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ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978
(18) A. W. Wells, S. M. Norman, and F. P. Atrops, J . Gas. Chromatogr., 1, 19 (1963). (19) P. L. Davis and K. A . Munroe, J . Agric. Food Chem., 25, 426 (1977). (20) H. Beernaert, J . Chromatogr., 77, 331 (1973).
RECEIVEDfor review December 8, 1977. Accepted January
30, 1978. This work was supported by grant F-690 from the Robert A' U'elch Foundation and a seed grant Obtained through the Biomedical Research Support Grant awarded from the National Institutes of Health to the University of Texas a t Austin.
Liquid-Liquid Extraction of Zinc from Aqueous Iodide Solutions with 4-(5Nonyl)pyridine in Benzene Shamas-ud-Zuha and Mohammad E j a z " Nuclear Chemistry Division, Pakistan Institute of Nuclear Science and Technology, Nilore, Ra walpindi, Pakistan
An investigation has been made on the system 4-(5-nonyl)pyridine-Zn( 11)-I. Optimal conditions for the extraction of zinc lave been given, based on a critical survey of the relevent factrapssuch as the effects of the acids, iodide ions, salting-out and complexing agents, and the metal concentration. The mechanism underlying these extractions is discussed on the basis of the results obtained from partition, slope-analysis and loading-ratio data. Distribution coefficients and separation factors of several elements relative to zinc have been reported for the optimum concentrations of hydrochloric, nitric, and sulfuric acid solutions containing 1 M potassium iodide. The presence of iron does not interfere with extraction. It has been shown that in neutral and weakly acid solutions, 445nony1)pyridine is a better extractant for iodide complexes of zinc than the commonly used aliphatic tertiary and quaternary amines, and carbon and phosphorus bonded oxygen-donor extractants.
High molecular-weight pyridine amines are an interesting and versatile class of extractants. Depending on conditions, these compounds behave as liquid anion exchangers and give salts with various acids ( 2 , 2 ) or are incorporated as ligands in t h e complex ions of elements, forming penetration complexes (3-5). Complex formation and extraction of some transition metal ions in a thiocyanate system using 4-(5nony1)pyridine and its analogues have been studied ( 3 , s ) . It has been shown that the weaker hydration of thiocyanate ions favors the formation of 4-(5nonyl)pyridine solvates whereas t h e strong hydrophilic character of common anions like chloride and nitrate does not. The present investigation makes use of hydrophobic iodide ions for the extraction of zinc by 445-nony1)pyridine dissolved in benzene from aqueous mineral acid solutions containing potassium iodide, instead of hydroiodic acid which decomposes on storage leading to a drop in iodide ion concentration. T h e use of these mixtures also makes it possible to control the selectivity of the separation by varying t h e concentration of the acids and alkali-metal iodide. Extraction of zinc from aqueous iodide solutions by liquid anion exchangers and oxygen-containing solvents has been studied (6-8). Our investigation reveals t h a t 4-(5nonyllpyridine extracts zinc from aqueous iodide solutions much more efficiently than the previously used extractants (6-8). In addition, the method has the advantage that zinc can be quantitatively extracted in a single extraction from 0003-2700/78/0350-0740$0 1 O O / O
water and a wide range of acid concentrations; a strict control of acidity is unnecessary.
EXPERIMENTAL Reagents. 4-(5-Nonyl)pyridine (NPy) was used as an extractant. The characteristics of this compound are reported elsewhere ( 5 , 9). Solutions of potassium iodide were made by AnalR). All dissolving anhydrous chemically pure salt (B.D.H. other chemicals were reagent grade or of the highest purity available. Deionized water was used for the preparation of all aqueous solutions. Procedure. Extractions were carried out at room temperature (23 & 3 "C) in 20-mL glass vials; equal phase volumes were used. The stock solution of the mineral acid containing trace amounts (
