Pulp mineralogy and chemistry, leaching and rheological behaviour relationships of refractory gold ore dispersions

Abstract

Abstract In this paper, the influential role of ore mineralogy, pulp interfacial chemistry and alkali type (cautic soda and quicklime) in temporal rheological behaviour of two refractory flotation concentrates and their bio-oxidised mineral dispersions have been investigated. Caustic soda modified pulps showed different particle zeta potentials from the quicklime modified pulps over pH range 2–12. At high pH (>10), the two flotation concentrates displayed positive zeta potentials, regardless of the pH modifier. On the other hand, quicklime pH modified bio-oxidised pulp particles were electropositive at high pH whilst the caustic soda modified pulps showed deprotonated particles. In addition, the predominant chemical species leached from the flotation concentrates and their bio-oxidised products at pH 10.5 were Ca and S, followed by incongruent leaching of Cu, K, As, Ni, Zn, Fe, Al and Au. This encouraged lower zeta potential and reduced the particle electrostatic repulsions within the ore dispersion. Significant back precipitation of the Ca ions during leaching was mainly observed when caustic soda was deployed in comparison with the quicklime modified pulp. Mineralogically-driven, rapid back precipitation of Ca, As, Cu and S was, however, noticeable in only the jarosite-bearing bio-oxidised product when quicklime was employed. Generally, it was evident that the alkaline cyanide leaching contact time, mineralogy and alkali-type markedly influenced the pulp chemistry and particle interactions. Non-Newtonian, plastic, thixotropic rheological behaviour was displayed by the pulps at pH 10.5 over a 480\u2009min leaching time. The flotation concentrate dispersions showed shear thickening, time-invariant behaviour, however, the bio-oxidised pulps exhibited pH modifier, leaching time, shear and ore mineralogy dependent rheological behaviour. The results suggest emergence of van der Waals and non-DLVO attractive forces such as adsorbed Ca(II) ion-particle bridging, surface nucleation and cementation for the stronger rheology of quicklime modified pulps, in contrast with caustic soda modified pulps.