Technology Research And Industrialization Of Zinc Recovery From The Low-grade Zinc Oxide Ore Leaching Residue

The natural resources are of vital importance to the sustainable development of non-ferrous metallurgical industry, and the efficient use of the existing natural resources is the critical and pressing issue faced by non-ferrous metallurgical industry. In this dissertation an economic and feasible process of recovering zinc from the residue of leaching zinc oxide ore is developed. This process comprehensively utilizes the discarded resources of low grade, abates enviromental pollution, generates high profits and meets the requirements of circulation economy.This dissertation can be divided into three main sections:1 Investigation into the fundamentals of extraction of zinc with D2EHPA(1) According to the results of study of the extraction mechanism and analysis of the infrared absorption spectrum of the organic phase, it is concluded that the chemical equation of extraction of zinc with D2EHPA from ZnSO₄-H₂SO₄-H₂O solution is:And the structural formula of extraction species is:(2) The extraction equilibrium is studied systematically and a chemical equilibrium model for the extraction equilibrium is obtained. By use of this model and the overall equilibrium principle, if the initial concentrations of zinc and H⁺ in the feed liquid, the initial concentration of D2EHPA in the organic phase and the phase ratio are given, the concentration of zinc in the raffinate can be calculated when a single-stage extraction reaches equilibrium. The model is verified by use of the results of 33 extraction experiments and 9 stripping experiments, and the calculated equilibrium concentration of zinc in the aqueous phase accords closely with the experimental results. The average relative errors of extraction and stripping are 7.62% and 2.88%, respectively, and the errors are lower than those of several models reported in foreign literature.2 Research on the technologyThe laboratory-scale experimental conditions of various operations are tested, and the technological process is determined. As to the key operation-extraction, the small-scale continuous extraction and stripping in a mixed settler extractor, the extended continuous tests of extraction and stripping in a mixed settler extractor are carried out, and satisfactory results are obtained. Some Critical technological problem are found and solved. The main research contents are:(1) In small-scale extraction test the effects of the extractant concentration in the organic phase, the phase ratio of extraction, the zinc concentration in the feed liquid, the pH of the aqueous phase, the Zn-loading ability of the organic phase, the phase ratio of stripping and the concentration of stripping acid on the results of extraction and stripping are investigated respectively. The optimal extraction conditions obtained are: the organic phase consists of D2EHPA and kerosene(30%:70%), three-stage counterflow extraction is adopted, the phase ration(O/A) is 1:1, the mixing time of extraction is 1 minute, the settling time of extraction is 2 minutes, the pH of feed liquid≥3, and the extraction rate is 66%.And the optimal stripping conditions obtained are:Two-stage counterflow stripping is adopted, the phase ratio(O/A) is 5:1, the H2SO4 content in the stripping agent > 180g/L, the mixing time is 1 minute, and the stripping efficiency can be greater than 90%.(2) The removal of cadmium by cementation with Zn dust and the removal of impurities by washing in extraction operation are studied. The contents of impurities in the solution obtained after stripping meet the requirements of electrowinning, and qualified cathode zinc can be produced. This demonstrates that the technological process of washing the residue of leaching zinc oxide ore-D2EHPA solvent extraction-electrowinning is feasible.(3) The behavior of calcium in the process is examined, and the conclusion is that the formation of CaSO₄ during stripping is unavoidable.(4) In order to save water resource and use the aqueous phase circularly, the neutralization of the acid in the raffinate with lime and zinc oxide ore is studied. The results show that the raffinate neutralized with zinc oxide ore can return to washing the leached residue and meet the requirements of extraction, and the acid in the raffinate is also utilized effectively.(5) It is discovered that the additions of matter A in a certain proportion can raise the extraction efficiency of D2EHPA remarkably, and matter A is not be extracted. This method is applying for a nation invention patent.(6) The extended continuous tests (2m³/day) in a mixed settler extractor are carried out, and the results are as follows:When the feed liquid contains Zn 10-13g/L and the phase ratio is 1-1.5, the extraction of zinc is 60-67%; When the phase ratio of stripping is 7-8 and the concentration sulfuric acid in the stripping agent is greater than 180g/L, the stripping rate of zinc is greater than 90% and the content of zinc in the stripping solution is greater than 90g/L.In the extended tests the problem of CaSO₄ crystallization is solved by restructuring the mixed settler extractor and selecting the materials.By modifying the technological process of extended tests and referring to the results of extended tests, the commercial-scale technological process is determined.3 Industrialization of the process(1) On the basis of the data of extended tests and relative information the key technology of Zn recovery is developed and the commercial-scale mixed settler extractor treating 3000m³ of residue-washing water is designed.(2) The process was put into commercial run in the August of 2005. The author attended in-situ commissioning test run and troubleshooting. The indices of full load run for over one year are relatively stable, and vary small in comparison with the results above. From the industrialization of the process, the main conclusions are as follows:Production practice demonstrates that this process is feasible, and its advantages are: low capital and running costs, short flowsheet, simple operations, stable technical indices, quick payback and high profit. This process is under application for an invention patent The production data show that the technical running is stable and the technical indices are good. When the phase ratio of extraction is about 1:1 and the phase ratio of stripping is controlled between 5:1-8:1 according to Zn concentration in the spent electrolyte, the content of zinc in the a stripping solution is about 100g/L and the loss of D2EHPA is less than 1 kg/tZn.By improving the structure of mixer-settler for stripping, adopting auxiliary measures and selecting suitable materials, the problem of CaSO₄ crystallization is solved successfully, and the whole process runs smoothly.The economic indices of this process are also good. 3000m³ of feed solution are treated and about 22 tons of zinc are recovered per day. Annually, 0.3 million tons of the leached residue are treated, 8000 tons of zinc are recovered, the sale income is 0.19 billion yuan and the profit is 0.14 billion yuan. The industrialization of this process not only lessens the pressure of resource shortage, but also brings the enterprise in enormous economic benefit.The production results show that by use of the mixer settler designed by us own the effects of extraction.and stripping are good, the separation of organic phase from aqueous phase is complete, the entrapment loss is small and the efficiency is high.In whole process, the organic phase and aqueous phase are in closed-circuit circulation and no liquor is discharged, so the environmental pollution is abated.The adaptability of this process is high. After suitable modification, it can be integrated with the technology of acid leaching of low-grade zinc ore to recovery zinc from the leaching solution. It can also be used to treat other low-acid and low-zinc waste waters.Innovations of this research(1) A technological process of recovering zinc from the leached residue of low-grade zinc oxide ore is developed on us own and applies for a nation invention patent. The results of up-to-date back-check of literature indicate that this process has not been reported at home and abroad.(2) Originally, the process of extraction of zinc with D2EHPA is industrialized at home, and the enterprise can make a health profit of 0.14 billion yuan per year. A key technical problem-the crystallization of CaSO₄ is solved during the industrialization by improving mixer-settler structure, selecting suitable materials and adopting some auxiliary measures, thereby the whole process runs smoothly.(3) Matter A, as an extraction aid is added into the extraction system to raise the extraction efficiency of D2EHPA remarkably, and this method is under application for a nation invention patent.(4) An equilibrium model for extraction of zinc with D2EHPA is obtained. This model is distinguished from those reported in foreign literatures, and its accuracy is better than that of those models.