由低品位菱镁矿制备高纯Mg(OH)2的“绿色”新工艺

New "green" technology of preparing high-purity Mg(OH)_2 from low-grade magnesite

将低品位菱镁矿经900℃煅烧3 h制得轻烧镁粉,按不同比例与硫酸铵混合后,在不同温度下焙烧不同时间,使MgO转化成MgSO4,同时将焙烧过程中产生的氨气用水吸收得到回收氨水;将焙烧产物分散于水中,过滤分离其中的Si、Ca、Fe、Al等杂质而得到MgSO4溶液,然后加入回收的氨水使MgSO4转化成Mg(OH)2,经过滤、洗涤、干燥后得到最终产物氢氧化镁。主要研究了轻烧镁粉-硫酸铵混合物的配比、焙烧温度和焙烧时间对MgO转化为MgSO4过程中镁转化率的影响,并对最终产物进行XRD分析、X射线荧光光谱分析和扫描电镜观察。结果表明:在轻烧镁粉-硫酸铵混合物中,当n((NH4)2SO4)∶n(MgO)=0.9∶1,焙烧温度为475℃,焙烧时间为3 h时,镁的转化率可达90%;最终产物氢氧化镁中Mg(OH)2的质量分数高达99.7%,氢氧化镁颗粒呈球形,粒径均匀,平均粒径2μm。

The light-burned magnesia powder calcined from low-grade magnesite at 900 ℃ for 3 h was mixed with （NH4） 2SO4 by different proportions ;then the mixtures were fired at different temperatures for different holding times, transforming MgO to MgSO4. Meanwhile, the NH3 generated during the calcinations was absorbed by water,obtaining ammonia;the mixture after calcination was dispersed in water to filtrate impurities such as Si, Ca, Fe and Al, obtaining MgSO4 solution. Then the recycled ammonia was added into MgSO4 solution ; after filtering,washing and drying,the final product Mg （OH） 2 was prepared. The effects of mole ratio of light-burned magnesia powder and （NH4）=SO4, calcining temperature and holding time on the conversion rate of MgO to MgSO4 were studied. The final product was detected by XRD,XFS and SEM. The results indicated the conversion rate of magnesium reached 90% when the calcination temperature was 475 ℃, n（ （NH4） zSO4） ： n（MgO） = 0.9 ： 1 and holding time lasted for 3 h. The purity of Mg （OH） 2 in the final product reached 99.7%. The grains of Mg（OH）2 were spherical with the average grain size of 2 μm.