RU2374343C1 - Method of vanadium extracting of water sodium-bearing solutions - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: invention relates to methods of vanadium sedimentation from water solutions and can be used in hydrometallurgy of rare refractory metals, particularly receiving of vanadium oxide (V+5) of high purity. Method of vanadium extraction from sodium-bearing solutions includes electrodialysis of solution for membrane withdrawal of sodium cation from solution and sedimentation of ammonium pol-vanadate. Electrodialysis is implemented at circulation of solution through working chamber of electrodialysis apparatus and at achievement of pH 6.5-7.5 circulating solution is treated by ammonia water or ammonia. Treatment is implemented up to molar ratio Na:V<0.1. ^ EFFECT: providing of intensification of sedimentation process of vanadium, improvement of finished product and elimination of discharge of industrial flows. ^ 1 dwg, 4 ex

Description

The invention relates to methods for the deposition of vanadium from aqueous sodium-containing solutions and can be used in the hydrometallurgy of rare refractory metals, in particular the production of high purity vanadium oxide (V ⁺⁵ ) from sodium orthovanadate solutions, as well as the preparation of pure salts of molybdenum and tungsten.

A known method of precipitation of vanadium from solutions of sodium orthovanadate using ammonium salts. The process is accompanied first by an exchange reaction with the conversion of sodium into an inert sulfate, nitrate or chloride salt, and then by the physical crystallization of ammonium vanadate (magazine "Complex use of mineral raw materials", Almaty, 1997, No. 1, pp. 56-61) .

The method is intended to extract vanadium compounds from solutions with an increased background of salts that pollute the finished product. The method is associated with a high consumption of ammonium salts (four times against the theoretically necessary), the presence of drain water containing chlorides, nitrates or sodium sulfates, the disposal of which is not economically justified.

Known precipitation of vanadium by the method of dehydration decomposition of solutions with the formation of poorly soluble salts of vanadium acids (Production of technical vanadium pentoxide. Technological instruction TI 127-f-06-96, Tula, 1996). In this method, solutions of weakly acid leaching with a pH of 2.5 are mixed with acidic solutions (pH 1.0). The combined solution (pH 1.6) with a molar ratio of Mn: V = 0.5 is heated to a temperature not lower than 98 ° C and boiled. Manganese salts of vanadium acid containing 4-5% Mn are precipitated.

The disadvantages of the method include the low quality of the finished product (92-93%

V ₂ O ₅ ), an additional washing operation of technical vanadium oxide from manganese with iron or magnesium sulfate.

A known method of producing vanadium salts by thermal dehydration decomposition of mixed solutions of sodium metavanadate and vanadium-containing sulfuric acid solution (Production of technical vanadium pentoxide. Technological instruction TI 115 - F - 10 - 2003, Chusovoy). Precipitation is carried out at a pH of 1.8-2.0 and a molar ratio (MO) of Na: V = 0.5.

The disadvantages of the method are the low quality of technical vanadium oxide (80-85% V ₂ O ₅ ) containing from 5 to 8% Na, the complex salt composition of wastewater containing VI-valent chromium compounds.

The closest to the proposed method for the deposition of vanadium from solutions of sodium orthovanadates is the membrane withdrawal of the sodium cation and two-stage precipitation of sodium and calcium vanadates (Ph.D. dissertation. V.V. Yurenko. Research and development of technology for extracting vanadium from converter slags using soda. M., 1980).

The disadvantages of the method include:

- the inability to completely purify the vanadium solution from sodium;

- part of the vanadium ions at pH 2.0 goes into the cationic form and begins to migrate to the cathode chamber;

- poorly soluble vanadium salts are deposited on the electrodes;

- the electrical resistance of the solution increases relative to the original value:

at MO 1.0 and pH 6.5 1.35 times, and

at MO 0.2 and pH 2.0 2.50 times.

This indicates that, starting from pH 6.5, the conductivity of the solution is associated with a poorly dissociable supramolecular vanadium compound, and despite the duration of the process, a decrease in the Na: V MO of less than 0.2 is not achieved.

Currently, from the patent and scientific literature there is no known method for the isolation of vanadium from solutions of sodium orthovanadate with ammonia water.

Solutions after soda or bicarbonate leaching contain, as a rule, in addition to the sodium vanadium salt, a certain amount of excess soda with MO Na: V equal to 2.5-3.0. The processing of such solutions involves the removal of the sodium cation through a membrane with alkali regeneration in the cathode chamber. In this case, the ortho- and pyrovanadates are completely decomposed, and then the vanadium gradually polymerizes with a decrease in the sodium-vanadium molar ratio and the formation of a supramolecular compound with low electrical conductivity, from which sodium withdrawal is difficult.

