Waste control by waste: A comparative study on the application of carbide slag and quicklime in preparation of phosphogypsum-based ecological restoration materials

This study explored the potential applications of quicklime and carbide slag in the preparation of phosphogypsum (PG)-based ecological restoration materials. The migration and transformation behavior of large amounts of soluble impurities (PO43−, F−, NH3-N, Cr6+, Mn, and Cu) in PG were studied. A solid–solid phase reaction was innovatively employed, and PHREEQC was used as the simulation software to investigate the solidification/leaching mechanism of pollutants in PG treated with different amounts of alkaline materials. The results showed that acid–base condition is a dominant factor controlling the migration and transformation of P, F, NH3-N, and heavy metals. The addition of a small amount of quicklime or carbide slag to PG considerably improved its pH. Quicklime and carbide slag exhibited remarkable stabilization effects on PO43−, F−, Cr6+, and Mn, and the leaching concentration of water-soluble fluorine and NH3-N in PG added with quicklime decreased substantially. In general, when preparing PG-based ecological restoration materials, the addition of carbide slag exhibited a stronger acid buffering capacity, pollutant stabilization capacity, and potential nutrition than that of quicklime. In particular, the use of carbide slag instead of quicklime in PG treatment can reduce the cost of PG treatment by approximately $1.3–1.5 per ton.