Patented Jan. 22, 1952 PREELECTROLYSIS EATMENT OF PICKLE LIQUOR John '1. Oliver, Berca, Ohio. 'assignor, by mesne assignments, to Union 'Garbide and Carbon fiorporation, a corporation of New York iNo'Drawing. Application March 25, 1947,
Serial No. 737,093
This in ention relates to the elect olysis of waste pick e liquor and to the treatment of'such liquor to prepare it for electrolysis, particularly electrolysis in a cell of the type shown in my copending application Serial No. 736,939, filed March 25, 19-l'7, wherein the pickle liquor is the electrolyte, and iron is plated from the electrolyte on a suitable cathode which maybe iron, or iron alloys, copper or any of the commonly-used starting materials for metal plating.
- Iron ispickled by treating it with a water solution of an acid (usually sulphuric acid or, less generally, hydrochloric or other acid) to which has been added an inhibitor, the latter prevent ing or materially decreasing the attack of the acid on the clean metal but allowing the acid to attack and remove scale. The Waste pickle liquor, after filtering to remove dirt, scale and other undissolved materials, contains residual pickling acid, the ferrous salt of the acid used and a small amount of inhibitor. When such a solution is electrolyzed to deposit iron at the cathode, it is difficult to prevent rough deposits and treeing, and to build up desirably thick plates of iron at relatively high cathode efficiency. I have found that the character of the plate may be improved in a very simple manner and with great ease and rapidity and that longer periods of satisfactory cell operation between cathode renewals may be obtained by chemically treating the waste liquor in such a manner as to destroy the corrosion-inhibiting properties of the inhibiting addition agent in the raw pickle liquor. It is not at all obvious that treating the pickle liquor to destroy the action of a benefactive additive (the pickling inhibitor) which assists in evening the pickling action of the acid on iron (essentially an electromechanical action) should be beneficial in another electrochemical action,
that is, the plating of iron. Nevertheless, and
more specifically, I have discovered that the desired results can be obtained by treating the pickle liquor before electrolysis with a small amount of nitrous acid, or of a nitrite which releases nitrous acid in the pickle liquor under the action of the free pickling acid present in the waste pickle liquor.
It appears that the nitrite or the nitrous acid very thoroughly removes or kills the inhibitor which is residual in the waste pickle liquor and that the inhibitor, unless removed, has a bad effect in the electrolysis of the pickle liquor making it difiicult to obtain a deposit in the form of a smooth, thick plate and to prevent treeing. By the removal or killing ofthe inhibitor is i A test for the sufficiency of the nitrite addition is to obse ve the evolution of hydrogen on a strip of iron placed in the liquor; before the addition of the nitrite ve y little hydrogen forms on the iron, whereas after such addition hydro en is evolved more copiously from the iron. The nitrite may be added in small increments to a sample of the liquor until a further addition of the nitrite does not increase the rate at which hydrogen is yielded on the iron. The main body of the liquor is then treated with a. proportionate amount of the nitrite. Smaller amounts of nitrite im rove the electrolysis over that obtained with no removal of inhibitor; and an excess of nitrite, at least in moderation, for instance up to 190%, appears to have no undesirable e ect' on the electrolysis. For the usual run of pickle liouors, 1 gram of sodium nitrite per gallon of pickle liquor has proven adequate, enabling the subsequent electrolysis to be efiected smoothly and efficiently after being properly started. This is about 0.7 gram of N02 per gallon of lquor whether the N02 be added as nitrous acid or a nitrite.
It is preferred to treat the pickle liouor with nitrites rather than nitrous ac d or its anhydride N203. If the nitrites which are used form precipitates in the liq or, for instance as the nitrites of barium and strontium form insoluble sulphates, advantage may be taken of this to remove the metal of the nitrite from the electrolyte Where the nitrites are those of metals such as sodium or potassium which neither precipitate nor plate out, the metals will remain in solution; whether or not such nitrites are to be used, depends upon the purity desi ed in the final products obtained from the solution. Nitrites of ammonia and similar non-metallic bases may also be used, ammonia, in particular, introducin'g no iorei'rn'matter into the final product. Organic "nitrites or nitrito-compounds or the nitroacids'as nitroacetic acid may be used.
