Lithium tetraborate-atomic absorption

The introduction of atomic absorption spectroscopy has resulted in major advances in the rapid analysis of many elements. Initially, atomic absorption was applied only to aqueous systems or to materials that could be readily solubilized. There are methods to analyze major elements in such complex materials as silicates and vitreous siliceous coal ashes (1-5). More recently, lithium metaborate has been reported to be a good fluxing agent (6) and has also been used in conjunction with atomic absorption analysis in silicate analysis (7). This paper describes a lithium tetraborate-atomic absorption analytical technique which is being used to analyze coal ash. 

The commercial ores, beryl and bertrandite, are usually decomposed by fusion using sodium carbonate. The melt is dissolved in a mixture of sulfuric and hydrofluoric acids and the solution is evaporated to strong fumes to drive off siUcon tetrafluoride, diluted, then analy2ed by atomic absorption or plasma emission spectrometry. If sodium or siUcon are also to be determined, the ore may be fused with a mixture of lithium metaborate and lithium tetraborate, and the melt dissolved in nitric and hydrofluoric acids (17). 

The presence and concentration of various metallic elements in petroleum coke are major factors in the suitability of the coke for various uses. In the test method (ASTM D5056), a sample of petroleum coke is ashed (thermally decomposed to leave only the ash of the inorganic constituents) at 525°C (977°F). The ash is fused with lithium tetraborate or lithium metaborate. The melt is then dissolved in dilute hydrochloric acid and the resulting solution is analyzed by atomic absorption spectroscopy to determine the metals in the sample. However, spectral interferences may occur when using wavelengths other than those recommended for analysis or when using multielement hollow cathode lamps. 

Siliceous materials—Si, Al, Fe, Ti, Ca, Mg, Na, K, Mn, Ni, Ba, Ag, Au, Ca, Cr, Cu, Ga, In, Mo, Sb and Zn—may be analyzed by a lithium tetraborate fusionr-acid dissolution technique using atomic absorption spectroscopy. Mercury, tin, and lead volatilize by this technique, and gold and silver in concentrations above 0.5 wt% cannot be held in solution. Coal ash is preconcentrated prior to analysis, and there is possible silica interference. Analytical results, where possible, are compared statistically with other reported values. 

---