Application of column flotation technology for reduction of silica in zinc concentrate at Rajpura -Dariba mines, India

Abstract

A 3000 t1d lead-zinc ore beneficiation plant was comm-issioned in 1983 to produce lead and zinc concentrates suitable for Hindustan zinc Limited 's smelters. The problems encountered in individual concentrates are mainly high graphite and lower lead grade in lead concentrate and comparatively high silica in zinc concentrate. Due to inherent nature of ore quality (graphite mica schist) the incidence of high graphite,lower grade of lead concentrate can be explained and taken care by use of effective graphite depressant or gravity techniques. It is observed during extensive laboratory scale tests by in-house R&D of HZL and by National laboratories in India and plant operations for decade, that type of ore quality (i.e. calc- silicate or graphite micaschist) does not affect zinc flotation and invariably the silica in zinc concentrate is reported between 5 to 8%, where as the requirement of HZL's smelters is 2.5% max. In this paper an account of extensive testing done at Central Research and Development laboratory of HZL (India), with operating plant at Rajpura-Dariba Mines is elaborated. It is observed that due to interlocking of gangue with sphalerite up to 2 micron size, fine grinding requirement for liberation of sphalerite and flotation of some gangue due to smearing of graphite on gangue during conintunition in ball mill, it is very difficult to effectively use graphite/gangue depressant for cont-rolling silica to a level of 2.5 % from 5-6%, without sacrifice of zinc recovery After careful and detailed study of zinc concentrate mineralogy and metallurgical results, the route of column flotation for zinc cleaning in place of conventional mech-anical cells was tried. Preliminary experiments were conducted on 3" diameter Diester make Flotaire column set-ulp at CRDL. The study indicated that flotation by use of column is effective in controlling free silica in conc-entrate by froth washing. The study was supplemented with detailed experimentation aimed at generating basic design data for pilot column for Rajpura Dariba concentrator.The data obtained was simulated on simulator developedby , M/s Engineers India limited and reconciled data was processed using computer software developed by EIL. The exercise indicated that by column flotation used in cleaning operations, the silica in zinc concentrate is reduced to a level of 4 %, the recoveries in cleaning operation remained nearly same.