Heliyon (Jan 2025)
Preparation of slow-release fertilizer derived from rice husk silica, hydroxypropyl methylcellulose, polyvinyl alcohol and paper composite coated urea
Abstract
There is a growing trend toward utilizing agricultural waste to create value-added products, addressing environmental concerns associated with their disposal. This study focuses on developing slow-release fertilizers (SRFs) using amorphous silica derived from rice husk, hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA), waste paper, and urea. Experimental optimization was carried out using the response surface methodology central composite design (RSM-CCD). The optimal formulation included 8.63 g of silica, 1.04 g of HPMC, and 0.27 g of PVA. Two SRFs were prepared under these conditions: SRF1, consisting of silica, HPMC, and PVA, and SRF2, which additionally incorporated coated waste paper. Characterization techniques such as Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD) Scanning Electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis were used to examine the materials. The rice-husk-derived silica exhibited a pore size of 2.140 nm and a BET surface area of 690 m2/g, providing an excellent surface for nutrient encapsulation. Although the addition of coated waste paper minimally influenced the slow-release behaviour of SRF2, however the other components effectively reduced nutrient leakage by trapping the nutrients. The swelling behaviour of the SRFs was analyzed in different media after 72 h, showing values of 2.66, 2.54 (g/g) in distilled water, 2.20, 2.58 (g/g) in pH 4, and 1.86, 3.09 (g/g) in pH 9 solutions. The swelling kinetics aligned with Scott's second-order kinetic model. Urea release tests in water revealed a release of 94 % and 97 % at 24 h for SRF1 and SRF2, respectively, compared to 98 % release of pure urea within 1 h. SRF2 demonstrated optimal nutrient release after 48 h. The release kinetics followed the first-order kinetic model for both SRF1 and SRF2, highlighting their potential as effective slow-release fertilizers.
