Study of electrochemical removal of phenanthrene in bentonite clay by physicochemical indicators

Adsorption of humic acid from different organic solid waste compost to phenanthrene, is fluorescence excitation or quenching?

Humic acid (HA) from different organic solid waste (OSW) compost has been shown good adsorption properties for phenanthrene. However, the raw material of HA can affect its structure, resulting in differences in adsorption capacity. Therefore, this study focused on the adsorption characteristics of phenanthrene by HA from different OSW compost. In this work, chicken manure (CM), rice straw (RS) and lawn waste (LW) were selected as sources of composted HA. The adsorption mechanism of HA from different OSW compost were revealed through analytical techniques including three-dimensional fluorescence spectroscopy (EEM), two-dimensional correlation spectroscopy (2DCOS), and Fourier-transform infrared spectroscopy (FTIR). The results suggested that HA from LW compost had a better adsorption affinity for phenanthrene because of its more complex fluorescent component, where C1 as a simple component determined the adsorption process specifically. Furthermore, after HA from LW compost adsorbed phenanthrene, the increase in aromatic -COOH and -NH was the main reason for fluorescence quenching. These results indicated that HA from LW compost had better adsorption effect for phenanthrene. The results of this study were expected to provide a selection scheme for the control of phenanthrene pollution and environmental remediation.

Experimental and mechanistic research on modifying the mechanic properties of the high water backfill material by electrochemical treatment

To promote the engineering applications of high water backfill materials (HWBM) in mining, a series of experiments are performed to investigate the effects of the direct current (DC) electric field on the mechanic properties and electrical resistivity of HWBMs. Based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) investigations, the influence of electrochemical treatment on the hydration products and the microstructure of the HWBM was studied. The results show that the peak strength, elastic modulus, deformation modulus and electrical resistivity of the HWBM samples all first increased and then decreased with the increasing of the potential gradient, and the peak points appeared when the potential gradient was 0.2 V/cm. The anisotropy of content of ettringite and calcium silicate hydrates (C–S–H) increased betweent the anodic and cathodic regions of samples. Meanwhile, microstructure in the anodic region of the samples was more stable after electrochemical treatment, which indicates that the different variation of mineralogical compositions and microstructures in different regions of the samples are the primary factors affecting the mechanic properties and electrical resistivity of the HWBM. Therefore, the electrochemical method is a potential technology to modify the engineering properties of the HWBM.

Effect of processing time on removal of harmful emerging salt pollutants from saline-sodic soil during electrochemical remediation

The recent climate change has spawned a new emerging environmental hazard known as soil salinity. The lacks of rainfall and global warming have drastically increased the concentration of harmful emergent salt pollutants (HESPs) to toxic levels for natural and human assets. Electrochemical remediation (ECR) has been successfully used in remediation of contaminated soils. This research aims to investigate the effect of processing time (PT) on the removal of HESPs during ECR. The experiments were operated in a designed laboratory cell, using two different PT of 3 and 5 days with a voltage gradient of 1.5 V/cm. The results show that the increase of PT enhances the removal of monovalent cations, including sodium (Na⁺) and potassium (K⁺), reaching an efficiency of 63 and 83%, respectively. However, calcium (Ca²⁺) and magnesium (Mg²⁺) have exhibited irreversible behavior, where the increase of PT seems hindering their removal, namely near the cathode. Longer periods induce sharp increase in the basic front, which curb their desorption and mobilization. For the anionic salts, the raises of PT lead to better elimination of monovalent anions, with a removal of 92 and 63% for nitrate (NO₃^-) and chloride (Cl^-), respectively. Nevertheless, the effect of PT was less significant on the elimination of sulfate (SO₄^2-), due to their chemical nature. It can be concluded that the removal rate is an intrinsic parameter, strongly related to set of parameters, including the soil pH, chemical nature, ionic valence of the targeted salts and their selectivity on clay particles in clay-water-electrolyte system.