CN and heavy metal removal through formation of layered double hydroxides from mixed CN-containing electroplating wastewaters and pickle acid liquor

The common ligand CN− has been widely used in some core industries, such as electroplating and mining, as it significantly enhances process efficiency and product quality. The use of CN− however generates a vast amount of CN-containing heavy-metal wastewaters, harming both environmental and human health. In this research paper, we present a co-precipitation strategy to treat CN-containing heavy-metal wastewaters (Ni, Zn, Cr and Fe) and pickle acid liquor (Fe) via formation of layered double hydroxide (LDH). Our experimental data demonstrate that Zn, Cr and Fe were completely removed and Ni was reduced from 100–400 to 3.0 mg/L, and about 60% CN− was simultaneously removed (from 6–8 to 2.5–4 mg/L). This efficiency was constantly achieved under varied experimental conditions, including a wide range of heavy metal concentrations and their ratio with pH in 7–11 at 25–60 °C.

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• CN-containing electroplating wastewaters and pickle acid liquor were co-treated.
• The main removal mechanism was formation of layered double hydroxide (LDH).
• Heavy metals were mainly removed by forming hydroxyl layers of LDH.
• CN− was primarily eliminated via intercalating into interlayer of LDH.