Carbon Monoxide Reduction Decomposition Of Phosphogypsum

Phosphogypsum is a by-product from wet-processes for phosphoric acid. It brings in environmental hazards for massive production and discharge, while wasting enormous human, materials and financial resources. Facing economic loss and environmental double pressure, it is large-scale resource utilization of phosphogypsum that has become the key of realizing sustainable development in phosphorous chemical industry. It is one of the best influential utilization approaches for phosphogypsum to product sulfuric acid through decomposition of it. However, it will need a high temperature and lots of energies for the process, so the decomposition of phosphogypsum under carbon monoxide atmosphere was studied concerning the problem in the paper. The results of the study could provide the basic data and theoretical reference for utilization technology about phosphogypsum.It was discussed with chemical thermodynamics software HSC Chemistry that thermodynamic behavior of the reductive decomposition of phosphogypsum under carbon monoxide atmosphere. Molar Gibbs free energy change (△,Gm), molar enthalpy change (△rHm) and molar enthalpy change (△rSm) of the twenty probable reactions were all calculated with the reaction equation module of HSC software, which were involved in the reductive decomposition of phosphogypsum under carbon monoxide atmosphere. It shows that these most reactions are endothermic, and that is why the reductive decomposition of phosphogypsum needs lots of energies. It was simulated with the equilibrium composition module of HSC software that the equilibrium composition of the reductive decomposition of phosphogypsum under carbon monoxide atmosphere. It shows that most reactions of the process are coupled with others, instead of one by one being unaided. and what is more, reaction coupled by CaSO4(s)+4CO(g)=CaS(s)+4CO2(g) and CaSO4(s)+1/3CaS(s)= 4/3CaO(s)+4/3SO2(g) and the reaction coupled by CaSO4(s)+1/3CaS(s)=4/3CaO(s) and CaS(s)+3CO2(g)=CaO(s)+SO2(g)+3CO(g) are the main lines.Microstructure of phosphogypsum was observed with scanning electron microscope (SEM), and it shows that phosphogypsum particles are erose sheets and there are lots of gaps between different particles which are sticked together. Elemental composition of phosphogypsum was achieved with help of Energy Dispersive Spectrometer (EDS), it shows that different regions have different elements with oxygen, Sulfur, silicon and calcium as main elements. Phase of phosphogypsum was characterized with X-ray powder diffractometer (XRD), and it shows CaSO4·2H2O is main and SiO2 is a little in it. Particle size of phosphogypsum was measured with particulate size description analyzer, and it shows that the particle size distribution of phosphogypsum is the approximate normal distribution.With the help of thermal Analysis, the influencing factors were investigated, and the result shows that reductive atmosphere is of advantage to the reductive decomposition of phosphogypsum; there are two stages in the process of the reductive decomposition of phosphogypsum under carbon monoxide atmosphere, one is the dehydration stage, and the other is the reductive decomposition stage; 5wt.% CaCl2 added is of advantage to the reductive decomposition of phosphogypsum under carbon monoxide atmosphere.It was investigated that the kinetics behaviors of the reductive decomposition of phosphogypsum under carbon monoxide atmosphere, and it shows that the process is under the control of chemical reaction, and kinetic equation of the reductive decomposition stage isand the kinetic compensation effect isIn,A= 0.1115E+0.0211, and the activation energy value increases the conversion percentage of phosphogypsum.