Hebei Messi Biology Co., Ltd. stated that it used active magnesium oxide precipitation method to separate cobalt and nickel from magnesium from sulfuric acid solution, and then used P507-N235 non-saponification extraction system to separate cobalt and nickel. The factors affecting the separation of cobalt and nickel from magnesium and the extraction separation of cobalt and nickel, as well as the cobalt and nickel precipitation mechanism, magnesium oxide recovery and water phase loss during the extraction process were studied. The extraction and separation effects of cobalt and nickel by P507-N235 system and sodium saponification P507 system were compared.
The main research contents and results of the full text are as follows:
(1) The sodium saponification P507 system has a better phase separation effect than O/A=2:1, but cobalt and nickel are almost completely extracted, making it difficult to separate cobalt and nickel; when O/A decreases from 2:1 to 1:30, the extraction rates of cobalt and nickel both decrease, but the nickel extraction rate decreases more significantly, so β(Co/Ni) gradually increases; under the condition of O/A≤1:1, the extraction phase separation time is longer, all greater than 1h. Compared with the case of O/A of 1:30, β(Co/Ni) is 119.6, which can achieve the preliminary separation of cobalt and nickel; the loaded organic phase is washed with 0.05 mol/L sulfuric acid at O/A of 3:1 for three stages, and the co-extracted nickel can be completely washed off; the washed loaded organic phase is stripped with 0.25 mol/L sulfuric acid at O/A of 2:1 for two stages, and the cobalt can be stripped completely. The extraction rates of cobalt and nickel both decrease with the increase of Mg2+ concentration in the feed solution. The sodium saponification P507 system separates cobalt, nickel and magnesium. The extraction rates of cobalt, nickel and magnesium decrease with the decrease of O/A, but the extraction rates of nickel and magnesium decrease by a large margin, so β(Co/Ni) and β(Co/Mg) gradually increase.
(2) The P507-N235 system extracts and separates cobalt and nickel. The extraction rate of cobalt increases with the increase of the pH value of the feed solution, but the increase gradually decreases, while the increase of nickel is small. With the increase of O/A, the extraction rates of cobalt and nickel gradually increased, but the increase of cobalt extraction rate was greater than that of nickel extraction rate; the equilibrium pH value of the aqueous phase first increased with the increase of the pH value of the feed solution and then remained almost unchanged, but did not change with the change of O/A. With the increase of the amount of organic phase P507 (the amount of kerosene decreased accordingly), the cobalt extraction first increased gradually and then decreased, and the nickel extraction rate increased slowly; the extraction phase separation time was prolonged with the increase of P507 dosage and O/A, and first prolonged and then shortened with the increase of N235 dosage. In the sulfuric acid medium, N235 did not participate in the extraction reaction of Co and Ni, but could extract the H+ released by P507 and the original H+ in the sulfuric acid medium, so N235 could be used to adjust the acidity of the aqueous phase. The loss of the aqueous phase in the extraction process increased with the decrease of the initial pH value of the feed solution and the increase of O/A and N235 dosage, but the influence of N235 dosage was relatively large. The suitable conditions for the separation of cobalt and nickel in the P507-N235 system are: the initial pH of the feed liquid phase is 4.6, the phase O/A is 2:1, the organic phase composition is P507 30%, N235 15%, and sulfonated kerosene is 55%. The cobalt extraction rate of the first-stage extraction is 41.5%, the nickel is 1.6%, and the separation coefficient β (Co/Ni) is 42.53. After five-stage cross-current extraction, the cobalt extraction rate reaches 97.1%, and the nickel is 15.9%. Water is used as the washing solvent for the loaded organic phase, the O/A is 4:1, and the washing time is 2min. After two-stage washing, the nickel can be completely washed, and the loss rate of Co is 2.45%; 0.05mol/L sulfuric acid is used as the stripping solution for the loaded organic phase, the O/A is 2:1, and the stripping time is 5min. After two-stage stripping, the cobalt stripping rate is close to 100%. The E-pH curve of the P507-N235 system is different from that of the saponified P507 system. The cobalt extraction rate of the P507-N235 system is high in the equilibrium pH range of 4-4.8, but the cobalt extraction rate no longer increases but decreases after the equilibrium pH is 4.6. The pH range with high nickel extraction rate is above pH 4.9. The cobalt extraction rate and cobalt-nickel separation coefficient β (Co/Ni) of the P507-N235 system are lower than those of the saponified P507 system, but the extraction phase separation time is shorter, and the acidity required for washing and stripping is lower. Magnesium has a significant effect on the separation of cobalt and nickel in the P507-N235 system. In order to avoid the influence of Mg2+ on the separation of cobalt and nickel, the Mg2+ concentration in the feed solution should be controlled to be no more than 0.1g/L.
(3) The magnesium oxide precipitation method recovers cobalt and nickel from sulfuric acid solutions containing cobalt, nickel and magnesium. The equilibrium pH, magnesium oxide dosage and temperature are the main influencing factors. Increasing the temperature and reducing the magnesium oxide dosage can reduce the magnesium content in the precipitated product. The suitable conditions for separation of cobalt, nickel and magnesium are: magnesium oxide dosage nMgO: (nNi + nCo) is 2.0, reaction time is 2h, reaction temperature is 60℃, stirring speed is 300rpm, under which the cobalt precipitation rate is 99.5%, nickel precipitation rate is 97.2%, magnesium precipitation rate is 0.2%, and the equilibrium pH of the solution after the reaction is 8.9.
(4) The process of recovering cobalt and nickel by magnesium oxide precipitation may involve two types of reactions, namely, the reaction of magnesium oxide with hydrogen ions in the solution and the hydrolysis reaction of metal ions; the higher the equilibrium pH (the more magnesium oxide dosage), the more magnesium oxide is entrained in the precipitation product. The cobalt and nickel precipitate can be dissolved with 0.05mol/L sulfuric acid, and the pH value of the resulting solution is 4.7, and the metal ion content is: Co0.11g/L, Ni0.99g/L, Mg5.2mg/L. The sulfuric acid leaching solution of the cobalt-nickel precipitation product can be extracted and separated from cobalt and nickel using the P507-N235 system (composition P507 30%, N235 15%, sulfonated kerosene 55%), and the separation effect is the same as that of the cobalt-nickel solution without magnesium.
Therefore, the magnesium oxide precipitation method and the P507-N235 system can be used to separate cobalt, nickel and magnesium from the sulfuric acid solution. The process is pollution-free, with less loss of cobalt and nickel, no consumption of alkali solution and no wastewater discharge.