Abstract: Aida Gold Mine is located in a middle-low mountainous area with a cold winter climate. It is designed to not be able to produce below 0℃. This article combines the production process, equipment conditions and cyanide leaching theory to explore the production experience of using FKN environmentally friendly gold dressing agent for gold leaching in the full peat slurry process under low temperature (-15℃) conditions. The measures taken are: ① The pre-soaking operation of FKN gold leaching agent leaching gold is advanced to the first stage of grinding; ② 0.4kg of lead acetate is added per ton of ore, and a corresponding dosing system is formulated; ③ The slurry level adjustment gate is added to the slurry outlet of the pump pool. Improve the connection method of the inflatable tube. The implementation of these methods has extended the leaching time of gold, improved the dissolved oxygen status in the FKN gold extraction agent leaching gold slurry, reduced FKN gold dressing agent’s consumption, extended the production time of the dressing plant by 2-3 months every year, and significantly improved the comprehensive benefits. .

Keywords: Environmentally friend gold dressing agent, gold leaching agent, gold extraction agent, gold dissolving agent, gold recovery agent, gold collecting agent, gold stripping agent, gold extraction; FKN carbon slurry gold leaching; low temperature gold leaching

Aida Gold Mine, Gansu was built in 2005. It has a designed daily ore processing capacity of 110t, and the actual annual average daily ore processing capacity reaches 137t. It is a small gold mining and dressing mine. Since the mine is located in the mid-to-low mountainous area of Altay, and the road is blocked by heavy snow in winter and the climate is cold, the dressing plant is designed to operate for half a year without indoor insulation measures. In spring and autumn, the natural minimum temperature reaches 0℃ as the limit for starting and shutting down the dressing plant. The mineral processing plant started production on April 20, 2010. Due to many reasons such as the temperature reaching minus 15°C, the production indicators were disordered. Therefore, a series of adjustments to the production process conditions under low temperature conditions were carried out, and all-sludge cyanide carbon was explored. Successful production experience of pulp technology under low temperature conditions.

1. Ore properties

The analysis results of the main chemical components of the raw ore are as follows:

The mineral composition of raw ore is simple. The main metal minerals are natural gold, limonite, magnetite, hematite, and a small amount of pyrite, chalcopyrite, galena, malachite, etc.; the gangue minerals are mainly quartz and pomegranate. Zishi, chlorite, biotite, mica, actinolite, clay, etc. The ore types include orange-yellow hematite-based granular quartz vein type, and limonite-based chlorite-biotite quartz schist type containing quartz veinlets. The metal sulfide content is 4%, which is a low-sulfide gold ore. Most of the gold in the ore is produced in the form of independent mineralization, and its occurrence status is: interstitial gold accounts for 50%, encapsulated gold accounts for 36.6%, and fissure gold accounts for 13.4%.

2. Carbon slurry gold leaching process and design production conditions

After the raw ore is ground in two stages of closed circuit, the slurry is thickened and pumped from the pump pool to the 1# pre-leaching tank for slurry adjustment, and then goes through the leaching process of the 2# and 6# carbon slurry leaching tanks; activated carbon is added from the 6# carbon leaching tank. The reverse slurry flows to the front tank to string the carbon. After reaching the gold-loading amount, the gold-loaded carbon is taken out from the 2# carbon leaching tank to complete the carbon slurry gold leaching process.

Lime is added to the first stage of the grinding machine along with the raw ore to adjust the pH value of the slurry; after the FKN gold-dissolving agent solution is prepared, it is added to the 1# prepreg tank at a dosage of 3.8kg/t; after the gold-loaded carbon reaches a gold-loading capacity of 4g/kg, it is added to the 2# carbon Dip tank raised. Design indicators: raw ore grade 5.63g/t, grinding fineness - 0.074mm accounting for 90%, adsorption rate 97%, leaching rate 92.8%, leaching time 40h, leaching temperature 20-25°C. The design also points out that if lead acetate is added as a pre-soaking agent in the 1# pre-soaking tank, the consumption of FKN gold dressing agent can be reduced, and the dosage is 0.4kg/t.

3. Problems existing in production under design process conditions

From 2017 to 2019, production was carried out according to the design in the spring and autumn. In the spring, the plant was selected to start production when the temperature rose above 0℃, and in the autumn, the plant was shut down when the temperature dropped below 0℃. The annual production time of the three-year dressing plant was too short, less than 6 months: 143 days in 2017, 157 days in 2018, and 171 days in 2019. The 10-day average indicators before and after shutdown in spring and autumn of normal years are shown in Table 1.

