Solidification Effect of an Iron-based Biochar Heavy Metal Stabilizer on River and Lake Sediments

To address heavy metal pollution in river and lake sediments amid China's urbanization, this study developed an iron-based biochar stabilizer using corn straw modified by chemical-physical methods. The modification significantly increased the biochar's surface roughness, forming a 50 – 200 nm iron oxide adhesion layer. While its specific surface area slightly decreased from 418 m²/g to 376 m²/g, the proportion of mesopores rose, creating more sites for heavy metal adsorption. Characterization results show that the iron-based biochar binds heavy metals through surface functional groups like -OH and C=O, demonstrating stable adsorption performance for various heavy metals (including Cr(VI), Cd(II), Pb(II), and As(III)). Compared with unmodified biochar, it improved the average solidification rates of Zn, Cu, Cr, Pb, Ni, and as by 23.5 %, 18.7 %, 27.3 %, 25.1 %, 19.8 %, and 21.2 %, respectively. Notably, the solidification of Cr(VI) was particularly effective due to the redox catalytic action of Fe³⁺/Fe². After adsorption, the material's porosity recovered to 72 %, indicating enhanced recyclability through iron-based modification. The leaching concentration of heavy metals in the treated sediment meets national standards, and the treatment cost is over 60 % lower than that of traditional technologies. Additionally, the solidified sediment can be safely reused for land improvement or building material production, offering an economical and efficient resource-oriented solution for controlling heavy metal pollution in sediments.