Treatment Of Methyl Orange Simulated Wastewater By Persulfates Activated With FeS

It is reported that China's average daily discharge of dye wastewater is about 3 to 4million tons,of which azo dye pollution is the most serious.Most of them have the same characteristics such as deep coloration,high water content,high organic content,difficult to biodegrade,and large fluctuations in water quality,etc.If not properly handled,it will not only damage the ecological environment,but also affect human health.Methyl orange is a typical azo dye,and it is difficult for the conventional method to destroy its azo functional group.In this paper,methyl orange simulated wastewater is treated with persulfate advanced oxidation technology.It is known that persulfate can quickly generate strong oxidizing substances such as SO₄^-· and ·OH under the action of heat,ultraviolet,transition metals,etc.,and can effectively degrade organic pollutants.Besides,SO₄^-· can stably exist under both neutral and acidic conditions.Compared to the fenton reaction,this method broadens the reaction conditions.In this study,potassium persulfate was used as the oxidant and Fe S was the activator.The effects of potassium persulfate concentration,Fe S concentration and pH on the treatment of methyl orange were investigated.It was found that the removal rate of methyl orange after80 min was 88.11% when the pH was about 6.5,the concentration of potassium persulfate was8mmol/L,and the concentration of Fe S was 0.8g/L.According to experimental data,the reaction takes a long time and the removal rate of methyl orange is less than 90%.In order to further increase the removal rate of methyl orange and shorten the reaction time,this experiment was conducted by adding hydroxylamine hydrochloride,transition metal ions,organic acid radicals and ascorbic acid to strengthen Fe S activation and K₂S₂O₈ for the degradation of methyl orange.The experimental results show that:?1?the addition of hydroxylamine greatly shortens the degradation time of methyl orange: when the removal rate is the same,the reaction time is shortened by about 1h.When the pH was about 6.5,the concentration of K₂S₂O₈ was 8mmol/L,n?Fe S?:n?hydroxylamine?was 10:10,the removal rate of methyl orange reached 90.46% after 15 min reaction.?2?According to the principle of co-precipitation,transition metals Cu²⁺and Ag⁺have a catalytic effect on the original system.When the molar ratio of transition metal ions and Fe S is 10:10,the removal effect of methyl orange is relatively best.Moreover,the strengthening effect of Cu²⁺ on the original system is stronger than that of Ag⁺;the low concentration of La³⁺ has only a faint promoting effect on the original system.?3?The low concentration of formate and oxalate in organic acid ions alsopromoted the original system,while acetate inhibited the degradation of methyl orange in the original system.?4?Low concentration of ascorbic acid also has a promoting effect on the original system,but the effect is not obvious.In summary,hydroxylamine has the most obvious promoting effect on the original system.Therefore,the following studies have focused on the experiments of hydroxylamine-enhanced Fe S-activated K₂S₂O₈ for the degradation of methyl orange.Later,the orthogonal experiments showed that pH had a greater effect in the hydroxylamine-enhanced system,and Fe S still had better activity after five cycles of utilization.In the final experiment,the mechanism of the hydroxylamine-enhanced system was analyzed based on the analysis of the reaction kinetics,Fe³⁺ content in the system,characterization of Fe S before and after reaction,identification of free radical species,optimal absorption of methyl orange before and after reaction,comparison of different systems,and products generated after reaction,etc.The experimental results show that:?1?the reaction kinetics,Fe³⁺ content in the system,characterization of Fe S before and after reaction,identification of free radical species,optimal absorption of methyl orange before and after reaction,comparison of different systems,and products generated after reaction,etc.can all prove that hydroxylamine does promote the degradation of methyl orange by K₂S₂O₈ activated by Fe S,and the addition of hydroxylamine promotes the circulation of Fe³⁺/Fe²⁺ in the system,which in turn promotes the production of free radicals by K₂S₂O₈ and accelerates the degradation of methyl orange.?2?The free radical species identification test and the process analysis showed that the primary active free radical in the hydroxylamine fortification system was ·OH.