In 2020, the gold price dropped. In order to ensure the efficiency of the enterprise, the dressing plant was scheduled to start production on April 20. The lowest temperature at that time was minus 15°C, and the slurry temperature in the 1# prepreg tank was 5-8°C; in order to reduce production costs, FKN gold-dissolving agent was used instead; furthermore, the properties of the raw ore changed, and its sulfide content increased, making leaching more difficult. ;The gold grade of the raw ore dropped, with an average of less than 2.3g/t in 10 days.

Table1   Average production-indexes for normal years

4. Plans for adjusting production processes under low temperature conditions

Under the existing equipment and production process conditions, from the perspective of cost reduction, the factors affecting the leaching rate under low temperature conditions are comprehensively analyzed.

4.1 The basis for referring the pre-soaking operation to the grinding stage

(1) Ensure leaching time. The original design of the dressing plant was to have a daily processing capacity of 100t, with 6 leaching tanks, each tank having a volume of 52m³, and a leaching time of 40 hours. Now the actual daily processing capacity is 137t. Calculate the leaching time according to the following formula:

t = 24V／〔Q（R +1/δ)〕

In the formula: V is the total capacity of the leaching tank, 312m3; Q is the actual daily ore processing volume, t/d; R is the liquid-to-solid ratio. When the leaching slurry concentration is 41%, the liquid-to-solid ratio is 1.439; δ = 2.69, which is the relative density of the ore. density.

Calculation results show that when the daily ore processing capacity is 137t, the leaching time of the six leaching tanks is 30 hours, which is far from the designed leaching time. In order to ensure sufficient leaching time, on the one hand, consider reducing the ore processing volume, which will inevitably increase production costs and reduce output value, seriously affecting the economic benefits of the enterprise; on the other hand, the pre-leaching operation can be brought to the front of the process. According to the start-up records every spring, it takes 12 hours from the time when the ball mill feeds the ore to the time when the thickener releases the qualified underflow. This means that the ball mill is used as a pre-soaking operation at the same time, and FKN gold extraction agent is added to the ore feeding port. Ensure that the leaching time reaches the design requirement of 40h.

(2) Increase the temperature of the prepreg process. The design leaching temperature is 20-30℃. Laboratory research results have shown that in order to maintain a certain dissolution rate of gold, the leaching temperature must be maintained at no lower than 15°C. Under low temperature conditions, according to the original production measurement records, the temperature of the slurry in the leaching tank is only 5 to 8°C. Using a thermometer to measure the temperature at various points in the process, it was found that the temperature of the slurry at the second-stage grinding outlet was as high as 40°C, which means that grinding has a negative impact on the slurry. Has a warming effect. When the room is not insulated, the temperature of the slurry cannot reach the slurry temperature that must be maintained for leaching after it reaches the 1# prepreg tank after being ground through a series of long processes such as thickening, pump pools, and pipelines. For this reason, the pre-soaking operation is changed to one stage of ball milling, so that the pre-soaking operation under low temperature conditions can be heated by two stages of grinding to improve the leaching effect.

(3) Improve the dissolved oxygen situation in FKN gold-leaching agent slurry. The oxygen concentration in the FKN gold-soluble agent slurry is an important factor affecting the leaching rate. In order to strengthen the dissolution process of gold, it is necessary to increase the oxygen concentration in the FKN gold-soluble gold agent slurry. As a pre-soaking operation, grinding is beneficial to increasing the concentration of oxygen in the FKN gold-soluble slurry from the following aspects: ① heating of the slurry during the grinding process; ② strong stirring of the slurry and enhanced interaction with air during ball milling operations Contact; ③FKN gold recovery agent slurry undergoes a series of processes such as two-stage ball milling, cyclone and sand pump, thickening and sand pump, etc., which greatly increases the chance of contact between the slurry and the air.

4.2 One-stage grinding as a feasible condition for pre-soaking operation

The plan to advance the pre-soaking operation to the first stage of ball milling is only feasible if the process management of the dressing plant is strict and the closed-circuit circulation of ground water in the dressing plant is implemented. During the infrastructure construction period, this dressing plant selected a design unit and installation construction unit with experience in the FKN gold-dissolving agent full mud immersion gold process. The slopes of each process pipeline and the size of the inlet and outlet of the dressing plant were reasonably designed. Quality was strictly controlled during installation and construction. Production management is strict to prevent "running, popping, dripping, and leaking" in the process; and a closed-circuit circulation of the ground waterway of the dressing plant is designed, that is, the ground ditches on each step of the dressing plant form a system, which is uniformly collected into the return water pump pool, and impurities are collected The pump pumps the surface water to the return pool and returns to the grinding process for additional water, forming a closed-circuit circulation of all water in the dressing plant.

