Phosphorus Extraction from Sludge Incinerated Bottom Ash with Hydrochloric Acid at Low Liquid-Solid Ratio

Abstract

Phosphorus recovery from sludge incinerated bottom ash (SIBA) is one of the effective methods to realize phosphorus reuse. Extracting phosphorus efficiently from SIBA is the first step. In this study, hydrochloric acid (HCl) was used to extract phosphorus from SIBA at low liquid-solid ratios (≦5 mL/g). The phosphorus extraction conditions were studied. The results revealed that the maximum extraction occurred in 10 min when the HCl concentration was 2.0 mol/L at a temperature of 25°C. The best stirring rate was 200 rpm, and the liquid-solid ratio was 3 mL/g. Under the best conditions, the phosphorus extraction efficiency was 92.9%, and the concentration of phosphorus in the extraction solution was 23.2 g/L. The adsorption and release processes of phosphorus and metals under different HCl concentrations were also studied. It was observed that under low HCl concentration (0.5 mol/L), phosphorus and metals were initially released into the extraction solution and subsequently adsorbed by the sludge incinerated bottom ash residues. The adsorption kinetics followed the pseudo-first-order model. At high HCl concentration (2.0 mol/L), phosphorus and metals exhibited a sustained release, which could be described by the Drozdov equation. The mechanism of migration of the metals was also investigated. Most metals remained in SIBA at low and high HCl concentrations. This study reveals that it is feasible to extract phosphorus with HCl at a low liquid-solid ratio.