Separation of Arsenic from Antimony and Bismuth by Solvent Extraction H. C. BEARD and L. A. LYERLY' Chemistry Department, Florida State University, Tallahassee, Flu.
b Benzene serves as a highly selective and sensitive extraction for arsenic (111) from hydrochloric acid medium. Above 8N in hydrochloric acid, essentially 100% of arsenic(ll1) is extracted. Separations from antimony and bismuth ions have been investigated and checked using radioactive tracer techniques. The influence of hydrochloric acid concentrations on the extractability of arsenic(ll1) has been investigated and found to b e very critical. The procedure is rapid and yields accurate results.
and warm on a steam bath until there is no further liberation of free iodine. Add concentrated hydrochloric acid until the resulting solution is 8 to 10N in hydrochloric acid. Extract the arsenic(II.1) with an equal volume of benzene by shaking the solution in a separatory funnel for about 3 minutes and allow the layers to separate. Remove the benzene layer, now containing the arsenic, and back-extract the arsenic with an equal volume of water. Make the aqueous layer 3 to 6N in hydrochloric acid. Dissolve in the acid solution about 0.5 gram of NaHZP02 and warm on a steam bath for 30 to 45 minutes or until the upper liquid begins to clear, Filter the precipitated arsenic, wash with water and acetone, and dry for about 15 minutes a t 110' C. Weigh gravimetrically to determine the chemical yield.
'"v /
T
HE literature contains numerous procedures for separating and determining arsenic, but the majority are based on distillation and hydrogen sulfide precipitation methods. Reduction of arsenic to the elemental state is the best form for weighing, since errors in factor calculations might be prevalent in the sulfide precipitate (1). Methods involving complexation and solvation are becoming more numerous because of the simplicity and the rapidity of the analyses. Boyd and Easley found that extraction of arsenic(II1) from 6N hydrochloric acid with a saturated solution of catechol in benzene was the basis for a sensitive qualitative test for arsenic in the presence of group 2 ions in the qualitative analysis scheme (2). A study of the concentration of catechol on the extractability led to the development of two quantitative separations of arsenic. It was revealed that a t higher acid concentration, catechol has little or no effect on the amount of arsenic extracted. Benzene alone then serves as an extractant for the arsenic(II1) ion.
EXPERIMENTAL
Apparatus. A tall-form filtering column, made from a 24/40 groundglass joint, was used for isolation of the precipitated metals. Just enough of the end of the ground-glass joint was removed so that a 2.1-cm. diameter sintered-glass disk could be tightly sealed in the end of the joint. Present address, R. J. Reynolds Tobacco Co., Winston-Salem, N. C.
2-0
MOLARITY OF HCI
Figure 1 . Extraction of As(lll) from HCI with organic solvents
- with catechol in benzene --- HCI HCl with benzene alone
Table 1.
With this assembly, it is possible to recover a precipitate with a minimum loss. It is used with a regular suction flask connected to a water aspirator. A 2.1-cm. glass fiber filter mat is very satisfactory for the filtration. Reagents. All chemicals were analytical reagents. Solutions of arsenic, antimony, and bismuth containing about 10 mg. per ml. were prepared from As,Oa, . Sbz08, and BiOCI, each in hydrochloric acid medium. The arsenic was standardized by reduction to the metal with sodium hypophosphite. Antimony and bismuth were both standardized by reduction to the metal with chromous chloride.
(CHCl/Cor*.
HC1 Concn., M 0
2 4 6 8 10
aolvent)
Method Catechol in benzene Benzene 13.2 9.4 1.o 0.4 0.2 0.07
03
m
12.2 0.05 a
a
Values too low to be accurately determined.
Table 11. Separation and Determination of Arsenic, Antimony, and Bismuth
PROCEDURE
Ion
Transfer by pipet 2.0 ml. each of standard arsenic, antimony, and bismuth solutions. Add a few drops of 0.25M ammonium iodide to assure reduction of arsenic to the +3 state
Table 111.
Acidity vs. Distribution Ratio
As(II1) Sb(II1) Bi(II1)
(Without tracers) Recovered Added, Mg. (Std.Mg. Dev.), 20.11 21.51 23.44
19.92 =t 0.04 21.21 =t 0.03 23.23 =t 0 . 0 4
Separation and Determination of Arsenic, Antimony, and Bismuth in Presence of As76, Sb1*2, and Biz10
Ion As( 111) Sb(111) Bi( 111)
Added,
Recovered,
20.11 21.50 23.28
19.70 21.17 23.17
Mg.
Mg.
