Magnetic nanomaterials recovered from co-treatment of CN-containing electroplating wastewaters and pickle acid liquor

•LDHs were synthesized from CN-containing electroplating waste water and pickling acid liquor.•The synthesized LDHs were successfully converted into superparamagnetic nanomaterials.•Fe amount in LDHs influenced saturation magnetization of the formed magnetic material.•During the conversion, secondary pollution resulting from CN was significantly reduced.

CN− has been widely used in electroplating and mining, generating a vast amount of CN-containing heavy-metal wastewaters. In this research paper, we present a strategy to recycle these cyanide-containing electroplating wastewaters (Ni, Zn, Cr and Fe) with pickle acid liquors (Fe) and produce magnetic nanomaterials. The process includes formation of layered double hydroxides (LDH) as the intermediates and their conversion to valuable magnetic materials. LDH intermediates were first precipitated from these two wastewaters and then thermally converted into superparamagnetic mixed oxide nanomaterials, with the crystallite size of 10–25 nm and the saturation magnetization up to 40 emu/g. Specifically, during the conversion, secondary pollution resulting from CN− was significantly reduced. This research thus demonstrates a cost-effective and safe way to treat CN-containing wastewaters and transfer to useful nanomaterials.

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