Significance of Acid Washing after Biooxidation of Sulfides in Sequential Biotreatment of Double Refractory Gold Ore from the Syama Mine, Mali

Cindy Cindy,Diego M Mendoza,Keiko Sasaki,Ryotaro Sakai,Kojo T Konadu

doi:10.3390/min11121316

Abstract

Environmentally friendly pretreatment of double refractory gold ores (DRGO) to improve gold recovery without emitting pollutant gas is challenging. Sequential biotreatment, including iron-oxidizing microorganisms to decompose sulfides, followed by the enzymatic decomposition of carbonaceous matter, was recently developed. The effect of acid washing by 1 M HCl for 24 h between two bioprocesses was evaluated using a real double refractory gold ore from the Syama mines, Mali, which includes 24 g/t of Au and 5.27 wt% of carbon with a relatively higher graphitic degree. The addition of the acid washing process significantly improved gold recovery by cyanidation to yield to 84.9 ± 0.7% from 64.4 ± 9.2% (n = 2). The positive effects of acid washing can be explained by chemical alteration of carbonaceous matter to facilitate the accessibility for lignin peroxidase (LiP) and manganese peroxidase (MnP) in cell-free spent medium (CFSM), although the agglomeration was enhanced by an acid attack to structural Fe(III) in clay minerals. Sequential treatment of DRGO basically consists of the oxidative dissolution of sulfides and the degradation of carbonaceous matter prior to the extraction of gold; however, the details should be modified depending on the elemental and mineralogical compositions and the graphitic degree of carbonaceous matter.

Highlights

The sulfide minerals, pyrite and arsenopyrite, tend to occur in ores that have a significant amount of gold enclosed in them compared to other minerals and the gold confined in sulfides
This was confirmed by X-ray fluorescence (XRF) (Table 1), where the relative intensities of C, O, Mg, and Ca to Si decreased
Acid washing after the biooxidation of sulfides before enzymatic reaction to degrade carbonaceous matter was evaluated in a sequential pretreatment using a real double refractory gold ores (DRGO) from the Syama mine, Mali, which includes 5.27 wt% of carbon with a relatively higher graphitic degree

Summary

Introduction

Double refractory gold ores are distributed all over the world, for example, the Prestea and Bogoso goldfield in Ghana, the Syama mine in Mali, the Sao Bento Mineracao in Brazil, the Carlin Gold Mine of Nevada, the California motherlode, and the Pogo mine of Alaska in the USA, the Kerr Addison Mines in Canada, the Bakyrchik mine in Kazakhstan, the Natalkinsk in Russia, and the Ratatotok district, North Sulawesi in Indonesia [1,2,3,4,5,6], which include relatively high contents of gold They are not commercially developed to recover gold due to the presence of very fine carbonaceous matter particles (5–8 wt%) that can adsorb Au(CN)2 − during cyanidation, causing a significant gold recovery loss. Carbonaceous matter is not well separated from sulfide minerals, so carbonaceous matter

Methods

Results

Conclusion