Synthesis of high-efficient low-cost fertilizer carriers based on biodegradable lignin hydrogels

Conventional fertilizers face environmental and economic challenges due to their high solubility, leading to significant losses via runoff and leachate. This study presents a biodegradable hydrogel, synthesized from lignin and polyvinyl alcohol (PVA), designed as an eco-friendly carrier for struvite (fertilizer) with controlled phosphate release. The hydrogel was analysed through scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC). Furthermore, the prepared hydrogels demonstrated high water absorption capacities (963.4 %, 706.4 %, and 410 % for LH₄, LH₈, and LH₁₂, respectively) and exhibited Fickian diffusion behaviour. Phosphate release studies showed a gradual release over 6–8 h with concentrations of 20.5 ppm, 19.45 ppm, and 17.85 ppm for St-LH₄, St-LH₈, and St-LH₁₂. These lignin-based hydrogels offer a promising, cost-effective solution for slow-release fertilizers with high efficiency.