Column leaching of a manganese dioxide ore: a study by using fractional factorial design

Abstract

Reductive acid leaching of a manganese dioxide ore has been carried out in a fixed bed column in order to monitor and evaluate the effect of some process parameters on the manganese, iron and calcium extraction yields: although manganese is the metal of interest, iron and calcium were selected as representative of the most significant contaminants of the leach liquor. A two-level fractional factorial design was planned to study the effect of five process factors: temperature, reagent concentration, ore particle size, solid/liquid ratio and flow rate of leaching solution were taken in consideration in the experimental tests. The main effects and the interaction among the factors investigated were obtained by ANOVA, carried out for each selected leaching time, taking into consideration manganese, iron and calcium extraction yields as response of the process. This analysis permitted to establish temperature and reagent concentration exerting the most important positive effect on the manganese extraction yield: 93% of manganese dissolution was obtained after 4 h of leaching in the following experimental conditions: temperature 70°C, S/L ratio 1/2, specific flow rate 1223 L/m 2 h, +50% of reagent excess (H 2SO 4 and glucose) and 208–252 μm as ore size fraction. Each statistically significant main and interaction effects, evaluated in the selected leaching time, were correlated by empirical models in order to build a general model to perform simulation studies valid in the investigated range of experimental conditions but helpful for further modelling studies. Besides these experimental and simulation studies, the potential application of column leaching conditions in the extraction of manganiferous ores has been shown, although further work should be carried out in order to investigate a much more wide range of process conditions.