A Study Of Potassium Salt Recovery From Municipal Solid Waste Incineration(MSWI) Fly Ash

With the continuous development of economy and society in China,the acceleration of urbanization and the rapid growth of urban population,there is a significant increase in the quantity of municipal solid waste(MSW)with an annual rate of 8% to 10% increments.Municipal Solid Waste Incinerating(MSWI)power generation,one of the ways of MSW disposal,makes the quantity of MSW incineration fly ash considerable.Some kind of MSWI fly ash contains potassium,which can be reclaimed as potash fertilizer.So not only can reduce the import dependence of potash fertilizer,but also realize the utilization and sustainable development of resources.At present,with the construction of MSWI power plant,the extraction of potassium from MSWI fly ash has been widely recognized.At first,several physical and chemical detections were used to study the basic properties of municipal solid waste incineration(MSWI)fly ash,and multiple single-factor water leaching experiments were designed and carried out in order to investigate the leaching regularity of potassium salt from the fly ash.The experiment of leaching potassium from MSWI fly ash was studied in this paper and the technical conditions were explored.The effect of technical conditions such as leaching time,leaching temperature,the leaching pH and the stirring rate of MSWI fly ash on the recovery rate of potassium was investigated to find out the optimal conditions and increase the recovery rate of potassium.The experiments demonstrated that the stirring rate,the ratio of liquid to solid and the leaching temperature had a significantly effect on leaching speed and recovery rate of potassium leaching from MSWI fly ash.Through the water leaching experiment,the other conditions were unchanged,the recovery rate of potassium leaching was increased with the speedup of the stirring rate.When the stirring rate was above 400 rpm,external diffusion weakened and the leaching rate of potassium was no longer improved.The leaching speed of potassium ion increased with the decrease of the ratio of liquid to solid,at the same time the relative loss of potassium ion and the concentration of potassium ion in leaching solution decreased,on the other hand,that increase the energy consumption of the subsequent crystallization and the cost.The leaching rate of potassium increased under the high pH,at the same time,there was less impurity element in the leaching liquor,which was helpful for subsequent purification.Rising the leaching temperature could lead to faster leaching speed and higher recovery rate.From the results of orthogonal experiment,it was concluded that the fractor affected the recovery rate followed this order: the ratio of liquid to solid > leaching temperature > stirring rate >time of leaching.The optimal leaching conditions as following: leaching pH was unchanged,the ratio of liquid to solid was 5:1,stirring rate was 400 rpm,90 ?,and leaching time was about 60 minutes.After leaching under the conditions above,94.02% potassium ccould be extracted in a solution.The leaching solution containing potassium was obtained by a series of impurity removal,solid-liquid separation,concentration evaporation,twice crystallization,washing and other steps to become KCl crystal.The purity of KCl can reach 90% after being tested,which is much higher than that of agricultural grade potassium chloride(mass fraction,60%)...