An equilibrium model for absorption of multiple divalent metals by alginate gel under acidic conditions

An extended Langmuir model was proposed in this work to describe the simultaneous absorption of multiple divalent metal ions and hydrogen ions from acidic metal-containing aqueous media by an absorbent having one kind of active functional group. A viscous Na–alginate solution was directly dispensed dropwise into the acidic aqueous media containing dissolved copper and zinc to form spherical Cu–Zn–H–alginate gels which subsequently absorb these ions until final equilibrium was reached in batch experiments. Initial pH of the aqueous media was in the range of 2.6–5.4. Binding group density and binding stability constants of alginic acid, cupric alginate and zinc alginate were obtained simultaneously by fitting data to the proposed model developed in this work. Application of the constants obtained to the prediction of the extent of absorption of copper and zinc from an aqueous medium having an initial pH in the range of 2.6–5.4 is illustrated and compared with experimental results.