4.3 Reasonable control of cyanide concentration in leaching pulp

When gold is dissolved, the cyanide concentration in the slurry is an important factor. The relationship between the dissolution rate of theoretical research gold and the concentration of cyanide is:

When the cyanide concentration is below 0.05%, the dissolution rate of gold rises almost linearly to the maximum value as the cyanide concentration increases; when the cyanide concentration is between 0.05% and 0.10%, the dissolution rate of gold tends to be slow. As the cyanide concentration continues to increase, the dissolution rate of gold will tend to decrease. Based on the research results and previous production experience, taking into account the dissolution speed of gold and the sufficient cyanide concentration in the slurry, FKN gold-extracting agent was added in stages, that is, first, the cyanide concentration in the overflow slurry of the grinding stage was controlled to 0.08 About %, after the leaching slurry is consumed for a period of time, FKN gold extraction agent is added to the original 1# prepreg tank to maintain a sufficient cyanide concentration in the slurry during the entire leaching process, which is beneficial to the leaching of gold.

4.4 Give full play to the catalytic effect of lead acetate on gold leaching and formulate its addition system

The mechanism of using lead acetate as a prepreg to increase the dissolution rate of gold is: when the leaching solution contains an appropriate amount of lead, lead and gold form a "primary battery", and gold serves as the anode and is transferred into the leaching solution; but when the leaching solution contains lead, When the concentration is excessive, lead interacts with the cyanide on the gold surface to form an insoluble film of pb(CN)2, which is deposited on the gold surface and seriously hinders the cyanide dissolution of gold. The appropriate lead concentration in the leaching solution is 0.5mg/L.

Summarizing past experience and combining it with the production site, the addition of lead acetate must form an institutionalized production system for workers. The capacity-controlled dry powder addition method is used. Based on the designed lead acetate addition amount of 0.4kg/t, the addition amount every half hour is 1.14kg. The production technician makes a square shovel that can only hold 1kg of lead acetate dry powder. Specific adding method: Each shift weighs 15kg of lead acetate separately from the warehouse, and adds a shovelful of dry lead acetate powder to a section of the grinding and feeding belt every half hour.

4.5 Measures to improve the fineness of leached ore

Measures to improve the cyclone classification fineness are shown in Figure 2. Referring to the slurry level adjustment gate of the flotation machine, a slurry level adjustment gate is added to the slurry outlet of the sand pump pool of the cyclone to maintain a stable slurry level in the pump pool to ensure that the sand pump does not inhale air and stabilize the slurry. The ore feeding amount and pressure of the flow device can be improved to improve its classification efficiency and improve the fineness of the leached ore.

4.6 Measures to reduce the resistance of the inflatable tube

Remove all the small facilities such as the inflatable gate valve and elbow of the original design, and directly use a piece of leather air duct to connect the branch air duct and the inflatable pipe. That is, there is no need to control the direct connection between the branch air duct and the inflatable pipe. How much air is filled depends on the capacity of the equipment. And the combination of slurry and oxygen reduces the inflation resistance and facilitates operation. Before the transformation, the branch air duct and the air duct after the fan stopped during production were often blocked by mineral sand, and it was very laborious to open up the air duct and the air duct. After the transformation, it was only necessary to remove the skinned air duct and tap the branch while the fan was supplying air. Air ducts or inflatable pipes can eliminate mineral sand blockage, small measures can solve big problems, and ensure that the air supply path is smooth.

5. Achievements achieved by adjusting production processes

After the above-mentioned adjustments were made to the production process conditions in the spring of 2000, the production indicators quickly returned to normal. In the fall of that year, when the temperature was below 0°C, the production technical indicators were extremely stable and exceeded previous levels by adopting the above-mentioned adjustment plan. See Table 2 for comparison of indicators.

Table 2 Comparison of production indicators before and after adjustment of process conditions

In that year, the autumn dressing plant production was extended to mid-to-late November, which was 45 days longer than in normal years, increasing the company's output value by about 1.79 million yuan, and greatly improving the company's efficiency.

6. Conclusion

(1) In order to improve the leaching index of gold under low temperature conditions, the pre-leaching operation of FKN gold leaching agent leaching is advanced to a stage of grinding, the leaching time is increased, the pre-leaching process is heated, and the dissolved oxygen situation in the cyanide leaching gold slurry is improved. Reduce cyanide consumption.

(2) Lead acetate is used as a pre-soaking agent for cyanide leaching gold. Because of its small amount, it can be added stably in the pre-soaking operation in the form of dry powder. The operation must form a working system. Lead acetate can reduce FKN dressing agent's consumption and significantly improve the leaching effect, which is especially necessary for the FKN gold leaching process under low temperature conditions.

(3) The production experience of cyanide leaching gold under low temperature conditions introduced in this article has great practical significance for FKN leaching gold dressing plants in cold northern regions, which extends the operation time of gold leaching dressing plants in spring and autumn. 2 to 3 months, greatly improving corporate efficiency.