Basic Research On Harmless Disposal Of Metallurgical Desulfurization Gypsum Enhanced By Ultrasoni

Calcium sulfite and trace element arsenic in metallurgical flue gas desulfurization gypsum are key indicators that affect the utilization efficiency of desulfurization gypsum.In order to improve the utilization efficiency of metallurgical flue gas desulfurization gypsum in China at present,this article proposes a new harmless treatment technology for flue gas desulfurization gypsum using hydrogen peroxide as oxidant,sulfuric acid as a leaching agent,and ultrasound as strengthening means.The research content of the project is divided into two parts:The first part is to use ultrasound combined with hydrogen peroxide to eliminate the unoxidized calcium sulfite in the limestone gypsum wet flue gas desulfurization process,aiming to improve the usability of the flue gas desulfurization gypsum and establish primary conditions for subsequent use of sulfuric acid leaching of arsenic.The second part is to use sulfuric acid as the leaching agent and ultrasound as the strengthening method to leach arsenic from flue gas desulfurization gypsum on the basis of oxidation pretreatment.The effects of H₂O₂ dosage,reaction temperature,liquid-solid ratio,and ultrasonic power on oxidation efficiency were discussed through single-factor experiments.The optimal process parameters for the leaching process were obtained through orthogonal experiments.The mechanism of ultrasound combined with hydrogen peroxide oxidation of calcium sulfite and ultrasound-enhanced sulfuric acid leaching of arsenic was studied through thermodynamics,kinetics,and modern analytical characterization techniques such as XRD,XPS,SEM,and EPMA.The main conclusions are as follows:（1）Compared with a single H₂O₂ oxidation system,ultrasound combined with H₂O₂can oxidize more than 95%of calcium sulfite in flue gas desulfurization gypsum under conditions of 1.2 times the amount of H₂O₂,reaction temperature of 313 K,time of 40min,liquid-solid ratio of 8:1,and ultrasound operating power of 420 W.The kinetic analysis results show that the oxidation process conforms to the internal diffusion control equation of the unreacted core model,and the activation energies of the H₂O₂system and the H₂O₂/US system are 28.81 k J·mol^-1 and 12.40 k J·mol^-1,respectively.（2）The orthogonal experimental results show that the optimal process parameters for ultrasound-enhanced sulfuric acid leaching of arsenic are leaching temperature 338 K,leaching time 60 min,liquid-solid ratio 8:1,H₂SO₄ concentration 9%,ultrasound power intensity 0.087 W/ml,and the leaching efficiency of arsenic higher than 97%.The thermodynamic and kinetic research results show that arsenic in desulfurization gypsum enters the leaching solution in the form of arsenic acid and arsenious acid,and the leaching reaction rate is controlled by internal diffusion,with a reaction activation energy of 13.38 k J·mol^-1.（3）The toxicity leaching assessment results showed that the arsenic concentrations in the leaching solution before and after harmless disposal of desulfurization gypsum were 383 mg/L and 3.57 mg/L,respectively.After the harmless disposal of metallurgical desulfurization gypsum,the hazardous characteristics are eliminated,laying the foundation for its efficient resource utilization.To sum up,it is a new idea with practical significance to implement harmless disposal of metallurgical flue gas desulfurization gypsum using ultrasonic combined with H₂O₂ and H₂SO₄.In the oxidation pretreatment stage,ultrasound can improve the oxidation efficiency of calcium sulfite by hydrogen peroxide and can also change the reaction path of calcium sulfite oxidized by hydrogen peroxide.During sulfuric acid leaching of arsenic,the mechanical effect of ultrasound can improve arsenic leaching efficiency and the particle size uniformity of flue gas desulfurization gypsum.