Modified activated carbon for the removal of copper,zinc, chromium and cyanide from wastewater

Modified activated carbon are carbonaceous adsorbents which have tetrabutyl ammonium iodide (TBAI) and sodium diethyl dithiocarbamate (SDDC) immobilised at their surface. This study investigates the adsorption of toxic ions, copper, zinc, chromium and cyanide on these adsorbents that have undergone surface modification with tetrabutyl ammonium (TBA) and SDDC in wastewater applications. The modification technique enhance the removal capacity of carbon and therefore decreases cost-effective removal of Cu(II), Zn(II), Cr(VI) and CN⁻ from metal finishing (electroplating unit) wastewater. Two separate fixed bed modified activated carbon columns were used; TBA-carbon column for cyanide removal and SDDC-carbon column for multi-species metal ions (Cu, Zn, Cr) removal. Wastewater from electroplating unit containing 37 mg l⁻¹ Cu, 27 mg l⁻¹ Zn, 9.5 mg l⁻¹ Cr and 40 mg l⁻¹ CN⁻ was treated through the modified columns. A total CN⁻ removal was achieved when using the TBA-carbon column with a removal capacity of 29.2 mg g⁻¹ carbon. The TBA-carbon adsorbent was found to have an effective removal capacity of approximately five times that of plain carbon. Using SDDC-carbon column, Cu, Zn and Cr metal ions were eliminated with a removal capacity of 38, 9.9 and 6.84 mg g⁻¹, respectively. The SDDC-carbon column has an effective removal capacity for Cu (four times), Zn (four times) and Cr (two times) greater than plain carbon.     

Oxidation catalysts prepared from biosorbents supported on zeolites

The catalytic oxidation of 1,2-dichlorobenzene was investigated over NaY and NaX zeolites, loaded with chromium through the action of a robust biosorption system consisting of a bacterial biofilm supported on the zeolites. The results of biosorption showed that the maximum metal removal efficiency was 20%, in both systems based on NaY or NaX, starting from solutions with chromium(VI) concentrations ranging from 50 to 250 mg_Cr/L. The bacterial biofilm, Arthrobacter viscosus, supported on the zeolite reduces Cr(VI) to Cr(III). The Cr(III) is retained in the zeolite by ion exchange. The new catalysts were characterized by spectroscopic methods (FTIR ), chemical analyses (ICP-AES), surface analysis (XRD) and thermal analysis (TGA). The various techniques of characterization show that this biosorption process does not modify the morphology and structure of the FAU-zeolites. These catalysts, Cr/FAU, prepared through this new procedure present good activity and selectivity for dichlorobenzene oxidation in wet air at 350 °C. The Cr₅₀-Y was selected as the most active, selective and stable catalyst for oxidation of 1,2-dichlorobenzene in wet air.     

Adsorption of basic dyes in a fixed bed column

The adsorption of basic dyes from aqueous solution onto granular activated carbon and natural zeolite has been studied by using a fixed bed column. The design procedures for fixed bed adsorption columns have been investigated for two basic dyes, Maxilon Goldgelb GL EC 400% (MG-400) and Maxilon Shwarz FBL-01 300% (MS-300). The effects of process variables such as bed height, volumetric flow rate, and dye concentration have been investigated. The results have been used to predict the effect of parameter changes on the system by using the bed depth service time (BDST) approach. The performances of the column charged with the natural zeolite were compared with those of the column charged with activated carbon.     

铁氧体法去除废水中的镍、铬、锌、铜离子

采用铁氧体法处理含镍、铬、锌、铜的废水,研究了pH及硫酸亚铁投加量对重金属离子去除效果的影响.对于镍、锌、铜离子,最佳絮凝pH分别为8.00～9.80、8.00～10.50和10.00,投加的亚铁离子与其摩尔比均为2～8;六价铬的最佳还原pH为4.00～5.50,最佳絮凝pH则为8.00～10.50,最佳投料比为20....     

