Zinc and manganese sorption behavior by natural zeolite and bentonite

Understanding the sorption process in natural zeolite and bentonite is necessary for effective utilization of these minerals as nutrient adsorbents and on the other side for controlling release of plant nutrients. This research was undertaken to characterize the ability of natural zeolite and bentonite minerals to adsorb and release zinc and manganese. The potentials for sorption of these ions were evaluated by applying the Langmuir and Freundlich equations. The results showed that Langmuir constant [maximum adsorption (b mmol kg−1)] of both Zn and Mn were for bentonite > zeolite. While the binding strength values (k in L mmol−1) for zeolite > bentonite. Zn in the case of zeolite showed the lowest desorbed percentage particularly at high levels of sorbed Zn. Only, 74.7% is readily extractable by DTPA after three successive extractions leaving, 25.3% Zn retained by the mineral. In the case of bentonite, 82.26% of sorbed Zn is readily extractable by DTPA after three successive extractions leaving, 17.74% Zn retained by the mineral. In the case of Mn, 84.63% of Mn sorbed by zeolite is readily extractable by DTPA after three successive extractions leaving, 15.37% Mn retained by the mineral. In the case of bentonite, 89.79% of adsorbed Mn is readily extractable by DTPA after three successive extractions leaving, 10.21% Mn retained by the mineral. This finding may reflect clearly the possibility of using natural zeolite and bentonite as slow release fertilizers for Zn and Mn and on the other hand preventing soil pollution with heavy metals.