| 摘要 |
Process for the recovery of pigment-grade iron oxide and technical hydrochloric acid of predetermined molarity, from iron chloride solutions such as pickling solutions containing hydrochloric acid. The iron chloride solution is concentrated until the molarity of the chloride ion therein is the same as the molarity of the hydrochloric acid which it is desired to produce. Concentrated sulfuric acid in slight stoichiometric excess relative to the iron, is then added to the iron chloride solution, which solution is thereafter evaporated to dryness. The distillation from this evaporation is hydrochloric acid of the predetermined molarity, and the dry residue is iron sulfate. The iron sulfate is calcined to drive off sulfur dioxide and sulfur trioxide and to leave iron oxide which may contain sulfates; and to remove these latter, the iron oxide is leached with dilute hydrochloric acid and is thereafter washed with water. The washed iron oxide is dried and micropulverized to produce a red iron oxide pigment. The sulfur oxides driven off during calcination may be washed with concentrated sulfuric acid and recycled to the sulfating step, the concentrated sulfuric acid absorbing the sulfur trioxide and letting pass the sulfur dioxide which can if desired be used in the catalytic production of further sulfuric acid. Alternatively, the sulfur oxides can be washed with lime milk to produce calcium sulfite and calcium sulfate, which upon filtration and air drying becomes hydrated calcium sulfate usable as gypsum.
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