Investigation on the effects of fluid intensification based preconditioning process on the decarburization enhancement of fly ash

Fly ash(FA)is a complex and abundant solid waste created by humans,and has caused environmental issues,for which flotation is an effective technique employed before its comprehensive utilization.However,the complex and hydrophilic characteristics of FA particles cannot naturally fulfill the selective separation by common flotation.Therefore,this study aims to provide an insight into fluid intensification effects on flotation to achieve the enhancement of FA surface property and decarburization.The relevant effects and mechanisms are investigated,based on the measurements of zeta potential,infrared spectroscopy,contact/wrap angle,induction time,size distribution and scanning electron microscopy–energy dispersive spectrometry.Experimental results manifested that the maximum unburned carbon recovery(73.25%)and flotation rate(0.2037 s^(-1)) were achieved with preconditioning energy inputs of 14.23 and6.57 W·kg^(-1) respectively.With increasing preconditioning energy inputs,fluid intensification effects could promote the inter-particle collision/attrition,detachment of hydrophilic existence and collector adsorption on particles.Correspondingly,absorbance of some hydrophobic and hydrophilic functional groups was strengthened and weakened respectively,which accounted for the improved interfacial properties,reflected as the increased contact and wrap angles,together with declined induction time.Overall,this article revealed the positive influences of fluid intensification based preconditioning process on rendering particle surface hydrophobic and improving separation performance.

Highly inhibited transport of dissolved thallium(I) in manganese oxide-coated sand: Chemical condition effects and retention mechanisms

Thallium contamination in water can cause great danger to the environment.In this study,we synthesized manganese oxide-coated sand(MOCS)and investigated the transport and retention behaviors of Tl(I)in MOCS under different conditions.Characterization methods combined with a two-site nonequilibrium transport model were applied to explore the retentionmechanisms.The results showed that Tl(I)mobility was strongly inhibited in MOCS media,and the retention capacity calculated from the fitted model was 510.41 mg/g under neutral conditions.The retention process included adsorption and oxidative precipitation by the manganese oxides coated on the sand surface.Cotransport with the same concentration of Mn(II)led to halving Tl(I)retention due to competition for reactive sites.Enhanced Tl(I)retention was observed under alkaline conditions,as increasing pH promoted electronegativity on the media surface.Moreover,the competitive cation Ca^(2+)significantly weakened Tl(I)retention by occupying adsorption sites.These findings provide new insights into understanding Tl(I)transport behavior in water-saturated porous media and suggest that manganese oxide-coated sand can be a cost-effective filter media for treating Tl-contaminated water.

Release of deposited MnO2 nanoparticles from aqueous surfaces

Changes in solution chemistry and transport conditions can lead to the release of deposited MnO2 nanoparticles from a solid interface,allowing them to re-enter the aqueous environment.Understanding the release behavior of Mn02 nanoparticles from naturally occurring surfaces is critical for better prediction of the transport potential and environmental fate of Mn02 nanoparticles.In this study,the release of Mn02 nanoparticles was investigated using a quartz crystal microbalance with dissipation monitoring(QCM-D),and different environmental surface types,solution pH values and representative macromolecular organics were considered.Mn02 nanoparticles were first deposited on crystal sensors at elevated NaN03 concentrations before being rinsed with double-deionized water to induce their remobilization.The results reveal that the release rate of Mn02 depends on the surface type,in the decreasing order:SiO2>Fe304>Al2 O3,resulting from electrostatic interactions between the surface and particles.Moreover,differences in solution pH can lead to variance in the release behavior of Mn02 nanoparticles.The release rate from surfaces was significantly higher at pH 9.8 that at 4.5,indicating that alkaline conditions were more favorable for the mobilization of Mn02 in the aquatic environment.In the presence of macromolecular organics,bovine serum albumin(BSA)can inhibit the release of Mn02 from the surfaces due to attractive forces.In presence of humic acid(HA)and sodium alginate(SA),the Mn02 nanoparticles were more likely to be mobile,which may be associated with a large repulsive barrier imparted by steric effects.