Crosslinked Calcium Alginates Porous Beads for Adsorption Removal of Ammonium Ions

Abstract

Ammonia pollution of natural water can promote adverse undesirable environmental impacts on aquatic fauna, human and environment. Different techniques were elaborated for treatment of this pollution. Recently, polymer hydrogels have been successfully used as adsorbents of ammonium ions. Among the polysaccharides that can be used in the wastewater treatment, the alginates have the ability to adsorb various pollutants in the flexible channels by electrostatic interaction between the ${\text{NH}}_{4}^{ + }$ ions in aqueous solution and the –COO^– groups of the polymeric network. Alginates are natural biopolymers; they could be obtained from the brown seaweeds, extraction of alginates is often effectuated in a sodium form related to their fast solubility in cold water. In this work, sodium alginate solution was crosslinked by calcium divalent cations in the beads forms. The resulting beads are roughly spherical, when they are swollen; they become bigger in size, they were characterized by several techniques, which revealed that the sample contains different mineral and organic functional groups. Indeed, optimization of the contact time, temperature, pH, initial adsorbate concentration and initial adsorbent concentration has been studied. So, the maximal removal efficiency was 47.72% after 60 min, the favorable temperature of adsorption was 30°C where the maximal removal efficiency was 69.54%, the optimal pH is 7 with a maximum removal efficiency of 69.54%. Moreover, the removal efficiency decreased considerably from 69.54 to 34.26% at initial EAC varied from 10 mg-${\text{NH}}_{4}^{ + }$/L to 1000 mg-${\text{NH}}_{4}^{ + }$/L and an optimal initial adsorbent amount of 0.1 g where the removal efficiency was 69.54% and the equivalence EAC was 30.46 mg-${\text{NH}}_{4}^{ + }$/L. Furthermore, study of adsorption isotherms indicated that the process was obeyed to both models of Langmuir and Freundlich with R² values of 0.994 and 0.98 respectively, with a maximal adsorption capacity of 58.82 mg/g that calculated from Langmuir model. Finally, the spectral and the structural analyses after the adsorption process proved this phenomenon and allowed to apply these crosslinked beads-A in the treatment of waters charged with ammonium ions.