Removal of manganese by adsorption onto newly synthesized TiO2-based adsorbent during drinking water treatment

Abstract

Manganese is naturally present in water, but its increased concentration in potable water is undesirable for multiple reasons. This study investigates an alternative method of demanganization by a newly synthesized TiO₂-based adsorbent prepared through the transformation of titanyl sulphate monohydrate to amorphous sodium titanate. Its adsorption capacity for Mn²⁺ was determined, while a range of influential factors, such as the effect of contact time, adsorbent dosage, pH value, and added ions was evaluated. The adsorbent appeared highly effective for Mn²⁺ removal owing to its unique characteristics. Besides adsorption via electrostatic interactions, ion-exchange was also involved in the Mn²⁺ removal. Although the Mn²⁺ removal occurred within the whole investigated pH range of 4-8, the maximum was achieved at pH 7, with q_e = 73.83 mg g^-1. Equilibrium data revealed a good correlation with Langmuir isotherm in the absence of any ions or in the presence of monovalent co-existing ions, while the results in the presence of divalent co-existing ions showed a better fit to Freundlich isotherm. Additionally, the presence of monovalent cations (Na⁺, K⁺) only slightly decreased the Mn²⁺ removal efficiency as compared to divalent cations (Ca²⁺, Mg²⁺) that caused a greater decrease; however, the effect of anions (Cl^-, SO₄^2-) was insignificant. To provide insight into the adsorbent safety, the toxicity assessment was performed and showed no harmful effect on cell activity. Furthermore, the residual concentration of titanium after adsorption was always below the detection limit. The results imply that the synthesized TiO₂-based adsorbent is a safe promising alternative method for demanganization.Highlights The synthesis of amorphous TiO₂-based adsorbent was presented.The TiO₂-based adsorbent was found to be efficient for Mn²⁺ removal.The Mn²⁺ removal mechanisms were adsorption and ion-exchange.Increasing pH enhanced the efficiency of Mn²⁺ removal.Divalent cations decreased the Mn²⁺ removal efficiency more than monovalent cations.

Keywords: Adsorption; drinking water treatment; ion-exchange; manganese; titanium dioxide.