Stellerite-seeded facile synthesis of zeolite X with excellent aqueous Cd2+ and Ni2+ adsorption performance

Zeolite X was synthesized by a two-step hydrothermal method using natural stellerite zeolite as the silicon seed, and its adsorption performance for Cd²⁺ and Ni²⁺ ions was experimentally and comprehensively investigated. The effects of pH, zeolite X dosage, contact time, and temperature on adsorption performance for Cd²⁺ and Ni²⁺ ions over were studied. The adsorption process was endothermic and spontaneous, and followed the pseudo-second-order kinetic and the Langmuir isotherm models. The maximum adsorption capacitiesfor Cd²⁺ and Ni²⁺ ions at 298 K were 173.553 and 75.897 mg·g^-1, respectively. Ion exchange and precipitation were the principal mechanisms for the removal of Cd²⁺ ions from aqueous solutions by zeolite X, followed by electrostatic adsorption. Ion exchange was the principal mechanisms for the removal of Ni²⁺ ions from aqueous solutions by zeolite X, followed by electrostatic adsorption and precipitation. The zeolite X converted from stellerite zeolite has a low n(Si/Al), abundant hydroxyl groups, and high crystallinity and purity, imparting a good adsorption performance for Cd²⁺ and Ni²⁺ ions. This study suggests that zeolite X converted from stellerite zeolite could be a useful environmentally-friendly and effective tool for the removal of Cd²⁺ and Ni²⁺ ions from aqueous solutions.     

离子交换树脂分离富集Cr(Ⅵ)和Cr(Ⅲ)的研究和应用

文章较系统地研究了201×8阴离子交换树脂、HD-8阳离子交换树脂分离富集Cr(Ⅵ)和Cr(Ⅲ)的最佳条件,探讨了洗脱液的选择,减压微型交换柱对铬的富集倍率和富集限,Cr(Ⅵ)和Cr(Ⅲ)的淋洗曲线,有机物存在对Cr(Ⅲ)回收的影响以及共存离子的最大允许量,最后还结合二苯碳酰二肼光度法用水样分别上阴柱和阳柱测定了西湖水和自来水中Cr(Ⅵ)和Cr(Ⅲ)的含量,水样中Cr(Ⅵ)加标回收率在97%～99%。     

煤矸石制备沸石-活性炭复合材料的吸附性能研究

利用煤炭生产的废弃物煤矸石为原料,在不同的条件下,制得A型和X型沸石-活性炭新型复合材料,通过X射线粉末衍射、低温N2(77 K)吸附、水和正己烷的吸附等表征:该复合材料具有中孔和微孔双重孔结构特征,同时具有亲水性和亲油性以及离子交换性质。对其应用性能的研究表明:复合材料对水和正己烷有高的吸附容量,并可一次性脱除废水中的重金属Cr3+和有机酚等有毒污染物。     

Mechanisms of Cr(VI) removal from water by various types of activated carbons

The removal mechanisms of Cr(VI) from water using different types of activated carbons, produced from coconut shell, wood and dust coal, were investigated in this project. Different types of activated carbons have different surface characteristics. The coconut shell and dust coal activated carbons have protonated hydroxyl groups on the surface (H‐type carbons), while the surface of the wood‐based activated carbon has ionised hydroxyl groups (L‐type carbons). The adsorption kinetics of chromium onto the activated carbons at pH values ranging from 2 to 6 were investigated. It was found that the optimum pH to remove total chromium was 2 for wood‐based activated carbon, while for coconut shell and dust coal activated carbons, the optimum pH was around 3–4. The difference in the optimum pH for different activated carbons to remove Cr(VI) from water can be explained by the different surface characteristics and capacity of the activated carbons to reduce Cr(VI) to Cr(III). © 1999 Society of Chemical Industry     

Kinetics and mechanism of chromium electrodeposition from formate and oxalate solutions of Cr(III) compounds

Kinetics of multistep reaction of Cr(III) ions discharge to metal was studied on a stationary electrode and on a rotating disk electrode from the solutions containing formic acid or oxalic acid. The electroreduction of Cr(III) complex ions in aqueous solutions is shown to proceed via the formation of relatively stable intermediates—Cr(II) compounds which are partially removed into bulk solution. The effect of pH, organic ligand concentration and disk rotation velocity on the partial current density of chromium electroplating was demonstrated. The kinetic equations of the studied process were derived and compared with the experimental data. Kinetic parameters for the discharge of Cr(II) ions were calculated. The mechanism of chromium electrodeposition reaction was proposed. The electrodeposition of chromium from formate bath is suggested to proceed with the participation of hydroxocomplexes of bivalent chromium. The oxalate complexes of bivalent chromium directly discharge in the electrolytes containing oxalic acid. The partial polarization curves of chromium electrodeposition exhibit a current peak which may be caused by blocking the electrode surface with poorly soluble Cr(III) hydroxide.     

