Phosphate removal using compounds prepared from paper sludge and fly ash

Using waste as a resource to control phosphate pollution is a rising trend. This study describes the use of paper sludge (PS) and fly ash (FA), industrial solid wastes, to prepare materials with high phosphate uptake efficiency. The process consisted of pretreatment (mechanical milling), calcination, acidification (HCl), and post-treatment (aging, drying and grinding). The maximal phosphate uptake (>92 %) was achieved using PS together with FA either at PS/FA = 0.5 g/g or at PS/FA = 2.0 g/g, both calcined at 900 °C for 2 h and stirred with HCl (HCl/FA = 3 mL/g) for 1 h. With increasing calcination temperature and decreasing acid, the crystallinity of samples declined, and phosphate uptake (PU) increased. The PU process could be well described by the pseudo-second order kinetic model, while equilibrium state could be reasonably modeled by Langmuir isotherm. Neutral and weak alkaline pH promoted the PU efficiency, and 0.3 g sample/100 mL was the cost-effective dosage under the experimental conditions. The enhanced phosphate uptake of PS and FA provides alternative materials for phosphate removal from wastewater by the use of solid wastes in paper-making industries.