Ferrocyanide Wastewater Treatedby Precipitation-Electrolytic Oxidation Process

The recycling and compliance efflux of cyanide waste water is the key of the energy conservation and cost reduction in gold smelting industry.Therefore,the harmless treatment or comprehensive utilization of it has important practical significance.In this paper,the precipitation-electrolytic oxidation combined technology was used to comprehensively treat high-ferric cyanide gold-lifting wastewater of a gold smelter.It mainly studied the process and main influencing factors of precipitation,electrolytic oxidation.At the same time,based on the basis of relevant basic theoretical calculations,it further reveals the reaction mechanism of the combined precipitation-electrolytic oxidation treatment of cyanide wastewater.The results have shown that after adding 3.0g CuCl₂ to 100mL cyanide-containing wastewater at room temperature and stirring for 40min,the precipitation rates of CN_T,CN^-and Fe?CN?₆^4-can reach 95.29%,98.00%and 100%,respectively.With the increase of the amount of CuCl₂ added,the precipitation rate of the main ions in the cyanide wastewater gradually increased,and the formation order of the precipitates was CuCN,Cu₂Fe?CN?₆,CuSCN.Titanium?Ti?plate is used as cathode and anode,and the electrode system of one cathode and two anodes is used to perform electrolytic oxidation treatment on the precipitated liquid.When the concentration of the electrolytic solution is 60%,the electrolysis time is 5h,the applied voltage is 6V,and the electrode plate spacing is 15mm,the total removal rates of CN_T and CN^-in cyanide wastewater reached 99.76%and 99.90%,respectively.As the applied voltage increases,Zn?CN?₄^2-,Cu?CN?₃^2-,CN^-,SCN^-,and Cl^-remaining in the wastewater will migrate directionally to the anode under the action of an electric field.The Cl^-on the anode surface undergoes the anodic oxidation reaction,the generated Cl₂/ClO^-oxidizes the cyanide to N₂ and CO₂,and the released Cu and Zn cations migrate to the cathode for the reduction reaction to obtain the metal element.Thus,the removal rates of the free cyanide remaining in the wastewater and the complex ions with metal cyanide gradually increased.The study on kinetic shows that the precipitation process of thiocyanate and free cyanide conforms to the second-order kinetic model,and the rate constants are 8.637dm3/?mol·min?and0.797dm3/?mol·min?,respectively.The electrolytic oxidation process of total cyanid e conforms to the first-order kinetic model,and the reaction rate constant increases with the increase of the applied voltage.