The Adsorption Characteristics of Uranium(VI) from Aqueous Solution on Leonardite and Leonardite-Derived Humic Acid: A Comparative Study

Preparation of graphene based composites using silane and Pyracantha fortuneana and their application in Metformin adsorption from aqueous solution

Metformin, a typical pharmaceutical and personal care product (PPCPs), has a significant role in protecting brain cognitive function and delaying multiple organs aging, as well as causes seriously endocrine and reproductive interference to aquatic organisms due to drug abuse. Graphene that is of stable structure, flexible connection between carbon atoms, and the conjugated large pi bonds has been used to wastewater treatment, while Graphene-based materials used to remove PPCPs are rarely reported. Therefore, two graphene oxide (GO) based materials, including silane coupling agent modified product (CTOS-mGO) and Pyracantha fortuneana proanthocyanidin extract reduced product (PFPA-rGO), were used for metformin removal from aqueous solution as well as revealed the mechanism in this adsorption process. The results showed that metformin could be quickly and effectively removed by GO, CTOS-mGO and PFPA-rGO, of which the best material of adsorption effects was CTOS-mGO. The pseudo-second-order kinetic could effectively describe their adsorption process, and they achieved more than 80% removal rate within 15 to 20 min. Metformin adsorption by GO, CTOS-mGO and PFPA-rGO were all spontaneous and exothermic. CTOS-mGO was of the largest adsorption capacity and recycling utilization for metformin removal in comparison with GO and PFPA-rGO. The optimal adsorption temperature and pH for the GO and CTOS-mGO, PFPA-rGO adsorbents were 293 K and pH 6.0, 293 K and pH 7.0, 303 K and pH 6.0, respectively. Our results suggested that the aromatic rings and the abundant oxygen-containing functional groups distributed on the surface of the sheets endowed them with the characteristics of π-electron acceptors or donors, and metformin with dissociative properties could serve as a stabilizer for this π-π interaction. In addition, the electrostatic interaction between the positively charged metformin and the negatively charged GO and CTOS-mGO were also important contributors to the adsorption reaction. Our results emphasized that the GO based materials might be an effective method for alleviating metformin and other PPCPs pollution, which also provided a reference for environmental remediation of similar pollutants.

Insight into sequestration and release characteristics of uranium(VI) on phlogopite in the presence of humic acid

Knowledge of the sorption speciation and surface configuration of uranium(VI) at the mineral/water interface is essential to construct reliable retention and migration models. However, the ubiquitously existing natural organic substances at U(VI)-contaminated sites readily interact with U(VI) and interfere with the environmental fate of U(VI). In this work, the adsorption behavior and mechanism of U(VI) on phlogopite in the presence of humic acid (HA) were investigated by combining batch experiments, cryogenic time-resolved laser fluorescence spectroscopy (TRLFS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The batch sorption experiments at different HA concentrations suggested that HA had little effect at pH < 4 but suppressed U(VI) sorption on phlogopite from pH 4 to 12. Fluorescence spectral characteristics indicated the formation of multiple surfaces and aqueous U(VI)-humate species, whose abundances varied with pH. The TRLFS coupled with EXAFS spectra suggested that the HA-U(VI) hybrids preferentially bind to surface sites via U(VI) rather than HA. The humate uranium species increased uranium release and migration risk in the natural environment. These findings elucidate the species characteristics and environmental behavior of U(VI) in the presence of natural humic acid and provide guidance for remediation treatments and safety assessment of uranium-contaminated sites.

Effect of humic acid derived from leonardite on the redistribution of uranium fractions in soil

Humic acids (HAs) are complex organic substances with abundant functional groups (e.g., carboxyl, phenolic-OH, etc.). They are commonly distributed in the soil environment and exert a double-edged sword effect in controlling the migration and transformation of uranium. However, the effects of HAs on dynamic processes associated with uranium transformation are still unclear. In this study, we used HAs derived from leonardite (L-HA) and commercial HA (C-HA) as exogenous organic matter and C-HA as the reference. UO₂, UO₃, and UO₂(NO₃)₂ were used as the sources of U to explore the fractionations of uranium in the soil. We also studied the behavior of the HA. The incubation experiments were designed to investigate the effects of HA on the soil pH, uranium fraction transformation, dynamic behavior of exchangeable, weak acid, and labile uranium. The observations were made for one month. The results showed that soil pH decreased for L-HA but increased for C-HA. Under these conditions, uranium tended to transform into an inactive fraction. The dynamic behavior of exchangeable, weak acid, and labile uranium varied with the sources of HA and uranium. This study highlighted that HA could affect soil pH and the dynamic redistribution of U fractions. The results suggest that the sources of HA and U should be considered when using HA as the remediation material for uranium-contaminated soils.

Comparison of Cr(VI) adsorption and photocatalytic reduction efficiency using leonardite powder

It is very important to treat Cr(VI) from the aquatic environment due to its toxic and harmful effects. Conventional treatment methodology involving biological pathways is generally ineffective for wastewater containing Cr(VI). Therefore, it is necessary to develop environmentally friendly and economical methods to remove Cr(VI) from the aquatic environment. In this study, leonardite, which is a natural mineral that has no harmful effects on the environment, was used for Cr(VI) removal. Leonardite was used in both adsorption and photocatalytic treatment systems by only pulverizing without any chemical treatment. Characterizations of leonardite were obtained using X-ray fluorescence (XRF), fouirer transform infrared spektrofotometre (FTIR), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) analyses methods. The effects of solution pH (2-10), particle size (45-300 μm), adsorbent dose (0.25-3 g/L), and initial concentration (10-30 mg/L) on Cr(VI) removal efficiency were investigated in both adsorption and photocatalytic experiments. In the adsorption process, a complete removal efficiency (100%) was obtained for 3 g/L of adsorbent dose with an initial Cr(VI) concentration of 10 mg/L at pH 2 for 2 h. In the photocatalytic process, 100% removal efficiency of Cr(VI) was obtained when four times less adsorbent dosage was used under the same conditions. In addition, the reuse of leonardite powder was also investigated under optimum experimental conditions. Leonardite powder preserved approximately 70% of its activity in the photocatalytic process while it lost 50% of its activity after 5 reuses in adsorption process.