RU2289638C1 - Method for waste acidic solution regeneration after etching titanium alloys - Google Patents

Abstract

FIELD: regeneration of waste acidic etching solutions, recovery of waste materials formed at etching titanium alloys.

SUBSTANCE: method comprises steps of reducing titanium fluorides by alkali metal compounds; filtering and drying titanium-containing salt formed out of solution at temperature 30 - 60°C; in addition subjecting filtrate to dialysis with use of ion exchange membranes; then returning mineral acids to production process and recovering hydroxides of alloying elements.

EFFECT: complete recovery of waste etching acidic solutions at producing products such as potassium hexafluotitanate salts, hydroxides and purified mineral acids suitable for industrial usage.

2 cl, 1 dwg

Description

The invention relates to chemical acid etching of metals, leading to the formation of spent metal-containing etching solutions and wash water. More specifically, the present invention relates to the regeneration of spent pickling acid solutions (OCR) and the disposal of waste generated from the etching of titanium alloys.

In industry, titanium alloys are produced in the form of ingots, which are then processed into semi-finished products and parts by forging, rolling, machining. For a number of technological operations, heating of the metal is required to deform it without cracking. When the metal is heated in air, an oxide layer forms on its surface, which must be removed at subsequent stages. The layer is removed by the methods of shot and sandblasting, abrasive, followed by etching in acids to remove a small layer of metal from the treated surface.

Etching is carried out in an aqueous solution of hydrofluoric acid containing 2-7 wt.% HF, while titanium fluorides are formed

The etching rate increases when one of the strong mineral acids is added to the solution: nitric, hydrochloric, sulfuric at a concentration of 5 to 20% (wt.).

Reaction (2) depends on the presence of nitric acid (HNO ₃ ) or another oxidizing agent.

Nitric acid also acts as a hydrogen inhibitor in the titanium alloy during etching. Mineral acids also dissolve some alloying elements in titanium alloys and oxidize trivalent titanium to tetravalent. To increase the durability of the solution, hydrofluoric acid and mineral acids are periodically added. When the etching solution is saturated with titanium fluorides, as well as depending on the etching temperature, titanium oxidation state, acid concentration and impurities, the reaction drastically slows down and a solid hydrogenated titanium fluoride layer settles on the surface. The acid pickling solution becomes spent (OCR).

OCR contains titanium fluorides (in terms of metallic titanium from 25 to 50 g / l), mineral acids, which are used for etching by 25-30%, sometimes an excess of hydrofluoric acid and various alloying components: aluminum, vanadium, chromium, manganese, tin, zirconium.

A known method of disposal of OCR by neutralizing with lime to obtain solid waste in the form of a mixture of metal hydroxides, gypsum and calcium fluoride. (Environmental protection. Handbook. L.P. Sharikov, Leningrad, 1978, p. 320).

The disadvantages of this method are:

- the formation of a large amount of solid waste;

- the presence of toxic discharges at the end of processing of OCR;

- loss of titanium compounds contained in OCR;

- incomplete use of expensive mineral acids suitable for further processing of titanium alloys.

A known method of electrochemical regeneration of OCR with electrodialysis using ion-exchange membranes (V.P. Kochergin, G.K.Aksenova "Production of titanium alloys", issue Sat. 2, Collection of VILS, publishing house "Metallurgy"; B.N. Laskorin , N.M.Smirnova, M.N. Gantman “Ion-exchange membranes and their application”, Gosatomizdat, 1961, Moscow; “Demineralization by the method of electrodialysis (ionite membranes)”, translated from English, edited by B.N. .Laskorina and F.V. Rausen, Gosatomizdat, Moscow, 1963; “Design assignment of the OTR VSMOZ regeneration workshop, volume 1, order No. 872-62, archive No. 48037 Sverdlovsk branch of Uralgiprokhim, 1963).

This method is intended for the isolation from OCR of free mineral acids of increased concentration in order to reuse them in production.

The disadvantage of this method of regeneration of OCRs formed during the etching of titanium alloys is that when the titanium concentration in OCRs is in the range from 25 to 50 g / l in catholyte during electrolysis, a bulk mass of insoluble precipitate of titanium hydroxide (Ti (OH) ₄ ) is formed in the form jelly, particles of which clog the holes of anion exchange membranes. As a result of this phenomenon, the electrolysis rate decreases, and the process stops.

