Surface characteristics of shales and implication on metal sorption

Differences in surface characteristics between alkaline and acidic shales are demonstrated in the present study. The alkaline shales are characterized by convex surface titration profiles, while the acidic shale exhibits a concave titration profile. Analysis of surface functional groups reveal that carboxylic acids predominate in alkaline shales and the acidic shale is characterized by C=S, C=N (pyridine derivative) and urea (C=O) functional groups, while it lacks –COOH group. The close proximity between pH and point of zero charge for the most acidic and alkaline shales indicate that surface complexation may not play a dominant role in sorption when the system pH is controlled by these sediments.