Solvent Extraction As Purification Measurement Of Cobalt Electrolyte

Solvent extraction of major impurities such as copper,lead in cobalt electrolyte with N₂₃₅(namely TOA or Alamin336,saturated with hydrochloride in advance)when copper is reduced from Cu(â…¡)to Cu(â… )is investigated.Experiment results shows copper in form of Cu(â… )is easier to be extracted after being reduced by Na₂SO₃,which can promise a intensive separation of copper from cobalt electrolyte.Cobalt co-extraction is also considered and relevant result reveals appreciate low extraction rate at proper organic phase composition and chloride concentration.Ideal organic phase system which insures the best Co/Cu separation consist of 20%N₂₃₅,10%isooctyl alcohol as modifier and 70%kerosene as diluent.This particular organic phase composition also makes it easy for cobalt to be recovered from loaded organic phase by water striping.Thermodynamic data calculated explain why Cu(â… ) has advantage to be extracted.Test shows extraction enthalpy variationâ–³H for Cu(â… )is 15.89 kJ·mol^-1and for Cu(â…¡)is 10.62 kJ·mol^-1,which indicate both extraction processes are endothermic.Gibbs energy variationâ–³G for Cu(â… )extraction is-4.04 kJ·mol^-1and for Cu(â…¡)extraction is -0.49 kJ·mol^-1at the same condition,which means the former is predominate in extraction and it is quite feasible to reduce copper into Cu(â… )in advance before extracting operation with N₂₃₅.A series of experiments were performed to compare the two forms of copper extraction using N₂₃₅under single varying factor.Extractant concentration test shows with increasing of N₂₃₅concentration(volume/volume),when extracting reactions get to equilibrium,copper concentration in aqueous decrease,another notable fact is N₂₃₅extraction of Cu(â… )is always higher than Cu(â…¡)with the increase of N₂₃₅concentration.Then comparison experiment of Cu(â… )and Cu(â…¡)extraction with increase of chloride in cobalt electrolyte at optimize organic composition obtained results similar to the extractant concentration test.Initial copper concentration ranging from 0.1 g/L to 0.6 g/L were carried out and result shows when copper concentration decrease,the difference between Cu(â… )and Cu(â…¡)extraction shrink.A simulate continuous countercurrent extraction is applied to examine how many grades it needs to obtain an required copper removal that can meets cobalt purity of 99.98%.Test result shows after first contact in aqueous phase 0.04g/L copper is left,and relevant copper extraction is 96%,but aftermath low copper concentration makes it difficult to maintain a copper extraction rate.It requires more contact to meet copper concentration below 0.0001 g/L.In striping process,water is applied to recover cobalt selectively which doesn't form a stable complexion,copper and other impurities can hardly be stripped by water since their anionic chloride complexions are more stable.A basic aqueous solution containing ammonium chloride plus ammonia then is applied to counter-extract copper and other impurities such as lead,zinc and cadmium.Total cobalt recovery rate is satisfactory.In the end,blank organic phase is saturated with hydrochloride and applied in the next purification process,after being recycled for ten times,it's loading capacity isn't affected significantly.