Abstract: A precursor of high purity magnesite was prepared from bischofite (MgCl2?6H2O) as raw material，Na2CO3 as precipitant，dropping into the reactor at the same time through peristaltic pumps at 35 ℃. The main composition of the precursor was MgCO3?2H2O by XRD. MgCO3?2H2O was calcined at 800 ℃ for 2 h in order to obtain high purity active MgO powders with good particle size distribution. Then coconut shell activated carbon，nut shell activated carbon and tar activated carbon were added as the second phase in the process of vacuum sintering. Coconut shell activated carbon was proved to be the best choice under the same conditions. Subsequently，0.03%～0.05% of coconut shell activated carbon distinctly improved the sintering performance of magnesia. Consequently，sintered magnesia was prepared by sintering at 1600 ℃ for 5 h under vacuum sintering ，whose bulk density was higher than 3.4 g /cm3，purity was higher than 98.5%.

Key words: precursor, coconut shell activated carbon, vacuum sintering, high purity magnesia

摘要： 研究了以MgCl2?6H2O为镁源，Na2CO3为沉淀剂，在反应温度为35 ℃的条件下，通过恒流进料，制备出高纯镁砂的前体。由XRD表征结果可知：前体的主要成分为二水合碳酸镁（MgCO3?2H2O）。在800 ℃温度下，将前体煅烧2 h，得到高纯度、粒径分布均匀的活性MgO颗粒。后续高温真空烧结致密化的过程中，与果壳、焦油活性炭相比，当椰壳活性炭作为第二相添加剂时，高纯镁砂的气孔率降低和体积密度提高效果最为明显。对比可知，椰壳活性炭的添加量为0.03%～0.05%时效果最优，经1600 ℃真空烧结5 h得到烧结镁砂的体积密度高于3.4 g/cm3，纯度高于98.5％。

关键词: 前体, 椰壳活性炭, 真空烧结, 高纯镁砂