Experimental Studies On Preparing Building Plaster By Suspended-state Dehydration Of Phosphogypsum

Phosphogypsum is one of the largest solid waste emissions in chemical industry. As the content of CaSO4·2H2O in phosphogypsum is generally more than 90 percent, it was supposed an important resource to be exploited. The resource of phosphogypsum has great commercial value and practical significance in environmental security and sustainable development of phosphorus chemical industry. The object of this study is the two-steps preparation of building plaster phosphogypsum dehydrated process route developed by Xi’an University of Architecture and Technology. As described in this paper, we do the research to find the best optimal control parameters in the dehydration process of phosphogypsum.Dehydration of the thermodynamic calculations show that the reaction temperatur of the dehydration of phosphogypsum in the first step in theory is 110.55℃,and the second step is 223.94℃. Results of the dehydration process mass and energy balance calculation showed that when the feeding amount is 30t/h, the yield of 23.32t/h; the actual heat rate is 1143.65 kJ/kg; the system thermal efficiency is 62.38%. It provieded a theory basis for the dehydration of phosphogypsum industry equipment design follow-up.Suspended-state dehydration of phosphogypsum results show that the ratio of temperature and solid-gas is the most important factor influence the dehydration; Semi-hydrated gypsum exitence tempreture range from 150℃to 190℃; Anhydrite begin to appear in the tempreture of 170℃. The tempreture of producing semi-hydrated gypsum should be controlled between 150℃to 17℃. Under the existing system, the best operating parameters are:solid-gas ratio than Z= 0.24, dehydration temperature T =190℃.Peformance testing analysis of dehydrated phosphogypsum showed that when the average size of phosphogypsum 20μm, dehydration temperature about 170℃; aging time is 5 days, the products meet the quality requirements of the building plaster 2.0 level.