Study On Hydration Reaction Kinetics Of Quenching Magnesium Slag

Magnesium slag is a kind of solid waste,which is of desulfurization capacity. The desulfurization performance of the magnesium slag can be improved by modification methods,including hydration activation,steam activation and hydration with fly ash.But it is difficult that the technology is used in industry.In order to further improve the utilization and desulfurization efficiency of magnesium slag,it is necessary to explore a new modified method.Based on the research methods of quenching slag and liquid-solid reaction,this thesis carries out a serials of continuous and non-continuous hydration experiments under different conditions,such as quenching temperature,hydration time,liquid/solid ratio and hydration temperature.The designed hydration device is used in all of experiments. During the hydration process,the electrical conductivity,pH and hydration degree of the reaction slurry is measured to characterize the reaction.With the help of hydration degree,different kinetics models are used to analyze hydration reaction kinetics and to obtain the corresponding kinetic parameters.In order to further understand the desulfurization performance of the hydrated samples and the relationship between hydration and desulfurization,the desulfurization experiments are carried out in TGA experimental system. ICP-AES is applied for the determination of elemental composition and oxide composition of magnesium slag.The change of the phase composition and morphology of the samples are investigated by XRD and SEM respectively.The main results are as follows:(1)Both the electrical conductivity and pH increase first and then tend to be stable during the hydration process.The relationship between conductivity or pH and the hydration degree is exponent,respectively.(2)The process of non-continuous hydration can be described by modified KD model.With the analysis of the hydration degree and reaction kinetics,when the quenching temperature is 950℃ and hydration temperature is 80℃,the hydration is the best.(3)With the quenching temperature increasing,the control process changes from chemical to diffusion,while the reaction rate constant decreases first and then increases.The reaction rate constant increases with the hydration temperature increasing.The activation energy of this hydration reaction is 59.37kJ/mol and the reaction kinetics equation is obtained under this condition.(4)With the analysis of the orthogonal test,the optimum hydration is obtained,that is,the quenching temperature is 950℃,liquid/solid ratio is 80℃,hydration time is 8h.What’s more,the influence of the three factors on the hydration reaction is hydration time > quenching temperature > liquid/solid ratio.(5)The process of orthogonal test can be described by modified KD model.The reaction rate constant slowly increases with the increasing of liquid/solid ratio.When the quenching temperature is 150℃ and 950℃,the control is chemical and diffusion respectively.The hydration degree and the reaction rate constant will become much bigger with the increasing of quenching temperature and liquid/solid ratio.(6)In single factor experiments,the influence of hydration temperature on hydration reaction can be analyzed by Renedo mixed control model.The control process will change with different stages of hydration reaction.In the early stage,the reaction is controlled by chemical reaction.While in the later stage,the control process contants chemical reaction and diffusion.Higher temperature and lower temperature are controlled by mixed process and diffusion,respectively.(7)In single factor experiments,the Avrami equation is adopted to analyze the influence of hydration temperature on hydration reaction.The results show that the reaction is in accordance with homogeneous and heterogeneous nucleation.Nucleation rate decreases with increasing of the quenching temperature higher than 750℃,while it increases with decreasing of the quenching temperature lower than 750℃.With the analysis of reaction combined with different quenching temperature and hydration,the hydration reaction kinetics model is obtained based on Avrami equation.(8)The experimental results of desulfurization show that the relationship between hydration degree and calcium conversion rate is a positive correlation.The desulfurization performance of continuous hydration sanmples is better than that of non-continuous hydration,while the desulfurization performance of natural cooling of magnesium slag is the worst.