The nitrites may be added to the liquor before or after it is filtered for pass-age into the cell. It is preferred, however. to add the nitrite to the raw liquor pri'or'to the filtration that precedes electrolysis and thus to remove any insoluble substances that might have been formed by the addition of the nitrite.
Inhibitors which are in frequent use today for commercial pickling are organic materials; and, while a number of them are proprietary products, typical organic inhibitors are those containing nitrogen, oxygen or sulphur and the other elements of groups 5 and 6 of the periodic table which can form onium compounds (of. Organic Inhibitors of Corrosion by Charles A. Mann, Transactions of The Electrochemical Society, vol. 69, page 115 (1936); also Organic Inhibitors of Corrosion by Mann, Lauer and Hultin, Industrial and Engineering Chemistry, vol. 28, pages 159 and 1048 (1936)). Organic compounds containing amino or amido (or imino or imido) nitrogen are excellent inhibitors, for instance protein materials as casein and animal glue or degraded protein materials or synthetic materials containing nitrogen of this type, for instance materials of the type of those mentioned in the articles previously noted. Excellent inhibitors are those containing both combined sulphur and nitrogen with or Without oxygen or the other elements of groups 5 and 6 of the periodic table which form onium compounds. These inhibitors are generally sulfonated organic compounds containing nitrogen, preferably in a plurality of basic or amino groups. The organic part of the inhibitor molecule may be of substantially any type but the molecules presenting long carbon chains are generally the preferred inhibitors. Amino organic acids or their esters or salts, preferably sulfonated, are excellent inhibitors as they contain combined nitrogen and, where sulfonated, also contain combined sulphur and oxygen in a relatively large molecule. At normal temperatures the inhibitors may be solids or liquids and they are preferably water-soluble or at least partially so. The present invention is principally concerned with inhibitors of any of the types mentioned which contain amino groups. Typical inhibitors of this type are those referred to in the articles as well as proprietary inhibitors containing amino groups and selling under such trade names as Rodine and Duponol.
Example vWaste sulphate pickle liquor which had been filtered to remove dirt, sludge and the like and which contained, per liter, about 80 grams of ferrous sulphate, 8 grams of free sulphuric acid, and 30 grams of ammonium sulphate and which had been treated with sodium nitrite in the proportion of 1 gram of the nitrite per gallon of liquor produced a good smooth non-treeing and non-ridged plate on the cathode of the cell shown in said patent application Serial No. 736,939, and plate thickness in excess of 4 inch was readily attainable. When the same liquor (except that it had not been treated with the nitrite) was electrolyzed in the same cell under exactly the same conditions, the plate was rough, characterized by numerous nodules and trees, the latter sufficiently well developed to give rise to local concentrations of current or even to short-circuits. Also continuous attention and frequent removal of deposit were required for cell operation with untreated liquor, as a deposit in excess of inch (usually much less) could not be obtained at cathode efiiciencies of 75% to 85% on continuous operation, which were obtained with the nitrite-treated liquor.
Though it is possible to electrolyze pickle liquor without killing the inhibitor and, by means of a special cell, for instance a Castner cell, recover the iron (of. Patent No. 2,389,691 to Schumacher and Heise) without the nitrite (or nitrous acid) treatment, iron does not plate from pickle liquor in the most advantageous manner unless the inhibitor is killed; and, although the inhibitors may be removedfrom pickle liquor in various other ways, the advantages of the present method are its low cost, effectiveness and simplicity.
The invention is susceptible of modification within the scope of the appended claims.
