Tuning sedimentation of clay particles through surface charge interactions*

Clays are abundant in natural environments and have various applications in industrial processes. Featuring a platelike morphology, clay particles typically have negatively charged faces and positively charged edges that encourage their aggregation when suspended in water. The screening of repulsive surface charges by dissolved cations facilitates particle aggregation, while intercalation of negatively charged ions can impose repulsion that suppresses aggregation. Here we tune the interaction of kaolinite clay particles from attractive to repulsive to examine the effects of surface charge on the rate and style of sedimentation. Classic hindered settling theory reasonably describes sedimentation rate for repulsive particles, which form a concentrated jamming front. The hindered settling description breaks down for attractive particles, which aggregate to form a clay gel that consolidates under its own weight. As the gel compacts, expulsion of interstitial water drives upward flow, which opens fracture-like channels in the bulk of the gel; these channels disappear as the gel enters a creep regime. Results help towards understanding the transport and erodibility of cohesive sediments.