Investigation of norsethite solubility as a fundamental contribution for a better understanding of the formation of Mg-containing carbonate minerals

白云石[CaMG(CO3)2]是地球上最丰富的碳酸盐矿物之一。然而，白云石在常温下的生长动力学仍然不清楚--实验室在无添加剂的水溶液中的合成通常都是失败的。这一失败的原因被认为是镁的缓慢脱水，这也被认为是普遍存在的无水碳酸镁矿物生长问题的原因。然而，有一种无水的含镁碳酸盐矿物在室温下很容易从水溶液中沉淀出来，它的结构和化学结构与白云石相似：诺森石[BAMG(CO3)2]。在BaCO_3-MgCO_3-体系中，钠钠铝石占主导地位，并在不同的溶解条件和温度下出现，由于钠钠石的溶度积仅在25℃时实验测定，其他温度下含Ba2和Mg2的水的地球化学模型是非常不可靠的。然而，这些模型对于任何定量评估矿物稳定性和高温下的生长动力学是必不可少的。准确了解含镁矿物在高温下的生长动力学具有重要意义(例如，对于评估含镁矿物在地质二氧化碳封存中的相关性或计算工业过程中的结垢)。因此，该项目的目的是确定不同高温(50-175°C)下诺森石的溶解产物。这些溶度积对未来碳酸盐矿物的研究具有重要的基础性贡献。此外，与白云石的溶度积进行对比，可以为解开白云石问题和了解诺森石的易形成提供有价值的信息。此外，有关诺森石生长的知识可以更好地评估含镁碳酸盐矿物生长过程中镁脱水障碍的重要性。

Dolomite [CaMg(CO3)2] is one of the most abundant carbonate minerals on Earth. The growth kinetics of dolomite at ambient temperature, however, is still not clear - laboratory syntheses in additive-free aqueous solutions fail generally. The reason for this failure is assumed to be the slow dehydration of Mg2+, which is also thought to be the reason for the growth problems of anhydrous Mg-carbonate minerals in general. Nevertheless, there is an anhydrous Mg-containing carbonate mineral which easily precipitates at room temperature from aqueous solution and which is structurally and chemically similar to dolomite: norsethite [BaMg(CO3)2]. In the BaCO3-MgCO3-system, norsethite is prevailing and occurs at variously different solution conditions and temperatures.As the solubility product of norsethite has only been determined experimentally at 25 °C, geochemical models of Ba2+ and Mg2+ containing waters at other temperatures are highly unreliable. Such models, however, are indispensable for any quantitative evaluation of mineral stability and growth kinetics at elevated temperatures. Accurate knowledge of the growth kinetics of magnesium containing minerals at elevated temperatures is of great significance (e.g., for an evaluation of the relevance of Mg-containing minerals in geological CO2 sequestration or for calculations of scale formation in industrial processes).Aim of the project, therefore, is to determine the solubility products of norsethite at various elevated temperatures (50-175 °C). These solubility products can make a significant and fundamental contribution to future carbonate mineral research. Furthermore, a comparison to the solubility product of dolomite can give valuable information to unravel the dolomite problem and to understand the easy formation of norsethite. Moreover, knowledge about norsethite growth allows a better assessment of the significance of the Mg2+ dehydration barrier during growth of Mg-containing carbonate minerals.