United Kingdom Atomic Energy Authority

Michael R Hill

Andrew Derek Turner

Mark D Neville

Christopher Peter Jones

Edward S Lane

Patrick Timothy Moseley

An electrochemical cell (50) for deionizsation utilizes electrochemical ion-exchange to remove ions from a feed solution. Under the influence of an electric field, ions are adsorbed into, are scored within and pass through a permeable layer (54, 64) of particulate ion-absorbing material and binder, the sheet being several millimeters thick. Water from the feed solution also permeates through the layer (54, 64), so a concentrated solution of the ions emerges from the rear (58) of the layer. The cell does not require separate sources of feed and eluant solutions and can be operated substantially continuously. In a modified cell (70) the flow path for the feed solution passes through a highly porous ion exchanger structure (77), which may be located between two such microporous layers (54, 64). Absorption in such a cell may be effective in the absence of an electric field, elution requiring the periodic application of the electric field.

Electrochemical deionization

Effluent streams from photographic processes contain both silver and thiosulphate ions, and because of the formation of complex anions it is difficult to remove the silver. The silver may be removed using a cell (12) with a cathode (24) exposed to the effluent liquid, and an anode (25) separated from the liquid by a barrier (22) permeable at least to anions. Some silver sulphide is formed electrochemically at the cathode (24); at the anode (25) water is electrolysed and becomes acidic, so the complex anions migrating through the barrier (22) generate silver sulphide chemically. The resulting silver sulphide precipitate is separated from the liquid by a filter (14).

Silver removal

A nickel oxide electrode is made by impregnating a porous nickel substrate with a dispersion of a nickel compound, converting the compound in situ to nickel hydroxide, and removing reaction products. In order to overcome corrosion problems, facilitate removal of by-products and improve electrode performance, the dispersion is provided in a non-aqueous medium (e.g. as a methanolic solution of NiCl.sub.2.6H.sub.2 O) such that the in situ conversion gives rise to the nickel hydroxide in the form of a gel and to easily removable (e.g. volatile) reaction products. Such a conversion may be carried out by contacting the methanolic solution with an epoxy compound such as propylene oxide.

Electrode preparation

The positive electrode for a lead acid electric storage cell is made by preparing by a chemical route particulate beta lead dioxide, mixing together the beta lead dioxide with a relatively low proportion of a binder, and applying the mixture to a perforated electrically conductive support structure.

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Michael R Hill