GB621741A - Improvements in or relating to apparatus for recovering water soluble metallic saltsin waste plant effluents or spent process liquors - Google Patents

Abstract

In a recovery apparatus for treating waste plant effluents containing metal salts and solid material, the effluent is treated with caustic solution to precipitate metal hydroxide, the liquid is aerated to cause at least the solid material to rise to the surface, and is then drawn by a vacuum into a chamber wherein the solid material and the hydroxides are separated from the liquid, the separated material being thereupon treated with acid to dissolve the hydroxides. As applied to the treatment of a synthetic rubber-coagulant effluent solution containing aluminium sulphate and suspended particles of rubber (Fig. 3), 50 per cent caustic soda solution and the effluent are admixed in sump 11, aeration being effected by agitator 14, and by the introduction of air through a porous carborundum plate 36. The alkali supply valve 33 is actuated by a <PICT:0621741/III/1> pH control unit 34. The liquid is drawn into vessel 12 by a vacuum pump 40 via a wide flared pipe 27, the rubber fines 17 collecting at the surface of the liquid, and the alumina particles in a layer just below. The former are swept by a rotating skimmer 45 into funnel 16 which is provided with a ramp (not shown) just below the liquid surface, the outside metal strips 47 of the skimmer being hinged to swing backwards and upwards as they traverse the ramp. The fines are washed down the funnel by a water spray 38, and together with the aluminium hydroxide escaping via duct 55, pass to reaction chamber 22 fitted with a stirrer 24 and supplied with concentrated sulphuric acid under control of pH unit 26. Sump 23 receives the overflow, the concentrated aluminium sulphate solution being pumped out and added to another portion of the effluent solution to yield the proper aluminium sulphate concentration required for re-use in coagulation. The purified effluent escapes under weir 61 to sump 64. In another apparatus, the porous plate 36 is absent, whereby in consequence of the lower degree of aeration the aluminium hydroxide particles sink to the bottom of vessel 12, and are with drawn separately to tank 22, the rubber fines being passed directly to sump 13. They are removed periodically. Reference is also made to the collection of the rubber fines in sump 64.