Removal of Heavy Metals From Aqueous Solutions with Calcium Alginate Beads
T. Luna-Pineda, O. Perales-Pérez, F. Román-Velázquez
University of Puerto Rico at Mayagüez, PR
Keywords: uptake, heavy metals, sodium alginate
Abstract:The present research is focused on the development of a bio-sorbent based on alginate beads. The alginate is a natural polymer extracted from brown seaweed with capability of hosting divalent cations in gel state, which allows the cross-linking with Ca or Ba ions to form egg-box like structures. The absorption capability is associated with ion exchange between protons of the free carboxylic functional groups of the alginate and metal ions in solution. We prepared Ca-alginate beads (CAB) by drop-wise addition of low viscosity sodium alginate solution to a calcium chloride solution. CAB at a concentration as low as 0.2g/L were capable to remove up to 47%As after 24 hours of contact at room-temperature with an initial pH4.5 and final pH3.3. Prolonging the contact time caused some release of metal species. This desorption behavior was attributed to the drop in pH observed at the end of the contact stage in batch experiments. In order to improve the stability in pH along this stage, a pH-stat unit was used to precise control of the pH during the whole duration of a Cu(II) sorption test. Under this pH-controlled condition (pH6.4), CAB was capable of removing 98%Cu from starting 6ppm solutions in 10 hours.