Study On The Dealkalization,Iron Leaching And SO₂ Removal Of Red Mud Treated By Supercritical Water

Red mud,as a kind of industrial waste generated in the alumina production process,has become the most intractable industrial solid waste in the non-ferrous metal smelting industry due to its strong alkalinity,large emissions,and high environmental risk.Not only can it be used as a whole in the form of raw materials,the red mud is also rich in a variety of valuable metals.Therefore,realizing the comprehensive utilization of red mud has always been a very important and difficult point urgent to be solved at home and abroad.In view of the poor dealkalization effect and high cost in the old technology,the supercritical water treatment method was applied in this study.We used the red mud derived from Bayer process as the main raw material and explored the effects of temperature,pressure,reaction time,leaching agent,liquid-solid ratio on the red mud dealkalization and iron leaching efficiency,respectively.In addition,the effect of red mud treated by supercritical water on the flue gas desulfurization was measured.In order to further evaluate the effect of this method,the solid phase composition and micro morphology of red mud were analyzed by scanning electron microscope(SEM),X-ray diffraction(XRD)and Fourier transform infrared spectroscopy(FTIR).According to the research,we draw the following conclusions:(1)The temperature,pressure,time and liquid-solid ratio of the reaction in the supercritical water treatment process can affect the dealkalization and iron leaching efficiency of red mud without the presence of the leaching agent.When the temperature is 385?,the pressure is 23 MPa,the reaction time is 45 min,and the liquid-to-solid ratio is 10 mL/g,the dealkalization rate of the red mud is 42.3%,and the iron leaching rate is 31.7%,which reaches the best conditions of the experiment.(2)The experiment showed that CaO is the best leaching agent,which can remove over 97.9%of alkali and leach 82.7%iron under the experimental conditions(T=385?,P=23 MPa,t=60 min and liquid-solid ratio is 20 mL/g,the mass ratio of red mud and CaO is 8).The related characterization results indicated that the cancrinite and garnet in the treated red mud were converted into simple compounds such as calcium carbonate and calcium silicate.Meanwhile,the surface of the red mud became smooth and the aggregates disappeared,which means that the reappearance of alkalinity is structurally prevented.(3)The desulfurization results showed that the desulfurization performance of the treated red mud has been greatly improved.The best desulfurization effect can be achieved under the conditions of 25?,air flow rate is 400 mL/min,SO₂ volume ratio of 0.2%,and liquid-solid ratio is 100:5.The analysis results showed that the alkali in the red mud can completely react with SO₂ and the main products of desulfurization are CaSO₄ and other calcium silicon slag.In addition,the microscopic surface of the product became smooth and some large particles are decomposed into small particles after the reaction.