Simultaneous Removal of Cu2+, Zn2+ and Cd2+ from Aqueous Solutions by Alkali Activated Slag

Abstract

Electric Arc Furnace (EAF) slag containing larnite, gehlenite, wuestite, montcellite and calcite as the main crystal phases was alkali activated using the alkali activator prepared by the mixing of two solutions, sodium silicate and NaOH. Alkali Activated (AA) slag based on EAF slag is used as an adsorbent for Cu²⁺,Cd²⁺ and Zn²⁺ from aquatic solutions performing the batch adsorption test at the range temperature between 20 and 45 °C. AA slag sample is characterized by XRPD, FTIR and SEM/EDS analysis and the results indicate crystalline-amorphous structure of AA slag that contains Calcium Aluminate Silicate Hydrate (C-A-S-H) phase. Concentration of Cu²⁺, Cd²⁺ and Zn²⁺ in aqueous solution was determined using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The results obtained indicate that, in a multicomponent system of three dissolved ions, AA slag shows highest affinity towards the Cu²⁺. The order of the metal ion adsorption onto AA slag was: Cu²⁺, Cd²⁺ and Zn²⁺. The highest adsorption of Cu²⁺ is attributed to the highest electronegativity and lowest hydrated ionic radii of cation in comparison to Cd²⁺ and Zn²⁺. Pseudo-first-order and pseudo-second-order kinetics models, Langmuir and Freundlich isotherm models were applied in order to investigate the adsorption process. The results have shown that data better fitted the pseudo-second kinetic and Langmuir isotherm models The investigation of mechanism of adsorption indicate that both film diffusion and intra-particle diffusion have occurred during the adsorption process. The thermodynamics parameters of adsorption process indicate the spontaneous and endothermic character of heavy metals adsorption on the AA slag.