Thermal decomposition studies on magnesium hydroxychlorides

This work presents the results of thermal decomposition studies on the 2-form (2MgO center dot MgCl2 center dot 6H(2)O) and 3-form (3MgO center dot MgCl2 center dot 11H(2)O) magnesium hydroxychlorides. Magnesium hydroxychlorides form from the reaction of MgO with MgCl2 brines. They have historically been of importance as the components of Sorel cements. More recently, they have taken a central role in proposed flowsheets for chloride leaching of laterite nickel ores, with the chloride units being captured in magnesium hydroxychloride precipitates. Differential thermal analysis (DTA), thermogravimetric analysis (TGA), and mass spectrometry (MS) curves have been obtained for both the 2-form and the 3-form. In addition, results of an isothermal kinetic study on the 2-form are presented. The DTA-TGA-MS curves reveal a two-stage decomposition pathway for both hydroxychlorides, passing through currently unknown intermediates. An empirical equation is presented describing the decomposition rate of the 2-form, predicting 100% decomposition within 1 min at similar to 560 degrees C.