Probing
Contaminant Transport to and from Clay Surfaces
in Organic Solvents and Water Using Solution Calorimetry
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Abstract
Clays, in tailings, are a significant
ongoing environmental concern
in the mining and oilsands production industries, and clay rehabilitation
following contamination poses challenges episodically. Understanding
the fundamentals of clay behavior can lead to better environmental
impact mitigation strategies. Systematic calorimetric measurements
are shown to provide a framework for parsing the synergistic and antagonistic
impacts of trace (i.e., parts per million level) components on the
surface compositions of clays. The enthalpy of solution of as-received
and “contaminated” clays, in as-received and “contaminated”
organic solvents and water, at 60 °C and atmospheric pressure,
provides important illustrative examples. Clay contamination included
pre-saturation of clays with water and organic liquids. Solvent contamination
included the addition of trace water to organic solvents and trace
organic liquids to water. Enthalpy of solution outcomes are interpreted
using a quantitative mass and energy balance modeling framework that
isolates terms for solvent and trace contaminant sorption/desorption
and surface energy effects. Underlying surface energies are shown
to dominate the energetics of the solvent–clay interaction,
and organic liquids as solvents or as trace contaminants are shown
to displace water from as-received clay surfaces. This approach can
be readily extended to include pH, salts, or other effects and is
expected to provide mechanistic and quantitative insights underlying
the stability of clays in tailings ponds and the behaviors of clays
in diverse industrial and natural environments