G. Roy Chaudhury

Removal of Cr(VI) by thermally activated weed Salvinia cucullata in a fixed-bed column

The present study evaluates the feasibility of using a thermally activated fresh water weed in removing Cr(VI) from wastewater through column studies. The effect of flow rate, bed height and Cr(VI) concentration of the feed solution on the adsorption capacity of the activated weed was investigated. The adsorption capacity increased with decrease in both flow rate and bed height but increased with an increase in initial adsorbate concentration. Four different kinetic models, such as. Adams-Bohart, Bed Depth Service Time (BDST), Thomas and Yoon-Nelson models were first applied to the experimental data to predict the breakthrough curve and to determine the characteristic parameters of the column useful for designing large-scale column studies. Different statistical methods such as Sum of the Square of the Error (SSE), Sum of the Absolute Error (SAE), Average Relative Error (ARE), Average Relative Standard Error (ARS) and regression coefficient, were applied to evaluate the prominent and unique characteristic features of the experimental and predicted parameters under the respective models to find out the best fit. The performance stability of the adsorbent was tested by continuous adsorption-desorption studies.

A preliminary study on the adsorptive removal of Cr(VI) using seaweed, Hydrilla verticillata.

The Cr(VI) adsorption efficiency of the seaweed, Hydrilla verticillata, was studied in batches. The adsorbent was characterized using SEM, BET surface area analyzer, Malvern particle size analyzer, EDAX and FT-IR. Cr(VI) removal efficiency of the adsorbent was studied as a function of different adsorption parameters such as contact time, stirring speed, pH, adsorbent dose, particle size, adsorbate concentration, and temperature. Langmuir, Freundlich, and Temkin adsorption isotherm equations were used in the equilibrium modeling. The adsorption process followed pseudo second-order kinetics and intra-particle diffusion was found to be the rate-controlling step. Experimental data follow Langmuir adsorption isotherm. Thermodynamic parameters such as Gibbs free energy and enthalpy of the adsorption process were evaluated to find out the feasibility of the adsorption process. The negative values of Gibbs free energy and positive enthalpy values show the feasibility and endothermic nature of the process. The significance of different adsorption parameters along with their combined effect on the adsorption process has been established through a full 2(4) factorial design. Among the different adsorption parameters, pH has the most influential effect on the adsorption process followed by adsorbate concentration and combined effects of all the four parameters were tested. The correlation among different adsorption parameters were studied using multi-variate analysis.

Bioleaching kinetics and multivariate analysis of spent petroleum catalyst dissolution using two acidophiles

Bioleaching studies were conducted to evaluate the recovery of metal values from waste petroleum catalyst using two different acidophilic microorganisms, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Various leaching parameters such as contact time, pH, oxidant concentration, pulp densities, particle size, and temperature were studied in detail. Activation energy was evaluated from Arrhenius equation and values for Ni, V and Mo were calculated in case of both the acidophiles. In both cases, the dissolution kinetics of Mo was lower than those of V and Ni. The lower dissolution kinetics may have been due to the formation of a sulfur product layer, refractoriness of MoS(2) or both. Multivariate statistical data were presented to interpret the leaching data in the present case. The significance of the leaching parameters was derived through principle component analysis and multi linear regression analyses for both iron and sulfur oxidizing bacteria.

Arsenic(V) adsorption mechanism using kaolinite, montmorillonite and illite from aqueous medium

The present work investigates the adsorptive behavior of As(V) ions with kaolinite, montmorillonite and illite in aqueous medium as a function of As(V) concentration, pH, contact time and temperature. As(V) adsorption on studied clays were pH dependent and maximum adsorption were achieved in the pH range 2.0–5.0. The adsorption data gave good fits with Langmuir isotherm and yielded Langmuir monolayer capacity of 0.86, 0.64 and 0.52 mg As(V) /g of kaolinite, montmorillonite and illite, respectively. An increase in adsorption temperature resulted in a decrease in the amount of As(V) adsorbed. The results of leaching study showed that, kaolinite was very active clay constituent regarding both As(V) adsorption and mobility. The electrokinetic behavior of both the kaolinite and montmorillonite were modified in the presence of As(V). The shift in isoelectric point indicated that adsorption involves inner sphere surface complexation and strong specific ion adsorption. Kaolinite was successfully tested as an adsorbent for the removal of arsenic from two contaminated groundwater samples containing arsenic in the range 1.36–1.41 mg/L.

