Influence of ligand type and solution pH on heavy metal ion complexation in cellulosic fibre: model calculations and experimental results

Complexation of heavy metal ions such as Cu²⁺, Zn²⁺ and Co²⁺ by cellulosic fibres cotton, lyocell and viscose was studied in the pH range from pH 7–13. Glycine and sodium D-gluconate complexes were studied. Complex formation in the cellulose matrix depends on ligand, solution pH, complex species formed and type of cellulosic fibre. Species distribution in solution was calculated using the program SPE and literature data for formation constants of M²⁺-glycine and M²⁺-gluconate complexes. The calculated data permit explanation of the experimental heavy metal uptake in the cellulose matrix. In presence of GLY lower heavy metal concentrations were observed. Heavy metal complexation decreases with increasing pH between 7 and 11. For Cu²⁺ and Zn²⁺ a strong increase in metal binding capacity in the fibres was observed at pH 13 for Cu²⁺ and pH 11–12 for Zn²⁺ respectively. Low Zn²⁺ content is analysed at pH 13 due to zincate formation.