Gypsum production and hydrochloric acid regeneration by reaction of calcium chloride solution with sulfuric acid

One critical issue in chloride hydrometallurgy is the regeneration of the lixiviant HCl that is commonly achieved by pyrohydrolysis. It is the scope of this thesis to investigate a low temperature HCl regeneration process, which regenerates HCl and produces saleable gypsum. Experiments were performed to determine the optimum conditions of the chemical reaction that involved the reactive mixing of calcium chloride (CaCl2) solution with sulfuric acid (H2SO4) solution at low temperature and atmospheric pressure.;The results showed that the crystallization chemistry of the CaCl 2-H2SO4 reaction can be controlled in such away that favors the production of well grown gypsum crystals with the simultaneous regeneration of practical strength HCl. High strength HCl (= 4 M) was regenerated by the reaction of (3.5 M) CaCl2 leach solutions with (8 M) sulfuric acid in the temperature range of 20-60°C. Acid addition in stages to simulate the titration procedure, seeding and recycling, and increasing temperature were found to favor crystal growth and filterability. Finally, this research showed that there is negligible metal uptake with the exception of lead, making the production of marketable gypsum possible.