanced the DOM uptake, mainly due to the increase in accessible surface area and surface basicity. Iron-impregnated carbons indicated an enhanced affinity of iron-laden carbon surface toward the DOM species, if the surface was not negatively charged.     

Application of Chattim tree (devil tree,Alstonia scholaris) saw dust as a biosorbent for removal of hexavalent chromium from contaminated water

“Devil tree saw dust”; a novel biosorbent has been utilised successfully for the removal of hexavalent chromium from contaminated water. Batch adsorption procedure is utilised to test the ability of saw dust as an adsorbent for hexavalent chromium (reduction coupled adsorption). The contribution of various parameters on sorption, such as contact time, sorbate concentration, pH of the medium and temperature were estimated and maximum uptake of hexavalent chromium from contaminated water was 333.33 mg g^?1 at pH 2.0 and temperature of 35°C. Hexavalent chromium uptake from contaminated water followed the pseudo‐first‐order rate expression. The standard free energy change (ΔG⁰), standard enthalpy change (ΔH⁰) and standard entropy change (ΔS⁰) have also been evaluated and it has been concluded that the sorption was feasible, spontaneous and endothermic in nature. The process follows well Langmuir isotherm. Fourier Transform Infra‐Red (FTIR) spectroscopy and scanning electron microscopy (SEM) of hexavalent chromium loaded and unloaded saw dust were performed, SEM clearly indicates chromium adsorption. FTIR spectroscopy revealed the involvement of carbonyl, hydroxyl and amide groups on the cell surfaces in chromium binding. Very good adsorption capacity and low cost or cost free of devil tree saw dust makes this biosorbent as one of the best adsorbents for removal of hexavalent chromium from contaminated water. © 2012 Canadian Society for Chemical Engineering     

The use of exhausted olive cake ash (EOCA) as a low cost adsorbent for the removal of toxic metal ions from aqueous solutions

The removal characteristics of cadmium (Cd(II)) and nickel (Ni(II)) ions from aqueous solution by exhausted olive cake ash (EOCA) were investigated under various conditions of contact time, pH, initial metal concentration and temperature. Batch kinetic studies showed that an equilibrium time of 2 h was required for the adsorption of Ni(II) and Cd(II) onto EOCA. Equilibrium adsorption is affected by the initial pH (pH₀) of the solution. The pH₀ 6.0 is found to be the optimum for the individual removal of Cd(II) and Ni(II) ions by EOCA. The adsorption test of applying EOCA into synthetic wastewater revealed that the adsorption data of this material for nickel and cadmium ions were better fitted to the Langmuir isotherm since the correlation coefficients for the Langmuir isotherm were higher than that for the Freundlich isotherm. The estimated maximum capacities of nickel and cadmium ions adsorbed by EOCA were 8.38 and 7.32 mg g⁻¹, respectively. The thermodynamic parameters for the adsorption process data were evaluated using Langmuir isotherm. The free energy change (ΔG°) and the enthalpy change (ΔH°) showed that the process was feasible and endothermic respectively. As the exhausted olive cake is discarded as waste from olive processing, the adsorbent derived from this material is expected to be an economical product for metal ion remediation from water and wastewater.     

Eco friendly adsorbents for removal of phenol from aqueous solution employing nanoparticle zero-valent iron synthesized from modified green tea bio-waste and supported on silty clay

The present research investigated a novel route for the synthesis of nanoparticle zero-valent iron(NZVI) utilizing an aqueous extract of green tea waste as a reductant with ferric chloride. Also, the supported nanoparticle zerovalent iron was synthesized using natural silty clay as a support material(SC-NZVI). The NZVI and SC-NZVI were characterized by infrared spectroscopy(FTIR), scanning electron microscope(SEM), X-ray diffraction(XRD),Brunauer–Emmett–Teller(BET), and zeta potential(ζ). The interpretation of the results demonstrated that the polyphenol and other antioxidants in green tea waste can be used as reduction and capping agents in NZVI synthesis, with silty clay an adequate support. Additionally, the experiments were carried out to explore phenol adsorption by NZVI and SC-NZVI. To determine the optimum conditions, the impact of diverse experimental factors(i.e., initial pH, adsorbent dose, temperature, and concentration of phenol) was studied. Langmuir, Freundlich,and Tempkin isotherms were used as representatives of adsorption equilibrium. The obtained results indicated that the adsorption processes for both NZVI and SC-NZVI well fitted by the Freundlich isotherm model. The appropriateness of pseudo_first_order and pseudo_second_order kinetics was investigated. The experimental kinetics data were good explained by the second-order model. The thermodynamic parameters(ΔH0, ΔS0, andΔG0) for NZVI and SC-NZVI were determined. The maximum removal rates of phenol at optimum conditions,when adsorbed onto NZVI and SC-NZVI, were found to be 94.8% and 90.1%, respectively.     

Preparation and characterization of iron(III) complex of an amino‐functionalized polyacrylamide‐grafted lignocellulosics and its application as adsorbent for chromium(VI) removal from aqueous media

The growth and decay processes of optically induced birefringence in two novel azobenzene compounds [one was a hyperbranched poly(aryl ether) containing azobenzene groups, and the other was a hydrogen‐bonded complex] were studied. The temperature dependence of the birefringence signal was investigated. The curves for the buildup and decay of birefringence fit well to biexponential functions. The dependence of the fitting parameters on the temperature is also discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Application of apdc coupled polyurethane foam sorbent for the removal and recovery of toxic heavy metals Hg,Cd and Pb from industrial effluents

A novel, highly stable, selective and efficient sorption medium was synthesized for the removal of toxic metals from industrial effluents by coupling a chelating agent Ammonium pyrrolidine dithiocarbamate (APDC) with flexible open cell polyether polyurethane foam. The performance efficiency of the new sorbent was evaluated by static and dynamic methods for removing toxic heavy metals Hg, Cd and Pb from effluents. In fixed bed downflow column studies, a quantitative uptake of Hg (II) 400 mg/L, Cd (II) and Pb (II) 60 mg/L was attained at flow rates of 3.68 L/m²s. The design parameters using the APDC‐PUF as sorption material for a batch reactor and for column reactor and cost effectiveness of the process were evaluated. The sorption potential of the APDC‐PUF was demonstrated for the treatment of real industrial wastes from a common effluent treatment plant, Chloro alkali industry and municipal sewage.     

Design,synthesis, and nanoengineered modification of spherical graphene surface by layered double hydroxide (LDH) for removal of As(III) from aqueous solutions

In this study, new nano spherical graphene modified with LDH (Layered Double Hydroxide) was prepared and used to remove As(III) ion from aqueous solutions. At first, graphene oxide was synthesized from graphite using a well-known Hammer method. The obtained graphene oxide solution was sprayed in octanol solution under different temperatures and sprayed speed as influenced variables. The structure and physical characterization of synthesized spherical graphene oxide were determined by various techniques, including FT-IR, N₂ adsorption–desorption, SEM, TEM, and EDX. In the next step, the hydrothermal method was applied to deposition LDH on the spherical graphene oxide. The synthesized spherical graphene modified by LDH was used to remove As(III) as a toxic heavy metal ion. The effect of influenced variables including pH, contact time, amount of sorbent, and type eluent studied and the optimum values were as 8, 30, 50, and HCl (0.5 mol·L^-1), respectively. After optimization, the studied sorbent was shown a high adsorption capacity (149.3 mg·g^-1). The adsorption mechanism and kinetic models exhibited good agreement with the Langmuir isotherm and pseudo-second-order trends, respectively. Besides, the synthesized product was tested for seven times without significant loss in its sorption efficiency.