Influence of fluorite on the isothermal leaching and rheological behaviours of chlorite mineral pulps at low pH

Chlorite clay gangue mineral leaching at low pH may produce viscous slurries, which deleteriously impact on value metal extraction and recovery in metallurgical plant operations. The presence of fluorite as a minor or an accessory mineral phase with chlorite may markedly exacerbate the pulp rheology and reduce the leaching dramatically. In the present work, isothermal leaching and rheological behaviours of chlorite were investigated in the presence of fluorite (chlorite/fluorite mass ratios of 20, 10 and 5 to 1) at pH 1 and 70 °C. Fluorite was found to dramatically enhance the kinetics of chlorite leaching, the mechanism of which was incongruent. The leach dispersion rheology showed a distinctly non-Newtonian behaviour characterized by thixotropy, shear thinning and time and fluorite concentration-dependent shear yield stress. The highest, maximum shear yield stress and apparent viscosities were observed at chlorite/fluorite ratio of 10:1, below and above which weaker gels formed. Solution-state 27Al and 29Si NMR studies indicated that polycondensation reactions involving solution Al(III) six to four fold coordination and a plethora of Si(IV) tetrahedra complexes led to the formation of aluminosilicate gels. The chlorite/fluorite ratio had a striking impact on the formation and development of the strongly viscous gel structures. The findings suggest that the resulting maximum yield stresses (40-200 Pa) and apparent viscosity (10-25 Pa·s) are highly detrimental to plant chlorite clay-fluorite rich, low grade laterite ores' leaching and handling operations.