Adsorptive removal of Cd2+, Pb2+, and Fe2+ from acid mine drainage using a mixture of waste orange and lemon activated carbon (WOLAC): equilibrium study

• Published in: Journal of the Iranian Chemical Society 2023-05, Vol.20 (5), p.1119-1133
• Main Authors: Ramutshatsha-Makhwedzha, Denga, Mbaya, Tresor, Mavhungu, Avhafunani, Mavhunga, Mapula Lucey, Mbaya, Richard
• Format: Article
• Language: English
• Subjects: Acid mine drainage; Activated carbon; Adsorption; Adsorptivity; Analytical Chemistry; Biochemistry; Cadmium; Chemistry; Chemistry and Materials Science; Citrus fruits; Diffusion rate; Inorganic Chemistry; Isotherms; Mathematical models; Mixtures; Organic Chemistry; Original Paper; Parameters; Phosphoric acid; Physical Chemistry; Pore size; Sorbents
• ISSN: 1735-207X; 1735-2428
• DOI: 10.1007/s13738-022-02739-w

The mixture of 1:1 waste orange and lemon peel activated carbon (WOLAC) by phosphoric acid (H 3 PO 4 ) activation agent was prepared and reported for the first time for the removal of Cd 2+ , Pb 2+ and Fe 2+ from acid mine drainage (AMD). Characterization results on WOLAC material showed a pore size and BET surface area of 5.18 nm and 168.29 m 2 /g, respectively. The pore size was mesoporous according to the IUPAC classification, and it was confirmed by the broad peak observed on the XRD spectra. The univariate approach was used to optimize parameters such as pH, adsorbent mass, concentration, and contact time in the batch adsorption study. The sorbent's adsorption capacity for WOLAC was determined to be 60, 50.2, and 35 mg/g for Cd 2+ , Pb 2+ , and Fe 2+ , respectively. The nature of the adsorption process was studied using the Langmuir, Freundlich, Temkin, and Dubinin–-Radushkevich isotherm models. The data obtained fit better with the Langmuir isotherm model with R 2 that ranged from 0.975 to 0.990, which indicates a homogeneous adsorption process. Kinetic studies showed that the adsorption process was best described by a pseudo-second-order model. Although intraparticle diffusion is involved in regulating the overall rate of the adsorption process, it is not the only rate-controlling step. The thermodynamic parameters indicate that Cd 2+ , Pb 2+ , and Fe 2+ adsorption on WOLAC is spontaneous and endothermic. In addition, the WOLAC was found to be reusable for up to 5 cycles.