GALLIUM. I. ARC SPECTROGRAPHIC DETECTION AND ESTIMATION OF GALLIUM. 11. EXTRACTION OF GALLIUM FROM LEPIDOLITE‘ BY JACOB PAPISH AND DONALD A . HOLT
I. Arc Spectrographic Detection and Estimation of Gallium General. Arc spectroscopy is well suited to the needs of the analytical chemist. When the visible and the ultraviolet spectral ranges are considered it will be noticed that the great majority of metals and a number of nonmetals have their persistent lines in these ranges. Arc spectra, as a rule, are intense and this makes them especially adaptable to spectrographic observation. If the substance to be analyzed is a good conductor of electricity, such as a metal or an alloy, and is in the form of wire or rod, it can be used directly as electrode material. Ordinarily the chemist is confronted with the handling of substances that are non-conductors; even in the case of metals he has to work frequently with granules, powders, borings and lumps which cannot be made into electrodes, at least, not conveniently. In such cases and also in the case of liquids, use is made of graphite rods of suitable diameter and length to hold the substances to be subjected to spectral excitation. Artificial graphite of a very high degree of purity is procurable for spectroscopic work. When an arc is made between two such graphite rods, the spectrum will be found to contain, in addition to the lines and bands due to carbon and to some of its compounds, also lines due to a number of impurities such as magnesium, sodium, calcium, lithium, silicon, iron and manganese. Other things being equal, the intensity and the number of these lines will depend upon the quantities of the respective impurities. The direct current is used for the production of the arc, and it is the practice to make the lower electrode the anode. The anode is considerably hotter than the cathode. This fact can be observed any time on breaking the arc: the anode will be red-hot over a longer distance and it will continue to glow some time after the cathode has become dark. When the lower electrode is made the anode, and the substance to be analyzed is placed on it, it will be observed that the spectroscopic test, in a great many cases, is much more sensitive than in the event of reversed polarity. X quartz spectrograph fitted with one Cornu prism, or a larger autocollimating Littrow type of instrument, is suitable for work in the ultraviolet region. The latter instrument gives very good results also in the visible range. For the detection of gallium which has persistent lines in the visible, a glass instrument can be used. Ordinary photographic plates with a sensitivity between h 5000 and h 2 3 5 0 give very good results, and of course special plates should be used for ranges other than this. The method of developing I
The experlrnental work described in this article was made possible through a grant
from the Heckscher Foundation for the Advancement of Research, established by .‘iugust
Heckscher a t Cornel1 University.
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GALLIUV
and fixing is similar to the one followed in ordinary photographic work with one outstanding difference : I n spectrography the chemist is after hardest contrasts obtainable. Ezperimental W o r k wzth Gallmm. Freshly precipitated gallium hydroxide, which on spectrographic examination was found to contain only negligible traces of sodium, iron, calcium, magnesium and silicon, was converted to the chloride with the aid of hydrochloric acid. The gallium content of this solution was determined gravimetrically and water was added to bring the concentration to 0.1 percent. From this stock solution, solutions containing 0.01, 0.001 and 0.0001 gm. of gallium per IOO cc. were prepared. X small, definite portion (0.1 cc.) of each solution, delivered from a graduated capillary pipette, was placed on the lower graphite electrode and subjected to arc ex0.01, 0.001 and 0.0001mg. of gallium citation. These portions contained 0.1, respectively. Fresh electrodes were used in connection with each test. The spectral lines observed at the different concentrations are recorded in Table I. TABLE
A 4172.0 4033.0 2944.2 2943.6 2874. z 2719.
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3659.9 v v vf 2500.2 v V vf 2450. I V f 2338.6 vf Note. “I”’designates the fact that the line is visible, “f”, that it is faint and “vi” that it is very faint.
