| Industrial by-product gypsum is the by-product with calcium sulphate （including zero to two crystallization water） as the main composition generated by chemical reaction in the industrial production, a large number of its accumulation used land, polluted the environment, and also caused the serious waste of calcium sulfur resources. In this paper, we used the raw materials were phosphogypsum （PG） and desulfurization gypsum （FGD） from Sichuan Shifang Jin He Lin Kuang and Yanshan Limited Company Mongolia respectively. Based on the study of the chemical composition, phase analysis, micro morphology and thermal properties, the research idea was resource utilization of calcium sulfur from dissolving the industrial by-product gypsum. Firstly, this article performed the salt leaching experiments in ammonium chloride solution, to determine the optimized salt leaching process parameters. Salt immersion with alkaline environment used to fix carbon dioxide preparation of calcium carbonate. By means of controlling carbon sequestration, we got the best process parameters of preparation of rhombic and spherical calcium carbonate. Secondly, prompted the dehydrate calcium sulphate from industrial by-product gypsum to dissolve in dilute hydrochloric acid solution. In order to determine the best process conditions, the paper researched the effects of hydrochloric acid concentrations and hydrochloric acid leaching temperature on the solubility. And this paper may prepared calcium sulphate whisker by precipitation crystallization with cooling acid leaching solution. In order to make the pickle liquor recycling, this article also studied the influence of acid circulation to its solubility. By revealing the mechanism of ammonium chloride solution leaching for dissolving experiment, dilute hydrochloric acid solution leaching for dissolving experiment and salt immersion prepared shaped calcium carbonate carbon experiment, this paper theoretically verified the feasibility of the research ideas. Finally the evaluation research was studied from environmental impact, technological feasibility, product market and economic aspects.The results show that, the main chemical composition were CaO and SO2, they accounted for about 85% of the industrial by-product gypsum quality; The main mineral composition of the industrial by-product gypsum was dehydrate gypsum. Average particle size of PG was greater than FGD. Using salt leaching process effectively improved the solubility of calcium sulphate in industrial by-product gypsum. The biggest solubility of dehydrate calcium sulphate were 0.95g/100mL and 0.93g/100mL in PG and FGD respectively. Compared with the solubility in water increased 4.5 and 4.4 times respectively. Salt immersion fixed CO2 with alkaline environment, when the presence of crystal shape control agent H2O2, obtained the uniform rhombic、calcium carbonate of calcite type, the average grain size was between 3 to 9 μm. When there was no H2O2, obtained the uniform、spherical and vaterite content accounted for more than 50% of the calcium carbonate, the average particle size was bigger than calcite. Shaped calcium carbonate whiteness were greater than 99% and purity higher than 97%. Products conformed with the national industrial calcium carbonate using indicators. The industrial by-product gypsum treated with acid leaching, the biggest solubility of dihydrate calcium sulphate were 5.78g/100mL and 5.55g/100mL in PG and FGD respectively. Compared with the solubility in water increased 27.7 and 26.6 times respectively. Under the condition of different acid leaching for precipitation crystallization products were all white fibrous dihydrate gypsum. The slenderness ratio of PG and FGD acid immersion precipitation crystallization products were 89 and 100 respectively. Pickle liquor recycling could reduce the solubility of the industrial by-product gypsum to balance the value of 2.5g/100mL, but the solubility increase effect still was better than salt laeching, and could reduce the cost of enterprise’s processing, reduce the secondary pollution to the environment.The industrial by-product gypsum salt leaching and acid leaching to promote the advantages of dissolving process basically had the following several aspects. Separated calcium sulfur resources from insoluble impurity effectively; Prepared the chemical products with high added value; Owned highly efficient resource utilization; This technology had strong feasibility. At the same time, the salt immersion with ammonium chloride and ammonium sulfate could be the sand materials of fertilizer, which used in alkaline soil. And pickling liquid could be recycled. The rational use of liquid waste effectively reduced the load to the environment, achieved industrial by-product gypsum ecological use, and had the high economic and environmental benefits. |
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