An efficient process for the preparation of magnesium thiosulfate involves reaction
of magnesium hydrosulfite and sulfur at elevated temperature. Magnesium hydrosulfite
can be prepared from commercial magnesium oxide and sulfur. Sulfur dioxide can
be used to maintain pH. The resulting product is an emulsion of liquid magnesium
thiosulfate and solid byproducts. Under controlled conditions, including mole ratios
of MgO to sulfur, temperature of the reaction process, and pH, as well as rate
and duration of SO2 purging, production of byproducts can be reduced
to less than about 2% by weight. The magnesium thiosulfate solution can be prepared
with concentrations of at least about 25%, preferably at least about 30%.
