Simultaneous Electrodeposition of Copper and lead from Nitric Acid-Hydrofluoric Acid-Beryllium Nitrate Solution CHARLES GOLDBERG New E n g l a n d S m e l t i n g Works, I n c . , West S p r i n g f i e l d , Mass.
suggested the electrodeposition of copper in brasses M CKAY containing tin from a nitric-hydrofluoric acid solution. (2)
Results were somewhat high because of hydrofluoric acid attack upon the platinum anode and subsequent plating of the platinum upon the cathode (the average deposition of platinum on the cathode was 0.5 mg.). Re-solution of the cathodic deposit and electrolysis from a nitric-sulfuric acid solution was necessary to secure quantitative results. McKay also noted that when lead was present the lead dioxide deposit was always contaminated with some form of fluorine, and a second plating from nitric acid solution had to be made. Ravner ( 4 ) confirmed these findings for manganese bronze and suggested conditions under which the hydrofluoric acid attack upon the anode was lessened (0.1 mg.). Xorwits (3) replaced the hydrofluoric acid with phosphoric acid, eliminating the platinum contamination, and excellent copper results were secured. However, lead peroxide deposits only partially or not a t all in the presence of phosphoric acid.
Table 1. Electrolytic Copper and Lead Results from Various Electrolytes Copper Taken, Mg. 888.0 767.0 813.0 890.0 650.0 746.0
I n HNO, 879.6 767.2 813.0 890.2 649.8 745.9
Lead, Mg. 43.80 43.80 43 80 AY. P b
43.81 43.80 43.82 43.80
Lead, M g . 68.50 68.50 68.50 Av. P b
68.45 68.47 68.51 68.47
Found, Mg. In HNOrHF 881.0 767.8 813.7 890.9 650.8 746.9
46.80 47.34 48.00 17.38 71.70 71.20 71.41 71.43
I n HNOa-HF-Be 880.1 767.0 813.1 890.2 650.0 746.1
+
43.90 44.00 43.80 43.90
followed by 1.0 ml. of 10% sulfamic acid as a depolarizer (8) and 1 drop of 0.1 N hydrochloric acid ( 5 ) . The electrolysis was continued for another 30 minutes, and the completion of copper deposition checked by raising the water level and noting any additional copper deposition on the previously unexposed portion of the cathode. After electrolysis, the electrodes were removed from the solution, and a beaker containing 200 ml. of distilled water was quickly substituted. The electrodes were rinsed in two successive containers of ethanol and dried in an oven a t 110’ C.the copper for 2 minutes, the lead dioxide for 30 minutes. They were cooled in a desiccator and weighed. After weighing, they were stripped in 40y0 nitric acid to which a few drops of 3% hydrogen peroxide solution had been added and f i e d over a burner to red heat. They were then cooled to room temperature in a desiccator and reweighed. Results for copper and lead are shown in Table I. DISCUSSION
It was found that the beryllium nitrate must be dissolved in the nitric acid, rather than added to the solution of the sample. The accuracy of copper and lead determinations under the proposed conditions was further checked with National Bureau of Standard samples and the results were averaged, as shown in Table 11. The empirical factor for lead in lead peroxide was determined by electrolysis in nitric acid solution of 12 samples of lead previously estimated by the molybdate method (7) and waa found to be 0.8621.
Table 11. Electrolytic Copper and Lead Results from Nitric-Hydrofluoric-Beryllium Electrolyte Copper Present (Certificate Value),
68.60 68.55 68.51 68.55
Feigl and Schaeffer ( 1 ) have noted the avidity with which beryllium ion forms fluoberyllate (BeF4--), even to taking the fluorine from complexes formed by aluminum, iron, boric acid, and zirconium. I t was also noted by them that lead fluoride dissolves in an excess of beryllium nitrate solution. It seemed pqssible, then, that the presence of sufficient beryllium ion might prevent the deposition of some form of fluorine on the anode, and experiments were conducted to explore that possibility. EXPERIMENTAL
Various amounts of C.P. analyzed lead nitrate were weighed and corrected for stated impurities. The actual lead contained was determined by the molybdate method (6). Weighed amounts of lead-free, precipitated copper were used. Individual samples were dissolved in 10.0 ml. of C.P. 1 to 1 nitric acid, or i n 10.0 ml. of C.P. 1 to 1nitric acid in which 1.0 gram of beryllium nitrate was dissolved plus 1.0 ml. of hydrofluoric acid, or in 10.0 ml. of C.P. 1 to 1 nitric acid plus 0.5 ml. of C.P. 48y0 hydrofluoric acid. The use of a n insufficient amount of hydrofluoric acid may result in reprecipitation of the tin due t o beryllium ion reduction of the fluoride concentration. Beakers of 96% silicate glass were used to minimize glass attack by the hydrofluoric acid and the platinum anode was rotated. The electrolyses were commenced a t room temperature. Volume of the sample was 200 ml., and 2 amperes were used. After 30 minutes, 0.5 ml. of C.P. 1 to 1 sulfuric acid was added,
a
Sample NBS 63aa containing 9.76% Sn Av.
% 78.48
NBS 37d containing 0.97% Sn
70.78
Cu Found,
%
78.50 78.51 78.47 78.49
70.80 70.81 70.77 AY. 70.79 0.5-Gram sample t o prevent PbOn flaking.
Pb Present (Certificate Value),
%
Pb Found,
9%
8.92
8.91 8.93 8.90 8.913
0.94
0.94 0.95 0.94 0.943
Drying the lead dioxide plate a t a higher temperature than 110’ C. did not affect results, in agreement with Ravner ( 4 ) . The determination of lead by the molybdate method was found to be more accurate and consistent than the sulfate method (6). The toxic properties of beryllium compounds should be remembered and the usual precautions taken. LITERATURE CITED
(1) Feigl, F., and Schaeffer, A., ASAL. CHEM., 23, 351-3 (1951). (2) McKay, L. W., J . Am. Chem. SOC.,36, 2375-81 (1914). (3) Norwitz, G., ANAL. CHEM., 21, 523-5 (1949). (4)Ravner, H., IND.ENG. CHEM., ANAL.ED., 17, 41-3 (1945). (5) Scherrer, J. A., Bell, R. K., and Mogerman, W. D., J . Research Natl. BUT.Standards, 22, 697 (1939). (6) Scott, W. W., “Standard Methods of Chemical Analysis,” 5th ed., pp. 504-5, New York, D. Van Nostrand Co.,1939. (7) Ibid., p. 506. (8) Silverman, L., IND. ENG.CHEM., ANAL.ED., 17, 270 (1945). RECEIYED for review January 12, 1953. Accepted M a y 13, 1953.
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