Dewatering and Washing

The washing process is included in this section, as the extent of washing feasible will depend upon the amount of dewatering possible afterwards. 

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Some attempts have been made to reslurry the filter cake without having to open the filter press. However, a number of problems appear, eg, bending of the plates due to uneven cake deposition or cavitation, uneven dewatering and washing within the frames, and plugging of the inlet ports. 

Objective Determine the filter size and vacuum capacity required to dewater and wash 15 mtph of dry solids while producing a final washed cake with a moisture content of 25 wt % and containing 0.10 wt % TDS based on dry cake solids. 

To recover barite from drilling muds, a direct flotation without prior dewatering and washing of the drilling muds has been described [809]. An alkyl-phosphate is used as a collecting and frothing reagent. 

Practical operation of a sludge separator, of course, requires that the solids be heavier than the liquid and not be resuspended by the action of the conveyor. A modification known as an axial-flow conveyor centrifuge (described later) is more effective in separating fine light solids than the full-scroll centrifuge shown in Fig. 30.44. Even so, the liquid effluent from these machines is usually not completely free from solids and may require subsequent clarification. Within these restrictions sludge separators solve a wide variety of problems. They separate fine particles from liquids, dewater and wash free-draining crystals, and are often used as classifiers. 

Rushton A., 1981. Centrifugal filtration, dewatering and washing, Filtr. Sep., 18,410-415. 

Coarse materials are dewatered and washed on fine mesh screens and stockpiled for further processing. Metallics may simply be melted in a pot or standard lead kettle or can be melted in a short rotary furnace, with some collection of a htharge slag to separate antimony and arsenic and produce a soft lead. Separator plastics are usually disposed of in landfill but polypropylene is thoroughly washed, and extruded as pellets for sale to battery manufacturers for new case production. 

This variety of end-use separation applications can be grouped into five broad types clarification, classification, thickening, dewatering and washing according to the main purpose of the separation process. It is. of course, very probable that more than one of these may be involved in a particular application. 

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