Study On The Treatment Of Fluorine-containing Wastewater By Iron-carbon Microelectrolysis-alkali Precipitation Technology

With the vigorous development of modern fluorine industry,the problem of fluorine-containing wastewater pollution is becoming more and more serious.Such as iron and steel smelting,fluorine-containing ores mining,semiconductors,electronics,chemicals,pesticides,fluoride processing and manufacturing and other industrial processes will produce a large amount of fluorine-containing wastewater.Fluorine-containing wastewater has the characteristics of wide distribution,strong electronegativity,complex composition,and difficult treatment.Moreover,fluoride is harmful to animals,plants,and humans in the environment.The treatment of fluorine-containing wastewater has always been an important problem in the field of environmental protection.The development of practical,low-cost and high-efficiency treatment technologies and processes has important practical significance and is a hot spot and trend in current research.In this paper,the performance of iron-carbon micro-electrolysis-alkali precipitation technology to treat fluorine-containing wastewater was studied,and the effects of dosage,pH,reaction time,initial fluorine concentration,coexisting anions and other influencing factors on the fluorine removal effect were investigated.Through the combination of iron-carbon micro-electrolysis and alkali precipitation,the fluorine removal effect of iron-carbon micro-electrolysis is strengthened,and a new process for fluorine-containing wastewater treatment is developed based on this.Through SEM,EDS,XRD,XPS and other characterization analysis of iron-carbon materials and new deposits before and after the reaction,combined with filtration,alkali-adjusted precipitation and other treatment methods,and the effect of iron ions alone complexation to remove fluorine,explored the Mechanism of iron-carbon microelectrolysis for defluorination.The main research conclusions are as follows:（1）Through single factor experiments,the performance of carbon micro-electrolysis-alkali precipitation technology for treating fluorine-containing wastewater was optimized.The results show that this technology has a good treatment effect on high-concentration fluorine-containing wastewater.When the fluorine concentration is less than 2000 mg/L,the fluorine removal efficiency can reach more than 80%.When the initial pH is 2,the dosage of iron-carbon is 2 g/100 m L,and the reaction time is 2h,the defluorination rate of iron-carbon micro-electrolysis-alkali precipitation can reach 97.8%in the simulated wastewater,and the defluorination rate of the actual wastewater can reach 97.8%.The rate can reach 95.0%.In the process of coupling Fenton synergistic treatment of COD,when the pH value before the Fenton reaction was 4,the dosage of H₂O₂ was 1 m L/50 m L,and the reaction was performed for 150min,the COD synergistic removal rate of the actual wastewater could reach 52.7%.Under acidic conditions,the initial pH has a great influence on the defluorination effect of iron-carbon micro-electrolysis-alkali precipitation technology.With the increase of initial pH,the defluorination effect gradually decreases;With the increase of reaction time,the fluorine removal effect will gradually increase.By investigating the influence of different anions on the fluorine removal effect of this technology,it is found that HPO₄^2-has the greatest influence on the fluorine removal performance,and the order of influence of different anions is:HPO₄^2->Cl^->SO₄^2->NO₂^->CO₃^2-.（2）The defluorination mechanism of iron-carbon micro-electrolysis-alkali precipitation technology was studied in depth through the phase characterization of iron-carbon materials and sediments before and after the reaction.EDS,XPS,XRD and other analysis results show that Fe₂F₅·2H₂O,Fe₂F₅ and Fe F₂ are formed from iron and fluorine through iron-carbon micro-electrolysis reaction.During the reaction,Fe²⁺/Fe³⁺,which can be converted into each other based on the electrochemical principle of metal corrosion,is released under the condition that the initial pH is acidic,and Fe²⁺/Fe³⁺is combined with F^-to form an iron-fluorine complex;Alkaline,iron-fluorine complexes then form iron-fluorine complex precipitates,and some iron-fluorine complexes dissociate;Fe²⁺/Fe³⁺generates Fe（OH）₂/Fe（OH）₃ colloids with a large specific surface area,and then flocculates again It can adsorb fluoride and iron-fluoride complex and polymerize with each other to form floc precipitation,so as to achieve the fluorine removal effect of synergistic co-precipitation.Therefore,iron-carbon micro-electrolysis and alkali precipitation have a synergistic co-precipitation removal effect on fluorine in water,and the primary and secondary relationship of fluorine removal is:complex adsorption>synergistic co-precipitation>liquid-phase dissolution of iron.（3）Based on the iron-carbon micro-electrolysis-alkali precipitation technology,a new two-stage iron-carbon defluorination process was developed.The results show that the process has good defluorination effect,and the continuous operation shows strong stability and defluorination performance.With the increase of operating time,the filler is continuously worn out and the surface deposits are more and more wrapped with iron-carbon materials,resulting in a continuous decrease in the fluorine removal efficiency.Backwashing treatment can improve the fluorine removal effect of the process and improve the utilization rate of iron-carbon fillers.