Patent GB-862204-A (GB)
Title: Process for recovering metal valves utilising organic orthophosphate extractants
IPC: F02B3/06
Filed: 1957-06-17
Abstract: A metal value is extracted from a material containing such value by contacting said material with a liquid phase containing either a mono-alkyl orthophosphoric acid ester of the formula ROP(O)(OH)2 or a mixture of said ester with a dialkyl orthophosphoric acid ester of the formula (RO)2P((O)OH, R in each case being a C9-C17 alkyl group and the alkyl radical-phosphorus linking oxygen bond being attached to a non-terminal carbon atom of the alkyl group R.  The metal value may be extracted from acidic or neutral solutions or leached from solids or from aqueous or nonaqueous slurries thereof and the ester or ester mixture used as extractant may be used in admixture with an organic solvent-diluent capable of dissolving the phosphate esters and the extracted metal value.  The phosphate esters are suitably those derived from 2,6-dimethyl heptanol-4; 2,6,8-trimethyl nonanol-4; 2-methyl-7-ethyl decanol-4; 2-methyl-7-ethyl undecanol - 4; and 3,9 - diethyl - tridecanol - 6.  Suitable solvent-diluents are aliphatic, aromatic, and halogenated hydrocarbons, ethers, and hydrocarbons derived from petroleum, e.g. diesel oil, aromatic oils, distillates, gasoline and petroleum ethers.  Preferred solvents are kerosene, Stoddard solvents and isopropyl ether.  The process is particularly suitable for leaching or extracting trivalent metal ions, e.g. Fe and Ti, and polyvalent ions such as those of the lanthanide and actinide series, especially Th+4 and U+4.  Vanadium ions of the +4 and +5 oxidation state and dipositive ions such as UO2++ are also extracted with high efficiency.  By adjusting the oxidation state and thus the relative degree of ionization of the ions in the system extraction of a desired material may be favoured and extraction of an impurity repressed or vice versa.  Thus an acidic solution containing uranium and iron may be treated with a reducing agent, e.g. Fe, Al, or Zn, sodium thiosulphate or titanium trichloride, to place the uranium in the more easily extracted uranous state and the iron in the less extractable ferrous state. Suitable materials containing the metal values are leach solutions obtained from various ores, e.g. primary or secondary uranium ores, containing in addition to uranium, thorium, vanadium and/or lanthanide rare earths.  The process is suitable for the recovery of uranium and other metal values from superphosphate produced by the reaction of sulphuric acid on uraniferous phosphate rock.  The extraction conditions may be regulated so as to effect selective extraction of one metal value and then more rigorous extraction conditions may be employed using a similar extractant phase to extract the more difficulty extracted metal values.  The extraction may be a liquid-liquid extraction or may be a direct leaching of solids containing the metal values using a mixture of the extractant and a solvent-diluent or the solid which is extracted may be in the form of an aqueous slurry which may contain a mineral acid, e.g. sulphuric, nitric, hydrochloric or phosphoric acid and an oxidizing or reducing agent.  Alternatively, the solid may be extracted under non-aqueous slurry conditions by contacting it with a low moisture content mineral acid, e.g. sulphuric acid of over 95% concentration and an extractant phase comprising a solvent-diluent and the phosphate ester extractant.  The metal value may be recovered from the extract by precipitation, evaporation and stripping or by re-extraction with an aqueous phase.  Purification of the lanthanides and actinides from the extract can be effected by the addition of aqueous HF when the metal value is in an oxidation state corresponding to an insoluble fluoride.  Other substances which may be used in the recovery of the metal values from the extract phase are ammonia, NaOH, methyl or ethyl alcohol, and the precipitate formed may be calcined to yield a phosphatic product or additional purification may be carried out, e.g. by re-extraction using aqueous mineral acids, e.g. HF, HCl, H2SO4 or HNO3 to recover various metal values.  Alternatively, sodium carbonate solutions of at least 0.3 molar may be used.  Several examples are given for the recovery of uranium and other metal values from various ores and for comparative purposes the use of other orthophosphate ester extractants derived from alcohols containing less than 9 carbon atoms, e.g. n-octyl, capryl and 2-ethyl hexyl orthophosphates is also referred to.  