Estudo sobre zeólitas 4A de liberação lenta de nutrientes

Abstract

The intensive use of conventional water-soluble fertilizers has been a concern, because in excess they are not efficiently used by the plants, in addition to losses in the environment due to leaching and/or volatilization. Studies have been performed for the development of more efficient fertilizers as an alternative attractive strategy to conventional fertilizers, due to optimization of processes associated with slow release of nutrients, preventing the loss of component species leaching or volatilization and reduce the cost of this resource. Zeolites are crystalline hydrated aluminosilicates with adsorption, cation exchange and water retention properties; and can be used as fertilizers as they are able to provide nutrients and water. Ashes produced through the combustion of fossil fuel are of technological interest. The large amount of residue produced allows the use as raw material for synthesis of zeolites, in addition to reducing the environmental impact caused by this industrial byproduct. This work aims at the preparation of zeolites 4A fertilizers, synthesized from fly ash from brown coal and enriched with salts for slow release nutrients. The synthesized and occluded zeolites were characterized by SEM-EDS, XRD, IR and TGA, commercial zeolite 4A was used as reference. The enrichment of the zeolite synthesized and occluded with nitrogenous salt in a ratio of 1: 2 (zeolite: NH4NO3) presented a 21.1% incorporation of the salt, while the commercial zeolite 19.8%, estimated by thermogravimetric analysis. Leaching tests in static and dynamic systems, conducted in water and salt solution, resulted in different behavior of ammonium and nitrate ion release, showing the mechanisms of salt dissolution and ion exchange intermediated by zeolite in electrolyte solution. The slow release of nutrients, in particular ammonium, trials was observed in both flow and static, with measurable concentrations in relatively long times (from 100 to 1000 h). The results of IR and TGA of the zeolite synthesized occluded after 1,032 h of contact in saline (static system), presented evidence regarding the salt, suggesting the use of enriched zeolite as an ideal fertilizer material in the slow release of nutrients. The results showed a better performance for the zeolite synthesized, compared to the commercial ones, releasing the ions more slowly, suggesting their potential use as fertilizer matrix for controlled release of nutrients.