RU2596564C1 - Method of regenerating of the spent acid dips formed when processing of titanium products - Google Patents

Abstract

FIELD: electroplating.

SUBSTANCE: invention relates to acid etching of surface of metal titanium and its alloys and can be used in regeneration and deactivation of spent acid etches (SAE) of titanium production. In the method of regenerating SAE is treated with alkali to pH 7.6-7.8, formed titanium hydroxide is filtered, and the filtrate is subjected to electrochemical processing in a four-chamber membranous electrolyzer, in which the first and the fourth chambers, cathode and anode, separated by cation-exchange membranes, between the second and third chambers placed anion-exchange membrane, the filtrate is pumped via the second chamber, in the first chamber is given 0.1N sodium hydroxide solution, in the third - 0.1N solution of hydrofluoric acid, through the fourth chamber is pumped 0.1N solution of sulfuric acid, the filtrate is processed at current density of 200-800 A/m² with producing of alkali in the first chamber and a mixture of acids in the third chamber, which used during process of etching titanium.

EFFECT: technical result - creation of the method of processing SAE to produce titanium hydroxide and a mixture of acids, used for preparation of etching solution used in production of titanium products.

1 cl, 2 dwg, 2 tbl

Description

The invention relates to the field of acid etching of the surface of metallic titanium and can be used in the regeneration and neutralization of spent acid etching solutions (OCTR) of titanium production.

Etching of titanium products is carried out in an aqueous solution of hydrofluoric acid containing about 2 weight. % HF. To increase the etching rate and the efficiency of the etching solution, one of the strong acids is added to it: nitric, sulfuric, hydrochloric at a concentration of from 6 to 33 weight. % (Usova V.V., Plotnikova T.P., Kushakevich S.A. Etching of titanium and its alloys. - M.: Metallurgy, 1984. - S. 55-62). OCTR, which contains titanium fluorides and mineral acids in its composition, is quite toxic and must be either diluted or recycled before discharge.

There is a method of recycling and neutralizing OCTR by neutralizing them with milk of lime to obtain solid waste in the form of a mixture of titanium hydroxide, gypsum and calcium fluoride (Sharikov LP Environmental protection. Handbook. Leningrad, 1978, p. 320).

The disadvantage of this method is the formation of a significant amount of solid waste, the loss of titanium contained in the OCTR, the incomplete use of mineral acids used in titanium etching technology.

There is a method of disposal and disposal of waste etching of titanium production by processing OCTR spent alkaline melts (OSR). When OCTR and ASCR are mixed, a precipitation of titanium hydroxide occurs and the mineral acids that are part of the OCTR are neutralized. Filtered titanium hydroxide can be used as a filler in the manufacture of varnishes, paints and ceramics, as well as for coating welding electrodes. The filtrate can be added with slaked lime to form gypsum and calcium fluoride or drained into an industrial sewer (Pat. 2176288 Russia, IPC C23F 1/46 Method for utilization and neutralization of titanium production pickling waste / Trubin AN, Grill G.I. (Russia) - No. 2000105528/02; notified on March 6, 2000, published on November 27, 2001).

The disadvantage of this method is the formation of toxic solid waste gypsum and calcium fluoride or runoff containing fluoride ions. In addition, there is an incomplete use of mineral acids used in titanium etching technology.

A known method of recovering titanium fluorides from OCTR by adjusting the molar ratio of titanium to fluorine to critical ranges, followed by adding an excess of an alkali metal salt and obtaining an alkali metal hexafluorotitanate salt precipitated. The precipitate is filtered, washed and dried, and the filtrate is neutralized with lime (US Pat. No. 4,943,419, IPC C01G 23/00 Process for recovering alkali metal titanium fluoride salts from titanium pickle acid baths / Joseph A. Megy (USA). - No. US 07 / 331.583; claimed March 30, 1989, published July 24, 1990).

The disadvantage of this method is the loss of unused mineral acids that are part of the etching solution. When neutralizing the filtrate obtained after separation of the precipitate of hexafluorotitanate salt, lime produces toxic toxic neutralization products that pollute the environment.