In this regard, this method of regeneration of OCR containing compounds, titanium did not find industrial application.

There is a method of recovering titanium fluorides from OCR by adjusting the molar ratio of titanium to fluorine to critical ranges, followed by the addition of an excessive amount of alkali metal compounds to produce potassium hexafluorotitanate salt (K ₂ TiF ₆ ), which precipitates. The salt is filtered, washed and dried, and the filtrate is neutralized with lime. (US patent No. 4943419 from 07.24.1990, Dr. Joseph A. Megy) - a prototype.

The disadvantage of this method is:

- loss of unused free mineral acids contaminated with alloying elements that quickly accumulate in OCR during etching and make the filtrate (after removal of titanium fluoride salts) unsuitable for etching; in addition, impurities of alloying elements pollute the salt of potassium hexafluorotitanate, the salt crystallizes “dirty” and finely divided;

- when neutralizing the filtrate with lime, neutralization products are formed that pollute the environment.

The challenge to which the claimed invention is directed is the comprehensive regeneration of OCR.

The technical result achieved by the implementation of this invention is:

- obtaining valuable marketable products: salts of potassium hexafluorotitanate; mineral acids purified from titanium salts and hydroxides of alloying elements suitable for industrial use;

- eliminates environmental pollution with harmful products of neutralization of OCR with lime;

- sharply reduced capital costs for facilities to neutralize pickling waste lime.

The solution of this problem is achieved by the fact that in the method of regeneration of spent pickling acid solutions formed during the processing of titanium alloys, including the reduction of titanium fluorides with alkali metal compounds, filtration and drying of a titanium-containing salt obtained from a solution, the filtrate is additionally subjected to electrodialysis using ion-exchange membranes, after which mineral acids are returned to production, and the hydroxides of the alloying elements are disposed of.

It is advisable to dry the salt at a temperature of from 30 to 60 ° C.

The implementation of the method of regeneration of OCR is illustrated by the process diagram shown in the drawing.

OCR is fed into reactor 1, where titanium fluorides are reduced by alkali metal compounds to form a precipitate of potassium hexafluorotitanate salt (K ₂ TiF ₆ ). Next, filtration is carried out in a vacuum filter 2 and washing of the precipitate obtained, followed by drying in a drying unit 4. When washing potassium hexafluorotitanate, a single-water compound K ₂ TiF ₆ · H ₂ O is formed in the form of small crystals that are not suitable for technical use as alloying and modifying component in aluminum production. For the enlargement of the crystals, the salt is exposed to moisture in air in a known manner. In this case, “aging” of crystals occurs, but this process takes from 12 to 24 hours.

To accelerate the aging process and increase the size of crystals by 1.5-3 times (compared with exposure to air) it is proposed to heat the salt, which is easily dehydrated, starting at a temperature of 30 ° C, and ends at a temperature of 60 ° C, while the crystals are enlarged , the duration of the process is reduced by 6-12 times.

K ₂ TiF ₆ · H ₂ O → K ₂ TiF ₆ + H ₂ O

After filtration, the filtrate was subjected to electrodialysis in an electrodialyzer 3 using an anion exchange membrane to purify it from doping impurities. Under the influence of the direct current field created by the rectifying unit (VAC), fluorine anions F ^1- and free mineral acids not used during etching through the ion-exchange membrane from the cathode chamber to the anode migrate, and the pH of the medium rises in the cathode chamber and as a result precipitation of hydroxides of alloying elements with partial reduction of metals at the cathode and the release of free hydrogen. Hydroxides of alloying metals are placed in a container 6. Due to the fact that titanium is removed from OCR as a salt of potassium hexafluorotitanate and the concentration of doping impurities in OCR is small, a small amount of metal hydroxides is formed in the cathode chamber; they do not clog holes in anion exchange membranes and do not affect the rate of electrolysis.

The industrial applicability of the claimed method for the regeneration of spent pickling acid solutions formed during the etching of titanium alloys is confirmed by the following specific example.

1000 ml of OCR taken from the workshop pickling bath containing 48.1 g / l of titanium, 33.6 g / l of fluorine, 1.2 g / l of aluminum, 0.8 g / l of vanadium, 28.1% sulfuric acid, placed in a crystallization reactor, the calculated amount of nitric acid was added as an oxidizing agent - 168 ml (for the oxidation of trivalent titanium to tetravalent), the calculated amount of hydrofluoric acid (40%) - 210 ml was added (to adjust the ratio of molar fractions of T1 / P to 6, 4), the last added potassium chloride in excess - 185.6 g (to adjust the ratio of molar fractions of Ti / KCl to a value of 3.86).

