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Soil heavy metal contamination is a severe issue. The detrimental impact of contaminated heavy metals on the ecosystem depends on the chemical form of heavy metals. Biochar produced at 400 °C (CB400) and 600 °C (CB600) from corn cob was applied to remediate Pb and Zn in contaminated soil. After a one month amendment with biochar (CB400 and CB600) and apatite (AP) with the ratio of 3%, 5%, 10%, and 3:3% and 5:5% of the weight of biochar and apatite, the untreated and treated soil were extracted using Tessier's sequence extraction procedure. The five chemical fractions of the Tessier procedure were the exchangeable fraction (F1), carbonate fraction (F2), Fe/Mn oxide fraction (F3), organic matter (F4), and residual fraction (F5). The concentration of heavy metals in the five chemical fractions was analyzed using inductively coupled plasma mass spectroscopy (ICP-MS). The results showed that the total concentration of Pb and Zn in the soil was 3023.70 ± 98.60 mg kg−1 and 2034.33 ± 35.41 mg kg−1, respectively. These figures were 15.12 and 6.78 times higher than the limit standard set by the United States Environmental Protection Agency (U.S. EPA 2010), indicating the high level of contamination of Pb and Zn in the studied soil. The treated soil's pH, OC, and EC increased significantly compared to the untreated soil (p > 0.05). The chemical fraction of Pb and Zn was in the descending sequence of F2 (67%) > F5 (13%) > F1 (10%) > F3 (9%) > F4 (1%) and F2~F3 (28%) > F5 (27%) > F1 (16%) > F4 (0.4%), respectively. The amendment of BC400, BC600, and apatite significantly reduced the exchangeable fraction of Pb and Zn and increased the other stable fractions including F3, F4, and F5, especially at the rate of 10% of biochar and a combination of 5:5% of biochar and apatite. The effects of CB400 and CB600 on the reduction in the exchangeable fraction of Pb and Zn were almost the same (p > 0.05). The results showed that CB400, CB600, and the mixture of these biochars with apatite applied at 5% or 10% (w/w) could immobilize lead and zinc in soil and reduce the threat to the surrounding environment. Therefore, biochar derived from corn cob and apatite could be promising materials for immobilizing heavy metals in multiple-contaminated soil. [ABSTRACT FROM AUTHOR]

Heavy metal contamination in agricultural land is an alarming issue in Vietnam. It is necessary to develop suitable remediation methods for environmental and farming purposes. The present study investigated the effectiveness of using peanut shell-derived biochar to remediate the two heavy metals Zn and Pb in laboratory soil assays following Tessier's sequential extraction procedure. The concentration of heavy metals was analyzed using Inductively coupled plasma mass spectrometry (ICP-MS). This study also compared the effectiveness of the blend of biochar and apatite applied and the mere biochar amendment on the chemical fractions of Pb and Zn in the contaminated agricultural soil. Results have shown that the investigated soil was extremely polluted by Pb (3047.8 mg kg−1) and Zn (2034.3 mg kg−1). In addition, the pH, organic carbon, and electrical conductivity values of amended soil samples increased with the increase in the amendment's ratios. The distribution of heavy metals in soil samples was in the descending order of carbonate fraction (F2) > residue fraction (F5) > exchangeable fraction (F1) > Fe/Mn oxide fraction (F3) > organic fraction (F4) for Pb and F5   ≈   F2 > F1 > F3 > F4 for Zn. The peanut shell-derived biochar produced at 400 °C and 600 °C amended at a 10% ratio (PB4:10 and PB6:10) could significantly reduce the exchangeable fraction Zn from 424.82 mg kg−1 to 277.69 mg kg−1 and 302.89 mg kg−1, respectively, and Pb from 495.77 mg kg−1 to 234.55 mg kg−1 and 275.15 mg kg−1, respectively, and immobilize them in soil. Amending the biochar and apatite combination increased the soil pH, then produced a highly negative charge on the soil surface and facilitated Pb and Zn adsorption. This study shows that the amendment of biochar and biochar blended with apatite could stabilize Pb and Zn fractions, indicating the potential of these amendments to remediate Pb and Zn in contaminated soil. [ABSTRACT FROM AUTHOR]