Removal of Pb2 + ions from aqueous solutions by fixed-BED column using a modified brick: (Micro)structural, electrokinetic and mechanistic aspects

Brick was pre-activated with HCl and subsequently coated with ferrihydrite. To assess the potential of this modified brick for Pb2+ removal, adsorption experiments were conducted in a fixed-bed continuous-flow column system. The prediction of breakthrough curves was obtained by using the Thomas model. MINTEQ computations revealed that Pb2+ and Pb(OH)+ are the major species present in the column solution. Potentiometric analysis and electrophoretic mobility measurements provided strong evidence of the surface basicity of coated brick due to the existence of sodic negatively charged sites: >SO−Na+ with SFe; Si; or Al. Using Environmental Scanning Electron Microscopy (ESEM) equipped with an Energy Dispersive X-Ray Spectroscopy (EDS), micro-analyses showed clearly that Na atoms present in coated brick are preferentially bound to ferrihydrite specimens. The ESEM/EDS technique allowed to further highlight discrete PbFe combinations and to contend that Pb2+ ions are better adsorbed onto Fe-rich aggregates than onto SiO2 and alumino-silicates (clays). Before the breakthrough time, the pH in the effluent solution was found to be dependent upon the electrokinetic characteristics of coated brick. After this time, the pH was instead governed by the acidity of not adsorbed lead(II). To support this, simulation calculations relative to the pH evolution in the column medium were made. The addition of a background electrolyte (Na+NO3−) led nevertheless to a weaker adsorption capacity of Pb2+ on coated brick, because positively charged Na ion competed favorably at the expense of lead(II) via electrostatic attraction forces.