Investigation of the effect of mineralogy as rate-limiting factors in large particle leaching

Yousef Ghorbani,Megan Becker,Jochen Petersen,Aubrey N Mainza,Jean-Paul Franzidis

doi:10.1016/j.mineng.2013.03.006

Abstract

Although heap leaching is by now well established in the mining industry, the process remains limited by low recoveries with different rate-limiting factors that are not clearly understood. In this study, three large particle size classes (+19/−25, +9.5/−16, +4.75/−5mm) were prepared from a sphalerite ore by two different methods of comminution (HPGR and cone crusher). The particles were then packed into leach reactors that were operated continuously for 11months with well-mixed internal circulation of the leach solution. Characterization of the residue of the leach reactors indicated that there are areas within the ore particles where although sphalerite grains are accessible to the solution, they remain unreacted. X-ray tomography and QEMSCAN® analysis of the selected samples before, during and after leaching, showed increased leaching of sphalerite grains associated with pyrite due to galvanic interactions. Mineral chemistry (Fe, Mn content of sphalerite) and jarosite precipitation were also investigated as factors influencing sphalerite leaching.

Highlights

Heap leaching is well established in the mining industry, the process remains limited by low recoveries, long extraction times, and high operating costs, especially in terms of acid consumption
Characterization of the residue of the leach reactors indicated that there are areas within the ore particles where sphalerite grains are accessible to the solution, they remain unreacted
The most specific focus was on the effect of mineral chemistry and impurity content, mineral association and mineral precipitation on the rate of sphalerite leaching

Summary

Introduction

Heap leaching is well established in the mining industry, the process remains limited by low recoveries (up to 60-70 %), long extraction times (over a 1-2 year period), and high operating costs, especially in terms of acid consumption. Recent experimental evidence suggests that leaching from large particles occurs only at the surface and in subsurface regions, which are accessible from the surface by cracks and pores (Malmström et al, 2008; Sracek et al, 2006; Strömberg and Banwart, 1999; Ghorbani et al, 2011b). This would suggest that leaching behaviour might be closely related to the method by which the ore has been crushed prior to leaching (Rawlings, 1999; Rawlings et al, 2005; Watling, 2006)

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Results

Conclusion