The growth process of saponite: A study based on particle size distributions and morphological evolution

Smectite growth is of great importance for the geochemistry of clay minerals on the Earth’s surface and their applications in industries. However, the growth process and mechanism controlling the physicochemical properties of smectite are still poorly understood. Through an effective integration of particle size distributions (PSDs) and morphology of particles, this study has enhanced the understanding of smectite growth by investigating the growth processes of a synthetic tri-octahedral smectite (saponite). The starting materials were equimolar Mg-saponite and Ni-saponite that had been hydrothermally synthesised at 220 °C. Two Mg-Ni-saponite samples were obtained through further hydrothermal treatment of the starting materials at 400 and 500 °C. A systematic measurement of the size in the ab-plane of numerous saponite particles was performed to obtain their PSDs. The parameters α and β2, derived from PSDs and the morphology of saponite, indicate that saponites grow mainly via surface-controlled growth and likely via supply-controlled growth in open systems. Particle attachment via the edge surfaces of saponite is an accompanying growth mechanism, and talc-like layers favour the “three-dimensional growth”. In addition, the heterogeneous tetrahedral Al distribution of saponite could lead to the formation of elongated laths.