Study On The Treatment Of Cyanide-Containing Wastewater From Gold Mine By Na₂S₂O₅/Air Method And Na₂S Precipitation Method

At present,cyanidation is widely used in gold extraction.If large amount of cyanide-containing wastewater produced by this process poses a serious threat to the environment and ecosystem.The wastewater in this study was obtained from a gold mine in Shandong Province with a total cyanide concentration of 297.0 mg/L,a copper ion concentration of 102.4 mg/L,and a pH of 6.7.As the high concentration of copper ions in the wastewater,it can be used as a catalyst in the Na₂S₂O₅/air method,and the high efficiency and low cost of the method for treating cyanide-containing wastewater.This paper intends to study the treatment of cyanide-containing wastewater by Na₂S₂O₅/air method combined with Na₂S precipitation method,so that the total concentration of cyanide and copper ions in the treated wastewater reaches the first-class standard.Comprehensive wastewater discharge standard?GB8978-1996?.The total cyanide concentration is less than 0.5mg/L and the copper ion concentration is less than 0.5mg/L).The aeration column?adding agitation?and the XFD flotation machine were used as the reactor.The removal rule of total cyanide in simulated wastewater and the strengthening mechanism of flotation machine on removal rate under different stirring speed,pH value,sodium metabisulfite dosage,temperature,reaction time and aeration amount were analyzed.The results show that with the increase of stirring speed,the pH value,the aeration rate,the total cyanide removal rate increases first and then decreases.As the reaction time prolonged,the total cyanide removal rate increased to a stable level after 60 minutes;the increase of water temperature increased the removal rate of cyanide.The optimal reaction conditions are:The pH value is 9.0,the amount of sodium metabisulfite is 6g/L,the aeration amount is 130L/min,the reaction time is 1h,the water temperature is 30°C,and the optimal stirring speed of the flotation machine is 1600 r/min.The optimum agitation speed for aeration column agitation is 100 r/min.Under this condition,the flotation machine has better treatment effect than the aeration tower,wherein the total cyanide residual concentration is 0.43mg/L,the copper ion residual concentration is 3.60 mg/L,the total cyanide removal rate is 99.86%,copper ion removal rate 96.49%;The residual concentration of total cyanide in the aeration column was 1.56 mg/L,the residual concentration of copper ions was 8.34 mg/L,the removal rate of total cyanide was 99.47%,and the removal rate of copper ions was 91.85%.The total cyanide concentration in the wastewater after the flotation machine treatment reaches the first-class standard,but the copper ion does not reach the first-class standard.The spatial distribution of dissolved oxygen and redox potential in aeration column and flotation machine shows that the mechanism of removal and strengthening of flotation machine is:negative pressure suction-stirring and bubble formation,which can evenly distribute bubbles in solution.Under the optimal conditions,the average dissolved oxygen in the flotation machine was 7.50 mg/L at30 min,the oxidation-reduction potential was above 160 mV,and the utilization rate of sodium metabisulfite was 17.77%.The average dissolved oxygen in the aeration column under the same conditions was 5.40 mg/L,the oxidation-reduction potential was lower than 160 mV,and the utilization rate of sodium metabisulfite was 17.62%.The secondary pollution of Na₂S₂O₅/air method is mainly the release of cyanide and ammonia.Under the optimal reaction conditions,the flotation rate of cyanide in the flotation machine was 1.59%,the residual concentration of ammonia nitrogen was24.35 mg/L,and the stripping rate of ammonia was 87.22%.The stripping rate of cyanide in the aeration column was 2.03%,the residual concentration of ammonia nitrogen was 26.12 mg/L,and the rate of ammonia stripping was 86.15%.The higher dissolved oxygen in the flotation machine causes more cyanide to be oxidized to ammonia and bicarbonate,so the cyanide is blown off less than the aeration column,and the ammonia stripping rate is higher.The thermodynamic calculation results show that:Copper cyanide is present in the form of Cu?CN?₃^2-?Cu?CN?₄^3-?CN^-?CN?aq?and the corresponding free form.After the reaction,the concentration of Cu?CN?₂^-3was slightly changed,and the concentrations of Cu?CN?₄^3-?CN-and HCN?aq?were greatly reduced.Combined with previous analysis,Cu?CN?₃^2-is the main catalytic component,and in other forms,cyanide is oxidized and copper is precipitated.The particulate matter in the wastewater treated with sodium metabisulfite/air method was precipitated by PAM,and the residual copper ions in the wastewater were removed by Na₂S precipitation.The results show that with the increase of pH value,the removal rate of copper ions increases first and then decreases.As the amount of Na₂S and PAM increases,the removal rate of copper ions continues to increase.The optimum reaction conditions were:pH 9.0,Na₂S addition amount 3.09 mg/L?Cu:S molar ratio 2:1.4?,0.1%PAM dosage 4 mL/L,residual copper ion concentration in the solution after treatment was less than 0.5 mg/L,reaching the first grade standard.The actual cyanide-containing wastewater was treated under the optimal reaction conditions.The residual concentration of total cyanide after treatment was 0.46 mg/L,and the residual concentration of copper ions was less than 0.5 mg/L.The total pharmaceutical cost of the method is about 12.64 yuan/m³.