Leaching and Adsorption of Gold from Waste Printed Circuit Boards Using Iodine-Iodide Solution and Activated Carbon
Iodine-iodide leaching and activated carbon adsorption processes for recovery of gold (Au) from waste printed circuit boards (WPCBs) were discussed in this paper. A pressure oxidative acid leaching (POAC) was carried out in an autoclave using diluted sulfuric acid (1M H 2 SO 4 ) solution in order to remove high concentrations of some base metals especially copper (Cu), aluminum (Al), iron (Fe) and zinc (Zn) due to their negative effect on gold dissolution from WPCBs. The factors affecting the performance and efficiency of the iodine-iodide leaching process; such as iodine/iodide concentration, pulp density, leaching time and leaching temperature were optimized in order to maximize the gold dissolution efficiency from the WPCBs in the iodine-iodide solution. Results indicated that the vast majority (> 99%) of gold was dissolved in the solution from the WPCBs under the optimized leaching conditions. Adsorption tests were conducted on leach liquor solutions resulting from the iodine-iodide leaching using activated carbon. Nearly 98% of gold was adsorbed from the liquor solution onto the carbon under the condition optimized in this study. The results obtained revealed that gold can be successfully recovered from this secondary resources, where the percent recovery amounts to nearly 97% for gold.
Study of Merrill-Crowe processing. Part I: Solubility of zinc in alkaline cyanide solution
Abstract A comprehensive study of zinc solubility was carried out in de-aerated alkaline cyanide solutions. Parameters investigated were: dissolved oxygen, cyanide and lead nitrate concentrations and pH. Zinc solubility increases significantly with increased dissolved oxygen and cyanide concentrations. Eh-pH diagrams have been developed and used to predict regions of stability of zinc hydroxide, which may inhibit gold precipitation. The interaction between cyanide and hydroxyl ion activities to prevent the formation of zinc hydroxide is presented. With lead nitrate additions, maximum solubility of zinc occurs in the range of 10–15 mg/l lead nitrate. SEM photomicrographs of zinc particles in the presence of lead nitrate are presented.
Thermodynamics on the Carbochlorination of Titanium-bearing Ores
The equilibrium compositions of the multi-component, multi-phase and multi-reaction system of carbochlorination of titanium-bearing ores are calculated with HSC, a computational chemistry software. The thermodynamic equilibrium calculation of the reaction system shows that a complete conversion of titanium-bearing ores is feasible at a temperature near 200oC. At temperatures ranging from 800 to 1600oC, the products of the reaction system are all in gaseous phase. Thermodynamic analysis accords with the industrial practice. The simulated results provide reasonable scientific basis for improving suitable technological conditions of the carbochlorination reduction.