Incorporation of mineral phosphorus and potassium on leather waste (collagen): a new N(collagen)PK-fertilizer with slow liberation.

The feasibility of using a solid waste (rich in nitrogen) from the leather industry, after chromium extraction, as adsorbent for P and K, for possible utilization as NPK fertilizer was evaluated. The materials, with and without the addition of P and K, were characterized by chemical analyses, infrared spectroscopy, EDS (energy dispersive X-ray spectrometry) and SEM (scanning electronic microscopy). Langmuir and Freundlich equations were used for analyzing the experimental data, which showed a better fit to the Freundlich model, thus suggesting a multilayer adsorption process on the surface of the adsorbent. A preliminary test in greenhouse demonstrates that the P and K incorporation on the matrix rich in nitrogen (collagen) is a interesting alternative to use such material as NPK fertilizer. The application of N(collagen)PK formulations, as a source of nutrients for the growth of rice plants, showed promising agronomic results.