RU2363666C2 - Method for oxidative decomposition of anion of 1-hydroxyethane-1,1-diphosphonic acid in water solution - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention refers to the methods for decontamination of the toxic wastes of galvanic and radioelectronic processes and can be used for neutralisation of the waste solutions of galvanic and chemical metal coatings (coppering, nickeling, zinking etc) containing the 1-hydroxyethane-1,1-diphosphonic acid anion. The oxidative decomposition of the said anion is carried out by its treatment with chrome (+6) compounds including the ones containing in the galvanic waste. In the preferable version chrome (+6) is used in the amount in the range from 0.5 to 5.0 moles for 0.1 mole of the of 1-hydroxyethane-1,1-diphosphonic acid anion containing in the waste solution of the electrochemical or chemical metal coating at pH less than 8.0.

EFFECT: claimed method allows to convert into orthophosphate more than 99% of 1-hydroxyethane-1,1-diphosphonic acid anion and to reduce the material cost of the toxic wastes decontamination.

9 cl, 8 ex

Description

The invention relates to methods for the neutralization of toxic waste from galvanic and electronic production and can be used to neutralize spent solutions for the deposition of galvanic and chemical coatings with metals that contain the anion of 1-hydroxyethane-1,1-diphosphonic acid as a ligand for binding the metal to the complex, and can also used to neutralize waste solutions containing chromium (+6).

Complex electrolytes and solutions containing the anion of 1-hydroxyethane-1,1-diphosphonic acid CH ₃ C (OH) (PO ₃ H ₂ ) ₂ as a ligand are used for applying high-quality coatings of copper, nickel, zinc, cadmium, noble and others metals (Haynes RT, Irani RR, Langguth RP US 3475293 (publ. 1969). Kowalski X. US 3706634 (publ. 1972). Kowalski X. US 3706635 (publ. 1972). Nobel FI, Yoen LC US 3833486 (publ. 1974) Kowalski X. US 3914162 (publ. 1975). Kowalski X. US 3928147 (publ. 1975). Mallory GO, Johnson CE DE 2942792 (publ. 1980). Tomaszewski LC, Tremmel RA US 4462874 (publ. 1984) Berezina S.I., Sageeva R.M., Amirov R.R. // Protection of metals, 1987, v.23, No. 6, p.1032. Gan Y. // Plating a nd Surface Finishing, 1992, V.79, No. 6, P. 81. Ratajewicz Z., Saneluta C. // Plating and Surface Finishing, 1999, V. 88, No. 7, P.50. Lvovsky V.M., Afonin E.G. RU 2276205 (publ. 2006). Lvovsky V.M., Afonin E.G. RU 2293144 (publ. 2007)). The anion of 1-hydroxyethane-1,1-diphosphonic acid is a low-toxic substance (Dyatlova N.M., Temkina V.Ya., Popov K.I. Complexes and complexonates of metals. - M .: Chemistry, 1988, p. 498), however, it binds metal cations into thermodynamically strong, water-soluble complexes, which prevents the precipitation of metal cations in the form of hydroxides and other water-insoluble compounds in the processes of reagent and physico-chemical cleaning of spent solutions. Therefore, the anion of 1-hydroxyethane-1,1-diphosphonic acid must be neutralized in spent solutions of electrochemical and chemical coatings with metals. One of the methods for neutralizing the anion of 1-hydroxyethane-1,1-diphosphonic acid is its oxidation to orthophosphate, which is non-toxic and does not bind metals to soluble complexes.

A known method of oxidative decomposition of the anion of 1-hydroxyethane-1,1-diphosphonic acid, comprising treating an aqueous solution containing the anion of 1-hydroxyethane-1,1-diphosphonic acid with ammonium peroxodisulfate in a sulfuric acid medium (Maklakova V.P., Zalozhkova K.I. . // Factory laboratory, 1975, t. 41, No. 8, p. 944). Oxidative decomposition to orthophosphate is carried out during the chemical analysis of the cooling water of thermal power plants.

