China Nonferrous Metallurgy

The annual production of incineration fly ash in China has exceeded 1×10⁷t. Before utilization of fly ash resources, it needs to washing. The main metal components of fly ash washing solution are NaCl, KCl, CaCl₂ and other heavy metals. In this paper, hemihydrate calcium sulfate whiskers were prepared by adding sodium sulfate and crystal growth agent cetyltrimethylammonium bromide by removing impurities, detoxification and removing heavy metals from ash washing solution. The process combines the preparation of calcium sulfate hemihydrate whiskers and the treatment process of fly ash washing liquid by using an improved atmospheric pressure method. The effects of material ratio, boiling time and settling time on hemihydrate calcium sulfate whisker products were investigated. The results show that the recovery rate of Ca²⁺ can reach 95.16% under the conditions of n(calcium ion)∶n(sulfate ion)=1∶5, boiling time 1h and settling for 1.5h; the prepared hemihydrate calcium sulfate whiskers can meet the composition requirements of hemihydrate calcium sulfate whiskers in the standard of calcium sulfate whiskers (DB43/T 1155—2016)，and the products are uniform in appearance, with a length of 30~100μm, a diameter of 2~7μm, an aspect ratio up to 40, and a high density of whiskers. The process has the advantages of low production cost, environmental friendliness and easy industrial production, which provides a new solution for treatment and resource utilization of fly ash washing liquid.