Effect of modified humic acid residue on the adsorption and passivation of Hg2+/Pb2+in solution and soil

In the process of extracting humic acid from low -rank coal, such as weathered coal and lignite, a large amount of humic acid residue (HAS) is generated. The HAS is an underutilized waste resource and has the potential as a simple and relatively inexpensive heavy metal adsorption material. In this study, we devel-oped a new HAS -based heavy metal adsorbent by modifying HAS with H2SO4 (HAS -SO4) to improve its adsorption capacity for Hg2+ and Pb2+. HAS and HAS -SO4 were characterised using FTIR, SEM, and XRD. The adsorption process was fitted to the Langmuir isotherm model and the adsorption kinetics followed the pseudo -second -order model. The saturation adsorption (Qm) values of HAS -SO4 for Hg2+ and Pb2+ were 123.12 and 399.69 mg center dot L-1, respectively (1.12 and 1.38 times that of HAS). Thermodynamic analysis showed that the adsorption process is spontaneous and endothermic. Finally, the passivation effects of HAS and HAS -SO4 on Hg2+ and Pb2+ contaminated soil were investigated. HAS -SO4 passi-vated 96.2% and 61.4% of the Hg2+ and Pb2+ in the soil, respectively. The addition of HAS -SO4 resulted in a change in the morphology of heavy metals in the soil, with a reduction of 46.76% and 8.91% in the weak acid extraction state of Hg and Pb, respectively. In addition, the addition of HAS -SO4 can effec-tively reduce the risk of leaching heavy metals from soil and has a broad application prospect.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

A new heavy metal adsorbent based on humic acid residue modified by sulfuric acid (HAS-SO4) was developed, showing improved adsorption capacity for Hg2+ and Pb2+. The adsorption process followed Langmuir isotherm and pseudo-second-order kinetic models. HAS-SO4 effectively passivated Hg2+ and Pb2+ in contaminated soil, reducing their leaching risk and changing their morphology.