Development of a technique for analysis of tungsten-containing sludge using inductively coupled plasma atomic emission spectrometry (ICP-AES)
A technique for analysis of secondary tungsten-containing raw materials (tungsten-containing sludge) using inductively coupled plasma atomic emission spectrometry in combination with microwave autoclave sample preparation has been developed. The composition of the acid mixture and algorithm of microwave heating of the autoclave are chosen to provide a complete quantitative transfer of the sample into a convenient analytical form for subsequent ICP-AES determination of the main components (sample heating to 220°C in the acid mixture of NH<sub>4</sub>F, HNO<sub>3</sub>, and HCl provides a quantitative transfer of the sample components to be determined, into the solution). Analytical lines free from spectral interference were selected to determine Ti, Cr, Fe, Co, Ni, and W. We used real industrial samples of secondary raw materials obtained in product manufacture from VK-type hard alloys [solid solution of tungsten carbide grains (WC-phase) in cobalt (Co-phase)], presented in the form of tungsten-containing powders, grinding sludge of solid sintered alloys, dust waste, defective mixtures, waste ventilation systems, and carbide powders. Correctness of the element determination was proved in analysis of ferrotungsten standard samples upon determination of the matrix component (tungsten) and by the methods of additives and sample weight variation upon determination of the alloying elements and impurities. The method of internal standard (with Sc as the element of comparison) was used to improve the precision and accuracy of the tungsten determination. The relative standard deviation was thus reduced from 0.03 to 0.004. The developed precise rapid technique was tested in analysis of industrial samples of secondary tungsten-containing sludge of hard alloys. The technique is recommended to control the composition of the secondary tungsten-containing sludge of hard alloys in a wide range of concentrations.