| Cobalt,nickel and magnesium often coexist in the sulphate leach liquor of nickel oxide ore.Saponified P507 is often used to separate cobalt and nickel,which has disadvantages of introducing impurities ions,long process flow and discharging wastewater.In this paper,the sulphate solutions containing cobalt,nickel and magnesium were treated to separate cobalt,nickel from magnesium with magnesium oxide precipitation method firstly,then the cobalt-nickel precipitation products were dissolved by sulphuric acid into the solution,then the solution were treated to separate cobalt and nickel using P507-N235 system.Therefore,the influences of the precipitation of cobalt,nickel and magnesium,and extraction separation of cobalt and nickel,the precipitation mechanism of cobalt and nickel,magnesium oxide recycling and the aqueous phase loss in extraction process were studied.The separation abilities of cobalt and nickel in P507-N235 system and Na-saponified P507 system were also compared.The main contents and results are as follows:(1)In the Na-saponified P507 system,the effect of phase disengagement was better at O/A ratio of 2:1,but cobalt and nickel were almost completely extracted and could not be separated.The extraction percentages of cobalt and nickel decreased while that of nickel decreased significantly with decreasing O/A ratio from 2:1 to 10:1,leading to the increase of the separation factor(β(co/Ni)).The time of phase disengagement was very long and exceeded 1h at O/A ratios≤1:1.The separation factor of cobalt to nickel was 119.6 at O/A ratio of 2:1,which the separation of cobalt and nickel could be achieved in this condition.The co-extracted nickel in the loaded organic phase was completely scrubbed via 3 stages of scrubbing with 0.05mol/L sulfuric acid solution at O/A ratio of 3:1.The loaded organic phase after scrubbing was stripped with 0.25mol/L sulfuric acid solution at O/A ratio of 2:1,and cobalt could be completely stripped via 2 stages of stripping.The extraction percentages of cobalt and nickel decreased with increasing Mg2+concentration in the feed solution.The extraction percentages of cobalt,nickel and magnesium decreased with decreasing O/A ratio,but that of nickel and magnesium decreased significantly so that β(Co/Ni)and β(Co/Mg)gradually increased.(2)In P507-N235 system,the extraction percentages of cobalt increased with increasing feed solution pH but the increasing extent gradually decreases,while that of nickel increases slowly.The extraction percentages of cobalt and nickel gradually increased with increasing O/A ratio and the increasing extent for cobalt was much higher compared to nickel.The equilibrium pH of the aqueous phase increased firstly with increasing the feed solution pH and then nearly kept unchanged,but did not vary with the change of O/A ratio.The extraction percentages of cobalt gradually increased and then decreased while that of Ni increased slightly with increasing vol.%P507(the vol.%sulfonated kerosene decreases accordingly).The time of phase disengagement increased with increasing vol.%P507 and O/A ratio,and that firstly increases and then decreases with increasing vol.%N235.In sulfate media,N235 does not participate in the extraction of Co or Ni,but extracts the H+ released from P507 and the H+ in the initial sulfate solution,and thus can adjust the acidity of the aqueous phase.The aqueous phase loss increased with decreasing the initial feed solution pH,and increasing O/A ratio and vol.%N235,but the influence of vol.%N235 was more obvious.The appropriate conditions for separating cobalt and nickel using P507-N235 system are as follows:the initial feed solution pH is 4.6,O/A ratio is 2:1,the composition of the organic phase is 30vol.%P507,15vol.%N235 and 55vol.%sulfonated kerosene.The extraction percentages of cobalt is 41.5%and that of nickel is 1.6%via one-stage extraction,and β(co/Ni)is 42.53.Four-stage cross current extraction was carried,which the extraction percentages of cobalt is 97.1%and that of nickel is 15.9%.The co-extracted nickel in the loaded organic phase was completely scrubbed via 2 stages of scrubbing with water at O/A ratio of 4:1 for 2min while the cobalt loss was 2.45%.Then the loaded organic phase after scrubbing was stripped with 0.05mol/L sulfuric acid solution at O/A ratio of 2:1 for 5 min,the stripping percentage of cobalt nearly reached 100%via 2 stages of stripping.The E-pH curve in P507-N235 system is different from the E-pH curve in P507 system.In P507-N235 system,the extraction percentage of Co was relatively high in the equilibrium pH range of 4-4.8,and decreased at pH>4.6,the equilibrium pH should be greater than 4.9 to obtain high extraction percentage of Ni.Compared with Na-saponified P507 system,the P507-N235 system has a lower separation factor(β(Co/Ni))and a lower Co extraction percentage,but has a shorter time of phase disengagement,and lower scrubbing and stripping acidities.In the P507-N235 system,Mg2+ concentration have a significant effect on the separation of cobalt and nickel,and the effect could be negligible when Mg2+ concentration was lower than 0.1g/L.(3)During recovery of cobalt and nickel from sulfate solution containing cobalt,nickel and magnesium using magnesium oxide precipitation method,the equilibrium pH,the amount of MgO and temperature were the main influence factors.Rising the temperature and lowering the amount of MgO were found to decrease the magnesium content of the precipitate.The appropriate conditions for separating cobalt,nickel and magnesium are as follows:the amount of MgO(nMgO:(nNi+nCo))is 2.0,reaction time is 2h,reaction temperature is 60 ℃ and stirring speed is 300rpm.The precipitation rate of cobalt,nickel and magnesium is 99.5%,97.2%and 0.2%,respectively,and the equilibrium pH of solution after reaction is 8.9.(4)The recovery process of cobalt and nickel may involve two types of reactions using magnesium oxide precipitation method,namely the reaction of MgO and H+ in solution,and the hydrolysis reaction of metal ions.The MgO content of the precipitate increased with increasing the equilibrium pH or the amount of MgO.Cobalt-nickel precipitate could be dissolved with 0.05mol/L sulfuric acid solution,and the pH value of the leaching solution was 4.7,and the contents of metal ions of the leaching solution were:Co 0.11g/L,Ni 0.99g/L,Mg 5.2mg/L.The separation effect of cobalt and nickel from the sulfuric acid leaching solution of cobalt-nickel precipitate using P507-N235 system was the same as the results in section(2).Therefore,cobalt,nickel and magnesium can be separated from the sulfuric acid leaching solution of nickel oxide ore using magnesium oxide precipitation method and P507-N235 system.This process has the advantages of no pollution,no loss of cobalt and nickel,no consumption of alkali liquor and no waster water. |
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