A known method of oxidative decomposition of the anion of 1-hydroxyethane-1,1-diphosphonic acid, comprising treating an aqueous solution containing the anion of 1-hydroxyethane-1,1-diphosphonic acid with a 4% solution of potassium permanganate at room temperature or by boiling the solution (Martynov A.P., Gorodetsky V.I. Collection of "Modern methods of analysis of industrial materials and natural objects. Materials of a scientific and technical short-term seminar. Society" Knowledge. Leningrad DNTP, 1992, part 1, p.46). Oxidative decomposition to orthophosphate is carried out during chemical analysis of the electrolyte coating with zinc-iron alloy containing 0.1-0.4 g / l of 1-hydroxyethane-1,1-diphosphonic acid anion. The disadvantage of this method is the need for high material costs for the reagent-oxidizing agent potassium permanganate.

Closest to the claimed method is the oxidative decomposition of the anion of 1-hydroxyethane-1,1-diphosphonic acid, comprising treating an aqueous solution containing the anion of 1-hydroxyethane-1,1-diphosphonic acid with an oxidizing reagent, which uses hydrogen peroxide, the presence of a catalyst - vanadium (+5) (Appelman EH, Jache AW, Muntean JV The vanadium (V) -catalyzed oxidation of (1-hydroxyethylidene) bisphosphonic acid,

CH ₃ C (OH) (PO ₃ H ₂ ) ₂ , by hydrogen peroxide in aqueous solution. // Journal of Molecular Catalysis A: Chemical, 1996, V.106, P.197). The prototype method is based on the reactions:

CH ₃ C (OH) (PO ₃ H ₂ ) ₂ + 2H ₂ O ₂ → CH ₃ COOH + 2H ₃ PO ₄ + H ₂ O;

CH ₃ C (OH) (PO ₃ H ₂ ) ₂ + 5H ₂ O ₂ → HCOOH + CO ₂ + 2H ₃ PO ₄ + 5H ₂ O;

CH ₃ C (OH) (PO ₃ H ₂ ) ₂ + 6H ₂ O ₂ → 2CO ₂ + 2H ₃ PO ₄ + 7H ₂ O.

Oxidation of the anion of 1-hydroxyethane-1,1-diphosphonic acid is carried out at a temperature of 50-80 ° C, the optimal pH value of 1.0. The oxidation of 1 mole of 1-hydroxyethane-1,1-diphosphonic acid anion requires about 4 moles of hydrogen peroxide. The disadvantage of this method is the need for high material costs for hydrogen peroxide and for the catalyst, as well as for heating the reaction solution. Another disadvantage of this method is the unproductive expenditure of the oxidizing reagent as a result of its catalytic disproportionation:

2H ₂ O ₂ → 2H ₂ O + O ₂ .

The method does not provide for the oxidative decomposition of the anion of 1-hydroxyethane-1,1-diphosphonic acid in the composition of the spent solutions of electroplating and chemical coatings with metals, and also does not provide for the use of industrial wastes for the oxidative decomposition of the anion of 1-hydroxyethane-1,1-diphosphonic acid.

The aim of the claimed invention is to develop a method for decomposing the anion of 1-hydroxyethane-1,1-diphosphonic acid in spent solutions of electrochemical and chemical coating with metals by oxidation to orthophosphate, reducing material costs for the neutralization of toxic waste from galvanic production and production of printed circuit boards.

The goal is achieved in that the method of oxidative decomposition of the anion of 1-hydroxyethane-1,1-diphosphonic acid in an aqueous solution involves treating an aqueous solution containing the anion of 1-hydroxyethane-1,1-diphosphonic acid with an oxidizing reagent. New in this method is that the aqueous solution is a liquid waste product - a spent solution of an electrochemical coating with metal or a spent solution of a chemical coating with metal, and the oxidizing reagent is chromium (+6). As a source of chromium (+6), it is desirable to use liquid waste from galvanic production, in particular, a spent solution of electro-polishing of steel, which contains chromium (+6), chromium (+3), sulfuric acid, and phosphoric acid as the main components. The spent metal electrochemical coating solution is, for example, a spent galvanic copper plating solution containing copper (+2) as the main components, a 1-hydroxyethane-1,1-diphosphonic acid anion, or a spent galvanizing solution containing zinc as the main components (+2), anion of 1-hydroxyethane-1,1-diphosphonic acid. The spent solution of a chemical coating with metal is, for example, a spent solution of chemical copper plating, containing as the main components

copper (+2), anion of 1-hydroxyethane-1,1-diphosphonic acid, a reducing agent, an oxidation product of a reducing agent, or a spent chemical nickel solution containing nickel (+2), anion of 1-hydroxyethane-1,1- as the main components diphosphonic acid, a reducing agent, a product of the oxidation of a reducing agent. It is desirable to treat with chrome (+6) the spent solution of the electrochemical or chemical coating with metal at a pH below 8.0, and it is desirable to add chromium (+6) in an amount of 0.5 to 5.0 mol per 1.0 mol of 1-hydroxyethane anion -1,1-diphosphonic acid.

