Experimental Study On The Fluidized Calcinations Of Iron Dichloride Tetrahydrate

In metallurgical industry,acid pickling process will produce acidic waste water containing ferrous chloride which can cause serious pollution to the environment.A process has been developed to treat the acidic waste water,which consists of the acidic waste liquid concentrated crystallization and FeCl₂·4H₂O crystals calcination.The crystals fluidization calcined to form Fe₂O₃,and the tail gas was absorbed to get high concentration HCl solution for acid pickling process.It was found that in addition to the generation of HCl,Cl₂ was also generated in the calcination process,and the air moisture content affected the generation rate of HCl and Cl₂.The existence of Cl₂ affected the concentration of regenerated acids.In this thesis,the fluidized calcination experiments of FeCl₂·4H₂O crystals were carried out to study the effects of air moisture content and bed temperature to the calcination process,which includes the production of HCl and Cl₂,the generation rate of HCl and Cl₂,HCl yield and HCl selectivity.The results show that the increase of air moisture content or the decrease of bed temperature will increase the HCl selectivity and HCl yield.When the air moisture content increased from 29 to 71 g water/kg dry air,the HCl yield increased from 3%to 52%,the stable HCl selectivity increased from 0 to 2 under the circumstance of bed temperature reaching 500°C.At an air moisture content of 62 g water/kg dry air,when the bed temperature increased from 295°C to 500°C,the stable HCl selectivity decreased from 1.5 to 1,the HCl yield decreased from 53%to 39%.The characteristics of FeCl₂·4H₂O particles and FeCl₂·4H₂O particles after calcining for two minutes were observed by scanning electron microscope.The scan picture shows that the surface and interior of the FeCl₂·4H₂O particles are dense,while the particles after calcining for two minutes is still dense inside,but the outer layer is loose.Combined with the experimental phenomena,it is judged that the process of calcination is a shrinkage process,and the reaction is carried out on the surface of particles.A kinetic equation is established.It is considered that the fluidization calcination process of FeCl₂·4H₂O crystals can be divided into two steps:The first step is the oxidation of FeCl2·4H2O crystals to generate Fe₂O₃ solid and FeCl₃ gas.The second step is a parallel reaction,in which the FeCl₃ gas react with O₂ and H₂O to generate HCl and Cl₂ gas respectively.The kinetic model of the first step was established with conditions which were average grain size 0.735mm of FeCl₂·4H₂O crystals,apparent gas velocity of 0.73 m/s at room temperature,bed temperature of 295⁵00?,and air moisture content of 29⁷1g water/kg dry air.The results were:k=0.58exp?-2.46×10⁴/RT?;t=?R_p[1-?1-X?^1/2]/4kC_BoUnder the experimental conditions,the reaction order of the H₂O is 4 in the reaction which generated HCl.And the activation energy of Cl₂ generation reaction is8.87kJ/mol,which is larger than that of HCl generation reaction.