At present, stirring cyanide leaching process widely used in gold mines includes: conventional cyanide leaching process (CCD method for short), including leaching, washing and zinc replacement; Carbon in Pulp process (CIP method for short) and Carbon in Leach gold process (CIL method for short). The method of adsorbing gold from cyanide leaching solution of gold-bearing pulp by using the adsorption of activated carbon is called Carbon in Pulp method, while the method of simultaneous deuteration leaching process and activated carbon adsorption process is called Carbon in Leach method. The gold in gold-containing desorption solution can be recovered by zinc replacement method or desorption electrolysis method. Currently widely used is desorption electrolysis.
Composition of the cyanide leaching system
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The conventional cyanide gold recovery process in cyanide gold processing plant generally includes three steps: leaching process, washing process, and zinc powder replacement process. In the CIP and CIL process, we use activated carbon to extract gold, so the last step of these two processes becomes activated carbon adsorption process.
The main gold recovery equipment used in the cyanide gold processing plant are as follows: the leaching agitation tank, the high efficiency low consumption rapid desorption electrowinning system, the washing thickener, the zinc powder replacing device, and etc. The leaching agitation tank is applied to the conventional cyanide leaching process, the CIP and the CIL process; the desorption and electrowinning system is mainly applied in the stage of activated carbon adsorption; the zinc powder replacement device is the main equipment used in the zinc powder replacement stage; The thickener is the primary equipment used in the washing stage of the conventional cyanide leaching process.
This article will be followed by a separate explanation for each device.
Leaching Agitation Tank
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The leaching agitation tank is a mechanical agitation equipment used in cyanide leaching operation of gold mine. There are two kinds of leaching agitation tank: single impeller leaching agitation tank and double impeller leaching agitation tank. The working principle of leaching agitation tank is: the slurry flows from the top to the bottom in the center under the action of impeller pushing and throwing. Then, it is diffused through the peripheral baffles, and air is supplied to the lower end of the shaft (the air is fed by the hollow shaft) and the slurry is circulated upward to form a uniform suspension mixture.
Compared with the single impeller leaching agitation tank, the advantages of the double impeller leaching agitation tank are fourfold:
(1) The movement of ores is smooth, the slurry is evenly mixed, and the power consumption is small.
(2) The air is uniform because the air entering the tank through the drive center shaft will be agitated by the impeller.
(3) The device has the compact structure and is easy maintenance.
(4) The impeller has low speed and long service life because of the rubber liner.
The shortcomings of the long double impeller leaching agitation tank are as follows:
(1) The double impeller leaching agitation tank limits the fineness of raw materials----usually -200 mesh is required to be more than 90%, which requires that the raw materials must be finely ground to use. And the fine grinding equipment have high power consumption, fast wear, and maintenance troubles.
(2) The double impeller leaching agitation tank limits concentration. When the concentration is in the range of 40-45%, the leaching effect would be best. Now the mines and refineries need continuously leaching, so the slurry concentration deeply affects the leaching rate of gold. If the slurry concentration was too low, the leaching time of pulp would be reduced; if the slurry concentration was too high, the requirements on the pump would be stricter (Generally, the conveying concentration of slurry pump should not exceed 30%. Once it exceeds 30%, the conveying quantity would be affected). In short, double impeller leaching agitation tank has the following advantages, reliable, easy to operate,convenient to maintain, and highly applicable, except requiring high concentration and fineness of the slurry, which made it widely used in the gold processing industry.
Desorption Electrolysis System
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The desorption electrolysis system is used for extracting gold adsorbed in activated carbon, which usually work under high temperature and high-pressure conditions, including carbon lifting pump, carbon screen, desorption solution tank, desorption column and others. The advantages of this equipment system are as follows:
1. Fast desorption, short time and high efficiency
The working temperature of desorption electrolysis system is as high as 150°C, which is about 55°C higher than the working temperature of the heating and atmospheric pressure process; the pressure is up to 0.5 Mpa, which is 0.2 Mpa to 0.5 Mpa higher than the normal temperature and pressure process. Under this high temperature and pressure condition, the desorption electrolysis rate of gold-loaded carbon is obviously accelerated----only 2 to 6 hours to desorb 98% of the gold, which greatly improves the absorption efficiency, shortens the desorption time by nearly ten times, and reduces the lean carbon grade to 50 g/t. It also has a regenerative activation effect on activated carbon.
2. Nocyanogen desorption, low energy consumption
Compared with the heating atmospheric pressure process, the desorption electrolysis system only needs sodium hydroxide as the desorption solution, and does not need sodium cyanide, which not only reduces the operating cost, but also meets the requirements of environmental protection. In addition, the whole desorption process is basically carried out under the same temperature and pressure, desorption solution can be directly into the electrolytic cell without cooling treatment, which greatly saves the consumption of heat energy, and the consumption of electricity is only 1/2 ~1/4 of the heating atmospheric pressure process, truly realizing cyanogen free low-consumption desorption.