The method of oxidative decomposition of the anion of 1-hydroxyethane-1,1-diphosphonic acid consists in mixing spent solutions of an electrochemical or chemical coating with metals, which contain metal complexes with the anion of 1-hydroxyethane-1,1-diphosphonic acid, with chromium compounds (+6) which use solid reagents (for example, chromium trioxide, dichromates of potassium, sodium, ammonium), aqueous solutions of these substances or spent chromium (+6) containing solutions of various compositions (liquid chromium waste steel, electro-polishing of steel, chemical oxidation of aluminum, zinc chromating and other technological processes).

The claimed method is based on reactions, for example:

3CH ₃ C (OH) (PO ₃ H ₂ ) ₂ + 2K ₂ Cr ₂ O ₇ + 8H ₂ SO ₄ → 3CH ₃ COOH +

6H ₃ PO ₄ + 2Cr ₂ (SO ₄ ) ₃ + 2K ₂ SO ₄ + 5H ₂ O;

3CH ₃ C (OH) (PO ₃ HNa) ₂ + 4CrO ₃ + 12HCl → 3CH ₃ COOH +

6NaH ₂ PO ₄ + 4CrCl ₃ + 3H ₂ O;

3CH ₃ C (OH) (PO ₃ H ₂ ) ₂ + 10CrO ₃ + 15H ₂ SO ₄ → 3HCOOH + 3CO ₂ +

6H ₃ PO ₄ + 5Cr ₂ (SO ₄ ) ₃ + 15H ₂ O;

3K ₆ [Cu (CH ₃ C (OH) (PO ₃ ) ₂ ) ₂ ] + 4Na ₂ Cr ₂ O ₇ + 28H ₂ SO ₄ → 3CuSO ₄ +

6CH ₃ COOH + 12H ₃ PO ₄ + 4Na ₂ SO ₄ + 9K ₂ SO ₄ + 4Cr ₂ (SO ₄ ) ₃ + 10H ₂ O;

3Na ₂ [Ni (CH ₃ C (OH) (PO ₃ H) ₂ ) ₂ ] + 4Na ₂ Cr ₂ O ₇ + 22H ₂ SO ₄ → 3NiSO ₄ +

6CH ₃ COOH + 12H ₃ PO ₄ + 7Na ₂ SO ₄ + 4Cr ₂ (SO ₄ ) ₃ + 10H ₂ O.

According to experimental data, about 1.5 moles of chromium (+6) go to the complete oxidation of 1.0 mol of the anion of 1-hydroxyethane-1,1-diphosphonic acid to orthophosphate. If less than 0.5 mole of chromium (+6) is added per 1.0 mole of 1-hydroxyethane-1,1-diphosphonic acid anion, the degree of oxidative decomposition may not be high enough. In addition, with a lack of chromium (+6), oxidation can stop at the stage of formation of acetylphosphonic acid:

which is undesirable. With an excess of chromium (+6), oxidation to orthophosphate occurs:

When more than 5.0 moles of chromium (+6) are added per 1.0 mol of the anion of 1-hydroxyethane-1,1-diphosphonic acid, the rate increases and the duration of the oxidation reaction decreases, but an excess of chromium (+6) that is not consumed in the oxidation reaction must be neutralized by conversion to chrome (+3) and precipitation. Therefore, chromium (+6) is preferably added in an amount of from 0.5 to 5.0 mol per 1.0 mol of anion 1-hydroxyethane-1,1-diphosphonic acid.

As follows from the equations of oxidation reactions of the anion of 1-hydroxyethane-1,1-diphosphonic acid with chromium (+6), the conversion of the anion of 1-hydroxyethane-1,1-diphosphonic acid into orthophosphate is accompanied by the consumption of hydrogen ions (acids). In addition, according to experimental data, the reaction rate of the anion of 1-hydroxyethane-1,1-diphosphonic acid with chromium (+6) decreases with increasing pH. Therefore, it is desirable to treat with chromium (+6) the spent solution of the electrochemical or chemical coating with metal at a pH below 8.0. As a source of hydrogen ions, various mineral acids can be used, for example, sulfuric, hydrochloric, nitric, tetrafluoroboric, hexafluorosilicic, sulfamic, orthophosphoric.

