The mining of soluble potassium salts (potash) is essential for manufacturing fertilizers required to ensure continuous production of crops and hence global food security. As of 2014, potash is mined predominantly in the northern hemisphere, where large deposits occur. Production tonnage and prices do not take into account the needs of the farmers of the poorest countries. Consequently, soils of some regions of the southern hemisphere are currently being depleted of potassium due to the expansion and intensification of agriculture coupled with the lack of affordable potash. Moving away from mined salts towards locally available resources of potassium, such as K-bearing silicates, could be one option to improve this situation. Overall, the global potash production system and its sustainability warrant discussion. In this contribution we examine the history of potash production and discuss the different sources and technologies used throughout the centuries. In particular, we highlight the political and economic conditions that favored the development of one specific technology over another. We identified a pattern of needs driving innovation. We show that as needs evolved throughout history, alternatives to soluble salts have been used to obtain K-fertilizers. Those alternatives may meet the incoming needs of our century, providing the regulatory and advisory practices that prevailed in the 20th century are revised.

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.