Experimental Study On Extraction And Resource Utilization Of Potassium Salt From Waste Incineration Fly Ash

In this thesis,a process of salt and potassium extraction and resource utilization for municipal solid waste incineration fly ash is proposed,and the four key nodes of the process,namely,fly ash water washing,water washing solution hardness removal,water washing solution heavy metal removal and salt and potassium extraction,are optimized by means of experiments and theoretical analysis.The effects of water cement ratio,leaching time,ambient temperature,stirring speed,p H and washing times on the dissolution of chloride and calcium ions were investigated by single-stage washing single factor experiment.The experimental results show that the water cement ratio,ambient temperature and washing times are positively correlated with the dissolution of Cl^-,Ca²⁺ions.The stirring speed and leaching time have no significant effect on the dissolution of Cl^-,Ca²⁺,and the p H is negatively correlated with the dissolution of Cl^-,Ca²⁺.On the basis of single factor experiment,four influencing factors such as water cement ratio,p H,washing time and ambient temperature were selected for orthogonal experiment.The results of orthogonal test showed that the factors influencing the dissolution of chloride ions from large to small were:water cement ratio,temperature,p H and washing time.The optimum conditions for chloride ion elution in the investigated range are as follows:water cement ratio of 8,p H of 7,water washing time of 5min,and ambient temperature of 40℃.The factors influencing the dissolution of calcium ions from large to small are:water cement ratio,p H,temperature and washing time.Based on the single-stage water washing experiment,a counter current water washing process was designed to improve the elution efficiency and reduce the water consumption.With the increase of water cement ratio,the amount of chloride ion elution shows an increasing trend,and the curve change rate decreases with the increase of water cement ratio,which indicates that the effect of changing water cement ratio on the amount of chloride ion elution is small when the water cement ratio is large.The effect of countercurrent washing was compared with that of single-stage washing.The results showed that the elution effect of countercurrent washing was significantly higher than that of single-stage washing.The material balance of the three-stage countercurrent washing process is calculated and a mathematical model is established.The model describes the quantitative relationship between the mass concentration of chloride ion in the first-stage washing solution and the water cement ratio.The empirical formula for specific water washing process is determined by means of nonlinear fitting,and the fitting correlation coefficient reaches 0.99769 The experimental results are substituted into the formula to verify its reliability.The experimental values are used as abscissa,and the calculated values are used as ordinate for plotting and linear fitting.The correlation coefficient reaches 0.99807The orthogonal experiment of removing calcium from the leaching solution of MSW incineration fly ash was carried out by using soda ash method.The results show that the factors affecting the removal rate of calcium ions from primary to secondary are:dosage ratio>temperature>reaction time.The optimum process conditions for calcium removal are as follows:the dosage ratio is 1.05,the temperature is 35℃,the reaction time is 45min,and the removal rate reaches 99.99%The influence of the dosing ratio of soda ash on the content of heavy metal ions in the water washing solution during calcium removal was investigated.The results showed that soda ash had a precipitation effect on the heavy metal ions in the fly ash leaching solution,and the removal curve of heavy metal ions showed the characteristics of first falling,then rising,and then stabilizing to a certain level.When the dosing ratio n was less than 1.15,the removal rate of heavy metal ions by soda ash decreased first and then increased;When the dosing ratio n>1.15,the removal rate of heavy metal ions by soda ash tends to be stable.The orthogonal experiment of removing heavy metals by sulfuration was designed by selecting three influencing factors:dosing ratio,p H and reaction time.The results showed that ra>rb=rc for zinc ions,so the main factor affecting the removal rate of zinc ions was dosing ratio;For lead ions,ra>rb>rc,so the order of factors affecting the removal rate of lead ions from primary to secondary is:dosing ratio>p H>reaction time;For copper ions,rc>rb>ra,so the order of factors affecting the removal rate of copper ions from primary to secondary is:reaction time>p H>dosing ratio.The optimum technological conditions for removing heavy metals by sulfuration are as follows:the dosage ratio is 1.5,the p H is 11,and the reaction time is 15min.At this time,the total removal rate of heavy metals can reach99.93%.The experiment of extracting potassium salt from the leaching solution of fly ash after removing calcium and heavy metal ions was carried out.Guided by the phase diagrams of Na⁺,K⁺//Cl^--H₂O ternary system at 100℃and 25℃,the process route and material balance of evaporative crystallization and cooling crystallization were determined.The results of material balance calculation show that the single-stage theoretical yield of Na Cl is78.79%and that of KCl is 52.06%.In addition,salt and potassium were extracted from the leaching solution of waste incineration fly ash after removing calcium and heavy metals,and Na Cl and KCl products meeting the current national standards were extracted.The single-stage actual yield of Na Cl was 74.56%,and that of KCl was 36.87%.The XRD images of Na Cl and KCl are in good agreement with the standard PDF cards of Na Cl and KCl respectively.The difference between the evaporation process of Fly Ash Leaching Solution and the crystallization law of 100℃pure component equilibrium Na⁺,K⁺//Cl^--H₂O ternary system was investigated.At the same time,the changes of physicochemical properties and chemical composition of mother liquor with evaporation loss rate were investigated.In the process of evaporation,the density of mother liquor,the content of potassium ion and sulfate ion have obvious positive correlation with the evaporation loss rate.In the evaporation and concentration stage,Cl^-concentration increases with the change of evaporation loss rate.After the precipitation of sodium chloride,the Cl^-content decreased.With the continuous concentration of the solution and the continuous precipitation of Na Cl,KCl in the solution is gradually enriched and Cl^-concentration rises.