Solid reagents, for example, chromium trioxide GOST 2548-77, potassium chromate GOST 4459-75, sodium dichromate dihydrate GOST 2651-78, potassium dichromate GOST 2652-78, ammonium dichromate GOST 3763 can be used as a source of chromium oxidizing agent (+6) -76 grades of "h", "chda", "hch" or technical quality. Chromium trioxide, chromates and dichromates of alkali metals, ammonium are soluble in water, therefore, aqueous solutions of these substances can be used as a source of oxidizing reagent. As a source of chromium (+6), it is desirable to use chromium (+6) containing industrial wastes, for example, spent solutions of chromium plating of steel, copper, zinc, aluminum, spent solutions of electro polishing of steel and aluminum, a spent solution of chemical oxidation of aluminum, a spent solution of zinc chromating ( GOST 9.305-84, Metallic and non-metallic inorganic coatings - Operations of technological processes for producing coatings - M .: IPK Publishing House of Standards, 2003. Smirnov DN, Genkin VE, Cleaning of sewage water in the processing of metals. - M .: Metallurgy, 1989. Kudryavtsev NT Electrolytic coating with metals. - M: Chemistry, 1979). In particular, the spent solution of electro polishing of steel and aluminum has the composition:

Chromium Trioxide (+6) 40-160 g / l Chromium Sulphate (+3) 50-170 g / l Sulphuric acid 100-550 g / l Orthophosphoric acid 500-1100 g / l

and can serve as a source of not only chromium (+6), but also acid, which can further reduce the material costs of neutralizing production waste.

Spent solutions of electrochemical coating with metals (copper, zinc, nickel, iron, cobalt, cadmium, tin, lead, antimony, silver, gold, platinum group metals) contain the metal compound and the 1-hydroxyethane-1,1-diphosphonic anion as the main components acids, for example:

Copper Sulfate (+2) 0.1-0.5 mol / L Potassium or sodium 1-hydroxyethane-1,1-diphosphonate 0.1-2.0 mol / L pH 6-13,

or

Zinc Sulfate (+2) 0.05-0.5 mol / l Potassium or sodium 1-hydroxyethane-1,1-diphosphonate 0.1-2.0 mol / L Organic supplement 0.001-1.0 mol / L pH 6-13.5.

Spent chemical coating solutions with metals (copper, nickel, iron, cobalt, silver, gold, platinum, palladium) also contain a metal compound, the anion of 1-hydroxyethane-1,1-diphosphonic acid and additionally include a reducing agent and oxidizing products of a reducing agent, for example:

Copper Sulfate (+2) 0.01-0.1 mol / L Potassium 1-hydroxyethane-1,1-diphosphonate 0.1-0.3 mol / L Formaldehyde 0.1-1.0 mol / L Sodium formate 0.10-2.0 mol / L pH 4-14,

or

Nickel Chloride (+2) 0.01-0.2 mol / L Potassium 1-hydroxyethane-1,1-diphosphonate 0.1-0.4 mol / L Sodium Hypophosphite 0.05-0.2 mol / L Sodium phosphite 0.1-1.0 mol / L Sodium Acetate 0.0-0.2 mol / l pH 2-7,

or

Nickel Chloride (+2) 0.01-0.2 mol / L Sodium 1-hydroxyethane-1,1-diphosphonate 0.1-0.4 mol / L Sodium borohydride 0.1-0.3 mol / L Sodium borate 0.1-1.0 mol / L Hydroxide and Sodium Carbonate 0.2-2.0 mol / L pH 10-14.

The reaction between chromium (+6) and the anion of 1-hydroxyethane-1,1-diphosphonic acid proceeds at a rather high rate even at room temperature. To increase the speed, an oxidation reaction can be carried out at elevated temperature; the consumption of chromium (+6) remains the same.