Adsorption of trivalent chromium from aqueous solutions onto activated carbon

The adsorption of chromium (III) onto activated carbon was investigated as a possible alternative method for its removal from aqueous solutions. The adsorption data were obtained in a batch adsorber and fitted the Langmuir adsorption isotherm well. The effect of pH on the adsorption isotherm was investigated at pH values of 2, 4, 5 and 6. It was found that at pH values below 2 the Cr(III) was not adsorbed and at pH values above 6.4 the Cr(III) was precipitated as Cr(OH)₃. Maximum adsorption occurred at pH 5. The pH plays a very important role in the adsorption of Cr(III) since Cr(III) can form different complexes in aqueous solutions. The adsorption capacity was increased by about 20% as the temperature was raised from 25 to 40°C. It was concluded that Cr(III) is adsorbed to an appreciable extent on activated carbon and that the adsorption is highly dependent upon pH.     

Biosorption of chromium (III) by orange (Citrus cinensis) waste: Batch and continuous studies

The present study explores the ability of orange waste biomass to remove Cr (III) from aqueous solutions. Batch kinetic and isotherm studies were carried out on a laboratory scale to evaluate the adsorption capacity of orange waste. The effects of particle size, adsorbent dose and solution pH on Cr (III) removal were also studied. The results showed that the higher the adsorbent dosage and the pH, the higher the percentage of metal removal. No significant influence of particle size on sorption capacity was observed in the experimental conditions studied. A kinetic study revealed that the adsorption of Cr (III) onto orange waste was a gradual process and equilibrium was reached within 3 days. A pseudo-second order model was the most appropriate to describe the kinetic experimental data. Equilibrium assays displayed a maximum sorption capacity ranging from 0.57 mmol/g to 1.44 mmol/g when the pH increased from 3 to 5, according to the Sips model, which along with the Redlich–Peterson equation, is very suitable for correlating equilibrium data. The use of the studied adsorbent in the removal of chromium in continuous mode was successful and the breakthrough curves were adequately represented by BDST model. Due to the slow kinetics of chromium sorption onto orange waste, the sorption capacity in batch assays was higher than that in continuous assays.     

Removal of Cr(III) in the fixed bed column and batch reactors using as adsorbent zeolite NaX

In this work, the uptake capacity of Cr(III) ions in NaX zeolite was investigated. The experiments were carried out in continuous and batch systems at . The batch isotherm evidenced an irreversible shape with a maximum chromium uptake of 3.61 meq/g. The column experiments were carried out at pH=3.5, with a flow rate of 9 ml/min and an average particle size of 0.180 mm. The dynamic system provided a distinct ion-exchange mechanism, which generated a favorable isotherm with a chromium uptake of 3.27 meq/g. A mathematical model was also applied to represent the dynamics of the sorption of the column. The model considered the axial dispersion in the column and the intraparticle diffusion as the rate-controlling step. The dynamic isotherm was successfully modeled by the Freundlich equation and the mathematical model described well the experimental dynamic data for the feed concentrations from 0.3 up to 3.0 meq/g.     

Adsorption of Cr(III) ions by Turkish brown coals

The equilibrium and kinetic properties of Cr(III) ion adsorption by two brown coals from Anatolia, Turkey, have been investigated in batch stirred-tank experiments. The effects of adsorbent dose, initial sorbate concentration and contact time on the adsorption of Cr(III) by Isparta-Yalvaç-Yarikkaya (YK) and Kasikara (KK) brown coals were evaluated. The Cr(III) ions are able to form complex compounds with carboxylic and phenolic groups of brown coals and they were also bounded with phenolic groups even at low pH reaction of the solution (<3). Mechanisms including ion exchange, complexation and adsorption to the surface are possible in the sorption process. Our batch adsorption studies show the equilibrium adsorption data fit the linear Langmuir adsorption isotherm. Adsorption equilibrium was achieved in about 15–20 min for chromium(III). The Langmuir adsorption isotherm was used to describe the observed sorption phenomena. The maximum equilibrium uptake was 0.05 mmol of Cr(III)/g for KK, and 0.26 mmol of Cr(III)/g for YK, respectively, at a pH of 4.5. More than 90% of chromium(III) was removed by KK and YK from an aqueous solution after 60 min. In every experiment, the maximum Cr(III) was sequestered from the solution within 60 min. It is proposed that KK and YK brown coals can be used as potential sorbents for Cr(III) removal from aqueous solutions.     

