Adsorption of hexavalent chromium from aqueous solutions by wheat bran

In this research, adsorption of chromium (VI) ions on wheat bran has been studied through using batch adsorption techniques. The main objectives of this study are to 1) investigate the chromium adsorption from aqueous solution by wheat bran, 2) study the influence of contact time, pH, adsorbent dose and initial chromium concentration on adsorption process performance and 3) determine appropriate adsorption isotherm and kinetics parameters of chromium (VI) adsorption on wheat bran. The results of this study showed that adsorption of chromium by wheat bran reached to equilibrium after 60 min and after that a little change of chromium removal efficiency was observed. Higher chromium adsorption was observed at lower pHs, and maximum chromium removal (87.8 %) obtained at pH of 2. The adsorption of chromium by wheat bran decreased at the higher initial chromium concentration and lower adsorbent doses. The obtained results showed that the adsorption of chromium (VI) by wheat bran follows Langmuir isotherm equation with a correlation coefficient equal to 0.997. In addition, the kinetics of the adsorption process follows the pseudo second-order kinetics model with a rate constant value of 0.131 g/mg.min The results indicate that wheat bran can be employed as a low cost alternative to commercial adsorbents in the removal of chromium (VI) from water and wastewater.     

Adsorption kinetics of chromium(III) removal from aqueous solutions using natural red earth

Laboratory-scale-simulated experiments were carried out using Cr(III) solutions to identify the Cr(III) retention behavior of natural red earth (NRE), a natural soil available in the northwestern coastal belt of Sri Lanka. The effects of solution pH, initial Cr(III) concentration and the contact time were examined. The NRE showed almost 100 % Cr(III) adsorption within the first 90 min. [initial [Cr(III)] = 0.0092–0.192 mM; initial pH 4.0–9.0]. At pH 2 (298 K), when particle size ranged from 125 to 180 μm the Cr(III) adsorption data were modeled according to Langmuir convention assuming site homogeneity. The pH-dependent Cr(III) adsorption data were quantified by diffused layer model assuming following reaction stoichiometries: $$ \begin{aligned} 2\, {>}{\text{AlOH}}_{{({\text{s}})}} + {\text{ Cr }}\left( {\text{OH}} \right)_{{ 2\,({\text{aq}})}}^{ + } \, \to \, \left( { {>}{\text{AlO}}} \right)_{ 2} {\text{Cr}}_{{({\text{s}})}}^{ + } + {\text{ 2H}}_{ 2} {\text{O}} \quad {\text{log K 15}}. 5 6\\ 2\, {>}{\text{FeOH}}_{{({\text{s}})}} + {\text{ Cr}}\left( {\text{OH}} \right)_{{ 2\,({\text{aq}})}}^{ + } \, \to \, \left( { {>}{\text{FeO}}} \right)_{ 2} {\text{Cr}}_{{({\text{s}})}}^{ + } + {\text{ 2H}}_{ 2} {\text{O}}\quad {\text{log K 5}}.0 8.\\ \end{aligned} $$ The present data showed that NRE can effectively be used to mitigate Cr(III) from aqueous solutions and this method is found to be simple, effective, economical and environmentally benign.     

Adsorption of copper onto goethite in aqueous systems

The adsorption of copper(II) onto goethite was studied as a function of pH, total dissolved copper concentration, surface area of goethite, and ionic strength. The adsorption of copper was similar to that of other hydrolyzable metals. A tenfold increase in goethite surface area had a significant effect on the adsorption edge, but a tenfold increase in the ionic strength of the medium did not effect the adsorption edge. The distribution coefficients increase sharply with increase in pH and ranged from 10 to 60,000 ml/g over a range of two and half pH units, depending on the goethite surface area and copper concentration. A tenfold decrease in ionic strength as well as a tenfold increase in surface area of goethite did not have any effect on the magnitude of distribution coefficients. Distribution coefficients were used to calculate the number of protons released per mole of copper adsorbed during the adsorption process. The average number of protons released per mole of copper adsorbed was estimated to be 1.40 ± 0.10.Managed by Martin Marietta Energy System, Inc., for the U.S. Department of Energy under contract no. DE-AC05-840R21400.     

