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Valorization of manganese-containing groundwater treatment sludge by preparing magnetic adsorbent for Cu(II) adsorption

Zhu, Suiyi, Lin, Xue, Dong, Ge, Yu, Yang, Yu, Hongbin, Bian, Dejun, Zhang, Lanhe, Yang, Jiakuan, Wang, Xianze, Huo, Mingxin
Journal of environmental management 2019 v.236 pp. 446-454
X-ray diffraction, X-ray fluorescence spectroscopy, adsorbents, adsorption, aluminum oxide, ascorbic acid, copper, ferrihydrite, groundwater treatment, hematite, hot water treatment, intermediate product, ions, iron, magnetism, manganese, manganese oxides, models, recycling, reducing agents, rhodochrosite, siderite, silicon, sludge, sodium, sorption isotherms, titration, wastewater
Mn-containing sludge from groundwater treatment was converted to magnetic particles (MPs) via a one-step hydrothermal method using sodium ascorbate (SA) as the reductant. The MPs were characterized by X-ray diffraction spectroscopy, Mössbauer spectroscopy, X-ray fluorescence spectroscopy, magnetometry and Gran titration and the results showed that magnetic jacobsite was obtained as an intermediate product in transformation of Fe/Mn oxides to siderite and rhodochrosite. When the molar ratio of SA to Mn in the sludge was two, the produced MPs-2 contained a mixture of ferrihdyrite, hematite, jacobsite and Si/Al oxides, and could magnetize at 2.4 emu/g. Ferrihydrite content in MPs decreased with increase of the SA/Mn molar ratio, leading to decrease of the surface sites concentration (Hs). Thus, MPs-2 contained optimized Hs of 6.7 mmoL/g and a desirable adsorption capacity of Cu(II) (73.1 mg/g). The adsorption isotherms of MPs-2 on Cu(II) complied with the Langmuir model and the adsorption kinetics fitted well with the pseudo-second-order model. The major mechanism of adsorption was cationic exchange of the coordinated H and Na ions on MPs-2 surface sites with the Cu(II) ions. This study was the first time to report preparation of MPs by recycling Mn-containing sludge, which could be used as a high-capacity and low-cost adsorbent in treatment of heavy metal-containing wastewater.