Bioadsorption of Pb(II), Cd(II), and Cr(VI) on activated carbon from aqueous solutions

The bioadsorption of Pb(II), Cd(II), and Cr(VI) using bacteria and activated carbon has been studied. Preliminary studies yielded the chemical and textural characterization of the carbons. The adsorption of bacteria on the activated carbons modified their surface characteristics, reducing the volume of pores and the pH of the point of zero charge, with a resulting increase in the density of the negative charge of their surface. The adsorption of the above metals was studied in both static and dynamic conditions and in the absence and presence of bacteria (Escherichia coli). The presence of bacteria in aqueous solution enhances the adsorption of Pb(II) and Cd(II) and reduces the adsorption of Cr(VI). These results can be explained by changes in the surface charge density of the carbons when bacteria are adsorbed, and by considering the structural and chemical characteristics of the bacterial cell walls. Investigation of the effect of electrolytes on the bioadsorption of these metals showed, in general, a resulting reduction in the amount of metal adsorbed, mainly in the presence of divalent cations. According to the divalent cation bridging theory, these results derive from competition between the Pb(II) or Cd(II) cations and the electrolyte cations for the negatively charged functional groups of extracellular polymeric substances.     

活性炭表面热氧化对其吸附二苯并噻吩性能影响

本文主要研究活性炭表面氧化对其吸附二苯并噻吩性能的影响。将活性炭在不同低温下氧化制得表面氧化活性炭，用静态吸附法进行了二苯并噻吩在初始及氧化活性炭上的吸附等温线，应用Langmuir方程对吸附等温线进行拟合，用漫反射红外谱（DRIFTS）表征活性炭表面含氧基团，用Boehm滴定测定活性炭表面官能团含量，讨论了活性炭表面化学性质对其吸附二苯并噻吩的影响。结果表明：活性炭表面酸性含氧基团对二苯并噻吩的吸附有重要影响，酸性含氧基团越多，其吸附量越大。低温气相氧化活性炭提高了活性炭表面酸性含氧基团，提高了其对二苯并噻吩的吸附。氧化温度越高，其表面含氧基团含量越多，其对二苯并噻吩的吸附量也越大。Langmuir吸附等温线可适用于描述二苯并噻吩在活性炭表面上的吸附。     

Adsorption of Cr(VI) and As(III) on coaly activated carbon in single and binary systems

In single component system, the adsorption of Cr(VI) and As(III) increase with contact time. Solution pH is found influencing the adsorption. Cr(VI) removal is found to be maximum (98%) at pH = 2. While, As(III) removal is found to be maximum at pH = 6 (77.2%). The adsorption capacity of Cr(VI) is greater than that of As(III) in single component system. Several adsorption isotherms were used to fit the equilibrium data. The adsorption kinetic data of Cr(VI) and As(III) were analyzed and is found fitting well in a pseudo-second-order equation both in single and binary systems. In binary system, the adsorption of As(III) is generally higher than that in single system. The pseudo-second-order rate constant k₂ is 0.5037 g/mg min in binary system larger than 0.0782 g/mg min in single system. However, the presence of As(III) in solution does not significantly influence the capacity of Cr(VI) adsorption on coaly activated carbon (CAC). The complexation between Cr(VI) and As(III) influence the adsorption, resulting in increased adsorption of As(III). The complexation structure of As(III), Cr(VI) and CAC was proposed as A-Cr(VI)-As(III) (A represents the adsorption site on the CAC).     

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     

Electrochemical regeneration of chrome etching solution

A metal surface is chromatized with a chromic acid solution to obtain a good adherence of polymer coatings. In this process Cr(VI) is reduced to Cr(III). The oxidation strength of the solution decreases during use. The chrome solution needs to be regenerated and purified. A new anode material, namely boron-doped diamond, was used to investigate the oxidation of Cr(III) to Cr(VI). It was found that the current efficiency for Cr(III) oxidation decreases with increasing total current density. The current density of Cr(III) oxidation increases linearly with increasing Cr(III) concentration and is practically independent of the Cr(VI) concentration. It was concluded that the diffusion of Cr(III) is the rate-determining step for the Cr(III) oxidation at Cr(III) concentrations form 40 to 160 mol m^–3. The surface of the boron-doped diamond shows no signs of chemical corrosion or mechanical destruction. A filter-press type cell divided into two compartments by a cation exchange membrane was proposed. A cost calculation was carried out for the oxidation of 1.28 mmol s^–1 Cr(III) in a 40 mol m^–3 chrome(III) solution. Factors affecting the feasibility of this process include the costs of chemical waste disposal, the costs of chromic acid, government legislation and to a great extent the costs of the new anode material.     

