Biotransformation of phosphogypsum and its potential for soil-based applications: a preliminary study

Promoting the resource utilization of phosphogypsum (PG) is an urgent challenge, and its potential use as a soil amendment has attracted increasing attention. In this study, representative organic acids, the oxalate-producing fungus Aspergillus niger, and the oxalate-degrading bacterium Azospirillum brasilense OX-1 were used, together with a 45-day pot experiment with Suaeda salsa, to investigate the mineral transformation of PG and its potential for soil-based applications. Among the three organic acids tested under identical conditions, only oxalic acid induced the transformation of CaSO₄·2H₂O in PG into whewellite. During A. niger cultivation, the pH decreased from 5.12 on day 0 to 2.82 on day 8, accompanied by a progressive decrease in the PG mineral phase and the formation of whewellite and weddellite. Calcium oxalate generated from PG through either chemical oxalic acid treatment or A. niger-mediated transformation was further converted to calcite by OX-1. In the pot experiment, the combined PG and OX-1 treatment resulted in the highest mean plant height (11.03 ± 0.67 cm) and stem diameter (0.81 ± 0.07 mm), compared with 4.67 ± 0.40 cm and 0.32 ± 0.19 mm, respectively, in the control. The combined application of PG and OX-1 also significantly altered soil pH, available phosphorus, and other physicochemical properties. These findings provide experimental evidence for the stepwise biological transformation of PG and indicate its potential value as a soil amendment. Further studies are needed to determine whether these transformation processes can occur sequentially in the rhizosphere and to evaluate their long-term environmental effects.

The online version contains supplementary material available at https://doi.org/10.1007/s13205-026-05064-8.