Determination of Lithium in Rocks

Abstract

The gravimetric method in general use for the determination of lithium is tedious, and the final weighed product often contains other alkali metals. A fluorometric method was developed to shorten the time required for the analysis and to assure that the final determination is for lithium alone. This procedure is based on the complex formed between lithium and 8-hydroxyquinoline. The fluorescence is developed in a slightly alkaline solution of 95% alcohol and measurement is made on a photoelectric fluorometer. Separation from the ore is carried HE difficulties inherent in the gravimetric determination of T lithium in minerals have been reviewed by Kallmann (6) and by Fletcher ( 2 ) . In nearly all methods previously reported for this determination, partial separations from t,he other alkalies are made and a correction factor is used t'o compensate for the sodium and potassium remaining with the lithium; or very careful separations are made and the final residue is weighed as a pure lithium salt. However, even after a supposedly "complete separation," as in the sulfate gravimetric method, the final lithium sulfate residue contains traces of calcium and magnesium as well as some sodium and potassium. Seedless to say, it would be far better to be able to determine the lithium directly instead of having to depend on the complete separation of all other ions.In an effort to develop a direct method for the determination of lithium, a group of compounds was studied with the hope of finding a specific colorimetric or fluorometric reagent. Inasmuch as lithium has been frequently described as an interference in reactions involving beryllium, attention was directed to those compounds (chiefly the hydrosyanthraquinones) that had been reported (8) to give either direct color or fluorescence responses with beryllium. None of these compounds was found sensitive enough to serve for quantitative purposes; but oxine (&hydroxyquinoline) formed an intensely fluorescing chelate complex wit.h lithium and appeared to be the best reagent available.Oxine will give a quantitative response wit'h as little as 5 micrograms of lithium oxide in 25 nil. of solution and does not form a fluorescent substance with either sodium or potassium. Lithium may be determined with this reagent to an accuracy of 1 part in lo00 in solutions that contain no other cations. Appreciable quantities of sodium decrease the intensity of the fluorescence of the lithium-oxine complex; therefore, a partial separation of the sodium is necessary. The advantages of using the oxine reaction for the determination of lithium are that a direct quantitative determination may be made without a complete separation of the other alkalies or the use of correction factors; and at the same time, greater accuracy is achieved in shorter time than is possible with the sulfate gravimetric determination. REAGENTS AND APPARATUSAlcohol. Redistilled 95% ethyl alcohol wr.as used for the preparation of all solutions in the fluorometric procedure. Commercial alcohol contains a highly fluorescent...

The Reactions Of 8-Quinolinol

“…The alkali metals form salts in alkaline solution with 8-quinolinol that increase in solubility with increasing atomic weight of the alkali metal (280). The lithium salt has a sufficiently pronounced fluorescence that this property has been suggested for lithium determination (296).…”

Inorganic Microchemistry

“…Bock has studied ( 17) the extraction of various metal thiocyanates, and Bock, Kusche, and Bock have separated metallic bromides by ether extraction (18). Miscellaneous extraction methods include: the separation of antimony (197); bismuth (87, 201); molybdenum (118); sodium and potassium (203); platinum (41); nickel (64); and iron, gallium, hafnium, indium, scandium, tellurium, uranium, vanadium, and zirconium (56).…”

Fluorometric Analysis

“…White and associates (173) have used the lithium-8-quinolinol complex for the determination of lithium in rocks. This serves as one of the simplest methods of comparing the lithium content of reagents to a standard.…”