In many mining applications the residual waste, or tailings, contains a mixture of different clays and mineral oxides dispersed in an aqueous medium that also consists of ions at relatively high concentrations and residual organics.  One strategy to process the tailings is to add coagulation and flocculation agents to aggregate the particles, followed by a dewatering step to generate a solid waste material that can be used in land reclamation.  Our group is interested in monitoring the water structure at these interfaces to determine whether we can identify a spectral signature of the water structure that can be associated with successful dewatering.  To this end we use a second-order nonlinear optical spectroscopy, vibrational sum-frequency generation (SFG), as it is intrinsically sensitive to water or other molecules with an anisotropic net orientation at the interface.  Using SFG we monitor the binding of kaolinite clay particles to planar silica in the presence of background electrolyte.  We then monitored the water structure as well as the vibrational SFG modes associated with the clay as the pH was increased with either lime (calcium oxide and hydroxide) or sodium hydroxide.  In conjunction with these experiments, we measured the zeta potential on the same type of planar silica and clay samples in the presence of increasing amounts of lime or sodium hydroxide.  How the water spectra evolve with pH using the two different caustic agents will be discussed as well as the proposed spectral signature associated with dewatering conditions.

Monitoring the pH-dependent interfacial water structure at the kaolinite/silica/aqueous interface

ACS Fall 2021

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