Kinetics of gangue aluminosilicate clay (e.g. muscovite) and oxide (e.g. hematite, quartz) minerals play a pivotal role in determining the processability and recovery of valuable minerals (e.g. copper, gold). During mix minerals leaching at low pH (~1) and elevated temperature (~70 °C), the formation of a highly viscous gel ascribed to attractive particle interactions, facilitated by polycondensation of Si(IV) and Al(III) species, may occur. Adhoc methods, such as water dilution and temperature reduction, for alleviating gelation may be implemented; however they adversely impact on valuable mineral recovery rate and yield. Whilst the clay minerals component is known to characteristically consume most of the acid in the leaching process, the mechanism and kinetics are as yet not well established. Synergistic or antagonistic effects invariably prevail in the ore leaching process, making it difficult to deconvolute the exact contributions of the individual minerals. Hence, fundamental studies involving a single, gangue model mineral component (muscovite) are warranted.
The kinetic behaviour of muscovite (K_1.82, Na_0.13)(Al_3.64, Fe_0.29, Mg_0.16)[(Al_1.86, Si_6.14)O₂₀](OH)₄) dispersions as a function of pH (1 vs. 7) and temperature (25 °C vs. 70 °C) in a batch system was investigated. The leach process follows, sequentially, ephemeral and perennial kinetics regimes, based upon evolution of major constituents (Al(III), Si(IV), K⁺ and Fe(II/III)). Incongruent leaching behaviour was displayed by the framework species Al(III) and Si(IV), which progresses as a function of time. Impacts of temperature and pH on the leach kinetics and rates are discussed in terms of the chemistry underpinning the leach process.