Effect of pH on the absorption of Cu(II) by alginate gel

The absorption of copper from synthetic solutions of cupric sulfate (initial Cu concentration: 200 ppm, initial pH: 2.4 or 3.4) in a batch loop fluidized bed reactor by alginate gels was investigated. Compared to the results obtained without addition of sulfuric acid [Jang L. K., Geesey G. G., Lopez S. L., Eastman S. L. and Wichlacz P. L., Wat. Res. 24, 889–897 (1990)], the copper-binding efficiency of the alginate gels at pH 3.4 was affected mildly by the acidity of the solution; at pH 2.4, the percent copper recovered was reduced by roughly one-half. In this work, an extended Langmuir model that took into account the competition between monovalent hydrogen ions and divalent cupric ions for the carboxyl groups on the alginate molecules was derived. This model yielded the binding group density of the alginate gel and binding stability constants for cupric alginate and alginic acid simultaneously. The new model was shown to be superior to the simple Langmuir model that expressed the results as conditional copper binding stability constant and capacity at a given pH. Application of the extended Langmuir model to the prediction of copper binding at pH 2 is also illustrated.