US3215611A - Process for deposition of fine grained deposits in the refining and reduction electrolysis of metals - Google Patents

Description

United States Patent 3,215,611 PROCES FOR DEPOSITION OF FINE GRAINED DEPOSITS IN THE REFINING AND REDUCTION ELECTROLYSIS 0F METALS Franz Pawlek and Hans-Wilhelm Lieber, Berlin, 5

and Wennemar Strauss, Dusseldorf-Holthausen, Germany, assignors to Dehydag Deutsche Hydrier- Werke, G.m.lJ.H., Dusseldorf, Germany, a corporation of Germany No Drawing. Filed July 16, 1963, Ser. No. 295,526 Claims priority, application Germany, July 20, 1962,

D 39,422 6 Claims. (Cl. 204-108) This invention relates to the electrorefining of heavy metals in electrolytic solutions.

It is known that electrochemical processes are employed for refining of heavy metals such as copper, nickel, zinc, and the like, wherein the raw metal is dissolved in the electrolytic bath from anodes and is deposited in pure form at the cathode. It is further known to subject solutions containing heavy metals to electrolysis using insoluble anodes, in order to deposit the metal to be recovered at the cathode. Both of these processes are widely employed, for instance, in the recovery of copper.

However, a number of difficulties arise in the cathode deposition process, and efforts have been made to overcome these difficulties. For this reason organic compounds are added to the electrolyte, such as glue, casein, polyvinyl alcohol, polyvinyl amides and the like. These additives produce a more favorable form of deposit due to a certain refinement of the grain size, but they have the disadvantage that they cause strong polarization, which requires substantial additional cost in energy for the metal depositions.

Another problem in the refinement and reduction electrolysis of copper is the formation of buds and dendrites Buds and dendrites very often produce short circuits which reduce the current yield and thereby at the same time increase the operating cost. The problem of reducing or completely eliminating the formation of buds and dendrites by the addition of organic products has also not yet been satisfactorily solved.

Finally, it is also of great practical importance that the recovered cathode metal, such as copper, have as low a content of impurities as possible, such as sulfur, nickel, arsenic, antimony, and the like, which are known to be caused by components contained in the electrolyte. This problem has heretofore also been inadequately solved.

It is, therefore, an object of our invention to provide a process for the electrorefining of metals wherein the metal is obtained in a high degree of purity.

A further object is to provide a process for electrorefining of metals wherein the metal obtained has a smooth surface and the structure is free from crystalline imperfections such as dendrites and buds.

Another object of our invention is to provide an electrorefining process which may be operated for longer periods without removing the deposited metal, and whereby thicker metal deposits may be obtained.

A further object is to provide an electrorefining process wherein additives are used which maintain good electric current efiiciency.

Another object is to provide an electrorefining process wherein the refined metal is in a directly utilizable form without remelting or other operations. 65

These and other objects of our invention will become apparent as the description thereof proceeds.

We have now made the surprising discovery that substantial improvements are made with respect to the above described shortcomings and therefore a very substantial 70 advance can be achieved by the addition of certain sulfur- 3,215,611 Patented Nov. 2, 1965 'ice containing organic compounds which comprise water-solubilizing and especially acid groups. These agents are particularly characterized in that they lead to a very fine grained copper deposit upon electrolysis and do not result in substantial polarization phenomena. The copper deposits are practically free from buds and dendrites. The remarkable aspect in connection with these organic products is, in addition, that despite their sulfur content they lead to copper deposits which are practically free from sulfur impurities and, as a rule, completely obviate the customary removal of sulfur from the cathodes.

The organic sulfur compounds used in accordance with the present invention comprise as the essential component the atom grouping in addition to the previously mentioned externally attached water-solubilizing groups, especially acid groups such as sulphonic acid groups, sulfuric and phosphoric acid ester groups or carboxylic acid groups; the essential atom grouping may occur in the molecule once or several times, and examples of typical representatives are the iso-thi-ourea group and dithiocarbamic acid ester group.

Compounds of this type may be represented by the general formula wherein G represents a carbon atom bonded exclusively to the hetero atoms oxygen, nitrogen and sulfur wherein the hetero atom connected to the R radical is a sulfur atom, R is a lower alkyl radical, and Z is a water solubilizing radical.

Compounds of this type may, for example, have the following structure Sulfonic acids of this structure are derived, for example, from di-thiocarbamic acids.