3. High degree of automation and intelligence
During the operation of the system, the amount of liquid in the system will fluctuate to some extent due to the liquid vaporization and pressure change of the system. Therefore, technicians specially set up a liquid level buffer mechanism to automatically offset liquid level changes and maintain the normal operation of the system. In addition, for it is configured with a temperature control system, when the temperature reached set value, the system will automatically pick the open part of the electric heater, residual electric heater automatically maintain system working temperature, when the system temperature is lower than the set limit, was torn open electric heater automatically into start, ensuring that the system has been stable in temperature range.
4. Triple security protection measures
Considering the safety of the system, the technicians took three safety measures.
(1) the system itself is intelligent. The electric heater can be automatically put into or stop working according to the circulating pump running state or pressure level, without manual operation.
(2) Automatic pressure limiting and pressure releasing mechanism. When the system pressure rises to a certain value, this mechanism will automatically open the pressure relief and adjust the pressure to the normal value.
(3) Safety valve. If the above two measures fail, the safety valve will automatically start to avoid causing great losses.
Zinc Powder Displacement Device
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Zinc powder displacement process includes three stages: purification of pregnant solution, deoxidation and displacement filtration. The suspended substance in the gold-bearing pregnant solution is removed by purification stage. The dissolved oxygen in the pregnant solution has an obstructive effect on the gold recovery by zinc displacement, so the oxygen in the pregnant solution must be removed to ensure the smooth progress of gold recovery. The displacement filtration stage includes zinc powder addition and displacement operation. The displacement reaction starts once the zinc powder is added into the pregnant solution. And the final displacement and filtration of gold mud are completed by the displacement device.
Therefore, zinc powder displacement devicemainly includes deoxygenation tower, zinc powder feeder and displacement device.
Here are some points we should notice when operate the zinc powder displacement device:
1. Observe if the running pump is normal, and check the inlet pressure and leakage condition of the replacement and purification frame.
2. Pay attention to the air tightness of the zinc powder displacement system, which ensures that the deoxygenation can meet the technical requirements. And determine the amount of pregnant solution according to the reserves of pregnant solution and lean solution, which can reduce the fluctuation range.
3. Since the displacement operation is featured with strong continuity, it is generally not stopped, otherwise the quality of gold mud and displacement effect will be affected. If necessary, the stop cannot exceed four hours.
4. Regularly check the pulp situation of submerged pump, and start it timely when the pump tank is filled
5. Tour inspection to prevent the lean solution from increasing; check if the solution level of pregnant solution tank and lean solution tank is up to standard; check if the water temperature and water level of circulating water tank are normal.
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Washing thickener is the professional gold recovery equipment for the solid-liquid separation and washing of pulp after cyanidation, which has two types of two-layer and three-layer. It has advantages such as small occupied area, energy-saving and simplification of process flow. Successive discharging was applied for reducing several circling of liquid gold and early to recovery. At same the period during pulp in thickener was reduced and leaching rate was increased. The washing thickener realizes reverse washing, continuous operation, large volume and high washing efficiency. Small area, reasonable structure, low operation and maintenance cost.
The working principle of washing thickener is that: Pulp by feeding tube into the,free settling in the pulp of rake area by the pressure of scraper step into a concentrated, gradually by rake to pool center, by the row ore mouth by gravity into the next layer in the pool, water is entered into the most lower level for material washing distribution box, the bottom of spillway flow distribution box to enter the upper material for washing, the overflow of the first floor of the overflow weir discharge, after washing the bottom material is twice.
Classic Cyanidation Project Case and Equipment
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Tanzania 1200tpd Gold Processing Project
Processing Flow: All-slime cyanidation gold processing technology including thickening – leaching – desorption electrolysis– tailings dry stacking.
Equipment: Double-impeller leaching agitation tank, desorption electrolysis system, washing thickener
Malaysia 700tpd Gold Processing Project
Processing Flow: Grinding and classifying –cyanidation and leaching – tailings dry stacking - sewage treatment
Equipment: Wet energy-saving grid ball mill, wet energy-saving overflow ball mill, high-efficiency improved thickener,double-impeller leaching agitation tank, XPA high lifting wear-resistance rubber slurry pump, chamber filter press, XPA wear-resistance rubber slurry pump
Zimbabwe 700tpd Rock Gold Processing Project
Processing Flow: Two close circuit grinding– gravity separation – thickening – cyanidation and leaching
Equipment: Jig, shaking table,hydrocyclone, double-impeller leaching agitation tank, desorption electrolysis system