PROCESS FOR THE PREPARATION OF IRON OXIDE PIGMENTS AND SODIUM SULPHATE

In the production of iron oxide pigments and substantially iron-free sodium sulphate from iron sulphate by passing an oxygen-containing gas through an alkalized iron sulphate-containing solution at a temperature of about 40 DEG to 100 DEG C., and separating iron oxide pigment formed from the solids-free sodium sulphate-containing solution, the improvement of which comprises crystallizing out part of the sodium sulphate from the solids-free solution in a first crystallization step, separating the crystals from the sodium sulphate-containing mother liquor, dividing the mother liquor into first and second portions, dissolving solid iron sulphate hydrate in the first portion, adding to the second portion sodium hydroxide thereby to crystallize additional sodium sulphate, separating the additional crystals of sodium sulphate from the rest of the mother liquor, and using the rest of the mother liquor containing sodium sulphate and sodium hydroxide to alkalize further iron sulphate solution in the precipitation of further iron oxide pigment.