Adsorption Properties and Mechanism of Copper Ions from Wastewater by Lessonia nigrescens and Lessonia nigrescens Residue

Given the advantages of readily availability, low cost, convenient operation, and large adsorption capacity, brown seaweed has been studied extensively as a biosorbent for heavy metal remediation from aqueous media. Herein, raw Lessonia nigrescens and brown seaweed residue, a waste product from the manufacturing of alginate from L. nigrescens, were employed as low-cost and renewable adsorption materials for effective copper removal in wastewater streams. The influences of temperature, sample loadings, adsorption time, initial metal ion concentrations, and pH on the efficiency of the metal ions adsorption process were investigated. The thermodynamics and kinetics of Cu (II) adsorption for both the raw seaweed and seaweed residue were studied in order to determine the maximum removal efficiency and capacity. The characterization of the seaweed and seaweed residue before and after copper adsorption with SEM, FTIR, EDS, etc., coupled with the thermodynamics study, confirmed the ion exchange mechanism involved in the adsorption process. Under optimal conditions, the removal efficiencies were 75% and 71% for L. nigrescens and seaweed residue, respectively, and the adsorption capacities can reach 12.15 mg/g and 9.09 mg/g within 10 min for L. nigrescens and seaweed residue, respectively. The slight reduction in removal efficiency was because the active ion exchange sites were partially removed during the alginate extraction. The comparable metal ion removal efficiency between raw seaweed and seaweed residue suggesting the L. nigrescens residue is viable as bio-adsorbent and potential for industrial applications in adsorption process. The results provided a novel way to upgrade seaweed biomass in a biorefinery concept.