Flotation Process for Calcium Carbonate Recovery from Water Treatment Sludges

Flotation Process for Calcium Carbonate Recovery from Water Treatment Sludges 

The calcium carbonate recovered can be calcined to give lime for recycle to the treatment process as well as by-product lime for marketing. In addition, removal of the calcium carbonate, the major ingredient in sludge from water softening treatment plants, reduces the disposal problem to a fraction of that previously required. 

In order for the flotation to be effective, the sludge must be recycled to increase the particle size of the calcium carbonate. This recycle also gives heavier flow in the settling basins, which results in faster settling rates. For the flotation to be effective, the magnesium hydroxide in the sludge must also be completely dissolved by the carbon dioxide and washed out. In the froth flotation process (used to separate the calcium carbonate from the clay, silt, or other water contaminants), an aqueous slurry of the sludge is first conditioned (mixed) with soda ash and sodium silicate to disperse the clay and 

Many theories have been advanced concerning the mechanisms involved in surfacing the mineral particles so as to create a hydrophobic hydrocarbon film on the mineral surface, and many investigations have been carried out to define these mechanisms. When firoth flotation is used in an aqueous medium that carries the solids to be separated (together with dispersed air bubbles and possibly an organic liquid) a three- or possibly a four-phase system must be considered. In most froth flotation processes, the solid particles are initially completely water-wetted, and the solid-liquid interface must be replaced by 

The organic portion, R, in the xanthate is generally obtained from alcohols ranging from ethyl to amyl (C2H5OH to C Hj OH). 

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