Adsorption of chromium by activated carbon from aqueous solution

Adsorption isotherms of Cr(III) and Cr(VI) ions on two samples of activated carbon fibres and two samples of granulated activated carbons from aqueous solutions in the concentration range 20–1000 mg/l have been studied. The adsorption isotherms have been determined after modifying the activated carbon surfaces by oxidation with nitric acid, ammonium persulphate, hydrogen peroxide and oxygen gas at 350°C and after degassing at different temperatures. The adsorption of Cr(III) ions increases on oxidation and decreases on degassing. On the other hand, the adsorption of Cr(VI) ions decreases on oxidation and increases on degassing. The increase of Cr(III) and the decrease of Cr(VI) on oxidation and the decrease of Cr(III) and the increase of Cr(VI) on degassing have been attributed to the fact that the oxidation of the carbon surface enhances the amount of acidic carbon–oxygen surface groups while degassing eliminates these surface groups. Thus while the presence of acidic surface groups enhances the adsorption of Cr(III) cations, it suppresses the adsorption of Cr(VI) anions.     

Preparation of CPB-modified FAU zeolite for the removal of tannery wastewater contaminants

The preparation of organomodified zeolites with different framework structures (FAU, LTA and MOR) using N-cetylpyridinium bromide (CPB) as tailoring agent was studied. The sorption properties of CPB-modified zeolites were evaluated in the removal of tannery contaminants from aqueous solution. The CPB-modified FAU-type zeolite presented the highest Cr(VI) retention capacity (37 mmol/kg) due to the higher Cr(VI) retention of its unmodified form (larger pore opening) and its high CPB sorption capacity. CPB-modified FAU zeolite also exhibited high thermal stability as consequence of special interactions between the CPB molecules and the zeolite surface. In addition, the intrinsic Cr(III) exchange capacity of FAU zeolite increased with CPB loading (162–527 mmol/kg), which appear to be due to an additional retention mechanism provided by the sorbed cetylpyridinium surfactant layer. On other hand, CPB-modified FAU zeolite also exhibited high toluene retention capacity (62 mmol/kg) due to of the hydrophobic character of its surfactant-modified surface and toluene adsorption on internal sorption sites of FAU zeolite. Thus, CPB-modified FAU zeolite appears as a promising adsorbent for simultaneous removal of Cr(III), Cr(VI) and toluene contaminants from aqueous solution.     

Electrochemical synthesis of Cr(II) at carbon electrodes in acidic aqueous solutions

The electrochemical synthesis of Cr(II) has been investigated on a vitreous carbon rotating disc electrode and a graphite felt electrode using cyclic voltammetry, impedance spectroscopy and chronoamperometry. The results show that in 0.1 M Cr(III) + 0.5 M sulphuric acid and in 0.1 M Cr(III) + 1 M hydrochloric acid over an electrode potential range of –0.8 to 0.8 V vs SCE, the electrochemical reaction at carbon electrodes is essentially a surface process of proton adsorption and desorption, without significant hydrogen evolution and chromium(II) formation. At electrode potentials more negative than –0.8 V vs SCE, both hydrogen evolution and chromium(II) formation occurred simultaneously. At electrode potentials –0.8 to –1.2 V vs SCE, the electrochemical reduction of Cr(III) on carbon electrodes is controlled mainly by charge transfer rather than mass transport. Measurements on vitreous carbon and graphite felt electrodes in 1 M HCl, with and without 0.1 M CrCl₃, allowed the exchange current density and Tafel slope for hydrogen evolution, and for the reduction of Cr(III) to Cr(II), to be determined. The chromium(III) reduction on vitreous carbon and graphite electrodes can be predicted by the extended high field approximation of the Butler–Volmer equation, with a term reflecting the conversion rate of Cr(III) to Cr(II).     

