The surface chemistry of δMnO 2 in major ion sea water

Abstract

The surface chemistry of δMnO 2 in major ion seawater is defined by determining the stoichiometry of the reactions which describe the association of the surface hydroxyl groups with Na, Mg, Ca, and K ions, the intrinsic equilibrium constants which define these reactions, and the speciation of the surface at pH 8. The results indicate: 1. 1) that the surface forms monodentate complexes with Na and K ions and bidentate complexes with Mg and Ca ions; 2. 2) that pK 2 INT = 4.2, p ∗K INT Na = 3.0 ± 0.3 , p ∗K INT K = 2.0 ± 0.2 , p ∗K INT >Mg = 3.9 ± 0.1 , and p ∗K INT >Ca = 3.3 ; and 3. 3) ion exchange processes other than with H are important and as a result 84.8% of the surface sites of δMnO 2 in major ion seawater at pH 8 are complexed by H, 8.4% by Mg, 4.6% by Ca, 1.6% by Na, and 0.6% by K. Chloride and sulphate do not adsorb on δMnO 2 in the pH range of natural waters.