Heavy Mental Precipitation Characteristics Of Fly Ash Wastewater During Aeration Of Cement Kiln

Nowadays,the production of domestic garbage and industrial waste is increasing year by year.The waste reduction is an ideal resource-saving measure.As a result,incineration technology has been rapidly developed.The large amount of fly ash generated by waste incineration has become a problem to be solved at present.Due to the high content of salt in fly ash,the washing process can be effectively removed.However,heavy metals can also leach into the solution.Cement kilns discharge a large amount of tail gas in actual production,and tail gas emissions cause air pollution.Utilizing the high content of CO₂ in the tail gas of the cement kiln to aerate the fly ash treatment fluid not only protects the atmospheric environment but also effectively removes the leached heavy metals.In this paper,the leaching characteristics of heavy metals（Cu,Zn,Pb,Fe,Ni,As and Cr）under different water washing conditions（L/S ratio,washing time,washing temperature and washing times）and the effects of different aeration conditions（aeration temperature,aeration rate and gas ratio）on the removal of heavy metals were studied.The precipitation characteristics of heavy metals were simulated by using PHREEQC software.XRD analysis showed that the diffraction peaks of the chlorine salts in fly ash disappeared obviously after being washed by water.Overall,the leaching amount of heavy metals decreases with the increase of liquid-solid ratio and washing time,and the removal rates of Cl^-and SO₄^2-increase gradually.As,Cr and Ni show volatility.According to the orthogonal experiment,the optimum condition of washing was L/S ratio of 8,washing time of10 min,washing at room temperature for 1 time.In this paper,different aeration temperature（25,50,and 80℃）,aeration rate（10,15ml/min）,CO₂ gas proportion（15 and 33%）aeration,on the whole carbonation process of heavy metal removal effect was ideal,Cu,Zn and Pb removal effect is more obvious,Cr and Ni can be achieved by carbonation emissions standards.The results of PHREEQC simulation show that heavy metal precipitation mainly consists of precipitation,iron/aluminum colloid adsorption and CaCO₃ adsorption.During the early aeration,the heavy metal concentration is controlled by its own precipitation,and mainly controlled by iron/aluminum colloids and CaCO₃ adsorption during the late aeration period.