Characteristics of olive mill solid residue and its application in remediation of Pb2+, Cu2+ and Ni2+ from aqueous solution: Mechanistic study

This study investigated the use of untreated olive mill solid residues (OMSR) as a solid extractant for Pb2+, Cu2+ and Ni2+ ions from aqueous solution. It was shown that the solution initial pH value affected the metal adsorption capacity and behavior. However, over the pH range of 3.0-5.0, pH-related effects were not significant. Meanwhile, at lower pH values the uptake capacity decreased. It was found that the qmax values are (0.54, 0.59 and 0.63), (0.46, 0.63, and 0.69) and (0.31, 0.42, and 0.47) meq/g for Pb2+ Cu2+ and Ni2+ at 298, 308, and 328 K; respectively. The uptake capacity order is: Pb2+ > Cu2+ > Ni2+. It was also concluded that the R-P and Langmuir models clearly described the metals adsorption onto OMSR more than that of Freundlich and D-R models. The thermodynamics constants ΔH0, ΔS0 and ΔG0 of the adsorption process showed that the adsorption of Pb2+ and Cu2+ was endothermic and spontaneous in nature and an opposite finding was observed for Ni2+ ions. In conclusion, the mode of interaction between Pb2+, Cu2+ and Ni2+ ions and OMSR was investigated by comparing the changes in the position and intensity of the surface functional groups using FTIR technique.