Long-term stabilization of chromium, copper, and zinc co-contaminated soil using phosphorylated zero-valent iron

Heavy metal contamination of soil, particularly the co-contamination of chromium, copper, and zinc, has emerged as a significant threat to ecological systems and human health. This study developed a phosphorylated zero-valent iron (ZVI/PR) material through a ball milling process that combines natural phosphate rock with iron powder, aiming to detoxify and stabilize heavy metals in soil simultaneously. Experimental results demonstrated that ZVI/PR exhibited superior removal efficiencies for Cr(VI), Cu(II), and Zn(II)-6.49, 4.85, and 21.32 times higher, respectively, than those of ball-milled phosphate rock (BMP), and 5.99, 6.98, and 21.00 times higher than those of ball-milled zero-valent iron (BMZ). ZVI/PR demonstrated increased reactivity and effective pH self-regulation capabilities. The ZVI/PR promoted the sustained release of Fe(II), facilitating the simultaneous stabilization of Cr, Cu, and Zn. ZVI/PR significantly reduced heavy metal concentrations in the soil, with Cr(VI) removal efficiency reaching 99.04 %, and the stabilization efficiencies of DTPA-extractable Cu and Zn exceeded 60 % in the co-contaminated soil. Soil treated with ZVI/PR showed a significant increase in stable fractions (residual and organic matter-bound fractions) of Cr (16 % to 41 % in seven days), Cu (16.8 % to 59.6 % in one day), and Zn (11.56 % to 23.46 % over 28 days) compared to untreated soil. Notably, after 180 days of the toxicity characteristic leaching procedure test, ZVI/PR demonstrated long-term stability in soil remediation. This study offers a cost-effective method for remediating soils co-contaminated with multiple heavy metals.