Phosphogypsum-based artificial substrate: A possible effective sustainable approach for waste valorization and vegetation restoration through physicochemical optimization

Valorizing phosphogypsum (PG) and red mud (RM) into beneficial resources is crucial, underscoring the need for cost-efficient approaches for sustainable utilization and ecological restoration. This study aimed to transform PG into a soil-like matrix by varying percentages of RM, soil, organic fertilizer, and Bacillus subtilis to stabilize the substrate pH and improve its physicochemical properties for plant growth. Brassica rapa subsp. chinensis was selected as the test crop for a 46-day pot experiment across eight different treatments (T1-T8) with varying amendment percentages. Significant improvements were observed in soil nutrient content and plant growth parameters after PG soilization and B. rapa cultivation. The content of heavy metals (chromium, cadmium, arsenic, mercury, and lead) in soil decreased in most treatments after plantation. It remained below the threshold limits, whereas plant shoots and roots showed high levels of Cr, Cd, As, Hg, and Pb in most treatments. Treatments with high PG and RM ratios (T1-T3 and T8) retained heavy metals in the soil with low plant growth, while treatments (T4-T7) with high soil and low PG:RM ratios increased plant growth with high soil-plant transfer of heavy metals, highlighting the importance of proper selection of amendments and their mixing ratios to enhance PG soilization efficacy. This study emphasizes the soilization as a cost-effective and sustainable approach for managing PG and RM waste and restoring the ecosystems. However, continuous monitoring of heavy metals is crucial to ensure the safe and sustainable utilization of potentially toxic industrial byproducts. This study explored an innovative cost-effective approach to transform PG into a soil-like matrix by incorporating various amendments (red mud, soil, organic matter, and Bacillus subtilis). The method significantly improved the physicochemical properties and heavy metal stabilization, thereby supporting its cost-effective utilization and environmental restoration. • PG was transformed into a soil-like matrix using different amendments; • Substrate fertility and Bok choy biomass were effectively improved with amendments; • The heavy metal content decreased after the plantation and was below the risk standard.