Low-grade Refractory Ores Research Articles

A sustainable approach for gold recovery from refractory source using novel BIOX-TC system

This study developed a sustainable method for gold extraction from low-grade refractory ore by combining acidic biooxidation and thiocyanate (SCN) leaching (BIOX-TC) in one system to avoid neutralization and minimize the complexity of the process. Among leachant candidates, thiocyanate was proposed as a less toxic reagent for gold leaching. Furthermore, thiocyanate requires ferric iron as an oxidant for gold extraction and ferric iron can be provided by the microorganisms during biooxidation. In the first step, acidic biooxidation was done using a mixture of acidophiles including Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans resulting in 59.6% sulfur oxidation. A preliminary static incubation of Acidithiobacillus thiooxidans also improved biooxidation efficiency achieving higher sulfur oxidation of 87.8%. Following biooxidation, thiocyanate leaching using 0.2 M SCN was performed under three different conditions: (1) in a separate flask with 0.01 M ferric iron addition; (2) in-situ leaching, in the biooxidation flask with the mixed bacterial culture); (3) in-situ leaching in the biooxidation flask with the bacterial culture and with 0.01 M additional ferric iron. It was found that in-situ thiocyanate leaching of the biooxidized ore in the presence of the bacterial culture and without ferric iron addition resulted in the highest gold recovery (86.9%). The biooxidation mechanism and its kinetics have been extensively discussed in this paper.

Comprehensive recovery of gold and base-metal sulfide minerals from a low-grade refractory ore

The comprehensive recovery of small amounts of valuable minerals such as gold and base-metal sulfide minerals from a low-grade refractory ore was investigated. The following treatment strategy was applied to a sample of this ore: gold flotation–gold concentrate leaching–lead and zinc flotation from the gold concentrate leaching residue. Closed-circuit trials of gold flotation yielded a gold concentrate that assayed at 40.23 g·t−1 Au with a recovery of 86.25%. The gold concentrate leaching rate was 98.76%. Two variants of lead-zinc flotation from the residue—preferential flotation of lead and zinc and bulk flotation of lead and zinc—were tested using the middling processing method. Foam from the reflotation was returned to the lead rougher flotation or lead–zinc bulk flotation, whereas middlings from reflotation were discarded. Sulfur concentrate was a byproduct. The combined strategy of flotation, leaching, and flotation is recommended for the treatment of this kind of ore.

Application of Chelating Collectors in the Flotation of Copper Minerals

The application of new chelating reagents on the flotation of copper minerals has been paid much attention in recent years. These collectors have successfully extracted the copper minerals from the low-grade refractory ores, and one of the most important collectors is the alkylhydroxamate-based chelating reagent which shows the excellent flotation performance to the copper oxide minerals. Furthermore, the mixture of various chelating reagents can recover the copper sulfides and oxides simultaneously from the complicated copper ores, which is attributed to the synergy among collectors. Thus we conclude that it is an important flotation method by using chelating collectors in conjunction with other traditional collectors, by which the synergy can break through the limitation of single reagent and enhance the flotation efficiency.

Aeration pretreatment of low grade refractory gold ores

Aeration curing, over a long duration in wetted stockpiles, shows promise as an affordable pretreatment method for oxidizing gold encapsulating sulfide minerals, and possibly organic matter, in low grade refractory ores. Following aeration pretreatment, the ore is reclaimed, neutralized, and cyanide leached by conventional practices. Large tonnages of subeconomic material, including mine stripping waste, may be converted into ore by this new technology. The results presented show that a successful application of this technology will likely require crushing to about −2 cm (−3/4 in.), followed by aeration in a wet stockpile for long periods, up to three years. Natural convection may be inadequate, but forced air ventilation, at modest pressures and power consumption, is affordable.