Comparing Mn-based oxides filters started by KMnO_(4)versus K_(2)FeO_(4)for ammonium and manganese removal:Formation mechanism of active species

A pilot-scale filtration system was adopted to prepare filter media with catalytic activity to remove manganese(Mn^(2+))and ammonium(NH_(4)^(+)-N).Three different combinations of oxidants(KMnO_(4)and K_(2)FeO_(4))and reductants(MnSO_(4)and FeCl_(2))were used during the start-up period.Filter R3 started up by KMnO_(4)and FeCl_(2)(Mn^(7+)→MnO_(x))exhibited excellent catalytic property,and the NH_(4)^(+)-N and Mn^(2+)removal efficiency reached over 80%on the 10th and 35th days,respectively.Filter R1 started up by K_(2)FeO_(4)and MnSO_(4)(MnO_(x)←Mn^(2+))exhibited the worst catalytic property.Filter R2 started up by KMnO_(4)and MnSO_(4)(Mn^(7+)→MnO_(x)←Mn^(2+))were in between.According to Zeta potential results,the Mn-based oxides(MnO_(x))formed by Mn^(7+)→MnO_(x)performed the highest pHIEP and pHPZC.The higher the pHIEP and pHPZC,the more unfavorable the cation adsorption.However,it was inconsistent with its excellent Mn^(2+)and NH_(4)^(+)-N removal abilities,implying that catalytic oxidation played a key role.Combined with XRD and XPS analysis,the results showed that the MnO_(x)produced by the reduction of KMnO_(4)showed early formation of buserite crystals,high degree of amorphous,high content of Mn3+and lattice oxygen with the higher activity to form defects.The above results showed that MnO_(x)produced by the reduction of KMnO_(4)was more conducive to the formation of active species for catalytic oxidation of NH_(4)^(+)-N and Mn^(2+)removal.This study provides new insights on the formation mechanisms of the active MnO_(x)that could catalytic oxidation of NH_(4)^(+)-N and Mn^(2+).

Laboratory simulation of CO_(2) immiscible gas flooding and characterization of seepage resistance

CO_(2) flooding can significantly improve the recovery rate, effectively recover crude oil, and has the advantages of energy saving and emission reduction. At present, most domestic researches on CO_(2) flooding seepage experiments are field tests in actual reservoirs or simulations with reservoir numerical simulators. Although targeted, the promotion is poor. For the characterization of seepage resistance, there are few studies on the variation law of seepage resistance caused by the combined action in the reservoir. To solve this problem, based on the mechanism of CO_(2), a physical simulation experiment device for CO_(2) non-miscible flooding production manner is designed. The device adopts two displacement schemes, gas-displacing water and gas-displacing oil, it mainly studies the immiscible gas flooding mechanism and oil displacement characteristics based on factors such as formation dip angle, gas injection position, and gas injection rate. It can provide a more accurate development simulation for the actual field application. By studying the variation law of crude oil viscosity and start-up pressure gradient, the characterization method of seepage resistance gradient affected by these two factors in the seepage process is proposed. The field test is carried out for the natural core of the S oilfield, and the seepage resistance is described more accurately. The results show that the advancing front of the gas drive is an arc, and the advancing speed of the gas drive oil front is slower than that of gas drive water;the greater the dip angle, the higher the displacement efficiency;the higher the gas injection rate is, the higher the early recovery rate is, and the lower the later recovery rate is;oil displacement efficiency is lower than water displacement efficiency;taking the actual core of S oilfield as an example, the mathematical representation method of core start-up pressure gradient in low permeability reservoir is established.