The role of natural organic matter in suspension stability: 1. Electrokinetic–rheology relationships

The electrokinetics and rheology of a model alumina suspension has been investigated in the presence of a series of natural organic matter (NOM) fractions from soil and aquatic sources. The role of natural organic matter in changing both the dispersed state of the solids and the rheology of concentrated suspensions has been investigated. The data shows that at high surface coverage there is a good correlation between the nature of the adsorption layer and the electrokinetic and rheology responses. The data highlights key differences between the different fractions in aiding dispersion. At intermediate surface coverage, the correlation is less robust particularly for the more hydrophilic NOM fractions. The measured value of the electrokinetic potential is no longer a good indicator of colloidal stability as indicated by a DLVO type analysis. The reason may be due to the adsorbed layer showing a different response to particle movement in electrokinetic measurements than it does in static rheology measurements. In the latter case, the behaviour is dominated by particle interaction.