Hexavalent chromium removal from aqueous solutions by using low-cost biological wastes: equilibrium and kinetic studies

The batch removal of hexavalent chromium from aqueous solutions using almond shell, activated sawdust, and activated carbon, which are low-cost biological wastes under different experimental conditions, was investigated in this study. The influences of initial concentration, adsorbent dose, adsorbent particle size, agitation speed, temperature, contact time, and pH of solution were investigated. The adsorption was solution pH dependent and the maximum adsorption was observed at a solution pH of 2.0. The capacity of chromium adsorption under equilibrium conditions increased with the decrease in particle sizes. The equilibrium was achieved for chromium ion after 30?min. Experimental results showed that low-cost biosorbents are effective for the removal of pollutants from aqueous solution. The pseudo-second-order kinetic model gave a better fit of the experimental data as compared to the pseudo-first-order kinetic model. Experimental data showed a good fit with the Freundlich isotherm model. Changes in the thermodynamic parameters, including Gibbs free energy (??G_o), enthalpy (??H_o), and entropy (??S_o), indicated that the biosorption of hexavalent chromium onto almond shell, activated sawdust, and activated carbon was feasible, spontaneous, and endothermic in the temperature range 28?C50?°C.     

Adsorption phenomena in hydrometallurgy, 2. Electrophoretic behavior of oxides in aqueous ammoniacal solutions of copper,nickel and cobalt

The electrophoretic mobilities of finely divided oxides in aqueous ammoniacal solutions of copper, nickel, and cobalt have been measured. The solids used were rutile, alumina, quartz, and hematite. The effects of pH, ammonia-ammonium concentration, and metal-ion concentration on the electrophoretic behavior were investigated. The experimental results indicate that oxide colloids may undergo as may as five charge reversals in aqueous ammoniacal solutions of hydrolyzable ammine-forming metal ions.     

Adsorption phenomena in hydrometallurgy, 1 The uptake of copper,nickel and cobalt by oxide adsorbents in aqueous ammoniacal solutions

The uptake or adsorption of copper, nickel and cobalt by finely divided oxide solids in aqueous ammoniacal medium has been investigated experimentally in order to determine how adsorption on leach residues can affect the recovery of leachable metals. Hematite, rutile, alumina and quartz were used as model solid adsorbents. In the case of ammoniacal leach solutions the controlling metal species appears to be the aqueous neutral hydroxo species. Adsorption behavior was found to have maxima and minima as a function of pH, the magnitude of which depends on ammonia concentration, the metal cation, and the adsorbent.     

Removal of chromium (VI) from aqueous solutions using Lewatit FO36 nano ion exchange resin

The removal of the chromium (VI) ion from aqueous solutions with the Lewatit FO36 ion-exchange resin is described at different conditions. The effects of adsorbent dose, initial metal concentration, contact time and pH on the removal of chromium (VI) were investigated. The batch ion exchange process was relatively fast and it reached equilibrium after about 90 min of contact. The ion exchange process, which is pH dependent showed maximum removal of chromium (VI) in the pH range 5.0–8.0 for an initial chromium (VI) concentration of 0.5 mg/dm³. The equilibrium related to Lewatit FO36 ion- exchange capacity and the amounts of the ion exchange were obtained using the plots of the Langmuir adsorption isotherm. It was observed that the maximum ion exchange capacity of 0.29 mmol of chromium (VLVg for Lewatit FO36 was achieved at optimum pH value of 6.0. The ion exchange of chromium (VI) on this cation-exchange resin followed first-order reversible kinetics.     

Adsorption of molybdenum on to anatase from dilute aqueous solutions

Adsorption of Mo on to hydrous TiO₂ (anatase) particles was investigated. Batch experiments were conducted at 19 and 90 °C over a pH range of 2 to 12 and Mo concentrations ranging from approximately 10⁻⁶ to 10⁻⁴ M. The extent of sorption was strongly dependent on pH and surface loading. Maximum sorption was observed in the acidic pH range at low surface loading. Adsorption behavior was described using the empirical Langmuir adsorption model. A constant capacitance surface complexation model was also used to fit the adsorption isotherms using a ligand exchange reaction for a hydroxyl surface site on anatase. Comparison of experimental data at two different temperatures (19 and 90 °C) indicates that Mo sorption in the acidic pH range decreases with increasing temperature.     

