Enrichment Of Low Concentration Rare Earth And Removal Of Ca²⁺ And Mg²⁺ In Rare Earth Industrial Wastewater

Rare earth?RE?is China's strategic resource.In the process of rare earth mining and smelting,a large amount of low-concentration RE solution will be produced.If it is not effective recovery,it will not only cause waste of rare earth resources,but also cause environmental pollution.In addition,in the process of rare earth smelting and separation,the process of saponification of extractants will also produce a large amount of ammonia nitrogen wastewater,which contains high concentration of Ca²⁺and Mg²⁺.Ca²⁺and Mg²⁺are easily scaled when using mechanical vapor recompression?MVR?technology to treat ammonia-nitrogen wastewater,resulting in reduced equipment handling capacity and increased equipment operating and maintenance costs.In view of the above problems,this dissertation proposed an extraction-precipitation strategy and synthesized novel phenoxycarboxylic acid extract-precipitants including BPAA,BPBA and BZAA to achieve the enrichment of concentrated rare earth in wastewater and the removal of calcium and magnesium ions in ammonia-nitrogen wastewater.This dissertation draws the following conclusions:?1?The synthesized BPAA was used to enrich low concentration rare earth elements?REEs?from RE industrial wastewater.The RE could be completely precipitated in 5 minutes,the formed precipitates sizes of BPAA-REEs were much larger than the other precipitants?such as oxalic acid,NH₄HCO₃,CaO and MgO?,the formed precipitates were easily separated from water,and BPAA had a higher loading capacity than the other extract-precipitants?BPBA and BZAA?synthesized.The REEs were enriched from simulated industrial wastewater containing the RE concentration of159 mg/L using BPAA.The precipitation efficiency of RE was 97.3%,and the RE concentration in the raffinate was less than 5 mg/L.After stripping the RE enrichment solution?30.0 g/L and 6.54g/L?could be obtained,the total recovery was 93.9%.The solubility of BPAA in the raffinate was less than 50 mg/L,and the COD value in the raffinate was less than 45 mg/L.The novel extraction precipitation method also shown its application prospects in non-ferrous metal hydrometallurgy,secondary resource recovery,thorium-containing radioactive waste treatment and heavy metal pollution treatment.?2?In this dissertation,a softening process for extracting-precipitating calcium and magnesium ions using H₂IPOAA had also been developed.The precipitated particles had a size of 30?m could be formed,which was larger than the precipitate formed by H₂C₂O₄,Na₂C₂O₄ and Na₂CO₃,and was easy to solid-liquid separation.The effect factors,i.e.,equilibrium time,pH value of aqueous phase and saponification degree were investigated.The extraction mechanism was proposed to be cation exchange.With a saponification degree of 85%,H₂IPOAA was successfully used for the precipitation of Ca²⁺and Mg²⁺from ammonia nitrogen wastewater within 10 minutes and the precipitation efficiency of Ca²⁺and Mg²⁺could reach 84%and 91%,respectively.The concentrations of Ca²⁺and Mg²⁺in the raffinate were 84 mg/L and 291 mg/L,respectively,which meets the standards for MVR treatment of ammonia-nitrogen wastewater.In addition,H₂IPOAA could be reused with minimal loss.The recycling performance of H₂IPOAA helps reduce costs and reduce pollution.