Sorption behavior of phosphate by fly ash discharged from biomass thermal power plant

Abstract

This study evaluated the characteristics and mechanism of phosphate adsorption by fly ash discharged from a biomass thermal power plant (BTP-FA) under various environmental conditions in order to increase the recyclability of BTP-FA. The phosphate adsorption properties of BTP-FA and fly ash derived from coal thermal power plant (CTP-FA) were better matched by those predicted by the Langmuir isothermal model and the pseudo-second-order model, and their maximum adsorption capacities were 62.1 and 4.1 mg/g, respectively. It was found that the adsorption of phosphate by BTP-FA was predominantly influenced by the outer boundary layer rather than the inner diffusion in the pores. The phosphate adsorption process by BTP-FA was greatly influenced by the initial pH and the BTP-FA dose. Therefore, to effectively treat phosphate using BTP-FA, the concentration and flow rate of phosphate in the incoming wastewater must be considered. The concentration of dissolved calcium from BTP-FA decreased sharply during the phosphate adsorption process compared to that in the phosphate-free solution. This was thought to be due to surface adsorption/reaction between calcium and phosphate. The SEM–EDS and FTIR results also supported the surface adsorption/precipitation reaction of Ca-P. Recycling fly ash discharged from biomass power plants as phosphate adsorbents is expected to contribute not only to waste reduction, but also to wastewater purification.