Patent GB-824396-A (GB)
Title: Extraction of thorium from aqueous solution
Inventor: RYAN WALTER
IPC: C01F15/00
Filed: 1957-02-08
Abstract: Thorium is extracted from an acidic aqueous thorium-containing solution in which an interfering metal is present by treating the solution with a substantially water-immiscible liquid phase which includes a water-immiscible liquid diluent, e.g. a hydrocarbon or chlorinated hydrocarbon, and an alkyl ester of phosphoric acid having one or two free hydroxyl groups bonded direct to the phosphorus atom to effect preferential extraction of thorium into the water-immiscible phase.  The interfering metal is defined as a metal which tends to precipitate when ammonia solution is added as precipitant reagent for the thorium, specified interfering metals being aluminium and iron, and any iron present must first be reduced to the ferrous state before effecting the extraction process.  After separation of the aqueous phase from the thorium-containing water-immiscible phase the latter can be treated to decompose the thorium complex present e.g. by means of aqueous sulphuric or hydrochloric acid, and the resulting thorium-containing aqueous phase and the non-aqueous phase comprising the regenerated alkyl phosphate are then separated. Thorium is recovered from the thorium-containing aqueous phase, e.g. by adding ammonia to precipitate thorium hydroxide.  The acid alkyl phosphates are preferably those in which the alkyl group is C4 to C15, e.g. di-n-octyl or di-2-ethylhexyl-hydrogen phosphates or 3,5,5-trimethylhexyl dihydrogen phosphate.  The invention is particularly applicable to the treatment of solutions containing thorium sulphate in dilute sulphuric acid, especially the barren liquor resulting as effluent when uranyl sulphate solutions obtained from thorium-containing uranium ores are treated with an anion exchange resin for the recovery of uranium.  Such a barren liquor can be treated to reduce any ferric iron present to the ferrous state by adding scrap iron and, if desired, a little sulphuric acid to decrease the pH, and the pH then readjusted if necessary to a pH higher than 1, e.g. between 1.5 and 2.5, before proceeding with the extraction process.  An Example is given for the recovery of thorium from a sulphuric acid solution (pH 2) containing Fe(ferrous), Al2O3, and ThO2 by a three-stage extraction process using di-(2-ethyl hexyl)-monohydrogen phosphate in kerosene, the volume ratio of non-aqueous phase to aqueous phase being 1 : 8.  The resulting non-aqueous thorium-containing phase is then decomposed with hydrochloric acid of constant boiling-point and the aqueous phase formed is then heated to distil off hydrochloric acid of constant boiling-point thus leaving solid thorium chloride which is dissolved in water and treated with ammonia solution to precipitate thorium hydroxide which is then ignited to form thoria.ALSO:Thorium is extracted from an acidic aqueous thorium-containing solution in which an interfering metal is present by treating the solution with a substantially water-immiscible liquid phase which includes a water-immiscible liquid diluent, e.g. a hydrocarbon or chlorinated hydrocarbon, and an alkyl ester of phosphoric acid having one or two free hydroxyl groups bonded direct to the phosphorus atom to effect preferential extraction of thorium into the water-immiscible phase.  The interfering metal is defined as a metal which tends to precipitate when ammonia solution is added as precipitant reagent for the thorium, specified interfering metals being aluminium and iron and any iron present must first be reduced to the ferrous state before effecting the extraction process.  After separation of the aqueous phase from the thorium-containing water-immiscible phase the latter can be treated to decompose the thorium complex present, e.g. by means of aqueous sulphuric or hydrochloric acid, and the resulting thorium-containing aqueous phase and the nonaqueous phase comprising the regenerated alkyl phosphate are then separated. Thorium is recovered from the thorium-containing aqueous phase, e.g. by adding ammonia to precipitate thorium hydroxide.  The acid alkyl phosphates are preferably those in which the alkyl group is C4 to C15, e.g. di-n-octyl or di-2-ethylhexylhydrogen phosphates or 3,5,5-trimethylhexyl dihydrogen phosphate.  The invention is particularly applicable to the treatment of solutions containing thorium sulphate in dilute sulphuric acid, especially the barren liquor resulting as effluent when uranyl sulphate solutions obtained from thorium-containing uranium ores are treated with an anion exchange resin for the recovery of uranium.  Such a barren liquor can be treated to reduce any ferric iron present to the ferrous state by adding scrap iron and, if desired, a little sulphuric acid to decrease the pH and the pH is then readjusted if necessary to a pH higher than 1, e.g. between 1.5 and 2.5, before proceeding with the extraction process.  An example is given for the recovery of thorium from a sulphuric acid solution (pH 2) containing Fe (ferrous), Al2O3, and ThO2 by a three-stage extraction process using di-(2-ethyl hexyl)monohydrogen phosphate in kerosene, the volume ratio of non-aqueous phase to aqueous phase being 1:8.  The resulting non-aqueous thorium-containing phase is then decomposed with hydrochloric acid of constant boiling-point and the aqueous phase formed is then heated to distil off hydrochloric acid of constant boilingpoint, thus leaving solid thorium chloride which is dissolved in water and treated with ammonia solution to precipitate thorium hydroxide which is then ignited to form thoria.