Kaolin minerals surface

Kaolin most commonly originates by the alteration of feldspar or other aluminum siHcates via an intermediate solution phase (97,98) usuaHy by surface weathering (26,99) or by rising warm (hydrothermal) waters. A mica, or hydrated alumina soHd may form as an intermediate phase during the alteration from parent material to kaolin minerals. 

The 1 1 kaolin structures are chemically simpler the tetrahedral sites are occupied by silicon and the octahedral sites by aluminum. There is a minor amount of substitution, largely of ferric iron for aluminum, but the amounts are generally only a few tenths of a percent by weight of oxide. The kaolin minerals do not expand in the presence of water and their surface area, approximately 10 to 15 m2/g, represents the external area of the crystals. 

GIESE AND COSTANZO Water on the Surface of Kaolin Minerals... 

Kaolin Minerals. The 1 1 structures include a group of aluminosilicate minerals which are termed collectively the kaolin minerals specifically these are kaolinite, dickite, nacrite, and halloysite. The basic 1 1 layer for all of these minerals has the composition AlgSigOj-fOHJj, there is a small amount of substitution of iron for aluminum, ana fluoride for hydroxyl ion. All, except halloysite, are normally anhydrous and do not expand (as do the smectites) upon exposure to water and most organic molecules. As a result, they generally have a rather small surface area, on the order of 10 nr... 

The amount of substitution in the tetrahedral and octahedral sheets and the ratio of octahedral to tetrahedral sheets are the primary differentiating characteristics between the many clay minerals (Fig. 3.6). For example, clays that have one tetrahedral sheet and one octahedral sheet are known as 1 1 clay minerals (e.g., kaolin group) (Fig. 3.7) clays that have two tetrahedral sheets and one octahedral sheet are known as 2 1 clay minerals (e.g., smectite group) (Fig. 3.8) or mica and vermiculite (Fig. 3.9), while clays that have two tetrahedral sheets and two octahedral sheets are known as 2 2 clay minerals (e.g., chlorite) (Fig. 3.10). These sheet arrangements give rise to various mineral surface identities such as magnitude (specific surface), functional groups, and interactions with solution species. 

XPS can be used to quantify HPAM adsorption onto minerals at various polymer bulk concentrations. It is seen here that kaolinite has twice the affinity for HPAM than feldspar at pH 9.0 and 50 ppm. Little or no adsorption was monitored on the surface of quartz or mica. Imaging XPS to monitor selective adsorption of mineral mixes proved difficult. Flocculating a mineral mixture of kaolinite, mica and quartz caused the kaolin floes to encapsulate the other minerals. This created a layer of kaolin on the quartz and mica prohibiting polymer mapping on their surfaces. It is shown that the effectiveness of the kaolin recovery is more strongly affected by encapsulation of other minerals during flocculation rather than the selective adsorption process. 

---