Yosep Han

Bioleaching of arsenic from highly contaminated mine tailings using Acidithiobacillus thiooxidans

The behavior of arsenic (As) bioleaching from mine tailings containing high amount of As (ca. 34,000 mg/kg) was investigated using Acidithiobacillus thiooxidans to get an insight on the optimal conditions that would be applied to practical heap and/or tank bioleaching tests. Initial pH (1.8-2.2), temperature (25-40 °C), and solid concentration (0.5-4.0%) were employed as experimental parameters. Complementary characterization experiments (e.g., XRD, SEM-EDS, electrophoretic mobility, cell density, and sulfate production) were also carried out to better understand the mechanism of As bioleaching. The results showed that final As leaching efficiency was similar regardless of initial pH. However, greater initial As leaching rate was observed at initial pH 1.8 than other conditions, which could be attributed to greater initial cell attachment to mine tailings. Unlike the trend observed when varying the initial pH, the final As leaching efficiency varied with the changes in temperature and solid concentration. Specifically, As leaching efficiency tended to decrease with increasing temperature due to the decrease in the bacterial growth rate at higher temperature. Meanwhile, As leaching efficiency tended to increase with decreasing solid concentration. The results for jarosite contents in mine tailings residue after bioleaching revealed that much greater amount of the jarosite was formed during the bioleaching reaction at higher solid concentration, suggesting that the coverage of the surface of the mine tailings by jarosite and/or the co-precipitation of the leached As with jarosite could be a dominant factor reducing As leaching efficiency.

Relationship between synthesis conditions and photocatalytic activity of nanocrystalline TiO 2

The degradation efficiency of methylene blue by TiO2 nanoparticles, which were synthesized under different synthesis conditions (i.e., molar ratio of water and titanium tetraisopropoxide (TTIP), pH, and calcination temperature) in a sol-gel process, was systematically investigated. The results showed that increasing themolar ratio of water and TTIP led to the enhanced photocatalytic activity of TiO2 nanoparticles, which were likely attributed to the increased specific surface area of TiO2 nanoparticles synthesized with high molar ratio. The results were supported by the relative increase in the size of interaggregated pores of the aggregated TiO2 nanoparticles. The best photocatalytic activity of TiO2 nanoparticles was observed at acidic synthesis conditions; however, the results were not consistent with physical properties for the crystallinity and the crystallite size of TiO2 nanoparticles but rather explained by the presence of abundant hydroxyl groups and water molecules existing on the surface of TiO2 under acidic synthesis environments. Furthermore, methylene blue degradation experiments revealed that the photocatalytic activity of TiO2 nanoparticles was maximized at the calcination temperature of 700°C. The trend was likely due to the combined effect of the anatase crystallinity which showed the highest value at 700°C and the crystallite size/specific surface area which did not excessively increase up to 700°C.

Processable high internal phase Pickering emulsions using depletion attraction

High internal phase emulsions have been widely used as templates for various porous materials, but special strategies are required to form, in particular, particle-covered ones that have been more difficult to obtain. Here, we report a versatile strategy to produce a stable high internal phase Pickering emulsion by exploiting a depletion interaction between an emulsion droplet and a particle using water-soluble polymers as a depletant. This attractive interaction facilitating the adsorption of particles onto the droplet interface and simultaneously suppressing desorption once adsorbed. This technique can be universally applied to nearly any kind of particle to stabilize an interface with the help of various non- or weakly adsorbing polymers as a depletant, which can be solidified to provide porous materials for many applications.

Porous Ca-based bead sorbents for simultaneous removal of SO2, fine particulate matters, and heavy metals from pilot plant sewage sludge incineration

In this study, a porous calcium-based sorbent was prepared for simultaneous removal of SO2, particulate matter (PM), and heavy metals generated during incineration of sewage sludge. The prepared sorbent was confirmed to have a 3-dimensional-network pore structure, a high specific surface area of 68.5m(2)/g, and gas permeability of 1.12 × 10(-10)m(2). Laboratory-scale tests indicated that there was an improvement in the performance of SO2 removal as the porosity and the specific surface area of the sorbent increased. Additionally, increasing reaction temperature led to greater SO2 removal. Meanwhile, the SL-4 and LS-3 sorbents prepared in this study were installed for operation during pilot tests treating the sewage sludge combustion gas generated by a fluidized incinerator in order to compare and evaluate their feasibility for use in industrial applications. The results showed that the reactivity between SO2 and the starting material of the sorbent (Ca(OH)2>CaCO3), as well as the high specific surface area of the sorbent, were confirmed to be critical factors that improved the performance of SO2 removal. Notably, the results confirmed that both fine PM (≤ 1 μm) and heavy metals were simultaneously removed with increasing efficiency over the time of operation.