Simultaneous adsorption of aniline and Cr(VI) ion by activated carbon/chitosan composite

Activated carbon/chitosan composite has been used as an adsorbent to remove aniline and Cr(VI) ions from aqueous solutions simultaneously. The effects of preparation conditions such as the ratio of activated carbon to chitosan, crosslinking reagents, crosslinking time, and adsorption conditions including adsorbent dosage, pH value of solution, and contact time on simultaneous adsorption of aniline and Cr(VI) ion were investigated. Experimental results showed that epichlorohydrin was the proper crosslinking reagent, and the ratio of activated carbon to chitosan was kept at 1. When the adsorbent dosage was 4.0 g/L, and the concentrations of aniline and Cr(VI) were lower than 50 and 100 mg/L, respectively, both aniline and Cr(VI) were simultaneously removed at natural pH with high removals (>95%). The presence of Cr(VI) enhanced the adsorption of aniline, while the presence of aniline almost had no influence on the adsorption of Cr(VI). The adsorption processes of both aniline and Cr(VI) followed the pseudo‐second‐order kinetics model, but the sorption of Cr(VI) was preferential to that of aniline by this composite. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39903.     

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.     

Surface modification and adsorption of eucalyptus wood-based activated carbons: Effects of oxidation treatment, carbon porous structure and activation method

The incorporation of oxygen functional groups onto the surface of eucalyptus activated carbon and its surface chemistry were investigated as a function of oxidation conditions, carbon porous properties and carbon preparation method. Under all treatment conditions of increasing time, temperature and oxidant concentration, liquid oxidation with HNO₃, H₂O₂ and (NH₄)₂S₂O₈ and air oxidation led to the increase of acidic group concentration, with carboxylic acid showing the largest percentage increase and air oxidation at the maximum allowable temperature of 350 °C produced the maximum content of both carboxylic acid and total acidic group. Nitric acid oxidation of chemically activated carbon produced higher total acidic content but a lower amount of carboxylic acid compared to the oxidized carbon from physical activation. The increased contents of acidic groups on oxidized carbons greatly enhanced the adsorption capacity of water vapor and heavy metal ions.     

Catalytic oxidation of Fe(II) by activated carbon in the presence of oxygen.: Effect of the surface oxidation degree on the catalytic activity

The catalytic oxidation of Fe(II) species in aqueous solution by activated carbons with different degrees of surface oxidation is described. The parent activated carbon was oxidized with aqueous solutions of nitric acid or hydrogen peroxide, and submitted to thermal treatment at 373, 523 and 773 K. The activated carbons prepared were characterized by N₂ adsorption and temperature-programmed desorption, and their catalytic behavior was determined by measuring the oxidation rate of Fe(II) to Fe(III) and the generation of hydrogen peroxide. Catalytic activity is a function of the nature of oxygen surface groups generated by oxidation.     

Catalytic oxidation of Fe(II) by activated carbon in the presence of oxygen.: Effect of the surface oxidation degree on the catalytic activity

The catalytic oxidation of Fe(II) species in aqueous solution by activated carbons with different degrees of surface oxidation is described. The parent activated carbon was oxidized with aqueous solutions of nitric acid or hydrogen peroxide, and submitted to thermal treatment at 373, 523 and 773 K. The activated carbons prepared were characterized by N₂ adsorption and temperature-programmed desorption, and their catalytic behavior was determined by measuring the oxidation rate of Fe(II) to Fe(III) and the generation of hydrogen peroxide. Catalytic activity is a function of the nature of oxygen surface groups generated by oxidation.     

Adsorption performance and physicochemical mechanism of MnO2-polyethylenimine-tannic acid composites for the removal of Cu(II) and Cr(VI) from aqueous solution

In this work, an adsorbent, which we call MnPT, was prepared by combining MnO₂, polyethylenimine and tannic acid, and exhibited efficient performance for Cu(II) and Cr(VI) removal from aqueous solution. The oxygen/nitrogen-containing functional groups on the surface of MnPT might increase the enrichment of metal ions by complexation. The maximum adsorption capacities of MnPT for Cu(II) and Cr(VI) were 121.5 and 790.2 mg·g⁻¹, respectively. The surface complexation formation model was used to elucidate the physicochemical interplay in the process of Cu(II) and Cr(VI) co-adsorption on MnPT. Electrostatic force, solvation action, adsorbate–adsorbate lateral interaction, and complexation were involved in the spontaneous adsorption process. Physical electrostatic action was dominant in the initial stage, whereas chemical action was the driving force leading to adsorption equilibrium. It should be noted that after adsorption on the surface of MnPT, Cr(VI) reacted with some reducing functional groups (hydroxylamine-NH₂) and was converted into Cr(III). The adsorption capacity declined by 12% after recycling five times. Understanding the adsorption mechanism might provide a technical basis for the procedural design of heavy metal adsorbents. This MnPT nanocomposite has been proven to be a low-cost, efficient, and promising adsorbent for removing heavy metal ions from wastewater.     

