Ball milled nanosized zeolite loaded with zinc sulfate: A putative slow release Zn fertilizer

Commercially available zeolite was ball milled and the resultant nano sized product was characterized with powder XRD, SEM, FT-IR and BET. Ball milled nano-sized zeolite was mixed with zinc sulfate solution at various concentrations. Zinc sorption and desorption studies were carried out. Nano zeolite loaded with zinc sulfate showed the highest sorption among native and ball milled zeolite and montmorillonite, halloysite and bentonite. The results showed that the highest sorption of 429.5 mg kg⁻¹ was observed for nano-zeolite with highest bonding energy (0.33 mmol⁻¹ × 10⁻³) and regression coefficient (0.99). The nano-zeolite recorded 47.9% higher adsorption than nano-montmorillonite. Nano-zeolite showed the release of zinc in three stages. Zn levels decreased sharply in the first 220 hours (k₁ = 0.53), and stabilized thereafter. The result also showed that from 300 to 500 hours it follows second stage (k₂ = 9.44 × 10⁻³). In this stage it supplies 2 ppm of Zn²⁺. The next stage falls from 500 hours (k₃ = 1.7 × 10⁻³) and it supplies 1.5 ppm of Zn²⁺ and this condition is static even after 1000 hours. This study suggests that nano-zeolite based Zn fertilizers may be used as a strategy to achieve the slow release of Zn which in turn would improve Zn use efficiency in crops.