| The consist of Baotou mixed rare earth ores is complex.It's mainly tratement by third-generation acid method at now,which is using sulfuric acid under high temperature to decompose,water leaching,impurity removing,and transformation by using ammonium bicarbonate precipitation and hydrochloric acid to dissolve,then to extraction and separation by P507 or directly extraction and separation by P507/P204.However,a large of ammonia nitrogen wastewater is produced in the process of ammonium bicarbonate precipitation transformation,which is high cost to recycle and difficult to discharge meet standard.This one of the factors to restrict the developing green cleaning product.A new green precipitator Mg(HCO3)2 was used to precipitate rare earth sulfate solution in this paper,this mothd would be eliminate ammonia nitrogen wastewater pollution,and coupled with a process of Mg(HCO3)2 produce to reach magnesium cycle.The green and friendly concept of rare earth smelting and separation has been developed.In this paper,the basic research on the precipitation crystallization of rare earths carbonate(La/Ce/Pr/Nd)in sulfuric acid system was carried out.On these basis,the preparation process of crystalline mixed rare earth carbonate was explored,and the fine product required by GB/T 16479-2008 was finally obtained.The main contents are as follows:(1)Study on the behavior of SO42-in the preparation of rare earth carbonate.Combing Fraction-pH diagram of single rare earth carbonate(La/Ce/Pr/Nd)system,The effect of feeding method on the behavior of SO42-in rare earth carbonate in sulfuric acid system was investigated.The results showed that the content of SO42-in the precipitates obtained by the lanthanum/cerium system with forward feeding method was more than 16%among the normalized components,and it was in the form of double salt La2(CO3)2.15(SO4)0.85.4H2O and Ce2(CO3)2.15(SO4)0.85.3H2O respectively.(2)Study on precipitation and crystallization process of rare earth carbonate.The effects of reaction temperature,aging time and stirring strength on the precipitation and crystallization of single rare earth carbonate were investigated in a parallel feeding method.The results show that the reaction temperature had a significant effect on lanthanum/cerium/neodymium carbonate.When lanthanum carbonate in above 50? by needle formed omnidirectional flake;Cerium carbonate in less than 50? when cross shaped crystal precipitation,and moisture content is low.Above 50? appered plate shaped,and the moisture content has risen to 80%;Neodymium carbonate changes from amorphous to crystalline precipitate as temperature increases.Prolonging aging time is advantage on the crystallization of neodymium carbonate.(3)Preparation of crystalline mixed rare earth carbonates.Combined with the precipitation crystallization behavior of single carbonate(La/Ce/Pr/Nd),the effects of addition ratio,aging temperature and time on the crystallization performance of mixed rare earth carbonate were investigated,and the effects of seed accelerating crystallization were explored.The results showed that in the n(HCO3-):n(RO3-)=3.15,then aged at 40? for 6 h to obtain the product meet the national standard requirements,and the content of REO was up to 45.96%.Combined with the growth mechanism of dissolution and recrystallization of mixed rare earth carbonate in the aging process,the rare earth carbonates at a certain stage was selected as the crystal seed,and the preparation time of mixed rare earth carbonates was reduced from 6h to 3h under the optimization seed dosage and feeding speed,the crystallization efficiency was improved.(4)Recovery and recycling of magnesium-containing wastewater.The Mg(HCO3)2 solution prepared by alkali transfer and carbonization of magnesium-containing wastewater,and the contents of Fe,Al and Si were all less than 5ppm.The Mg(HCO3)2 can be reused to realize the cycle of magnesium salt and effectively couple the existing Mg(HCO3)2 preparation process. |
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