Study on the carbonization process of magnesium hydroxide
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摘要: 研究了氢氧化镁碳化制备碳酸氢镁的过程，考察了液固比、浆料温度、二氧化碳气速、搅拌速度以及氢氧化镁原料差异对碳化过程的影响。结果表明：在常温常压下，液固比为40、二氧化碳气速为400 mL/min、搅拌速度为300 r/min时碳化效果最佳；氢氧化镁粒度越小、分散性越好，对碳化过程越有利；分析纯与自制氢氧化镁碳化所得碳酸氢镁溶液中镁离子浓度分别为0.315 mol/L以及0.203 mol/L；同时对碳化过程氢氧化镁缩壳模型进行了简要探讨，碳化过程拟合呈现出较好的线性。Abstract: With the rapid progress of seawater desalination technology, concentrated brine has not been effectively used due to the lack of mature development and treatment process. Direct emissions of concentrated brine are seriously harmful to the ecological environment. At the same time, massive emissions of carbon dioxide have exacerbated the greenhouse effect. Aiming at the resource utilization of concentrated brine and carbon dioxide, combined with the previous research basis of using calcium hydroxide as the precipitant to prepare magnesium hydroxide, this paper proposes a carbonization technical process to prepare magnesium bicarbonate using magnesium hydroxide as the precursor from low magnesium systems. The research focuses on the carbonization process of magnesium hydroxide, investigating the influence of liquid-solid ratio, temperature, carbon dioxide gas velocity, stirring speed, and raw material difference on the carbonization process, and monitoring the change of calcium and magnesium ion concentration and pH value during the carbonization process. It was found that under room temperature and atmospheric pressure, the carbonization effect is the best when the liquid-solid ratio is 40, the carbon dioxide gas velocity is 400 mL/min, and the stirring speed is 300 r/min, the concentration of Mg2+ in the carbonization solution from analytical purity magnesium hydroxide is 0.315 mol/L and there exists no Ca2+, the concentration of Mg2+ in the carbonization solution from self-made magnesium hydroxide is 0.203 mol/L, the concentration of Ca2+ is 3.2×10−4 mol/L, calcium impurities are basically separated. The particle size and dispersion of magnesium hydroxide have significant impact on the carbonization effect: smaller particle size and better dispersion promote the carbonization process. The shrinking core model of magnesium hydroxide is briefly discussed at the same time, the fits of the carbonization process at different slurry temperatures show good linearity.
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Key words:
- magnesium hydroxide /
- carbonization method /
- carbon dioxide /
- magnesium bicarbonate
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图 1 Mg(OH)2碳化实验装置图
Figure 1. Drawing of experimental device for the carbonization process of Mg(OH)2
图 2 不同液固比下Mg2+浓度与pH随时间变化曲线
Figure 2. Concentration of Mg2+ and pH change curves with time under different liquid-solid ratios
图 3 不同浆料温度下Mg2+浓度与pH随时间变化曲线
Figure 3. Concentration of Mg2+ and pH change curves with time at different slurry temperatures
图 4 不同CO2气速下Mg2+浓度与pH值随时间变化曲线
Figure 4. Concentration of Mg2+ and pH change curves with time under different CO2 gas velocity
图 5 不同搅拌速度下Mg2+浓度与pH随时间变化曲线
Figure 5. Concentration of Mg2+ and pH change curve with time under different stirring speeds
图 6 不同CO2气速下自制氢氧化镁浆料Mg2+、Ca2+浓度与pH随时间变化曲线
Figure 6. Concentration of Mg2+ and Ca2+, pH change curve with time under different CO2 gas velocity
图 7 一次碳化（a）、二次碳化（b）后固体XRD谱图
Figure 7. XRD patterns of solid after primary (a) and secondary carbonization (b) (Gas velocity of CO2: 400 mL/min)
图 8 1−(1−x)1/3-t, 1−(1−x)2/3-t线性拟合图
Figure 8. 1−(1−x)1/3-t, 1−(1−x)2/3-t linear fitting diagram
表 1 分析纯与自制氢氧化镁指标对照表
Table 1. Index comparison table of analytical grade and self-made magnesium hydroxide
Reference Index D[3,2]
/µmD[4,3]
/µmD50
/µmw/% Mg(OH)2 CaO SO42− Cl− Mg(OH)2(AR) 1.35 2.13 1.92 95.00 − − 0.01 Mg(OH)2(self-made) 4.79 6.49 5.48 92.50 1.59 2.18 0.10 D[3,2]— D[4,3]— D50— 
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