There is a known method for regenerating OCTR generated during the processing of titanium alloys, which involves the reduction of titanium fluorides with alkali metal compounds, filtering and drying the titanium-containing salt (potassium hexafluorotitanate) obtained from the solution, and the filtrate is further subjected to electrodialysis using ion-exchange membranes, after which the mineral acids are returned to production .

или $$N{O}_3^{-}$$

из катодной камеры в анодную.(Pat 2289638 Russia, IPC C23F 1/46. Method for the regeneration of spent etching acid solutions formed during the processing of titanium alloys / A.N. Trubin, G.I. Gil (Russia). - No. 2005122756/02; claimed 18.07.2005, published on December 20, 2006). To reduce titanium fluoride to potassium hexafluorotitanate, nitric acid (to convert trivalent titanium to tetravalent), hydrofluoric acid (to adjust the ratio of molar fractions of F / Ti to a value of 6.4), and excess potassium chloride in excess (to adjust the ratio of molar fractions to magnitude 3.86). The resulting precipitate of potassium hexafluorotitanate salt is filtered off, washed and dried, obtaining crystalline K ₂ TiF ₆ . The filtrate, which contains hydrofluoric acid, potassium chloride and one of the strong acids: nitric, sulfuric or hydrochloric, is subjected to electrodialysis using an anion exchange membrane. Under the influence of a direct current field, the fluorine anions F ^- , chlorine Cl ^- and one of the strong acids migrate: $$S{O}_{\mathrm{four}}^{2-}$$

or $$N{O}_3^{-}$$

from the cathode chamber to the anode.

The disadvantage of this method is that, migrating from the cathode to the anode chamber, the F ^- and Cl ^- ions ^are discharged at the anode with the formation of gaseous fluorine and chlorine. This leads to the loss of hydrofluoric and hydrochloric acids and the need to clean the anode gases from F ₂ and Cl ₂ before they are released into the atmosphere. In the anode chamber of the electrodialyzer, only oxygen-containing (H ₂ SO ₄ and HNO ₃ ) acids are concentrated.

The present invention solves the technical problem of processing OCTR to produce titanium hydroxide and a mixture of acids used to prepare the etching solution used in the manufacture of titanium products.

The problem is achieved in that in the method for the regeneration of spent acid etching solutions formed during the processing of titanium products, according to the invention, the OCTR is treated with alkali (mainly NaOH) to a pH of 7.6 ÷ 7.8. Titanium hydroxide is filtered off, and the filtrate is subjected to electrochemical processing in a four-chamber membrane electrolyzer, in which the first and fourth chambers, the cathode and the anode, are separated by cation-exchange membranes, an anion-exchange membrane is placed between the second and third chambers, the filtrate is pumped through the second chamber, into the first chamber 0 , 1 N sodium hydroxide solution, in the third - 0.1 N hydrofluoric acid solution, a 0.1 N sulfuric acid pump is pumped through the fourth chamber, the filtrate is processed at current flow rate of 200-800 A / m ² to produce alkali in the first chamber and a mixture of acids in the third chamber, used in the process of etching of titanium. Alkali is used to process OCTR, and the acid mixture after adjustment is used to etch titanium.

The implementation of the OCTR regeneration method is illustrated in the process diagrams shown in FIG. 1 and 2. OCTR (Fig. 1) is treated with alkali (predominantly NaOH) to a pH of 7.6 ÷ 7.8. In this case, a precipitate of titanium hydroxide Ti (OH) _{4 is formed} , which, after filtration, can be dried and calcined, and a filtrate containing the following salts: sodium fluoride NaF and sodium salt of one of the strong acids used to prepare the etching solution (NaCl or NaNO ₃ or Na ₂ SO ₄ ). The filtrate is processed in a membrane electrolyzer to obtain a mixture of HF acids and one of the strong acids (HCl or HNO ₃ or H ₂ SO ₄ ) and sodium hydroxide NaOH. Sodium hydroxide is used to neutralize the OCTR, and the mixture of acids after adjustment is sent to the etching of titanium.

