Study On The Removal Of Chloride Ions From Wastewater By Cyclic Precipitation Of Cuprous Chloride Based On Typical Reductants

With the expansion of China’s industrial scale,the amount of industrial wastewater is gradually increasing,including a large number of chlorine-containing wastewater.Chlorine-containing substances in industrial wastewater are highly corrosive,which will have adverse effects on industrial production and factory equipment.At the same time,a large number of chlorine-containing wastewater will seriously damage the ecological environment and endanger human health and safety.Therefore,it is particularly important to study an efficient method of chloride ion removal.At present,the treatment methods of chlorine-containing wastewater mainly included physical method,chemical precipitation method and electrochemical method.The sedimentation method had been widely studied because of its advantages of simple operation,stable operation and short processing time.However,the common precipitation method is easy to produce a large amount of solid waste,which brings difficulties for subsequent treatment and utilization.The research used Na₂SO₃ and other reducing agents to remove Cl^-for research,but the waste gas SO₂ was produced in the reaction.In this paper,ascorbic acid and hydroxylamine sulfate were used as dechlorination agents to explore the feasibility of removing chlorine ions from wastewater in the form of cuprous chloride precipitation.The molar ratio of dechlorination agents（ascorbic acid or hydroxylamine sulfate）to copper sulfate pentahydrate,the reaction p H,the reaction time,the reaction temperature,the molar ratio of copper sulfate pentahydrate to chloride ions and the initial chloride ion concentration on the removal effect of chloride ions were investigated.The phases and morphologies of the precipitation products were characterized by X-ray diffraction（XRD）,energy dispersive spectroscopy（EDS）and scanning electron microscopy（SEM）,and the reaction mechanism was preliminarily explored.On this basis,the combined use of ascorbic acid and hydroxylamine sulfate,the effects of Fe³⁺,Mg²⁺and SO₃^2-on chlorine removal were also discussed,and the conclusions were as follows:（1）Removal of chloride ions from wastewater by precipitation based on ascorbic acid.The results showed when the reaction p H was 3.6,the molar ratio of copper sulfate pentahydrate to ascorbic acid was 3:1,the reaction time was 20 min,the reaction temperature was 20℃,and the molar ratio of copper sulfate pentahydrate to chloride ion was 1.5:1,the precipitation method based on ascorbic acid had the best effect on chloride ion removal.When the initial chloride ion concentration in the solution increased from 1000 mg/L to 4000 mg/L,the chloride ion removal rate increased from 92.8%to 96.6%,while the residual chloride ion concentration in the solution decreased from 4000 mg/L to 135 mg/L.（2）Removal of chloride ions from wastewater by precipitation based on hydroxylamine sulfate.The results showed when the reaction p H was 4.4,the molar ratio of copper sulfate pentahydrate to hydroxylamine sulfate was 3:1,the reaction time was 20 min,the reaction temperature was 30℃,and the molar ratio of copper sulfate pentahydrate to chloride ion was 1.5:1,and the initial chloride ion concentration in the solution was 4000 mg/L,the precipitation method based on hydroxylamine sulfate had the best effect on chloride ion removal.The chloride ion removal rate reached 95.9%,and the residual chloride ion concentration in the solution could be reduced from 4000 mg/L to 161.5 mg/L.（3）Ascorbic acid and hydroxylamine sulfate reduced Cu²⁺to Cu⁺,and Then Cu⁺and Cl^-rapidly formed Cu Cl.The mechanism showed that the white precipitates were characterized and analyzed by XRD,EDS,SEM and other methods,and the precipitated products of the two dechlorination methods were cuprous chloride.The final results showed that in chlorine-containing wastewater,Ascorbic acid reduces Cu²⁺to Cu⁺and reacts with Cl^-to produce cuprous chloride.In the wastewater,hydroxylamine sulfate first reacts with Cu²⁺to generate Cu⁺and N₂,and then Cu⁺and Cl^-quickly generate Cu Cl.Chloride ions in the wastewater were removed in the form of cuprous chloride precipitation.（4）Mg²⁺had no effect on the two chlorination methods.Fe³⁺could reduce the chlorination effect of the two methods.ascorbic acid and SO₃^2-could improve the chlorination effect of hydroxylamine sulfate method.The results showed that:Mg²⁺had no effect on the removal of chloride ions by the method of ascorbic acid or hydroxylamine sulfate.The presence of Fe³⁺reduced the effect of the two dechlorination methods.When the concentration of iron ion in wastewater increased from 0 to 1000 mg/L,the removal effect of chloride ions by ascorbic acid method decreased gradually from 96.6%to 91.8%,and that by hydroxylamine sulfate method decreased from 96.0%to 95.1%.The presence of Fe³⁺had a great influence on the ascorbic acid method.Ascorbic acid could obviously enhance the removal effect of chloride ions of hydroxylamine sulfate method.When the initial chloride concentration was 1000 mg/L and the ascorbic acid dosage was n（vc）:n（Cl）=0.6:2,the removal effect of chloride ion of hydroxylamine sulfate method was increased from 73%（without ascorbic acid）to 91.1%.When the initial chloride ion concentration of wastewater was less than 2000 mg/L,it was beneficial to remove chloride ion by hydroxylamine sulfate method if the wastewater contains sulfite.When the initial chloride concentration of wastewater was greater than 2000 mg/L,sulfite had little influence on the effect of chlorine removal.