Browsing by Author "Annandale, Gideon Johannes"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    An evaluation of liberation models for the prediction of diagnostic leaching results
    (Stellenbosch : Stellenbosch University, 1995) Annandale, Gideon Johannes; Lorenzen, L; van Deventer, J. S. J.; Stellenbosch University. Faculty of Engineering. Department of Process Engineering.
    ENGLISH ABSTRACT: The interrelationship between mineral liberation and leaching behaviour of a gold ore is ill defined and lacks understanding mainly due to the complexity of the individually processes, i.e. leaching and mineral liberation. An understanding of this relationship could result in lower costs, since an increase in the efficiency of gold dissolution and a decrease in costs related to the crushing and grinding operations, could be expected. Diagnostic leaching was used as the analytical method to investigate the mineralogy (gold deportment) of various gold-bearing ores designating from different goldfields in South Africa. A thorough literature survey was also conducted to determine the availability of theoretical models which could describe the relationship between liberation and leaching behaviour. From the experimental results obtained, it was concluded that the leachability of an ore is not only dependent on the degree of liberation of that ore when comminuted, but that it is also very much dependent on the degree of exposure of gold grains throughout the whole of the ore. It was found that all the theoretical liberation and exposure models underestimated the amount of leachable gold in each particle size fraction, mainly due to the neglecting of exposed gold grains situated in minor cracks and fractures. It became evident in this research, that in order to model the leachability of gold fundamentally, the data obtained from diagnostic leaching tests alone are insufficient. Data concerning the amounts of gold bearing minerals, present in the ores as well as SEM data of the gold grains, are needed together with diagnostic leaching results. However, an empirical model was developed that predicts the degree of liberation (leachability) of an ore milled to 70% -75μm fairly accurately as a first attempt to model this highly complex process. The degree of liberation (leachability) was found to be a function of the particle size and the gold deportment of the unmilled ore. It was decided to extend the King liberation model and the exposure model developed by Hsih and co-workers empirically to provide for the fraction of gold not directly related to liberation. Both the models showed good agreements with the experimental results. Neural network analysis of the diagnostic leaching results were done with partial success, but unfortunately more data is still needed to assist in the development of an accurate leaching or liberation model.