I. Current status and research direction of gold extraction technology for sulfuric acid slag
Currently a marked use of gold resources in China can not keep up exploration and production requirements of the situation, which restricts the increase of China's gold production, at the same time, and hard rock mineral recovering gold from gold-bearing technology and support policies waste but not ideal This part of the gold resources has not been fully utilized. The gold recovery technology containing gold sulfuric acid slag is in urgent need of development.
China produces hundreds of thousands of tons of gold-containing sulfuric acid slag per year. At present, only more than 3 grams/ton of slag is used. Only 75,000 tons of processing capacity per year, and the remaining slag or waste is discarded or more than ten yuan/ton. The price is sold to the cement factory as raw materials, and the gold contained in it is lost. It is a pity.
From the technical literature at home and abroad, the technology for recovering gold from slag is limited to the cyanidation process. Re-election, flotation, magnetic separation, and thiourea processes are all in the research stage.
The current cyanidation process is only suitable for the treatment of sulfuric acid slag with a gold grade above 2.5 g/? ton. If the grade is low, the profit is too low, and the investment is difficult to recover in a short period of time. Therefore, although it has good social benefits, the economic benefits are not Obviously without the enthusiasm of the construction of the gold plant; although the heap leaching method can reduce the production cost, but can not be continuously produced and can not be produced in winter, so this process is also difficult to promote; re-election, magnetic separation and flotation can be recycled A part of the gold in the slag, but the recovery rate is not as high as the cyanidation method, and the recovery rate is not ideal when the gold is recovered from the produced concentrate, and it is difficult to promote it. The cost of thiourea method is high and the leaching conditions are not easy to control. The method for recovering gold in solution is still in the exploration stage, which is far from industrial application.
We believe that there are two main factors affecting the withdrawal of gold from slag. One is that the investment is too large, and the other is that the production cost is too high. If these two problems can be solved, the low-grade sulfuric acid slag gold extraction technology will be successfully promoted. .
Through the research on the cyanidation process promoted and used in China, it is found that the process has the following problems:
(1) Years of research by Changchun Gold Research Institute has proved that sulfuric acid slag can be ensured without the need to re-cyanide leaching rate. The purpose of using the grinding section is only to ensure that the slurry is stirred evenly during the cyanidation reaction. The investment of the miner section is more than 400,000 yuan, and the production cost is as high as 15 yuan/ton. If the section can be cut by other methods, the investment and production cost of the cyanide method will be greatly reduced.
(2) Because the overflow of the thickener after the discharge of the grinding is carried out to remove the impurities such as iron and copper dissolved in the slag, cyanide cannot be added during the grinding process, so the lean liquid cannot be recycled completely, and the lean liquid can not be recycled. After the liquid treatment, the discharge not only increases the production cost, but also causes environmental pollution problems. In some areas with high environmental quality requirements, the environmental protection department will not approve the establishment of a cyanide plant.
(C) the number of sulfuric acid plant was built within the city? Without enough space to build a large tailings. When using the cyanide process now, whether or replaced with zinc powder by CIP must be separated by filtration cyanide tail The waste is discharged and the slag is transported to it by a motor vehicle. The filtration section increases the investment, and the fineness of the slag due to grinding increases the difficulty of filtration and increases the production cost.
(4) The replacement of zinc powder will increase the concentration of zinc in the lean liquid, worsen the leaching conditions, and reduce the recovery rate of gold. Because of the high hardness of the slag, the carbon used in the carbon slurry is worn out, the gold loss is much, and the production cost is increased.
(5) The biggest shortcoming of the cyanidation method is not that the reaction time is too long, generally it takes at least 16 hours, which requires the construction of a large volume of leaching tank, increased investment, increased power consumption, and increased plant area.
In summary, the extraction of gold from low-grade sulfuric acid slag requires the development of new leaching techniques or new processes that reduce investment and costs. The specific research content includes the following ways:
1. Using the new leaching equipment , the leaching reaction can be carried out smoothly without grinding. Moreover, the leaching power consumption does not increase or increase less.
2. Using a leaching method with a fast leaching speed, the leaching time is only a few hours or less. The stirring strength can be increased to ensure the leaching effect, and the unit power consumption does not increase much due to the short reaction time.
3, the use of lean liquid full cycle process, no drainage, save wastewater treatment costs, save leaching of chemicals.
4. The gold is recovered from the precious liquid by the fixed bed adsorption method. There is no washing section or carbon slurry section, and the direct filtration after immersion increases the gold concentration of the noble liquid to increase the gold grade of the adsorbent, thereby reducing equipment investment and production cost.
