Under The Conditions Of Continuous Heating Up Of High-sulfur Coal To Restore Phosphogypsum Characteristics Of The Products

Phosphogypsum is defined as a kind of dangerous solid waste, it impacts on the Environmental sustainability. Producting sulfuric acid integrated with cement by phosphogypsum, it is a good way to consume lots of phosphogypsum. At the same time, ecomomic cost savings and good for the environment. The reduction reaction of Phosphogypsum used to by coke, and the SO2 concentration was low. Now, the reduction and decomposition of phosphogypsum by high-sulphur coal can make the SO2 concentration higher, it characterizes by the high-sulphur coal in that sulphur content is higher.In this paper, study on the trend of SO2 concentration and quality of the solid production, which in continuous heating, different reaction temperature, different C/SO3 ratio, different particle size of high-sulphur coal and kinds of high-sulphur coal condition.At the same time, TG-DTA, XRD and SEM are used for studying the reaction mechanism of the reduction reaction of phosphogypsum by high-sulphur coal. Main research conclusions are as follows:(1) Thermogravimetric analysis was used for the study on weight loss, enthalpy and stability of the reduction and decompositon of phosphogypsum by high-sulphur coal in different conditions. The result indicates that thermal analysis curves all have two weight loss stages. At 1100℃, there is a heat absorption peak in the DTA curves of phosphogypsum, which shows the phosphogypsum has beginning to melt and decompose. When the temperature is from 1230℃to 1300℃, it is the stage of heat releasing of phosphogypsum intensely decompose, while the weight loss is 24.541%. The thermogravimetric analysis curve of the reduction and decompositon of phosphogypsum by high-sulphur coal, at 1018-1101.5℃, the weight loss is 29.758%, and the heat absorption peak is 1060.64℃. It indicates that the high-sulphur coal can lower the reaction temperature of decomposing phosphogypsum. Comparing with the thermogravimetric analysis curves in different particle size of high-sulphur coal conditions, it can find that when the particle size of high-sulphur coal is smaller, the heat absorption temperature interval is shorten, and the temperature of heat absorption peak is lower, but the weight loss rate is not very different. In some temperature interval, the weight loss rate increases when the heating rate increases. The initial and termination temperature of the reaction are corresponding to the high-temperature direction.(2) Study on the concentration of SO2, decompose rate and desulphurization rate of phosphogypsum in different reaction temperature, different C/SO3 ratio, different particle size of high-sulphur coal and kinds of high-sulphur coal condition. It shows that decomposition of phosphogypsum by high-sulphur coal can increase the SO2 concentration greatly,at the 700～800℃and 1000～1100℃, there are two peaks of SO2 concentration. When the temperature less than 800℃, undering the stronger reducing atmospheres are good for produing SO2, the situation is opposite when the temperature more than 800℃. At 700～800℃, the particle size of high-sulphur coal is affected SO2 concentration most obviously, there is about 15% at most. The smaller the particle size of high-sulphur coal is, the lower the SO2 concentration is produced firstly, and then is more and more. The trends of SO2 concentration are almost as same as in different kinds of high-sulphur coal, just the temperature intervals of high SO2 concentration and low SO2 concentration are different. The decompose rate and desulphurization rate of phosphogypsum become lower firstly and then higher when the temperature is continuously rising. In different C/SO3 ratio conditions, decompose rate of phosphogypsum changes obviously, but not for the desulphurization rate. And in different the particle size of high-sulphur coal condition, the decompose rate and desulphurization rate of phosphogypsum do not change obviously.(3) Study on the CaO content, the total fluorine content and the total phosphor content of the solid product, and take those as the indexs of cement raw material. The experimental results show that the CaO content grows slowly with temperature rising. When the reaction temperature is low, the total fluorine and the total phosphorus content are smaller. In different C/SO3 ratio condition, the CaO content can basically meet the standard of cement raw material, while the total fluorine content can meet the requirements in any reaction conditions. At the Strong reduction atmosphere, the total fluorine and the total phosphorus content do not change significantly in different kinds of high-sulfur coal condition. In different particle size of high-sulphur coal condition, the CaO content change with the decomposition rate and the desulfurization rate. When the high-sulfur coal particle size is larger, the total fluorine and the total phosphorus content are less.(4) Combinating of the foregoing experimental analysis results, it characterizes and analyzes the solid products of decomposing phosphogypsum by high-sulphur coal by XRD and SEM. The result shows that, there is some C3A in the solid product at 1100℃.