In any technological schemes, only ammonia technology allows to obtain high purity vanadium oxides. But at the same time, sodium must be converted into a neutral salt (Na ₂ SO ₄ , NaNO ₃ or NaCl), which makes it difficult to solve the problem of closed water circulation. The problem of closed water circulation can only be solved by the complete removal of sodium from the vanadium-containing solution.

In the electrochemical acidification of a solution of sodium orthovanadate, the sodium withdrawal limits depend on the presence of competing transfer of hydrogen ions appearing in the solution. Hydrogen ions either protonate vanadium polyanions or bind to water, and their mobility remains low up to the maximum molar ratio of sodium to vanadium.

During the electrochemical treatment of a solution of sodium orthovanadate in the system, the following processes of decomposition of free soda, sodium bicarbonate, sodium vanadate, supramolecular compound with sodium MO to vanadium 0.7 proceed sequentially. The mobility of sodium and proton ions is inhibited under these conditions, and this system can be "rocked" by displacing sodium ions by other cations. The most suitable may be an ammonium group. Although the mobility of the ammonium group in comparison with sodium cations is 1.47 times higher. However, during electrodialysis processing of a solution of a supramolecular compound in the system, the process of neutralizing excess ammonium hydroxide proceeds according to the reaction

NH ₄ OH + H ⁺ → H ₂ O + NH ₄ ,

which, on the one hand, displaces the sodium ion, and on the other hand, together with sodium, passes into the catholyte and is released into the gas phase in the form of NH ₃ , because against the background of an increased alkali concentration of more than 20%, ammonium hydroxide is unstable and decomposes.

The objective of the invention is to develop a method for the most complete membrane removal of the sodium cation from solutions of polymerized supramolecular vanadium compounds with a molar ratio to sodium (MO 0.7) in the presence of an ammonium group (NH ₄ ⁺ ), displacing sodium from polymer ionized forms of vanadium to a sodium to vanadium ratio <0.1 and partial migration of the ammonium group through a membrane with a sodium cation, regeneration in the cathode chamber of alkali (NaOH) and ammonia water (NH ₄ OH), the latter decomposes in concentrated alkali solutions with the release of ammonia (NH ₃ ), ammonia is used in the circulation cycle to maintain a pH of 6.5-7.5 in a vanadium-containing solution, to remove ohmic resistance and crystallization of ammonium polyvanadates.

The technical result of the invention is to increase the selectivity and intensification of the process of deposition of vanadium, the organization of a closed cycle of the main reagents and the elimination of the discharge of industrial effluents.

A method is proposed for the precipitation of vanadium compounds of the highest oxidation state from solutions, including the membrane withdrawal of the sodium cation from the solution and the precipitation of ammonium polyvanadate, while the withdrawal of the sodium cation is carried out in the presence of an ammonium group to a molar ratio Na: V <0.1, and vanadium is precipitated with ammonia water protonated by the generated hydrogen ion.

Membrane processes, in which the electric field is the driving force of mass transfer through the ion-selective partitions, in a number of cases can reagentlessly control the compositions of the initial solutions. The electrolyzer is an aggregate consisting of anode and cathode elements separated by membranes. To ensure the stability of the anode material in the process of membrane electrolysis, a three-chamber system with two separating cation-exchange membranes was used. All cells have fittings through which the gas-liquid mixture is discharged. Sulfuric acid, which is practically not consumed, is used as anolyte. At acceptable concentrations (5% H ₂ SO ₄ ) its electrical conductivity is quite high, the dissolution rate of the anode material is negligible; the additional cation exchange membrane is in the most electrically conductive H ⁺ form; its contribution to the system resistance is insignificant. As catholyte, a mother liquor with a concentration of Na ⁺ 2-4 g / l is used (to ensure electrical conductivity).

The main object of research was sodium orthovanadate solutions, for which the use of electro-membrane treatment methods can provide not only the removal and regeneration of the leaching agent, but also a deep conversion of vanadium salts with a gradual increase in the ammonium-metal ratio in the complex vanadium salt.

A diagram of the simultaneous membrane removal of an alkali metal from a solution of vanadium in the presence of NH ₄ ⁺ and the deposition of polyvanadates is shown in the drawing.

The sodium orthovanadate solution circulates through the working chamber of the electrodialyzer. As sodium is removed from all chambers, gas is discharged through separate paths: from the working chamber —CO ₂ , from the cathode space — gaseous ammonia, and from the anode — oxygen. After reaching a pH of 6.5-7.5 and a Na: V MO of 0.7, the vanadium solution circulating in the system is treated with ammonia water or gaseous ammonia to a pH of 6.5-7.5 and a molar ratio of vanadium to sodium <0.1 in a two-phase crystallizer, the discharge of which after control filtration is sent to the working chamber of the electrodialyzer. The rate of sodium removal from the vanadium solution increases sharply due to the maintenance of pH 6.5–7.5, and the mother liquor after crystallization of ammonium polyvanadate does not contain impurities and can be returned to the reverse cycle. And the presence of ammonia allows selective sodium removal from vanadium solutions.