OSR-SO;H

Sulfonic acids which can be derived from Z-mercaptothiazols or Z-mercapto-benzthiazoles and thiocyanates have this structure.

G-SR-S0zMe These sulfonic acids are based upon corresponding 2- r. (3 thiobenzoxyazols and 2-thiocumazols (Z-thiobenzometoxazine).

C-S-R-SOaMe Sulfonic acids of this type are derivatives of carbaminothiol acids.

In the above formulas R represents an unsubstituted or substituted low molecular weight alkylene radical with preferably 2 or 3 carbon atoms. In place of the sulfonic acid radical there can also be a sulfuric acid radical or a carboxyl group or also another suitable water-solubilizing radical, especially, a polyethylene oxide radical or another water-solubilizing radical rich in oxygen. The unsatisfied valences of the nitrogen, oxygen and sulfur atoms are substituted with hydrogen to the extent that they are not connected with hydrocarbon radicals.

Compounds which are suitable for this purpose and which are without exception characterized by a carbon atom attached only to heteroat-oms and have also a sulfonic acid group include the following known substances: betaines of iso-thiourea-S-butane-w-sulfonic acid as well as of N-phenyl-isothiourea-S-propane-w-sulfonic acid and the like, 2-mercaptobenzthiazol-S-propane-w-potassium sulfonate, thiocyanic acid-S-n-propylester-w-sodium sulfonate, 2-thiobenzoxazol-S-propane-w-sodium sulfonate, 2- thiometoxazin-S-butane potassium sulfonate, N,N dimethyl-dithiocarbamic acid-n-propylester-w-sodium sulfonate, N,N-diethyl-dithiocarbamic acid-n-propylester-wsodium sulfonate, N,N-pentamethylene-dithiocarbamic acid-n-propylester-w-sodium sulfonate, N-butyl-dithiocarbamic acid-n-butylester-w-sodium sulfonate, N-p-tolyldithiocarbamic a-cid-n-propylester-w-potassium sulfonate, dithiocarbamic acid-n-propylester-ammonium sulfonate, carbaminothiol acid-n-propylester-potassium sulfonate, and the like.

Further suitable are the following:

N,N"-di-benzylthiocarbaminyl diethylenetriamine N'- dithiocarbonyl-S-propane-w-sulfonic acid copper, piperazine-N,N-bis-dithiocarbonyl-S propane w sodium sulfonate, N stearyl-dithiocarbaminyl-S-propane-w-sodium sulfonate, piperazine N,N' bis-dithiocarbonyl-S-sodium propionate, N phenylthio carbaminyl-piperazine-N'-dithiocarbonyl-S-propane-w-sulfonic acid copper, N,N"-dibenzylthiocarbaminyl-diethylenetriamine N dithiocarbonyl-S-propane-w-sodium sulfonate, and the like.

In the above mentioned products the first mentioned group is readily soluble in the electrolyte liquid, and the second mentioned group is difiicultly soluble. The low solubility gives rise to a particularly interesting technical embodiment in that it is possible to operate electrometallurgical baths which are self-regulating and in which the effective concentration of the additives is automatically adjusted by a gradual dissolution of the substances.

As a rule, from 1 mgm. to 20 gm./liter of electrolyte solution of the readily soluble substances are used, and the operating temperatures and current densities are in both cases those which are customary, that is, the bath is operated at temperatures from 40 to 80 C., preferably about 60 C. and at current densities of 1 to 3 amps./dm. preferably about 2 amps./dm If difficultly soluble products of the type described above are employed, they are added to the baths as solids which lie at the bottom, or they are introduced in suitable fashion in the electrolyte recycling line, for instance, with the aid of a filter.

After the desired thickness of metal at the cathode is obtained, the cathodes are removed from the baths, washed and further treated in customary fashion. A separate treatment of the cathodes for removal of the sulfur is not necessary.

In connection with these processes, it has often been found to be advantageous to add high molecular weight water-soluble products to the electrolyte for the purpose of further improvement of the cathodes. A synergistic effect is obtained thereby which results in particularly high quality cathode material.

