Hydrothermal treatment at low temperature of Sardinian clinoptilolite-bearing ignimbrites for increasing cation exchange capacity

Two clinoptilolite-bearing ignimbrites belonging to Tertiary Sardinian volcanism and out-cropping in different localities were treated with 2M NaOH, 3M NaOH and 2M NaOH + AI(OH), at 100, 80 and 70 degrees C in order to enhance their cation exchange capacity. Bronze Teflon-lined autoclaves and a reactor equipped with magnetic stirrer were used for hydrothermal interactions, with interaction times ranging from 30 minutes to 36 hours. In all experimental cycles, clinoptilolite dissolution was followed by Na-P1 zeolite crystallization. The newly-formed zeolite changes from typical ball-shaped morphology to star-shaped grains with interaction increasing. The best interacting solution was 2M NaOH+Al(OH)(3). The cation exchange capacities (CEC) of the reacted products were higher than those of the raw materials (up to 2.5 times, i.e., from 88 to 268 meq/100 g). The use of a reactor equipped with magnetic stiffer strongly reduces interaction times for complete clinoptilolite dissolution and Na-P1 crystallization. (e.g. < 6 hours at 80 degrees C).