s•Reaction between ferrous and cokingwastewater was a two-step process.•Mechanisms of the first step includedFeS precipitation, CN−complex andorganics coagulation.•Mechanism of the second step wasdominated by the immobilization ofmetal–cyanide compounds.•The biodegradability of cokingwastewater was achieved at the endof the first-step process.•The optimal ferrous dosage should bedetermined by the characteristics ofcoking wastewater.