Effect And Mechanism Of Trichloroethylene Removal From Water With Potassium Ferrate Enhanced By Biochar

Trichloroethylene（TCE）,often used as cleaning agent and degreasing agent,has been widely used in printing,chemical industry,electronic manufacturing and other fields.However,due to non-standard storage and site relocation,TCE has become one of the common pollutants in groundwater.Ferrate is a green and efficient oxidant.Under acidic conditions,its redox potential is second only to hydroxyl radical.It has a good removal effect for organic pollutants,but it is extremely unstable in aqueous solution and has high cost price.Therefore,it is of great significance to explore a method to enhance the removal of chlorinated hydrocarbons in water by ferrate.It was found that potassium ferrate was the most stable in aqueous solution at p H9,and the decomposition rate was 58.6%after 15 h,which was much lower than that at p H 6（93.7%）.Fe³⁺,Mg²⁺,Ca²⁺will promote their decomposition by reacting with potassium ferrate;In the presence of CO₃^2-,it will promote the decomposition of potassium ferrate through heterogeneous catalytic process;When the concentration of fulvic acid increased to 10 mg/L,the decomposition rate of potassium ferrate increased from 35%to 50%;The increase of temperature is also not conducive to the stability of potassium ferrate.Potassium ferrate has a good removal effect on TCE in aqueous solution.When p H=9,the removal rate of TCE is the highest,reaching 88%.Fe³⁺and Mg²⁺can enhance the removal of TCE by activating potassium ferrate;The existence of Cl^-is conducive to enhance the stability of high valence iron in the system,so it is conducive to the removal of TCE;Fulvic acid inhibited the removal of TCE through competition at high concentration.Straw based biochar has good adsorption capacity for TCE.The adsorption process conforms to the quasi second-order kinetic equation and Langmuir equation.The maximum adsorption capacity q_m is 21.55 mg/g.it is mainly chemical adsorption and mainly monolayer adsorption,involvingπ-πbond,hydrogen bond,hydrophobicity and pore filling.Biochar significantly enhanced the removal of TCE by potassium ferrate.When the concentration of biochar increased from 0 to 333 mg/L,the removal rate of TCE increased from 39.9%to 86.5%.When the iron carbon ratio was 1:130,it showed the strongest strengthening effect,and the actual TCE removal rate was 1.34 times of the theoretical value at 10 min.The addition of biochar can make the TCE removal rate of5 m M potassium ferrate show the same as that of 16 m M potassium ferrate.The results show that the oxidation of potassium ferrate in the composite system is the main reason for TCE removal,and the adsorption is inhibited by competition.The mechanism of biochar enhanced potassium ferrate removal of TCE is mainly that it promotes the electron transfer process of potassium ferrate.When the concentration of biochar increases to 333 mg/L,the decomposition rate of potassium ferrate in aqueous solution increases from 37.6%to 93.1%in 30 min.Energy dispersive spectroscopy and X-ray photoelectron spectroscopy analysis also showed that the number of oxygen-containing functional groups on the surface of biochar increased after the reaction,indicating that there was a reaction between biochar and potassium ferrate.