Abstract: Adsorption of Mn²⁺ to natural surface coat ings developed in the South Lake was carried out for the purpose of investigatin g pH changes of different systematic solutions, which were prepared by minimal m ineral salts (MMS) and distilled-deionized water (dd water) with Mn²⁺ present and absent, respectively. The results show that the pH values of the four solutions employed increased remarkably during the initial adsorption perio d first, subsequently decreased to a stationary value gradually. In addition, the pH values of MMS solutions were higher than those of dd water solutions without MMS accordingly, and solutions without Mn²⁺ higher than those of solutions with Mn²⁺ presen t. The variety of pH in the study could be described by an oxide surface adsorp tion conjugate model.

Key words: natural water, surface coating, Mn²⁺, pH, adsorption mechanism