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In this study, the adsorption of hexavalent chromium and zinc ions from the solution is investigated by raw red mud and mechanical-chemical activated red mud along with the possibility of selective reclamation of these ions from the solution. The mechanical-chemical activation of red mud was done by employing high-energy milling and subsequent acid treatment with HN03. Raw red mud (RRM) and mechanical-chemical activated red mud (MCARM) adsorbents were characterized with Fourier transform infrared spectroscopy (FUR), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and Brmauer-Emmett-Teller (BET) methods. In order to determine the suitable adsorption conditions, effects of pH of the solution, amount of adsorption, temperature, and time of adsorption were investigated. It was found that the optimum pH for the adsorption of hexavalent chromium and zinc ions by MCARM adsorbent was 2 and 6, respectively. According to these pH values, MCARM had the ability to separately adsorb more than 95 and 79% of hexavalent chromium and zinc ions from the solution, respectively. Experimental results were in good agreement with Langmuir and Freundlich isotherms. By considering the kinetic models of adsorption, the kinetics of the adsorption of both ions followed the pseudo-second-order reaction model. It was also determined that almost 25.8 and 61.8% of the hexavalent chromium and zinc ions adsorbed in MCARM could be recovered. [ABSTRACT FROM AUTHOR]

Red mud (RM) is the industrial waste of alumina production and causes serious environmental risks. In this paper, a novel activation procedure for RM (mechano-chemical processing) is proposed in order to improve the nitrate adsorption from water. High-energy milling and acidification were selected as mechanical and chemical activation methods, respectively. Synthesized samples of adsorbent were produced considering two parameters of activation: acid concentrations and acidification time in two selected milling times. Optimization of the activation process was based on nitrate removal from a stock solution. Experimental data were analyzed with two-way analysis of variance and Kruskal-Wallis methods to verify and discover the accuracy and probable errors. Best conditions (acceptable removal percentage >75) were 17.6% w/w for acid concentrate and 19.9 minutes for acidification time in 8 hours for milling time. A direct relationship between increase in nitrate removal and increasing the acid concentration and acidification time was observed. The adsorption isotherms were studied and compared with other nitrate adsorbents. Characterization tests (X-ray fluorescence, X-ray diffraction, Fourier transform infrared spectrophotometry, dynamic light scattering, surface area analysis and scanning electron microscopy) were conducted for both raw and activated adsorbents. Results showed noticeable superiority in characteristics after activation: higher specific area and porosity, lower particle size and lower agglomeration in structure. [ABSTRACT FROM AUTHOR]

• CNZF nanocomposite synthesized with co-precipitation method for the first time. • CNZF represented a considerable specific surface area and remarkable magnetic properties. • Arsenic (V) adsorption application of CNZF was investigated for the first time. • Processed nanocomposite remediated the arsenic contaminated wastewater successfully. N i 0.5 Z n 0.5 F e 2 O 4 Ferrite (NZF) and N i 0.5 Z n 0.5 F e 2 O 4 /CNTs nanocomposite (CNZF) were prepared by inverse co-precipitation method as novel magnetic adsorbents. The characteristic consequences of XRD, FTIR, FESEM and XPS analysis indicated that the adsorbents were favorably produced. The results revealed that the saturated magnetization (M s) of the NZF and CNZF powders was 35 and 15 emu/g, respectively. The reason of this decrease for the CNZF nanocomposite was the existence of CNT with a weak magnetic property in the complex of CNZF compared to the NZF. However, the both adsorbents have a fast-magnetic response that can be effective for separation of adsorbents from the solution by an external magnetic field. The adsorbents were then assessed for removal of arsenic(V) contaminated anions from simulated industrial wastewater. Batch reactor model was utilized to investigate the performance of adsorption and modifying efficient parameters like pH, adsorbent dosage and contact time to enhance the maximum adsorption capacity (q m). The maximum adsorption capacities of NZF and CNZF were found to be 56 mg/g and 66 mg/g, respectively at contact time of 30 min, adsorbent dosage of 6 g/l and pH of 2. The adsorption isotherm as a function of adsorbent dosage was assessed. It was shown that Langmuir isotherm had the highest consistency with the experimental data for both adsorbents. The kinetic behavior of adsorption over the time was evaluated. The pseudo-second order model provided the finest agreement to the experimental data. The dominant mechanism of adsorption was estimated to be surface complexation. [ABSTRACT FROM AUTHOR]