или

через анионообменную мембрану (А) мигрируют в камеру 3 электролизера. Дальнейшему движению анионов к аноду препятствует катионообменная мембрана, разделяющая камеру 3 и анодную камеру 4 электролизера. На электродах происходит разложение воды. На катоде этот процесс протекает с выделением газообразного водорода и образованием ионов ОН^-:In FIG. 2 shows a diagram of the process of electrochemical processing of the filtrate, carried out in a four-chamber membrane electrolyzer. The four-chamber membrane electrolyzer consists of 4 chambers: the cathode chamber 1, adjacent to the cathode chamber 2, adjacent to the anode chamber 3, the anode chamber 4. Distilled water or a weak (mainly 0.1 N) sodium hydroxide solution is placed in the cathode chamber 1 of the electrolyzer. The latter is used to create initial conductivity in the cathode chamber 1. A filtrate containing sodium salts of hydrofluoric and hydrochloric or hydrochloric or nitric or sulfuric acid is pumped through a chamber 2 of the electrolyzer adjacent to the cathode from a tank 5 by a pump 6. In the chamber 3 of the electrolyzer adjacent to the anode, a weak solution (mainly 0.1 n) of hydrofluoric acid is placed. Through the anode chamber 4 of the electrolyzer from the tank 7, the pump 8 is pumped a weak (mainly 0.1 N.) sulfuric acid. The cathode 1 and anode 4 chambers of the electrolyzer are separated by cation-exchange membranes (K), and an anion-exchange membrane (A) is placed between 2 and 3 chambers of the electrolyzer. In the electric field created in the electrolyzer when voltage is applied to the electrodes from the direct current source 9, Na ⁺ ions are transferred from chamber 2 through the cation exchange membrane (K) to the cathode chamber of the electrolyzer. Ions F ^- and Cl ^- or

or

through the anion-exchange membrane (A) migrate into the chamber 3 of the electrolyzer. Further movement of the anions to the anode is impeded by a cation exchange membrane separating the chamber 3 and the anode chamber 4 of the electrolyzer. The electrodes decompose water. At the cathode, this process proceeds with the release of hydrogen gas and the formation of OH ^- ions:

2H ₂ O + 2e → H ₂ + 2OH ^- ,

and on the anode, water decomposes with the release of gaseous oxygen and the formation of H ⁺ ions: 2H ₂ O-2е → O ₂ + 4Н ⁺ .

или

. В результате в катодной камере электролизера концентрируется гидроксид натрия, а в камере 3 электролизера концентрируется смесь кислот. По мере накопления гидроксид натрия, вытекая из катодной камеры электролизера, собирается в емкости 10, а смесь кислот, вытекая из камеры 3 электролизера, собирается в емкости 11. Процесс электрохимической переработки фильтрата проводят при плотности тока, равной 200÷800 А/м².H ⁺ ions migrate into the chamber 3 of the electrolyzer through a cation exchange membrane (K) and are locked in it by an anion exchange membrane (A). Thus, from chamber 2, Na ⁺ cations and F ^- and Cl ^- or

or

. As a result, sodium hydroxide is concentrated in the cathode chamber of the electrolyzer, and a mixture of acids is concentrated in the chamber 3 of the electrolyzer. As the accumulation of sodium hydroxide, flowing out of the cathode chamber of the electrolyzer, is collected in the tank 10, and a mixture of acids, flowing out of the chamber 3 of the cell, is collected in the tank 11. The process of electrochemical processing of the filtrate is carried out at a current density of 200 ÷ 800 A / m ² .

Example 1

To determine the precipitation pH of titanium hydroxide, an OCTR containing 21.9 g / L TiF ₃ , 1.7 g / L HF and 6.2 g / L HCl was treated with sodium hydroxide. For this, various amounts of sodium hydroxide were added to a number of samples containing 50 ml of OCTR. After the formation of a precipitate of titanium hydroxide, it was filtered off, dried, calcined at a temperature of 900 ° C for 1 hour (titanium hydroxide turned into dioxide) and weighed. The maximum amount of titanium dioxide (TiO ₂ ), which in this case can be obtained from OCTR, is 0.835 g. The pH value was determined in the obtained filtrate. The dependence of the degree of extraction of titanium from OCTR on the pH of the filtrate is presented in table 1.

