Potassium fertilizer via hydrothermal alteration of K-feldspar ore

Abstract

Fertilizers ensure the necessary agricultural yields to feed an increasing world population. Augmenting fertilizer use conflicts with environmental concerns such as eutrophication and soil pollution, as well as with limited availability of fertilizers in the Global South. Currently, potassium fertilizers are soluble salts such as KCl, which are mined in the northern hemisphere. Two key issues arise for tropical agriculture. First, the inherent solubility of potassium salts questions their efficacy in weathered soils. Second, long-distance transportation leaves unsolved the problems of limited local supplies and infrastructure, freight-related CO₂ emissions and cost of the fertilizer for the end user. In this work, we synthesize according to green-chemistry principles a novel potassium-bearing material which mineralogy and elemental release have the potential to overcome the limitations of KCl. We process in mild hydrothermal conditions (T = 200 °C; P∼ 14 atm; t = 5 h) locally available K-feldspar ore (ultrapotassic syenite) and CaO. The resulting hydrothermal material is characterized using X-Ray Powder Diffraction (XRD), Electron Microscopy (EM), Electron Probe Micro-Analyzer (EPMA), Particle Size Distribution (PSD) and Specific Surface Area (SSA). Additionally, leaching tests are performed, showing that the availability of potassium in the processed material is two orders of magnitude higher than in the raw K-feldspar ore. This work introduces a green-chemistry paradigm for the synthesis of potassium fertilizers.