Surface charging and adsorptive properties of pyrolusite (β-MnO2)

Pyrolusite (β-MnO2) is a reactive mineral that is highly abundant in the environment. Pyrolusite plays an important role in reactions such as biogeochemical cycling of heavy metals, toxic trace elements and soil nutrients. These reactions are thought to be mediated by the high solubility of pyrolusite. Pyrolusite was selected for this study as it is the most stable of the MnO2 polymorphs. Although pyrolusite may assist in remediation, there is still a lack of interface data on these minerals. A commercial pyrolusite sample was used in all experiments. Prior to use, the sample was washed and characterized extensively. Characterization included N2-BET analysis, XRD analysis, and SEM imaging. XRD scans confirmed that the sample was pure, crystalline pyrolusite. The SEM images showed that the sample had a blocky morphology and ranged from 5 to 65 µm. A titration protocol development was created to get reproducible surface charge data on pyrolusite. Potentiometric titrations were used to gather surface charge data on pyrolusite in the presence and absence of Ca2+ in NaCl media. Titrations were performed at ionic strength values of 0.03m, 0.1m, and 0.3m while maintaining a temperature of 25ºC. Samples were collected from the titration for later ICP-AES analysis. ICP data was used to calculate MnO2 dissolution and Ca2+ adsorption.

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