蛇纹石硫酸浸出液制备超细高纯氢氧化镁

Preparation of superfine and high-purity magnesium hydroxide from solution obtained by sulfuric acid leaching serpentine

以NH_(3)·H_(2)O沉淀硫酸镁溶液制备超细氢氧化镁,用NaOH脱硫得到超细高纯氢氧化镁,研究MgSO4浓度、NH_(3)·H_(2)O浓度、反应温度以及分散剂十六烷基三甲基溴化铵(CTAB)添加量对氢氧化镁粒度与纯度的影响,分析添加剂的作用机理。研究结果表明:以蛇纹石硫酸浸出液为原料,用质量分数为10%的活性MgO悬浮液为沉淀剂,H_(2)O_(2)为氧化剂,控制终点pH为7.5,反应温度为80℃,能完全脱除浸出液中的Fe^(3+)、Al^(3+)、Cr^(3+)、Ni^(2+)、Co^(2+)、Mn^(2+),得到纯净的硫酸镁溶液;采用直接沉淀法制备超细氢氧化镁最佳工艺条件,即反应温度为35℃,MgSO4浓度为0.15 mol/L,NH_(3)·H_(2)O浓度为4 mol/L,CTAB添加量为3%,在此最佳工艺条件下制备的氢氧化镁产品平均粒度为2μm,氢氧化镁纯度大于98%;加入CTAB后,合成体系中氢氧化镁ζ电位由4.53 mV升高到15.40 mV,抑制了氢氧化镁颗粒间的团聚,粒度分布范围变窄;同时,氢氧化镁(001)与(101)晶面衍射峰强度之比I(001)/I(101)增大,优先在(001)晶面生长,得到晶形完整、呈六方片状、分散性好的晶体。

The effects of MgSO4 concentration,NH_(3)·H_(2)O 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 NH_(3)·H_(2)O and ultrafine high-purity magnesium hydroxide obtained by desulfurization with NaOH.The results show that Fe^(3+),Al^(3+),Cr^(3+),Ni^(2+),Co^(2+)and Mn^(2+)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,H_(2)O2 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 NH_(3)·H_(2)O 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 2μm and more than 98%,respectively.Under the action of CTAB,theζpotential 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.