Examples of the method of the prototype.

Example 1. Take 500 ml of sodium orthovanadate solution (molar ratio of Na: V = 3, pH 11.2, Na content of 61.8 g / l, V 45.7 g / l). Electrodialysis is carried out to pH 6.5 and the Na content is 18.4 g / L, V 45.7 g / L, and MO 0.8. And then for 3 hours they continue to conduct electrodialysis of the solution to pH 2 and the content of Na 3.5 g / l and V 42.6 g / l, MO 0.2. The solution is treated with ammonia water at pH 8.5. Precipitation of vanadium proceeds slowly; after a day, the content of vanadium in the mother liquor remains at the level of 5.2 g / l. According to chemical analysis, the mass fraction of vanadium in the precipitate of polyvanadate in terms of V ₂ O ₅ is 71.6%, the thermal decomposition of which will lead to the production of vanadium oxide with a content of 91.1% V ₂ O ₅ and Na - 5.6%.

Example 2 by the proposed method.

Upon reaching pH 6.5, ammonia water is continuously introduced and circulated through the working chamber. The change in sodium concentration is controlled by selecting aliquots.

Time min Contents Na, g / l Consumption of NH ₄ OH, ml MO Na: V twenty 2.3 25.0 0.60 40 0.6 33.0 0.33 60 0.2 35.0 0.11

The polyvanadate precipitated from the final solution contained V ₂ O ₅ - 76.5%, from which 99.2% vanadium oxide, Na - 0.3% were obtained, and in the mother liquor the content of vanadium was 0.3 g / l and sodium 0.6 g / l.

Example 3 by the proposed method.

The mother liquor from example 2 is mixed with the initial solution of sodium orthovanadate in a ratio of 1: 1 (the vanadium content in the solution is 23.0 g / l, sodium 31.8 g / l, MO 3.06). Electrodialysis is carried out to pH 6.5, the content in the solution is Na 10.5 g / l, V 23.0 g / l, MO 1.0.

At the second stage, ammonia water is introduced to pH 7.5 and circulated through the working chamber. The results are shown below.

Time min Contents Na, g / l Consumption of NH ₄ OH, ml MO Na: V twenty 2.1 15.0 0.40 40 0.4 20.0 0.23 60 0.1 25.0 0.08

The polyvanadate precipitated from the final solution contained V ₂ O ₅ - 77.0%, from which 99.5% vanadium oxide, Na - 0.2% were obtained, in the mother liquor the content of vanadium was 0.21 g / l and sodium 0.3 g / l.

Example 4 by the proposed method.

The mother liquor from example 3 is mixed with the initial solution of sodium orthovanadate in a ratio of 2: 1 (the vanadium content in the solution is 23.0 g / l, sodium 31.9 g / l, MO 3.06). Electrodialysis is carried out to pH 6.5, the Na content in the solution is 7.1 g / L, V 23.0 g / L, and MO 0.70.

Ammonia water is introduced to pH 7.5 and circulated through the working chamber at the same technological parameters of electrodialysis.

Time min Contents Na, g / l Consumption of NH ₄ OH, ml MO Na: V twenty 2.0 10.0 0.15 40 0.1 15.0 0.210 60 0.05 20.0 0.05

After which the precipitate is filtered off, dried in air.

According to chemical analysis, the mass fraction of vanadium in the precipitate of ammonium polyvanadate in terms of V ₂ O ₅ is 76.8%, from which 99.6% of vanadium oxide are obtained, Na - less than 0.1%, in the mother liquor, the sodium content is 0.1 g / l.

From the above examples it follows that the ammonium group (KS) is a transporting agent for the withdrawal of sodium and its removal time is significantly reduced. Membrane withdrawal of sodium and deep precipitation of vanadium allow mother liquors to return to the reverse cycle. The attached drawing also shows how gaseous ammonia and carbon dioxide are used, in the first case for the treatment of vanadium solutions, and in the second for the conversion of sodium hydroxide into soda.

Claims (1)

A method for isolating vanadium from aqueous sodium-containing solutions, including electrodialysis of a solution for membrane withdrawal of sodium cation from a solution and precipitation of ammonium polyvanadates, characterized in that the electrodialysis is carried out when the solution is circulated through the working chamber of the electrodialyzer and, when the pH reaches 6.5-7.5, the circulating solution is treated with ammonia water or ammonia to a molar ratio of Na: V <0.1.

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