Magnesium sulfate, thermodynamics

The reduction of magnesium sulfate is thermodynamically feasible at reactor temperatures of 900°F and above, especially if H2S is the product. Figure 19 shows the standard AG for the reduction of magnesium sulfate with hydrogen or methane as a function of temperature to make either H2S or SO2 as the reduction product. (The calculations have all been made on the basis of 1 mole of SO2.) Also shown are the values for the reduction of SO2... 

CAS Castro, B.D. and Aznar, M., Liqnid-Uqnid eqnilibrinm of water + PEG8000 + magnesium sulfate or sodium sulfate aqueous two-phase systems at 35°C Experimental determination and thermodynamic modeling, Braz. J. Chem. Eng., 22, 463, 2005. 

However, the phenomena of super-saturation of brines containing magnesium sulfate, borate is often found both in natural salt lakes and solar ponds around the world. Especially for salt lake brine and seawater systems, the natural evaporation is in a autogenetic process with the exchange of energy and substances in the open-ended system, and it is controlled by the radiant supply of solar energy with temperature difference, relative humidity, and air current, etc. In other word, it is impossible to reach the thermodynamic stable equilibrium, and it is in the status of thermodynamic non-equilibrium. 

Hypothesis 3, Diffusion of DIC together with DOC, sulfate, and cations from confining bed pore waters to the Black Creek aquifer provides sources of electron donor (organic carbon) and electron acceptor (sulfate) for microbial metabolism and additional inorganic carbon to drive low-magnesium calcite precipitation. The combination of magnesium-calcite dissolution from shell material driven by microbially produced carbon dioxide, and the precipitation of more thermodynamically stable low-magnesium calcite cement in the aquifer, can explain major ion and carbon isotope composition of Black Creek aquifer water. 

Both resistance of the electrolyte and polarization of the electrodes limit the magnitude of current produced by a galvanic cell. For local-action cells on the surface of a metal, electrodes are in close proximity to each other consequently, resistance of the electrolyte is usually a secondary factor compared to the more important factor of polarization. When polarization occurs mostly at the anodes, the corrosion reaction is said to be anodically controlled (see Fig. 5.7). Under anodic control, the corrosion potential is close to the thermodynamic potential of the cathode. A practical example is impure lead immersed in sulfuric add, where a lead sulfate film covers the anodic areas and exposes cathodic impurities, such as copper. Other examples are magnesium exposed to natural waters and iron immersed in a chromate solution. 

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