Example 1

100 ml of the spent solution of galvanic copper plating of steel with a concentration of copper (+2) 0.45 mol / l, 1-hydroxyethane-1,1-potassium diphosphonate 1.02 mol / l (pH 9.2) is mixed with 230 ml 10% - aqueous solution of potassium dichromate and with stirring, concentrated sulfuric acid is added until a pH of 0.1 is reached. The solution is left to stand at room temperature for 10 days. The conversion of 1-hydroxyethane-1,1-diphosphonic acid anion to orthophosphate is 98.5%. 1.43 moles of chromium (+6) are consumed for the oxidation of 1.0 mol of the anion of 1-hydroxyethane-1,1-diphosphonic acid.

Example 2

To 100 ml of the spent solution of electrochemical galvanizing of steel with a concentration of zinc (+2) 0.11 mol / L, 1-hydroxyethane-1,1-potassium diphosphonate 0.25 mol / L (pH 8.2), 57 ml of spent a solution of electro polishing of steel with a concentration of chromium (+6) 45.8 g / l, chromium (+3) 15.4 g / l, sulfuric acid 250 g / l, phosphoric acid 950 g / l. The solution is left to stand at a temperature of 28-30 ° C for 5 days. The conversion of 1-hydroxyethane-1,1-diphosphonic acid anion to orthophosphate is 98.0%. The oxidation of 1.0 mole of 1-hydroxyethane-1,1-diphosphonic acid anion requires 1.55 moles of chromium (+6).

Example 3

To 100 ml of the spent solution of electrochemical copper plating of steel with a concentration of copper (+2) 0.38 mol / L, potassium 1-hydroxyethane-1,1-diphosphonate 0.98 mol / L (pH 9.0), 150 ml of the spent a solution of electro polishing of steel with a concentration of chromium (+6) 54 g / l, chromium (+3) 12.1 g / l, sulfuric acid 265 g / l, phosphoric acid 980 g / l. The solution is left to stand at room temperature for 10 days. The conversion of the 1-hydroxyethane-1,1-diphosphonic acid anion to orthophosphate is 97.5%. The oxidation of 1.0 mole of 1-hydroxyethane-1,1-diphosphonic acid anion requires 1.44 moles of chromium (+6).

Example 4

Mix 100 ml of the spent solution of electrochemical galvanizing of steel with a concentration of zinc (+2) 0.10 mol / l, 1-hydroxyethane-1,1-potassium diphosphonate 0.24 mol / l (pH 8.5) and 402 ml of the spent chemical solution oxidation of aluminum with a concentration of chromium (+6) 5.4 g / l, chromium (+3) 3.2 g / l, ammonium hydrofluoride 1.8 g / l, potassium hexacyanoferrate (III) 0.8 g / l. To the resulting solution were added 100 ml of concentrated hydrochloric acid and the solution was allowed to stand at a temperature of 25-28 ^{° C} for 25 days. The degree of conversion of the 1-hydroxyethane-1,1-diphosphonic acid anion to orthophosphate is 79.0%. The oxidation of 1.0 mole of 1-hydroxyethane-1,1-diphosphonic acid anion requires 1.06 mole of chromium (+6).

Example 5

Mix 100 ml of the spent solution of electrochemical galvanizing of steel with a concentration of zinc (+2) 0.10 mol / l, 1-hydroxyethane-1,1-potassium diphosphonate 0.24 mol / l (pH 8.5), 402 ml of the spent chemical solution oxidation of aluminum with a concentration of chromium (+6) 5.4 g / l, chromium (+3) 3.2 g / l, ammonium hydrofluoride 1.8 g / l, potassium hexacyanoferrate (III) 0.8 g / l and 60 ml of concentrated sulfuric acid. The resulting solution for 1 hour is kept at a temperature of 96-100 ° C. The conversion of 1-hydroxyethane-1,1-diphosphonic acid anion to orthophosphate is 99.4%. The oxidation of 1.0 mole of 1-hydroxyethane-1,1-diphosphonic acid anion requires 1.51 mole of chromium (+6).

Example 6

In 100 ml of a spent solution of chemical copper plating with a concentration of copper (+2) 0.005 mol / l, potassium 1-hydroxyethane-1,1-diphosphonate 0.15 mol / l, formaldehyde 0.05 mol / l, potassium formate 0.35 mol / l (pH 12.5), 9.5 g of potassium dichromate are dissolved and concentrated nitric acid is added with stirring until a pH of 0.5 is reached. The solution is left to stand at room temperature for 5 days. The conversion of the 1-hydroxyethane-1,1-diphosphonic acid anion to orthophosphate is 99.5%. The oxidation of 1.0 mol of the anion of 1-hydroxyethane-1,1-diphosphonic acid consumes 1.45 mol of chromium (+6).

Example 7

In 100 ml of a spent solution of chemical nickel plating with a concentration of nickel (+2) 6.1 g / l, sodium hypophosphite 7.0 g / l, sodium phosphite 35 g / l, 1-hydroxyethane-1,1-diphosphonate (2-) sodium 30 g / l with stirring, dissolve 7.5 g of sodium dichromate dihydrate and with stirring add 12 ml of concentrated sulfuric acid. The resulting solution is kept at a temperature of 80-90 ° C for 6 hours. The conversion of 1-hydroxyethane-1,1-diphosphonic acid anion to orthophosphate is 99.5%. The oxidation of 1.0 mol of the anion of 1-hydroxyethane-1,1-diphosphonic acid consumes 1.51 mol of chromium (+6).

Example 8

100 ml of the spent chemical nickel plating solution are mixed with a nickel concentration of (+2) 0.061 mol / L, sodium hypophosphite 0.049 mol / L, sodium phosphite 0.21 mol / L, potassium 1-hydroxyethane-1,1-diphosphonate 0.20 mol / l, sodium acetate 0.15 mol / l and 100 ml of the spent solution of electro polishing of steel with a concentration of chromium (+6) 45.8 mol / l, chromium (+3) 15.4 g / l, sulfuric acid 250 g / l, phosphoric acid 950 g / l. The resulting solution was left to stand at room temperature for 3 days. The conversion of 1-hydroxyethane-1,1-diphosphonic acid anion to orthophosphate is 96.5%. 1.38 moles of chromium (+6) are consumed for the oxidation of 1.0 mole of 1-hydroxyethane-1,1-diphosphonic acid anion.

As can be seen from the above examples, the claimed method allows the decomposition of more than 99% of the anion of 1-hydroxyethane-1,1-diphosphonic acid contained in spent solutions of electrochemical and chemical coating with metals by oxidation to non-toxic products - orthophosphoric and acetic (formic) acids. At the same time, both chromium compounds (+6) and production waste - spent solutions containing chromium (+6) can be used as an oxidizing reagent. Material costs are significantly reduced due to the mutual neutralization of two types of liquid production waste.

Claims (9)

1. The method of oxidative decomposition of the anion of 1-hydroxyethane-1,1-diphosphonic acid in an aqueous solution, comprising treating an aqueous solution containing the anion of 1-hydroxyethane-1,1-diphosphonic acid with an oxidizing reagent, characterized in that the aqueous solution is liquid production waste - spent solution of electrochemical coating with metal or spent solution of chemical coating with metal, and the oxidizing reagent is chromium (+6). 2. The method according to claim 1, characterized in that chromium (+6) is part of the liquid waste of galvanic production. 3. The method according to claim 2, characterized in that the liquid waste of galvanic production is a spent solution of electric polishing of steel, containing chromium (+6), chromium (+3), sulfuric acid, orthophosphoric acid as the main components. 4. The method according to claim 1, characterized in that the spent metal electrochemical coating solution is a spent electroplating copper plating solution containing copper (+2), the anion of 1-hydroxyethane-1,1-diphosphonic acid as the main components. 5. The method according to claim 1, characterized in that the spent solution of the electrochemical coating of metal is a spent solution of galvanic galvanizing containing zinc (+2), the anion of 1-hydroxyethane-1,1-diphosphonic acid as the main components. 6. The method according to claim 1, characterized in that the spent solution of a chemical coating with metal is a spent solution of chemical copper plating, containing copper (+2), anion of 1-hydroxyethane-1,1-diphosphonic acid, a reducing agent, a product as the main components oxidation of the reducing agent. 7. The method according to claim 1, characterized in that the spent chemical coating solution with metal is a spent chemical nickel plating solution containing nickel (+2), 1-hydroxyethane-1,1-diphosphonic acid anion, reducing agent, product as main components oxidation of the reducing agent. 8. The method according to claim 1, characterized in that chromium (+6) is added in an amount of from 0.5 to 5.0 mol per 1.0 mol of anion of 1-hydroxyethane-1,1-diphosphonic acid contained in the spent solution electrochemical or chemical metal coating. 9. The method according to claim 1, characterized in that the chromium (+6) treatment of the spent solution of the electrochemical or chemical coating with a metal is carried out at a pH below 8.0.