In this study, the performances of various adsorbents—red mud, zeolite, limestone, and oyster shell—were investigated for the adsorption of multi-metal ions (Cr3+, Ni2+, Cu2+, Zn2+, As3+, Cd2+, and Pb2+) from aqueous solutions. The result of scanning electron microscopy analyses indicated that the some metal ions were adsorbed onto the surface of the media. Moreover, Fourier transform infrared spectroscopy analysis showed that the Si(Al)-O bond (red mud and zeolite) and C-O bond (limestone and oyster shell) might be involved in heavy metal adsorption. The changes in the pH of the aqueous solutions upon applying adsorbents were investigated and the adsorption kinetics of the metal ions on different adsorbents were simulated by pseudo-first-order and pseudo-second-order models. The sorption process was relatively fast and equilibrium was reached after about 60 min of contact (except for As3+). From the maximum capacity of the adsorption kinetic model, the removal of Pb2+ and Cu2+ were higher than for the other metal ions. Meanwhile, the reaction rate constants (k1,2) indicated the slowest sorption in As3+. The adsorption mechanisms of heavy metal ions were not only surface adsorption and ion exchange, but also surface precipitation. Based on the metal ions’ adsorption efficiencies, red mud was found to be the most efficient of all the tested adsorbents. In addition, impurities in seawater did not lead to a significant decrease in the adsorption performance. It is concluded that red mud is a more economic high-performance alternative than the other tested adsorption materials for applying a removal of multi-metal in seawater.

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A B S T R A C THeavy metal ions (Pb 2+ , Cd 2+ , Cu 2+ , Ni 2+ , and Zn 2+ ) were adsorbed by recycled aggregate (RA), which was pretreated with acidic or basic solution. Brunauer-Emmett-Teller analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy/energy dispersive spectroscopy were used to investigate the differences in the physicochemical and adsorption characteristics between RA and pretreated RA. The results suggest that RA treated with NaOH (NRA) had improved physical and chemical characteristics. The adsorption kinetics of NRA for heavy metals was pseudo-second-order, and most of the heavy metal ions were bound to the NRA within 360 min. The maximum adsorption capacities assumed by Langmuir isotherms were in the order Pb 2+ > Cu 2+ > Cd 2+ > Ni 2+ > Zn 2+ . Equilibrium adsorption data for the heavy metal ions fit well with the Langmuir model with regression coefficients R 2 > 0.95. At solution pH lower than 5, the adsorption specificity of the NRA for heavy metals was Pb 2+ ≥ Cu 2+ > Cd 2+ > Zn 2+ ≥ Ni 2+ . Moreover, in harmful substance tests, all the heavy metals were detected in small amounts, but were found to be below the corresponding acceptance standards (as defined by the waste official test and toxicity characteristic leaching procedure).