Abstract:

During the precipitation of calcium and magnesium ions by absorbing CO₂ in concentrated seawater, MgO was used to regulate the pH of the solution at 6.5-7.2 to precipitate calcium ions from concentrated seawater. After the equilibrium of calcium ion precipitation was reached, NaOH was used as the pH regulator for precipitating magnesium ions in the solution, so as to obtain two pure carbonate precipitates. The effects of MgO addition, gas flow, temperature in the first step, and gas flow, temperature, and pH in the second step on precipitation were studied through single factor experiments, and the suitable experimental conditions were initially determined. Then, the first and second step reaction conditions were optimized using response surface methodology. The optimal experimental conditions for the first step precipitation were determined to be MgO dosage of 7.43 g/L, temperature of 42 ℃, and gas flow time of 23 min. The optimal conditions for the second step precipitation were determined to be temperature of 45 ℃, pH of 9.0, and gas flow time of 25 min. The predicted calcium and magnesium ion concentrations after the concentrated seawater reaction were basically consistent with the simulated results under the optimal experimental conditions obtained by response surface methodology. The actual calcium and magnesium ion removal rates were slightly lower than the simulated results, but the calcium ion and magnesium ion removal rates were still 90.2% and 85.6%, respectively. XRD analysis of the precipitated sediment showed that the purity of the calcium salt and magnesium salt was high. The results provided a new method for utilizing concentrated seawater to reduce CO₂ emissions and recover resources.

Key words: concentrated seawater, carbon sequestration, carbonate, stepwise sedimentation, soften

摘要：

浓海水吸收CO₂沉淀钙镁离子的过程中，使用MgO调控溶液的pH在6.5~7.2，沉淀浓海水中的钙离子，钙离子沉淀平衡后，使用NaOH作为第二步沉淀的pH调节剂，沉淀溶液中的镁离子，从而得到两种纯度较高的碳酸盐沉淀。通过单因素实验对第一步反应中MgO添加量、气体流量、温度和第二步反应中气体流量、温度、pH等对沉淀的影响进行研究，初步确定了适宜的实验条件，之后分别对第一步和第二步反应条件进行响应面优化，得到第一步沉淀的最佳实验条件为MgO添加量7.43 g/L、温度42 ℃、通气时间为23 min；第二步沉淀的最佳条件为温度45 ℃、pH 9.0、通气时间25 min。在响应曲面优化得出的最佳实验条件下，模拟浓海水反应后钙镁离子浓度与预测结果基本一致，实际浓海水反应后钙镁离子去除率略有下降，但钙离子、镁离子去除率仍分别高达90.2%、85.6%，且对沉淀物的XRD分析结果表明沉淀得到的钙盐和镁盐纯度较高。研究结果为利用浓海水减排CO₂并回收资源提供了一种新方法。

关键词: 浓海水, 固碳, 碳酸盐, 分步沉淀, 软化

CLC Number: 

• X703