Phosphorus-enriched biochar for the remediation of heavy metal contaminated soil

Phosphorus-rich materials (PRMs) are widely used soil remediation agents because they are biocompatible, abundant, non-toxic, and have a high affinity for heavy metals in soil. However, PRMs tend to aggregate at the nanoscale and are susceptible to phosphorus leaching, which limit their application in soil remediation. Dispersing PRMs on porous biochar (BC) is a promising solution to the aggregation and phosphorus leaching issues. The resulting phosphorus-enriched BC (PBC) has excellent adsorption capabilities for heavy metals. This review focuses on recent advances in PBC synthesis and their application in soil remediation. A thorough evaluation of the biomass and phosphorus precursors used for PBC synthesis and a summarization of the common approaches in the synthesis of PBC are carried out in this review. Advantages of PBC for soil remediation are surveyed and reviewed in brief. Thereafter, heavy metal immobilization mechanisms (e.g., precipitation, ion exchange, sorption, etc.) of PBC in soil is highlighted. Finally, the preparation of engineered PBC (ePBC) composites by incorporating auxiliary components (e.g., iron, microorganisms, layered double hydroxides, etc.) with PBC is discussed along with the advantages of ePBC over PBC in soil. This review aims to convene disseminated knowledge and provide a detailed array of information required to gain a thorough understanding of PBC. •PBC outperforms both the phosphorus source and BC in soil heavy metal remediation.•BC is an ideal carrier for phosphate due to its porous structure and binding sites.•The main mechanism of heavy metal immobilization by PBC is precipitation.•Auxiliary components can be combined with PBC for enhanced performance.