Synthesis of hierarchical MoO2/MoS2 nanofibers for electrocatalytic hydrogen evolution

Perpendicularly attached MoS2 nanosheets on MoO2 conductive nanofibers were synthesized by combining electrospinning, calcination, and sulfurization processes. Compared to randomly stacked MoS2 nanosheets on MoO2 nanofiber, they show greater hydrogen evolution reaction (HER) performance (i.e., onset potential of -180 mV versus normal hydrogen electrode with the Tafel slope of 59 mV dec-1). HER performance decreases with increasing MoS2 nanocrystal size.

Stability of carboxyl-functionalized carbon black nanoparticles: the role of solution chemistry and humic acid

Carboxyl-functionalized carbon black nanoparticles (CB-NPs) are widely used in various industries. Studies on the dispersion and aggregation of nanomaterials in the aquatic environment are being actively conducted these days. In this study, the aggregation and sedimentation of carboxyl-functionalized CB-NPs were investigated according to the changes in the solution chemistry (0.1–10 mM NaCl and 0.01–1 mM CaCl2) and in the presence/absence of natural organic matter (1 and 5 mg L−1 humic acid) in the aquatic environment. Overall, humic acid was found to have the greatest effect on the stability of CB-NPs under the aquatic conditions investigated. Specifically, the sedimentation caused by CB-NP aggregation was more actively observed in NaCl than in CaCl2. With the increase in the ionic strength of the NaCl solution, the aggregation rate of CB-NPs also increased, whereas in the CaCl2 solution, the CB-NPs suspension stability was almost insensitive to the ionic strength. The reason was that the divalent cation Ca2+ was specifically adsorbed onto CB-NPs in the CaCl2 solution to reverse the negative CB-NP zeta potential, and increase the electrostatic repulsive force between CB-NPs. In the presence of humic acid in the NaCl and CaCl2 solutions, stability improved in the whole ionic strength range. A comparison of the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory with the modified DLVO theory considering the steric force revealed that the enhanced stability of a CB-NP suspension in the presence of humic acid is attributed to a steric repulsive force as well as a stronger electrostatic repulsive force caused by humic acid adsorption.

Transport of carboxyl-functionalized carbon black nanoparticles in saturated porous media: Column experiments and model analyses

The aim of this study was to investigate the transport behavior of carboxyl-functionalized carbon black nanoparticles (CBNPs) in porous media including quartz sand, iron oxide-coated sand (IOCS), and aluminum oxide-coated sand (AOCS). Two sets of column experiments were performed under saturated flow conditions for potassium chloride (KCl), a conservative tracer, and CBNPs. Breakthrough curves were analyzed to obtain mass recovery and one-dimensional transport model parameters. The first set of experiments was conducted to examine the effects of metal (Fe, Al) oxides and flow rate (0.25 and 0.5 mL min(-1)) on the transport of CBNPs suspended in deionized water. The results showed that the mass recovery of CBNPs in quartz sand (flow rate=0.5 mL min(-1)) was 83.1%, whereas no breakthrough of CBNPs (mass recovery=0%) was observed in IOCS and AOCS at the same flow rate, indicating that metal (Fe, Al) oxides can play a significant role in the attachment of CBNPs to porous media. In addition, the mass recovery of CBNPs in quartz sand decreased to 76.1% as the flow rate decreased to 0.25 mL min(-1). Interaction energy profiles for CBNP-porous media were calculated using DLVO theory for sphere-plate geometry, demonstrating that the interaction energy for CBNP-quartz sand was repulsive, whereas the interaction energies for CBNP-IOCS and CBNP-AOCS were attractive with no energy barriers. The second set of experiments was conducted in quartz sand to observe the effect of ionic strength (NaCl=0.1 and 1.0mM; CaCl2=0.01 and 0.1mM) and pH (pH=4.5 and 5.4) on the transport of CBNPs suspended in electrolyte. The results showed that the mass recoveries of CBNPs in NaCl=0.1 and 1.0mM were 65.3 and 6.4%, respectively. The mass recoveries of CBNPs in CaCl2=0.01 and 0.1mM were 81.6 and 6.3%, respectively. These results demonstrated that CBNP attachment to quartz sand can be enhanced by increasing the electrolyte concentration. Interaction energy profiles demonstrated that the interaction energy profile for CBNP-quartz sand was compressed and that the energy barrier decreased as the electrolyte concentration increased. Furthermore, the mass recovery of CBNPs in the presence of divalent ions (CaCl2=0.1 mM) was far lower than that in the presence of monovalent ions (NaCl=0.1 mM), demonstrating a much stronger effect of Ca(2+) than Na(+) on CBNP transport. Mass recovery of CBNPs at pH 4.5 was 55.6%, which was lower than that (83.1%) at pH 5.4, indicating that CBNP attachment to quartz sand can be enhanced by decreasing the pH. The sticking efficiencies (α) calculated from the mass recovery by colloid filtration theory were in the range from 2.1×10(-2) to 4.5×10(-1), which were far greater than the values (2.56×10(-6)-3.33×10(-2)) of theoretical sticking efficiencies (αtheory) calculated from the DLVO energy by the Maxwell model.

