Cadmium removal using waste residue generated after recovery of base metals from manganese nodules

The laboratory scale investigations on Cd removal characteristics of waste manganese leach residue (wMNR), generated by reduction roasting – ammonia leaching of manganese nodules have been studied. Adsorption studies show rapid kinetics of Cd adsorption. About 90% of total Cd adsorption occurs within 15 min contact time and equilibrium is attained within 30 min. The quantity of Cd adsorption increases with increase in leached residue dose but decreases with increase in initial Cd concentrations. The adsorption is found to be dependent on initial pH of Cd solution, which increases with increase in initial pH of the solution. Adsorption data are satisfactory fitted to the Langmuir isotherms. The loading capacity of Cdon leached residue calculated from Langmuir data is 32.26 mg g at pH 5.5 and 303 K, which improves to 38.17 mg g at 323 K. Pseudo second-order kinetics is applicable for the Cd adsorption. Thermodynamic studies indicate spontaneous (∆G= -3.88, -5.04 and -6.0 kJ mol at 303, 313 and 323 K respectively) and endothermic (∆H= 28.3 kJ mol) nature of adsorption. The activation energy for Cd adsorption onto wMNR is calculated to be 50.76 – 65.14 kJ mole, suggesting chemisorption type adsorbate-adsorbent interaction.