Solid/liquid separation cake washing

Staff profile page - the Engineering Faculty at Loughborough. .. Broad Interests and Expertise. Compressible cake filtration Selection, scale-up and process simulation of solid/liquid separation equipment Washing and. .. http //WWW. Iboro. ac. uk/departments/eng/research/staff/html/tarleton. html [More Results From www.lboro.ac.uk]... 

Wakeman, R.J., 1990b. Filter cake washing. In Solid-liquid separation, 3rd edition. Ed. L. Svarovsky. Oxford Butterworth-Heinemann. 

Crystal morphology (i.e., both form and shape) affects crystal appearance solid-liquid separations such as filtration and centrifugation product-handling characteristics such as dust formation, agglomeration, breakage, and washing and product properties such as bulk density, dissolution kinetics, catalytic activity, dispersability, and caking. 

Solid-liquid separation systems generally consist of four stages including pretreatment, solid concentration in thickeners, solid separation in filters or centrifuges, and post-treatment by expression and washing operations. There are different types of SLS equipment served for different functions in relation to the four stages. Product specification, characteristics of solid-liquid suspension, solid settling velocity, rate of cake... 

In solution crystallization product purity is controlled to a great extent by the efficiency of solid-liquid separation. Impurities dissolved in the ciystallizer liquid are normally removed by spinning liquor from the crystals and then washing the resulting cake. The residual impurity level is a function of factors listed in the following equation ... 

One of the most commonly used solid-liquid separation methods in crystallization processes is centrifugal filtration, such as continuous pusher and batchwise peeler centrifuges shown schematically in Figure 64.10. A manufacturer of centrifuges used in crystallization processes is KMPT AG [52]. In addition, Nutsche filters, frame pressure filters, and belt filters have also been used. Most of these filters have a possibility of cake washing which is important for the final purity as discussed earlier. 

The term post-treatment refers to processes vdiich are used after the principal solid-liquid separation has been achieved. The final step in the latter operation is usually some type of cake filtration which will leave a cake that may be fully saturated with liquid or partially drained and it is extremely unlikely that the solids are in an acceptable condition for any subsequent operation such as thermal drying. Thus the post treatment processes are washing and deliquoring which are concerned req>ectively with removing the soluble solids from the liquid remaining in the cake and then purging the major proportion of the liquid fi om the cake pores. 

Many solid-liquid separation systems must recover a valuable solid product fi om a su ension which has undesirable constituents such as soluble dissolved solids in its liquid coirponent. Crystallisation and precipitation are obvious exanq>les where a solid phase has to be produced in a pure state firom a contaminant liquor. In such a Nation the cake must be washed with a clean wai fiquor to reduce the contaminants to an acceptable level. 

Wakeman R.J., 1981a. Cake washing, in Solid-Liquid Separation , 2nd Edition, Ed. L. Svarovsky, pp. 408-451, Butterworths, London. 

In a 2-1. three-necked, round-bottomed flask fitted with a mechanical stirrer and two reflux condensers are placed 68 g. (0.68 mole) of succinic anhydride (Org. Syn. 12, 66) and 350 g. (4.5 moles) of dry, thiophene-free benzene (Note i). The stirrer is started and 200 g. (1.5 moles) of powdered, anhydrous aluminum chloride is added all at once. Hydrogen chloride is evolved and the mixture becomes hot (Note 2). It is heated in an oil bath and refluxed, with continued stirring, for half an hour (Note 3). The flask is then surrounded by cold water, and 300 cc. of water is slowly added from a dropping fimnel inserted in the top of one of the condensers. The excess benzene is removed by steam distillation, and the hot solution is at once poured into a 2-1. beaker. After the mixture is cold the liquid is decanted from the precipitated solid and acidified with concentrated hydrochloric acid (about 20 cJs is required) 5 to 15 g. of benzoylpro-pionic acid separates and is filtered off (Note 4). The residual suspension in tl e beaker is. boiled for five hours with 1500 cc. of water containing 360 g. of commercial soda ash the resulting solution is filtered with suction, the filter cake washed with hot water, and the filtrate acidified with concentrated hydrochloric acid (about 300 cc.). The precipitated benzoylpropionic acid is filtered and washed with hot water after dr3dng for a day it weighs 95-100 g. (77-82 per cent of the theoretical amount) and... 

From the flash tanks the slurry flows by gravity to the solids and liquid separation phase, first to the leach thickener. Thickener underflow slurry is pumped to the filter feed tank. The filter cake is washed to remove the acidic and PLS solution in the cake. The filtrate is pumped back to the main process. The further treatment of the leach residue depends of the amount of precious metals in the matte. If the precious metals concentration is high in the matte, filter cake containing insoluble precious metal components (such as iron silicates etc.) may be transported to the PGM cake treatment area. If the precious metals do not play important part, the filter cake is transported to the disposal pond. 

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