Application of phosphogypsum and phosphate-solubilizing fungi to Pb remediation: From simulation to in vivo incubation

Abstract

Phosphogypsum (PG) is the produced solid waste during phosphorus (P) extraction from phosphate rocks. PG is featured by its abundant PO43− and SO42−. This study investigated the utilization of PG as a material for lead (Pb) remediation, with the assistance of functional fungus. Aspergillus niger (A. niger) is a typical phosphate-solubilizing fungi (PSF), which has high ability to secret organic acids. Oxalic acid is its major secreted organic acid, which is often applied to enhance the P release from phosphate minerals. In this study, synthetic oxalic acid increased the immobilization rate of Pb2+ up to >99 % with the addition of PG. Then, it was observed that biogenic oxalic acid from A. niger can achieve comparable remediation effects. This was due to that PG could provide sufficient P for fungal growth, which allowed sustainable remediation. Subsequently, oxalic acid secreted by A. niger significantly increased the release of active P from PG, and then induced the formation of PPb minerals. In addition, other metabolites of A. niger (such as tyrosine-like substance) can also be complexed with Pb2+. Simultaneously, A. niger did not induce evidently elevation water-soluble fluorine (F) as PG contained abundant Ca2+. Moreover, this study elucidated that oversupply of PG promoted the formation of anglesite (Ksp = 1.6 × 10−8, relatively unstable), whereas the formation of lead oxalate (Ksp = 4.8 × 10−10, relatively stable) was reduced. This study hence shed a bright light on the sustainable utilization of PG for fungus-assisted remediation of heavy metals.