Multi-energy calibration for determining critical metals in nickel-metal hydride battery residues by microwave-induced plasma atomic emission spectrometry.

Nickel-metal hydride batteries (NiMH) are a secondary source of high aggregate value elements, such as nickel, manganese, cobalt, and rare earths, for which recycling typically involves acid lixiviation. Designing the recycling process requires accurate determination of the elements in the leachates, which is hindered by the high complexity of the matrix. In the present study, microwave-induced plasma atomic emission spectrometry (MIP-OES) was selected as the quantitative method for elemental analysis because of its environment friendliness and cost-effectiveness. Multi-energy calibration (MEC) was also pioneeringly evaluated to circumvent matrix effects and simplify the determination of Ce, La, Ni, Co, and Mn in sulfuric acid leachates of NiMH batteries by MIP-OES. The method's analytical performance and accuracy were critically compared with external standard calibration and the standard additions method. MEC yielded superior results, with analyte recoveries within 90-110%, precision (coefficients of variation) from 1.8% to 5.8%, and limits of detection of 10, 20, 1, 400, and 60 μg kg for Ni, La, Mn, Ce, and Co, respectively. The results demonstrated the ability of MEC-MIP-OES to minimize matrix effects, as well as simplify and speed up the analysis of NiMH battery leachates, which is compatible with this high-demand analytical application.