Gold Ore Beneficiation Plant Process Flow and Cyanide Tailings Treatment

In order to improve the efficiency of gold ore dressing and resource utilisation, a gold ore dressing plant adopts the combined process of ‘re-election + flotation’, combined with centrifuge primary screening, shaking screen selection and other technologies, which significantly improves the recovery rate and product quality. This paper systematically introduces the whole process of this beneficiation plant from crushing, grinding to re-election and flotation, and focuses on the harmless treatment of cyanide tailings and cyanide-containing wastewater. The high efficiency removal of cyanide and resource recovery is achieved through the biochemical combined treatment technology.

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I. Process flow of ore dressing plant

Gold ore beneficiation process mainly includes crushing, grinding, re-election, flotation and other core links, each link synergistic action to improve the recovery of gold elements and product quality. The following is the specific process:

1. Crushing process

After initial storage, the ore material first enters the jaw crusher for rough crushing, which crushes the ore to medium size (about 150-200mm). Subsequently, the material is conveyed to the cone crusher for intermediate crushing to further refine it to less than 10mm. During the crushing process, double-deck circular screen is used for closed-circuit screening, the screened material is returned to the cone crusher for secondary crushing, and the screened material (<10mm) directly enters the concentrate store for temporary storage, providing uniform raw materials for the subsequent grinding process.

2. Grinding process

The materials from the concentrate store are conveyed to the lattice ball mill via belt for one stage of grinding, and the fineness of grinding should reach -200 mesh accounting for more than 90%. Grinding products are classified by spiral classifier, coarse particles are returned to ball mill for regrinding, while fine particles enter hydrocyclone for secondary classification. The fine-grained slurry overflowed from the hydrocyclone (concentration of about 40%) enters the flotation process, and the underflow returns to the mill for recycling, forming a closed-circuit grinding system to ensure that the slurry fineness meets the requirements of flotation.

3. Re-election process

Aiming at the characteristics of coarse-grained gold distribution in the ore, a jigger is installed at the discharge of the ball mill for roughing to enrich high-grade heavy minerals. The jig concentrate is transported to the shaking table for concentration, and further purified by gravity separation, finally obtaining a re-election concentrate with a grade of about 294.87g/t. The tailings of the shaking table are returned to the grinding mill. The shaker tailings are returned to the grinding circuit for reprocessing to minimise metal loss. The re-election process effectively recovers the free gold in the ore and reduces the consumption of flotation chemicals.

4. Flotation process

The slurry enters the flotation system after being adjusted by the mixing tank, and adopts the process of ‘one coarse, two sweeps and two fines’. In the roughing stage, trapping agent (such as yellow medicine) and foaming agent are added to make the gold minerals selectively attached to the surface of bubbles, forming a foam layer and scraping out as rough concentrate. Roughing tailings are swept twice to recover the residual gold, the swept concentrate is returned to the roughing stage, and the tailings are fed into the cyanide leach or tailings storage. The rough concentrate is purified twice in the concentrating stage, and the flotation tailings are thickened and enter the cyanide tailings treatment system, with an overall recovery rate of more than 90%.

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II, cyanide tailings treatment process

Although the cyanide gold extraction process can efficiently extract gold, the cyanide-containing tailings and wastewater generated are an environmental risk. This processing plant adopts ‘biochemical combined treatment method’ to achieve harmless and resourceful cyanide, the specific flow is as follows:

1. Pre-treatment stage

Cyanide tailings are crushed, screened and decomposed into particles with a particle size of less than 5mm to increase the contact area for subsequent reactions. Cyanide-containing wastewater, on the other hand, is separated from high-concentration and low-concentration wastewater by fractionation, and enters the microbial reactor and chemical treatment system respectively.

2. Microbiological treatment

After pre-treatment, the tailings and wastewater enter the microbiological reactor, where specific bacteria (such as Thiobacillus, Pseudomonas, etc.) are injected to convert cyanide into low-toxicity substances such as thiocyanate and ammonia-nitrogen by using adsorption and metabolism of microorganisms. This stage can remove about 70% of cyanide and degrade some heavy metal ions at the same time.

3. Chemical treatment

The product of microbiological treatment enters the chemical reactor, where ferrous sulphate, hydrogen peroxide and other agents are added to completely decompose the residual cyanide into carbon dioxide, nitrogen and harmless salts (e.g. sulphate) through redox reaction. At this stage, the cyanide removal rate is increased to more than 99%, and the cyanide concentration in the wastewater is reduced to less than 0.1mg/L, which meets the national emission standards.

4. Resource recovery and utilisation

The treated tailings still contain valuable metals such as lead and zinc, which are recovered in metal concentrates by secondary flotation with additional flotation columns. The harmless tailings can be processed into building materials or soil conditioners, and the harmless salts in the wastewater (e.g. sodium sulfate) are used as industrial raw materials after evaporation and crystallisation. This process not only reduces metal loss, but also creates additional economic benefits for the enterprise.

5. Expected results

The treatment solution can achieve near-zero discharge of cyanide, increase the comprehensive utilisation rate of resources by more than 30%, save treatment costs by about 15% per year, and at the same time avoid the environmental risk of tailing ponds, which is in line with the requirements of green mine construction.

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Conclusion

The combination of ‘re-election + flotation’ and biochemical tailings treatment technology has significantly improved the gold recovery rate and resource utilisation in the gold processing plant. In the future, we can further optimise the ratio of microbial flora and chemicals to promote the development of beneficiation process in the direction of high efficiency, environmental protection and sustainability.