If gallium in quantities larger than 0.1 mg. be arced, the following spectral lines, in addition to those given in Table I will be observed: 3020.5, 2418.7, 2371.3, and 2249.2. Because the human eye is much more sensitive to visible radiation than the photographic plate, X 4172.0 and X 4033.0 are visible when t,he concentration of gallium is lower than the lowest given in the table. This is especially true of the lower frequency line. The gallium line 2874.2 is coincident with an iron line of practically the same wave length. I t should be borne in mind, however, that this iron line is of low persistence, and if it is visible, many other lines due to this element should be present. Fifty-five minerals were examined spectrographically for the presence of gallium. The observations are recorded in Table 11. The term trace as employed in this table designates quantities in the neighborhood of 0.0017~; large trace, stands for quantities in the neighborhood of o.or‘; and small trace for quantities less than 0.00157~. To illustrate how thcse have been arrived at, the case of lepidolite (from San Bernardino Coiinty, (‘nlifornia) will be briefly considered.
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JACOB PAPISH AKD DONALD 4.HOLT
TABLE I1 Mineral
Albite Albite Alunite Analcite Apatite Ball clay Bauxite Bauxite Beryl Beryl Beryl Chlorite Corundum Emery Enargite Feldspar Franklinite Garnet Garnet Indiananite Kaolin Kunzite Labradorite Labradorite Lazurite Lepidolite Lepidolite Leucite Lithiophylite Microcline Microcline Microcline Microcline Microcline Microcline Microcline Muscovite Satroloite Kephelite Oligoclase Orthoclase Orthoclase (pebble)
Place of origin
Bedford, Kew York Richville, New Tork Marysvale, Utah Table Mountain, Golden, Colorado Buckingham, Quebec Tennessee Linnwood, Georgia Bauxite, Arkansas South Australia Bedford, Kew York Canada Putnam County, New York Iredell County, Xorth Carolina Peekskill, New York Chiapas, Mexico Quebec, Canada Franklin Furnace, S e w Jersey Franklin Furnace, S e w Jersey Warren County, S e w York Huron, Indiana Holly Springs, Pennsylvania Palo County, California St. John County, Quebec Maine, Labrador Andes de Ovalle, Chile San Bernardino County, California Oxford County, Maine illbeno, Italy Black Hills, South Dakota El Paso County, California Verona, Ontario Franklin Furnace, New Jersey Chestnut Flat Mine, Xorth Carolina Godfrey, Ontario Davis Mine, New Hampshire Virginia Asheville, Korth Carolina Medford, Oregon Bancroft, Ontario Orange County, New York Quebec Pacific Grove, California
Ga content
Trace Small trace Absent Small trace Absent Small trace Small trace Absent Absent Absent Small trace Absent Small trace Small trace Absent Trace Absent Absent Absent Absent Small trace Trace Trace Trace Small trace Large trace Trace Small trace Absent Large trace Trace Trace Trace Trace Trace Large trace Trace Trace Trace Trace Small trace Trace
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GhLLICY
T.4BLE
Mineral
Sodalite Sodalite Spodumine Stilbite Stilbite Tourmaline Tourmaline Tourmaline Tourmaline Tourmaline Turquois Wavellite Willemite
11 (Continued)
Place of origin
Litchfield, Maine Hastings County, Ontario California Peekskill, S e w York West Paterson, New Jersey El Paso County, California San Diego County, California Winter Harbor, Maine Richland, New York Bedford, New York Yew Mexico Montgomery County, Arkansas Franklin Furnace, New Jersey
Ga content
Small trace Small trace Trace Absent Absent Large trace Large trace Trace Trace Trace Absent Absent ilbsent
Finely powdered lepidolite in five and ten milligram portions was subjected to arc excitation. The spectrograms in the case of the higher quantity contained the gallium lines 4172.0,4033.0, 2944.2 (faint), 2943.6 and 2874.2. This would seem to indicate that a quantity higher than 0.001mg. and lower than 0.01mg. of gallium was present in the zone of excitation. Expressed in percentages, the galliutn content is estimated to be between 0.001and 0.01. The shortcomings of this method of estimating the quantity of an element are obvious: The reactions in the arc are beyond the control of the operator. However, if the limits are wide, it is possible in many cases to differentiate between traces and larger quantities, especially if the element has spectral lines of great sensitivity.
