Formulating and Optimizing a Novel Biochar-Based Fertilizer for Simultaneous Slow-Release of Nitrogen and Immobilization of Cadmium

This study aimed to develop and optimize a novel biochar-based fertilizer composed of rice husk biochar and urea–hydrogen peroxide (UHP), which can simultaneously slowly release nitrogen and immobilize cadmium (Cd). Response surface methodology (RSM) was adopted to optimize the fertilizer formulation with the lowest nitrogen release rate. Under the optimized conditions, the cumulative nitrogen release rate of the biochar-based fertilizer was 17.63%, which was significantly lower than that of ordinary fertilizer. Elementary analysis, scanning electron microscopy (SEM) images, and Fourier transform infrared (FTIR) spectroscopy proved that UHP attached to the porous structures of the biochar. The adsorption test showed that the adsorption of Cd onto biochar-based fertilizer quickly reached equilibrium with an equilibrium adsorbing quantity (Qe) of 6.3279 mg·g−1 with an initial concentration of 10 mg·L−1. Compared to original biochar, the Cd immobilization ability of biochar-based fertilizer was significantly better. The adsorption of Cd on biochar-based fertilizer is mainly based on a monolayer adsorption behavior. Finally, improved crop growth was demonstrated by pot experiments, which showed a significant increase in the biomass of cabbage. The concept and findings presented in this study may be used as references in developing a novel biochar-based fertilizer for simultaneously enhancing crop yield and reducing environmental risk.