Experimental Research On Regeneration Of Waste Mixed Acid By Fluidized Bed Roaster

China is the world’s largest producer and user of acid,as well as the largest producer of stainless steel.In the process of pickling stainless steel,a large amount of waste mixed acid is generated.In order to prevent the pollution of the environment and the waste of resources,the resource recovery of waste mixed acid is a matter of urgency.Among the many waste acid regeneration technologies,fluidised bed roasting can achieve effective recovery of acid and heavy metal ions without causing secondary pollution to the environment.At present,domestic and international research on the treatment of waste acid by fluidised bed roasting only focuses on waste hydrochloric acid,and there are no research reports and engineering applications on the treatment of waste mixed acid by fluidised bed roasting.In order to address the research gap of regeneration of waste mixed acid by fluidised bed roasting,a fluidised bed roasting device for regeneration of waste mixed acid was designed and constructed in this paper.The influence of the temperature of the dense phase zone and the particle size of the initial bed material on the regeneration characteristics of the fluidized bed method of waste mixed acid was investigated.The experimental results show that the fluidized bed roasting method can effectively recover HNO₃and HF from the waste mixed acid;the recovery rate of HNO₃increases with the increase of the dense-phase zone temperature and reaches the peak at 750℃with the recovery rate of 71.71%;the recovery rate of HNO₃decreases slightly when the temperature of the dense-phase zone continues to increase;the recovery rate of HNO₃decreases slightly when the initial bed size is increased at a certain temperature of the dense-phase zone.The HF regeneration characteristics are mainly influenced by the temperature in the dense phase zone and the immobilisation of Ca O.As the temperature in the dense phase zone increases,the HF recovery increases,reaching a peak at750℃with a recovery of 55.79%;as the temperature in the dense phase zone continues to increase,the HF recovery decreases significantly as the fluorine fixation effect of Ca O in the bed material increases.When the temperature in the dense phase zone was lower,the HF recovery rate decreased by increasing the initial bed material particle size;when the temperature in the dense phase zone exceeded 800℃,the HF recovery rate increased slightly by increasing the initial bed material particle size,because the fluorine fixation effect of Ca O in the bed material was weakened.In addition,it was found that the HF recovery rate also decreased due to the small amount of calcium ions contained in the waste mixed acid.The effects of temperature in the dense phase zone,initial bed size,acid injection time,solute components and iron ion concentration on the regeneration characteristics of elemental metals by fluidised bed roasting with waste mixed acids were further investigated.The experimental results show that the granulation process of metal oxides on the surface of the bed material is different from the granulation process of"onion-like"layered structure on the surface of the particles at low temperatures during the regeneration of metal elements by the fluidized bed process of waste mixed acid.At high temperatures the waste mixed acid reacts with evaporation in the interstices of the bed material particles to produce fine particles,some of which are adsorbed on the surface of the bed material and no layered structure is observed.The temperature in the dense phase zone and the initial bed size have a significant effect on the regeneration characteristics of the metal elements.The amount of fine particles adhering to the surface of the bed material particles increases with increasing temperature in the dense phase zone,reaching a peak at 850℃with an adsorption amount of 0.011 mm³;the amount of adherence decreases slightly with increasing temperature.The proportion of Fe on the surface of the bed material decreases with increasing temperature in the dense phase zone.At a certain temperature in the dense phase zone,increasing the initial particle size of the bed material can effectively increase the adhesion of fine particles on the surface of the bed material;the proportion of iron on the surface of the bed material increases with the increase of the initial bed material particle size.With the increase of acid spraying time,the percentage of iron on the surface of the bed material decreases and the amount of fine particles attached increases,the rate of increase decreases and then increases.In order to study the effect of different components of waste mixed acid on the regeneration characteristics of metal elements,different concentrations of iron nitrate solution were prepared by ourselves.Under the conditions of iron nitrate solution,the adsorbed fine particles on the surface of the bed material were of uniform size,with an average size of about 100 nm.As the concentration of iron ions in the iron nitrate solution increased,the adsorption of fine particles on the surface of the bed material increased and the rate of increase increased;the proportion of iron elements on the surface of the bed material increased with the concentration of iron ions and reached 98.44%.The adsorption of fine particles on the surface of the bed material,the roughness and the percentage of Fe on the surface of the bed material all increased with the increase of the spraying time under the iron nitrate solution condition.