Study On The Key Technology And Preliminary Design Of Zero Discharge Project For Separation Of Wastewater From Ion Rare Earth Smelting

There are many kinds of ion rare earth elements and complex raw materials,which lead to complex smelting process,long process,and discharge diverse wastewater even with radioactive substances.With the publication and implementation of the related standards,norms and plans of rare earth industry,the government requires the rare earth industry to reduce the discharge of pollutants and improve the recovery and utilization of resources.The recycling of wastewater has become the urgent demand of rare earth smelting enterprises.In order to meet the requirements of national environmental protection and industry policy,a rare earth smelting enterprise of ion type carried out a zero discharge project of production wastewater in its new plant area.After investigation and analysis,the idea of zero discharge process was preliminarily determined.However,to date,two key technologies in zero discharge process,namely,recovery of mother liquor from oxalic acid precipitation and reduction of high salt wastewater,have not been successfully applied.In the present work,the key technology of zero discharge of ion rare earth smelting wastewater was studied in pilot scale,and a feasible zero discharge process was put forward and the preliminary engineering design is carried out based on the pilot test.A pilot scale study on the recovery of mother liquor from oxalic acid precipitation by three-effect evaporation process was conducted.The results showed that the mother liquor of oxalic acid precipitation could reach the goal of zero discharge of wastewater and recover different concentrations of hydrochloric acid and oxalic acid for rare earth smelting process at the same time.The recovered hydrochloric acid and oxalic acid can be reused in rare earth smelting process.The concentration of concentrated hydrochloric acid recovered reached 5.4 mol/L and the amount of concentrated hydrochloric acid recovered was 320L/t.The recovered concentration of dilute hydrochloric acid reached 0.14mol/L and 0.06mol/ L,and the amount of recovered dilute hydrochloric acid reached 279L/t and 328L/t,respectively.The purity of recovered oxalic acid reached 96%,and the amount of recovered oxalic acid was 6.9kg/t.The value of recovery was about ?79.47 /t,and the operating cost was about ?78.15/t.The value of recovery is slightly higher than that of operation cost,but the environmental benefit is significant.The reduction of high salt wastewater by DTRO process was studied in a pilot scale.The results showed that when the operating pressure was 11 MPa,the recovery rate of the wastewater with salt content of 4%,3%,and 2% were 63%,71%,and 79%,,which were concentrated to 2.7,3.4,and 4.8 times,respectively.The process design of DTRO should be designed as two stages in one pass,the maximum operating pressure should be 11 MPa,and the maximum recovery rate should be 79%.Combined with the results of the pilot scale study on recovery of mother liquor from oxalic acid precipitation and reduction of high salt wastewater,the preliminary design of zero discharge engineering was carried out to determine the wastewater of sodium soap and oxalic acid precipitation mother liquor.This paper synthesized the process flow of wastewater treatment,determines the parameters of each technological process,drew up the list of main structures and process equipment,estimated the project investment,and analyzed the operation cost and the economic benefit of resource recovery.