| In the process of rare earth production, large amount of sulfuric acid, hydrochloric acid and ammonia (or salvolatile) are consumed, However, there are large amount of sulfuric acid, hydrochloric acid or ammoniacal nitrogen in solutions or discharged waste water which need to be treated. At present, traditional means namely neutralization is usually used to treat these acids in order to meet production requirements, which means great waste of acid and alkali, As to high concentration of amrnoniacal nitrogen, since there is no economic and feasible means yet, it is usually discharged directly without any treatment, which has great effects on the surrounding environment. And so, reuse of these sulfuric acid, hydrochloric acid and ammoniacal nitrogen in the production process will evidently decrease production cost, which shows good economic effects, furthermore, it will decrease salts and even waste water discharge, which shows good social effects. The idea of application of modern and new-style membrane separation techniques-vacuum membrane distillation(VMD) and diffusion dialysis(DD) in the process of rare earth production is proposed for the first time in this paper, the purpose is to achieve resource recovery and improved environment. Recovery by membrane separation techniques from the following three typical solutions-HC1-REC13-H2CK H2SO4-RE2(SO4)3-H2O and NH4C1 or (NH4)2SO4 -H2O were detailed studied.Hydrochloric acid recovery from rare earth chloride solutions by VMD is studied for the first time, it can achieve recovering high concentration of hydrochloric acid, and concentrating low concentration of rare earth at the same time.First, the equilibrium between gas-liquid phases in the system of HC1-REC13-H2O was analyzed based on the calculation of H2O activity and HC1 activity coefficient, the results indicate that salt effect of REC13 is very beneficial to hydrochloric acid recovery. And then, the influence of temperature, A1C13 concentration and downstream pressure on HC1 separation was studied for A1C13-HC1-H2O system the stimulation of rare earth chloride system, the experimental results agree with the thermodynamic analysis results satisfactorily. The VMD experiments whose feed solutions were put up according to the actual constitute of one rare earth plant's middle and heavy rare earth stripping solutions were carried out, and the experimental results indicate that, hydrochloric acid recovery ratio can be as high as 80% if only the concentrating multiple of REC13 is up to 3, furthermore, pure acid can be obtained in the permeate side since rejection ratio of rare earth is as high as 98%.There is no study relating to azeotropic mixture separation by continual MD up to now, Concentrating rare earth chloride solutions by continual VMD is studied for the first time in this paper. The experimental results show that, if only maintaining REC13 concentration in circulating solutions, hydrochloric acid concentration will keep invariable although REC13 and HC1 concentration in feed solutions change, Increasing REC13 concentration inABSTRACTfeed solutions increases treating capacity per membrane, however, change of HC1 concentration within a certain range shows no evident influence on treating capacity per membrane. Increasing REC concentration in circulating solutions decreases treating capacity per membrane, and HC1 concentration decreases at the same time, which means hydrochloric acid recovery ratio increases. Lastly, mass balance of continual VMD was calculated and the process was mathematically stimulated according to the experimental results. As to given feed solutions and concentrating multiple of RECla, treating capacity per membrane, hydrochloric acid concentration in concentrated solutions, recovery ratio of hydrochloric acid and hydrochloric acid concentration in recovered solutions can be obtained through the mathematical model.Sulfuric acid recovery from rare earth sulfate solutions by VMD-DD process is studied in this paper, namely concentrating low concentration of rare earth sulfate sol...
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