About 10.0 g of soil samples from Londrina, Floraí, and Tibagi and clays, bentonite, montmorillonite, kaolinite, were put into porcelain crucibles, heated for 15 min at either 280, or 400, or 650 °C in a muffle furnace, and cooled to room temperature. Samples were kept in a desiccator until use. The samples were split in two portions and one was treated with GPS