Study On The Performance Of Potassium Ferrate Composite Oxidant In Treating Oily Sewage

In recent years,most of oil fields in our country have entered the middle and late stage of oil production,the innovation of fracturing technology and the application of various new fracturing fluids have made great contributions to the production increase of oil fields,but the increasing treatment volume of fracturing flowback fluid has also become a big problem in oil field water treatment technology.Among the methods for treating fracturing flowback fluid,chemical oxidation method can effectively reduce the viscosity and COD value of fracturing flowback fluid,and has been widely used with quick effect and low cost.In this paper,potassium ferrate,a green oxidizing agent with both oxidation and flocculation functions,was selected to improve its stability,and sodium hypochlorite was combined with sodium hypochlorite to treat fracturing flowback fluid.Through degradation experiments,the best use conditions of potassium ferrate-sodium hypochlorite compound oxidizing agent were explored.(1)Hypochlorite oxidation method was used to prepare potassium ferrate,and through a series of single factor and orthogonal experiments,the best reaction conditions for preparing potassium ferrate were determined.The purity and yield of potassium ferrate reached the maximum of 88.07% and 34.12% when the dosage of sodium silicate 9-hydrate was 1.5 g/L,the reaction temperature was 25 ℃,the reaction time was 45 min,the dosage of potassium hydroxide was 30 g and the concentration of recrystallization solution was 10 mol/L.(2)Low temperature and alkaline environment are beneficial to improve the stability of potassium ferrate in aqueous solution.Potassium ferrate is more stable when the temperature is below 25 ℃ and the p H value is above 10.Sodium acetate can significantly improve the stability of potassium ferrate,and the best effect is 10 times the molar concentration of potassium ferrate.Sodium acetate can also effectively improve the degradation rate of phenol and other organic compounds by potassium ferrate oxidation.Sodium acetate with molar concentration of 5 times potassium ferrate has the best effect,which can effectively save the amount of potassium ferrate.Sodium hypochlorite can also significantly improve its stability,which has a certain timability.The higher the concentration,the longer the stable time of potassium ferrate.It can be considered that sodium hypochlorite of equal molar concentration can maintain potassium ferrate stable for3～4h.(3)After the primary flocculation of fracturing flowback fluid,potassium ferrate oxidation treatment was selected.The optimal reaction conditions were determined as reaction temperature 25 ℃,p H 10,potassium ferrate concentration 2.5 g/L and reaction time 35 min.The viscosity,COD and turbidity values decreased by 30.79%,37.39% and 44.25%,respectively.(4)In order to improve the removal rate of viscosity,COD and turbidity value of the fracturing flowback fluid,sodium hypochlorite and potassium ferrate were introduced to treat the fracturing flowback fluid.The optimal reaction conditions were determined to be 25 ℃,p H8,potassium ferrate concentration of 2.5 g/L,sodium hypochlorite concentration of 2.0 g/L and reaction time of 40 min.The viscosity,COD and turbidity values decreased by 40.87%,45.86%and 48.37%,respectively,and the effect of potassium ferrate alone increased by 10.08%,8.47%and 4.12%,respectively.After combined treatment,the flowback fluid is still turbidity.After secondary flocculation,the viscosity,COD and turbidity values are reduced by 41.78%,57.39%and 93.54% compared with the raw fluid,respectively.