Davide Ciceri

Historical and technical developments of potassium resources.

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.

Microfluidic Leaching of Soil Minerals: Release of K+ from K Feldspar

The rate of K+ leaching from soil minerals such as K-feldspar is believed to be too slow to provide agronomic benefit. Currently, theories and methods available to interpret kinetics of mineral processes in soil fail to consider its microfluidic nature. In this study, we measure the leaching rate of K+ ions from a K-feldspar-bearing rock (syenite) in a microfluidic environment, and demonstrate that at the spatial and temporal scales experienced by crop roots, K+ is available at a faster rate than that measured with conventional apparatuses. We present a device to investigate kinetics of mineral leaching at an unprecedented simultaneous resolution of space (~101-102 μm), time (~101-102 min) and fluid volume (~100-101 mL). Results obtained from such a device challenge the notion that silicate minerals cannot be used as alternative fertilizers for tropical soils.

Potassium fertilizer via hydrothermal alteration of K-feldspar ore

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.

Terahertz scattering and water absorption for porosimetry

We use terahertz transmission through limestone sedimentary rock samples to assess the macro and micro porosity. We exploit the notable water absorption in the terahertz spectrum to interact with the pores that are two orders of magnitude smaller (<1μm) than the terahertz wavelength. Terahertz water sensitivity provides us with the dehydration profile of the rock samples. The results show that there is a linear correlation between such a profile and the ratio of micro to macro porosity of the rock. Furthermore, this study estimates the absolute value of total porosity based on optical diffusion theory. We compare our results with that of mercury injection capillary pressure as a benchmark to confirm our analytic framework. The porosimetry method presented here sets a foundation for a new generation of less invasive porosimetry methods with higher penetration depth based on lower frequency (f<10THz) scattering and absorption. The technique has applications in geological studies and in other industries without the need for hazardous mercury or ionizing radiation.