No-ammonia Precipitation Enrichment Technology And Process Control Of Low Concentration Rare Earth Sulfate Leaching Solution

At present,(NH4)2SO4 leaching in situ and subsequent precipitation using NH4HCO3 are usually applied in the extracting process of ion-adsorption type rare earth ore.In this process,a large amount of ammonia-nitrogen wastewater are generated because of the use of ammonium salts,resulting in serious environmental pollution.In this paper,based on the in situ leaching of magnesium sulfate,the enrichment process of leachate was studied to develop a new process to eliminate or reduce ammonia-nitrogen pollution.The main contents and results are as follows:1?This study used low REs containing sulfate leachate produced from Guangxi ion-adsorption type rare earth with magnesium sulfate to investigate the effect of various precipitants on REs recovery,purity and impurities content of product.In the case of using NH4HCO3 or Na2CO3 as precipitant,the precipitation efficiency of REs reached 95%with a purity of 92%REO,moreover,the precipitate obtained in this process is free of sulfate ions.In the case of using CaO or MgO as precipitant,95%of REs recovery was reached,while the purity of REO in precipitate is as low as 81%.It is found that the main reason of low purity is that it is hard to reduce the high contents of sulfate radical in the filter cake,throuth filtration washing.2.In order to understand the form of sulphur presented as and the removing method of sulphur in the REs precipitation process with CaO and MgO.The chemical analysis and XRD patterns of the precipitates produced from Nd2(SO4)3 with CaO were compared with the ones obtained by Na2C03 precipitation.Experimental results shown that the calcination product obtained from CaO precipitation was Ndd2O2SO4 and Nd2O3 for the precipitation for the Na2CO3 process.Based on the thermogravimetric and infrared analysis,impurity of sulphur presented in a form of Nd2(OH)4SO4·1.H20 in the precipitate produced from CaO precipitation was confirmed.Aging offeed pulp under different conditions and various hydrothermal crystallization treatment of filter cake were investigate to reduce the sulfur content in precipitate,but no significant improvement was obtained.3.Complex precipitation with CaO-Na2CO3 for REs from RE sulfates solutions was adapt here.The precipitated product was tested by XRF and ICP.Detailed studies shown that sulphur content decreases with increasing dosage/concentration of Na2CO3 addition.Once the Na2C03 addition proportion reached 70%and the CaO addition proportion reached 40%,95%REs recovery and 92%REs purity of product was achieved which has meet the purity requirement of Chinese REs product.