Treatment Of Copper-containing Cyanide Wastewater In Gold Mine By Co-flocculation

The cyanidation method is currently widely used in China for gold extraction methods.Because gold ore is often accompanied by a large amount of soluble copper salt,there will be a large amount of copper ions in the cyanide-containing wastewater generated by the gold leaching process.The traditional cyanide method cannot recover copper ions when cyanide is broken.The co-flocculation method refers to the flocculating agent added to the wastewater,which not only has flocculation effect on the particulate matter,but also reacts with the dissolved pollutants to achieve the purpose of wastewater treatment.This paper intends to carry out co-flocculation treatment of copper-and cyanide-containing gold extraction wastewater,in order to achieve the purpose of reducing cyanide and copper removal at the same time.This paper takes the research of cyanide-depleted liquid produced by a gold enterprise in Shandong Province during the gold extraction process as the research object?total cyanide concentration is 310mg/L,copper ion concentration is 200mg/L,pH value is 6.8?,using simulated wastewater and actual wastewater respectively.The research was carried out using polymeric ferric sulfate?PFS?as a flocculant.The main conclusions are as follows:?1?Thermodynamic calculations show that the presence of cyanide and copper ions in wastewater mainly includes CuCN,Cu?CN?₂^-,Cu?CN?₃^2-,Cu?CN?₄^3-and their free ions.As the pH of the system decreases,the number of copper ion complexed cyanide ions decreases.When the pH is 7,Cu?CN?₃^2-is the main form with a content of77.56%.When the pH drops below 5,CuCN precipitation occurs in the system.?2?The effects of reaction pH,PFS dosage and reaction time on copper ion and total cyanide removal rate were investigated by single factor test and L₉?3³?orthogonal test using simulated wastewater.The results showed that with the increase of PFS dosage and reaction time,the removal rates of copper ions and total cyanide increased first and then decreased.As the pH of the system decreases,the removal rate of copper ions and total cyanide increases.When the pH is lower than 5,white copper cyanide precipitates.Repeated tests showed that the results were less fluctuating and the treatment effect was stable.The orthogonal test results showed that the optimal reaction conditions were:pH5,PFS dosage 1000 mg/L,and reaction time 12 h.The residual concentration of total cyanide after treatment was 5.72 mg/L,the removal rate was 98.3%,the residual concentration of copper ions was 9.78 mg/L,and the removal rate was 95.1%.The degree of influence on the removal of the two pollutants is ordered as follows:PFS dosage>reaction system pH>reaction time.?3?Based on XPS,XRD,FTIR and other analysis,it is shown that Fe?OH?₃ colloid,Fe₂[Cu?CN?₃]₃ and Fe₄[Fe?CN?₆]₃ appear in the flocs formed by the test,and The characteristic peaks of C?N are shifted,and both copper cyanide complex ions and free cyanide ions can be combined with PFS hydrolysis products Fe₂?OH?₃³⁺,Fe₂?OH?₂⁴⁺,Fe3?OH?₄⁵⁺,etc.Complexation precipitation occurs and the flocculation process occurs with a chemical reaction.The Fe?OH?₃ colloid is positively charged,and both cyanide and copper cyanide ions are negatively charged,so there is an adsorption neutralization effect.Therefore,the removal routes of cyanide and copper include:chemical precipitation,Fe?OH?₃ colloid adsorption,and adsorption neutralization.Based on TEM,floc size and system viscosity analysis,a part of the copper cyanide ion was adsorbed on the iron hydroxide colloid by electrostatic adsorption,and the zeta potential showed that the compressed electric double layer played a significant role.The flocs are mainly present in the form of flakes,and the individual flakes are joined together by a polymer.There are also flocculation effects such as net trapping,electric neutralization,and adsorption bridging in the co-flocculation process.?4?The actual wastewater was treated under the optimal test conditions,and the total cyanide ion concentration was reduced from 310 mg/L to 8.3 mg/L,and the removal rate was 94.1%.The copper ion concentration decreased from 202 mg/L to12.7 mg/L,and the removal rate reached 93.7%.The COD decreased from 8910mg/L to 800mg/L,and the removal rate reached 90.1%.The treated water sample can meet the recycling requirements of the enterprise.