Carbonation Of Municipal Solid Waste Incineration Fly Ash And Ion Removal Of Treated Wastewater

With the economic development and urbanization in recent years,the amount of urban solid waste in China is increasing rapidly.Because of the series of advantages such as volume reduction and energy recovery,waste incineration is being used as the main method of garbage disposal in China,and plays an increasingly important role in waste disposal.The by-product of waste incineration is Municipal Solid Waste Incineration(MSWI)fly ash,a toxic substance containing high concentrations of soluble salts and undesired metals,as well as many persistent organic pollutants.Leaching is an economical and effective dechlorination method of fly ash.After leaching with water,the residual free chloride can be as low as 0.5%or less.The leaching wastewater has a high content of chloride-rich calcium salt,and direct discharge will not only cause pollution,but also cause a large amount of waste of chloride-rich calcium salt resources.Therefore,it is considered to remove the chloride salt in the fly ash by an appropriate treatment method and utilize the calcium therein,and then treat the wastewater to reduce the negative impact on the environment.This study combines the technology of high-gravity rotating packed bed and Resin-wafer Electrodeionization(RW-EDI).It is expected to realize the utilization of calcium in solid waste incineration fly ash and the reduction of carbon dioxide in the atmosphere,providing conditions for the comprehensive utilization of waste.At the same time,the RW-EDI technology is used to remove the integrated wastewater generated during the carbonation process in this study,thereby reducing its pollution to the water environment,provides a technical basis for the harmlessness and resource utilization of MSWI fly ash.The main contents of this study include:exploring the properties of MSWI fly ash and ion changes during leaching process;evaluating the effects of different operating conditions on carbonation;finding the best conditions for ion removal using RW-EDI for wastewater generated during the experiment.This study mainly draws the following conclusions:(1)During the leaching process,the pH of the fly ash can reach 10 or more in the pre-reaction period and then remain stable,and the liquid-solid ratio of the leaching process has little effect on the pH change.The concentration of various major ions in the liquid phase can reach a maximum value about 10 min after the start of the leaching reaction,and the chloride leaching rate is the fastest.Under different liquid-solid ratio conditions,the change trend of each ion in the fly ash leaching process is basically the same,and the smaller the liquid-solid ratio,the higher the leaching ion concentration.(2)The product purity of calcium carbonate obtained by indirect carbonation of fly ash can be as high as 93.3%,which can be considered as an effective method for treating fly ash pollution;the conversion rate of direct carbonation is affected by rotating bed speed,liquid-solid ratio and reaction time.Considering the stable operation of the equipment and minimizing the energy consumption,it is recommended that the rotating packed bed be operated at a rotation speed of 600—900 r/min;the optimum carbonation ratio is 20 mL/g.(3)When the specified wastewater is treated with RW-EDI,different treatment effects can be achieved by changing the operating conditions.Increasing the voltage can increase the removal efficiency of ions,and the effect is more significant when the voltage is lower,and the change trend is closer when the voltage is higher;the appropriate change of the feed rate is mainly helpful on the boundary layer of the ion exchange membrane.The mass transfer is an important factor affecting the deionization process.However,the effect of flow rate on ion removal rate is limited relative to changes in voltage conditions.The selectivity of Ca2+/Na+ decreases with time and increases with the proportion of cationic resin.Different operating conditions can also cause changes in current efficiency,energy consumption and productivity.When RW-EDI is used to remove various ions,the trend of ion changes is consistent,but for some ions,the removal efficiency is lower than other ions.Although the initial concentration of each ion in the solution is different,the removal efficiency is considerable.