Recovery of metal values from spent zinc-carbon dry cell batteries

Abstract

Spent zinc-carbon dry cell batteries were characterized to identify the potential of recovering metal values from these batteries. Different component plIl1s of ooth new and spenl baTteries of all the five type (AAA, M, C, D and 9V) were ""amined. The outer st",,1 casings were found to be tin plat~'d. Sleel, zinc and manganc,;e consisted 63 percent of the lotal weight of the spI,"l balleric,. Average ",..,ighl of zinc and manganese were respectively 22 and 24 percent of the total weight in spent baUeries. In eiedrolyte paste of tile spent batteries, £inc and m3!1ganese oonslilutcd 22 and 60 percent of the tolal paste weight. The rest was chlorine, carbon. small amount iron and other impurity elements. Major phase" in lhe fresh batteries were carbon, MoO, and NH,Cl; while Zn{NI h),CI,. ZoO.Mo,O" l\1n,O. and Mn,O-, were the prom inent phases in the spent batteries. Presence of mereur)' and cadmium were not detected and a small percentage of lead wa. found in both the zinc anode and electrolyte paste of the batteries. The different component parrs in the ballery were .separately procesood to extract the metallic values. The UIlodie zinc parts were subjected to pyrometallurgieal processing. Ex1nletion of zinc was negligible when no fluxing agent wa, used. However, the recovery increased significanlly when chioride >alts: sodium chloride, calcium chloride and ammonium chloride "ere used as a fluxing agent. Among these, ammonium chloride gave the best result as flux. With 10% of each flux, the extraction of zinc was 90% for ammonium chioride; and around 75% for both ><Xliumchloride nnd calcium chloride. A maximum of 92% exlraetion of total zinc with purity over 99.5% could be "blained in presence of t2% ammonium chloride nux by heating at 600'C for 10 minutes. Spent eiectrolyte paste was subjectcd to hydrometallurgical processing to recover the manganese and zinc. Moisture conlCnl of the electrolyte paste was estimated to be 12.3%. Chemical analysis of the eiectro1ytc pa.'<lewas determined by X-ray fluorescence and elemental analysis. Water wa.hing to remove non metanie parts from the paste proved inefficient due to loss of some zinc through dissolution. Leaching of the electrolyte paste was carried out in sulfuric acid media in presence of hydrogen peroxide as a reducing agent Effect of process variahles, such as concentration of sulfuric acid and hydrogen peroxide, temperature, Slirring speed and solid/liquid ratio were studied 10 determine the optimum conditions. A maximum dissolution of 88% manganese from the paste was possible under the following conditions: Time: 27 minutes, Sulfuric acid concentration: 2.5M, Hydrogen peroxide concentration: 10%, Temperature; 60"C, Stirring speed: 600 rpm and Solid/iiquid ratio: 1:12. Zinc recovery under the >aJJlecondition was 97%. , I Kinetic parameters were established from the time versus extenl of dissolution cnrve for bolh manganese and zinc, using temperature as a variable. Leaching of hoth manganese and dnc were found to follow the chemical reaction conlrol1cd process with a very high correlation factor. Activalion energy of manganese and zinc were found to he 46.27 KJ/mol and 52.39 KJlmol respectively; whicb jll,tit1cd the appropriateness of the model. .1he reaclion order for manganese wilh respect to sulfuric acid wa, 1.12, in lhe concentration range for sulfuric aeid up to 2M. 7ine and manganese were precipitated from the leach liquor. Zinc extraction from the leaching solution in the oxalate fOTInwas 83.29% while the precipitation of manganese in the carbonate was 69.89%.