Examples of additives of this type are: polyvinyl alcohol, polyacrylic esters, polyacrylamides, polymethacryl alcohols, -esters or -amides. Further suitable are condensation products of melamine, urea, dicyandiamide and the like with aldehydes such as formaldehyde, and aromatic sulfonic acids or ligninsulfonic acids, where 1-2 mols of melamine, dicyandiamide or urea as such or in admixture with each other are used with 4 to 10 mols of formaldehyde and 0.20l.6 mol of an aromatic sulfonic acid or ligninsulfonic acid. Finally, polyalkylene oxides, especially polyethylene oxide, polyalkyleneoxide addition products to high molecular weight compounds containing exchangeable hydrogen atoms attached through nitrogen, oxygen or sulfur, as well as glue, casein, starch, and starch derivatives, dipenta-erythrite, mannitol, sorbitol, dior polysaccharides, polyglycerine and the like may also be used for this purpose. The amounts of these additives correspond to the amounts which are customary in practice for these products and must be adapted to the working conditions from one case to the other as well known in the art. The method of operation of the refining or reduction electrolysis can be further improved by concurrently using known wetting agents in certain cases, that is, anion-active or electroneutral surfactant surfaces, such as alkyl sulfates, alkyl sulfonates, alkylarylsulfonates, alkylether sulfates, and the like.

The process may not only be applied to copper but also to electrorefining of other metals such as zinc, nickel, lead, silver, and the like.

The following specific examples are presented to illustrate the invention and to enable persons skilled in the art to better understand and practice the invention and are not intended to be limitative.

Example I The following Examples I to V1 are based on a technical copper refining electrolyte which contained per liter of bath fluid about 40 gm. of copper, 200 gm. of sulfuric acid, 15 gm. of nickel, 6 gm. of arsenic, 0.5 gm. of antimony, 1 gm. of iron, 0.5 gm. of zinc, 0.3 gm. of bismuth and 1 gm. of aluminum. At an electrode interval of 30 mm. and an electrolyte temperature of 58 C., the bath was operated at a cathode current density of 2 amps./dm. The anodes which were used were those with customary impurities, that is, which contain 98.7% copper, 0.05 lead, 0.55% nickel, 0.05% tin, 0.04% arsenic, 0.16% antimony and 0.016% iron. The cathode substrates were those of the customary type, that is, the type which are peeled off from the base sheets after a deposition period of 24 hours. One side exhibits the known pattern caused by glazing of the base sheets, and the other side exhibits a certain roughness.

When 4 mgm. of polyvinyl alcohol, 2 mgm. of a mixture of the sulfuric acid ester salt of an addition product of 5 mols of ethyleneoxide to 1 mol of a coconut fatty alcohol mixture C3-C13 and 20 mgm. of N,N-diethyldi thiocarbamic acid n-propylester-w-sodium sulfonate was added to the above electrolyte per liter of bath liquid, a completely smooth, fine-grained, dense copper deposit was obtained. The bath potential was only 132 mv. Undesirable side phenomena did not occur.

When the same electrolyte was used without any additive whatsoever, a rough copper deposit was obtained which exhibits pronounced buds as usual. The bath potential was -135 mv. When only 4 mgm./liter of polyvinyl alcohol were added to this bath, that is, if it was operated without the addition of the above dithiocarbamic acid ester sulfonate, a smooth but streaky copper deposit was obtained, which in addition exhibited round buds. The bath potential increases to about 170 mv. due to the addition of the polyvinyl alcohol, and therefore required an increased supply of energy.

Example 11 When 1-5 mgm. of glue, mgm. of an addition product of 10 mols of ethyleneoxide to 1 mol of nonylphenol and 10 mgm. of morpholinodithiocarbamic acid ethylester-wsodium sulfonate were added per liter of bath fluid to a copper refining electrolyte of the same basic composition as in Example I, a smooth, fine-grained, bud-free copper deposit was obtained with a constant bath potential of 135 mv.

Example III 4 mgm. of polyvinyl alcohol, mgm. of the addition product of 10 mols of ethyleneoxide to 1 mol of a coconut fatty alcohol mixture C -C and mgrn. of 1;,3,5 triazinyl 2,4,6-tris-(3'-mercapto-2-hydroxy-propane 1- sodium sulfonate) Were added to a copper refining electrolyte of the basic composition given in Example I, fine-grained, very smooth and bud-free copper cathodes were obtained at a bath potential of 132 mv. under the otherwise identical conditions as in Example I.

