Effect of combined aging treatment on biochar adsorption and speciation distribution for Cd(II)

As a passivation material for heavy metals in-situ remediation, biochar (BC) has often been expected to maintain longterm adsorption performance for target pollutants. There is still lack of consensus about the impact of aging processes on biochar properties, particularly with respect to its long-term sorption performance. In this study, the changes to immobilization mechanisms as well as the speciation distribution of Cd(II) triggered by combined aging simulation (drywet, freeze-thaw cycle and oxidation treatment) on BC prepared under three levels of pyrolysis temperatures (300, 500 and 700 degrees C) were investigated. The results showed significant inhibition of aging on adsorption performance with the adsorptive capacity of BC300, BC500 and BC700 for Cd(II) decreased by 31.12 %, 50.63 % and 14.94 %, respectively. However, sequential extraction results indicated little influence of the aging process on the relative fractionation of Cd (II) speciation. The distribution of readily bioavailable, potentially bioavailable and non-bioavailable fractions of Cd (II) on BC showed only minimal changes post-aging. Overall, there was less Cd(II) sorption following aging, but the fractional availability (in relative terms) remained the same. Compared with 300 and 700 degrees C, the biochar prepared under 500 degrees C accounted the highest fraction of non-bioavailable Cd(II) (67.23 % of BC500, 59.17 % of Aged-500), and thus showed most promising for Cd(II) immobilization. This study has important practical significance for the long-term application of biochar in real environment.

Automated summary

This study investigates the impact of aging processes on the performance of biochar in adsorbing Cd(II) as well as the distribution of Cd(II) speciation. The results show that aging significantly inhibits the adsorption performance of biochar for Cd(II), but has little influence on the speciation distribution. Among the three pyrolysis temperatures, biochar prepared at 500 degrees C shows the most promising immobilization for Cd(II).