Crystalline potassium chloride was fed into the reactor in small portions for 40 minutes, at a temperature of 25 ° C, with slow stirring, these reaction conditions are optimal for a more complete precipitation of salt without breaking the crystals.

Salt K ₂ TiF ₆ was subjected to vacuum filtration in a plastic Buchner funnel with a polypropylene fabric. Wet sludge K ₂ TiF ₆ was 260.2 g, then it was washed 2 times from acid residues in 500 ml of water, the salt residue after washing was 208.16 g. When washing potassium hexafluorotitan, a single-water compound K ₂ TiF ₆ · H ₂ O was formed The crystals of this salt were dehydrated, raising the temperature from 20 ° to 100 ° C. Dehydration began at a temperature of 30 ° C and ended at a temperature of 60 ° C. After dehydration, the weight of the crystalline precipitate K ₂ TiF ₆ was 170.2 g with a Ti content of 19.3%.

After filtration, the filtrate volume was 700 ml. The composition of the filtrate: sulfuric acid - 27.6%, hydrofluoric acid - 1.38%, titanium - 1.04 g / l, aluminum - 1.08 g / l, vanadium - 0.5 g / l. The efficiency of cleaning OCR from titanium fluoride is 97.8%.

через ионообменную мембрану из катодной камеры в анодную, при этом в катодной камере повышается рН среды и вследствие этого выпадают осадки гидроокислов легирующих элементов с частичным восстановлением металлов на катоде и выделением свободного водорода. Гидроокислы легирующих металлов подлежат утилизации известными способами (например, возможно их восстановление методом алюмотермии). В связи с тем, что титан удален из ОТКР в виде соли гексафторотитаната калия, а концентрация легирующих примесей в ОТКР мала, в катодной камере образуется незначительное количество гидроокисей металлов, они не закупоривают отверстия в анионитовых мембранах и не влияют на скорость электролиза.The filtrate was subjected to electrodialysis using an anion exchange membrane to purify it from doping impurities. Under the influence of the direct current field created by the rectifying unit (VAK), fluorine anions F ^1- and groups migrate

through the ion-exchange membrane from the cathode chamber to the anode, while the pH of the medium rises in the cathode chamber and, as a result, precipitates of hydroxides of alloying elements with partial reduction of metals at the cathode and the release of free hydrogen. Hydroxides of alloying metals must be disposed of by known methods (for example, they can be reduced by aluminothermy). Due to the fact that titanium was removed from OCR as a salt of potassium hexafluorotitanate, and the concentration of dopants in OCR is low, a small amount of metal hydroxides is formed in the cathode chamber, they do not clog holes in anion exchange membranes and do not affect the electrolysis rate.

The regenerated filtrate solution contains 85-90% sulfuric acid from the initial concentration, alloying elements - 0.01%, titanium - not more than 0.1 g / l.

The regenerated spent pickling acid solution was tested to pickle samples of heat-treated 6A14V titanium alloy. The etching results indicate the possibility of the secondary use of mineral acids isolated from etching solutions.

The proposed method allows you to:

- completely dispose of the spent pickling acid solution resulting from the etching of titanium alloys;

- eliminate environmental pollution by technogenic waste of neutralization of OCR with lime;

- restore from OTCR the pure salt of potassium hexafluorotitanate with a titanium content of 19.5%, which is widely used in the aluminum industry for the production of parts with high viscosity, fatigue strength;

- regenerate OCR with the release of expensive mineral acids that are not contaminated with alloying elements and titanium, which can be reused for etching titanium alloys;

- reduce the capital costs of facilities for the neutralization of pickling waste lime.

Claims (2)

1. The method of regeneration of spent pickling acid solutions formed during the processing of titanium alloys, including the recovery of titanium fluorides with alkali metal compounds, filtering and drying the titanium-containing salt obtained from the solution, characterized in that the titanium-containing salt is dried at a temperature of 30-60 ° C, and the filtrate additionally subjected to electrodialysis using ion-exchange membranes, after which mineral acids are returned to production, and hydroxides of alloying elements are used. 2. The method according to claim 1, characterized in that the utilization of the hydroxides of the alloying elements is carried out by reduction - aluminothermy method.