ABSTRACT

Mixing of aqueous solutions is an important procedure in chemical laboratories. The chemical effects of mixing in the laboratory include changes in the concentration and electrical properties of a solution, shifts in homogeneous equilibria, and precipitation or dissolution of a solid phase. Similar chemical effects can be expected to occur in nature as a result of the mixing of natural waters, and in some instances these may result in diagenesis. A simple classification yields 14 distinct categories of natural waters with 91 possible combinations of mixing of pairs of such waters.

Examples are known of the precipitation of hydroxides and carbonates as a result of the mixing of chemically dissimilar surface waters. Documented examples of subsurface mixing and diagenesis are few. However, because of the great variety of chemically dissimilar subsurface waters, plus the existence of several types of potential fields which cause the movement of subsurface waters, mixing and diagenesis in the subsurface may be a common and significant geologic process.

The solubility of rock forming minerals is a non-linear function of such independent variables as salinity, partial pressure of gases, temperature, and so on. The dissolution of calcium carbonate as a result of "Mischungskorrosion" can be viewed in the light of the non-linearity of the solubility curve. Experimental data on the solubility of calcium carbonate and calcium sulfate as a function of added salts indicate that mixing of solutions which differ only in their content of dissolved electrolytes may cause either the precipitation or dissolution of the rock-forming minerals. Other common rock-forming minerals, with the exception of quartz at low temperatures, should exhibit similar behavior.