Selective recovery of high purity aluminium phosphate from incinerated sewage sludge ash with Zr-modified biochar

Phosphorus recovery from incinerated sewage sludge ash (ISSA) is critical for the sustainable development of phosphorus resources due to its non-renewable nature. An innovative strategy based on a Zr-modified rice-husk biochar (Zr-RB) adsorbent has been proposed for the selective recovery of high-purity AlPO4 products from ISSA. 0.1 mol/L H2SO4 was chosen to extract phosphorus from ISSA with a phosphorus extraction of 54.5 ± 1.6 mg/g. Phosphorus was selectively adsorbed by the Zr-RB adsorbent with a maximum adsorption capacity of 53.1 ± 0.6 mg/g according to the Langmuir isotherm model. The adsorption kinetics of phosphorus in the leachate followed the pseudo-second order model, suggesting phosphorus adsorption by chemisorption processes. After 5 phosphorus adsorption-desorption cycles, the Zr-RB adsorbent still showed good adsorption performance for phosphorus, indicating its high stability. Electrostatic attraction and ligand exchange on the Zr-RB adsorbent were mainly responsible for the adsorption of phosphorus from the leachate. The simulation and experimental results demonstrated the production of high-purity AlPO4 products at the pH = 3.0 without the addition of exogenous substances, indicating the application potential of recovering high-value AlPO4 products from ISSA based on the Zr-RB adsorbent.