Abstract
Phosphogypsum (PG) is not only a solid waste discharged from the phosphate fertilizer industry, but also a valuable resource. After high-temperature heat treatment, it can be decomposed into SO2 and CaO; the former can be used to produce sulfuric acid, and the latter can be used as building materials. In this paper, the catalytic thermal decomposition conditions of phosphogypsum were optimized, and the effects of the reaction temperature, reaction atmosphere, reaction time and carbon powder content on the decomposition of phosphogypsum were studied. The research shows that the synergistic effect of carbon powder and CO reducing atmosphere can effectively reduce the decomposition temperature of phosphogypsum. According to the results of the orthogonal test under simulated suspended laboratory conditions, the factors affecting the decomposition rate of phosphogypsum are temperature, time, atmosphere and carbon powder content in turn, and the factors affecting the desulfurization rate are time, temperature, atmosphere and carbon powder content in turn. Under laboratory conditions, the highest decomposition rate and desulfurization rate of phosphogypsum are 97.73% and 97.2%, and the corresponding reaction conditions are as follows: calcination temperature is 1180 °C, calcination time is 15 min, carbon powder content is 4%, and CO concentration is 6%. The results of thermal analysis of phosphogypsum at different temperature rising rates show that the higher the temperature rising rate, the higher the initial temperature of decomposition reaction and the temperature of maximum thermal decomposition rate, but the increase in the temperature rising rate will not reduce the decomposition rate of phosphogypsum.
Highlights
Phosphogypsum (PG) is a solid waste produced during the wet production of phosphoric acid in the phosphate fertilizer industry, and its main component is CaSO4·2H2O or CaSO4·0.5H2O [1,2,3]
The theoretical decomposition temperature of phosphogypsum is as high as 1700 ◦C, and the high energy consumption of phosphogypsum thermal decomposition and the instability of decomposition product components have not been completely solved, which greatly restrict the industrial application of phosphogypsum to produce sulfuric acid and lime [15,16,17,18,19]
In order to explore the influence of experimental conditions on the thermal decomposition reaction process of phosphogypsum, the reaction process analysis of phosphogypsum samples under two experimental conditions of self-decomposition, adding carbon powder into phosphogypsum and introducing CO atmosphere was carried out on a synchronous thermal analyzer with the same rate of temperature rise (10 ◦C/min)
Summary
Phosphogypsum (PG) is a solid waste produced during the wet production of phosphoric acid in the phosphate fertilizer industry, and its main component is CaSO4·2H2O or CaSO4·0.5H2O [1,2,3]. Phosphogypsum can be decomposed into SO2 and CaO after heat treatment at high temperature The former can be used to produce sulfuric acid, while the latter can be used as raw material of building materials. IItt ccaannbbee ccoonncclluuddeedd ffrroomm FFiigguurree 33 tthhaatt pphhoosspphhooggyyppssuumm iinn tthhee ssaammppllee mmaaiinnllyy eexxiissttss iinn tthhee ffoorrmm ooff ppllaattee oorr ssttrriipp aaggggrreeggaatteess,, wwiitthh aa rreegguullaarr ccrryyssttaall ffoorrmm aanndd ggoooodd ccrryyssttaalllliinniittyy. Mechanism of Experiment There are three possible chemical reactions in which CaSO4 decomposition, and its decomposition products may participate [32,33,34]
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