A step forward on mathematical modeling of barium removal from aqueous solutions using seaweeds as natural cation exchangers: Batch and fixed-bed systems

Abstract

A mechanistic and phenomenological model for multi-component cation exchange has been applied in order to describe the dynamic behavior of barium removal by seaweeds in batch and fixed-bed systems, instead of the empirical models usually applied. Initially, four macroalgae were tested as natural cation exchangers for barium removal: Arribadas, Gracilaria birdiae, Pelvetia canaliculata and Sargassum cymosum. Brown alga Pelvetia canaliculata showed the highest barium uptake capacity, mainly associated with the amount of carboxylic and sulfonic groups present in the biomass surface. A mechanistic model based on the mass action law was able to predict the cation exchange equilibrium for the Ba2+/Ca2+/H+ multi-component system, being able to determine the selectivity coefficients between all ionic species for the functional groups. The Pelvetia canaliculata in the calcium form, after acid pre-treatment was used for fixed-bed column tests. The operating capacity was 1.85 mEq/g (237 BV), treating 14 L of influent (0.45 L/g of natural resin) until the breakthrough point. Elution in counter-flow mode, using 1.0 M HCl as eluent, was fast and efficient (100%), using only 5 BV of eluent (181 g HCl/L resin; eluant ratio of 520%). The mass transfer model proposed, considering equilibrium given by the mass action law, was able to predict well the ion exchange process in batch or continuous operation mode during the saturation and elution steps for all chemical species in the liquid and solid phase.