A kinetic study of copper cementation with zinc in aqueous solutions

Cementation of copper from zinc containing copper solutions using metallic zinc was studied in this work. The effect of copper, zinc and ammonium chloride concentration, stirring speed, pH and temperature on the cementation of copper was determined. Cementation rate increased with initial copper concentration, stirring speed and temperature. pH variation from 1 to 4 increased the cementation rate but at higher pH, the rate was not significantly effected. The cementation rate of copper increased with Zn²⁺ ion concentration. However, the rate of this rise was slightly less compared to the rise that occurred in the Zn²⁺ ions free copper solution.     

Phosphorylated nanocellulose papers for copper adsorption from aqueous solutions

Copper is a major problem in industrial wastewater streams, seriously affecting the quality of potential drinking water. Several approaches, including continuous membrane processes or batch-wise application of adsorbents, are in use to tackle this problem. Unfortunately, these processes suffer from their particular drawbacks, such as low permeance or disposal of saturated adsorbents. However, a combination of these processes could constitute a step towards a more efficient copper removal solution. Here, we present a nanopaper ion-exchanger prepared from cellulose nanofibrils produced from fibre sludge, a paper industry waste stream, for the efficient, continuous removal of copper from aqueous solutions. This nanopaper ion-exchanger comprises phosphorylated cellulose nanofibrils that were processed into nanopapers by papermaking. The performance of these phosphorylated nanopaper membranes was determined with respect to their rejection of copper and permeance. It was shown that this new type of nanopaper is capable of rejecting copper ions during a filtration process by adsorption. Results suggest that functional groups on the surface of the nanopapers contribute to the adsorption of copper ions to a greater extent than phosphate groups within the bulk of the nanopaper. Moreover, we demonstrated that those nanopaper ion-exchangers could be regenerated and reused and that in the presence of calcium ions, the adsorption capacity for copper was only slightly reduced.     

Adsorption of copper(II) from aqueous solution by Beidellite

Dry lakes, degraded sandy grasslands, abandoned farmland and mobile dunes which are widely distributed throughout the arid areas of northern China have been investigated in this work. Gain-size distribution of the surface sediments of Manas lake in Junggar basin, Juyan lake in the Alxa plateau, Zhuye lake in Minqin basin and most deserts (such as Mu Us desert, Otindag desert, Horqin desert and Hulun Buir desert) in China have been analyzed. The results show clay with particle sized <10 μm on the surface sediments of dry lakebed and sandy grassland developed from dry lakebed, respectively, account for >60% and ∼50% of the total mass. Since the tiny particles on the surface of abandoned farmland are blown away easily and rapidly, the content of clay particles in Minqin basin is <14%. The grain-size distribution of mobile dunes in northern China mainly consists of particles >63 μm and few particles <10 μm. Consequently, although sand/dust storms originate primarily in the western deserts, the gobi areas of the Alxa plateau, the north and east of Hexi Corridor and in central Mongolia, the widely distributed dry lakebeds, sandy grasslands and abandoned farmland adjacent to the deserts also contribute to aeolian dusts. Hence, the material sources for sand dust storm in East Asia include inland deserts, but also dry lakes, sandy grasslands and abandoned farmland, which are widely distributed throughout the arid inlands of northern China.     

Efficient removal of hexavalent chromium from aqueous solutions using autohydrolyzed Scots Pine (Pinus Sylvestris) sawdust as adsorbent

In this work, a low-cost lignocellulosic adsorbent with high biosorption capacity is proposed, suitable for the efficient removal of hexavalent chromium from water and wastewater media. The adsorbent was produced by autohydrolyzing Scots Pine (Pinus Sylvestris) sawdust. The effect of the autohydrolysis conditions, i.e., pretreatment time and temperature, on hexavalent chromium biosorption was investigated using energy-dispersive X-ray spectroscopy (EDS) and UV–visible spectrophotometry. The Freundlich, Langmuir, Sips, Radke-Prausnitz, Modified Radke-Prausnitz, Tóth, UNILAN, Temkin and Dubinin-Radushkevich adsorption capacities and the rate constant values for pseudo-first- and pseudo-second-order kinetics indicated that the autohydrolyzed material exhibits significantly enhanced hexavalent chromium adsorption properties comparing with the untreated sawdust. The Freundlich’s adsorption capacity K _F increased from 2.276 to 8.928 (mg g^?1)(L mg^?1)^1/n , and the amount of hexavalent chromium adsorbed at saturation (Langmuir constant q _m) increased from 87.4 to 345.9 mg g^?1, indicating that autohydrolysis treatment at 240 °C for 50 min optimizes the adsorption behavior of the lignocellulosic material.     

