2 leaching process
The leaching process is mainly divided into acid leaching and alkali leaching processes. The main principle is to use the solution to selectively dissolve the target component in the material to achieve the purpose of enrichment of useful minerals.
Leaching Technology harsh conditions, technical difficulties, direct leaching of the ore grade requirements are higher, according to the current technical conditions, foreign leaching zinc containing about 25%, more than 30% of the domestic zinc leaching of zinc oxide ore before Have better technical and economic indicators.
2.1 acid leaching
Acid leaching is the main method of zinc oxide ore leaching, and sulfuric acid is the most commonly used leaching agent.
Yang Dajin et al. used a sulfuric acid heap leaching method for a low-grade zinc oxide ore with a zinc content of 11.49% in Yunnan. The stacking height was 1 m and the leaching temperature was between 20 and 32 °C. After aging with concentrated sulfuric acid, the pH of the intermittent spray and leaching end point is controlled at 1.0 to 1.5, and after 13 weeks of heap leaching, the leaching rate of zinc is more than 93%. Mai Zhenhai et al. conducted a pressurized acid leaching process on 18.81% zinc and 44.99% high silica low grade zinc oxide ore. Under the optimum conditions of 20-22 ml concentrated sulfuric acid/100g ore, pressure 0.8MPa, temperature 150°C and leaching time 120min, the slurry with good filterability was obtained, and the leaching rate of Zn was 98.5%. The SiO2 leaching rate was 0.7%.
Acid leaching of large equipment corrosion, leaching of iron, calcium and magnesium impurities in the aluminum, so that leaching solution purification is not easy, especially difficult due to the dissolution of the silica solid-liquid separation, resulting in technical difficulty. The consumption of sulfuric acid is relatively large, and the consumption of 1t zinc requires more than 1t of acid. Due to the influence of the grade of zinc oxide ore, the economic benefits are not obvious.
2.2 alkaline leaching
Alkali leaching has the advantages of high leaching rate and small environmental impact. The process is simpler and easier to control than acid leaching, less corrosive to equipment, and alkali can be recycled, low alkali loss rate and low energy consumption.
The alkali used in the alkali leaching process of zinc oxide mainly includes sodium hydroxide and ammonia water.
However, the current alkali process is not mature enough, and many research work is still in the laboratory research stage. Liu Sanjun et al. studied the leaching of Yunnan Lanping zinc oxide ore with sodium hydroxide and ammonia-carbonic acid solution. The zinc leaching rate was 92.6 when the sodium hydroxide concentration was 4 mol/L, the temperature was 70 ° C, and the liquid-solid mass ratio was 10:1. %; When the ammonia-carbonic acid solution concentration is 5 mol/L, the temperature is 25 ° C, and the liquid-solid mass ratio is 15:1, the zinc leaching rate is 91.3%. It indicates that both sodium hydroxide and ammonia-carbonate solutions are effective leaching agents for zinc oxide ore.
Zhang Baoping uses ammonium chloride-ammonia as a leaching agent to extract electric zinc directly from zinc oxide ore. Zinc in zinc oxide enters the leaching agent in the form of zinc-ammonia complex, and impurities such as arsenic , antimony , iron, etc. Remove. The results show that the zinc leaching rate is ≥93%; the concentration of arsenic and iron in the leaching solution is lower than 25mg/L, the concentration of iron is lower than 15mg/L; the quality of zinc in the electrowinning zinc after the leaching solution is removed by a zinc powder The score is 99.999% and the purity is extremely high.
Alkaline leaching is suitable for high-calcium-magnesium zinc oxide ore. The content of leaching impurities is low, and the leaching solution is easy to filter. However, alkali leaching is to ensure the leaching rate of zinc, and a higher liquid-solid ratio is required to make the zinc ion concentration of the leaching solution low. The ammonia leaching process has a serious loss of ammonia volatilization during actual operation and is extremely detrimental to the health of the operator.
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