Flowsheet development for selective Cu-Pb-Zn recovery at Rosh Pinah concentrator

Abstract

Rosh Pinah Zinc Corporation (Pty) Ltd (RPZC) is operating an underground mine and lead–zinc concentrator in southern Namibia, the major valuable minerals being chalcopyrite, galena and sphalerite. Consistent ore characteristics over many years have demanded only minor process changes; this is set to change with ore being sourced from two new ore zones, namely the WF3 Zone 2 characterized by low Cu grades (0.09% Cu, 2.5% Pb, 6–7% Zn), and WF3 Zone 1 which is characterized by high Cu and low Pb grades (0.48% Cu, 0.31% Pb, 10–12% Zn). A laboratory flotation test campaign was therefore undertaken to (1) establish whether the Zone 2 (low-Cu) ore could be processed through the current plant and identify any flowsheet changes that would need to be made, and (2) demonstrate the conditions required to produce a separate concentrate from the Zone 1 (high-Cu) ore.The results of the low-Cu ore indicated that it could be processed via the current RPZ flowsheet and operating conditions, but that Pb rougher and Zn rougher concentrate re-grinds would be required. This would enable the Pb circuit to produce a grade of 65% Pb at 81% recovery, and the Zn circuit, a grade of 57% Zn at 97% recovery. Mineralogical analysis of the final Pb and Zn products confirmed the need for the re-grinds.For the high-Cu ore, the challenge was to produce three distinct Cu, Pb, and Zn concentrates. Whilst the initial approach of exploiting relative flotation kinetics using the current RPZC operating conditions did not achieve the desired Cu-Pb selectivity, a feasible flowsheet was developed based on a modified Black Mountain (Cu-Pb-Zn concentrator) processing route for the Cu circuit, and the existing RPZC route for subsequent Pb and Zn recovery. However, dilution of the Cu product by carbon and gangue minerals, and the Pb product showing high Zn and Fe levels, required further depressant and concentrate re-grind optimization.This paper details the development philosophy and operational benefits of the proposed flowsheets, including improved efficiency resulting from the cleaners operating at reduced circulating loads. Further work is recommended on the WF3 Zone 1, high Cu feed to optimize the operating conditions and define the process design criteria more closely.