Complexing Abilities of Hydrous Manganese Oxide Surfaces and their Role in the Speciation of Heavy Metals

Abstract

Manganese oxides play an important role in regulating heavy metals in aquatic systems. In order to understand their physico-chemical properties, hydrous manganese oxides were synthesized and interactions with heavy metals, especially Cu²⁺, Pb²⁺, Zn²⁺ and Cd²⁺ have been studied. Complexing capacities as well as surface complexation constants at pH 5.5, 6.0 and 6.5 have been determined by differential pulse polarography (DPP). The DPP method enables one to do metal speciation measurements as it discriminates between free metal ion and complexed species. Surface complexation constants were evaluated by linearizing the titration data using two different methods viz. Scatchard and van den Berg-Ružić plot methods. The results yielded by both methods are in good agreement. Adsorption of heavy metals onto these oxides were also studied over a wide range of pH. Atomic absorption spectrometry was used for the analyses of these metals. The metal analyses were carried out in samples filtered through 0.2 μm filter. The drawback of this method is that filtrates are contaminated with fine oxide particles.