Preparation of superfine and high-purity magnesium hydroxide from solution obtained by sulfuric acid leaching serpentine
The effects of MgSO4 concentration,NH3·H2O concentration,reaction temperature and addition of dispersant cetyltrimethylammonium bromide(CTAB)on the particle size and purity of magnesium hydroxide were studied and the mechanism of additives was analyzed,which was based on ultrafine magnesium hydroxide prepared by the magnesium sulfate solution with NH3·H2O and ultrafine high-purity magnesium hydroxide obtained by desulfurization with NaOH.The results show that Fe3+,Al3+,Cr3+,Ni2+,Co2+and Mn2+in the leaching solution can be completely removed and pure magnesium sulfate solution can be obtained by taking the serpentine sulfuric acid leaching solution as raw material,active MgO suspension with mass fraction of 10%as precipitator,H2O2 as oxidant,and meanwhile,the final pH is controlled at 7.5 and reaction temperature is set as 80℃.The optimal condition for ultrafine magnesium hydroxide preparation is as follows.The reaction temperature is 35℃,the concentration of MgSO4 is 0.15 mol/L,the concentration of NH3·H2O is 4 mol/L,and the addition of CTAB is 3%,in the optimal condition,the average particle size and purity of magnesium hydroxide prepared under optimal condition is 2 μm and more than 98%,respectively.Under the action of CTAB,the ζ potential of magnesium hydroxide increases from 4.53 mV to 15.40 mV,which inhibits the agglomeration between magnesium hydroxide particles,and narrows the particle size distribution.Furthermore,the ratio of diffraction peak strength between(001)and(101)crystal plane becomes larger,and magnesium hydroxide prefers to grow on the(001)crystal plane.Ultimately,magnesium hydroxide is developed into the complete,hexagonal sheet and good-dispersity crystal.
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