For gold-antimony coexisting ores, direct application of pyrometallurgical processes leads to the dispersion and loss of gold in antimony oxide, antimony slag, and furnace slag, causing severe environmental pollution. Cyanide leaching is also ineffective due to the consumption of oxygen and cyanide by stibnite, a common antimony mineral. So, how can gold and antimony be comprehensively recovered from gold-antimony coexisting ores? Let's explore this case.
The large gold-antimony coexisting ore deposit is characterized by a ternary mineral assemblage of native gold, stibnite, and quartz. It represents a typical Sb-Au-Si system. The primary antimony mineral is stibnite, with trace amounts of orpiment. The main gold mineral is native gold, with minor amounts of antimony-bearing native gold. Quartz is the dominant gangue mineral, accompanied by small quantities of calcite, and traces of sericite, realgar, gypsum, and other minerals. Other trace metal sulfides include pyrite, arsenopyrite, cinnabar, sphalerite, chalcopyrite, and covellite.
Through tests on representative ore samples, two key characteristics of the ore were identified:
The stibnite in the ore is prone to oxidation during grinding.
There is a significant difference in size between gold and antimony minerals, with coarse-grained stibnite (0.1-0.3mm) and finer-grained native gold closely associated.
After unsatisfactory results from a simple gravity separation and flotation process, the beneficiation strategy was adjusted to obtain a mixed gold-antimony concentrate.
Taking into account the characteristics of the minerals and the test results, the final mineral processing flow was determined as a staged grinding, staged separation by gravity, and flotation process.
Obtaining a mixed gold-antimony concentrate and addressing the issues of stibnite mud formation by producing a middling product with an Au grade of around 3.50 g/t and Sb content of about 4.00%. The middling product is treated using an alkali pre-treatment cyanide leaching process to extract gold, achieving a gold leaching rate of 61.50% and enhancing the overall resource utilization and economic benefits of the metallurgical plant.
The staged grinding and separation process specifically addresses the challenges posed by stibnite's tendency to form mud during over-grinding and its susceptibility to oxidation during beneficiation. This process provides fresh mineral surfaces multiple times, effectively reducing the gold and antimony grades in the tailings while improving the recovery rates.
The mixed gold-antimony concentrate obtained from the beneficiation process has a particle size suitable for wet leaching, enabling effective separation of Au and Sb. As stibnite has a coarse particle size, it can be recovered through handpicking or gravity separation after coarse grinding. However, the obtained concentrate still requires additional grinding before wet leaching, introducing complexity into the metallurgical process.
The adopted process is feasible for large-scale mining operations, and it demonstrates good economic benefits. For large-scale joint beneficiation enterprises, multiple grinding mills are usually employed in the ore grinding stage. In this case, with the potential value of antimony accounting for two-thirds of the total resource value, the staged grinding and separation process achieves higher antimony beneficiation indicators, resulting in better economic returns.
The principle process for the comprehensive recovery of the mixed gold-antimony concentrate is as follows: Gold-antimony mixed concentrate → Wet separation of gold and antimony → Antimony leaching solution → Synthesis of sodium antimonate, etc. → Antimony leaching residue → Roasting → Cyanide gold extraction.
Wet Separation of Gold and Antimony: Several commonly used methods, such as sodium sulfide alkaline leaching and acid leaching, can be employed. Through systematic condition tests and comparative experiments with leaching agents, a new leaching agent called MS was selected.
Synthesis of Sodium Antimonate: After wet separation of gold and antimony, the antimony leaching solution undergoes impurity removal and oxidation to obtain a solution. Under specific conditions, the solution is hydrolyzed, and then NaOH is added to synthesize sodium antimonate.
Gold Extraction from Antimony Leaching Residue: After wet separation of Au and Sb, gold and sulfur are enriched in the antimony leaching residue. With a high sulfur content of 44%, direct sulfur roasting achieves a sulfur volatilization rate of 99%. The gold leaching rate reaches 97%, and the gold-bearing solution is extracted using conventional processes such as carbon adsorption, electrowinning, and smelting.
This case study involves a typical ternary system of native gold, stibnite, and quartz in gold-antimony coexisting ores. Challenges arise due to stibnite's easy dissociation, mud formation, and oxidation, coupled with significant differences in the particle sizes of gold and antimony. By adopting a beneficiation approach that treats mixed gold-antimony concentrate as the final product, the design is streamlined. The use of a staged grinding and separation by gravity and flotation process overcomes technical challenges and achieves satisfactory beneficiation results.