活性炭为载体的负载型高变催化剂的研制

选择活性炭作载体,用真空浸渍盐溶液制备了活性炭负载铁基低铬(Cr2O3的含量4%)及无铬高温变换催化剂。通过XRD、TEM及XPS等表征研究了活性炭为载体的负载型高变催化剂的结构、粒径和表面性质;讨论了载体表面处理及催化剂制备条件对催化剂性能的影响。     

Biocomposite based electrode for effective removal of Cr (VI) heavy metal via capacitive deionization

Abstract

This study focuses on the fabrication of biocomposite electrode and removal of Cr (VI) ions from wastewater using a capacitive deionization (CDI) method. The activated carbon (AC) was synthesized from Bael fruit shell (BS). The synthesized AC surface has a macroporous and mesoporous structure with the large specific surface area (617.72?m² g^?1) and high adsorption capacity. The cyclic voltammetry and CDI were performed for the detection and for the removal of chromium (VI) ions, respectively. The lower level of detection of Cr (VI) by a modified electrode was found to be 10 ppt. SEM, BET, and FTIR analyses were performed to explore the surface properties of electrode materials. The removal efficiency was achieved 100% by using biocomposite electrode with an applied potential of 15?V. The highest percent removal mechanism consists of electrosorption and electroreduction due to the affinity between polyvinyl alcohol modified electrode and Cr (VI) ions, under electrochemically faradic process.     

Kinetics and thermodynamic studies of Cr(VI) adsorption using environmental friendly multifunctional zeolites synthesized from coal fly ash under mild conditions

Abstract

The Na-P1 zeolite was produced from coal fly ash and modified with different environmental friendly surfactants. The potential of these green modified zeolites was investigated as adsorbents for Cr(VI) ions in a batch system. XRD, SEM, XRF, and ICP-AES analyses were used for the characterization of raw materials and zeolite samples. The environmental friendly modified zeolites successfully immobilized different toxic elements in their framework inhibiting the transfer of these toxic elements to the surrounding liquid phase. The effects of various operational parameters on Cr(VI) removal were studied. The Hexamethylenediamine (HDTMA) and Ammonyx KP (KP) modified zeolites had larger chromium removal potential than the other samples at all temperatures. The effectiveness of Cr(VI) ions elimination became greater as the pH decreased and the adsorbent dose increased. The Freundlich, Langmuir, and Dubinin–Radushkevich isotherms were fitted to the equilibrium data. The Dubinin–Radushkevich and Langmuir models gave a better fitness to equilibrium data of HDTMA-Na-P1 and KP-Na-P1, respectively. The positive and high ΔH° values showed the endothermic nature of the total Cr(VI) sorption procedure and indicated that Cr(VI) adsorption onto HDTMA-Na-P1 and KP-Na-P1 is a chemisorption. The negative ΔS° values also showed that chromium ions were stable on the surface of adsorbents. The adsorption potential of the developed eco-friendly KP-Na-P1 was higher than those of other adsorbents reported in the literature.     

Bacterial cellulose/PANi mat for Cr(VI) removal at acidic pH

Remediation of hexavalent chromium - Cr(VI) at acidic pH using polyaniline coated bacterial cellulose porous mat (BC/PANi) is presented and the possible mechanism is discussed. The efficacy of BC/PANi mats in remediation of Cr(VI) was studied by varying pH (pH 1, 2, 3, and 5) and initial Cr(VI) concentrations (250–1000 ppm) of the solution. The BC/PANi (50 mg) mat was able to completely reduce 2000 ppm Cr(VI) into Cr(III) in a 20 ml solution at pH ~ 1 in 24 h. An increasing chromium removal efficiency was observed with decreasing solution pH; reaching a maximum removal capacity of ~920 mg/g at pH 1. The proposed mechanism of negatively charged Cr(VI) ions removal by BC/PANi mat is adsorption and simultaneous reduction into Cr(III), followed by desorption of Cr(III) from the mat. The role of temperature and co-existing anions like sulphate, nitrate and chloride found in industrial sludge were also investigated for removal efficiency of Cr(VI) at acidic pH ~ 1. The adsorption kinetics of Cr(VI) on polyaniline surface followed a pseudo-second-order model with reduction of Cr(VI) into Cr(III) as rate-limiting step. The reduced Cr(III) from the media was further recovered by neutralizing the pH of the solution.