Dissolution and rheological behaviour of hematite and quartz particles in aqueous media at pH 1

In this study we investigate isothermal, atmospheric acid dissolution behaviour of quartz and hematite minerals which constitute two of the predominant host gangue phases of typical low grade limonitic laterite ores. Batch dissolution tests were carried out on 57 wt.% solid dispersions for 4 h at pH 1 and 25 and 70 °C to establish the influential role of oxide mineralogy/chemistry on rheology and leaching behaviour. The results show that the two minerals displayed a weakly temperature and time-independent, non-Newtonian rheological behaviour with low shear yield stresses (<4 Pa) and viscosities (9-17 mPa s). Hematite dissolution rate was significantly higher compared with that of quartz under similar conditions. Quartz dissolution mechanism was substantially volume diffusion controlled at lower agitation rate (600 rpm) whilst for hematite it was both volume diffusion and chemical reaction controlled. These mechanisms reflected activation energies of 17.7 ± 0.9 and 28.5 ± 1.4 kJ/mol, respectively, for quartz and hematite. At 800 and 1000 rpm, dissolution of both minerals was chemical reaction-controlled with similar activation energies (32.6 ± 1.7 and 32.2 ± 1.6 kJ/mol). The findings underscore the need for higher agitation rates and elevated temperatures, to overcome both volume diffusion and chemical reaction limitations for enhanced acid leaching of these two fairly refractory oxides studied herein.