Single and coadsorption of copper, cadmium, lead and zinc onto basic oxygen furnace slag

In this work, single adsorption removal of copper, cadmium, lead, and zinc from aqueous solution by basic oxygen furnace slag (BOFs) which was activated by the mechanochemistry process was investigated. Effects such as initial concentration, contact time, pH, and temperature, as well as adsorption isotherm and kinetics were discussed. The coadsorption capacity of these heavy metals was evaluated. Adsorption mechanism was interpreted by X-ray diffraction and possible reaction path in aqueous solution. In a single metal system, the adsorption equilibrium time was close to 180 min while increasing the initial concentration of adsorbates, pH value, and temperature was in favor of adsorption reaction and increased the maximum adsorption capacity of each metal onto BOFs. Freundlich model was well-fitted than Langmuir in description of adsorption isotherm while the pseudo-second-order model was closer to experimental results. In binary adsorption system, the equilibrium adsorption capacity of coexisting heavy metals Cd(II), Pb(II), and Zn(II) was almost invariably with an increase of initial concentration of Cu(II) in Cu–Cd, Cu–Pb, and Cu–Zn mixed solutions. Cu(II) showed the weak adsorption competitiveness of Cu(II) in the ternary system while the heavy metal competitive adsorption order was Pb(II)>Cd(II)>Zn(II)>Cu(II) in fourfold system. The possible reaction path showed that besides concentration of heavy metals and pH of a solution, the hydrated radius of heavy metal ion and co-efficient of solidity of product formed in the process of precipitation were contributing to adsorption competitiveness of heavy metals.