Calcium-doped magnetic humic acid nano particles for the efficient removal of heavy metals from wastewater: the role of Ca

ABSTRACT

Ca doping is an effective method for improving the adsorption capacity of HA–Fe aggregates and regulating their structures. Understanding the structural characteristics of Ca–HA–Fe aggregates can help explore their microscopic adsorption effect on heavy metals. However, the heterogeneity of HA results in an incomplete understanding of the structural characteristics of the ternary system of Ca–HA–Fe aggregates and adsorption of the quaternary system of Ca–HA–Fe–Pb/Cu/Cd. In this study, interactions between Ca–HA–Fe ternary and Ca–HA–Fe–Pb/Cu/Cd quaternary systems were discussed from a molecular perspective. The structures of the basic structural units of HA were identified. Density functional theory (DFT) was employed to calculate the stable states of basic structural units of HA and Ca²⁺. The results showed that hydroxyl and carboxyl groups exhibited the highest capacity to bind with Ca²⁺. The interactions among Ca, HA, and Fe led to the formation of network aggregates. The binding energies of functional groups for heavy metals and the feasibility of ion exchange were calculated by the method of experiment and DFT. According to the contribution of functional group complexation and ion exchange, the ion exchange values for Pb²⁺, Cu²⁺, and Cd²⁺ were 66.71%, 62.87%, and 60.79%, respectively, which indicated that Ca²⁺ ion exchange showed considerable potential in enhancing the adsorption capacity of heavy metals.

GRAPHICAL ABSTRACT

KEYWORDS:

• Humic acid
• adsorption separation
• structure–activity relationship
• calcium-doped
• heavy metal

Data availability

Date will be made available on request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Natural Science Foundation of China [grant number: 52004280]; Natural Science Foundation of Jiangsu Province of China: [grant number: BK20190629]; National Key Research and Development Programme of China: [grant number: 2021YFC2902602].