A N A L Y T I C A L CHEMISTRY
826 ACKNOWLEDGMENT
The authors wish to express their indebtedness to Milton Orchin for making the complexes available and to those who have prepared some of the compounds; their names may be found in the bibliography. Leslie Reggel assisted greatly with preparation of the manuscript.. LITERATURE CITED
(1) Frevel, L.K.,and Anderson, H. C., Acta C r y s t . , 4,186 (1951). 12) Hanawalt, J. D.,Rinn, H. W., and Frevel, L. K., IND. ENQ. CHEM.,ANAL.ED.. 10,457 (1938). (3)Hofer, L. J. E., and Peebles, W. C., ANAL. CHEM.,23, 690 ( 1951).
Hofer, L. J. E., Peebles, W. C.,and Guest, P. G., Ibid., 22, 1218 (1950). McKinley, J. B.,Nickels, J. E.,and Sidhu, S., IND.ENQ.CHEM.. ANAL.ED., 16, 304 (1944). Orchin, M., unpublished work. Orchin, M., and Friedel, R. A., J . Am. Chem. SOC.,71, 3002 (1949). Orchin, M., and Reggel, L.! Ibid., 69,505 (1947). Ibid., 73,436 (1951). Orchin, M., and Reggel, L., unpublished werk. Orchin, >I., Reggel, L., and Woolfolk, E. 0.. J. Am. Chem. S o . , 69, 1225 (1947). Orchin, M., and Wender, I., unpublished work. Orchin, &I., and Woolfolk, E. O., J. Am. Chem. Soc.. 68, 1727 (1946). RECEIVED for review November
14. 1951.
-4ccepted February 6. IS52
Separation of Manganese from Aqueous Using a Mercury Cathode BRUCE MCDUFFIE’ AND LEVEN S. HAZLEGROVE* Emory L’niversity, Emory University, Ga. In order to extend the usefulness of the mercury cathode method of separating metals from aqueous media, the electrolysis of manganese solutions of various composition and pH has been studied. Using a mercury cathode cell with a small platinum anode, manganese has been quantitatively deposited from sulfate, sulfite-sulfate, and oxalate-sulfate media at initial pH values in the region 2.41 to 4.70, the optimum initial pH being about 2.75. Starting with only 10.0 mg. of manganese in a volume of 100
E
LECTRODEPOSITION employing the mercury cathode is a convenient method for quantitatively separating many metals from their aqueous solutions ( 7 , 8). I n fact, because of the high overvoltage of hydrogen on mercury and the decrease in reactivity of metals due to amalgam formation, many of the more reactive metals such as chromium and molybdenum can be quantitatively deposited into mercury from acidic media, provided large concentrations of interfering elements are absent ( 1 ) . Therefore it was of interest to the authors to determine whether or not conditions could be established such that manganese, a still more reactive metal with a standard potential of 1.05 volts for the reduction of manganese(I1) ion (6), could be quantitatively removed from dilute solutions by electrolysis into mercury. Previous work on the electrolysis of manganese solutions with a mercury cathode has been summarized recently by Maxwell and Graham (8),who state, in agreement with Lundell and Hoffman ( 7 ) ,that ‘(manganeseis incompletely deposited on the anode and in the mercury.” Russell, Evans, and Rowell (IO)electrolyzed manganese(I1) chloride solutions with a mercury cathode to prepare manganese amalgams and reported that, in the presence of hydrochloric acid and alcohol, manganese could be driven quantitatively into the mercury. However, no data on the completeness of removal of manganese were given by these authors. Khlopin (Q), investigating the determination of aluminum in manganese steels, was able to remove 98% of the manganesei.e., all but about 1 mg.-along with all the iron by adding phos1 Present address, Department of Chemistry. Washington and Jefferson College, Washington, Pa. 2 Present a d d r e m Department of Chemistry, West Georgia College, Carrollton, Ga.
ml., at least 99.6% of the manganese was removed using the media cited; the time required varied somewhat with the medium. Deposition was fastest (2 hours) from sulfite-sulfate solutions. The changes in pH during electrolysis were observed and explanations are offered. The fact that manganese wan be quantitatively separated from aqueous solutions using the mercury cathode suggests that this technique might serve as the basis of methods for removal or determination of manganese.
phoric acid and hydrogen peroxide t o solutions of the steel in sulfuric acid. An acetic acid medium was used by Holler and Yeager (3),but a t least some manganese dioxide was filtered out of the solution after the electrolysis. Lingane and Rfeites ( 6 ) ,following the method of Khlopin (Q), used phosphoric acid to prevent the formation of manganese dioxide and permanganate ion a t the anode, but made no comment on the completeness of removal of manganese from the solution. Casto and others (2, 9, 11) were able t o remove 99.0 to 99.6% of the manganese from a solution 1.0 N in acid by electrolysis with a mercury cathode for 1hour, no further deposition occurring after 2,3, or 4 hours. As the acidity was increased, the removal became less complete, 82.9% bring deposited after 1 hour and 91.6% after 2 hours in 6 S acid. In the present communication experiments are reported 111 which manganese solutions of various composition and pH have been electrolyzed with a mercury cathode, leading in many casee to the practically complete removal of manganese from the colution. REAGENTS AND APPARATUS
Standard Manganese Solution. A weighed amount of 99.9+ 70 pure electrolytic manganese from the Electro Manganese Corp., Knowille, Tenn., was dissolved in a slight excess of sulfuric acid and diluted to a volume such that 1.00 ml. of the solution contained 1.00 mg. of manganese. For calibration purposes a solution containing 0.100 mg. per ml. was also prepared Reagents. Reagent grade chemicals and distilled water were used throughout. Apparatus. The type of electrolysis cell used in these experiments was a 250-ml., tall-form beaker with 20 ml. of mercury in the bottom as cathode; electrical contact was made through a glass-enclosed platinum electrode. A small platinum wire of 1mm. diameter, immersed in the electrolysis solution to a depth of 0.5 to 1.0 em., served as the anode.
V O L U M E 2 4 , NO. 5, M A Y 1 9 5 2 Table I.
a27
Electrodeposition of Manganese from Sulfate Medium
(Each solution contained initially 10.0mg. of Mn a n d 10 grams of NarSO4 in a total volume of 100 ml applied potential, 10 volts: current density a t mercury cathode. 0.02 ambere per sq. cm.: solutions stirred: temp. approx. 40° C.)
.
f2tiOs: Solutions 1.00
Analysis of Solutions after Electrolysis Time, t p H of Duplicate Manganese Left in Solutions Solutions. M g . t. hours 4 B A B 4 1.10.1.20 2 . 8 4 , 3.23 24 1.26, 1.24 2.14, 2.43
1.50
2 4
2.05
24
2.41
4
date was added, and the color was developed. Samples that had contained oxalate ion were fumed t o dryness with 5 ml. of 18 M sulfuric acid t o destroy the oxalic acid prior to the color development procedure. Sensitivity of'halytical Method. The lower limit of detection of manganese by the spectrophotometric method was 0.00004 mg. of manganese per ml. Therefore, assuming that a 1/20aliquot portion was taken for analysis and diluted to a final volume of 50 ml., the maximum amount of manganese that could remain undetected in an electrolyzed solution was 20 X 50 X 0.00004 or 0.04 mg.
1.60,1.64 1.70,1.70
1.94, 1.80 1.46, 1.46
0.88,
0 19 0.10.
