N. Greece using domestic HEU-type rich natural zeolitic material

The natural zeolite from Evros prefecture contains Ca-rich clinoptilolite (89 wt.%) and in total 92 wt.% microporous minerals (zeolite + mica + clays). Quartz and feldspars constitute the non-microporous minerals (8 wt.%). Acidic water (pH 5.5) from the Kokkinolakkas Stream and basic water (pH 9.5) from the Koronia Lake were treated with the Evros natural zeolite. An intense increase in the pH was recorded in the acidic Stream water, while a pH decrease occurred in the basic lake water. These observations demonstrate that the zeolite tends to neutralize the water acting either as a proton acceptor or as a proton donor, exhibiting thus an amphoteric character. It should also be emphasized that near the neutral pH range, a faster increase of the pH towards the basic area was initially observed, followed by a slower decrease until its stabilization. In addition, a remarkable improvement of the clearness of both waters was observed.

The studied zeolite-rich sample contains 89 wt.% Ca-rich clinoptilolite, 92 wt.% microporous minerals (clinoptilolite + mica + clays) and shows a remarkable ammonia ion exchange capacity (sorption ability) of 229 meq/100 g. Natural zeolitic sample shows an ability to neutralize the pH of acidic Kokkinolakkas Stream and basic Koronia Lake waters, showing an amphoteric character. An intense increase in the pH was recorded in the acidic Kokkinolakkas Stream water, while a pH decrease occurred in the basic Koronia Lake water. In addition, a remarkable improvement of the clearness of both waters was observed. Note that the pH reaches equilibrium faster in the acidic Stream water than in the basic Lake water. The increase of the pH in the acidic pH-range could mainly be attributed to the binding of the protons to the Lewis basic sites of the zeolite comprising the zeolitic material and to a lesser extent to the H+ absorption through ion exchange reactions. The decrease of the pH in the basic pH-range could be the result of the removal of protons from surface Brønsted acidic sites or even of the detachment of protons from water molecules surrounding the exchangeable cations, caused by OH− attack on the Ca-rich clinoptilolite.