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 1.79g/m3, weight loss in hydrochloric acid 4.46%, and the compressive strength absolutely meet the requirements of transport and use. And after 24h, the removal rate for 5mg / L phosphorus solution is 85.50%.