Potential of preparing cement clinker by adding the fluorine-containing sludge into raw meal.

Fluorine-containing sludge from semiconductor industries were one kind of hazardous wastes, there was hardly effective treatment to realize its safe disposal and utilization. This paper evaluated the potential of preparing cement clinker by adding the sludge into raw meal by a series of experiments. The results revealed 2.0 % addition of the sludge markedly improved the burnability of the produced clinker, and promoted the formation of alite with more amounts and smaller size, but the 5.0 % addition of the sludge resulted in the abundant formation of interstitial phases to inhibit the formation of alite and belite. The better workability was gained with the addition of 2.0 %, and the optimal 28 d compressive strength was 50.76 MPa. The distribution of fluorine was higher in silicate phases, and it was mainly accumulated in the interfaces of silicate phases. Fluorine in the sludge was immobilized by calcium to form the binding forms of calcium fluoride in produced clinker and hydration products. The immobilization ratios of fluorine, copper, zinc and nickel were more than 99.5 %, and the addition of the sludge (≤5.0 %) into raw meal could not induce further environment hazards.