以低品位菱镁矿为原料,经煅烧、氯化铵溶液浸出、镁的沉淀反应制备MgCO3.3H2O和Ca-CO3。采用质量分数为1%的MgCl2.6H2O作为添加剂,与低品位菱镁矿在650℃混合煅烧2h,煅烧产物为CaCO3和MgO。通过实验确定了由煅烧产物浸出镁的最佳工艺条件为：反应温度为80℃,反应时间为60min,NH4Cl过量30%,液固比为8,采用二次浸出的方法,此时镁溶出率为92%,浸出残渣的主要成分为CaCO3。用含MgCl2滤液与（NH4）2CO3反应制备MgCO3.3H2O,当反应温度为37℃,（NH4）2CO3过量50%,陈化时间为2h时,得到直径1～3μm、长15～20μm的棒状MgCO3.3H2O,纯度为96.5%。
Calcium carbonate and nesquehonite were prepared using low-grade magnesite as raw material.Firstly,the low-grade magnesite was calcined,and then reacted with ammonium chloride solution to obtain CaCO3 and the solution of MgCl2.Finally,nesquehonite was precipitated from the solution of MgCl2 by using ammonium carbonate as precipitant.The results showed that with 1% of MgCl2·6H2O as additive,the low-grade magnesite was calcined at 650℃ for 2h,thus the calcined product was mainly composed of CaCO3 and MgO.The influences of process conditions on the dissolution rate of magnesium were investigated,and the results showed that the optimal process conditions were： 80℃ for 60min,the excess coefficient of ammonium chloride was 30%,and the ratio of liquid to solid was 8 through two-step leaching,under which the dissolution rate of magnesium was 92%,and leaching residue was mainly composed of CaCO3.Nesquehonite with a diameter of 1-3μm and a length of 15-20μm obtained as precipitation reaction temperature was 37℃,the excess coefficient of ammonium carbonate was 50%,and aging time was 2h.In addition,the purity of nesquehonite was 96.5%.
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