Adsorption performance and physicochemical mechanism of MnO_(2)-polyethylenimine-tannic acid composites for the removal of Cu(Ⅱ) and Cr(Ⅵ) from aqueous solution

In this work,an adsorbent,which we call MnPT,was prepared by combining MnO_(2),polyethylenimine and tannic acid,and exhibited efficient performance for Cu(Ⅱ) and Cr(VI) removal from aqueous solution.The oxygen/nitrogen-containing functional groups on the surface of MnPT might increase the enrichment of metal ions by complexation.The maximum adsorption capacities of MnPT for Cu(Ⅱ) and Cr(Ⅵ) were 121.5 and 790.2 mg·g^(-1),respectively.The surface complexation formation model was used to elucidate the physicochemical interplay in the process of Cu(Ⅱ) and Cr(Ⅵ) co-adsorption on MnPT.Electrostatic force,solvation action,adsorbate-adsorbate lateral interaction,and complexation were involved in the spontaneous adsorption process.Physical electrostatic action was dominant in the initial stage,whereas chemical action was the driving force leading to adsorption equilibrium.It should be noted that after adsorption on the surface of MnPT,Cr(Ⅵ) reacted with some reducing functional groups(hydroxylamine-NH_(2))and was converted into Cr(Ⅲ).The adsorption capacity declined by 12% after recycling five times.Understanding the adsorption mechanism might provide a technical basis for the procedural design of heavy metal adsorbents.This MnPT nanocomposite has been proven to be a low-cost,efficient,and promising adsorbent for removing heavy metal ions from wastewater.

Effects of supercritical CO_(2) on viscoelastic properties of shales

Laboratory uniaxial compression creep tests,with differential stress of 30 MPa hold for 3 h,were performed on Chang-7,Longmaxi(LMX)and Barnett shales to study the influence of SC-CO_(2)on short-term viscoelastic properties.To this end,the wet shale samples were treated with SC-CO_(2)with a pressure of30 MPa and a temperature of 110℃for 14 days.We analyzed the creep data using the fractional Maxwell model.To investigate microscopic structural alterations,the surface morphology of the same location,before and after SC-CO_(2)-water exposure,was examined by SEM images.Compared with dry shales,dynamic and static elastic moduli decreased by up to 25.02%and 55.83%,respectively,but the creep deformation increased by 200%for LMX and Chang-7 shales,and 500%for the Barnett shale treated by SC-CO_(2).Compared to dry sample,there is an increase in calculated fractional orders of 0.02,0.07,0.22 for SC-CO_(2)treated samples,indicating that SC-CO_(2)treatment is likely to enhance shale creep.SEM investigation confirmed physicochemical mechanisms responsible for the observed elastic damage and creep enhancement,including mineral dissolution and swelling caused by SC-CO_(2).This work would further improve our current understanding of the time-dependent deformation of shale under chemicalmechanical coupling effects during CO_(2)capture utilization and storage.

Studying the stress-suction coupling in soils using an oedometer equipped with a high capacity tensiometer

In the context of research into deep nuclear waste disposal,various works have concerned the hydromechanical behavior of Boom clay,a stiff plastic clay extracted in the SCK-CEN Underground Research Laboratory near the Mol City(Belgium),at a depth of 223 m.Due to some amount of smectite minerals in the clay fraction,Boom clay exhibits swelling properties when hydrated under low stresses.To investigate some aspects of the hydromechanical behavior of Boom clay,oedometer compression tests were carried out on samples of Boom clay close to saturation and submitted to an initial suction.During oedometer compression,the changes in suction with increased vertical stress are monitored by means of a high capacity tensiometer installed at the bottom of the sample.Some aspects related to hydromechanical couplings are examined through the investigation of the changes in suction during oedometer compression,a somewhat delicate and poorly documented experimental approach.A comparison is also made with a completely different soil sample under suction,i.e.a statically compacted unsaturated low plasticity silt.Some technical difficulties typical of this new experimental approach are first described in detail so as to optimize the interpretation of the data obtained.The experiment allows the determination of the point at which suction is changed to positive pressure during compression.Below this point,the ratio between the vertical stress and the change in suction are determined.Above this point,the data show that positive pore pressures are dissipated in a common way.The suction/stress behavior during unloading is also described and discussed.Finally,an interpretation in terms of microstructure effects is provided for both samples.The experimental approach initiated here seems to provide interesting further application to better understand hydromechanical couplings in natural soils in relation with suction increase during stress release.