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• W2565911592 abstract "The extraction of molybdenum(VI) from aqueous peroxide solutions of sodium tungstate with a trialkylamine isooctyl alcohol mixture in kerosene was studied in relation to the ratio of the organic and aqueous phases, hydrogen peroxide and hydrogen chloride consumption, and the ratio of molybdenum(VI) and tungsten (VI) in the aqueous phase. A method for additional purification of the raffinate to remove molyb- denum was developed. In recovery of tungsten from its ore concentrates, along with the target metal, arsenic(V), phos- phorus(V), silicon(IV), and molybdenum(VI) impuri- ties also pass into the solution. This solution can be efficiently purified to remove As(V), P(V), and Si(IV) impurities by well-known methods widely used in industry (1). In contrast to As(V), P(V), and Si(IV), the purification of W(VI) to remove molybdenum is a more difficult problem, especially at high W : Mo ratios. In order to meet the consumers' requirements, the Mo content in tungsten must not exceed 0.02%. A common technique for tungsten purification to re- move molybdenum is based on Mo(VI) precipitation as sulfide MoS 3 . However, this procedure does not ensure preparation of tungsten meeting the require- ments with respect to molybdenum content. Further- more, with this technique, 0.2 0.3% of WS 3 is lost due to the coprecipitation of MoS 3 and WS 3 . One more drawback of this technique is the hydrogen sul- fide liberation. The most efficient tungsten purifica- tion to remove molybdenum can be carried out by solvent extraction or ion exchange. It is known that, in acidification of aqueous solu- tions containing Mo(VI) and W(VI), mixed poly- oxyanions of these metals are formed. When the molybdenum content in these polyanions becomes considerably lower than the tungsten content, the species similar to W(VI)-containing polyanions are formed. The mixed Mo(VI) W(VI) polyanions can be decomposed with H 2 O 2 . This agent is relatively cheap and does not contaminate solution with any impurities (2). Since aqueous peroxide solutions of W(VI) and Mo(VI) are stable at pH < 2, they can be processed by solvent extraction. For example, in extraction of W(VI) and Mo(VI) from aqueous peroxide nitric acid solutions at pH 0.4 0.9 with tributyl phosphate, W(VI) is separated from Mo(VI) with the separation factor Mo/W of about 40 (3). Currently the most ef- ficient purification of tungstates to remove Mo(VI) is achieved by selective solvent extraction of thio species (MoS 4 ) 2 (4 6). In this work we studied the solvent extraction of Mo(VI) from aqueous peroxide solutions of Na 2 WO 4 Na 2 MoO 4 mixture with the Mo(VI) content not exceeding 1% relative to the W(VI) content. The extraction system used in our experiments con- tained trialkylamine R 3 N( R =C H 3 (CH 2 ) 6 CH 2 , TAA, 7 vol %), isooctyl alkohol C 8 H 17 OH (14 vol %), and kerosene as diluent. This extraction system is used for industrial recovery of W(VI) from aqueous solutions preliminarily decontaminated from impurities, among them from Mo(VI) (7). The aqueous solutions of W(VI) and Mo(VI) were prepared from chemically pure grade sodium tungstate and molybdate Na 2 MO 4 2H 2 O (M = W, Mo). Imme- diately after preparation, 33% H 2 O 2 was added to the solution and the resulting mixture was acidified with concentrated HCl to the required pH (0 0.7). The HCl amount required for acidification is dependent on the initial tungstate concentration. In the course of extraction, the required pH was maintained at a con- stant level. The extraction was carried out at continu- ous stirring of the organic and aqueous phases to attain the equilibrium. The W(VI) and Mo(VI) content in both the initial solution and raffinate was deter- mined colorimetrically. Before analysis, the aqueous solution was boiled to decompose H 2 O 2 . The metal content in the extract was determined as the difference between its content in the initial solution and raffi-" @default.
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• W2565911592 date "2004-01-01" @default.
• W2565911592 modified "2023-09-24" @default.
• W2565911592 title "SORPTION AND ION-EXCHANGE PROCESSES Extraction of Molybdenum(VI) from Aqueous Peroxide Solutions of Sodium Tungstate with Trialkylamine" @default.
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