Bacterial leaching — Complex sulphides of copper, lead and zinc

Abstract Bacterial leaching of complex sulphides from Ambamata was carried out in shake flasks as well as in column. The copper and zinc dissolution obeyed the model of shrinking core-product layer diffusion. Attempts have also been made to evaluate the order of copper and zinc dissolution and it was found to be of first order in both cases with respect to substrate concentration. The Kp values for copper and zinc were also calculated. In the column leaching studies the copper leaching curve showed a sudden decrease after the formation of Cu1.95S. Analysis of the leached residue from the column showed extensive leaching at the top and the extent of leaching decreased progressively from top to bottom.

Kinetics of Zn2+ adsorption by Penicillium sp.

Abstract Zn 2+ ion adsorption studies were carried out using a biomass of Penicillium sp. The percentage adsorption increased with increasing pH and the amount of biomass and showed a reverse trend with temperature and initial Zn 2+ concentration. The adsorption kinetics were initially fast then slow. The initial faster rate corresponds to around 70% of the total adsorption. The activation energy was found to be 8.4 kJ/mol, which corresponds to a diffusion-controlled mechanism.

Removal of Cr(VI) from aqueous solution using waste weed, Salvinia cucullata

Biosorption studies of Cr(VI) were carried out using waste weed, Salvinia cucullata. Various adsorption parameters were studied, such as agitation speed, contact time, pH, particle size, and concentrations of adsorbent and adsorbate. The equilibrium was achieved in 12 h. A lower pH favoured adsorption of Cr(VI). The kinetics followed pseudo-second-order rate equations. The adsorption isotherm obeyed both the Langmuir and Freundlich models. The calculated activation energy (1.1 kJ mol−1) suggested that the adsorption followed a diffusion-controlled mechanism. Various thermodynamic parameters such as Δ G °, Δ H °, and Δ S ° were also calculated. The positive values of enthalpy indicated the endothermic nature of the reaction, and Δ S ° showed the increasing randomness at the solid liquid interface of Cr(VI) on the adsorbent, which revealed the ease of adsorption reaction. These thermo-dynamic parameters showed the spontaneity of the reaction. The maximum adsorption of uptake (232 mg g−1) compared well with reported values of similar adsorbents. The rate-determining step was observed to follow an intra-particle diffusion model.

Treatment of electronic waste to recover metal values using thermal plasma coupled with acid leaching--a response surface modeling approach.

The global crisis of the hazardous electronic waste (E-waste) is on the rise due to increasing usage and disposal of electronic devices. A process was developed to treat E-waste in an environmentally benign process. The process consisted of thermal plasma treatment followed by recovery of metal values through mineral acid leaching. In the thermal process, the E-waste was melted to recover the metal values as a metallic mixture. The metallic mixture was subjected to acid leaching in presence of depolarizer. The leached liquor mainly contained copper as the other elements like Al and Fe were mostly in alloy form as per the XRD and phase diagram studies. Response surface model was used to optimize the conditions for leaching. More than 90% leaching efficiency at room temperature was observed for Cu, Ni and Co with HCl as the solvent, whereas Fe and Al showed less than 40% efficiency.

Bioleaching of low-grade uranium ore using Acidithiobacillus ferrooxidans

Bioleaching of uranium was carried out with Turamdih ore sample procured from Uranium Corporation of India Limited, Jaduguda. The bacterial strain that was used in the leaching experiments was isolated from the Jaduguda mine water sample. Efficiency of bioleaching was studied by varying parameters like pulp density and initial ferrous concentration as source of energy. It is observed that the efficiency of bioleaching was 49% at 10% pulp density (w/v) and initial pH 2.0. Addition of external has no effect on efficiency of bioleaching showing domination of direct leaching mechanism over indirect.

Purification of an ammoniacal zinc leach liquor using a rotating zinc disc after copper solvent extraction

Abstract A process for purifying an ammoniacal complex sulphide leach liquor through a cementation route using pure zinc is described. Purification of the leach liquor is mandatory in order to improve the quality of electrowon zinc. The cementation studies were carried out using a rotating zinc disc. Various parameters such as rotation speed and the effect of copper ion vis-a-vis the cementation of cadmium, cobalt and nickel were studied. The presence of copper gives a marked improvement in the cementation of cobalt and nickel whereas cadmium cementation shows a negative trend. With an increase of rotation speed of the zinc disc, the rate of cementation becomes faster. Initially the cementation rate is faster and with time the rate falls off. The cementation of cadmium is much faster than that of cobalt and nickel.