Through a large number of researches and experiments, the water and chlorine process has been selected. The results of the small test show that the leaching rate is higher than that of the cyanidation method. The reason is that the film on the gold surface of the slag particles in the cyanidation process hinders gold leaching and diffusion. . Both are determined by the nature of the slag - the calcination temperature at which the cyanide tail slag is acid is critical.
Second, the technical and economic indicators of new processes and new equipment
(1) Technical process indicators
Gold recovery rate: 55%
Leaching time: 3min ? Lime consumption: 3kg/t
Power consumption: 15kwh / t
Water consumption: 0.15m 3 /t Liquid chlorine consumption: 3kg/t
Investment: 800,000 yuan
Production cost: 38.6 yuan / t Production staff: 35 people
(2) Gold production and output value and profit
According to the annual production of 300 days, the processing capacity is 100m 3 /d, the grade of slag gold is 1.5g/t, the recovery rate is 55%, and the gold production is as follows:
Gold production per ton of burning: 1 × 1.5 × 55% = 0.825g
Nissan Gold: 100×0.825=82.5g
Annual production of gold: 300 × 82.5 = 24750g
Production value per ton of calcined residue: 0.825×96=79.2 yuan
Nissan: 100×79.2=0.792 million
Annual output value: 300 × 0.792 = 23.76 million yuan
Annual profit: 300×100×(79.2-38.6)=1.2 million
Calculated according to the investment of 1 million yuan, the return period is 10 months.
The minimum economic grade for gold extraction with this process is 0.75 g/t.
(III) Comparison of new process and conventional cyanide process
New Technology:
┌──除æ‚——â”
↓ │
Slag → leaching → separation ─ → adsorption → smelting → finished gold ↓
Waste residue Original cyanidation process:
┌────┬───────â”
↓ ↓ │
Slag → Ball Milling → Grading → Thickening → Leaching → Filtration or Washing – ┠│
↓ │ │
Waste residue │ │
│ │
Finished product gold ↠smelting ↠adsorption or replacement â†-┘ │
│ │
│ │
└────────┘
(4) Characteristics of new solid-liquid separation equipment
The conventional solid-liquid separation equipment has a plate and frame filter press, a belt filter, a thickener, and the supporting high-pressure pump of the plate and frame filter press is vulnerable to corrosion, and a stirred tank balance flow is required before the filter press, and the equipment investment reaches 150. 10,000 yuan, large power consumption; ? Belt vacuum filter filter belt is vulnerable, not easy to prevent chlorine corrosion, investment up to 2 million yuan; thick machine is not easy to handle large particle materials. Moreover, it is not easy to prevent corrosion, and it covers a large area with an investment of 1.5 million yuan.
The new type of solid-liquid separation equipment is similar to the leaching tank for pool dipping. The multi-pool is connected in series, the upper part is provided with an overflow port, and the lower part is provided with a distribution plate. After the slurry enters, the large granular material is quickly settled to the lower part of the pool, and the water particle material will pass through the overflow port. Flowing into the back pool, after a long period of sedimentation, the clearer precious liquid flows out of the solid-liquid separation equipment, and enters the adsorption section. After the front pool is filled with slag, open the drain valve under the distribution plate and wash it with water from the upper part of the tank. The precious liquid from the distribution plate also enters the adsorption section. The new equipment is made of concrete and coated with anti-corrosion materials. The investment is only 300,000 yuan.
Third, the advantages of new processes and equipment
Advantages of the leaching method:
(1) The leaching method uses chlorine which is widely used in industry (starting with a small amount of salt) as a leaching agent and a small amount of auxiliaries to avoid cyanide contamination. The auxiliaries used reduce the consumption of chlorine gas, so that the cost of the agent is lower than cyanide. Law.
(2) The leaching time of the method is only 3 minutes, so the effective volume of the leaching equipment is only 0.2% to 0.4% of the cyanidation method. For the factory with a processing capacity of 100 t/d, the effective volume of the leaching equipment is only 0.3 cubic meters. Not only can the investment be reduced by 20%, but the power consumption of the leaching can also be reduced by 4 to 5kwh/t.
Advantages of the new leaching equipment:
A new reactor is used to accommodate the leaching of large particulate materials. Conventional leaching equipment is only suitable for the treatment of pulp below 200 mesh, otherwise there will be failures such as “sinking tank†and pressure mixing slurry. The volume of the device is small, and other methods are used to solve the reactor problem to avoid uneven mixing.
