Wet coating of calcite with silica nanoparticles in CO2 environment

Calcite particles coated with nano-silica find use in applications such as enhanced oil recovery, paper-making, and thermal energy storage. In this study, the surface coating of calcite particles by silica nanoparticles (nano-SiO2) in aqueous solutions assisted by a CO2 environment was investigated. The result indicates that the coating performance can be controlled by altering the electrostatic attraction between calcite and nano-SiO2, with the calcite surface charge being the predominant factor. An elevated CO2 partial pressure (up to 3.7 atm) is beneficial for the coating process. However, similar coating performance can be achieved under lower CO2 partial pressures by introducing calcium salt into the aqueous solution. With the addition of 15 wt% of nano-SiO2 in a 6.5 mM CaCl2 solution, a nano-SiO2 loading content of 12.6 wt% (with an average calcite particle size of 6.74 mu m) was achieved under 1 atm CO2 pressure after 24 h of the coating experiment. Overall, the coating of calcite surfaces with high contents of well-dispersed nano-SiO2 can be achieved in a CO2 environment, and calcium salts can be used to reduce the required CO2 pressure. As such, it is potentially feasible to integrate wet coating into aqueous carbonation-based CO2 mineralization processes to enhance process economics by making nano-SiO2-coated calcite a valuable byproduct.