It is essential and important to determine the adsorption mechanism as well as removal efficiency when using an adsorption technique to remove toxic heavy metals from wastewater. In this research, ...the removal efficiency and mechanism of chromium removal by a silica-based nanoparticle were investigated. A PEI-silica nanoparticle was synthesized by a one-pot technique and exhibited uniformly well-dispersed PEI polymers in silica particles. The adsorption capacity of chromium ions was determined by a batch adsorption test, with the PEI-silica nanoparticle having a value of 183.7 mg/g and monolayer sorption. Adsorption of chromium ions was affected by the solution pH and altered the nanoparticle surface chemically. First principles calculations of the adsorption energies for the relevant adsorption configurations and XPS peaks of Cr and N showed that Cr(VI), HCrO
is reduced to two species, Cr(III), CrOH
and Cr
, by an amine group and that Cr(III) and Cr(VI) ions are adsorbed on different functional groups, oxidized N and NH
.
•The shape of the hydrogel bead was determined by the alginate concentration.•Divalent metal stoichiometrically interacted with the carboxyl group of alginate.•The sorption of Pb2+ was unaffected by ...pH.•Selectivity followed the sequence of Pb2+>>Cu2+>>Ni2+>Ca2+>H+.•HCl is an effective regenerant without the loss of the alginate polymer.
To investigate the competitive sorption of divalent metal ions such as Ca2+, Cu2+, Ni2+, and Pb2+ on alginate hydrogel beads, batch and column tests were conducted. The concentration of carboxyl group was found to be limited in the preparation of spherical hydrogel beads. From kinetic test results, 80% of sorption was observed within 4h, and equilibrium was attained in 48h. According to the comparison of the total uptake and release, divalent metal ions were found to stoichiometrically interact with the carboxyl group in the alginate polymer chain. From the Langmuir equation, the maximum capacities of Pb2+, Cu2+, and Ni2+ were calculated to be 1.1, 0.48, and 0.13mmol/g, respectively. The separation factor (α) values for αPb/Cu, αPb/Ni, and αCu/Ni were 14.0, 98.9, and 7.1, respectively. The sorption capacity of Pb2+ was not affected by the solution pH; however, the sorption capacities of Cu2+ and Ni2+ decreased with increasing solution pH, caused by competition with hydrogen. According to the result from the fixed column test, Pb2+ exhibited the highest affinity, followed by Cu2+ and Ni2+, which is in exact agreement with those of kinetic and isotherm tests. The sorbent could be regenerated using 4% HCl, and the regenerated sorbent exhibited 90% capacity upto 9 cycles.
The separation of sulfur hexafluoride (SF6), a powerful anthropogenic greenhouse gas, was investigated using membrane technology. Permeation measurements in commercial polysulfone (PSf) hollow fiber ...membranes were performed using single gases (i.e. N2, O2 and SF6) to investigate the effect of temperature and pressure on separation performance. The permeation experiments of ternary gas mixtures (N2/O2/SF6) were also conducted under various operational conditions, including pressure, temperature, stage cut (permeation flow rate/feed flow rate) and gas compositions. The results showed that the SF6 treatment capacity increased with increase in temperature or pressure, but decreased with increasing stage cut and SF6 content in the feed gas mixture. At higher temperatures, the membrane exhibited higher performance for the separation, recovery and enrichment of SF6. A feed with a higher pressure or a lower stage cut resulted in lower SF6 separation and enrichment efficiency, but a higher recovery. The separation of SF6 from a gas mixture with higher contents of SF6 exhibited lower SF6 recovery and enrichment performance. Our current work demonstrated more realistic performance of the commercial PSf hollow fiber membrane for the separation, enrichment and recovery of SF6.
•A realistic performance of commercial PSf membrane for SF6 recovery is reported.•SF6 treatment capacity increased with increase in temperature or pressure.•Increasing stage cut diminishes the recovery, but increases the enrichment of SF6.•Membrane-based SF6 recovery and enrichment are improved at lower contents of SF6.
