Synthesis of K-Merlinoite zeolite from coal fly ash for fertilizer application

Due to the properties of zeolites, studies on the application of these materials as support for fertilizing elements, mainly NPK, have been carried out. Thus, this work aimed to obtain Merlinoite zeolites from coal fly ash, for later application as a fertilizer. The syntheses of the zeolites were performed by the classic hydrothermal method using a Factorial 23 planning. The chemical analysis confirmed the obtention of zeolites with a SiO2/K2O ratio between 1.41 and 3.46, K2O content above 17%, and CEC of 171.57–346.63 cmol.kg−1, values consistent with the literature. The solubility of K2O in water (0.89–3.23%) and 2% citric acid (14.22–18.57%) were following the requirements for single mineral fertilizers. In the K+ release tests in water and 0.01 M citric acid, the maximum values obtained up to 15 days of release were 6.119 mg.g−1 and 8.194 mg.g−1, respectively. The release rate of the nutrient showed that lower CEC values can contribute to a prolonged release of the nutrient, which may extend the time of action of the nutrient in the soil. Thus, we concluded that the synthesized materials fulfill their role of slow release of the nutrient proving that Merlinoite zeolites have great potential for application as K fertilizers.