11. Extraction of Gallium from Lepidolite The mineral, ground to pass through a 40 mesh sieve, was fused in a nickel crucible with twice its weight of potassium hydroxide, and while still in a pasty condition, the fused mass was broken up in small particles by stirring with an iron rod. It was transferred to a tall glass cylinder containing water, stirred with a current of air and allowed to settle. The supernatant liquid was siphoned off, more water was poured in the cylinder, stirred as before; the solid was again allowed t o settle and the liquid was removed. This was repeated till about ten liters of water were used for one kilogram of original mineral. The residue which contained practically all the aluminum and all the gallium, a fact established spectroscopically, was placed in an evaporator, treated with concentrated hydrochloric acid and heated to “crack” the silica gel. The aluminum and gallium were extracted with successive portions of dilute hydrochloric acid and the extraction was deemed completed when the residual silica showed no gallium or the merest traces when examined spectroscopically. The chloride solution was concentrated to a small volume
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JACOB PAPISH A S D DONALD A. HOLT
and the excess of mineral acid was neutralized with ammonium acetate and an excess of acetic acid mas added. Potassium arsenite was added to this and the whole was first saturated with sulphur dioxide to make sure that the arsenic is in the trivalent state, and next with hydrogen sulphide. The galliferous arsenious sulphide was removed by filtration. But the filtrate was not entirely free from gallium, and in order to recover this fraction it was necessary to repeat the procedure of adding potassium arsenite and saturating with sulphur dioxide and with hydrogen sulphide until a precipitate of arsenious sulphide was obtained which did not carry gallium. The galliferous precipitates were transferred to an evaporator and treated with nitric acid. The unoxidized sulphur was removed by filtration and washed till it was found to be free from gallium. The excess of nitric acid in the filtrate was driven off by evaporation and hydrochloric acid was added. The solution was saturated with sulphur dioxide and with hydrogen sulphide and the precipitated arsenious sulphide was removed by filtration. It was found on spectroscopic examination that even this residue on careful washing with hydrochloric acid retained minute traces of gallium. The filtrate which contained aluminum and gallium was concentrated to a small volume, made strongly acid with hydrochloric acid and an excess of potassium ferrocyanide was added to it. This brought about the precipitation of gallium as the ferrocyanide together with a comparatively large quantity of ferrocyanic acid. Since gallium ferrocyanide, like other ferrocyanides, is peptized by adsorption of the ferrocyanide ion, it was found necessary to employ egg albumin to facilitate the removal of the solids by filtration. The residue thus obtained was washed on the filter with dilute, warm hydrochloric acid until washings gave no test for aluminum. The residue and filter were ignited. Aqua regia was added and heat applied until complete solution was brough about. Successive portions of hydrochloric acid were next added and driven off by evaporation to insure the removal of the oxides of nitrogen. The hydrochloric acid in turn was neutralized with ammonium acetate; acetic acid was added and the iron was precipitated out by adding a freshly prepared hot solution of a-nitroso&naphthol in soqc acetic acid. The iron precipitate, when separated from the solution and washed on the filter, was found on spectroscopic examination to be free from gallium. The filtrate was made alkaline with ammonium hydroxide and boiled until gallium hydroxide precipitated out. This was removed by filtration, washed and ignited to the oxide. A spectrographic examination of the freshly precipitated gallium hydroxide proved that it contained negligible traces of the commoner elements ordinarily associated with substances of highest purity. The ignited oxide contained the same impurities, especially silicon and magnesium, to a somewhat higher degree. These, evidently, were derived from the incinerated filter paper. One kilogram of lepidolite treated in the manner just described yielded 0.0887 gm. of GaaOs. The gallium content of the mineral expressed as percentage is very close to 0.007.
GALLIUM
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summary
A method for the arc spectrographic detection and estimation of gallium was described. Fifty-five minerals were examined spectrographically for the presence of gallium and the results recorded. A method for the extraction of gallium from lepidolite was described. Cornell University.
