Study On Resource Treatment Of Rare Earth Oxalic Precipitation (REOP) Mother Liquor

The rare earth oxalic precipitation（REOP）mother liquor contains a large amount of hydrochloric acid,oxalic acid,a small amount of rare earth elements,as well as organic matter and heavy metal impurities.The hydrochloric acid concentration is about 2.5 mol/L,the oxalic acid concentration is 0.2 mol/L,and the rare earth element concentration is below 0.1 g/L.The treatment methods for hydrochloric acid,oxalic acid,and rare earth elements in the rare earth industry’s oxalic precipitation mother liquor mainly include end-of-pipe treatment to achieve standard discharge and waste resource recycling.However,these methods have the problems of being unable to achieve resource recycling and causing serious environmental pollution.This project explored the use of ion exchange resins/chelating agents to selectively recover residual rare earth elements in the oxalic precipitation mother liquor,and the use of ion exchange membranes to efficiently separated hydrochloric acid and oxalic acid in the mother liquor.It also studied the membrane fouling phenomenon and wastewater pretreatment to prevent membrane fouling in the electro-membrane system when treating actual REOP mother liquid,ultimately achieving the goal of recycling rare earth elements and separating oxalic acid and hydrochloric acid in the mother liquor.The research results of this project can provide new ideas for the resource utilization of REOP mother liquor.The main research progress achieved is as follows:（1）Comparison of the treatment effects of different chelating agents on rare earth ions in simulated REOP mother liquor.It was found that the type,amount,molecular weight,chelation time,solution p H,and other factors have a significant effect on the removal efficiency of rare earth elements.The results showed that aminotri（methylene phosphonic acid）（ATMP）had the best removal effect on rare earth elements in the simulated solution,with removal rates of 75%,90%,and 55%for Dy³⁺,Yb³⁺,and La³⁺,respectively.（2）Investigation of the recovery effect of chelating resin on Y³⁺in actual oxalic precipitation mother liquor.CH-93 resin was found to achieve the best removal rate of 100%on Y³⁺in the yttrium oxalic precipitation mother liquor,and the desorption and recycling effects were good.At the same time,it was found that this resin also had a significant effect on removing dissolved organic matter（DOM）in wastewater.（3）Exploration of the separation effect of hydrochloric acid and oxalic acid in simulated oxalic precipitation mother liquor by electrodialysis.The effects of anion exchange membrane materials,the molar ratio of oxalic acid to hydrochloric acid,applied voltage,and other factors on the separation effect of hydrochloric acid and oxalic acid were studied.It was found that the separation effect of using a selectively permeable anion exchange membrane was better than that of a homogeneous anion membrane and an alloy anion membrane.When separating actual oxalic precipitation mother liquor wastewater in a constant pressure mode,the purity of hydrochloric acid obtained in the concentrated chamber was greater than 92%.（4）The study investigated the separation effect of hydrochloric acid and oxalic acid in the treatment of actual wastewater from the REOP mother liquor using the electrodialysis process.The membrane fouling phenomenon during the electrodialysis process using selective ion exchange membranes at different constant voltages was examined.The membrane fouling properties are characterized by SEM,EDS,and ATR-FTIR,and the membrane fouling situation is evaluated based on parameters such as unit energy consumption and hydrochloric acid production.Electrodialysis separation experiments were conducted on the REOP mother liquor treated by the CH-93 resin group（R-T group）and the REOP mother liquor untreated by the CH-93 resin group（W-R-T group）.The results show that resin pretreatment can significantly reduce membrane fouling and improve the separation of hydrochloric acid and oxalic acid in the REOP mother liquor.The hydrochloric acid recovery rate of the W-R-T group was increased by 21.01%（12V）,and the unit energy consumption was reduced by 54.30%（12V）.