Original Partial Substitution of Lime-Dried Sludge as a Flux for Cement Sintering Ingredients

Municipal sewage sludge has a high content of phosphorus, which has a high utilization value. However, this useful resource is always wasted during sludge landfill and incineration processes. In this study, lime was used to regulate the stability of sludge and lime -dried sludge (LDS) was used as a substitute for raw meal and sintering additive for cement clinker production. The variation of phosphorus content or concentration and its threshold level in LDS was investigated. The results showed that after lime drying, 90% of the phosphorus in the sludge existed in the form of inorganic phosphorus (IP), of which 80% was in the stable apatite state. More than 85% of the phosphorus in LDS was eutectic with clinker, avoiding secondary pollution in the synergistic process of cement kiln. The addition of LDS as a phosphorus sintering flux for clinker plays a good role in promoting the formation of bauxite in clinker and improving the burnability of raw materials. The addition of up to 15 wt.% of LDS containing 0.53% P2O5 to cement raw meal does not affect the clinker reaction. As an important flux in cement production, LDS can save phosphate rock and replace flux as a cement sintering ingredient.