Kinetics, Thermodynamics, and Mechanism of Cu(II) Ion Sorption by Biogenic Iron Precipitate: Using the Lens of Wastewater Treatment to Diagnose a Typical Biohydrometallurgical Problem

Babatunde Oladipo; Elaine Govender-Opitz; Tunde V Ojumu

doi:10.1021/acsomega.1c03855

Kinetics, Thermodynamics, and Mechanism of Cu(II) Ion Sorption by Biogenic Iron Precipitate: Using the Lens of Wastewater Treatment to Diagnose a Typical Biohydrometallurgical Problem

ACS Omega. 2021 Oct 17;6(42):27984-27993. doi: 10.1021/acsomega.1c03855. eCollection 2021 Oct 26.

Authors

Babatunde Oladipo¹, Elaine Govender-Opitz², Tunde V Ojumu¹

Affiliations

¹ Department of Chemical Engineering, Cape Peninsula University of Technology, Bellville, Cape Town 7535, South Africa.
² Department of Chemical Engineering, University of Cape Town, Rondebosch, Cape Town 7700, South Africa.

Abstract

The feasibility of improving typical biohydrometallurgical operation to minimize copper losses was investigated by the use of biogenic iron precipitate for the uptake of Cu(II) ions from aqueous solutions. The iron precipitate was obtained from mineral sulfide bioleaching and characterized using SEM/EDS, XRD, FTIR, BET, TGA, and pH_pzc analyses. The results show that the precipitate is highly heterogeneous and that Cu(II) ion adsorption can be described by both Freundlich and Langmuir adsorption isotherms, with a maximum adsorption capacity of 7.54 mg/g at 30 °C and 150 mg/L. The sorption followed pseudo-second-order kinetics, while the major presence of -OH and -NH₂ functional groups initiated a chemisorption mechanism through an ion-exchange pathway for the process. Ionic Cu(II) (radius (0.72 Å)) attached easily to the active sites of the precipitate than hydrated Cu(II) (radius (4.19 Å)). With an estimated activation energy of 23.57 kJ/mol, the obtained thermodynamic parameters of ΔS° (0.034-0.050 kJ/mol K), ΔG° (8.37-10.64 kJ/mol), and ΔH° (20.07-23.81 kJ/mol) indicated that the adsorption process was chemically favored, nonspontaneous, and endothermic, respectively. The 43% Cu(II) removal within 60 min equilibrium contact time at pH 5 was indicative of the reduced efficiency of copper extraction observed in a real-life biohydrometallurgical process due to sorption by the iron precipitate. The result of this study might provide an insight into the management of the biohydrometallurgical process to minimize copper losses. It may also help mitigate environmental pollution caused by the disposal of these biogenic iron precipitate residues.