Marine macroalgae Pelvetia canaliculata (Linnaeus) as natural cation exchanger for metal ions separation: A case study on copper and zinc ions removal

• Marine macroalgae Pelvetia canaliculata showed to be a natural cation exchanger.
• Sequestration of Zn2+ and Cu2+ by raw biomass occurs by the release of light metals.
• The amount of weak acid carboxylic groups on the biomaterial surface is 1.5 mEq/g.
• The amount of strong acid sulfonic groups on the biomaterial surface is 1.0 mEq/g.
• Selectivity coefficients of the natural exchanger increases as Na+ < H+ < Zn2+ < Cu2+.

The aim of this study was to investigate the cation exchange capacity of the macro-algae Pelvetia canaliculata (Linnaeus) for Cu2+ and Zn2+ removal from aqueous solutions in a batch system. Carboxylic and sulfonic groups present in the surface of the macroalgae are the main functional groups responsible by Cu2+ and Zn2+ removal. Tests with the raw algae showed that sodium, potassium, magnesium and calcium are easily replaced by copper and zinc ions. Considering that the sodium chloride salt is the most abundant salt and available throughout the world at low price, all the binding sites of the natural cation exchanger were converted into the sodium form. The mass action law for the ternary mixtures, Cu2+/H+/Na+ or Zn2+/H+/Na+, was able to predict the equilibrium data, getting selectivity coefficients of copper vs. sodium higher than zinc versus sodium and hydrogen vs. sodium for the carboxylic groups. At pH 4.0, almost all binding sites were occupied by copper and zinc ions, achieving maximum uptake capacities near 2.4 mEq/g. A mass transfer model, using the mass action law to describe the ternary equilibrium, and considering a linear driving force model to describe the intraparticle mass resistance, was able to predict the kinetic profiles for both ternary systems in a batch system.

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