Example IV 4 mgm. of polyvinyl alcohol, 20 mgm. of the addition product of 10 mols of ethylene oxide to 1 mol of a coconut fatty alcohol mixture C C and in each of the following cases the indicated amounts of the additives according to the present invention, were added per liter of bath fluid to a copper refining electrolyte of the same basic composition as indicated in Example I.

(1) 20 mgm. of the betaine of isothiourea-S-propanew-SUlfOIllC acid (2) 15 mgm. of N,N-diethy1-dithiocarbamic acid ethylester-sodium carbonate (3) mgm. of 2-thiobenzthiazol-S-propane-sodium sulfonate (4) 100 mgm. of Z-thiobenzoxazol-S-propane-sodium sulfonate 6 (5) mgm. of N,N-diethyldithiocarbamic acid-S- propane-diol-2,3

( 2 5)2N-(|S-CHzCH(OH)-CH;OH

(6) 150 mgm. of N-ethylisothiourea-S-ethanol phosphoric acid ester-2 In all cases smooth, fine-grained and bud-free copper deposits, which represented excellent cathode copper, were obtained at a bath potential of -135 mv. under otherwise identical conditions as those indicated in Example I.

Example V A copper refining electrolyte of the same basic composition as that indicated in Example I, which contained in addition 3 mgm. of glue and 30 mgm. of the addition product of 10 mols of ethyleneoxide to 1 mol of a comnut fatty alcohol mixture C C per liter of bath fluid, was during its operation continuously pumped with a circulation rate of 0.05 bath volume per hour through a solution filter containing diflicultly soluble N-octadecyldithiocarbamic acid n-propyl-ester-w-sodium sulfonate in powder form, with and without admixture with inert extending agents or deposited thereon. By means of this arrangement the concentration of this dithiocarbamic acid ester sulfonate in the bath was maintained constant near the saturation limit. The copper deposited from this bath at a bath potential of mv. was marked by a particularly uniform crystalline structure.

Example VI When the insoluble additive used in Example V was, under otherwise identical conditions, replaced by an equally difiicultly soluble, powdered condensation product of 2.6 mols of epichlorohydrin, 1 mol of dipropylenetriamine, 3 mols of carbon disulfide, 1.5 mols of benzylchloride and 1.5 mols of propane sultone, smooth, fine-grained and bud-free copper deposits with completely uniform crystalline structure were obtained at a bath potential of 130 mv.

In the previously customary techniques of copper deposition, the cathodes still contain substantial amounts of impurities, even under optimum conditions, which are .primarily due to impurities in the electrolyte. Good copper cathodes, in the usual sense, contain per ton 25 gm. of sulfur, 25 gm. of nickel, 4 gm. of arsenic and 15 gm. of antimony among other impurities. The amounts of these impurities can be reduced by more than 50% by using the method of operation described in Examples I to V1, so that the conductivity of the copper is increased on the one hand and so that a continuous cathode melting procedure without intermediate refining steps can be employed on the other hand.

Example VII In the electrolytic refining of raw nickel anodes, a sulfuric acid electrolyte is employed which contains, for example, 40 gm. of nickel, 40 gm. "of sodium sulfate, 15 gm. of sodium chloride and 20 gm. of boric acid per 'liter. Using this electrolyte bath, at an electrolyte temperature of 60 C. and a cathode current density of 1.5 amps./dm.

and an electrode interval of 80 mm., smooth, soot-free deposits were achieved on electrolytically produced cathode substrates when, for example, 4 mgm. of polyvinyl alcohol, 20 mgm. of the addition product of 10 mols of ethyleneoxide to 1 mol. of a coconut fatty alcohol C C and 40 mgm. of triazinyl-2,4,6-tris-(3'-mercapto 2 hydroxy-propane 1 -sodium sulfonate) were added to the electrolyte per liter of bath fluid. Without these additives, rough cathodes covered with buds were obtained, which cannot be utilized in this form and must therefore be remelted.

Example VIII In the reduction electrolysis of zinc, a virtually neutral, very poor Zinc sulfate solution is subjected to electrolysis until the content of free acid becomes so great that the current yield drops too sharply.

