Thickening and Flotation

Water Clarification. Process water that aeeds to be clarified comes from several differeat sources ia the recycling mill rejects from screeas and mechanical cleaners rejects from washers, thickeners, and flotation cells water that drains from the pulp as it is converted iato paper oa the paper machine (white water) and water from felt washers. These waters contain different dissolved chemicals and suspended soflds and are usually processed separately. 

Water from screens, cleaners, washers, thickeners, and flotation cells contain relatively high levels of ink. These waters also contain valuable chemicals, ie, sodium hydroxide and surfactants. Recycle of this water can save up to 10% ia chemical costs. 

As with thickening, air flotation is enhanced by the addition of polymers. Flotation has been successfully used with wholly inorganic metal hydroxide sludges. Polymers and surfactants are used as additives. Engineering details on air flotation equipment has been developed by and is available from various equipment manufacturing companies. Liquid removed during thickening and flotation is usually returned to the head end of the plant. 

Two methods are used to thicken slndges gravity thickening and flotation thickening. In gravitational thickening, solids are thickened as a result of solids piling... 

Cleaning flotation Thickening and regrinding Counter-current flotation Copper leaching Thickening and filtering... 

The recovery of valuable minerals and metals requires several stages of sequential processing operations. The mined ore must be crushed and ground to fine sizes prior to treatment by such bene-ficiation processes as heavy-medium separation, tabling, magnetic separation, electrostatic separation, flotation, selective flocculation, etc. Since most of these processes are carried out in aqueous media, solid-liquid separations by such operations as thickening and filtration are an integral part of the benefici-... 

The equipment used for dewatering includes filters and screening devices of various types, centrifuges, hydrocyclones, extrusion and expression presses, water extractors, and thickening, clarifying, and flotation hardware. The processing methods encompass a broad range of water-removal techniques. They... 

Sludge thickening and fiber separation by dissolved air flotation cells (2,3) are typical examples of nonfoaming flotation thickening in which the target sludges or fibers are originally in insoluble forms and ready to be floated. 

M. Krofta and L. K. Wang, Application of dissolved air flotation to the Lenox Massachusetts Water Supply sludge thickening by flotation or lagoon, J. N. Engl. Water Works Assc. 265-284 (1985). 

On cement slurry, ores and flotation concentrates the capacity will range from 200 to 1,300 lb. per 24 hr. per square foot of filter surface. Many plants will run under the smaller of these two figures through overestimation of the size of filter required, irregularities of operating, etc. Where the lower figure is reached with steady operation and giving the filter all the material it will handle and thickened as much as possible the limits of vacuum filtration for the substances mentioned have been... 

Liquid waste streams with a high-suspended solids content can be cleaned up by solids removal in clarifiers, thickeners, and liquid cyclones and by accelerated settling by inclined Chevron settlers or the like [73]. For waste streams with very finely divided solids in suspension (i.e., less than about 100 pm) dissolved air flotation techniques have been shown to be more efficient than methods employing sedimentation. Final dewatering of the sludges obtained may be carried out on a continuous filter or a centrifuge. The clarified water product can be accepted for more potential options of reuse or final disposal options than untreated water, and the separated solids may be burned or discarded to landfill, as appropriate [74]. 

In general, flocculants are used in solid-liquid separation processes such as thickening and filtration. Inorganic salts are also used sometimes to aggregate fine particles. Flocculation technique has been developed further for special applications of selective flocculation, selective dispersion and agglomeration flotation. 

At Mount Weld, Australia, physical concentration of the REE minerals is performed as follows the run of mine material is subjected to crushing, grinding and flotation to produce a concentrate with a grade of 40 % REO. The obtained concentrate is sent to a thickener, where the resulting pulp is dewatered by applying... 

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