Removal of hazardous hexavalent chromium from aqueous solution using divinylbenzene copolymer resin

This paper presents the removal of hazardous hexavalent chromium from liquid waste streams using divinylbenzene copolymer resin Amberlite IRA 96. Important sorption parameters such as contact time, pH, resin dosage and initial metal concentration were studied at 30?°C. The kinetic study was conducted using pseudo-first and pseudo-second-order kinetics at 30?°C. The sorption process was found to be pH dependent. Maximum removal was obtained at pH 2 under optimized conditions. The sorption process was rapid and 99?% of the removal was achieved in first 30?min. The equilibrium data were fitted to both Langmuir and Freundlich models. The better regression coefficient (R ²) in Freundlich model suggests the multilayer sorption process. The value of Gibbs free energy for sorption process was found to be ?12.394?kJmol^?1. The negative value indicated the spontaneity of the sorption process. Scanning electron microscope and energy dispersive X-ray spectroscopy studies were conducted to find the role of surface morphology during sorption process. The Fourier transform infrared study was conducted to identify the functional groups responsible for interaction between the resin and chromium. Desorption and regeneration studies were also carried out.     

Electrochemical reaction control of contact angles on copper and synthetic chalcocite in aqueous potassium diethyldithiophosphate solutions

The contact angles on synthetic chalcocite in potassium diethyldithiophosphate (KDTP) solutions have been compared with those on copper to delineate physico-chemical factors which might contribute to the flotation response of copper sulfides. The influence of a number of variables such as KDTP concentration, solution pH, gaseous environment and electrochemical pretreatment has been investigated. The results are discussed in terms of the thermodynamic and kinetic aspects of the system.     

Physical and chemical activation of pyrolyzed oil shale residue for the adsorption of phenol from aqueous solutions

Batch kinetics and isotherm studies were carried out to evaluate the sorption of phenol by pyrolyzed and activated Jordanian oil-shale. The effects of contact time, initial sorbate concentration, sorbent concentration, temperature, pH and inorganic salts (NaCl and KCl), on the adsorption process by different sorbents were considered. Chemically activated oil shale, pretreated with ZnCl ₂, gave the highest uptake of phenol. The isotherm experimental data fit well to Freundlich and Redlich-Paterson models and to a less extent to the Langmuir model. The increase in the initial sorbate concentration resulted in an increase in the uptake. Three kinetics models, namely the Morris-Weber model, the Lagergren model, and the pseudo-second-order model (PSOM), were applied to represent the experimental results for pyrolyzed and ZnCl ₂-oil shale sorbents. Pyrolyzed oil shale was prepared using a fluidized bed reactor at 520 °C in the presence of nitrogen. Physical activation was carried out by treating the resulted pyrolyzed oil shale with CO ₂ at 830 °C, while chemical activation of oil shale was carried out using KOH and ZnCl ₂ as impregnating agents.     

Electrochemical oxidation of succinic acid in aqueous solutions using boron doped diamond anodes

In this work, the electrochemical oxidation of succinic acid on boron-doped diamond (BDD) anodes was investigated. Voltammetric study had shown that no peaks appeared in the region of electrolyte stability which indicates that succinic acid oxidation can take place at a potential close to the potential region of electrolyte oxidation. Galvanostatic electrolyses achieved total chemical oxygen demand (COD) removals and high mineralization yields under different operating conditions (initial COD, current density and nature of supporting electrolyte). Oxalic, glycolic and formic acids were the main intermediates detected during anodic oxidation of succinic acid on BDD electrode and carbon dioxide as the final product. The mean oxidation state of carbon reached the value of 4 at the end of electrolysis which is indicative of mineralization of almost all organics present in aqueous solution. The exponential profile of COD versus specific electrical charge has shown that mass transfer is the limiting factor for the kinetics of electrochemical process. A simple mechanism was proposed for the mineralization of succinic acid. First, hydroxyl radicals attack of succinic acid leading to formation of glycolic, glyoxylic, fumaric and maleic acids. Then, theses acids undergo rapid and non-selective oxidation by hydroxyl radicals to be transformed into oxalic and formic acids which leads to further oxidation steps to mineralize these acids into carbon dioxide and water.     

