Nag-Choul Choi

Use of pyrophyllite clay for fluoride removal from aqueous solution

Abstract The aim of this study was to investigate the removal of fluoride from aqueous solution using pyrophyllite clay as an adsorbent. X-ray fluorescence analysis showed that Si (74.03%) and Al (21.20%) were the major constituents of pyrophyllite. Equilibrium test (adsorbent particle size < 0.15 mm) demonstrated that the maximum sorption capacity of pyrophyllite was 0.737 mg/g. Kinetic test showed that fluoride sorption to pyrophyllite arrived at equilibrium around 24 h. Thermodynamic test indicated that fluoride sorption to pyrophyllite increased with increasing temperature from 25 to 45°C, indicating the endothermic nature of sorption process. Further experiments indicated that fluoride removal was not sensitive to solution pH between 4.0 and 9.0. The influence of sulfate, carbonate, and phosphate on the removal of fluoride was important while the effect of nitrate and chloride was negligible. In addition, among the pyrophyllite thermally treated at different temperatures (untreated, 400, 600, 800, 1,...

Adhesion of bacteria to pyrophyllite clay in aqueous solution.

The aim of this study was to investigate the adhesion of bacteria (Escherichia coli) to pyrophyllite clay using batch and flow-through column experiments. Batch results demonstrated that pyrophyllite was effective in removing bacteria (94.5±2.0%) from aqueous solution (1 mM NaCl solution; pyrophyllite dose of 1 g/ml). At solution pH 7.1, negatively-charged bacteria could be removed due to their adhesion to positively-charged surfaces of pyrophyllite (point of zero charge=9.2). Column results showed that pyrophyllite (per cent removal of 94.1±2.3% ) was far more effective in bacterial adhesion than quartz sand (53.6±5.3%) under the given experimental conditions (flow rate of 0.3 ml/min; solution of 1 mM NaCl + 0.1 mM NaHCO3). Bacterial removal in pyrophyllite columns increased from 90 to 100% with decreasing flow rate from 0.6 to 0.15 ml/min due to increasing contact time between bacteria and filter materials. In addition, bacterial removal remained relatively constant at 94–97% even though NaHCO3 concentration increased from 0.1 to 10 mM (flow rate of 0.3 ml/min). This could be related to the fact that pyrophyllite remained positively-charged even though the solution conditions changed. This study demonstrates that pyrophyllite could be used as adsorptive filter materials in the removal of bacteria.

Removal of arsenate and arsenite from aqueous solution by waste cast iron

The removal of As(III) and As(V) from aqueous solution was investigated using waste cast iron, which is a byproduct of the iron casting process in foundries. Two types of waste cast iron were used in the experiment: grind precipitate dust (GPD) and cast iron shot (CIS). The X-ray diffraction analysis indicated the presence of Feo on GPD and CIS. Batch experiments were performed under different concentrations of As(III) and As(V) and at various initial pH levels. Results showed that waste cast iron was effective in the removal of arsenic. The adsorption isotherm study indicated that the Langmuir isotherm was better than the Freundlich isotherm at describing the experimental result. In the adsorption of both As(IH) and As(V), the adsorption capacity of GPD was greater than CIS, mainly due to the fact that GPD had higher surface area and weight percent of Fe than CIS. Results also indicated the removal of As(III) and As(V) by GPD and CIS was influenced by the initial solution pH, generally decreasing with increasing pH from 3.0 to 10.5. In addition, both GPD and CIS were more effective at the removal of As(III) than As(V) under given experimental conditions. This study demonstrates that waste cast iron has potential as a reactive material to treat wastewater and groundwater containing arsenic.

Two-dimensional modelling of benzene transport and biodegradation in a laboratory-scale aquifer.

In this study biodegradation of aqueous benzene during transport in a laboratory‐scale aquifer model was investigated by conducting a 2‐D plume test and numerical modelling. Benzene biodegradation and transport was simulated with the 2‐D numerical model developed for solute transport coupled with a Haldane‐Andrews type function for inclusion of an inhibition constant which is effective for high concentrations. Experimental data revealed that in the early stages the benzene plume showed a rather clear shape but lost its shape with increased travel time. The mass recoveries of benzene at 9, 16, and 22 h were 37, 13 and 8%, respectively, showing that a significant mass reduction of aqueous benzene occurred in the model aquifer. The major processes responsible for the mass reduction were biodegradation and irreversible sorption. The modelling results also indicated that the simulation based on the microbial parameters from the batch experiments slightly overestimated the mass reduction of benzene during transport. The sensitivity analysis demonstrated that the benzene plume was sensitive to the maximum specific growth rate and slightly sensitive to the half‐saturation constant of benzene but almost insensitive to the Haldane inhibition constant. The insensitivity to the Haldane inhibition constant was due to the rapid decline of the benzene peak concentration by natural attenuation such as hydrodynamic dispersion and irreversible sorption. An analysis of the model simulation also indicated that the maximum specific growth rate was the key parameter controlling the plume behaviour, but its impact on the plume was affected by competing parameter such as the irreversible sorption rate coefficient.

