Technology And Mechanism Of Recovery Zinc From Zn-Bearing Waste Stream By Solvent Extraction

With the increase of the emission of Zn-bearing waste streams, the loss of Zinc causes great waste of resource . Therefore, recovery of Zinc from Zn-bearing waste streams is of great importance to promoting comprehensive utilization of secondary resources. Among the methods for Zinc recovery, solvent extraction not only has the advantages of high balancing speed, good separation effect, large capacity, high metal recovery, low reagent consumption, simple device and easily achievable auto control, but also can effectively separate impurities, especially for Fe²⁺ and Cl^-, which strongly affect the following electrowinning. In this paper, aiming at processing industrial waste streams with Zinc of 30-40g/L and multiple impurities, application of solvent extraction is systematically studied to recover Zinc and remove impurities. Meanwhile, the mechanism of solvent extraction of Zinc is examined.The results of Zinc extraction showed that Zinc was extracted by using P204 as Zinc extractant and sulfonated kerosene as diluent. The extraction rate was increased by 20% by adding a neutralizes With a certain amount of neutralizer, the extraction rate increases as extractant concentration of increases or phase radio O/A increase. The extraction rate of Zinc reaches above 99.6% in a single-stage under the condition of 30% for extractant concentration, 20g/L for neutralizer amount, 20 minutes for extraction time, 1000rpm for agitation speed, and 3 minutes demixing time. The impurity ions such as Cd²⁺, Mn²⁺ and Cu²⁺ have little effect on the extraction of Zn , but Fe has a little effect, which can be amended by increase extractant concentration or phase ratio O/A. For Cl^-, no noticeable effect was found under low concentration (<500mg/L), but when it's concentration reaches 1000mg/L,a certain decreases of Zinc extraction rate turned up, and, when it's concentration was over 1500mg/L, the decrease got sharper.The results of strip showed that Zinc solutions was obtained with zinc concentrations over 150g/L after five-staged strips using 7.6% sulfur solution, under the condition of phase ratio O/A 60:40, agitation speed 1000rpm, strip time 20 minutes. Moreover, the impurities were effectively removed with the relative removal rate of 99.9% for Fe²⁺and Cl^-, and 93% to 97% for others. Consequently, effectively separartion of zinc from impurities was accomplished by solvent extraction and high concentration Zinc solutions with low impurities constant was obtained, which is favorable for the following electrowinning.The results of extraction mechanism showed that saturation capacity of zinc increases with the extractant concentration. Linear relations between saturation capacity of zinc and P204 concentration were established. With addition of neutralizer, Zinc extraction rate increases, and saturation capacity of zinc in organic solutions keeps constant. There are three complex compounds in the pregnant extractant solutions, namely ZnA₂, ZnA₂·HA and ZnA₂·2HA. The reactions are as follows:The occurrence of emulsification is related to such factors as P204 concentration, content of solid particulate, Zn²⁺ concentration. Decrease of interfacial tension was brought about by the formation of Zn-extractant complex. Hydrolization and structural change of P204 was resulted from neutralizer. Formation of insoluble Zinc compounds turned up to be the third phase inducement of emulsification. Emulsification compounds were mostly made up of Zinc complex compounds and deposit of Zinc compounds.