GB1434594A - Method and apparatus for the treatment of effluents containing in particular heavy metals - Google Patents

Abstract

1434594 Removal of metal ions from effluents SOC EPAP 27 March 1973 [31 March 1972] 14660/73 Heading C1C [Also in Division C7] Metal ions are removed from effluents by forming a treatment bath comprising a mixture of a metal in particulate form which is more electropositive than the metal to be removed, sand particles and the effluent so that the metal to be removed precipitates on the more electropositive metal particles, and bubbling gas through the bath to produce an abrasive action between the sand and the more electropositive metal particles thereby to detach the metal to be removed therefrom so that it can readily be separated from the effluent. In particular the processing may be applied to the waste waters of electroplating works and the recovery of copper from effluents containing copper sulphate, but it may also be applied to the recovery of copper from other effluents and to the recovery of other metals such as cadmium, palladium, lead and tin. If the metal bed is of iron particles and air under pressure is used for agitation the air also has the effect of causing ferrous ions to pass to the ferric state. This oxidation may also be achieved with javelle water or monopersulphuric acid. If the metal bed is of aluminium or zinc particles the treatment bath may also include an acid or basic agent to activate the metal by production of nascent hydrogen thereon. Aluminium may also be activated by traces of salts of mercury. The metal bed may also be activated by passing a continuous electric current through the particles. In a suitable apparatus for effecting the process the gas is blown upwardly through a perforated base-plate into the bed and when this occurs the mixture flows from the reaction zone over a partition into a decanting zone from which at least some of the decanted mixture returns through openings in the lower part of the partition into the reaction zone. Particles of iron drawn out with the effluent may be removed by an electromagnet. The hydroxide of the more electropositive metal may be precipitated in a second decanting basin. The treated effluent may be completely or partially recycled. Reference is also made to the use of the method with chromate- and cyanide-containing effluents, and effluents containing nitrates may be detoxified, the nitrates being converted to amines. Six figures illustrate various forms of suitable apparatus and complete treatment cycle and a graph showing degrees of precipitation of various metals in dilute aqueous environments according to pH is also provided.