Removal of Diclofenac from Aqueous Phase by Birnessite: Effects of pH and Common Ions

Abstract

In this study, the removal of diclofenac (DCF) from aqueous phase by birnessite, a layered manganese oxide, was investigated by batch experiments. The results indicated that 90% of DCF was removed by birnessite within 4 h in different initial concentrations of DCF, and the kinetic experiment data were well fitted with pseudo-first-order kinetic model (R² > 0.98). The removal of DCF by birnessite was pH-dependent, and low pH was beneficial to the reaction. The presence of Fe²⁺ and Mn²⁺ strongly inhibited the removal of DCF. However, Ca²⁺, Mg²⁺, Zn²⁺, Cu²⁺, and humic acid (HA) promoted the reaction and following the order: Cu²⁺ > Zn²⁺ > HA > Mg²⁺ ≈ Ca²⁺. In addition, some typical anions, such as NO₃⁻, PO₄³⁻, and SO₄²⁻, had slight effects on the reaction. Electrochemical results demonstrated that the adsorption of DCF on birnessite was reaction rate-limiting step.

Graphical Abstract

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