Carbon-in-Leach Gold Recovery from Fungi-treated Carbonaceous Ore: Effect of Entrained Biomass on Activity of Activated Carbon

Grace Ofori-Sarpong,Charles Ebenezer Abbey,Nelson Akuoko Sarpong,Richard Kwasi Amankwah

doi:10.11648/j.eas.20200504.11

Abstract

The ability of the fungus, Phanerochaete chrysosporium to reduce preg-robbing of carbonaceous matter (CM) in gold ores has been confirmed by many researchers, and studies are ongoing to minimize the effect of entrained biomass on subsequent gold leaching and adsorption processes. This paper presents a study on gold extraction from surrogate carbonaceous gold ore (CGO), and fungal-treated CGO to ascertain the influence of entrained biomass on the downstream carbon-in-leach (CIL) process. The surrogate CGO was prepared by adding 3% anthracite-grade CM to free-milling gold ore (FGO). The main minerals in the FGO were quartz, feldspar and sericite, with 8.4 g/t gold, 0.18% sulphide sulphur and 0.06% organic carbon. Aside biotreatment of the CGO with cell-free liquor of P. chrysosporium, anthracite and activated carbon (AC) were also contacted with P. chrysosporium to confirm the direct effect of biomass on the CMs’ ability to preg-rob aurocyanide. Preg-robbing effect of the as-received anthracite and AC were 95% and 80% respectively, and these reduced to 81% and 13% respectively. Water-washing, acid-washing and alkaline-washing of the treated CMs returned respective preg-robbing effects of 88%, 92% and 85% for AC and 32%, 38% and 28% for anthracite. Scanning electron microscopy and Raman spectroscopy of anthracite revealed a decrease in the degree of orderliness in the structure required for gold adsorption. The FGO and the prepared CGO gave cyanidation gold recoveries of 94.5% and 54.8% respectively. Following cell-free treatment of the CGO, direct cyanidation recorded 88.3% solution recovery, which was increased to 91.3% in CIL. The overall recovery onto activated carbon in CIL was 81%, which improved to 82% and 85% respectively after washing the fungal-treated CGO with water and NaOH. The results here affirm that thorough washing of fungal-treated CGO assists in removing some entrained biomass. However, the results also call for additional studies on purification of the cell-free liquor to further minimize the biomass effect, and sustainability of the enzyme activity during pretreatment to enhance the overall gold recovery.

Highlights

Extraction of gold from refractory ores poses serious challenges to mining companies, and raises scientific and engineering concerns regarding innovations in processing techniques
Fungal action led to changes in anthracite, and scanning electron microscopy (SEM) showed a disturbed surface while Raman spectra indicated an increase in amorphous nature
As-received anthracite and activated carbon preg-robbed 95% and 80% of aurocyanide respectively, and these decreased to 81% and 13% after fungal treatment

Summary

Introduction

Extraction of gold from refractory ores poses serious challenges to mining companies, and raises scientific and engineering concerns regarding innovations in processing techniques. In a typical gold processing plant treating refractory ores that contain sulphides, the main biotic pretreatment option is the biooxidation process where ironand sulphur- oxidising bacteria are used to liberate gold from the sulphides [1, 2]. Grace Ofori-Sarpong et al.: Carbon-in-Leach Gold Recovery from Fungi-treated Carbonaceous Ore: Effect of Entrained Biomass on Activity of Activated Carbon which it is conditioned appropriately and fed into the Carbon-In-Leach (CIL) circuit, where leaching of gold and adsorption of gold ions onto activated carbon (AC) are done simultaneously. There are challenges with recovery when the ore contains carbonaceous matter (CM), which being organic, is generally not degraded by the bacteria which are autolithotrophs [6,7,8]. The CM enters the CIL circuit and preg-robs dissolved gold, leading to decreased recovery and high tailings value [6, 9,10,11,12,13,14]

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Conclusion