Application Of Synergistic Extraction And Separation Of Zinc From Ammonia - Ammonium Sulfate Solution

As the continuous exploiting and utilization of zinc resources, zinc sulfide resource with high quality is drying up, and exploiting and utilization of non-traditional zinc resources, such as zinc-bearing low grade oxidized ores, have greatly attracted the attention of people. To guarantee the effective supply of zinc resources and the sustainable development of zinc industry, it is an important approach that exploits the new process to efficiently recovery zinc from zinc-bearing low grade oxidized ores for relieving the intense resource pressure. "Ammonia leaching-solvent extraction-electro winning" process is a new method for efficiently treating low-grade zinc oxide ores containing high basic gangues, and solvent extraction is the key link of this process.In this paper, The solvent extraction of zinc from ammoniacal/ammonium sulfate solutions using a mixture of 0-diketone (Mextra154-100), and hydroxyoxime (Mextral 84H) has been investigated, and the synergistic extraction mechanism of zinc has been elaborated. Furthermore, the performances of extraction systems, Mextral54-100 and Mextra154-100+TRPO, on extraction and separation of zinc and nickel from ammoniacal/ammonium sulfate solutions were investigated. The optimal process of zinc-nickel separation was determined, and the separation and recycling of zinc and nickel were achieved. The main research contents and conclusions are as follows:(1) Mextra154-100+Mextra184H extraction system shows evident synergistic effects on zinc extraction in ammoniacal/ammonium sulfate solutions. The Zn(Ⅱ) could react with Mextra154-100 and Mextra184H as a stoichiometric ratio of 1:1:1 to form the more stable ZnAR synergistic adduct. For both single and synergistic systems, as aqueous pH rises, the extraction percentage of zinc increases dramatically and reaches a maximum value at about pHini 7.2, but then decreases rapidly at higher pH. Because the keto-enol tautomerism of P-diketone can be promoted in alkaline solution, it is helpful to extract zinc by increasing pH. As aqueous pH rises, the average number of ammonia ligands per zinc ion increases constantly and the extraction activity of zinc decrease gradually, which lead to the decrease of extraction percentage of zinc at pHini>7.2.(2) The increase of total ammonia concentration and temperature makes a negative impact on zinc extraction. The decrease of extraction percentage of zinc can be elucidated with the increase of free ammonia concentration and the vast formation of zinc amine complexes with the increase of the total ammonia concentration. The extraction reactions proceed exothermically, therefore, the increase of temperature suppresses the extraction of zinc. The FT-IR spectra of zinc synergistic adducts confirms that the keto-enol tautomerization of α-diketone takes place and the enol configuration participates in the formation of coordination bond. Furthermore, FT-IR studies confirm that the ammonia molecules can be co-extracted into organic phase.(3) Two extraction systems, Mextral54-100 and Mextra154-100+TRPO, were used to research the extraction and separation of zinc and nickel from ammoniacal/ammonium sulfate solutions. As pHini rises, the extraction percentage of zinc and nickel increases originally and then decreases later, and the extraction of zinc is preferential to that of nickel. The mixture of Mextra154-100 and TRPO shows evident synergistic effects on zinc extraction. The separation method of zinc and nickel is that extract nickel at pHini; 9.0 with Mextral54-100 single system firstly and then extract zinc at pHini 7.2 with Mextral54-100+TRPO synergistic system.(4) In regard to extraction of nickel, the extraction ratio of nickel is more than 99.0% with four extraction stages under the conditions of 0.5 mol/L Mextral54-100 extraction system,0.05 mol/L zinc concentration,0.05 mol/L nickel concentration,3 mol/L total ammonia concentration,25℃, pHini 9.0 and phase ratio (O/A) 1:1, while the extraction ratio of zinc is less than 6% under the same conditions. For loaded organic phase containing 2.01 g/L nickel, the stripping ratio of nickel is more than 99.9% with two stripping stages. For extraction of zinc, the extraction ratio of zinc is more than 99.5% with two extraction stages under the conditions of 0.4 mol/L Mextral54-100+0.05 mol/L TRPO extraction system,0.05 mol/L zinc concentration,3 mol/L total ammonia concentration,25℃, pHini 7.2, and phase ratio (O/A) 1:1. For loaded organic phase containing 3.12 g/L zinc, the stripping ratio of zinc is more than 99.9% with two stripping stages. Through the above process, the effective separation and recycling of zinc and nickel were achieved.