Pb2+ ions adsorption onto raw and chemically activated Dibetou sawdust: Application of experimental designs

Abstract

Dibetou wood sawdust, SEM and IRTF characterized, collected from a local sawmill, was used in its raw and chemically activated forms using nitric acid and sodium hydroxide to retain Pb2+ ions, according to several parameters (pH, contact time, initial metal concentration, mass of adsorbent and temperature of the medium). The results obtained reveal that the removal rate of Pb2+ ions on raw and activated Dibetou sawdust reached a percentage of about 84% and 93% successively. The experimental design methodology using the full factorial design has enabled us to study and to check the influence of the various parameters on Pb2+ ions adsorption onto raw and activated Dibetou sawdust; it allowed us, also, to define the interactions between these latters. A response surface methodology (RSM) based on the central composite design (CCD) was used to optimize this process. The results obtained showed that initial concentration, pH, contact time and mass of adsorbent affected the lead (II) removal by adsorption. The optimum conditions were found as pH = 6, mass of adsorbent = 0.875 g per 100 mL of solution and contact time = 90 min for raw Dibetou and 47.5 min for activated Dibetou using a concentration of 275 mg.L−1 of metallic ion. In these conditions, removal rates of Pb2+ ions reach 94% onto raw sawdust and 99% using its activated form. The adsorption data are well fitted with Langmuir isotherm. The maximum adsorption capacities are 33.33 mg·g−1 for the raw sawdust and 61.73 mg·g−1 for its activated form. Kinetic modeling is well described by the pseudo-second order model (0.99 < R2 < 1). Raw and/or activated Dibetou sawdust have good efficiency for the removal of Pb2+ ions, which making them environmentally friendly decontaminants of choice of polluted waters. Keywords: Dibetou sawdust, Lead II adsorption, Chemical activation, Experimental designs