Adsorption behavior of lead, cadmium, and arsenic on manganese-modified biochar: competition and promotion.

Biochar adsorption of heavy metals has been a research hotspot, yet there has been limited reports on the effect of heavy metal interactions on adsorption efficiency in complex systems. In this study, the adsorbent was prepared by pyrolysis of rice straw loaded with manganese (BC-Mn). The interactions of Pb, Cd and As adsorption on BC-Mn were systematically studied. The results of the adsorption isotherms for the binary metal system revealed a competitive adsorption between Pb and Cd, resulting in decreased Pb (from 214.38 mg/g to 148.20 mg/g) and Cd (from 165.73 mg/g to 92.11 mg/g). A notable promotion occurred between As and Cd, showing an increase from 234.93 mg/g to 305.00 mg/g for As and 165.73 mg/g to 313.94 mg/g for Cd. In the ternary metal system, Pb inhibition did not counteract the promotion of Cd and As. Furthermore, the Langmuir isotherm effectively described BC-Mn's adsorption process in monometallic, binary, and ternary metal systems (R2 > 0.9294). Zeta and FTIR analyses revealed simultaneous competition between Pb and Cd for adsorption on BC-Mn's -OH sites. XPS analysis revealed that As adsorption by BC-Mn facilitated the conversion of MnO2 and MnO to MnOOH, resulting in increased hydroxyl radical production on BC-Mn's surface. Simultaneously, Cd combined with the adsorbed As to form ternary Cd-As-Mn complexes, which expedited the removal of Cd. These results help to provide theoretical support as well as technical support for the treatment of Pb-Cd-As contaminated wastewater.

Selenium-sulfur functionalized biochar as amendment for mercury-contaminated soil: High effective immobilization and inhibition of mercury re-activation.

The contamination of soils by mercury (Hg) seriously threatens the local ecological environment and public health. S-functionalized amendments are common remediation technology, yet, Hg re-activation often occurs in the commonly used immobilization remediation by S-functionalized amendments, resulting in an unsatisfactory remediation effect. In this study, a novel FeS-Se functionalized biochar composite (FeS-Se-BC) amendment was prepared and applied for the efficient remediation of Hg-polluted soil. An immobilization efficiency of 99.62% and 99.22% for H2O-extractable Hg and TCLP solution-extractable Hg was achieved with the application of FeS-Se-BC(0.05) after 180 d. The analyses of XPS, Hg-TPD, SEM-EDS demonstrated that excellent remediation performance by FeS-Se-BC resulted from the synergistic effect of FeS and Se to form HgS and HgSe concurrently. In comparison to the treatments of biochar and FeS-functionalized biochar (FeS-BC), FeS-Se-BC promoted the transformation of exchangeable, carbonate-bound, and Fe-Mn oxides-bound Hg fractions into organic material-bound, and residual fractions, effectively reducing the risk of Hg-contaminated soil from a highly dangerous level to a low risk. Furthermore, the introduction of Se clearly inhibited the re-activation of Hg and reduced the release of Hg by 81.12% compared to FeS-BC when the ratio of S2- to Hg was 5: 1 due to the formation of extremely stable HgSe. These results suggest that FeS-Se-BC has good potential for remediation of Hg-polluted soils which provides a new inhibitory idea for Hg re-activation after immobilization.