Jayhyun Park

Adaptation of a mixed culture of acidophiles for a tank biooxidation of refractory gold concentrates containing a high concentration of arsenic

We adapted a mixed culture of acidophiles to high arsenic concentrations to confirm the possibility of achieving more than 70% biooxidation of refractory gold concentrates containing high arsenic (As) concentration. The biooxidation process was applied to refractory gold concentrates containing approximately 139.67 g/kg of total As in a stirred tank reactor using an adapted mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The percentage of the biooxidation process was analyzed based on the total As removal efficiency. The As removal was monitored by inductively coupled plasma (ICP) analysis, conducted every 24 h. The results obtained with the adapted culture were compared with the percentage of biooxidation obtained with a non-adapted mixed culture of A. ferrooxidans and A. thiooxidans, and with their respective pure cultures. The percentages of biooxidation obtained during 358 h of reaction were 72.20%, 38.20%, 27.70%, and 11.45% for adapted culture, non-adapted culture, and pure cultures of A. thiooxidans and A. ferrooxidans, respectively. The adapted culture showed a peak maximum percentage of biooxidation of 77% at 120 h of reaction, confirming that it is possible to obtain biooxidation percentages over 70% in gold concentrates containing high As concentrations.

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.

[ De-NO x ] Characteristics for Pt/γ-Alumina/Cordierite Foam Filter of Beads Shape

Porous cordierite beads, of which the average pore size was and porosity was about 80%, were prepared by the foaming method and then their application as support of the catalyst for , reduction with propene was investigated. The pressure drop of a 2 mm porous beads filter was less than that of a 1 mm porous beads filter and the difference in pressure drop between these two increased as the flow rate increased. The catalytic activity of washcoated on the porous bead was tested with varying Pt loading mole ratio , space velocity and oxygen contents (1 and 8). Pt loading of showed the highest activity for conversion. The , test was operated in the temperature range of and the best operation temperature of the catalytic filter is about . As the C/N ratio increased, increase of the , conversion might result from the increase in exhaustion of the amount of oxygen by the reduction of hydrocarbon. conversion at of space velocity shows a maximum 34% higher conversion than that at . On condition that was 5%, space velocity was and the C/N ratio was 8, the conversion exhibited a maximum of 40% at .