Sorption of alkaline earth metal ions Ca2+ and Mg2+ on lyocell fibres

Ca2+ and Mg2+ content of cellulose fibres is of relevance for a wide range of applications e.g. textile processing, pulp/paper, food. Sorption of Ca2+ and Mg2+ ions were found on lyocell type regenerated cellulose fibres. Higher affinity was found for Ca2+ ions compared to Mg2+ ions. At pH 9, fibre saturation was observed at a calcium binding capacity of 18–20 mmol/kg. A carboxylic group content of 18 mmol COOH per kg fibre material was determined based on the Methylene Blue absorption. This indicates a 1:1 molar stoichiometry between the carboxylic groups present in the fibres and the bound Ca2+ ions. Thus it is proposed that the salt in fibre shows the general composition (Cell-O− Ca2+ X−), X− being an anion bound in the salt to achieve charge neutrality.The sorption of Ca2+ also can be demonstrated by complex formation with 1,2-dihydroxy-9,10-anthraquinone (alizarin) which forms a red-violet Ca2+-complex. Colour fixation thus can be used as an indicator for the Ca2+-ions bound in the fibre.