Salt, effect, flocculation

Advantage has been taken of this effect in fluidized bed flocculators in practice, which use micro-sand on which flocculation takes place. This development, which was pioneered in Hungary, now appears as the Cyclo-floc process. The sand is coated (activated) with an alginate flocculant, and incoming suspensions of flocculent aluminium or ferric salts are flocculated by the fluidized bed and retained on the sand. A continuous discharge of some floc-coated sand, recycles it through an external washing process which separates the floe and the sand. The cleaned sand is continuously fed into the tank inflow to sustain a steady-state process. 

The principal calcium salt used as a flocculant is calcium hydroxide [1305-62-0] or lime. It has been used in water treatment for centuries (see Calcium compounds). Newer products are more effective, and its use in water and effluent treatment is declining (10). It is still used as a pH modifier and to precipitate metals as insoluble hydroxides. Lime is also sometimes used in combination with polymeric flocculants. 

Various inorganic chemicals remove soluble contaminants encountered during drilling. Salt, NaCl, is a common contaminant that can be removed only by dHution. The adverse effects of salt, primarily clay flocculation, can be overcome by a deflocculant such as a Hgnosulfonate or sulfomethylated... 

Technology Description To achieve precipitation, acid or base is added to a solution to adjust the pH to a point where the constituents to be removed have their lowest solubility. Chemical precipitation facilitates the removal of dissolved metals from aqueous wastes. Metals may be precipitated from solutions as hydroxides, sulfides, carbonates, or other soluble salts. A comparison of precipitation reagents is presented in Table 7. Solid separation is effected by standard flocculation/ coagulation techniques. 

Figure 6 Effect of destabilisation by salt addition or pH control on flocculation with a non-ionic polymer...

Mineral segregation in industry relies heavily on the selective adsorption of macromolecules onto the surfaces of those minerals that have particular industrial applications. This selectivity is governed mainly by the surface chemistry of the mineral and the type of polymer used as a flocculant. " Effectiveness of flocculation depends upon the charge, concentration and molecular weight of the polymer, and also the pH and salt concentration of the clay suspension. The bonding between the anionic flocculant polyacrylamide (PAM) and clay mineral surfaces has been effectively reviewed recently by Hocking et al and the reader is referred to this should they require an in-depth literature review. For more information on general colloidal chemistry of clay suspensions the reader is referred to the review of Luckham and Rossi." ... 

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