Sorption of cadmium ions from aqueous solution by manganese nodules leached residue.

Abstract

Different industrial wastes, such as those from mining, electro-plating, lead smelting and metal finishing industries, etc., discharge significant amounts of heavy metals in various forms. Cadmium is of particular interest because of its high toxicity and its widespread presence in the industrial effluents. In the present study, the leach residue generated from processing of polymetallic sea nodules by reduction roast – ammonia leaching was utilized for removal of cadmium. Physico-chemical characterization of leach residue showed that leached residue was highly porous with reasonably high surface area, which was about 60.91 m2/g. Effects of various parameters like time, initial Cd(II) concentration, adsorbent dose, pH on cadmium adsorption were studied. The results showed that the equilibrium for Cd(II) adsorption was attained after 30 min. contact time (Fig. 1). It was found that an increase in the adsorbent dose with constant Cd(II) concentration resulted in greater metal removal from solution. An increase in the Cd(II) concentration with a constant sorbent concentration resulted in higher metal loading per unit weight of sorbent. Data obtained for adsorption of Cd(II) from different initial Cd(II) concentration at fixed adsorbent dose was fitted to Langmuir and Freundlich isotherms. Langmuir isotherm model was found to be applicable for the experimental data of cadmium uptake as shown by R2 value. The adsorption was found to be dependent on initial pH of cadmium solution, which increased with increase in initial pH of the solution. During Cd(II) uptake various metal ions were found to be released from leach residue, which decreased with increased pH and were practically negligible at pH~5-6. The loading capacity of Cd(II) on leached residue was 32.23 mg g-1 at pH 5.5. Based on regression coefficient value, pseudo-second order kinetics was applicable for the Cd(II) adsorption. The results from above studies suggested that leached manganese nodules residue could be employed for the adsorption of the cadmium from aqueous solutions with reasonable efficiency.