Cationic clay flocculation

Sang Y, Xiao H (2008) Clay flocculation improved by cationic poly(vinyl alcohol)/anionic polymer dual-component system. J Colloid Interface Sci 326 420... 

An example of heteroflocculation between large and small particles is that between day and cationic latex. Kaolin clay fully coated by polystyrene latex (U2 = 65 nm) is shown in Figure 1.11. At lower latex dosages, less than required for full coverage, the latex acts as a cationic polyelectrolyte, flocculating the clay. This can be seen in Figure 1.12, where the stability ratio W= 1/a, is shown as a function of latex addition, together with the electrophoretic mobility of the clay. 

The hot-water separation process involves extremely compHcated surface chemistry with interfaces among various combinations of soUds (including both silica sand and alurninosilicate clays), water, bitumen, and air. The control of pH is critical. The preferred range is 8.0—8.5, achievable by use of any of the monovalent bases. Polyvalent cations must be excluded because they tend to flocculate clays and thus raise viscosity of the middlings in the separation cell. 

Flocculants cause colloidal clay particles to coagulate thus promoting separation from the drilling fluid which has been circulated down the wellbore and returned to the surface. The treated fluid may then be pumped back down the well bore. Sodium chloride, hydrated lime, gypsum, sodium tetraphosphate, polyacrylamide, poly(acrylamide-co-acrylic acid), cationic polyacrylamides, and poly(ethylene oxide) have been used commercially. 

The method described here provides a convenient means of determining the specific filtration resistance of fairly dilute suspensions. Results for clay suspensions flocculated by cationic polymers show that the specific resistance gives a sensitive indication of flocculation and is a useful guide in the selection of optimum flocculant concentrations. In a series of trials not reported here, it has been shown that the specific resistance results are very well matched by re-filtration rate data, as expected. The results also agree well with other, unrelated techniques. For more concentrated suspensions, some discrepancies have been found between permeability methods and other measures of flocculation (4). 

After delivery to the ocean, clay minerals react with seawater. The processes that alter the chemical composition of the terrigenous clay minerals during the first few months of exposure are termed halmyrolysis. These include (1) cation exchange, (2) fixation of ions into inaccessible sites, and (3) some isomorphic substitutions. Another important transfiarmation is flocculation of very small (colloidal-size) clay particles into larger ones. 

Montmorillonites (smectite clays) have structures resembling that of pyrophyllite but the structure is not electrically neutral. Exchangeable cations are located in interlamellar regions of the clay and, furthermore, the clay can be flocculated such that the plate-like crystals compact with parallel c-axes to give coherent layers. The smectites are then attractive materials with which to modify electrodes. 

The U.S. Soil Salinity Laboratory Staff (1954) reported that SAR values of 10-15 (mmol L )1/2 usually correspond to ESP values in the range of 10-15 at which values clays will undergo dispersion. This relationship may vary among colloids with different mineralogy (Oster et al., 1980) and/or mixtures of colloids with different mineralogy (Arora and Coleman, 1979). Consequently, the force by which given types of colloidal particles attract or repulse each other in a Na-Ca or Na-Mg solution is a function of the total concentration of the salt, the type of divalent cation (Ca or Mg), and SAR. Therefore, pH, salt concentration, type of divalent cation, and SAR are expected to play important roles on soil colloid flocculation. 

From the discussion above, it can be seen how the atomic structure of phyllosilicate clays plays a key role in determining the final state of clay particles in aqueous media. The presence of structural charges, neutralizing cations, and the capacity of forming hydrogen bonds between different layers produces a system that can be completely delaminated, completely flocculated, or in an intermediate state having floes mixed with isolated layers. Whether the more stable situation corresponds to isolated layers, floes, or a mixture depends on the type of clay, its concentration, pH, concentration and type of supporting electrolyte, and so on. 

Deflocculated clay particles may re-flocculate where sufficient divalent cations are present (llluvation)... 

Goldberg, S. and Glaubig, R.A., Effect of saturating cation, pH. and aluminum and ii on oxide on the flocculation of kaolinite and montmorillonite. Clays Clay Miner., 35. 220, 1987. 

Flocculation and Restabilisation of Clays Using Cationic Surfactants... 

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