During the roasting of gold concentrate to improve gold recovery, arsenic is released into the air and valuable elements such as Fe, Cu, Zn, and Pb are converted into oxide minerals. In this ...research, we evaluated the release of As and the loss of valuable metals during the acid baking and hot water leaching processes used for gold concentrate. The acid bake tests were conducted for gold concentrate using an electric furnace by applying various concentrations of H2SO4 solution under different baking times. The water leaching process was enacted using 70 °C water for the baked samples. Chemical and mineral compositions of the raw and treated samples were analyzed using AAS and XRD, respectively. The results show that soluble metal sulfates, such as rhomboclase and mikasite, were formed in the baked samples, and that the leaching of valuable metals (Fe, Cu, Zn, and Pb) was accelerated during the hot water leaching procedure. During acid baking, arsenic was partially removed by volatilization, and the rest of the arsenic-containing minerals were converted to soluble minerals. The soluble arsenic-containing mineral resulted in a dissolution that was 60 times higher than in the roasted sample. The maximum gold grade of solid residues increased up to 33% through the acid baking–water leaching process. It was confirmed that acid baking with H2SO4 prevented As release into the air, as well as the recovery of valuable metals through hot water leaching, such as Fe, Cu, Zn, and Pb, which were formerly discarded in the tailings.
Tetracyclines (TCs) are the most widely used antibiotics for the prevention and treatment of livestock diseases, but they are toxic to humans and have frequently been detected in water bodies. In ...this study, the physical and chemical properties of the zirconium-based metal organic framework (MOF) UiO-66 and its NH2-functionalized congener UiO-66-NH2 were investigated along with batch TC adsorption tests to determine the effect of functionalization on TC removal. TC removal was highest at pH 3 and decreased with increasing pH. Pseudo-1st and pseudo-2nd-order kinetic models were used to study the adsorption equilibrium times, and Langmuir isotherm model was found to be more suitable than Freundlich model. The maximum uptake for UiO-66 and UIO-66-NH2 was measured to be 93.6 and 76.5 mg/g, respectively. Unexpectedly, the TC adsorption capacity of UiO-66-NH2 was observed to be lower than that of UiO-66. Density functional theory calculations revealed that the pore structures are irrelevant to TC adsorption, and that the –NH2 functional group could weaken the structural robustness of UiO-66-NH2, causing a reduction in TC adsorption capacity. Accordingly, robust MOFs with zirconium-based metal clusters can be effectively applied for the treatment of antibiotics such as TC in water.
Multi-dimensional transport studies are necessary in order to better explain the fate of contaminants in groundwater. In this study, a two-dimensional transport experiment with organic contaminants ...in saturated sand was conducted to investigate the migration of the organic contaminant plume in multi-dimensional flow conditions. The transport test was conducted using toluene as a model organic contaminant in a saturated sand box under steady flow conditions. The initial plume was generated via injection at a point source. After 24 h, the plume distribution was delineated by interpolating toluene concentrations in the porewater samples. The mass centers of the toluene and the conservative tracer were almost coincident, but the size of the toluene plume was significantly reduced in longitudinal as well as transversal directions. The appropriateness of several types of sorption models were compared to describe the toluene sorption in two-dimensional transport system using numerical modeling. Among the sorption models, the Langmuir model was found to be the most appropriate to describe the sorption of toluene during two-dimensional transport. The results showed that two-dimensional experiments are better than one-dimensional column experiments in identifying the adsorption characteristics that occur during transport in saturated aquifers.
A non-pumping reactive well (NPRW) is a subsurface structure that prevents contaminant spread using many non-pumping wells containing reactive media. For the construction of an effective NPRW, a ...sufficiently small spacing between wells is an important design factor to prevent contaminant leakage. However, close well construction is not recommended because of concerns about the decreased stability of adjacent wells under field conditions. In this research, we proposed a sawtooth array of NPRW as a practical configuration to minimize well spacing while meeting stability requirements in the field. To evaluate the performance of the novel NPRW configurations, a numerical modeling was conducted considering different well diameters and well spacings and their performance was compared taking into account the number of wells and the mass of the reactive material. The comparison results showed that the sawtooth configuration was more practical than a line of wells. The performance curve of NPRWs with the saw-toothed configuration was constructed from the relationship between the contaminant removal and configuration components (diameter and spacing of the well). This can be used to predict the contaminant removal performance of NPRWs with a sawtooth array.
