| Phosphogypsum as the typical stable of solid waste, the increase of its emission has seriously impacted the environment. At present, the phosphogypsum grand total stacking amount have already been over 3 million tons. Therefore, disposition of phoshogypsum has become one of the most serious problem of phosphorus chemical industry. Integrated production of sulfuric acid and cement from phosphogypsum is one way to largely consume it. However, its defects of excess in the phosphogypsum decomposition temperature and energy consumption restrict the further promotion of this technology. To overcome the shortcomings of the traditional process, mineralizer was used for the phosphogypsum reduction decomposition in this article, so as to decrease its decomposition temperature and increase the conversion of decomposition. We mainly researched the mineralizer action effects on phosphogypsum reduction decomposition and analyse from the aspect of kinetics and thermodynamics that influence its reduction decomposition process. Combining with phase change, microstructuring and element migration varying pattern and so forth, we explained the reaction mechanism of mineralizer on phosphogypsum reduction decomposition process. The primary study achievement gained from this article are following:Different mineralizers were used for phosphogypsum reduction decomposition, and the suitable mono mineralizer (CaF2) was chosen, which could effectively decrease the decomposition temperature and improve its effect of reduction decomposition. With 3 weight% of minerals CaF2 added, the optimum of technology parameters in the process of phosphogypsum reduction decomposition were mole ratio of materials C.S of 0.7, decomposition temperature of 950℃, resolving time of 60 min, the oxygen concentration set in the import carrier gas of 1.9～2.2% and PCO/PCO2 in reaction system of 13～18%, Phosphogypsum decomposition rate under the optimal conditions reached to 90.6%, and SO2 conversion also arrived to 70.4%, as well as SO2 volume concentration from the decomposition of tail gas was up to 11.9 volume%. All thesecan totally satisfy the demanding of preparing sulfuric acid in industry.The optimum recombination mineralizers of phosphogypsum reduction decomposition selected from orthogonal experiment were 2 weight% Na3AlF6,2 weight% CaF2. Decomposition temperature was a significant factor in the process of phosphogypsum reduction decomposition. The changes occurred in the microstructure of materials before and after the phosphogypsum decomposition. Phase and element content analysis showed that after adding the suitable mineralizer, the main components of phosphogypsum decomposition product were Ca2SiO4、Ca3SiO5 and a small quantity of CaSiO3 which were the major component of cement clinker.Kinetic study indicated that, the results of calculation using Coats-Redfern method in getting the activation energy of mineralizer for phosphogypsum reduction decomposition CaF? was E=380.06 kJ/mol and exponential factor was A=1.56×10116. The varying pattern of conversion rate and activation energy can be seen by using the equal conversion method for estimating the activation energy of phosphogypsum reduction decomposition. From Flynn-Wall-Ozawa method and Vyazovkin and Wight method used in analyzing the kinetics of phosphogypsum decomposition, the reaction mechanism of low conversion was very complicated with multiple parallel competitive reaction maybe involved.The finds in the element balancing study of phosphogypsum reduction decomposition illustrated that migration of solid phases and liquid phases were included in the sulfur element migration. In the decomposition of residue, sulfur mainly existed in the form of CaS and CaSO4. In addition to SO2 in the gas phase, there was also an unknown sulfur containing compound. Fluoride migration form mainly existed in the solid phase composition during the process of phosphogypsum reduction decomposition and the transfer and transformation of vapor-phase fluorine components were not obvious. |
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