The relative metal concentrations in the leachate as a function
of time were studied by dissolving 0.1 g of roasted NdFeB
magnet powder in 1 mL of diluted HCl with various acid
concentrations. The HCl concentration was chosen in this way
that the molar ratio between HCl and the rare earths molecules
n(HCl)/n(Ln), was kept constant at a value of 3.5. The sample
was heated and stirred at 80 C and cooled down aer each time
interval. An aliquot of the leachate (1 mL, 0.1 vol%) was removed
and directly, without dilution or addition of a standard,
measured on its relative metal content with TXRF. Aerwards,
the vial was placed back in the oil bath to continue the leaching
experiment. Only the four main metals present in the magnet
(Fe, Nd, Dy and Co) were considered and the relative mass
percentages in the leachate were calculated as: