Refractory gold ores and concentrates part 1: mineralogical and physico-chemical characteristics

Abstract

A comprehensive mineralogical and physico-chemical examination of two refractory gold ores and concentrates from the Ghanaian gold province was conducted to gain a better understanding of the differences in performance of gold cyanidation. Both ore were mainly silicates, carbonates, oxide, phosphate and sulphides. Flotation of the ground ores produced concentrates with noticeable differences. Whilst both mainly contained sulphides and silicates, apatite was present in one flotation concentrate and dolomite in the other. Biooxidation of the apatite-bearing concentrate produced jarosite-bearing bio-oxidised product. Bio-oxidation of the dolomite-bearing concentrate yielded a jarosite-free bio-oxidised product with lower bassanite content but higher gypsum, graphitic carbon, and pregrobbing effect compared with the jarosite-bearing bio-oxidised product. The jarosite minerals appeared to aid gangue mineral agglomeration and also encapsulated auriferous minerals which attenuated the bio-oxidation process and reduced gold extraction.

Specific Refractory Gold Flotation and Bio-Oxidation Products: Research Overview

“…For instance, upon extracting the EDTA extractable iron species which were insoluble in water only, other soluble mineral phases (e.g., gypsum) were dissolved. Photomicrographs showing complex association between jarosite and gypsum confirmed the EDTA results [20]. Figure 3 shows a schematic diagram of the influential role of jarosite and gypsum following bio-oxidation.…”

“…In our previous papers, the ore mineralogical and physico-chemical characteristics, gold mineralisation and deportment in host gangue minerals, effect of selected process variables on the kinetics and mechanism of alkaline cyanide leaching and temporal rheological behaviour, and refractory attenuation capability of mechano-chemical activation technique have been investigated, attempting to address critical questions and aspects of poor process performance [17][18][19][20][21][22][23]. This paper, therefore, aims at 1.…”

“…Breakdown in the mineral structures after bio-oxidation led tõ 1.4 times increase in the gold grade of both JF and JC. Surface chemistry investigations by EDTA extraction showed that jarosite minerals coated the surfaces of both soluble and insoluble minerals [20]. For instance, upon extracting the EDTA extractable iron species which were insoluble in water only, other soluble mineral phases (e.g., gypsum) were dissolved.…”

Characterisation of Biooxidation Feed and Products for Improved Understanding of Biooxidation and Gold Extraction Performance

“…To quantify the minerals, Rietweld quantitative analysis was performed on the XRD patterns using commercial package, SIROQUANT TM V3 from Sietronics Pty Ltd. OMS and SEM sample blocks of diameter 30 mm were prepared with EpoFix resin and hardener, and grinding/polishing was done using TegraPol and TegraForce units. The SEM samples were further coated with graphite and mounted onto double side sticky tape [16][17][18]. SEM analysis was carried out using Camscan Model CS44FE scanning electron microscope at an acceleration voltage of 20 kV and 30 kV, unless otherwise stated.…”

“…This above led to increased reagent consumption during cyanidation, and partly accounted for the high post-CIL solid residues. Other causes of high gold in tailings may be attributed to the formation of jarosite [17][18]27] that coats sulphides, and results in incomplete oxidation, and hence unliberated gold. Coatings on the gold surface as seen in Figure 10 from related investigations [18] led to decreased access of the coated gold particles to lixiviants during the cyanidation process, resulting in high leach residues.…”