Mechano-Hydrothermal Alteration of Potassium-Bearing Rock-Forming Minerals

Technology      

Sylvinite is the traditional natural source of potassium. However, rock-forming minerals such as potassium feldspars (KALSi­3O8) are earth-abundant and contain up to 16 wt% of K2O. This technique targets these rock-forming minerals. The process is two-step. The preliminary step is a course grinding of the mineral potassium aluminosilicate source down to approximately 5mm. After crushing, the first step is high intensity milling of the ground mineral and calcium hydroxide Ca(OH)2, with CaO:SiO2 = 0.1-0.3 and water:solid = 2:1-10:1. This high intensity milling must occur for at least an hour, but can be continued for as long as desired. The second step is the hydrothermal reaction. The mixture is placed in a pressure vessel at the appropriate temperature (150-300oC ) and corresponding water vapor pressure, while being stirred. The time in the pressure vessel depends on the ultimate temperature, pressure, and stirring conditions, but should be at least 3 hours. After the hydrothermal reaction, the final product can release potassium into ultra-pure water, acidic or basic aqueous solutions, and aqueous solutions containing cations. Using ultra-pure deionized water, more than 12% of the potassium contained in the mineral source can be extracted within 8 hours. The rate of potassium release can be changed by varying the surface specific area and the microstructure, which are controlled primarily by the stirring mode during the hydrothermal reaction and secondarily by the milling technique.

Problem Addressed

Currently, potassium is dominatly obtained from the mineral Sylvinite in specific regions of the world. The potassium is then shipped to agricultural regions and is very expensive. This technology allows for localization of potassium fertilizer manufacturing, through a technique that requires less economic risk and no solid waste.  

Advantages

• Does not require strong acids or bases
• Performed at moderate temperatures ( ≤300 oC)
• Avoids the formation of solid waste  

Publications

"Research Finds Feldspar Releases Potassium at a Higher Rate than Expected with Implications for Agriculture." Phys Org, November 11, 2015.

"Microfluidic Leaching of Soil Minerals: Release of K+ from K Feldspar." PLOS One, October 20, 2015.

"A New Source for Potassium Fertilizer." MIT News, April 8, 2014.