A Critical Evaluation of Optimizing the Potential for Ore Recovery from Mine Waste Using Multi-Elemental, Geochemical and Petrographic Analysis (MEGPA)

Abstract

The growing world demand for metals necessitates the economic extraction of metals from ores of lesser grades and scheduled waste with potential for metal recovery. In which case, efficient skilled-beneficiation is required to achieve such demand. This research paper examines the potential of ore recovery from magmatic Ni-Cu-PGE waste rock in an open pit mine operation. The waste material contains a marginal cut-off grade between the ore and what has been scheduled to be produced as waste throughout its life of mine (LOM). The waste material has the potential for metal recovery to extend the LOM. The main aim was to investigate the appropriateness of the potential for metal recovery using the already generated waste as a baseline model for subsequent waste production. To achieve this aim, the primary objective was to use Multi-elemental, Geochemical and Petrographic Analysis (MEGPA) on carefully selected waste rock samples. While the specific objectives were to examine the liberation of metals and establish optimal cut-off grade based on suitable size fractions for ore recovery. Multi-elemental, geochemical and Petrographic Analysis were carried out on selected size fractions using various instruments such as Scanning Electron Microscope Energy Disperse X-ray (SEM-EDX), X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF), reflected and transmitted microscopes. Categorization of results shown the predominant bulk mineral abundance to be tremolite, a member of the amphibole group of silicate minerals with composition Ca2Si8O22·(OH)2. Moreover, the result revealed that the economic Ni and Cu sulphides are hosted in pentlandite and chalcopyrite within the waste samples. Liberation of mineral and recovery of metal are in the finer fractions size below 1.5 mm, and that optimum metal recovery is at ≤1 mm. It was concluded from the study that, there is potential for metal recovery from mines waste in finer fractions below 1.5 mm without posing significant metalliferous acid mine drainage (AMD) risk to the mining environment. It is recommended that further study about the influence on the metallurgical processing of the waste at the selected optimum fractions size, and energy requirement for screening the sample is carried out. Since the PSD (particle size distribution) is critical to both the physical separation processes of the waste and the prediction of metalliferous AMD risk, other methods like advanced UAV 3D photogrammetry and digital image processing method could be used to test for both underestimation and overestimation of PSD. This is important as the amount of mineral liberation, metal recovery and sulphur generation are PSD dependent.