COMPLEX EQUILIBRIA IN THE SYSTEM M2+-POLYGALACTURONIC ACID (PECTIN) - H2O (M = Co, Ni, Cu, Zn, Cd AND Pb)

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Abstract
Ionisation constants for polygalacturonic acid (pectin) were determined by pH-metric titration in aqueous solution at different temperatures (283, 293, 303 and 313 K) and ionic strengths (0.1, 0.5, 1.0, 1.5 and 2.0), maintained with NaNO3. Complexing of pectin with Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ under the same conditions and M:L ratios of 1:2 or 1:4 was studied. It was found that ML complexes prevail. Stability constants were evaluated. Complexformation is a result of favourable entropy changes, whereas there is no significant change of enthalpy. The possibility of metal extraction by complex formation and ultrafiltration was examined. Selectivities in ultrafiltration and productivities of membranes for Cu2+ complexes of pectin were determined.

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