Removal of oxides from alkali metal melts by reductive titration to electrical resistance-change end points
AssigneeThe Dow Chemical Company
InventorFloris Y. Tsang
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Abstract
Alkali metal oxides dissolved in alkali metal melts are reduced with soluble metals which are converted to insoluble oxides. The end points of the reduction is detected as an increase in electrical resistance across an alkali metal ion-conductive membrane interposed between the oxide-containing melt and a material capable of accepting the alkali metal ions from the membrane when a difference in electrical potential, of the appropriate polarity, is established across it. The resistance increase results from blocking of the membrane face by ions of the excess reductant metal, to which the membrane is essentially non-conductive.
Claims11
The method of reducing the content of an alkali metal oxide, M.sub.2 O, dissolved in an alkali metal melt, comprising
- (1) adding to and dissolving in said melt an alkaline earth or lanthanoid series metal, M', thereby reducing said oxide and forming an oxide, M'O, which is essentially insoluble in said melt, according to the equation
- M.sub.2 O+M'.fwdarw.M'O.dwnarw.+2M,
- (2) disposing said melt in contact with a first face of a membrane which
- (a) is conductive to M.sup.+ ions but is essentially non-conductive to cations of the metal M', and
- (b) has an opposed face in contact with an electrically conductive counter-material which, when negatively polarized with respect to said melt, will accept M.sup.+ ions from the membrane,
- (3) imposing a potential difference, across the membrane, of such magnitude and polarity that M.sup.+ ions pass through the membrane from the melt to the counter-material,
- (4) monitoring the resistance to flow of cations from the melt to the counter-material through said membrane, and
- (5) continuing to add said metal M' to the melt until an abrupt, non-transient increase in said resistance occurs.
Dependencies are inferred from the claim text.