Indian Journal of Chemical Technology Vol. 20, November 2013, pp. 371-379 Cadmium removal using waste residue generated after recovery of base metals from manganese nodules N S Randhawa 1 , N N Das 2 & R K Jana 1, * 1 Metal Extraction & Forming Division, CSIR-National Metallurgical Laboratory, Jamshedpur 831 007, India 2 PG Department of Chemistry, North Orissa University, Baripada 757 003, India Received 29 May 2012; accepted 22 May 2013 The laboratory scale investigations on Cd 2+ 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 2+ adsorption. About 90% of total Cd 2+ adsorption occurs within 15 min contact time and equilibrium is attained within 30 min. The quantity of Cd 2+ adsorption increases with increase in leached residue dose but decreases with increase in initial Cd 2+ concentrations. The adsorption is found to be dependent on initial pH of Cd 2+ solution, which increases with increase in initial pH of the solution. Adsorption data are satisfactory fitted to the Langmuir isotherms. The loading capacity of Cd 2+ on leached residue calculated from Langmuir data is 32.26 mg g -1 at pH 5.5 and 303 K, which improves to 38.17 mg g -1 at 323 K. Pseudo second-order kinetics is applicable for the Cd 2+ adsorption. Thermodynamic studies indicate spontaneous (G 0 = -3.88, -5.04 and -6.0 kJ mol -1 at 303, 313 and 323 K respectively) and endothermic (H 0 = 28.3 kJ mol -1 ) nature of adsorption. The activation energy for Cd 2+ adsorption onto wMNR is calculated to be 50.76 – 65.14 kJ mole -1 , suggesting chemisorption type adsorbate-adsorbent interaction. Keywords: Adsorption, Cadmium, Chemisorption, Manganese nodules, Manganese nodules leach residue The surface water bodies on the earth are often polluted by the effluents from various types of industries. Heavy metals present in these effluents, when discharged untreated, are threat to ecosystem. These metals are non-biodegradable and tend to accumulate in living organisms, causing various life threatening disorders. Among the toxic heavy metals, mercury, lead and cadmium are known as the highly toxic ones, due to their major impact on the environment 1 . The toxic and harmful effects of cadmium to human body system are very well known 2,3 . Cadmium as a pollutant is found in discharges from electroplating, alkaline batteries, paints, plastics and paper manufacturing industries 4 . Among the important technologies available for remediation of cadmium contaminated effluents, adsorption technique has been viewed as most attractive due to factors like simple operation, effectiveness, etc 5 . In addition, many adsorption techniques regenerate the adsorbent and reduce the operational cost. The key factor for the selection of an adsorbent lies with its effectiveness and most importantly its cost. Apart from much studied adsorbents like activated carbon, bio-sorbents based on agriculture (stems, peals, husks, shells, leaves, etc.), agro-industries waste materials have also been tried for the removal of cadmium from waste water 5 . Metallic oxides (Fe, Mn and Al), especially of waste category, are of much interest due to their effectiveness towards remediation of heavy metals from contaminated aqueous bodies 5 . Residues generated after hydrometallurgical treatment of manganese nodules or polymetallic sea nodules contain oxides/oxy-hydroxides of Fe, Mn, Al and Si with a reasonable porosity and surface area. These residues have been utilized as an effective adsorbent for a variety of species 6-8 . The present study is aimed at investigating the sorption characteristics of residue, generated in the reduction–roast ammoniacal leaching of manganese nodules, for the removal of Cd 2+ from its aqueous solution. Emphasis has been given on characterization of leached residue of cadmium, its regeneration after adsorption and the underlying mechanism of adsorption. Experimental Procedure Materials The adsorbent material, i.e. leached manganese nodule residue (MNR), was obtained from large scale trial of reduction roasting - ammoniacal leaching of manganese nodules at CSIR-National Metallurgical ________________ *Corresponding author. E-mail: rkjana@nmlindia.org