MSc Project title Techno-Economic comparison of three process routes in order to refine zinc sulphide ore at Gamsberg
(Duration: 2013 to 2014)
There is an abundant availability of sphalerite ore (160 million tons at 7.40 % Zn) at Gamsberg, in South Africa. This is South Africa’s greatest unexploited base metal resource. Sphalerite is currently processed by crushing-milling-flotation, followed by the roast-leach-electrowinning (RLE) process. This route produces SO2 and cannot treat ores of low grade or higher complexity. Due to great pressure exerted on companies to be environmentally friendly and ore reserves not only diminishing but being of lower grade and higher complexity, alternative processes are being sought in order to circumvent the RLE route.
Black Mountain (Pty) Ltd intends to establish an open pit zinc mine at Gamsberg. The main aim of the study is to do a techno-economical comparison of three process routes for refining this ore. These routes include producing concentrates through the conventional method and shipping them for refining, producing concentrates and refining them locally and lastly heap leaching the ore refining locally (HydroZincTM process). The HydroZincTM process recovers zinc through heap leaching, neutralization, solvent extraction and electrowinning. Zinc heap leaching has not yet been commercialised due to the absence of solvent extraction reagents which can selectively extract zinc from a low tenor acidic pregnant leach solution without incorporating the neutralization stage. Although processes that include heap leaching are cost-effective, the additional neutralization step has a major impact on the economics of the HydroZincTM process.
These three routes are compared based on the amount of ore mined being the same. A process model which uses data from lab test work and literature has been developed using Microsoft Excel in order to produce 150 000 tpa of special high grade (SHG) zinc (>99.995% Zn) with the HydroZincTMprocess. As a result, the other routes produce more zinc due to higher recoveries.
Dlamini, Z., Petersen, J. and Franzidis, J.-P. 2014. Evaluation of the HydroZincTM process to refine zinc sulphide ore at Gamsberg. Paper presented at the 32nd annual SAIMM Mineral Processing Conference, 7-8 August, Cape Town.