Investigation of Shear Yield Stress, Zeta Potential and Particle Size in Kaolinite and Bentonite Suspensions
Author
Larsen, Joan
Term
10. term
Publication year
2009
Abstract
This thesis examines whether the shear yield stress (the stress needed to initiate flow) of clay suspensions can be inferred from more accessible measurements of particle surface charge (zeta potential) and particle size, to support improved assessment of tailings dewaterability. In several kaolinite suspensions, shear yield stress was measured using four-bladed vane rheometry following Nguyen and Boger (1985), zeta potential by electro-acoustic methods, and particle size by light scattering; with the sample preparation used it was not possible to determine the yield stress of bentonite, so correlations for that material could not be made. To relate the parameters, the product of shear yield stress and the surface-area-weighted particle size was plotted against the square of the zeta potential. For kaolinite with pH-dependent surface charge, this product increased as the zeta potential squared increased (interpreted as decreasing surface charge), consistent with the correlation based on the mathematical model proposed by Scales et al. (1998). For kaolinite with pH-independent surface charge, the product changed little, attributed to the minor variation in zeta potential between pH 4–10. These findings support a link between surface charge, particle size and yield behavior in kaolinite, while improved sample preparation is needed to evaluate bentonite.
Dette speciale undersøger, om shear yield stress (den spænding der skal til for at få en suspension til at flyde) i ler-suspensioner kan udledes af mere tilgængelige målinger af partiklernes overfladeladning (zeta-potentiale) og partikelstørrelse med henblik på bedre vurdering af afvanding af tailings. I flere kaolin-suspensioner blev shear yield stress målt med firebladet vane-reometri efter Nguyen og Boger (1985), zeta-potentiale med elektroakustik og partikelstørrelse med lysspredning; med den anvendte prøveforberedelse var det ikke muligt at bestemme shear yield stress i bentonit, og korrelationer for dette materiale kunne derfor ikke etableres. For at relatere parametrene blev produktet af shear yield stress og den overfladeareal-vægtede partikelstørrelse plottet mod zeta-potentialet i anden. I kaolin med pH-afhængig overfladeladning steg dette produkt, når zeta-potentialet i anden steg (tolket som faldende overfladeladning), i overensstemmelse med korrelationen baseret på den matematiske model foreslået af Scales et al. (1998). I kaolin med pH-uafhængig overfladeladning ændrede produktet sig ikke nævneværdigt, hvilket tilskrives de små ændringer i zeta-potentiale mellem pH 4–10. Resultaterne understøtter, at overfladeladning og partikelstørrelse kan knyttes til flydeadfærd i kaolin, mens forbedret prøveforberedelse er nødvendig for at udvide analysen til bentonit.
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