Coals as sorbents for the removal and reduction of hexavalent chromium from aqueous waste streams

The aim of this study is to demonstrate the potential of coals as a low-cost reactive barrier material for environmental protection applications, with the ability to prevent leaching of toxic Cr(VI) and other transition metals. Depending upon the type of ion and the surface functionalities, the uptake can involve ion sorption, ion exchange, chelation and redox mechanisms with the surface functionalities being considered as partners in electron transfer processes. The capacity for Cr(VI) uptake of low rank coals and oxidized bituminous coals has been found to lie within the range 0.2-0.6 mM g⁻¹. Air oxidation of bituminous coals can increase their Cr(VI) removal capacities. The effect of air oxidation of coals on uptake capacity was more pronounced for Cr(VI) than Cr(III), but less than for Hg(II) and the other ions (Ca²⁺, Ba²⁺, Zn²⁺, Cd²) investigated. As previously found for Hg(II), redox mechanisms play an important role in Cr(VI) uptake, with sorption of the resultant Cr(III) being aided by the functionalities arising from oxidation of the coal surface. In acidic media, much of the resultant Cr(III) is exchanged back into solution by hydrogen ions, but some of the sorbed chromium is irreversibly bound to the coal. The reduction of Cr(VI) alone is often considered a satisfactory solution in view of Cr(III) being essentially non-toxic.     

Lead(II) adsorption onto the graphene layer of carbonaceous materials in aqueous solution

Lead(II) adsorption from an aqueous solution onto a graphene layer (Cπ electrons) was investigated using activated carbon and charcoal. The carbonaceous materials were treated by several steps to prepare ash free and acidic oxygen free graphite surface by washing with HCl and H₂F₂ solution followed by out gassing at 1273 K. Changes in Pb(II) adsorption capacity were checked at each step to maximize the area of the graphene layer. As received activated carbon and charcoal and their HNO₃ oxidized counterparts were also used for the adsorption experiments for comparison with the ash free and the acidic oxygen free carbons. Boehm titration and Langmuir isotherms were used to evaluate the Pb(II) adsorption onto the adsorbents. The experimental results indicate that an acidic oxygen free graphene layer exhibits a basic character caused by Cπ electrons. When only a small amount of acidic oxygen groups was present, the Pb(II) adsorption strength onto the graphene layer (Cπ electrons) significantly diminished, and the Pb(II) adsorption sites were switched from the graphene layer to carboxylic and lactonic groups on the carbons in the results.     

Removal of chromium(III) from tannery effluents,using a system of packed columns of zeolite and activated carbon

The removal of chromium(III) in packed columns of zeolite and activated carbon has been studied. The process of Cr(III) exchange in 13X zeolite was optimized using mass transference parameters. In addition, the effects of pH, the presence of interfering ions and the anion associated with the chromium in the solution were studied. It was found that particle diameter controls the Cr(III) exchange in the zeolite, indicating that particle diffusion predominantly controls the process of Cr(III) exchange in 13X zeolite. A mixed system of zeolite and activated carbon columns increased the efficiency of chromium removal from diluted wastewater. This effect occurred due to the reduction of the organic matter (chemical oxygen demand), adsorption of chromium, and interfering ions on the activated carbon column. The activated carbon + zeolite column system emerges as an alternative method in Cr(III) removal from tannery effluents. Copyright © 2005 Society of Chemical Industry     

Adsorption of p-nitrophenol on an activated carbon with different oxidations

An activated carbon prepared from olive stones has been modified through oxidation by nitric acid or sodium hypochlorite. These treatments introduced large amounts of oxygen groups, which were characterized by mass-spectrometry, temperature-programmed desorption (DTP-MS). Both CO₂- and CO-evolving groups were created by these oxidation treatments. A part of these oxidized samples was then outgassed under vacuum up to 823 K in order to remove most of the CO₂-evolving groups from their surface. Oxidized samples have a smaller surface area than the original sample. The subsequent partial outgassing increases the surface area which, however, does not reach the value it had before oxidation. p-Nitrophenol (PNP) adsorption isotherms from aqueous solutions were determined at 298 K for the original, oxidized, and partly outgassed samples. The results confirm the presence of an intermediate plateau at low equilibrium PNP concentration (at about 10 mg/l). The relative effects of textural versus surface chemistry on PNP uptakes are then discussed. The presence of CO-evolving groups showed no influence on PNP uptakes. The conclusion is that models in which carbonylic groups are basic adsorption sites for substituted phenols can be ruled out for the entire isotherm of PNP obtained with the original carbon. These models are also unlikely for PNP adsorption on oxidized and partly outgassed samples.     

