The dissolution kinetics of major sedimentary carbonate minerals

Abstract

Among the most important set of chemical reactions occurring under near Earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals. These minerals comprise about 20% of Phanerozoic sedimentary rocks. Calcite and, to a significantly lesser extent, dolomite are the major carbonate minerals in sedimentary rocks. In modern sediments, aragonite and high-magnesian calcites dominate in shallow water environments. However, calcite is by far the most abundant carbonate mineral in deep sea sediments. An understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel CO 2 on climate, diagenesis of sediments and sedimentary rocks. It also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs, and the preservation of buildings and monuments constructed from limestone and marble. In this paper, we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century. Our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions. We will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments. Such complex topics are clearly worthy of review papers on their own merits. Calcite has been by far the most studied mineral over a wide range of conditions and solution compositions. In recent years, there has been a substantial shift in emphasis from measuring changes in solution composition, to determine “batch” reaction rates, to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy (AFM). However, there remain major challenges in integrating these two very different approaches. A general theory of surface dissolution mechanisms, currently lacking (although see Lasaga and Luttge [Science 291 (2001) 2400]), is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components. Studies of aragonite, high-magnesian calcites, magnesite, and dolomite dissolution kinetics are much more limited in number and scope than those for calcite, and provide, at best, a rather rudimentary understanding of how these minerals are likely to behave in natural systems. Although the influences of a limited number of reaction inhibitors have been studied, probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of “foreign” ions and organic matter on the near-equilibrium dissolution kinetics of carbonate minerals.