Reverse magnesite flotation

Abstract

The present investigation deals with the production, at bench scale, of a high purity magnesite concentrate by means of reverse cationic flotation as an alternative to the direct anionic flotation currently employed in a concentrator in Brazil. The specification of the presently produced concentrate, in terms of maximum SiO 2 content, is 0.30% (calcined basis) and the weight recovery of the circuit is approximately 84%. The aim of this study was to produce concentrates with SiO 2 content ≤ 0.20% (calcined basis) and weight recovery ≥ 84%. A two level factorial design was employed in the first stage to optimise the variables that affect the behaviour of the system. In the second stage, the best conditions defined in the first stage were utilised in a locked cycle test, with simulation of circulating load, to predict the stability of the circuit in a continuous process. The main variables investigated were: percent solids and pH of the pulp, collector (ether amine) dosage, depressant (corn starch) dosage and flotation residence time. The aim of the study was achieved and a concentrate with 0.17% SiO 2, at a weight recovery level of 92.17%, was produced in the tests with simulation of circulating load in a rougher - cleaner - recleaner circuit. Lower SiO 2 contents could be reached with a reduction in weight recovery.