An electrolyte of medium concentration generally contains about 100 gm. of zinc and 100 gm. of free sulfuric acid per liter. When such a solution was electrolyzed under customary conditions, for instance at 35 C., a cathode current density of 5 .5 amps./dm. and an electrode interval of 22 mm. and a bath potential of 3.1 v., a deposit was obtained on aluminum cathodes at a current yield of initially more than 90%, but the deposit soon became rough while the current yield steadily dropped off. Although colloids were added to the electrolyte, this dropping of the current yield could not be substantially delayed, so that the thin zinc deposits must be peeled off at frequent intervals, which requires much manual lab-or and a high degree of waste upon melting.

However, when 4 mgm. of polyvinyl alcohol, 20 mgm. of the addition product of mols of ethyleneoxide to 1 mol of a coconut fatty alcohol mixture (D -C and 30 mgm. of N,N-diethyldithiocarbamic acid n-propylester-wsodium sulfonate.

were added to such an electrolyte per liter of bath fluid, zinc cathodes of substantially improved consistency were obtained which did not require removal so frequently, so that the process could be performed substantially more economically.

Example 1X In the case of silver refining electrolysis, an electrolyte is used which contains, for instance, 20 gm. of silver in the form of the nitrate, about 13 gm. of free nitric acid and about 50 gm. of sodium nitrate per liter. Using this electnolyte, at an electrolyte temperature of 40 C., an electrode interval of 40 mm., a cathode current density of 5 amps./dm. and a cell potential of about 1.3 v., a very spongy deposit consisting of fine crystallites was obtained which soon caused short-circuits. When the electrolysis was performed in a wooden :cell, the deposit was also loose, but the arrangement of the crystallites was more dense. In order to obtain a compact, firmly adhering silver deposit from such refining electrolytes, it was possible to add gelatin to the electrolyte but the current density had to be considerably reduced at the same time.

However, if 4 mgm. of polyvinyl alcohol, 10 mgm. of an addition product of 10 mols of ethyleneoxide to 1, mol of nonylphenol and 20 mgm. of the betaine of isothioureawere added to such an electrolyte per liter of bath fluid, a smooth, compact, silver deposit was obtained on fine silver cathodes at 5 arnp-s./dm. and this deposit could be directly utilized.

Example X In the refining electrolysis of tin, the deposition of the metal from the stannous form, using a sulfuric acid electrolyte, is particularly economical. When tin was deposited on the cathode from such an electrolyte, which contained gm. of stannous sulfate and gm. of free sulfuric acid per liter, a loose deposit consisting of individual crystallites was obtained at about 35 C., a current density of 3 amps./dm. and a cell potential of about 1.2. v.

However, when 10 mgm. of an addition product of 10 mols of ethyleneoxide to 1 mol of a coconut fatty alcohol mixture C C 4 mgm. of polyvinyl alcohol and 50 mgm. of 2-thiobenzthiazol-S-propane-sodium sulfonate C-S-(CHQr-SOaNa s were added per liter to such an electrolyte, smooth, compact tin cathodes were obtained with good current yield.

Example XI In the electrolytic refining of lead, electrolytes are used to a large extent which contain about 50 gm. of lead in the form of silicofiuoride and 80 gm. of free fluorosilicic acid per liter. When leadvwas deposited on the cathode from such an electrolyte at 30 C. at a current density of 1.8 amps./dm. a coarse crystalline, jagged deposit was obtained which rapidly formed long dendrites particularly at the edges. Upon addition of gelatin the form of the deposit was more favorable, but the deposit was still rough and full of buds.

However, when 20 mgm. of an addition product of 5-12 mols of ethyleneoxide to 1 mol of a fatty alcohol mixture 0 43 4 mgm. of polyvinyl alcohol and 20 mgm. of morpholinodithiocarbamic acid ethylester-w.-sodium sulfonate per liter were added to such an electrolyte, smooth and dense cathode lead of high purity was obtained which could be directly utilized in this form.

While certain specific examples and preferred modes of practice of the invention have been set forth it will be understood that this is solely for the purpose of illustration and that various changes and modifications may be made without departing from the spirit of the disclosure and the scope of the appended claims.

We claim:

1. An electrorefining process for metals which comprises, electrolytically dissolving the crude metal to be refined as the anode in an electrolytic bath, said bath having additive compounds selected from the group consisting of compounds having the general structural formula and their salts, wherein G is an organic radical having a bivalent sulfur atom between R and a carbon atom, said carbon being bonded to a nitrogen atom and another atom selected from the group consisting of nitrogen, su lfur and oxygen, R is a bivalent saturated aliphatic radical containing two to four carbon atoms, and Z is a water solubilizing radical, and depositing said metal in a finegrain, purified state on a cathode substrate, said compound being added to said bath in a quantity suflicient to produce a purified and fine-grain metal deposit.

