Co-precipitation enrichment of Pb2+ in water by ball-milling-enhanced diatomite: synergistic effects of crystal structure and surface activity.

Abstract

Pb²⁺ was a typical heavy metal pollutant in industrial pollution. The treatment method of adsorbing Pb²⁺ in the wastewater by clay minerals was considered to be a quick and efficient method. Using diatomite (DE) as raw material, ball milled diatomaceous (MDE) was obtained through ball milling modification, and its structure and surface properties were characterized. Compared with DE, the specific surface area and CEC of MDE were increased by 18.88 times and 12.45 times respectively. The significant improvement in surface characteristics, crystal and pore structure and increase in the number of functional groups are important reasons for the significant improvement in MDE adsorption performance. Through batch adsorption experiments, the adsorption kinetics of Pb²⁺ by MDE was investigated using DE as a control. The pseudo-second-order kinetic model better fits the adsorption process of Pb²⁺ by MDE, indicating that the adsorption of Pb²⁺ by MDE was a complex mechanism of synergistic effects of physical adsorption and chemical adsorption. Intra-particle diffusion was one of the steps in the adsorption of Pb²⁺ by MDE, and it was mainly in the third stage. Both the Langmuir and Freundlich models can fit the adsorption isotherm well, indicating that the adsorption process of Pb²⁺ by MDE was a relatively complex multi-layer adsorption mechanism. The Temkin model infers that there were strong electrostatic interactions and ion exchange interactions during the adsorption of Pb²⁺ by MDE. DFT theoretical calculations confirmed that MDE adsorbs Pb²⁺ through coordination bonding, functional group complexation and electrostatic interaction. MDE had good surface properties and pore structure, and had a high adsorption capacity, and had good potential for removing Pb²⁺ from water.