Metal ion adsorption behavior of lignocellulosic fiber–ethylene vinyl acetate composites

This study describes the applicability of lignocellulosic fiber dispersed in ethylene vinyl acetate (EVA) to adsorb Pb(II), Cr(III), and Cr(VI) ions in aqueous solutions. Water absorption studies revealed that metal‐ion uptake does not only take place on the surface of the adsorbent but ions can also diffuse into the composite. The adsorption of the metal ions under different experimental conditions was studied. Solute concentration, pH, and contact time were used to assess the adsorption capacity and efficiency. The amount of metal adsorbed increased to 7 mg/g with an increase in solute concentration but compromising the efficiency. Adsorption equilibrium was reached after 3 h, when the maximum lead adsorption was above 80%. The optimum pH for the adsorption of Pb(II) and Cr(III) was 6.5, and pH 2.5 was used for the adsorption of Cr(VI). Competitive adsorption revealed the order of adsorption to be: Pb(II) > Cr(VI) > Cr(III). POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Modified activated carbon with an enhanced nitrobenzene adsorption capacity

To enhance nitrobenzene removal from aqueous solution, commercial activated carbon (AC) was modified by oxidation with HNO₃ followed by heat treatment in a nitrogen atmosphere. The modification process introduced oxygen-containing functional groups and changed the charge properties of the AC surface. The effects of surface chemical properties and pore structure on the adsorption of nitrobenzene by the AC were investigated through kinetics and equilibrium isotherms. HNO₃ oxidation modified the surface chemical properties and increased the number of acidic oxygen-containing surface groups, but had an almost negligible effect on the pore structure. Subsequent heat treatment caused decomposition of oxygen-containing functional groups on the AC surface, increased the pH point of zero charge (pH_PZC) and increased the number of mesopores. The maximum adsorption capacity achieved by the modified AC was 1,443.53 mg g^?1, 3.33 times of that unmodified AC. HNO₃ oxidation combined with heat treatment was an effective method for the preparation of AC with high nitrobenzene adsorption capacity and fast adsorption kinetics. An appropriate pH_PZC, amount of surface oxygen groups and the presence of well-developed mesopores together with micropores were the main reasons for the high nitrobenzene adsorption capacity of the modified AC.     

活性炭表面改性及其对Cr(Ⅵ)吸附性能的研究

分别用HNO3、H2SO4以及HNO3加乙酸铜溶液对活性炭进行了表面改性处理,测定了它们的表面化学性能,研究了改性活性炭对Cr(VI)吸附性能的影响。实验结果表明：通过上述改性,活性炭表面官能团数量发生了显著改变,特别是羧基增加较多;通过改性后的活性炭对Cr(Ⅵ)吸附性能有所提高。     

Surface‐Treated Activated Carbon for Removal of Aromatic Compounds from Water

Modifications of commercial activated carbons by chemical treatment with HNO₃ or HCl and HF and the adsorption behavior of simple aromatic compounds (aniline, pyridine, phenol, and benzene) on activated carbon and modified activated carbon were investigated. The results show that the textural properties change a little after these modifications, but the surface acidity (mainly oxygen‐containing groups) of activated carbon modified with HNO₃ increases greatly. The effect of ash of activated carbon on adsorption of the organic compounds mentioned above is insignificant. However, addition of surface acidity (mainly surface oxygen‐containing groups) decreases the adsorption capacity of compounds significantly. The adsorption uptake of compounds on activated carbon with oxidation of HNO₃ is low possibly due to dispersive interaction, water cluster blocking, or competition between water and compounds adsorbed on activated carbon's surface because of hydrophilic increase of the activated carbon surface. The solubility of aromatic compounds in water has an important effect on the adsorption capacity of activated carbon. q_m and K_L (Langmuir adsorption parameters) for the aromatic compounds vary similarly.     

Retention of Cr(VI) and Hg(II) in Eucalyptus globulus‐ and peach stone‐activated carbons

Retention rate of Cr(VI) and Hg(II), from an aqueous medium by activated carbons obtained from peach stones and Eucalyptus globulus chips, is reported. To describe the retention rate of these ions, the effects of the activated carbon preparation variables: activating agent (steam and CO₂), and burn‐off, are analyzed. In addition, the effect of the following adsorption process variable: initial concentration of the metallic ion, system temperature, pH of the medium and particle size of the adsorbent is discussed. Cr(VI) was retained at a higher rate in E globulus‐ activated carbon than in peach stone‐activated carbon due to the higher volume of the transport pores in the former material. The retention rate appears to include a micropore diffusional control in the Hg(II) retention and a transport pore diffusion control in Cr(VI) retention. The retention rate of Hg(II) is also dependent on chemical functionality of the activated carbon surface and the retention is enhanced when carbon dioxide is used as activating agent, whereas Cr(VI) retention is higher when steam activation is used. © 1999 Society of Chemical Industry