Abstract: There are a large number of magnesium ions and bicarbonate ions left in the system that after seawater decalcification using carbon dioxide,which can lead to scaling problem due to the low solubility of magnesium salts when the treated seawater is used.The new approach proposed in this article is that bicarbonate ions are transformed to carbonate ions and combined with magnesium ions by using sodium hydroxide as precipitant,which results in the further utilization of magnesium resources and mineralization of carbon resources.The effect of mole ratio between hydroxyl ion in the alkali resource and magnesium ions on magnesium removal rates was investigated under the temperature of 10℃,40℃ and 60℃,respectively.The corresponding sediments were characterized by XRD and SEM.And the relationship between the value of n(OH^-)/n(Mg²⁺) and the kinds and morphology of the sediment was obtained.The main conclusions are as follows:the magnesium removal rates increased with the increase of the amount of sodium hydroxide added,and the rates can reach over 98%.At 10℃,the precipitates existed in the form of pure MgCO₃·3H₂O,Mg₅(CO₃)₄(OH)₂·5H₂O and Mg (OH)₂ or their mixtures.At 40℃,MgCO₃·3H₂O disappeared,and the sediments were consist of pure Mg₅(CO₃)₄(OH)₂·4H₂O and Mg (OH)₂ or mixtures.This study provided a new approach for further utilization and mineralization of carbon dioxide of the decalcified seawater using flue gas,and provided a reference for detailed research on the extraction of magnesium resources.

Key words: magnesium extraction, mineralization of carbon dioxide, precipitation crystallization

摘要： 使用烟道气中的二氧化碳进行海水脱钙后的体系中存在大量的镁离子和碳酸氢根离子。如果未加合理利用，不仅会造成资源的浪费，同时体系中存在的大量镁离子在后续生产过程中仍然会引起结垢的问题。本文提出通过使用氢氧化钠作为沉淀剂将该体系中的碳酸氢根转化为碳酸根，并与镁离子结合生成沉淀的新思路，继而减少了溶液中的碳酸氢根及镁离子，同时实现了镁资源和碳资源的进一步矿化利用。通过考察10℃、40℃和60℃条件下碱源中的OH^-与Mg²⁺的摩尔比对镁提取率的影响，以及提镁后的固相的表征分析，得到了不同 n（OH^-）/n（Mg²⁺）比值与固相沉积物的种类与形貌的对应关系。得出以下结论：随着NaOH加入量的增多，镁提取率增加；NaOH足够过量时，镁提取率会达到98%以上。在10℃下，镁系物能够以MgCO₃·3H₂O、Mg₅（CO₃）₄（OH）₂·5H₂O和Mg（OH）₂纯物质或混合物形式存在。60℃时MgCO₃·3H₂O消失，固相以Mg₅（CO₃）₄（OH）₂·4H₂O和Mg（OH）₂的纯物质或混合物形式存在。本研究为海水提镁、海水资源化利用及CO₂矿化技术提供了一个全新的思路和发展方向，为今后更深入地研究镁资源的提取工作提供了参考。

关键词: 提镁, 碳矿化, 沉淀结晶