Production of precipitated calcium carbonate (PCC) via carbon dioxide (CO₂) pressure-swing mineral carbonation is a potential way to utilise calcium-rich steel slag and carbon dioxide. Calcium supersaturation and slag surface passivation are two aspects of the calcium extraction step that strongly influence the choice of operating conditions necessary for rapid and complete calcium leaching, which are investigated in the present work. To investigate these aspects, slag dissolution characteristics were studied in a closed high-pressure batch-reactor taking care to eliminate gas–liquid mass transport limitations. This experimental design has two distinct advantages: (1) rapid CO₂ absorption necessary for dissolution under acidic conditions and to gain insights into calcium dissolution kinetics and (2) the closed system allowing measurement of the drop in reactor pressure, which along with elemental analysis of leachate is sufficient to determine the ionic species concentration and solution saturation state. The results provide evidence against surface passivation of residual slag by silica or calcium carbonate layers. Further, the experiments confirm high supersaturation with respect to calcite during the dissolution step, which we hypothesise to be a consequence of unfavourable calcite precipitation kinetics due to the low pH and high calcium to carbonate ion ratio. The results show scope for further enhancement in calcium solubility, up to the solubility limit of amorphous calcium carbonate, which can substantially reduce the water volume and CO₂ pressure required for dissolution. Pressure-swing to atmospheric pressure led to spontaneous co-precipitation of rhombohedral calcite and amorphous silica, also a paper-filler with similar optical properties to PCC, with impurities less than 1.5 wt%.

中文翻译：

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旨在通过变压矿物碳化有效地从钢渣中提取钙并利用二氧化碳†

通过二氧化碳（CO ₂）变压矿物碳酸化生产沉淀碳酸钙（PCC）是利用富钙钢渣和二氧化碳的一种潜在方法。钙过饱和和炉渣表面钝化是钙提取步骤的两个方面，它们对快速和完全钙浸出所必需的操作条件的选择有很大影响，在当前工作中对此进行了研究。为了研究这些方面，在密闭的高压间歇式反应器中研究了炉渣的溶解特性，并注意消除了气液传质的局限性。此实验设计具有两个明显的优点：（1）快速CO ₂在酸性条件下溶解所必需的吸收，并深入了解钙的溶解动力学；（2）封闭系统允许测量反应器压力的下降，这与渗滤液的元素分析一起足以确定离子种类的浓度和溶液的饱和状态。该结果提供了反对残留的炉渣被二氧化硅或碳酸钙层表面钝化的证据。此外，实验证实了在溶解步骤中方解石具有较高的过饱和度，我们推测这是由于低pH值和高的钙碳酸盐离子比率导致方解石沉淀动力学不利所致。结果显示了进一步提高钙溶解度的范围，直至无定形碳酸钙的溶解度极限，溶解需要_2个压力。变压至大气压导致菱形方解石和无定形二氧化硅自发共沉淀，这也是一种纸张填充剂，其光学特性与PCC相似，且杂质含量小于1.5 wt％。