Research On The Fluidized Calcination Process Of FeCl₂·4H₂O And Its Kinetics

There is a very important pickling process in metallurgical industry,that is,removing the steel surface oxide with hydrochloric acid,which will produce a large number of acidic waste containing FeC l2,and its direct discharge will cause serious pollution to the environment.If the FeC l2 acidic waste solution is further concentrated and crystallized to obtain FeCl₂·4H₂O crystal,and calcinating it at high temperature to produce HC l gas and Fe₂O₃ powder,the energy consumption of the calcination process can be reduced,the HC l gas content in the exhaust gas will be increased,the regeneration Hydrochloric acid concentration will be improvd,and the impurity content in Fe₂O₃ powder will be reduced.In this paper,the fluidized calcination process was studied using FeCl₂·4H₂O crystal as raw material.The FeCl₂·4H₂O crystals were fluidized calcinated by air in fluidized bed reactor that has a diameter of 44 mm.The relation of conversion of FeCl₂·4H₂O crystals with reaction time was obtained by measuring the chloride ion concentration in tail gas absorption solutions with chloride ion selective electrode,and process influence factors was investigated,including superficial gas velocity,average grain d iameter and bed temperature.And the kinetic model of calcination reaction of FeCl₂·4H₂O crystal was established.The results showed that the Fe₂O₃ gennerated by FeCl₂·4H₂O crystal calcination was loose in texture and peeling off from the particle surface,flowing out of the calciner with the airflow in the fluidized state,which was similar to the shrinking reaction process.When the FeCl₂·4H₂O crystal was fluidized calcinated,the influence of external diffusion was significant with low apparent gas velocity;with the increase of apparent velocity,the influence of external diffusion was declined and the reaction rate was accelerated,the calcination time was shortened.When the apparent gas velocity get to 0.64 m/s,the influence of external diffusion the external diffusion was basically eliminated and it had no obvious effect on the calcination reaction with the increasing of the apparent gas velocity,and the process was controled by surface reaction.The smaller of the initial FeCl₂·4H₂O crystals' average particle size,the faster of the starting reaction rate,the more obvious declining rate with time,and the shorter of completing time of the calcination reaction.The bed temperature has a significant effect on the calcination reaction,and the calcination reaction is proportional to the particle surface areaThe fluidized calcination kinetic model of FeCl₂·4H₂O crystal was established with bed temperature of 295⁵00 ?,average grain size of 0.387⁰.777 mm,and apparent gas velocity of 0.64⁰.73 m/s,which were:In the experimental range,the calculated values of the model were in good agreement with the experimental results that the FeCl₂·4H₂O crystal fluidization calcining was control by surface reaction.When the apparent velocity is less than 0.64 m/s,the calculated value of the model was different from the experimental value,and the external diffusion effect could not be ignored.