Counter-current decantation

Figure 2 shows a continuous azeotropic column using a fixed amount of entrainer which remains in the unit. Since reflux is largely supplied by feed of the emulsion near the top of the column, the entrainer from the decanter passes to a reboiler and is fed back to the tower as vapors. This gives a more nearly counter-current action of the azeotropic distilling operation, and a lesser heat input required into the viscous oil at the base of the column, usually with more or less silt in suspension while... 

Continuous Counter-current Decantation.—This system is being quite generally used in the chemical world to replace the older intermittent agitation and decantation washing systems as well as more modern filter installations. It has as its basis the application of the Dorr thickener to remove suspended solids contin-... 

In Fig. 7 is shown a typical continuous counter-current decantation installation together with the continuous-agitation system as it would be applied to the manufacture of phosphoric acid from phosphate rock and other processes which is a representative leaching problem. 

The aqueous beryllium sulfate is separated from the solids by counter-current decantation thickener operations. A beryllium concentrate is produced by a counter-current solvent extraction process (Maddox and Foos 1966). This concentrate is stripped of its beryllium content with aqueous ammonium carbonate. By heating to 70 °C, aluminum and iron are precipitated and then removed by filtration. Precipitation of beryllium basic carbonate occurs when the solution is heated to 95 °C. The carbonate is filtered, deionized water is added, and heating to 165 °C yields a beryllium hydroxide product which is the common input to beryllium-copper alloy, beryllium oxide ceramics, or pure beryllium metal (Table 2.1-2). 

This involves bringing the wet solvent into contact with a solid, usually an electrolyte, which has the power to withdraw some of the water present to form a second phase that can be removed by decantation. The dehydrating substance may be either a solid or a saturated aqueous solution. The latter is more easily adapted to counter-current operations. 

Assuming no preferential sorption of mineral values from the solution on to the spent ore, the extraction efficiency of a counter-current decantation system may be calculated as follows ... 

Fio. 2.6. Counter-current decantation washing at the Port Pirie Uranium Plant (Almond, J.N. Ref. 4). 

The general post-leaching operations are again similar to those used in acid systems. Filtration and sedimentation rates of most minerals tend to be lower in sodium carbonate solutions than they are in dilute sulphuric acid, but the advent of synthetic flocculating agents has now made this difference of less practical importance in the design of processes. Aeroflox 300 and Separan 2610 have both been used in conjunction with counter-current decantation. 

The reaction product is obtained from the furnace in the form of free-flowing almost spherical granules, a few millimetres in size. These are crushed to pass a 100-mesh sieve and each ton is leached with approximately 7 tons of water containing about 1 per cent of hydrochloric acid for 1 -5 to 2 hr, with stirring, at 85°C. The hot extraction liquor is decanted and the residue washed with water, which is re-used for a later leaching operation, so giving an element of counter-current leaching. 

The feed solution is prepared by acid leaching, removal of gross solids by filtration or counter-current decantation, together with a final polishing filtration step, often in a sand-bed clarifier. Using such a feed, a typical cycle of operations for a four-column system with split elution is as follows ... 

The range of supply is that of the KHD/Humboldt Wedag company, acquired by Bird Machine Co. There are a dozen basic models, available in several different bowl lengths, with co-current as well as counter-current How, three-phase and screen-bowl versions. Also includes Censor" Twin beach machine, for separation of solids by density Decanter sales... 

An aqueous alkaline solution of potassium humulate is obtained by counter-current extraction of a trichloroethylene extract of fresh hops in a column packed with aqueous dipotassium carbonate (0.055 M). Upon saturation with potassium chloride, potassium humulate is precipitated. The supernatant is decanted and the solid material is isolated. 

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