Low Field 1H NMR Study of Water in Calcium Carbonate and Silica Particles at Various Saturation Levels

Due to the mineral-water interaction and the geometric restrictions, the pore water has different behaviors than bulk water, such as lower freezing point and less stability of gas hydrate. As a result, it is necessary to study the properties of water in pores constructed with various minerals for the fundamental understanding of the unfreezing or unclathratable water in sediment pore. In this work, we study the relaxation characteristics of water in calcium carbonate and silica particles (45-74 μm) filled at various saturation levels by a low field nuclear magnetic resonance (LF-NMR) instrument. Contact angle measurement and time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments are also conducted to help explain the NMR data. The variation of transverse relaxation time (T₂) distribution with water content indicates that the surface water on calcium carbonate and silica have different kinds of hydroxyl groups and liquid phase distribution. The former has bulk hydroxyl groups (T₂=0.139871ms) which don't interact with water molecules, thus has two liquid phase components in pores called surface water layer and bulk water layer. The latter has silanol groups which lead to the appearance of bound water layer, and the water activity decreases as the distance of water molecules from the particle surface decreases. Different surface groups lead to the difference of interaction strength between mineral and water, corresponding to the differences in liquid phase distribution and activity of water in pores. This research reveals that water confined in the pores constructed by calcium carbonate and silica particles have different properties.