Batch and continuous heavy metals biosorption by a brown seaweed from a zinc-producing plant

Abstract

The removal of heavy metals by a dry biomass of a brown seaweed was evaluated. A continuous system was used, with an effluent from a Brazilian zinc producing industry, containing zinc (88.0 mg/L), cadmium (1.4 mg/L), and manganese (11. 7 mg/L), as well as high levels of calcium (444 mg/L), magnesium (100 mg/L) and sodium (37.0 mg/L). Preliminary results, in batch conditions, indicated fast uptake kinetics for the heavy metals, whose equilibria were reached in a maximum of 30 minutes. The continuous run was conducted in a laboratory acrylic column, lm high, containing several samplers, filled with the dry biomass. The system operated in upflow condition, at a flow rate of 25 mL/min, f or approximately 70 hours, with high operational stability. The results showed high efficiency in the biosorption of heavy metals. Sodium, calcium and magnesium were not incorporated by the biomass, probably as they are present in the structural polysaccharides of the biomass, thus preventing the establishment of an effective ion-exchange process. Analysis of the obtained results did not indicate selective uptake of the metals, probably due to their marked concentration differences in solution. The continuous laboratory system initially showed an efficiency close to 100% in the biosorption of all heavy metals, followed by a gradual decrease, as a function of the saturation of binding sites in the biomass. A mathematical adjustment of the curves obtained for the uptake of the different metals was used for estimating the amount of biosorbed metals, through mathematical computer integration.