Complete precipitation of titanium in the form of hydroxide by OCTR treatment with sodium hydroxide occurs when the pH of the medium reaches 7.6–7.8.

Example 2

An OCTR containing 21.9 g / L TiF ₃ , 1.7 g / L HF and 6.2 g / L HCl was treated with sodium hydroxide to a pH of 7.6–7.8. After the formation of a precipitate of titanium hydroxide, the latter was filtered off, and the filtrate was processed in a four-chamber membrane electrolyzer (see Fig. 2). For this, 0.1 N was interfered with the cathode chamber of the electrolyzer. NaOH solution, 0.1 N was placed in the cell 3 of the electrolyzer. HF solution, the filtrate was pumped through the chamber 2 of the electrolyzer, and 0.1 N was pumped through the anode chamber of the electrolyzer H ₂ SO ₄ solution. The volumes of the filtrate and the H ₂ SO ₄ solution in all experiments were 1 liter. NaOH solutions and mixtures of HF and HCl acids generated in the cathode chamber and chamber 3 of the electrolyzer left the cell as they accumulated and were collected in appropriate containers. Every 0.5 hours, the NaOH content in the solution generated in the cathode chamber and the content of HF and HCl in the solution generated in the cell 3 of the electrolyzer were analyzed. The electrolysis process continued until the concentrations of NaOH, HF and HCl in the corresponding solutions became constant. The experiments were carried out at current densities on the membranes of 200, 400, 600, and 800 A / m ² . The values of the maximum concentrations of NaOH, HF and HCl obtained at different current densities are presented in table 2.

The concentration of NaOH in the solution generated in the cathode chamber of the electrolyzer, and the concentration of HF and HCl in the solution generated in the chamber 3 of the electrolyzer is determined by the current density on the membranes. So at a current density of 200 A / m ^{2, the} concentration of NaOH in the cathode chamber reaches 125 g / l, and the concentrations of HF and HCl in chamber 3 of the electrolyzer reach 47.6 and 44.5 g / l, respectively. An increase in the current density to 800 A / m ² leads to an increase in the concentration of NaOH in the cathode chamber to a value of 374 g / l, and the concentrations of HF and HCl in the chamber 3 of the electrolyzer to 66.5 and 63.4 g / l, respectively. An increase in current density of more than 800 A / m ^{2 is} undesirable, since this leads to a significant heating of the solutions involved in the electrolysis process.

Using the proposed method for the regeneration of spent acid pickling solutions formed during the processing of titanium products, compared with existing has the following advantages:

a) titanium hydroxide formed after OCTR treatment with sodium hydroxide after drying and calcination can be used as a filler in the paint and varnish industry;

b) obtained during the electrochemical processing of the filtrate, the mixture of acids can be used to prepare a solution used in the etching process of titanium, and sodium hydroxide can be used to process OCTR.

Claims (2)

1. The method of regeneration of the spent acid solution of etching of titanium, characterized in that the spent acid solution is treated with alkali to a pH of 7.6-7.8, the resulting titanium hydroxide is filtered off, and the filtrate is subjected to electrochemical treatment in a four-chamber membrane electrolyzer, in which the first and fourth the cathodic and anodic chambers are separated by cation-exchange membranes, an anion-exchange membrane is placed between the second and third chambers, the filtrate is pumped through the second chamber, and the first chamber is fed 0.1 N sodium hydroxide solution, in the third - 0.1 N hydrofluoric acid solution, a 0.1 N sulfuric acid pump is pumped through the fourth chamber, the filtrate is processed at a current density of 200-800 A / m ² to obtain alkali in the first chamber and mixtures of acids in the third chamber used in the etching process of titanium. 2. The method of claim 1, wherein the spent acidic pickling solution is treated with NaOH.

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