Counta/Minute Standard Sample 8,110 13,246 18,864
8,291 13,122 18,510
VOL. 33, NO. 12, NOVEMBER 1961
1781
If it is desired to determine the antimony and bismuth, the antimony may be extracted with isopropyl ether after oxidation to antimony(V), thus separating it from bismuth (3). Both ions may then be determined by reduction to the metal with chromous chloride and weighing gravimetrically. DISCUSSION AND RESULTS
Figure 1 shows the extractability of arsenic(II1) from hydrochloric acid solutions with catechol in benzene and with benzene alone, using the procedure noted. At lower acid concentrations, the extraction with catechol is more efficient. However, benzene alone is superior a t higher acid concentrations. The distribution ratio between concentrations of HCl and the organic phase is given in Table I. The dis-
tribution ratios with the acid and benzene a t 8N and 10N HC1 are extremely low and have not been accurately determined. Nuclear magnetic resonance and phosphorescence studies show a definite shift indicating a complex formation between arsenic(II1) and benzene. At this point, it has been difficult to classify the complex. Tables I1 and I11 show some of the results that have been obtained with this system. Each ion noted represents an average of six individual analyses and mas chosen a t random. This procedure was checked using Sblz2, and Bizlo (RaE). The sample activities were compared with the activities of separate standards not subjected to the separation procedure and proved to be very accurate. The identities of the isolated activities were further verified by beta absorption
measurements and half-life determinations. Other elements associated with this group are being investigated using the same principles of solvent extraction. ACKNOWLEDGMENT
Financial support in the form of a research contract from the U. S.Atomic Energy Commission is gratefully acknowledged. LITERATURE CITED
( I ) Beard, H. C., "The Radiochemistry of Arsenic," Nuclear Science Rept.
NAS-NS-3002 (January 1960).
(2) Boyd, C. C., Easley, W. K., J . Chem. Educ. 36,384 (1959). (3) Edwards, F. C., Voight, A. F., ANAL.
CHEM.10, 1204 (1949). RECEIVEDfor review May 11, 1961. Accepted September 7 , 1961.
Spectrophotometric Determination of Iron(111) by Means of 6-Hydroxy-1,T-phenanthroline JOAN M. DUSWALT with M. G. MELLON Purdue University, lafuyetfe, Ind.
b This new method for the colorimetric determination of iron(ll1) employs the colored chelate of 6-hydroxy-1,7phenanthroline dissolved in 40% 1 propanol. Along with the most desirable conditions for use of the method, the special effects of solvent, pH, and excess reagent on the color reaction are described. The system follows Beer's law, has a molar absorptivity of 6500, and in a borate buffer of pH 7 to 9 suffers no interference from citrate, tartrate, thiocyanate, or phosphate. Metallic ion interference depends upon pH, buffer system, and amount of excess reagent used. Preparation of the new reagent is described and its reactions are compared with those of the parent compound, 8quinolinol.
-
Various other 8-quinolinol reagents form iron cheIates which are insoiuble in water but give stable color systems in organic solvents. In general, this problem has been handled by extracting the chelate, keeping the p H below 4, or quantitatively precipitating, filtering, and dissolving the chelate in a solvent such as ethanol (7, IO, 14). At pH 4 or lower, the water-soluble, colored species are the 1:1, or mixtures of the 2:l and 1:l chelates (9). These colored systems are highly p H dependent. Preliminary studies showed that 6-hydroxy-l,7-phenanthroline was a promising reagent for the determination of iron. The recommended colorimetric method resulted from an investigation of this system. EXPERIMENTAL WORK
P
ROBLEMS associated
with the colorimetric determination of iron by reagents of the 8-quinolinol family are (1) the d,ependence of the color on pH, excess reagent, and concentration of certain anions and cations, and (2) the low solubility of many of the chelates in aqueous media. The purpose of this work was to find a derivative of 8-quinolinol which wouId be more nearly free of these limitations. The ferron (8-hydroxy-7-iodo-5quinolinesulfonic acid) chelate is water soluble but p H sensitive (IO). 1782
ANALYTICAL CHEMISTRY
Reagents. A standard solution of 0.100 mg. of ferric ion per ml. of solution was prepared by dissolving 0.7022 gram of ferrous ammonium sulfate hexahydrate in about 100 ml. of distilled water. Five milliliters of 3% hydrogen peroxide was added to oxidize the iron, with 2.5 ml. of concentrated hydrochloric acid. The solution was boiled 10 minutes to decompose the hydrogen peroxide, and then diluted to a liter. Analytical reagent grade chemicals were used for the buffer solutions. Solutions of 0.20M potassium hydrogen
phthalate and 0.20X potassium chloride-boric acid were prepared. The 1propanol was distilled. A 0.2% (w./v.) aqueous solution of the reagents was prepared by adding enough hydrochloric acid to dissolve each of the reagents. The 8-quinolinol mas recrystallized from petroleum ether (90" to 100" C. b.p.). Preparation of 6-Hydroxy-1,7phenanthroline (3, 6, 8). One-half mole (96 grams) of 4-aminobenzenesulfonic acid and 27 grams of anhydrous sodium carbonate were dissolved in 450 ml. of water by warming on a steam plate. After cooling the solution, 300 grams of crushed ice was added, followed by a cold solution of 35 grams of sodium nitrite in 100 ml. of water. Then 78 ml. of concentrated hydrochloric acid in 100 ml. of crushed ice was added dropwise. The system must be kept cold. Seventy-three grams of 8-quinolinol was dissolved in 50 ml. of concentrated hydrochloric acid and 50 ml. of water. This was cooled t o below 0" C. and the 4diazobenzenesulfonic acid salt solution was slowly added with stirring. The coupling reaction took place very slowly. The mixture was refrigerated overnight below 0" C. The solution was then warmed up to room temperature to complete the coupling reaction, which was indicated by the disappearance of the orange salt. The red precipitate was filtered. Sodium hydroxide was added to the filtrate until no more dye precipitated, and the remainder of
