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

Abstract

The laboratory scale investigations on Cd²⁺ removal characteristics of waste manganese leach residue (<i style="mso-bidi-font-style:normal">w</i>MNR), generated by reduction roasting – ammonia leaching of manganese nodules have been studied. Adsorption studies show rapid kinetics of Cd²⁺ adsorption. About 90% of total Cd²⁺ adsorption occurs within 15 min contact time and equilibrium is attained within 30 min. The quantity of Cd²⁺ adsorption increases with increase in leached residue dose but decreases with increase in initial Cd²⁺ concentrations. The adsorption is found to be dependent on initial <i style="mso-bidi-font-style:normal">p</i>H of Cd²⁺ solution, which increases with increase in initial <i>p</i>H of the solution. Adsorption data are satisfactory fitted to the Langmuir isotherms. The loading capacity of Cd²⁺on leached residue calculated from Langmuir data is 32.26 mg g^-1 at <i>p</i>H 5.5 and 303 K, which improves to 38.17 mg g^-1 at 323 K. Pseudo second-order kinetics is applicable for the Cd²⁺adsorption. Thermodynamic studies indicate spontaneous (ΔG⁰= -3.88, -5.04 and -6.0 kJ mol^-1 at 303, 313 and 323 K respectively) and endothermic (ΔH⁰= 28.3 kJ mol⁻¹) nature of adsorption. The activation energy for Cd²⁺ adsorption onto <i style="mso-bidi-font-style:normal">w</i>MNR is calculated to be 50.76 – 65.14 kJ mole^-1, suggesting chemisorption type adsorbate-adsorbent interaction.