Effects of alpha-Fe2O3 modified chicken manure biochar on the availability of multiple heavy metals and soil biochemical properties

The problem of increasingly severe soil heavy metals contamination is of great concern worldwide. Herein, chicken manure and potassium ferrocyanide were used as raw materials to prepare a alpha-Fe2O3 loaded biochar (Fe2O3/BC) composite material through a simple calcination method. We found Fe2O3/BC obtained at 350 degrees C (Fe2O3/BC-350) exhibited excellent immobilization efficiency on multiple heavy metals in soil. And then density functional theory (DFT) calculations explained the reason of Fe2O3/BC-350 exhibited better remediation performance than the Fe2O3/BC-250 and Fe2O3/BC-550. When cultured for 90 days, the passivation effect of the 1% Fe2O3/BC-350 dosage treatment achieved the highest with the immobilization rates for Cu(II), Cd(II) and Pb(II) reaching 62.5%, 45.56% and 42.56%, respectively. The composite material increased soil pH and cation exchange capacity (CEC), and promoted the transformation of Cu(II), Cd(II) and Pb(II) ions from acid-soluble to more stable forms through ion exchange, precipitation and complexation. The soybean pot experiment further verified that Fe2O3/BC-350 could reduce the phytoavailable fractions of heavy metal soil remediation material. In addition, Fe2O3/BC-350 increased the activity of soil urease and sucrase. Meanwhile, the diversity and richness of the soil microbial community were improved. These results demonstrated that Fe2O3/BC-350 not only had an excellent immobilization effect on heavy metals in the soil, but also Fe2O3/BC-350 exhibited environmentally friendly in soil. As a result, Fe2O3/BC can serve as a promising remediation agent for multiple heavy metal polluted soils.

Automated summary

In this study, a novel composite material of alpha-Fe2O3 loaded biochar (Fe2O3/BC) was prepared using chicken manure and potassium ferrocyanide, and demonstrated excellent immobilization efficiency on multiple heavy metals in soil. The Fe2O3/BC-350 showed better remediation performance than Fe2O3/BC-250 and Fe2O3/BC-550. Additionally, Fe2O3/BC-350 increased soil pH, cation exchange capacity (CEC), and promoted the transformation of heavy metal ions into more stable forms, while enhancing soil enzyme activity and improving soil microbial community diversity and richness.