Research On Preparation Of Calcium Sulfate Whiskers By Atmospheric Acidification Method

Gypsum is one kind of the richest natural minerals in China, and a large number of FGD gypsum existing as industrial by-products now. However, limited to the current technology, both are only applied in the construction industry. As the major components of gypsum and FGD gypsum are calcium sulfate dihydrate, using gypsum and FGD gypsum as raw materials, through the method of atmospheric acidification process, preparation of calcium sulfate whisker was researched in this paper. It has important practical significance for the research of the preparation of CSW, the development of the gypsum resources and the recycling of the FGD gypsum in China.Selection of one proper solution to improve the solubility of calcium sulfate, then to improve the solution concentration and the production rate of CSW is the first key problem of the study of atmospheric acidification method. The volumetric method had been used to measure the solubility, the solubility properties of plaster stone in different solutions were analysised in this paper. The experimental results showed that the solubility of plaster stone changes greatly in strong electrolytic solution,ammonium salt solution and hydrochloric acid solution, the solubility is effected by the acidity and the concentration of salt solution. Comparatively speaking, the solubility of plaster stone has a maximum in the ammonium citrate solution(30-40wt%), it can reach 2.04g/100ml in the mixed solution of hydrochloric acid(10wt%),magnesium chloride(5wt%) and sodium chloride(5wt%). These results are of certain guiding significance for the technology development of atmospheric acidification method.The preparation of gypsum whisker by atmospheric acidification method is an important research subject in the area of whisker, the technical process and influencing factors were studied in this paper, and the product of calcium sulfate whisker was attributed by thermogravimetry (TG), X-ray diffraction (XRD), three-dimensional digital microscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR). Many kinds of influencing factors of the product of calcium sulfate whisker morphology and length to diameter ratio were researched in this paper, including reaction time, slurry concentration, mol ratio of the SO42-/Ca2+, the crystal promoter, cooling time. At last, the optimal conditions are determined. The results show that:Using gypsum and FGD gypsum as raw materials, magnesium chloride as crystal promoter, the optimal conditions of the atmospheric acidification method to prepare CSW is as follows:the concentration of Ca2+ is 0.15mol/L, the mol ratio of the SO42-/Ca2+ is 10, the boiling time is 15min, the aging time is 6 hours, crystal promotor molar ratio of Ca to Mg is 13, the product should be dried under 200℃for 0.5h.In this paper, the mechanism of the preparation and the microscopic growth process of the calcium sulfate whisker was described, then different stages of change and growth pattern of calcium sulfate whisker was introduced, the growth process of calcium sulfate whisker growth mechanism as solid-liquid and dislocation growth system was proposed, Finally, the orientation for the development of the calcium sulfate whisker was expected.