Effect Of Co-processing Of Fluorine-containing Sludge In Cement Kiln On Cement Performance And Environmental Safety

With the rapid development of information and increasing output of electronic components,the fluorine-containing sludge generated from the electronics industry has increased,and the effective disposal methods and resource utilization of this kind of sludge are also getting more attention.It is unclear whether electronic fluorine-containing sludge is hazardous solid waste and what kind of hazardous waste,and cement kiln is an effective and economical method for co-processing various industrial solid wastes.Therefore,the effect of physicochemical performance of fluorine-containing sludge,used in cement kiln on the cement properties and environmental safety was investigated by X-ray fluorescence,X-ray diffraction,scanning electron microscopy,immersion extraction and leaching toxicity tests.The main conclusions are as follows:（1）The chemical composition of electronic fluorine-containing sludge is mainly calcium oxide,silicate,aluminate,fluorine and a small amount of heavy metal ions（e.g.Cr,Mn,Ni,Cu,Zn,etc.）,and fluorite is the major mineral phase,and secondary mineral phases are sphalerite and nantokite.There are organic substances attached to the surface of the crystal,so the crystal characteristics are not obvious.Insoluble sludge in the sludge accounts for more than 95%of the total fluorine.Fluorine in fluorine-containing sludge is mostly calcium fluoride,and its content reaches approxmately 30.0%.According to the standard"Solid Waste Leaching Toxicity Leaching Method"（HJ557-2010,HJ/T300-2007 and HJ/T299-2007）,the leaching toxicity of F and Cr is below the toxicity restriction.However,the leaching toxicity of Ni,Cu and Zn is above the toxicity restriction.Therefore,the fluorine-containing sludge is subordinate to a heavy metal solid hazardous waste.（2）The laboratory test of co-processing of fluorine-containing sludge in cement kilns shows that:co-processing of fluoride-containing sludge in cement kilns can significantly improve the flammability of clinker,and its suitable content is 2.0%of raw meal mass.Compared with the non-fluorinated sludge,when 2.0%of fluorine-containing sludge was mixed and calcined at 1350℃,1400℃,and 1450℃,the content of f-Ca O in the clinker decreased from 3.91%to 1.13%,from 2.59%to 0.50%,from 0.72%to 0.26%;compressive strength increased from 36.58 MPa to 49.25 MPa,42.73 MPa to 52.59 MPa,48.98 MPa to 45.68 MPa.This shows that doping appropriate amount of fluorine-containing sludge has an obvious effect on improving the quality of low-temperature calcined cement clinker.The main reason is that the addition of appropriate amount of sludge promotes the generation of C₃S during low-temperature calcination.（3）The industrial test of the co-processing of fluorine-containing sludge in cement kilns shows that:under the condition of the same raw meal ratio and calcination process,the raw belt containing 2.0%of raw meal mass is mixed with the original electronic fluorine-containing sludge.Compared with the sludge-free sludge,the C₃S content in the clinker increased by 4.92%,and the 28 d compressive strength increased by 9.6%.Doping 2.0%of fluorine-containing sludge has little effect on other properties of cement.（4）For the cement produced by the laboratory test with 5.0%and industrial test with 2.0%sludge,the toxic leaching test of the 3 d and 28 d cement paste hardened body was carried out.The results showed that:the toxic leaching of F and heavy metal ions in the hardened body is far less than the relevant standard leaching limits.Therefore,the cement kiln co-processing the cement produced by the fluorine-containing sludge will not cause a"secondary hazardous waste"risk to the environment.