Study On Heap Leaching-Solvent Extraction-Electro-deposit Of Low-grade Zinc Ore

Zinc and its compounds have wide-ranging usage because of their better physical and chemical properties, which leads to the rapid development of zinc metallurgy and gets favorable market ability and quotation. However, zinc metallurgy. has an inadequate supply for the lack of reserves. It is necessary to exploit all sorts of zinc reserves, especially resourceful low-grade zinc minerals to keep the sustaining and healthy development of zinc metallurgy. There have been many processes for extracting low grade zinc mineral reserves. Due to lack of methods which make these reserves be used economically and effectively at home, it is very important to develop new metallurgy techniques for these reserves and provide technical support of developing zinc metallurgy continually.The existing zinc metallurgy processes is comparative analysis, good process elicited to extract zinc from the low-grade zinc reserves is determined, which contains heap leaching→iron removal by oxidization and neutralization→solvent extraction→reverse-solvent-extraction→organic phase removal→electrolytic deposit in sequence.In this research, zinc can be leached availably from the low-grade zinc minerals by heap leaching and mixed bacteria leaching. Iron is removed from leaching liquor by oxidation and neutralization before extraction. The liquor after iron removed is extracted by single P204．During the extraction, free acid will not be neutralized and organic phase will not be saponification. Zinc electrodeposition scrap is reverse-extracted directly and organic phase is removed by activated carbon. With application of these new methods, consumption and cost reduce and new metallurgy technology of the low-grade zinc minerals is obtained.Zinc can be leached availably from the low-grade zinc by bacteria that have been gathered and cultured in situ. The results of bacteria agitation leaching, column leaching and heap leaching on different scales shows that bacterial leaching rate is more than 80% when the inoculums size of bacteria is 10～20%, inoculation many times and the leaching pH is 1．5～2．0．The investigation of the bacteria leaching process shows that zinc leaching from zinc sulphide ore is direct effect of bacteria and the effect of Fe³⁺ is not obvious. The low-grade zinc oxidized ore can be leached effectively by method of heap leaching. When the period of heap leaching is more than six months, the zinc leaching rate can be over 90%.Zinc cannot extract directly from the leaching liquor of low-grade zinc minerals. Iron will be extracted with direct extraction, resulting in the complicated regeneration technology of extractant and mass-produced waste acid. The appropriate process is that zinc is extracted when the leaching liquor oxidized and iron removed. In this process, the removal rate of iron is above 99% and the iron concentration in the liquor under 2mg/L under the condition: 1．2 times of the stoichiometric amounts of MnO₂ added, room temperature, 2～3 hours reaction time, limestone used for neutralize reagent added and the terminus pH of neutralization 5．1～5．3．The loss rate of zinc in this process is under2．5%.The liquor after iron removed is extracted by single P204．The appropriate extracting organic phase composition is 40% P204 and 60% kerosene. During the extraction, the free acid will not be neutralized and organic phase will not be saponification. The extraction rate of zinc is up to 85～88% for 10～15g/L zinc in liquor under the extracting condition: room temperature, 5～10 extraction stages, 5 minutes mixture time, 1～1．5:1 phase ratio A/O, and terminus pH about 1．0．The extracting rate of zinc is not increased obviously with the increasement of extracting stage and organic phase (with phase ratio O/A increasement), and it is enhanced the zinc extraction as the extraction temperature increases.In the extracting process, all impurity except iron cannot be extracted. A few extractions of Co and Ni have no effect on electrolytic deposit process of zinc and can be removed in the electrolytic refining.Zinc with laden organic phase can be reverse-extracted using electrolyte scrap directly. The results indicated 97～99% zinc can be reverse-extracted by electrodeposition waste solution which contains sulfuric acid 135～150g/l under the condition: 3～5 reverse-extraction stages, 3～3．5:1 phase ratio (A/O) and 5minutes mixture time. The organic phase after reverse-extracted contains about 0．3g/l zinc ion, the impurities except iron do not rich in organic phase and come into reverse-extracting liquor. The concentration of zinc ion in the liquor will increase by over 40g/l, up to 88～95g/l and the concentration of free acid will be up to 70～75g/l when zinc concentration in the laden organic phase is over 12g/l.Organic phase can be separated easily from aqueous phase, which separate and defecate rapidly. Emulsification occurs easily when P204 concentration in the organic phase is over 40%. Solubility of organic phase in the liquor increases with the increasement of temperature, and reduces with the increasement of acidity.Organic phase dissolved in the reverse-extracting liquor has an obvious effect on electrodeposition process, which results in cathode burned and surface blacked, zinc precipitated in the form of a powdery state, the leaky cathode surface, the electrodeposition cycle of cathode reduced obviously less than 14 hours, and zinc electrodeposition process not operated normally in the ultimate. The effect of organic phase in reverse-extracting liquor on electrodeposition can be avoided completely with the adsorbing of activated carbon. There is basically no effect of organic phase on zinc electrodeposition process with activated carbon of 40～80 g/l dosage and a size distribution of +40 meshes.Reverse-extracting liquor removed organic phase mixing with electrodeposition scrap can product 1# cathode zinc. The following electrolytic condition is elicited from the experiments: 70mm homopolar distance, 500A/m² cathode current density, about 20mg/l isinglass dosage, 24 hours electrodeposition cycle, temperature 40℃, the electrical current efficiency is 89～92%, and consumption of direct current is about 3000 degrees per ton zinc.The main innovation point of this paper is that the wholly hydrometallurgy process of low-grade zinc minerals is investigated. The sulfuric acid heap leaching technique is used in low-grade zinc minerals leaching process. Iron is removed from leaching sulphate liquor by oxidation and neutralization. The sulphate liquor removed iron is extracted by single P204．Free acid is not neutralized in the extraction process. Zinc electrodeposition scrap is reverse-extracted directly. Organic phase is removed by activated carbon.