Removal Technology Of Microscale Impurities From MgCl₂ As Electrolyte

Electrolytical production of magnesium from anhydrous MgCl2 is one of the most effi-cient pathways utilizing MgCl2 resource containing SO42-, iron and boron impurities which are harmful to electrolytic process of MgCl2. For the sake of avoiding adverse influences of these impurities, in brines which containing 33% MgCl2, the concentration of SO42-, iron and boron must be kept less than 75,15,25mg/L, respectively.Determining the concentration of SO42-, iron and boron in brine or brucite is the prereq-uisite to remove these impurities, so spectrophotometric determinations of SO42-, iron and boron in solutions with high MgCl2 content were investigated. Emphasis was placed on boron determination. Effects of Mg2+, color development temperature, color reaction duration and uncertainty were studied thoroughly. The results showed that, high concentration of Mg+ would increase absorbance which could reduced by suitable amount of EDTA solution, un-certainty introduced by preparation of boron standard solutions was the biggest contribution to total uncertainty.SO42- impurity in brine was removed through BaCl2 precipitation process whose influ-ence factors such as feed state, temperature, and addition amount of precipitant were exam-ined. NaOCl oxidation was adopted to lower iron content in brine, and effects of addition amount of NaOCl, duration on iron removal result were studied. XRD of brown precipitate showed that Fe(OH)3 could adsorb borate from brine.Existence states of SO42-, iron and boron in wet brucite were studied, and the result showed that boron impurity mainly existed in residual brine among brucite crystals, iron ex-isted as insoluble Fe(OH)3 covering brucite crystals, and SO42- distributed in residual brine and brucite crystals. Appropriate removal processes for SO42-, iron and boron were adopted according to their existing states. Wet sieving-centrifugation were suitable for removal of iron and boron impurities contained in wet brucite, and SO42-were precipitated by BaCl2 in satu-rated solution of brucite. Through these removal processes, all of above standards were achieved.