Silica Vs Calcite – A DLVO story
Saravana Kumar, Dirk van den Ende, Igor Siretanu, Frieder Mugele
Physics of Complex Fluids, University of Twente
Introduction
Mineral interfaces are important in many areas such as geology, mineral synthesis, carbon
capture, oil-recovery, nuclear waste storage etc… Understanding the physics that takes place at the mineral-liquid interface is of great importance in these fields.
Here, we study calcite and silica interfaces using an atomic force microscopy to compare and contrast between the two and to answer some of the recent theories out there in the field of interfacial science.
+ -+ + + + + + + + ? ? + + -? -? -? + + + + + ? + ? + -Silica ? ? ? ? ? ? ? ? Calcite + + + + + + + + + -+ -+ + + ? -+ + + + -? + + + + + + -+ + + + + +
Outlook
The silica interface behaves as expected(DLVO theory). Even at high concentrations of 4M, we do not see any unusual decay length for both calcite and silica.
The calcite on the other hand, does not show any discernable DLVO interaction even at 1mM NaCl. We ruled out the effect of roughness by measuring interactions locally
The calcium ions which are released from the surface might have screened the charge effectively and hence we see no interaction. This needs to tested
DLVO
The silica exhibits DLVO behavior over all concentrations and
temperature ranges
The magnitude of force changes with temperature indicating
surface charge density(increased deprotonation) changes with
change temperature
We did not see any long range decay lengths at high salt concentrations and is true for all temperatures probed, indicating no relation between decay length and
permittivity of the intervening medium[1]
????
In order to rule out the effect of
roughness on the probed force[2], we did force maps using blunted
sharp probes
Topography shows calcite with atomic steps
Again, no discernable interactions observed for local averaged and
total averaged spots except for the noise R = 10 nm k = 0.58 N/m Colloidal probe Substrate + + + + -- - -+ + + + + + + + + + + + -+ + -+ + + + + + + + + + + + + -- -+ + + + + + + -- -- -- -References
1. Smith, A. et al, J Phys Chem Letters 7.12 (2016): 2157-2163.
2. Ozcelik, H. G. et al, Phys Chem Chem Phys 21.14 (2019): 7576-7587.
How Silica behaves
The plot shows the
interaction force between two silica surfaces across NaCl of varying
concentration
As can be clearly seen the interaction length goes
down as the concentration increases
Silica obeys the DLVO theory and we observe no long range force at high concentrations
How Calcite behaves
The plot shows interaction force between silica and
calcite across NaCl at pH ~ 8.5 The pH is elevated to
minimize calcite dissolution. The calcite shows no
discernable decay length even in low concentrations
Calcite does not seem to be obeying the DLVO theory and we also don’t observe any longer decay lengths at high
concentration R = 750 nm k = 3.0 N/m