The orthophosphate esters containing from 9 to 17 carbon atoms in the alkyl group may be obtained by slurrying phosphorus pentoxide with an organic diluent, e.g. kerosene, benzene or isopropyl ether and then reacting the slurried P2O5 with the appropriate alcohol under critically controlled conditions to form an intermediate alkyl pyrophosphate ester which while still in admixture with the diluent is then hydrolysed with dilute acid, e.g. 1N-hydrochloric acid to form the monoester (complete hydrolysis) or a mixture of the mono- and di-alkyl esters (incomplete hydrolysis).ALSO:A metal value is extracted from a material by contacting with a liquid mono-alkyl orthophosphoric acid ester of the formula ROP(O)(OH)2 or a mixture of said ester with a dialkyl orthophosphoric acid ester of the formula (RO)2P(O)OH, R in each case being a C9-C17 alky group and the alkyl radical-phosphorus linking oxygen bond being attached to a non-terminal carbon atom of the alkyl group R.  The metal value may be extracted from acidic or neutral solutions or leached from solids or from aqueous or non-aqueous slurries thereof.  The extractant may be used in admixture with an organic solvent-diluent capable of dissolving the phosphate esters and the extracted metal value.  The phosphate esters are suitably those derived from 2,6 - dimethyl heptanol - 4; 2,6,8 - tri - methyl nonanol - 4; 2 - methyl - 7 - ethyl decanol - 4; 2 - methyl - 7 - ethyl undecanol-4; and 3,9 - diethyl - tridecanol - 6.  Suitable solvent-diluents are aliphatic, aromatic and halogenated hydrocarbons, ethers, and hydrocarbons derived from petroleum, e.g. diesel oil, aromatic oils, distillates, gasoline and petroleum ethers.  Preferred solvents are kerosene, Stoddards solvents, and isopropyl ether.  The process is particularly suitable for leaching or extracting trivalent metal ions, e.g. Fe + + + and Ti + + + and polyvalent ions such as those of the lanthanide and actinide series especially Th +4 and U +4.  Vanadium ions of the +4 and +5 oxidation state and dipositive ions such as UO2 + + are extracted with high efficiency, but aluminium is only extracted to a limited degree. By adjusting the oxidation state and thus the relative degree of ionization of the ions in the system, extraction of a desired material may be favoured and extraction of an impurity repressed or vice versa.  Thus an acidic solution containing uranium and iron may be treated with a reducing agent, e.g. Fe, Al, or Zn, sodium thiosulphate or titanium trichloride, to place the uranium in the more easily extracted uranous state and the iron in the less extractable ferrous state.  Suitable materials containing the metal values are leach solutions obtained from various ores, e.g. primary or secondary uranium ores, containing in addition to uranium, thorium, vanadium and/or lanthanide rare earths.  The process is suitable for the recovery of uranium and other metal values from superphosphate produced by the reaction of sulphuric acid on uraniferous phosphate rock.  The extraction conditions may be regulated so as to effect selective extraction of one metal value and then more rigorous extraction conditions may be employed using a similar extractant phase to extract the more difficultly extracted metal values.  The extraction may be a liquid-liquid extraction or may be a direct leaching of solids containing the metal values using a mixture of the extractant and a solvent-diluent or the solid which is to be extracted may be in the form of an aqueous slurry which may contain a mineral acid, e.g. sulphuric, nitric, hydrochloric or phosphoric acid and an oxidizing or reducing agent.  Alternatively, the solid may be extracted under non-aqueous slurry conditions by contacting it with a low moisture content mineral acid, e.g. sulphuric acid of over 95% concentration and an extractant phase comprising a solvent-diluent and the phosphate ester extractant.  The metal value may be recovered from the extract by precipitation, evaporation and stripping or by re-extraction with an aqueous phase and solid products may be calcined.  Purification of the lanthanides and actinides from the extract can be effected by the addition of aqueous HF when the metal value is in an oxidation state corresponding to an insoluble fluoride thereof.  Other substances which may be used in the recovery of the metal values from the extract phase are ammonia, NaOH, methyl or ethyl alcohol, and the precipitate formed may be calcined to yield a phosphatic product or additional purification may be carried out, e.g. by re-extraction using aqueous mineral acids, e.g. HF, HCl, H2SO4 or HNO3 to recover various metal values. Alternatively, sodium carbonate solutions of at least 0.3 molar may be used.  Several examples are given for the recovery of uranium, vanadium and other metal values from various ores and for comparative purposes the use of other orthophosphate ester extractants derived from alcohols containing less than 9 carbon atoms, e.g. n-octyl-, capryl-, and 2-ethyl hexyl-orthophosphates is also referred to.