2. The process of claim 1 wherein the electrolytic bath comprises in addition surface active compounds selected from the group consisting of anionic and electroneutral surface active compounds.

3. An electrorefining process for metals which comprises, electrolytically dissolving the crude metal to be refined as the anode in an electrolytic bath, said bath having additive compounds selected from the group consisting of compounds having the general structural formula and their salts, wherein G is an organic radical having a bivalent sulfur atom between R and a carbon atom, said carbon being bonded to a nitrogen atom and another atom selected from the group consisting of nitrogen, sulfur and oxygen, R is a bivalent saturated aliphatic radical containing two to four carbon atoms, and Z is an acid water solubilizing radical, and depositing said metal in a fine-grain, purified state on a cathode substrate, said compound being added to said bath in a quantity sufficient to produce a purified and fine-grain metal deposit.

4. An electrorefining process for metals which comprises, electrolytically dissolving the crude metal to be refined as the anode in an electrolytic bath, said bath having additive compounds selected from the group consisting of compounds having the general structural formula and their salts, wherein G is an organic radical having a bivalent sulfur atom between R and a carbon atom, said carbon being bonded to a nitrogen atom and another atom selected from the group consisting of nitrogen, sulfur and oxygen, and R is a bivalent saturated aliphatic radical containing from two to four carbon atoms, and depositing said metal in a fine-grain, purified state on a cathode substrate, said compound being added to said bath in a quantity from about 1 mgm./l. to about 20 gm./liter.

5. An electrorefining process for metals which comprises, electrolytically dissolving the crude metal to be refined as the anode in an electrolytic bath, said bath having additive compounds selected from the group consisting of compounds having the general structural formula and their salts, wherein G is an organic radical having a bivalent sulfur atom between R and a carbon atom, said carbon being bonded to a nitrogen atom and another atom selected from the group consisting of nitrogen, sulfur and oxygen, said nitrogen, sulfur and oxygen atoms being further substituted by hydrocarbon radicals, R is a bivalent saturated aliphatic radical containing two to four carbon atoms, and Z is a water solubilizing radical, and depositing said metal in a fine-grain, purified state on a cathode substrate, said compound being added to said bath in a quantity sufiicient to produce a purified and finegrain metal deposit.

6. An electrorefining process for metals, said metals being selected from the group consisting of copper, nickel, zinc, silver, tin and lead, which comprises, electrolytically dissolving the crude metal to be refined as the anode in an electrolytic bath, said bath having additive compounds selected from the group consisting of compounds having the general structural formula and their salts, wherein G is an organic radical having a bivalent sulfur atom between R and a carbon atom, said carbon being bonded to a nitrogen atom and another atom selected from the group consisting of nitrogen, sulfur and oxygen, R is a bivalent saturated aliphatic radical containing two to four carbon atoms, and Z is a water solubilizing radical, and depositing said metal in a finegrain, purified state on a cathode substrate, said compound being added to said bath in a quantity suflicient to produce a purified and fine-grain deposit.

References Cited by the Examiner UNITED STATES PATENTS 2,769,775 11/50 Schloen 204-108 2,798,040 7/57 Pye 204l08 2,849,351 8/58 Gundel 204-49 2,853,444 9/58 Pye 204-108 2,892,760 6/59 Gundel 204-49 3,101,305 8/63 Roth 20452 OTHER REFERENCES Mantell: Electrochemical Engineering, 4th edition, 1960, McGraw-Hill, pages 79, 192-193, 142-145. (Copy in Scientific Library.)

JOHN H. MACK, Primary Examiner.

MURRAY TILLMAN, WINSTON A. DOUGLAS,

Examiners.

Claims (1)

1. AN ELECTROREFINING PROCESS FOR METALS WHICH COMPRISES, ELECTROLYTICALLY DISSOLVING THE CRUDE METAL TO BE REFINED AS THE ANODE IN AN ELECTROLYTIC BATH, SAID BATH HAVING ADDITIVE COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF COMPOUNDS HAVING THE GENERAL STRUCTURAL FORMULA