Resource utilization of hazardous Cr/Fe-rich sludge: synthesis of erdite flocculant to treat real electroplating wastewater

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College of Forest Resources and Environmental Science


Cr/Fe-bearing sludge is a hazardous solid waste, produced at mass production in smelting, plating and surface finishing industries. Such waste is commonly treated by chemical detoxification and safety landfill, whereas only a few Cr-rich sludge is recycled as a tanning reagent. In this study, a novel route was developed to recycle Cr/Fe-bearing sludge as erdite-bearing flocculant for wastewater treatment. Results showed that two sludges were irregular aggregates, one of which contained 1.6 wt.% Cr (short for LS) and the other contained 4.2 wt.% Cr (HS). After hydrothermal treatment, stable Cr(III)/S-bearing product was formed from the Cr(VI) reduction in the sludges. Conversely, erdite was generated in nanorod form with diameter and length of 200 nm and 0.5–1 μm from LS, respectively, whereas grew radially to 1.5–2.5 μm for HS. The two erdite-bearing products were spontaneously hydrolysed to Fe/S-bearing flocs and showed similar performance in the treatment of real electroplating effluent with 91.55, 1.94 and 0.25 mg/L of Zn, Ni and Cr, respectively. For instance, by adding 1 g/L product of LS, the release of Cr from the products did not occur, and the residual Zn, Ni and Cr in the effluent was 0.25, 0.65 and 0.17 mg/L, respectively, which met the discharge standard of the electroplating industry. With the two converted products, the residual Zn/Ni/Cr concentrations were apparently lower than those of the raw sludges and other common reagents (e.g. polymeric ferric sulphate, activated carbon and diatomite). Thus, such erdite-bearing products could serve as a flocculant and then be applied in electroplating wastewater treatment.

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Journal of Environmental Health Science and Engineering