What is claimed is:
1. In the electrolytic recovery of iron from waste pickle liquor resulting from the commercial acid-pickling of iron in the presence of a pickling inhibitor, the step comprising electrodepositing iron on a cathode contacting an electrolyte; the electrolyte comprising the waste pickle liquor providing iron ions in aqeous solution for deposition by electrolysis and also comprising, as an addition agent, a member of the group consisting of nitrous acid, its salts and anhydride.
2. In the electrolytic recovery of iron from waste pickle liquor resulting from the commercial acid-pickling of iron in the presence of a pickling inhibitor, the step comprising electrodepositing iron on a cathode contacting an electrolyte; the electrolyte comprising the waste pickle liquor providing iron ions in aqueous solution for deposition by electrolysis and also comprising the reaction products of said pickling inhibitor and a member of the group consisting of nitrous acid, its salts and anhydride, the amount of reaction products corresponding, at least, to substantially complete reaction of the inhibitor.
3. In the electrolytic recovery of iron from waste pickle liquor resulting from the commercial acid-pickling of iron in the presence of a pickling inhibitor, the step comprising electrodepositing iron on a cathode contacting an electrolyte; the electrolyte comprising the waste pickle liquor providing iron ions in aqueous solution for deposition by electrolysis and also comprising the reaction products of said picklin inhibitor and a member of the group consisting of nitrous acid, its salts and anhydride, the amount of reaction products corresponding, at least, to substantially complete reaction of the inhibitor, the inhibitor being a material containing an element of groups 5 and 6 of the periodic table capable of forming an onium compound.
4. In the electrolytic recovery of iron from waste pickle liquor resulting from the commercial acid-pickling of iron in the presence of a pickling inhibitor, the step comprising electrodepositing iron on a cathode contacting an electrolyte; the electrolyte comprising the waste pickle liquor providing iron ions in aqueous solution for deposition by electrolysis and also comprising the reaction products of said pickling inhibitor and a member of the group consisting of nitrous acid, its salts and anhydride, the amount of reaction products corresponding, at least, to substantially complete reaction of the inhibitor, the inhibitor being an amine.
5. In the electrolytic recovery of iron from waste pickle liquor resulting from the commercial acid-pickling of iron in the presence of a pickling inhibitor, the step comprising electrodepositing iron on a cathode contacting an electrolyte, the electrolyte comprisin the waste pickle liquor providing iron ions in aqueous solution for deposition by electrolysis and also comprising, as an addition agent, a member of the group con- 5 sisting of nitrous acid, its salts and anhydride, and a free mineral acid.
6. Method of treating waste pickle liquor resulting from the commercial acid-pickling of iron in the presence of a pickling inhibitor to conditicn the liquor for electrolysis which comprises incorporating with the liquor an addition agent which is a member of the group consisting of nitrous acid, its salts and anhydride, the amount .of addition agent incorporated being sufiicient to materially increase the evolution of gas when iron is immersed in the pickle liquor containing the addition agent over the amount of gas evolved when iron is immersed in the pickle liquor containing none of said addition agent.
7. Method of treating waste pickle liquor resulting from the commercial acid-pickling of iron to condition the liquor for electrolysis, the liquor containing a nitrogenous corrosion-inhibitor, which comprises destroying the corrosioninhibiting properties of said inhibitor by addingto the liquor a member of the group consisting of nitrous acid, its salts and anhydride.
JOHN P. OLIVER.
6 REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 526,114 Placet et al Sept. 18, 1894 850,912 Edison Apr. 23, 1907 1,695,430 Klinger Dec. 18, 1928 1,922,853 Kissel Aug. 15, 1933 2,054,282 Clarkson et al Sept. 15, 1936 2,147,149 Clapsadle et a1 Feb. 14, 1939 2,306,471 Solomon Dec. 29, 1942 2,389,691 Schumacher et a1. Nov. 27, 1945 FOREIGN PATENTS Number Country Date 359,903 Great Britain Apr. 22, 1930 OTHER REFERENCES Holleman, edited by Jamieson and Walker, Textbook of Organic Chemistry, page 89, 5th edition, 1920.