The Basic Research Of Using Desulfurized Gypsum Produced In Metallurgical Sintering Process To Prepare Calcium Ferrite

Sintering is an indispensable process for long-process steel companies.With the implementation of China's new environmental protection standards,new or modified large-scale sintering machines are equipped with comprehensive desulphurization and denitrification flue gas purification and treatment devices.Lime/Limestone-gypsum wet desulfurization is widely used due to its relatively mature technology and high desulfurization efficiency.About 90%of the world's steel companies use lime/limestone-gypsum wet desulfurization flue gas devices..Desulfurized gypsum is the waste generated by the lime/limestone-gypsum desulfurization process.With the increase of iron and steel production year after year,a large number of desulfurization wastes in China cannot be rationally used,which has become an urgent problem for the steel industry.This article through experimental research,trying to explore the use of waste generated in the sintering process of long-process steel companies-desulfurized gypsum to prepare calcium ferrite,and the possibility of comprehensive recovery and reuse.The study performed the following work.?1?Analyze the composition and composition of desulfurized gypsum,and found that the main component of desulfurized gypsum is calcium sulfate dihydrate,which contains harmful elements such as Hg,and it is difficult to analyze the desulfurization gypsum;?2?Research the mechanism of gypsum decomposition,and query and calculate the thermodynamics On the basis of the data,the pure gypsum was placed in a tube-type atmosphere furnace to study the factors affecting the decomposition and desulfurization of gypsum by the proportion of CO/CO₂ mixture gas,gas flow rate,reaction time and reaction temperature;?3?Waste-desulfurized gypsum prepared as calcium ferrite to achieve the comprehensive utilization of green resources,the Ca SO₄ as a calcium source,adding iron oxide and coke,experimental research,analysis and exploration of the key technical parameters of calcium ferrite preparation.In this study,a thermogravimetric analyzer was used to determine the sintering temperature profile of desulfurized gypsum;the composition of the gypsum decomposition products under different conditions was determined and determined by XRD semi-quantitative analysis,and the desulfurization rate was calculated;the shape of the reaction product was characterized by OM and SEM.The appearance and determination of the kinetic mechanism.The experimental results of reduction and decomposition of gypsum in a microreduction atmosphere show that:?1?the desulfurization efficiency is not high under simple atmosphere control conditions.Under the condition of CO/CO₂=5×10^-2,when the decomposition temperature is 1323K,gypsum is decomposed by gas-solidification.The reaction turns into a solid-solid reaction joint control.The initial desulfurization reaction rate of gypsum increases with the increase of reaction temperature;however,when the SO₂ generated by the reaction cannot be rapidly eliminated,there is more CaS formation inside the reactants.CaS reacts with CaSO₄ to form CaO.?2?Under the condition of1323K and CO/CO₂ of 5×10^-2,the desulfurization rate is the largest,and its value is 18.1%.With the increase of CO/CO₂ ratio,the decomposition rate of SO₂ is difficult to eliminate,and CaS is generated,which reduces the desulfurization rate.?3?With a certain ratio of CO/CO₂,increasing the flow of mixed gas can improve the diffusion conditions of SO₂ and increase the desulfurization rate?CaO?.?4?Under the same conditions,after CaSO₄ and CaO were added to Fe₂O₃,the reduction and sintering products had the same phase and similar crystallinity and morphology.Therefore,CaSO₄ could be used as calcium source to prepare calcium ferrite.Under the conditions of argon protection and 1373K,the reduction and decomposition sintering experiments of gypsum+coke+iron ore showed that?1?the final product of the reaction system was CaO·Fe₂O₃+2CaO·Fe₂O₃,and the previous product was CaS.With the prolonged reaction time,the coke begins to participate in the reaction until the reaction is completed,and its reducing atmosphere is constantly weakening;the desulfurization rate reaches a maximum at about 3 h,and it reaches almost 99%?SEM-EDS surface scan results?.?2?At the 3h reaction time,OM images showed that a very small amount of CaSO₄ had not been decomposed,and the resulting calcium ferrite was in a massive or needle-like distribution;SEM images showed that the calcium sulfate was decomposed by lamellar flakes,uniformly distributed iron oxides and desulfurization The product reacts to form calcium ferrite.?3?The reaction mechanism is similar to that of carbon-containing pellets.The decomposition of gypsum is dominated by gas/solid reaction,and the decomposition of calcium sulfate is a restrictive link in the preparation of calcium ferrite.Because the physical and chemical properties of desulfurized gypsum and pure gypsum are similar,the results of this study will provide a clear technical route for the comprehensive utilization of the waste generated from the sintering process in the iron and steel plant-desulphurized gypsum.Calcium provides basic research data and key technical support.It is of great significance and potential value to realize the goals of green,recycling and sustainable development of steel enterprises.