Brown Seaweed as Biosorbent for the Removal of Divalent Heavy Metal Ions from Synthetic Mining Wastewaters

Abstract

Heavy metal contamination in mining-impacted water remains a treatment challenge. Conventional treatment methods can be effective, but they may require high chemical consumption, generate secondary waste, or become less practical. For this reason, biosorption has been studied as a possible alternative or complementary treatment. Brown seaweed is of interest because its cell wall contains functional groups that can interact with metal ions, while also being relatively low-cost and available. This thesis evaluated the brown seaweed biomass as a low-cost biosorbent for the removal of selected heavy metals from mining-relevant aqueous solutions under batch and fixed-bed column conditions. Batch sorption experiments were conducted using copper, lead, cadmium, nickel, and zinc salts to evaluate the effects of metal type, initial concentration, and solution chemistry on adsorption performance. The results showed that adsorption was strongly influenced by the metal ion and the counter-ion present in the solution. Copper nitrate showed higher uptake than copper chloride and copper sulfate, suggesting that the anions affected metal interaction with the seaweed surface. Lead and copper showed the highest overall adsorption performance, while Cadmium presented a limited uptake under the tested conditions. The equilibrium sorption data were described using Langmuir, Freundlich, and Sips models, while the sorption kinetic data were evaluated using the pseudo-first-order, pseudo-second-order, and Elovich models. The pseudo-second-order model provided the best overall description of kinetic behavior. Fixed-bed column sorption experiments were used to evaluate dynamic adsorption performance under continuous-flow conditions. The sorption breakthrough curves showed delayed breakthrough and greater treated volume for lead compared with cadmium, which reached exhaustion more rapidly. The modified dose-response model provided the strongest empirical description of the breakthrough curves. Overall, this study shows that the brown seaweed biomass has potential for the removal of selected heavy metals, particularly lead and copper, while further work with real mining wastewater, regeneration, and scale-up evaluation are needed for practical implementation.