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

白云岩[CaMg(CO3)2]是地球上最丰富的碳酸盐矿物之一。然而，白云石在室温下的生长动力学仍然不清楚，在无添加剂的水溶液中实验室合成通常失败。这种失败的原因被认为是Mg2+的缓慢脱水，这也被认为是一般无水碳酸镁矿物生长问题的原因。然而，有一种无水含镁碳酸盐矿物，在室温下很容易从水溶液中析出，其结构和化学性质与白云石相似：北长辉石[BaMg(CO3)2]。在baco3 - mgco3体系中，norsethite主要存在于不同的溶液条件和温度下。由于norsethite的溶解度产物仅在25℃下进行了实验测定，因此在其他温度下含Ba2+和Mg2+的水的地球化学模型非常不可靠。然而，这些模型对于任何在高温下的矿物稳定性和生长动力学的定量评价都是必不可少的。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，评估含镁矿物在地质CO2封存中的相关性或计算工业过程中结垢的形成）。因此，该项目的目的是确定norsethite在不同高温（50-175℃）下的溶解度产物。这些溶解度产物对未来碳酸盐矿物研究具有重要的基础性作用。此外，与白云岩溶解度的比较可以为解开白云岩问题和了解北菱石的易形成提供有价值的信息。此外，对norsethite生长的了解可以更好地评估Mg2+脱水屏障在含镁碳酸盐矿物生长过程中的重要性。

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.