Effects of impurities on the removal of heavy metals by natural limestones in aqueous systems

• Published in: Journal of environmental management 2012, Vol.93 (1), p.245-253
• Main Authors: Sdiri, Ali, Higashi, Teruo, Jamoussi, Fakher, Bouaziz, Samir
• Format: Article
• Language: English
• Subjects: Absorption; Adsorbents; Aluminum oxide; Animal, plant and microbial ecology; Applied ecology; Applied sciences; Aqueous solutions; Biological and medical sciences; Calcium Carbonate - chemistry; Chemical Precipitation; Conservation, protection and management of environment and wildlife; Contact; Exact sciences and technology; Feasibility Studies; Fundamental and applied biological sciences. Psychology; General aspects; Heavy metals; Hydrogen-Ion Concentration; Impurities; Kinetics; Limestone; Mathematical models; Metals, Heavy - chemistry; Pollution; Precipitation; Rocks; Sorption; Spectroscopy, Fourier Transform Infrared; Temperature; Wastewater treatment; Wastewaters; Water Pollutants, Chemical - chemistry; Water Purification - methods; Water treatment; Water treatment and pollution; X-Ray Diffraction
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2011.08.002

Effects of impurities on the removal of heavy metals by natural limestones in aqueous solutions were studied by evaluating various factors including limestone concentration, pH, contact time and temperature. Solutions of Pb(II), Cd(II), Cu(II) and Zn(II), prepared from chloride reagents at a concentration of 10 mg/L, were studied in a batch method. Four natural limestone samples, collected from the Campanian–Maastrichtian limestone beds in Tunisia, were used as adsorbents. Sorption experiments indicated that high removal efficiencies could be achieved. Limestone samples containing impurities, such as silica, iron/aluminum oxides and different kinds of clay minerals, demonstrated enhanced sorption capacity, nearing 100% removal in some cases. Kinetic experiments showed that the sorption of metal ions occurred rapidly at a low coverage stage, and that solutions were nearly at equilibrium after 60 min. Data trends generally fit pseudo-second order kinetic, and intra-particle diffusion, models. The following conditions were found to promote optimum, or near-optimum, sorption of heavy metals: 1) contact time of more than 60 min, 2) pH = 5, 3) >3 g/L limestone concentration and 4) T = 35 °C. The results of this study suggest that the limestones from northern Tunisia, that contain higher amounts of silica and iron/aluminum oxides, are promising adsorbents for the effective removal of toxic heavy metals from wastewaters.