Fractionation of metals in thermomechanical pulp by selective leaching and inductively-coupled plasma mass spectrometry

The total concentrations of Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb and Zn in thermomechanical pulps were determined using a combination of open and closed digestion with nitric acid and hydrogen peroxide and inductively-coupled plasma mass spectrometry. The metals were found to be inhomogeneously distributed in the pulp, and therefore relatively large samples must be taken for analysis. The accuracy of the method was tested by analysing the reference material Peach Leaves (GBW 08501). The release of the metals from the pulp was studied, by leaching with water, a chelating agent (DTPA) and sulfurous acid. Very little of the metals were extracted into water. The leaching agent concentration was found to be the most important leaching parameter, whereas the pulp concentration, temperature and time had a minor effect on the leaching efficiency. The optimum values of the leaching parameters were determined. Leaching with DTPA removed the transition metals, while Ca and Mg remained in the pulp. Sulfurous acid removed almost all the metals from the pulp.