Study On Adhesion Characteristics Of Particles During The Decomposition Of Phosphogypsum

Phosphogypsum is a by-product produced in the process of wet process phosphoric acid production.Because of its high yield and low comprehensive utilization rate,the development of phosphoric acid process and the waste of resources are seriously affected.In view of the practical problems of phosphogypsum recycling,it is found that the phenomenon of agglomeration and adhesion of phosphogypsum powder is more serious in the process of coproduction of sulfuric acid and cement with phosphogypsum.Considering the characteristics and reaction mechanism of thermal decomposition of phosphogypsum,this paper combines with previous research mainly studies the use of coal in two step reduction of oxidative phosphogypsum,study the reaction mechanism and the agglomeration mechanism of adhesion.Study on the cold state adhesion of phosphogypsum to the fluidization state,and the effect of SiO2 on adhesion and aggregation,exploration the influence of the desilication of phosphogypsum on the composition of cement clinker by the study on the effect of SiO2 through desilication of phosphogypsum.The main results of this paper are as follows:1.The results of the cold fluidization experiment of phosphogypsum are shown that the feed quantity of phosphogypsum mixed powder tends to a stable value at room temperature,and the adhesive value has a downward trend with the increase of temperature;the larger the gas velocity,the lower the adhesion degree of the particles.Besides,with the increasing of gas velocity,the adhesion degree tend to be stable.In the existing experimental conditions,the adhesion is stable when the wind speed is 2.2m/s.At the same temperature and aeration rate,the smaller the particle size of the powder particles,the easier it is to adhere to the wall.2.The results of the adhesion phenomenon of phosphogypsum in the two-step method thermal decomposition process indicate that in the process of heating,the adhesion degree of the pow ders decreases first,then increases and then decreases,and the agglomeration of particles and the adhesion of the wall are consistent.The degree of adhesion is different at different stages in cyclic aeration stage.The adhesion degree of the wall will decrease obviously in the oxidation stage,however the adhesion of particles will be increased when switching to the reducing atmosphere;Through the SEM analysis of the morphology of tube wall foulant and piping fluid found that the scale of the foulant is different,and the adhesion phenomenon is serious,however the overall shape of the particles in the fluid is regular.and the surface is relatively smooth.XRD analysis on tube wall foulant and piping fluid.it was found that during the fluidization process,the mineral elements such as Si and Al are easy to enrich in the wall and increase the adhesion of the wall.while in the process of cyclic aeration.CaO can effectively destroy the net structure,such as SiO2 and Al2O3,which can effectively reduce the adhesion of particles.3.In the adhesion study of different degree desilication of phosphogypsum(SiO2 content was 8.8%.4%and 2%respectively),it was found that the lower the SiO2 content.the smaller the aggregation adhesion degree,the overall trend is basically consistent with the change of temperature.4.Through the comparison of thermal decomposition and evaluation of cement clinker index of the phosphogypsum with different degree of desilication(SiO2 content is 8.8%,4%.2%),the results show that:In the thermogravimetric experiment,the weight loss rate of phosphogypsum was significantly higher than desilication phosphogypsum,and a decreasing amount of SiO2 in the temperature around 950 has a certain role in inpairing the reduction reaction of phosphogypsum.The desulfurization rate of phosphogypsum,phosphogypsum(original)(the content of SiO2 is 4wt%)and desilication phosphogypsum(the content of SiO2 is 2wt%)decomposed by two-step method was 86.45%.75.15%and 80.53%,respectively,it is indicated that the removal of SiO2 can inhibit the thermal decomposition of phosphogypsum to some extent.Through the analysis of the three kinds of phosphogypsum decomposition products,the rate of desilication phosphogypsum is more in line with the regulations of cement clinker,desilication of phosphogypsum will significantly reduce the rate of SM value,increase the rate of lime saturation coefficient KH and have little effect on IM rate.