The Effect of Chemical and Thermal Treatments on the Buffering Capacity of Phillipsite Tuff

Phillipsite tuff samples from Jebal Aritayn (Jordan) was treated chemically by acid, base, and salt and thermally at 200 and 400 °C. Both treated and untreated phillipsite samples were titrated with HCl and NaOH. The potentiometric titration curves showed that Jordanian phillipsite tuff exists in the base form (pH 8.5) and thus has a remarkable buffering capacity toward H^+. The effect of chemical and thermal treatments on the buffering capacity of zeolite was studied by employing a simple model. The model enables estimating the pKa values and the acid sites densities for zeolite samples. Depending on the pKa values of buffering regions and relative to what was reported in literature, it was concluded that the aluminosilicate sites ( SOH2^+ and SOH, S = Al or Si) as well as the associated silicates, carbonates and bicarbonates of Al, Mg, Ca, and Fe are responsible for the buffering behavior of phillipsite tuff samples. It was also clear that the buffering capacity of phillipsite tuff was reduced by treatment with salt (NaCl), acid (HCl), and base (NaOH). On the other hand, the buffering capacity of phillipsite tuff was enhanced by thermal treatment at 400 °C.