| Summary: | Alkaline chlorination, an efficient but high chemical cost process, is commonly employed for cyanide (CN<sup>−</sup>) removal from CN-rich wastewater streams. CN<sup>−</sup> removal and recovery through the precipitation of Prussian Blue (Fe<sub>4</sub><sup>III</sup>[Fe<sup>II</sup>(CN)<sub>6</sub>]<sub>3</sub>, PB) or Turnbull’s Blue (Fe<sub>3</sub><sup>II</sup>[Fe<sup>III</sup>(CN)<sub>6</sub>]<sub>2</sub>, TB) were realized using iron salts, leading to a cost-effective and sustainable process producing a valuable recovery product. However, the precipitation of PB and TB is highly affected by pH and dissolved oxygen (DO). CN<sup>−</sup> removal and recovery from CN-containing water by crystallization of PB and/or TB were investigated using dissolved iron that was electrochemically generated from a sacrificial iron anode under various pH values, initial CN<sup>−</sup> levels (10 to100 mg/L) and DO levels (aeration, mechanical mixing, and N<sub>2</sub> purging). It was shown that the complexation of CN<sup>−</sup> with Fe ions prevented the vaporization of HCN under acidic pH. At pH of 7 and initial CN<sup>−</sup> concentration of 10 mg/L, CN<sup>−</sup> removal efficiency increases linearly with increasing Fe:CN<sup>−</sup> molar ratios, reaching 80% at the Fe:CN<sup>−</sup> molar ratio of 5. A clear blue precipitate was observed between the pH range of 5–7. CN<sup>−</sup> removal increases with increasing initial CN<sup>−</sup> concentration, resulting in residual CN<sup>−</sup> concentrations of 8, 7.5 and 12 mg/L in the effluent with the Fe:CN<sup>−</sup> molar ratio of 0.8 for initial concentrations of 10, 50 and 100 mg CN<sup>−</sup>/L, respectively. A polishing treatment with H<sub>2</sub>O<sub>2</sub> oxidation was employed to lower the residual CN<sup>−</sup> concentration to meet the discharge limit of <1 mg CN<sup>−</sup>/L.
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