V. N. Singh

Copper(II) removal from aqueous solutions by fly ash

Abstract The removal of Cu(II) by adsorption on fly ash has been found to be concentration, pH and temperature dependent. The kinetics of adsorption indicates the process to be diffusion controlled. The Langmuir constants have been calculated at different temperatures, and the adsorption has been found to be endothermic ( ΔH = 15.652 kcal mol −1 ). The maximum removal is observed at pH 8.0, and variation in adsorption with pH has been explained on the basis of surface ionisation and complexation.

Removal of chrome dye from aqueous solutions by mixed adsorbents : fly ash and coal

The removal of Omega Chrome Red ME (a popular chrome dye) from its aqueous solutions by adsorption on a homogeneous mixture of fly ash and coal in different proportions has been carried out. It has been noted that low adsorbate concentration, small particle size of adsorbent, low temperature and acidic medium favour the removal of the dye. A 100% removal of the said dye was achieved at 10 mg1−1, 30°C, 2.0 pH and 53 μm particle size, using a 1:1 ratio of fly ash and coal. The kinetics and mass transfer studies were made using the models suggested by Lagergren and McKay et al. respectively. The equilibrium data fit well in the Langmuir model of adsorption, showing the formation of monolayer coverage of dye molecules at the outer surface of the adsorbent. Effect of temperature was explained on the basis of solubility and chemical potential of the adsorbate. An attempt has been made to explain the results thus obtained on the basis of various physiochemical properties of the solid-solution interface involved in the process of removal.

Defluoridation of water by adsorption on fly ash

The ability of fly ash to remove fluoride from water and wastewaters has been studied at different concentrations, times, temperatures and pH of the solution. The rate constants of adsorption, intraparticle transport, mass transfer coefficients and thermodynamic parameters have been calculated at 30, 40, and 50 °C. The empirical model has been tested at various concentration for the present system. The removal of fluoride is favorable at low concentration, high temperature and acidic pH.

As(III) removal from aqueous solution by adsorption

The removal of As(III) from aqueous solutions at different concentrations, pH and temperatures by haematite has been carried out successfully. The maximum removal was found to be 96 % at concentration 13.34 μmol L−1, temperature 20 °C and pH 7.0. The process of uptake follows first-order adsorption rate expression and obeys the Langmuirs model of adsorption. The removal of As(III) by haematite is also partially diffusion controlled and mass transfer coefficients, diffusion coefficients and thermodynamic parameters have been determined to explain the results.

Fly ash for the treatment of Cd(II) rich effluents

Abstract The removal of Cd(II) by adsorption on fly ash has been found to be contact time, concentration, temperature and pH dependent. The process of removal follows first order adsorption kinetics and the rate controlling step is intrap article transport into the pores of fly ash particles. The equilibrium nature of Cd(II) adsorption at different temperatures has been described by the Langmuir isotherm. The temperature dependence of Cd(II) adsorption on fly ash indicates the exothermic nature of adsorption. Alkaline aqueous medium favours the removal of Cd(II) by fly ash. The increase in adsorption of Cd(II) with pH has been explained on the basis of surface complex formation approach.

Removal of chrome dye from aqueous solutions by fly ash

The ability of fly ash to remove Omega Chrome Red ME (a chrome dye, mostly used in textile industries) from water has been studied. It has been found that low adsorbate concentration, small particle size of adsorbent, low temperature, and acidic pH of the medium favor the removal of chrome dye from aqueous solutions. The dynamics of adsorbate transport from bulk to the solid phase has been studied at different temperatures in light of the adsorption of dye on the outer surface as well as diffusion within the pores of fly ash. The applicability of Langmuir isotherm suggests the formation of monolayer coverage of dye molecules on the outer interface of adsorbent. The thermodynamics of chrome dye-fly ash system indicates spontaneous and exothermic nature of the process. The pronounced removal of chrome dye in the acidic range may be due to the association of dye anions with the positively charged surface of the adsorbent.

China clay as an adsorbent for dye house wastewaters

Abstract The ability of china clay to remove a popular chrome dye, Omega Chrome Red ME, from aqueous solutions has been studied. Maximum removal (i.e., 81.08%) was noted at 10 mg l−1 initial dye concentration, 53μm adsorbent particle size, 2.0 pH and 303 K. The process follows a first order rate kinetics. Intraparticle diffusion and mass transfer coefficients have been determined at different temperatures. The adsorption data fits well in the Langmuir adsorption model. The effect of temperature has been examined on the basis of boundary layer thickness and enthalpy change studies. Heat of adsorption has been found to be a function of surface coverage. The maximum removal of the dye in acidic range has been explained on the basis of surface hydroxylation, acid‐base dissociation and surface complexation probabilities. A 100% desorption of the dye from the adsorbent surface was noted at pH 12.0.

Use of wollastonite for the treatment of Cu(II) rich effluents

The adsorption technique using wollastonite has been applied for the removal of Cu(II) from aqueous solutions. The low concentration, high temperature and alkaline pH favor the removal of Cu(II). The Langmuir isotherm was used to represent the equilibrium data at different temperatures. The apparent heat of adsorption has been found to be 5.926 Cal mol−1. The uptake of Cu(II) is diffusion controlled and the mass transfer coefficient is 3.6 × 10−5 cm s−1. The maximum removal of Cu(II) in alkaline medium has been explained on the basis of the uptake of hydrolyzed adsorbate species by the active surface sites of adsorbent.

Mixed adsorbents for Cu(II) removal from aqueous solutions

Abstract Low cost mixed adsorbents have been used to study, the removal of Cu(II) at different concentrations, and pH of the solution. The uptake of Cu (II) is maximum by wollastonite‐china clay followed by fly ash‐wollastonite and fly ash‐china clay at the same concentration, temperature and pH of the solution. Equilibrium data of various systems at 30°C and pH 6.5 fit well in the Freundlich equation. Removal of Cu(II) increases with the pH of the solution and is maximum at pH 8.0. Significant desorption of Cu(II) from the surfaces of mixed adsorbents was noted at pH 2.0.

Removal of color from wastswater by sorption for water reuse

Abstract The removal of Metomega Chrome Orange GL, a commercial textile dye from wastewaters has been found to be nearly 99% under the optimal conditions (i.e. 3.0 pH and 30°C temperature) using fly ash as an sorbent. The process follows a first order kinetics and the value of rate constant, Kad is of the order 3 x 10−2 min−1. Intraparticle diffusion and mass transfer coefficients have been determined at different temperatures. The sorption data fits well in the Langmuir isotherm model. The effect of temperature has been explained on the basis of boundary layer thickness, activation energy (Ea = ‐0.87 Cal mole−1) and enthalpy change (AH = ‐13.04 Cal mole−1) study. Heat of sorption has been found to be a function of surface coverage.