Aggregation of montmorillonite and organic matter in aqueous media containing artificial seawater

The montmorillonite-only system increased the degree of aggregation with salinity increase, as would be expected for suspended colloids whose dispersion-aggregation behavior is largely controlled by the surface electrostatic properties and van der Waals forces. When montmorillonite is combined with humic acid or chitin, the aggregation of montmorillonite was effectively inhibited. The surface interaction energy model calculations reveal that the steric repulsion, rather than the increase in electronegativity, is the primary cause for the inhibition of aggregation by the addition of humic acid or chitin.These results help explain the range of dispersion-aggregation behaviors observed in natural river and estuarine systems. It is postulated that the composition of suspended particles, specifically the availability of steric polymers such as those contained in humic acid, determine whether the river suspension is rapidly aggregated and settled or remains dispersed in suspension when it encounters increasingly saline environments of estuaries and oceans.The dispersion-aggregation behavior of suspended colloids is important to the cycling of matter in rivers and estuaries. For example, the transport and fate of dissolved metal contaminants in rivers and estuarine environments are often directly determined by the potential co-aggregation and sedimentation along with the suspended colloids [1]. Excess nutrients that may be harmful to estuarine and coastal ecosystems and fisheries are sometimes removed through the natural processes of aggregation and sedimentation of suspended colloids [2]. The aggregation and dispersion of suspended colloids significantly alters the optical properties of coastal waters and thus a proper interpretation of remote sensing imagery requires the knowledge of the site-specific colloid aggregation-dispersion dynamics [3].Upon aggregation, river and estuarine colloids are settled to form bottom sediments. The sedimentary aggregates found in estuari