Formation of mesoporous materials from silica dissolved in various NaOH concentrations: effect of pH and ionic strength

We describe the effects of NaOH/SiO2 ratio and pH on the formation of mesoporous materials, which was synthesized via an alkalimetal hydroxide fusion method, from amorphous silica dissolved in NaOH. Physical properties (e.g., specific surface area, pore volume, and pore size) of mesoporous materials synthesized at different conditions (i.e., pH, NaOH/SiO2 ratio) were evaluated through X-ray diffraction, nitrogen adsorption-desorption, and transmission electron microscope analyses. The results showed that, at the NaOH/SiO2 ratios of 0.5, 1, and 2, gels were successfully synthesized while no product was formed at the NaOH/SiO2 ratios greater than 2. Additionally, mesoporous materials were found to be formed at both pH 10 and 11 while they were unstable under more alkaline conditions. The adsorption/desorption isotherm results for the mesoporous materials synthesized at around pH 11 and with NaOH/SiO2 ratios of 0.5-0.8 showed a hysteresis loop characteristic of the bottle-neck pore shape. Furthermore, mesoporous materials with good physical properties were synthesized from all gels at pH 10 regardless of sodium concentration.

Pore characteristics and hydrothermal stability of mesoporous silica: role of oleic acid

Silicate mesoporous materials were synthesized with nonionic surfactant and their surfaces were modified by oleic acid adsorption. Infrared spectrometer, nitrogen adsorption-desorption isotherm, scanning electron microscopy, and thermogravimetric analyses were used to investigate the structure of oleic acid modified mesoporous material. The effects of heat treatment at various temperatures on oleic acid modified materials were also studied. Oleic acids on silica surfaces were found to be bonded chemically and/or physically and be capable of enduring up to 180°C. The adsorbed oleic acid improved the hydrothermal stability of mesoporous silica and assisted mesopore structure to grow more in hydrothermal treatment process by preventing the approach of water.

Silver Coating on the Porous Pellets from Porphyry Rock and Application to an Antibacterial Media

The porous pellets were prepared from porphyry by slurry foaming method. The effect of sintering temperatures on pore structure of porous porphyry pellets with different extension ratio (E R ) was investigated by specific surface area, water absorption and porosity, which changed with sintering temperatures. When the sintering temperatures increased from 975℃ to 1075℃, specific surface area and water absorption of the all samples decreased. In case of the sample with an equal sintering temperature, E R =3.0 pellets had little influence on pore structure compared to the E R =2.0 pellets. As a results, it was shown by SEM that facilitated formation of micro pores at E R =2.0 pellets shrunk increasingly after sintering process. At E R =3.0 and sintering temperature at 1025℃, optimum conditions of the porous porphyry porous pellets was found. Also, Escherichia coli removal efficiency of the silver-containing porphoyry porous pellets was measured for the feasibility as a antibacterial media. The antibacterial activity of prepared silver-containing sample was maintained above 90% for 40 days.