Study on the adsorption mechanism of activated carbon removing low concentrations of heavy metals

This paper focused on the adsorption mechanism of activated carbon for the removal of low-concentration heavy metals in drinking water treatment. Two commercial activated carbon AC-1 and AC-2 were selected, which mainly were used for the terminal purification of drinking water. To investigate the differences of adsorption capacity of ACs for Pb, Hg, and As, scanning electron microscopy test (SEM), N2 adsorption/desorption isotherm, the surface functional groups (FT-IR), the point zero charge (PZC), and X-ray photoelectron spectroscopy analysis were conducted. Freundlich isotherms were used to describe the adsorption behavior of ACs on heavy metal ions. The results showed that both AC-1 and AC-2 have aptitude for low-concentration heavy metals retention; taking the removal capacity and cost into account, AC-1 is more efficient and economic than AC-2 for the low-concentration heavy metal ions (Pb and Hg) removal from water. The mechanism analysis showed that the adsorption of ACs on low-concentration heavy metals heavily depends on the properties of ACs (pore size distribution, pHPZC, surface functional groups etc.) and the experiment condition, which cannot only be explained by ion exchange, chemical adsorption, specific adsorption, and electrostatic effects.