Patent GB-932675-A (GB)
Title: Improvements in or relating to the production of phosphorus-containing extractants for uranium valves
IPC: C07F9/09
Filed: 1961-03-30
Abstract: Uranium values are recovered from an acidic aqueous solution containing said values and which may also contain a high concentration of phosphate ions by contacting said solution, preferably at room temperature, with an organic diluent and a polydialkylphosphoric acid which is the reaction product of phosphorus pentoxide and a substantially pure dialkyl acid of phosphorus having the formula (R1) (R2) P(O) OH wherein R1 and R2 are selected from alkyl and alkoxy radicals and contain a total of at least 10 carbon atoms (see Group IV(b)), whereby uranium values are transferred to the organic liquid, separating the resulting uranium-loaded organic liquid from the remaining uraniumdepleted aqueous solution, and recovering uranium values from the separated organic liquid.  In a preferred form a neutral organophosphorus compound of the formula (R3)(R4)P(O)R5, wherein R3, R4 and R5 are selected from alkyl and alkoxy radicals, is included in the organic liquid in addition to the polydialkylphosphoric acid.  The organic diluent is suitably an aliphatic or aromatic hydrocarbon, especially kerosene.  After the extraction step the uranium may be recovered from the loaded extractant by contacting the latter with an aqueous phase containing a stripping agent, preferably an alkaline stripping agent, e.g. a carbonate or hydroxide such as sodium or ammonium carbonate or hydroxide.  When the carbonate is used the uranium enters the aqueous stripping solution as the uranyl tricarbonate ion and when the hydroxide is used as stripping agent the uranium precipitates as the diuranate. The dialkyl phosphorus acid used to form the polydialkyl phosphoric may suitably be di(n-octyl)-, di(3,5,5-triamethylhexyl)- or di(2-ethylhexyl) phosphoric or phosinic acid, bis(diisobutylmethyl) phsophoric acid, butyl hexyl phosphonic acid or 2-ethylhexyl octylphosphonic acid.  Suitable neutral organophosphorus compounds which may be used in conjunction with the poly dialkyl phosphoric acid are tributyl-, tri(2-ethylhexyl)-, trioctyl-, and tridecylphosphates, dibutyl butyl phosphonate, butyl dibutyl phosphinate, tributyl phosphine oxide and tri(n-octyl) phosphine oxide.ALSO:A polydialkyl phosphoric acid suitable for use as an organic extractant for uranium values from an acidic aqueous solution containing said values (see Group III) is obtained by contacting phosphorus pentoxide with a substantially pure dialkyl acid of phosphorus having the formula (R1)(R2)P(O)OH wherein R1 and R2 are selected from alkyl and alkoxy radicals containing a total of at least 10 carbon atoms.  The ratio of phosphorus atoms to alkyl groups in the product may vary from 2 : 3 to 3 : 2 and the substantially pure dialkyl acid of phosphorus is defined as a dialkylphosphoric acid, dialkyl phosphinic acid or alkyl alkylphosphonic acid having at least ten carbon atoms and substantially free from monoalkyl acids of phosphorus, non-acidic alkyl phosphates, pyro- and polyalkylphosphorus acids, unreacted alcohol and neutral compounds, the total amount of such impurities being less than two per cent.  Suitable acids are di(n-octyl)-, di(3,5,5-trimethylhexyl), and di(2-ethylhexyl)- phosphoric and phosphinic acids, bis(diisobutylmethyl) phosphoric acid, butyl hexylphosphonic acid and 2-ethylhexyl octylphosphonic acid.  The polydialkyl phosphoric acid may suitably be obtained by agitating an excess of solid phosphorus pentoxide with the dialkyl acid of phosphorus at room temperature or by reacting the dialkyl phosphorus acid in a concentrated form or in an organic liquid diluent with phosphorus pentoxide.  Suitable diluents are aliphatic and aromatic hydrocarbons, especially kerosene, and it is preferred to react 1 mol of phosphorus pentoxide with 0.1 mol of a dialkyl acid of phosphorus in one litre of diluent.  The substantially pure dialkyl phosphoric acid may be obtained by reacting the appropriate alkyl alcohol with phosphorus oxychloride or phosphorus pentoxide, hydrolysing the poly- and pyrophosphoric acids and neutral compounds to di- and mono-alkylphosphoric acids by heating under reflux with an inorganic acid, e.g. 2M hydrochloric acid, separating the dialkylphosphoric acid from the monoalkylphosphoric acid by partitioning with ethylene glycol in which the monoalkyl phosphoric acid is highly soluble, removing the alcohol and other non-acid components (e.g. trialkyl phosphates) by partitioning them away from an aqueous solution of sodium dialkylphosphate with an inert hydrocarbon such as petroleum ether and then acidifying with a mineral acid, e.g. hydrochloric acid, to recover the substantially pure dialkyl phosphoric acid.