An XPS Study of the Reaction of Metal Ions with Borohydride Under Reductive Bleaching Conditions, 1991 Pulping Conference Proceedings

Metal ions in mechanical pulp brightening systems affect hydrogen peroxide (H2 O2 ) bleaching by accelerating decomposition of hydrogen peroxide and by forming coloured metal complexes with pulp. We have examined the effect of borohydride on Fe(III), Cu(II) and Mn(II), the predominant ions found in mechanical pulp and the associated white water. Metal precipitates were produced in solutions made alkaline by either adding both sodium borohydride and sodium hydroxide or by adding sodium borohydride alone. Subsequently, we applied X-ray photoelectron spectroscopy to determine the oxidation states of the metal ions in the precipitates. The ion Fe(III) was consistently reduced to Fe(O) except in the case of one treatment involving a borohydride charge of 0.038% with no caustic charge, where Fe(II) was produced. The results for Mn(II) were ambiguous. Cu(II) was reduced to Cu(I) and partially reduced to Cu(O), using borohydride charges of 0.038 and 0.378%, respectively, with or without the addition of caustic.