Preparation Of α-Hemihydrate Gypsum From Titanium Dioxide Waste Acid And Its Morphology Control

At present, the production of titanium oxide mainly includes sulfuric acid method and chlorination process. Due to mature technology of sulfuric acid method, most of domestic plants produce titania by this method. According to statistics, production of 1t titania was companied by 8~10t waste acid which contains about 20% sulfuric acid and 10% ferrous sulfate, and a large number of titanium salts. Dihydrate gypsum with the high impurity content is obtained by mixing limestone and waste acid at room temperature, which brings about waste of resources, and environmental pollution.Using the titanium white waste acid and limestone( or lime milk) as raw materials, α-hemihydrate gypsum(α-HH)was prepared by the use of double addition and salts solution method. The influences of process conditions and crystal modifier on the morphology of the product were studied. The research content mainly includes the following several aspects:1) With titanium white waste acid and lime milk as raw materials, α-HH of good crystal shape was synthesized by double addition method, controlling content of crystal modifier, reaction temperature, the feed speed and other experimental conditions. However, a lot of experiments establish that double addition(one of acidization method) was more suitable for the preparation of α-HH whisker with large ratio of length to diameter.2) The conversion process of titanium white gypsum in the Ca Cl2-Mg Cl2-KCl solution at constant pressure was studied by controlling temperature, slurry concentration, salt concentration, solution p H and crystal modifier content. Results show that a relative uniform α-HH with the closely 1:1 ratio of length to diameter is prepared by the 98℃ temperature,25% salt solution, 20% slurry concentration, p H=4.5, crystal modifier adding amount was 0.01%. Then the compressive strength could reach 32.6Mpa, when water gypsum ratio was 0.35.3) It was studied that the conversion process of titanium white gypsum in the Na Cl solution under constant pressure is influenced by temperature, slurry concentration, salt concentration, solution p H and crystal modifier content. Its results show that short column α-HH with the 1:1 ratio of length to diameter could be synthesized under 98 ℃ temperature in 15% salt solution with 20% slurry concentration, p H=2.5 and 0.5% crystal modifier adding amount. When water gypsum ratio was 0.33, after oven dry, the compressive strength could reach 35.6Mpa.