Abstract
M.Tech. (Extraction Metallurgy)
Copper Pressure Leach residue (CPL) contain unleached copper and at times significant amounts of sulphur. The issue of elemental sulphur formation may be handled using additives or surfactants, which act as dispersants of molten sulphur. This dispersion allows the transfer of dissolved oxygen (or ferric as an oxidant) to the sulphide surface where the reaction can occur. Test work was carried out in an autoclave on CPL residues at different conditions, seeking to identify the conditions which lead to the formation of elemental sulphur. An operating window was to be established that would significantly reduce the chances of formation of elemental sulphur balls. It was found that the use of lignosulphonate as a dispersant may mitigate the effects of sulphur ball formation during process excursions. While investigating sulphur ball formation, copper extraction efficiency was also tracked. This aided in establishing an ideal operating window. The pressure leaching behaviour of copper leach residue was studied under different operating conditions in a temperature range of between 120oC to 155oC to map the formation of sulphur balls. Varying acid dosages from low acid (5 g/L) to intermediate acid (30 g/L) to high acid (40 g/L) were investigated. The effect of varying oxygen partial pressure in the autoclave between 4 and to 6 bar was also investigated. The production of sulphur balls was observed under the following conditions - high acid and low oxygen partial pressure test work, high acid and low temperature test work and low temperature test work. Experiments where sulphur balls were found to be present, were repeated using surfactants. In this study, lignosulphonates were used and were found to be effective dispersing agents. A minimum dosage of 1 g/L lignosulphonate was found to mitigate the formation of elemental sulphur as its introduction managed to reduce the tendency to form elemental sulphur in the autoclave. The effect of lignosulphonate addition on copper recoveries saw a good association on test work number CPL_12 and test work number CPL_12B, Non-lignosulphonate testwork produced 85% copper recovery and the lignosulphonate testwork on CPL_12 with 2 g/L showed an increase to 94% and CPL_12B with 1 g/L showing a copper recovery of 97%. The high acid test work showed an increase in...