Chemically consolidated Cr(VI) Contaminated soil based on granulation of blast furnace slag and phosphogypsum

Cr(Ⅵ)-contaminated soil is frequently encountered at abandoned industrial sites, posing a significant threat to surrounding ecosystems and human health. In this study, a novel of slag-phosphogypsum-based environmental material (SPEM) was developed using granulated blast furnace slag and phosphogypsum as raw materials under alkaline activation. Unconfined compressive strength tests, volume shrinkage tests, and toxicity leaching tests were conducted to evaluate the mechanical strength, volume shrinkage, and Cr(Ⅵ) ion leaching concentration of the solidified contaminated soil. Characterization of the solidified environmental material blocks (EMB) was performed using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results indicate that as the SPEM content and curing period increase, the unconfined compressive strength of Cr(Ⅵ)-contaminated soil (cured for 14 days at a fivefold pollution level) increases by 58.457% before declining to 4.867 MPa. Meanwhile, the Cr(Ⅵ) ion leaching concentration decreases to 0.099 mg/L. The leaching concentration of Cr(Ⅵ) in SPEM containing 5%, 10%, 15%, and 20% for 14 days ranged from 0.099 mg/L to 0.379 mg/L, significantly lower than the emission limit specified in the "Integrated Wastewater Discharge Standard" (GB8978-1996). The heavy metal Cr(Ⅵ) is chemically immobilized and physically encapsulated within SPEM. This study provides experimental validation for the remediation and ecological restoration of Cr(Ⅵ)-contaminated soil.