Extraction Recycling Of Acid Produced In The Leaching And Separating Process Of Rare Earths And The Flow Optimization

Waste and residual acids generated during industrial production are the main factors of increasing environmental pollution and raw materials consumption.Because their neutralization needs a large of alkali and forms a lot of salt containing wastewater,the cost of subsequent treatment is high.Therefore,achieving the resource utilization of waste acid and residual acid is an effective method to reduce costs,consumption,and emissions.The extraction method is an effective method for recovering and utilizing acids,but it is necessary to choose extraction agents with excellent extraction and strip performance,determine the extraction and strip conditions for increasing the concentration of recovered acids,optimize the separation flow by coupled with the relevant processes.This article focuses on the problem of waste and residual acid treatment in the process of rare earth leaching and separation.The extraction and strip performance and extraction mechanism of common acids by triisooctylamine(N268),tri-n-octylamine(N235),and tributyl phosphate(TBP)were systematically studied.The results show that N268 and N235 can extract acids in the form of ion association,with N268 having better extraction and backwash stripping abilities than N235.However,TBP has weak extraction ability for hydrochloric acid and sulfuric acid,but can extract oxalic acid and nitric acid through intermolecular hydrogen bonding.Increasing the temperature is beneficial for improving the backwashing effect of the acid loaded organic phase.Based on this,a oxalic acid precipitation method was developed to separate rare earth from aluminum in various rare earth leaching solutions and prepare high concentration of rare earth chloride solution by dissolving the obtained rare earth oxalate with high concentration of hydrochloric acid and promptly extracting the formed oxalic acid with TBP to force the dissolution reaction complete.Subsequently,after the excess hydrochloric acid was extracted with N268,a qualified solution with rare earth chloride content greater than 1.5 mol/L and aluminum content less than 3 ‰ was obtained.Meanwhile the oxalic acid extracted by TBP can be recycled by reacting with rare earth chloride,or rare earth hydroxide,or rare earth carbonate for precipitation of rare earth oxalate.Similarly,oxalic acid in rare earth oxalate precipitation wastewater can be extracted using TBP with O/A ratio of 1:1 by a two stages of countercurrent extraction process,while hydrochloric acid can be extracted using N268 by a four stages of countercurrent extraction.The acid recovery rate exceeds 95%.For the leaching solution of Baotou concentrate by aluminum salt assisted acid decomposition,organic phase of N268 is used to extract excess sulfuric acid from the leaching solution,making it easy to a required p H value for the separation of rare earth from aluminum by N1923.In order to recover boric acid and residual acid from the acid leaching solution of neodymium iron boron calcination material,the extracting properties of boric acid by the solutions of isooctanol,2-ethyl-1,3-hexanediol(EHD)+isooctanol,and isooctanol+isoamyl alcohol were compared.It was found that EHD+isooctanol had the best extraction effect on boric acid and was not affected by the initial p H of the solution.The backwashing effect of ammonia water and sodium hydroxide solution on the loaded boric acid organic phase was better than that of water and lime water.Experiments have shown that using EHD+isooctanol organic phase to extract boric acid can eliminate the influence of boric acid on subsequent hydrolysis for iron and aluminum removal.After extraction,separation,and precipitation of rare earth elements,the impurity content of ammonium chloride wastewater obtained is very low,which can meet the requirements of direct evaporation crystallization and obtain high-quality ammonium chloride,enabling the wastewater to be fully recovered and reused.