RECOVERY OF VALUABLE METALS FROM ELECTRONIC WASTE USING ELECTROLYTIC ION EXCHANGE PROCESS

Abstract

This study focuses on novel dismantling of e-waste, acid leaching of metal values, separation and purification using chelating resins and electrowinning. Emphasis is placed on recovery of copper, zinc and nickel from silica rich integrated circuits (SRICs). The SRICs on printed circuits boards (PCBs) was depopulated using hot air gun, pulverized using hammer mill and roasted in the muffle furnace. Characterization of roasted SRICs powder revealed the presence of quartz (SiO2), tenorite (CuO), willemite (Zn2SiO4), nickel zinc oxide (NiO.Zn2O), iron copper oxide (CuFe5O8), wustite (Fe0.945O), ilmenite (Fe2TiO4) and cassieterite (SnO2). Chemical analysis of acid digested SRICs powder reveled that Si (45.5%), Cu (35.5%), Zn (1.7%), Ni (1.2%) and Fe (7.2%) were present. Direct acid leaching of the SRICs powder showed maximum leaching efficiency of 100 % for Cu with 1.0 M HNO3, 96.6 % for Zn with 1.0 M H2SO4 and 76.8 % for Ni with 1.0 M HCl at optimum conditions. Trifluoromethanesulfonic acid (TFMS) was used for the first time in the leaching of SRICs at a temperature of 90°C, where leaching efficiencies of 85.9, 60 and 28.4% were achieved for Cu, Zn, and Ni respectively. The problem of moderate leaching of Zn and low leaching of Ni by direct leaching with acids was overcome using sulphation roasting and water leaching. The optimum conditions for Cu, Zn, and Ni extractions were determined as H2SO4/SRIC ratio 0.5, roasting temperature 300 °C, roasting time 60 min, leaching temperature 50 °C, leaching time 60 min, and liquid–solid ratio = 10:1 (i.e., 100 mL/10 g) with extraction efficiencies of 61.9, 84.9, and 93.6 % for Cu, Ni, Zn, and 71.1 % co-extractions of Fe was observed. Thereafter, separation/purification studies of sulphate leach liquor using Dowex M 4195 and Purolite S 957 chelating resins was performed. After optimization, the results showed selective recovery of copper (51.1 %) at pH 0.7 while 40.0 % nickel was recovered from the raffinate at pH 2.0 with co-adsorption of iron and trace of zinc as impurities. 100 % elution of Cu and Ni was achieved using concentrated H2SO4. Iron was completely removed via the addition of Ca (OH)2 at pH 4.0 and the zinc sulphate solution was achieved. On the other hand, removal of iron from sulphate leach liquor was studied using Purolite S 957, the results showed high selectivity towards Fe3+ and other metals were retained in the solution. Oxalic acid solution performed excellently for the regeneration of Purolite S 957 and it was reused. The adsorption processes could be best described by the Freudlich, Temkin and scatchard isotherm model and pseudo-second-order adsorption kinetic. The fixed-bed column experiments showed that the breakthrough and exhaustion time slowly increased with increase in the flow rate and slightly decreased when the bed height was increased. The column parameters were evaluated and the adsorption data was best described by Thomas and Yoon-Nelson models. After optimization of electrolytic parameters, powder copper deposit was obtained by electrowinning using CuSO4 solution from eluted Dowex M 4195 at 100 A/ m2 while rough surface copper sheet was obtained by electrowinning of purified CuSO4 solution obtained after Fe3+ have been completely removed by Purolite S 957 resin. The complete process can be upscale for further study.