Preparation and Characterization of Fly Ash-Based Aggregate for Purifying Phosphorus

In order to obtain the optimum proportion and preparation conditions of fly ash (FA)-based aggregate for purifying phosphorus, orthogonal experiment was made on the mixture tests about the main raw materials - FA, the pore-forming material - dry sewage sludge (DSS) from the municipal sewage plant, the expanding agent - FGD gypsum from the thermal power plants and the binding agent - clay. And the impacts of main factors (drying time, presintering temperature, presintering time, sintering temperature, sintering time)on characteristics of aggregate (water absorption, apparent porosity, bulk density, weight loss in hydrochloric acid ) and the purification effects on low concentration phosphorus were studied. The results showed that the optimum proportion of fly ash to additives was that fly ash accounted for about 71%, dry sewage sludge about 25%, FGD gypsum about 2%, clay about 2%; The optimum preparation conditions were as follows: drying time 2 h, without presintering, sintering temperature 850 ~ 900°C and sintering time 24 min. Under these conditions, the characteristics of aggregate were obtained as follows: water absorption 26.97 %, apparent porosity 48.35%, bulk density 1.79 g/m3, weight loss in hydrochloric acid 4.46%, and the compressive strength absolutely meet the requirements of transport and use. And after 24 h, the removal rate for 5 mg / L phosphorus solution is 85.50%.