The new solid-liquid separation equipment has the characteristics of low investment, low production cost and easy corrosion prevention. The existing filtration equipment can not solve the problem of anti-corrosion, and the price is very high, about 1 million yuan is needed, and the investment of the new solid-liquid separation equipment is only 300,000 yuan.
Advantages of the new process:
(1) Eliminating the grinding and corresponding grading and thickening equipment, reducing investment by about 40%; saving 400 square meters; reducing material consumption by 10 yuan/t; reducing electricity costs by 5 yuan/t; reducing operators by 3-6 people.
(2) The non-grinding slag itself has a large particle size, generally accounting for more than 70% in -80 mesh, 45% in 40-80 mesh, and the remaining 5% in 20-40 mesh, and the sedimentation speed is fast. It is especially suitable for liquid-solid separation with new solid-liquid separation equipment. This device is easy to operate. Compared with the cyanidation process, the thickener and the filter press are omitted, and the balance of the amount of the leachate is easily controlled.
(3) The activated carbon adsorption method is used to recover the gold in the leachate. Considering that sediment may be generated during the adsorption process, the patented adsorption tank of our unit is adopted. The investment in the adsorption device is only 20,000 yuan.
(4) The gold-chloride complex is adsorbed in the acidic chlorine-containing solution, and the gold ion is finally converted into elemental gold. Therefore, the gold grade on the gold-loaded charcoal can be enriched to at least 10 kg/t, and the combined process of incineration-aqua regia dissolution-reduction can produce pure gold. The smelting process equipment is simple, only using conventional chemicals. Compared with the cyanide method, the smelting section saves equipment investment of 300,000 yuan, and the smelting cost is lower than the conventional process.
(5) The impurities in the poor liquid are mainly iron, zinc and copper, which can be precipitated with lime. The solution separating the impurities can be recycled; due to continuous chlorine addition, the acidity of the leachate will increase continuously, and the process of adding lime and impurities will start. To adjust the acidity.
(6) Compared with the conventional cyanide process, the gold extraction plant with 100t/d processing capacity can save equipment investment of 800,000 yuan and reduce production cost by 30 yuan/t. It is possible to extract gold from low-grade slag that is not profitable by cyanidation. In other words, the economic quality of the slag is greatly reduced.
For example, a factory with a processing capacity of 100t/d will invest 60-800,000 yuan, the power supply will not exceed 50kw, and the processing cost will be about 40 yuan/t. Even if the grade of slag is as low as 1.5g/t, the leaching rate is 55%. It can also reach 1 million yuan.
There are at least 10 factories in China that have such slag burning, and the gold grade is below 2g/t. If the process is promoted, at least 250kg of gold will be recovered every year. The profit is more than 10 million yuan.
4. Process design of gold extraction from sulfuric acid slag
(1) Process data
1, processing capacity: 100t / d
2. Leachate concentration: Chlorine gas 1.5kg/M 3 PH=1.5-2.5 Cl-4kg/M 3
3, liquid to solid ratio: 2 ~ 5: 1
4, reaction time: 3 minutes
5, the type of reaction: full backmix
6. Liquid-solid separation method: new solid-liquid separation equipment
7. Gold recovery method for noble liquid: Activated carbon fixed bed adsorption method
8. Lean liquid circulation measures: recycling after lime neutralization and precipitation of impurities
9, gold leaching rate: 55%
10, waste gas treatment method: adsorption and reuse of caustic soda
(2) Raw materials
1. Gold grade of burning slag: 1.67 g/t
2, liquid chlorine
3, lime
4, activated carbon: wood charcoal or fruit charcoal
5, tap water
6, caustic soda
(3) Material flow
1. Sulfuric acid slag: 4.17t/h
2. Leachate flow rate: 8.34~20M 3 /h
3, activated carbon adsorbent dosage: 1t
4. Exhaust gas treatment Exhaust volume: >500M 3 /h
5. Absorbent flow rate: 2-4M 3 /h
(four) process
┌──────────────────────────â”
↓ │
Screw feeder-→leaching equipment-→separator-→carbon adsorption tank-→lime neutralization→→impurity separation-┘
↑ ↓ │ ↓
│ Waste slag └─────┠Heavy metal └────────────┠↓
│ Roasting chlorine-containing waste gas-→solid-liquid adsorption tower-→sodium hypochlorite solution-— ┘ │
↑ ↓
│ Purification of ingots
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