Study On Recovery Of Rare Earth From Precipitated Slag In Rare Earth Plant Wastewater Tank

All kinds of waste water produced in the process of rare earth hydrometallurgy are usually collected in the waste water pool,with the production process,the bottom of the waste pool will deposit a large amount of solid slag,which contains a large number of rare earth and calcium,iron,aluminum,and other impurities.When the content of calcium,iron,aluminum,and other impurities is high,it tends to produce emulsion and be difficult in phase separation.In order to achieve the requirement of rare earth in the recycling of waste water tank,it needs to removl impurities and minimize the loss of rare earth at the same time.In this paper,the waste water sludge in a rare earth plant of Gannan is taken as the research object,and a new method for the removal of waste water from the waste water tank by the combination of ammonium sulfate and oxalic acid was studied.The main contents of this study are as follows:?1?The leaching process of rare earth in the product of precipitation slag roasting by hydrochloric acid was studied,First,the method of Roasting Pretreatment to precipitate slag was adopted.the phase and morphology of the precipitates before and after baking was characterized combined with XRD,SEM and other means of detection.Roasting can lead to the precipitate slag to oxidizing material easily leaching.The technological conditions for the extraction of rare earth from the hydrochloric acid leaching were studied,under optimum conditions,the best leachability for rare earth is 99.18% at a temperature of 80? and a liquid and solid ratio of 20:1,5mol/L hydrochloric acid and stirring speed of 400 r/min.The results showed that the hydrochloric acid could be used to extract the rare earth in the sludge of the waste water tank of the rare earth plant.?2?The effects of different pH values and different concentration of oxalic acid on the equilibrium of the system were explored.The analyses of thermodynamics indicates that the end value of pH should be strictly controlled by oxalic acid precipitation to ensure the precipitation rate of rare earth and the purity of the precipitation product,the best pH value of the rare earth oxalate precipitates in 1.5-2,and a moderate increase in the concentration of oxalic acid is beneficial to the precipitation of rare earth.?3?Excess of?NH₄?₂SO₄ and calcium can form soluble complexes?NH₄?₂[Ca?SO₄?₂] to achieve the purpose of removing calcium was explored.The effects of different initial calciumconcentration,ammonium sulfate concentration,reaction temperature,stirring time,initial pH and other factors on the solubility of calcium in calcium chloride solution were studied.Results indicated that adding the right amount of ammonium sulfate before adding oxalic acid,The calcium can be entered into the solution but not be precipitated by oxalic acid.It provided a strong foundation for the separation of RE3+? Ca²⁺ from oxalic acid leaching solution in oxalic acid system.?4?The process of removing calcium,iron and aluminium combined ammonium sulfate and oxalic acid was studied.RE are well precipitated and calcium ? iron and aluminium removal effect is the best under the conditions of?NH₄?₂SO₄ concentration of 80 g·L^-1,the ratio of oxalic acid of 1.2,and no stiring,temperature of 80?,pH of 2.0,the initial concentration of 20 g·L^-1,he precipitation rate of RE is as high as 99.02%,and the removal rate of calcium reachs 99.35%,the removal rate of iron and aluminium is more than 99%.The results show that the combined process of ammonium sulfate and oxalic acid can realize the recovery of rare earth and the removal of impurities,the content of calcium?iron?and aluminum impurities in rare earth deposits can be return to the extraction main system to meet the requirements in the process of smelting.