Study On The Semidry Desulfurization Ash Of The Production Of Sulfuric Acid And Al₂O₃ Extraction From Pulverized Fly Ash

Desulfurization ash is the by-product of flue gas desulfurization in coal-combustion and metallurgical industries. Arbitrarily stacking of the ash could result in excessive land occupation, serious secondary pollution and financial burden of the companies. Thermopower factories produce huge pulverized fly ash, which not only threatens our living environment but also limits the sustainable development of national economy. In this paper, the desulphurization ash and pulverized fly ash are utilized to produce sulfuric acid and Al₂O₃ simultaneously due to the scarcity of sulphur and bauxite resources in China.This paper is focused on: (1) Physical and chemical characteristics, mineral composition and microstructure of the desulfurization ash were studied by means of XRD, DSC, SEM, EDS etc. (2) The process of producing sulfuric acid and alumina from desulfurization ash and pulverized fly ash respectively is studied on the basis of thermodynamics analysis, and the possibility, final products of the chemical reactions were all studied in this paper. (3) In addition to the mixing amounts of coke and pulverized fly ash, the calcinations temperature on the ecomposition of CaSO₄ and the leaching of aluminium is also investigated in this paper. (4) The optimum reaction conditions were determined in the end.Four conclusions can be drawn from this study: (1) With a certain quantity of SiO₂ and Al₂O₃, the main chemical compositions of the desulfurization ash include CaSO₃, CaSO₄, Ca(OH)₂ and CaCO₃ etc. Hannebachite, anhydrite, calcite and portlandite are the main mineral phases in the the desulfurization ash, and some calcium chloride is also found in the system. The grains in the desulfurization ash occur as clastic particles, with irregular particle shapes and different particle sizes. (2) The reaction system studied in this paper possesses great complexity due to the appearance of some side reactions. The decomposition of CaSO₄ under the reducing atmosphere and with the pulverized fly ash responded produces C₁₂A₇ is triggered at 800°C, and with the rise of temperature the main reaction is more and more likely to occur. When the temperature rise to 900°C, compared with other side reactions the main reaction is more likely to occur and become the dominant reaction. (3) With the resistant coke adding to the system, the decomposition of CaSO₄ is apparently accelerated, while there is a optimal amount of coke when the mixing amounts exceed the optimal amount it will bring the opposite effect. The Al2O3 and SiO₂ react with the CaO from the decomposition of CaSO₄ and trigger complicated reaction, producing C₁₂A₇ and other sulfur-containing by-products, which affect the decomposition of CaSO₄. High pulverized fly ash content will lower the producing of aluminium, while the rising of the temperature is good for the decomposition of CaSO₄ and the producing of aluminium. According to the importance of each influencing factor, the can be ordered as follows: temperature> pulverized fly ash content>coke content. (4) Considering the decomposition of CaSO₄ and the producing of aluminium, the optimum conditions of the system is established as follows: 1200°C, C/DF1=0.085, Ash/DF1=0.294, at this time the CaSO₄ rate of dissociation is 81.73%, the aluminum extraction rate is 83.52%.The study in this paper shows that using desulphurization ash and pulverized fly ash to produce alumina can accomplish high decomposition rate of CaSO₄ and extraction rate of aluminiums, which reflect its vast application prospects in the disposition of desulphurization ash and pulverized fly ash.