Adsorption of Cd(II) from acidic aqueous solutions by tourmaline as a novel material

Abstract

Batch experiments were conducted to investigate the behavior and mechanisms for the adsorption of Cd(II) from aqueous solutions by tourmaline under acidic conditions. The results indicated that the adsorption of Cd(II) significantly depend on the adsorption time, temperature, and the initial concentration of the metal ion. Furthermore, tourmaline had a very good adsorption capacity for Cd(II) in acidic, neutral and alkaline aqueous solutions. This good adsorption capacity is attributed to the observation that tourmaline can automatically adjust the pH values of acidic (except pH 2.0 and 3.0), neutral or alkaline aqueous solutions to 6.4. Specifically, the removal capacity for Cd(II) was higher at strongly acidic pH values (in contrast to industrial wastewater pH values) compared to that obtained for other types of adsorbents. Furthermore, the results obtained in this study showed good fits to the Langmuir and Freundlich adsorption isotherms. However, the Langmuir model fit better than the Freundlich model. The maximum uptake of Cd(II) by tourmaline was 31.77, 33.11 and 40.16 mg/g at pH 4.0 at 15, 25 and 35°C, respectively. Therefore, tourmaline is an effective adsorbent for the removal of Cd(II) from acidic aqueous solutions. In addition, the kinetics for the Cd(II) adsorption by tourmaline closely followed the pseudo-second-order model. The thermodynamic parameters indicated that adsorption was feasible, spontaneous, and endothermic. Furthermore, the pH variation after adsorption, ζ-potential, metal ions desorbed and released, and FT-IR analysis indicated that the physisorption and chemisorption mechanisms of tourmaline for heavy metals. These mechanisms included water that was automatically polarized by tourmaline, the ion exchange process, and electropolar adsorption. Among the mechanisms, the automatic polarization of water caused by tourmaline is a unique adsorption mechanism for tourmaline. tourmaline, cadmium, acidic aqueous solutions, adsorption, mechanisms Citation:Wang C P, Wang B L, Liu J T, et al. Adsorption of Cd(II) from acidic aqueous solutions by tourmaline as a novel material. Chin Sci Bull, 2012Bull, , 57: 32183225, doi: 10.1007 With the increase in industrialization and urbanization, wastewater containing many heavy metals has been produced by electroplating, dyes, and the metallurgical and chemical industries. Furthermore, heavy metal pollution has become increasingly serious. Heavy metals have a negative impact on the environment because they are toxic to humans, animals, and plants, and they are not biodegradable. Therefore, heavy metals are prone to bioaccumulation in food chains, which results in a long-term toxic effect, even at low concentrations. Cadmium is one of the most dangerous heavy metals because of its presence in nature. Most of the cadmium that enters the body accumulates in the liver, kidney, pancreas and bones, which causes diseases such as anemia, hypertension, neuralgia, nephritis and secretion disorder [1]. Developing methods for effectively removing heavy metals from...

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