Test results of bacterial leaching with an enlarged continuous device

Moscow Institute of steel and alloys and research work of the Central Research Institute of Geological Survey scientifically proven bacterial leaching method is suitable for processing refractory arsenic concentrate. This concentrate is characterized by the inclusion of very fine-grained precious reconstituted parts in arsenopyrite. Compared with the calcination method, the bacterial leaching method does not have a phenomenon in which the surrounding environment is contaminated by harmful arsenic compounds when recovering precious metals.
Although the bacterial leaching method has many advantages, this method has not been out of the scope of laboratory research for a long time. It was only in 1974 by the Central Institute of Geological Exploration, the Moscow Institute of Steel and Alloys and the All-Su gold, platinum, diamond and tungsten- molybdenum industrial scientific research institute at the Central Geological Exploration Science Research Institute (in Tula City). After the development of the first experimental device in the Soviet Union, a bacterial leaching method for closed-circuit circulation under continuous culture of microorganisms was realized.
The results of the first bacterial leaching process expansion test are listed in this paper. Containing As 8.4%; S 24.1%; Fe 26.6% of gold-arsenic flotation concentrate requires bacterial leaching. The metal minerals in the concentrate have sulfides (about 60%), of which the ratio of pyrite to arsenopyrite is 2:1.5~1. Most of the gold is symbiotic with arsenic pyrite, while a small part is symbiotic with pyrite.
The microorganisms in the enlarged Patricia device are used to decompose the sulfides of arsenic and iron in order to dissociate the fine particles impregnated with gold in the sulfide. The equipment connection diagram of the expansion device is shown in Figure 1.

The processing capacity of the expansion device is 50~60 kg/day and night. Ten Pachuk troughs are arranged in series in two rows. The effective volume of each tank is 150 liters. A Pachuk trough is placed separately to prepare a solution containing bacteria.
The slurry is self-flowing by means of an overflow pipe connecting the Pachuk troughs. The slurry from the blower PMK-2 agitates the slurry at a pressure of 1.0-1.2 atmospheres. The temperature of the Pachuk tank is maintained between 28 and 32 ° C by means of a circulation of hot water around a "heating jacket" around the Pachuk trough.
The test was conducted in three main phases.
I. Prepare and obtain lively bacterial substances.
II. The starting device is placed in a normal operating state and leached under specified conditions.
III. Cyanide the bacterial leach residue.
In order to obtain a lively bacterial substance, a bacterial solution having the same microbial culture "P. ferrooxidans" in the laboratory was used. This microbial culture was cultured and diluted 4 times with Cna-nepuan and several yg-rpeE medium, and the concentrate to be studied must exist. The ratio of solution to medium was 1:2. The hydrogen ion is concentrated by H ₂ S0 ₄ , and the pH is 2.2 to 2.5. [next]
The method for preparing the solution is described below; in the flask or the Pachuk tank of the laboratory, after blowing air into the bacterial solution containing the medium and the concentrate, 10 to 15 liters of the bacterial solution is obtained at a temperature of 30 to 32 °C. The degree of solution preparation was determined based on the degree and rate of oxidation of the ferrous iron in the medium.
The resulting solution was re-diluted with medium. Repeat this operation until the number of bacteria has disappeared.
The solution (30 to 45 liters) is then fed to the expanded Patrice device and the amount of active bacterial material (600 to 800 liters) necessary to start the test is prepared under conditions of continuous culture of the microorganism.
The normal state is to gradually increase the concentration of the slurry along the Pachuk trough (from the first trough to the last trough), so that the very thin pulp (solid: liquid = 1:100) reaches a given concentration (solid: liquid = 1:4~5).
Continuously adding a thick bacterial slurry (solid: liquid = 1:5) from the contact tank to the first Pachuk tank containing the bacterial solution, thereby gradually filling all the Pachuk tank with the bacterial solution and making The pulp becomes thicker.
In this case, the best conditions for the culture activity and the leaching of the concentrate can be guaranteed. Leaching under optimal conditions is achieved after the density of the bacterial culture in all Pachuque tanks reaches 16-20%. The content of arsenic sulfide in the solid at the discharge port of the device is stabilized, which is one of the signs of achieving the prescribed process. When working under defined conditions, measure all of the process's metrics and gather the leaching products needed for the next study.
The work of the device consists of grinding the concentrate to a fineness of 90~93%-0.063 mm, preparing the slurry for the leaching of the first and second stages, purifying the arsenic in the waste bacterial solution, preparing the agent for the lime milk and the medium, and Control the leaching process, etc. The following parameters shall be controlled and tested during operation of the plant: slurry temperature, particle size characteristics of the concentrate, arsenic content in the solid and liquid phases, hydrogen ion concentration, concentration of Fe ²⁺ and Fe ³⁺ in the solution, per 1 ml of solution Bacterial content and bacterial activity (activity).
The kinetics of liquid phase composition changes were carefully studied during the experiment (Figure 2). The pH value of all Pachuk tanks decreases, the Fe3+ content increases, and the increase in arsenic concentration in the solution from one Pachuk tank to the other tank is a unique sign of normal process.

Studies of the bioactivity of cultures have shown that bacteria are least active at the beginning of the leaching process, as well as in contact tanks and circulating solutions. In the middle of the leaching process, when the optimal conditions for the development of the culture are formed, the bacteria are most active, and then fall again due to the accumulation of acid and arsenic at the end of the leaching (see table).

The degree of sulphide oxidation is the main indicator determining the effectiveness of the leaching process. Tests have shown that the major part of the arsenopyrite (>60%) is already oxidized during the preparation phase, ie in the contact tank (Fig. 3).
The stubborn and difficult-to-lead portions of the concentrate are fed to the Pachuk tank before leaching. At the end of the leaching (that is, after 120 hours), the degree of oxidation of arsenopyrite reached 80-82%, and the content of arsenic sulfide in the residue of bacterial leaching was 0.92~1.02%. Considering that the yield of this product is 83% of the original concentrate, the arsenic pyrite oxidation degree is 87-91%.
The recycling of the spent solution plays a large role when tested in a continuous unit. In this case, the recycled solution should remove components that inhibit bacteria, including arsenic.
The method of removing arsenic is to neutralize the used waste solution with lime milk to bring the pH to 2.9~3.0. At this pH, the arsenic content in the solution drops from 4 g/l to 0.2-0.4 g/l, and the iron content ranges from 9 g/liter to 2.5-2.0 g/l. The precipitate formed during the neutralization process is discharged by clarification and filtration. At a yield of about 50%, the precipitates of hydroxides containing arsenate, arsenite and iron should be stored in special tanks, while the decanted and filtrates are passed through H:SOt Acidification to pH: 2.0~2.2, the return process is recycled.
It should be noted that when using a circulating bacterial solution, the viability of the bacteria is rapidly recovered during the leaching process.
The residue obtained during the bacterial leaching process is cyanated like the original concentrate (solid: liquid = 1: 2 to 4; KCN 0.1%, CaO 0.01 to 0.02%). The test results show that the recovery rate of gold is only 7~10% for the direct cyanidation of the original concentrate, and the recovery rate of gold is 88~90% for the cyanidation of the residue after leaching.
Since the effect of cyanidation is very good, it is recommended to use a comprehensive process including the method of oxidizing sulfides with microorganisms in the treatment of gold-arsenic concentrates (Fig. 4). Tests have shown that the separation of fine-grained dispersion boxes from stubborn gold-arsenic concentrates by bacterial leaching is very effective, and all equipment and devices work stably and reliably, and are easy to operate.

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