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•Magnesium ferrite/biochar magnetic composites (MFB-MCs) have been synthesized.•MFB-MCs exhibited superior removal performance than either biochar or MgFe2O4 alone.•The phosphate ...adsorption follows an inner-sphere coordination mechanism.•Kinetic and isotherm results indicate the physisorption and endothermic in nature.•MFB-MCs could be separated magnetically and regenerated effectively.
In this work, magnesium ferrite (MgFe2O4)/biochar magnetic composites (MFB-MCs) were prepared and utilized to remove phosphate from aqueous solutions. MFB-MCs were synthesized via co-precipitation of Fe and Mg ions onto a precursor, followed by pyrolysis. Characterization results confirmed that MgFe2O4 nanoparticles with a cubic spinel structure were successfully embedded in the biochar matrix, and this offered magnetic separability with superparamagnetic behavior and enabled higher phosphate adsorption performance than that of pristine biochar and sole MgFe2O4 nanoparticles. Batch experiments indicated that phosphate adsorption on the MFB-MCs is highly dependent on the pH, initial phosphate concentration, and temperature, while it was less affected by ionic strength. Analysis of activation and thermodynamic parameters as well as the isosteric heat of adsorption demonstrated that the phosphate adsorption is an endothermic and physisorption process. Lastly, highly efficient recyclability of the MFB-MCs suggested that they are a promising adsorbent for phosphate removal from wastewater.
In this research, we studied the use of microwave pretreatment to enhance the efficiency of Au leaching from gold concentrate. The gold concentrate was pretreated using microwaves with different ...irradiation time. The sample temperature was increased up to 950 °C by the microwave irradiation. A scanning electron microscope-energy dispersive spectrometer showed the evolution of microcracks and the reduction of sulfur on the mineral surface. X-ray diffraction data also showed the mineral phase shift from pyrite to hematite or pyrrhotite. A leaching test was conducted for the microwave-treated and untreated gold concentrates using thiourea. Although the thiourea leaching recovered 80% of Au from the untreated concentrate, from the treated concentration, the Au could be recovered completely. Au leaching efficiency increased as the microwave irradiation time increased, as well as with a higher composition of thiourea.
Geogenic radon potential (GRP) is traditionally used for mapping radon-prone areas. However, this has challenges in the accurate assessment of radon risk because of limitations such as oversimplified ...soil measurements and lack of geological profiles. This study presents predictive geogenic radon potential (P-GRP), integrating geological characterization and advanced modeling for the emanation and transport of radon in the subsurface environment. Seoul, South Korea, was selected as the research area for the evaluation of hazards using P-GRP, while subway station A was selected for the assessment of indoor health risks. The geology was characterized by the layers of bedrock and soil using uranium contents and porosity. The emanation of radon was modeled considering the radioactive decay chain of uranium and the pore structures. The vertical transport of radon was modeled considering the porosity variation within geological media, which was used for the calculation of P-GRP. Without loss of continuity, the P-GRP map was constructed by calculating P-GRP at a specific depth over the Seoul area. The calculation of P-GRP in the case of subway station A demonstrates that the radon concentration in the bedrock at the platform depth was expected to be 382 million Bqm−3. The indoor radon risk was calculated using the P-GRP by coupling the vapor intrusion process. This presented a high cancer risk for the employees as well as commuters. The P-GRP map of Seoul demonstrated higher hazards in granite zones compared to banded gneiss zones. These results have demonstrated that the P-GRP could be a novel and promising approach for assessing hazard and risk by geogenic radon during subsurface development.
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•A novel approach for assessing hazard and risk by radon in subsurface development•Utilization of advanced 3D geological profiling and vertical transport dynamics•Scenario-driven insights facilitate effective risk mitigation strategies•Expanded assessment of radon hazard across various depths•Development of scalable solutions for urban radon risk management
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