Photocatalytic degradation of azo dye Orange II in aqueous solutions using copper-impregnated titania

During dyeing process, industries consume large quantity of water and subsequently produce large volume of wastewater. This wastewater is rich in color and contains different dyes. Orange II is one of them. In this article, metal-impregnated TiO₂ P-25 catalyst was used to enhance the photocatalytic degradation of Orange II dye. Photodegradation percentage was followed spectrophotometrically by the measurements of absorbance at λ _max = 483 nm. The effect of copper-impregnated TiO₂ P-25 photocatalyst for the degradation of Orange II has been investigated in terms of percentage removal of color, chemical oxygen demand (COD) and total organic carbon (TOC). As such 98 % color removal efficiency, 97 % percentage removal of COD and 89 % percentage removal of TOC was achieved with TiO₂ P-25/Cu catalysts under typical conditions. Copper-impregnated TiO₂ P-25 photocatalyst showed comparatively higher activity than UV/H₂O₂ homogeneous photodegradation. The relative electrical energy consumption for photocatalytic degradation was considerably lower with TiO₂ P-25/Cu photocatalyst than that with homogeneous photodegradation. Transmission electron microscopic analysis was used for catalyst characterization.     

Advantage of almond green hull over its resultant ash for chromium(VI) removal from aqueous solutions

The discharge of industrial effluents containing hexavalent chromium can be very harmful for the environment. Therefore, Cr(VI) should be removed from contaminated water, and especially from wastewater, to prevent its discharge into the environment. This study is aimed at analyzing the factors that affect the removal of Cr(VI) with the use of almond green hull and ash adsorbent. The effects of pH (2–10), adsorbent dose (2–24 g/L), Cr(VI) concentration (10–100 mg/L), exposure time (1–60 min), and temperature (5–50 °C) were examined. The surface morphology, pore size of adsorbent surfaces were characterized with SEM, EDX, FTIR. Maximum removal occurred at pH = 2. Results showed that the removal yield increased with the rise of exposure time and temperature. The data indicate that due to limited site on adsorbent surface, the removal efficiency decreased as initial Cr(VI) concentration increased. When the adsorbent dose was increased, the removal yield increased in the case of the bioadsorbent as well; however, in the ash adsorbent, there was an increase followed by a decreasing trend. The study highlights that almond green hull can be more efficient than its ash in the removal of Cr(VI) from aqueous solution. As a general result of study, it can be argued that almond green hull bioadsorbent and the obtained carbon are able to remove Cr(VI) from aqueous solutions; thus, they can be used as efficient and economical substitutes for existing adsorbents like activated carbon, for the removal of chromium from polluted aqueous solutions.     

Adsorption of reactive dyes from aqueous solutions by tannery sludge developed activated carbon: Kinetic and equilibrium studies

Adsorption kinetic and equilibrium studies of two reactive dyes, namely, Reactive Red 31 and Reactive Red 2 were conducted. The equilibrium studies were conducted for various operational parameters such as initial dye concentration, pH, agitation speed, adsorbent dosage and temperature. The initial dye concentration was varied from 10 - 60 mg/L, pH from 2–11, agitation speed from 100–140 rpm, adsorbent dosage from 0.5 g to 2.5 g and temperature from 30 °C -50 °C respectively. The activated carbon of particle size 600 μm was developed from preliminary tannery sludge. The dye removal capacity of the two reactive red dyes decreased with increasing pH. The zero point charge for the sludge carbon was 9.0 and 7.0 for the two dyes, respectively. Batch kinetic data investigations on the removal of reactive dyes using tannery sludge activated carbon have been well described by the lagergren plots. It was suggested that the Pseudo second order adsorption mechanism was predominant for the sorption of the reactive dyes onto the tannery sludge based carbon. Thus, the adsorption phenomenon was suggested as a chemical process. The adsorption data fitted well with Langmuir model than the Freundlich model. The maximum adsorption capacity(q⁰) from Langmuir isotherm were found to have increased in the range of 23.15–39.37 mg/g and 47.62–55.87 mg/g for reactive dyes reactive red 31 and reactive red 2, respectively.