Study On The Pretreatment Of Waste Liquid From Bromine Extraction Production Of High Purity Magnesium Oxide

Waste liquid from bromine extraction is the mother liquid of seawater after salt insolation, potassium extraction and bromine extraction. The content of MgCl2reach up to400-450g/L. It is a good material for magnesium of fine chemical productions (magnesium oxide, magnesium hydroxide, magnesium chloride). But due to the largely turbidity and chroma, the presently production is brown, high impurity content, low-price, low value-added, affect the enterprise economic benefit. In order to improve the quality of fine chemicals, pretreatment of waste liquid from bromine extraction was studied, obtain better pretreatment process and parameters, provide reliable theoretical basis for industrial production. At the same time, crystallization kinetics of magnesium chloride aqueous solution was also studied, obtain the nucleation rate and growth rate, and provide a theoretical basis for the design and scale-up of crystallizer.Physical and chemistry decolorizationin for waste liquid from bromine extraction was firstly studied. This study shows that the color of bromine liquid waste was mainly composed of organic coloring substances; sand leach effectively removed the suspended solids, reduced the turbidity from40.9BTU to around2BTU, the decolorization rate was only about41%, active carbon decolorization rate was60%, but the decolorization rate of both sand leach and active carbon was not ideal. Under the best experimental conditions, the decolorization rate of NaClO and H2O2was80%and79%, respectively, achieved better decolorizaiton effect. Comprehensive consideration of oxidation time and oxidation temperature, the decoloriation effect of NaClO was better than that of H2O2. The purification and decolorization technology of waste liquid of bromine system was pretreated by sand leach and decolorized through NaCIO, the best decolorization condition:the added amount of NaClO was8%, pH=6.0, oxidation time was40min and the decolorization rate was80%.Evaporation-cooling crystallization removal sulfate radical was also studied. By the five element phase diagram Mg2+, K+, Na+/SO42-, Cl--H2O, evaporation concen-tration and thermal subsidence for waste liquid from bromine extraction, MgSO4·H2O separation by crystallization, removal sulfate radical. At the same time, by the cooling crystallization, sulfate radical stay in mother liquid and Car(KCl·MgCl2·6H2O) separation, centrifugal separation removal sulfate radical. This study shows that the best condition of removal sulfate radical is termination boiling point136℃, holding temperature110℃, heat-retaining time3.5h. In that conditions, the content of sulfate radical in solution from27.29g/L reduce to9.18g/L, at the same time, the content of sulfate radical in crystallization production from0.53%reduce t00.042%,it is all to satisfied the requirement for subsequent operation.The crystallization kinetics of magnesium chloride aqueous solution was also studied. This study shows nucleation rate of magnesium chloride is B0=1.28×10-exp(-2.103×104/RT)·S5.23T0.513,and growth rate of magnesium chloride is G=1.4×10-6exp(-1.08×103/RT).S3.