a batch mode to carry out the process of the invention is not to be ruled out chemical analysis of crystals from crystallizer 14 indicates that the crystals are primarily magnesium sulfite hexahydrate crystals such crystals are relatively insoluble in h 2 o and are preferably converted to magnesium sulfate mgso 4 in an oxidation reaction carried out at oxidation unit 18 in such unit crystals from dewatering unit 15 are combined with hydrogen peroxide h 2 o 2 from source 19 for oxidation reaction mgso 3 h 2 o 2 u2192 mgso 4 h 2 o in batch tests carried out to determine optimum conditions for operation of the oxidation unit it was determined that a mixture of 50 ml u02dc 50 gms of deionized water 8 gms of magnesium sulfite hexahydrate crystals and 5 ml u02dc 7 gms of 30 h 2 o 2 gave the best oxidation results with the least temperature rise such results are contained in table ii in such batch test sample all the reactants stayed in solution when the sample was cooled and ion chromatography analysis indicated 0 ppm of so 3 and 66569 ppm of so 4 operation of the oxidation unit in light of the results of such batch test is carried out with proportions of the reactants substantially matching that of the batch test above it has been observed that magnesium sulfite hexahydrate crystals from the crystallizer if not immediately processed in the oxidation.