Non-roasting process for recovering gold from refractory arsenic-bearing ores and concentrates by bacterial leaching

At present, foreign countries by underground leaching and heap leaching from lean ore, ore and waste rock outside the balance sheet beneficiation plant tailings and mining enterprises in the leaching of copper and uranium, has been successfully using bacterial leaching method.
Now vigorously how processing non-ferrous metal and precious metal concentrate by leaching bacteria trough, from which to recover valuable components or impurities excluded.
Refractory Study bioleaching arsenic-containing concentrate showed that: in the best conditions of pH, temperature of the slurry, the particle size of the original concentrate, as well as oxygen and carbon dioxide feed concentration, sulfide leaching rate can be increased a hundredfold.
The trough bacterial leaching method is different from the underground leaching method and the heap leaching method, and has many unique features. Leaching is carried out in large tanks or Pachuca tanks. Therefore, bacteria are oxidized much faster in these devices than in subsurface leaching and heap leaching. Leaching is carried out in concentrated pulp, so the bacterial leaching method is suitable for treating concentrates having a much higher sulphide content than ore or waste rock.
Since the trough bacterial leaching method has the above characteristics, its leaching efficiency depends on a variety of special factors. A large amount of different elemental ions are accumulated in the leachate, for example, an arsenic content of up to 8 g/l and an iron content of up to 15 g/l or more. The concentration of these ions, especially trivalent arsenic ions, is too high to inhibit the growth of bacteria; viable wells reduce the activity of bacteria. An effective culture of microorganisms can be obtained by gradually adapting the bacteria to a combination of various physical-chemical and chemical factors that determine the leaching conditions of the particular product. This culture is stable both in the presence of the above elements and in the oxidation of sulfides. Only using this adaptable culture can greatly increase the rate of bacterial leaching.
The results of studying the interaction between microorganisms and mineral particles using an electron microscope and a manometer show that the microorganism (T. thermophilus) can be firmly fixed to the mineral surface after 10 to 15 minutes of contact during the leaching process. Other bacteria present in the slurry phase can only participate indirectly in the leaching process and allow the ferric sulphate to be regenerated.
In addition to conducting theoretical studies on a laboratory scale, several processes have been developed to deal with difficult gold-arsenic concentrates. These gold-arsenic concentrates are characterized by varying amounts of gold, arsenic, carbon, antimony and other elements.
Several processes include direct bacterial leaching, purification of the bacterial solution after leaching, return of the bacterial solution, and cyanidation of the leaching residue. One or two stages of bacterial leaching were carried out in a Pachuca tank with air agitation. The leaching conditions are as follows: solid: liquid = 1:5, concentrate particle size is 90~95%-0.074 mm, pulp temperature is 28-35 °C, pulp pH=2.2-1.7. The used bacterial solution is neutralized by lime milk to pH=2.8~3.2 to regenerate; the concentration of bacteria is usually 106~109/ml.
After leaching for 60~120 hours, the oxidation rate of the arsenopyrite can reach 80~90%. The leaching residue after bacterial leaching is subjected to cyanidation of the elbow, and the gold recovery rate can reach 86 to 91%. However, if the concentrate is cyanated directly without pre-leaching by bacteria, the gold recovery rate is only 10 to 32%.

[next]

The high arsenic-gold concentrate processing process (see Figure 1) consists of two stages of bacterial leaching. After the leaching of the I stage bacteria, the slurry is classified according to the 40 micron size to separate the qualified products suitable for cyanidation. The yield is 25~30% of the original ore. After the leaching of the II stage bacteria, the product is leached. The arsenic content decreased from 9-10% of the original concentrate to 1.3~1.4%. At this time, the recovery rate of arsenic sulfide is 89 to 91%. When the leaching residue is cyanated, the gold recovery rate is 90 to 91%, but the gold-carbon gold-arsenic concentrate which is not leached by the bacteria is very difficult to handle. Gold is symbiotic with poisonous sand in these concentrates. The carbonaceous shale contained in the concentrate has a high adsorption activity for the gold-cyanide complex.
The carbon-containing gold-arsenic concentrate treatment process (see Figure 2) stipulates that carbon shale is pre-separated by flotation, bacterial leaching is carried out on flotation tailings, and cyanidation of bacterial leaching slag is carried out. After 70 hours of bacterial leaching, the arsenic content in the concentrate decreased from 6.6% to 1.0-1.2%, and the arsenic sulfide oxidation rate was 93-95%. When the bacterial leaching residue is adsorbed and cyanated, the gold recovery rate is 92% (for operation); however, when the raw concentrate is cyanated directly without prior leaching of the bacteria, the gold recovery rate is only 5 to 10%. The carbonaceous concentrate obtained by flotation contains 20 g/ton of gold and 1% of arsenic. This concentrate can be reprocessed, for example, by adding it as a charge to other non-ferrous metal concentrates, which can be treated by smelting.

Laboratory studies have been confirmed by bacterial leaching expansion process tests. Expanded process testing includes trough continuous bacterial leaching, regeneration of bacterial solutions and their return to use. The expanded test results show that it is reasonable to carry out a period of bacterial leaching; in the case of containing carbonaceous materials in the concentrate, it is not necessary to pre-separate the carbonaceous material from the concentrate, and it is possible to directly carry out bacterial leaching on the concentrate. .
The preliminary technical-economic calculation proves that before the cyanidation of the sulfide ore, the bacterial leaching method is used to dissociate the fine-grained gold, which not only has good dissociation effect, but also is economically reasonable. In the treatment of arsenic-containing concentrates, the bacterial leaching method can avoid the pollution of the atmosphere by toxic gases containing sulfur and arsenic.
The application of the established bacterial leaching process in industrial production not only enables the development and utilization of many new gold deposits, but also enables companies dealing with gold-arsenic ores and other products to significantly increase the recovery rate of gold.