Photodegradation of Bisphenol A with ZnO and TiO 2 : Influence of Metal Ions and Fenton Process

In this study, photocatalytic degradation of bisphenol A (BPA) was investigated using two types of catalysts (TiO2 and ZnO) with various metal ion concentrations and amounts of added H2O2. A kinetic test was performed to observe the changes of BPA over time under UV irradiation in a photocatalytic reactor. Experimental results demonstrated that degradation efficiency of ZnO was higher than that of TiO2. The degradation rate increased as catalyst dosage increased until reaching optimum dosage, after which degradation rate decreased. The addition of H2O2 improved the degradation efficiency of BPA, with the degradation efficiency increasing with the amount of H2O2. All metal ions, including Fe2+, Ni2+, and Cu2+, inhibited the degradation of BPA by ZnO at natural pH, whereas Fe2+ and Ni2+ enhanced degradation efficiency of BPA at acidic pH. Comparison of BPA degradation with H2O2 only, ZnO/H2O2, Fe2+/H2O2, and ZnO/Fe2+/H2O2 revealed that Fe2+/H2O2 was more efficient than other processes at lower pH (pH = 3.44), whereas ZnO/H2O2 the most efficient at higher pH (pH = 6.44). These results indicate that ZnO/H2O2 process was observed to be the most efficient of all processes. Degradation efficiency of BPA by ZnO was also influenced by additional parameters, including H2O2 concentration, metal ions, and solution pH.

Attachment characteristic of indigenous acidophilic bacteria to pyrite surface in mine waste

Indigenous acidophilic bacteria living in a hot acidic spring near Hatchobaru thermal electricity plant in Japan were incubated and used for the bioleaching experiment. The indigenous acidophilic bacteria grew properly in the leaching (sulfur-rich) solution and, over the course of incubation, the pH decreased and Eh increased. In relation to the bacterial growth-curve, the lag phase was hardly shown while the exponential phase was significantly fast. Following Gram staining of the bacteria, they were categorized into Gram-negative and Gram-positive. When the bacteria were inoculated to pyrite, rod-shaped bacteria and round-shaped microbes were well attached to the surface of the pyrite. The size of the rod-shaped bacteria ranged from 1.05–1.10 μm to 4.01–5.38 μm. Round-shaped microbes were more than 3.0 μm in diameter. Paired cells of rod-shaped bacteria were linearly attached to the surface of the pyrite. The round-shaped microbes showed strong organic attachment. Twenty days after the indigenous acidophilic bacteria were inoculated to a pyrite-leaching medium, the bacterial sample had a greater concentration of Fe and Zn than within the control sample.

Enhancement of Au–Ag–Te contents in tellurium-bearing ore minerals via bioleaching

The purpose of this study was to enhance the content of valuable metals, such as Au, Ag, and Te, in tellurium-bearing minerals via bioleaching. The ore samples composed of invisible Au and Au paragenesis minerals (such as pyrite, chalcopyrite, sphalerite and galena) in combination with tellurium-bearing minerals (hessite, sylvanite and Tellurobismuthite) were studied. Indigenous microbes from mine drainage were isolated and identified as Acidithiobacillus ferrooxidans, which were used in bioleaching after adaption to copper. The effect of the microbial adaption on the bioleaching performance was then compared with the results produced by the non-adaptive process. The microbial adaption enhanced the Au–Ag–Te contents in biological leaching of tellurium-bearing ore minerals. This suggests that bioleaching with adapted microbes can be used both as a pretreatment and in the main recovery processes of valuable metals.

Modacrylic anion-exchange fibers for Cr(VI) removal from chromium-plating rinse water in batch and flow-through column experiments

ABSTRACT The aim of this study was to investigate Cr(VI) removal from chromium-plating rinse water using modacrylic anion-exchange fibers (KaracaronTM KC31). Batch experiments were performed with synthetic Cr(VI) solutions to characterize the KC31 fibers in Cr(VI) removal. Cr(VI) removal by the fibers was affected by solution pH; the Cr(VI) removal capacity was the highest at pH 2 and decreased gradually with a pH increase from 2 to 12. In regeneration and reuse experiments, the Cr(VI) removal capacity remained above 37.0 mg g−1 over five adsorption–desorption cycles, demonstrating that the fibers could be successfully regenerated with NaCl solution and reused. The maximum Cr(VI) removal capacity was determined to be 250.3 mg g−1 from the Langmuir model. In Fourier-transform infrared spectra, a Cr = O peak newly appeared at 897 cm−1 after Cr(VI) removal, whereas a Cr–O peak was detected at 772 cm−1 due to the association of Cr(VI) ions with ion-exchange sites. X-ray photoelectron spectroscopy analyses demonstrated that Cr(VI) was partially reduced to Cr(III) after the ion exchange on the surfaces of the fibers. Batch experiments with chromium-plating rinse water (Cr(VI) concentration = 1178.8 mg L−1) showed that the fibers had a Cr(VI) removal capacity of 28.1–186.4 mg g−1 under the given conditions (fiber dose = 1–10 g L−1). Column experiments (column length = 10 cm, inner diameter = 2.5 cm) were conducted to examine Cr(VI) removal from chromium-plating rinse water by the fibers under flow-through column conditions. The Cr(VI) removal capacities for the fibers at flow rates of 0.5 and 1.0 mL min−1 were 214.8 and 171.5 mg g−1, respectively. This study demonstrates that KC31 fibers are effective in the removal of Cr(VI) ions from chromium-plating rinse water.

Enhancement of gold recovery during lead fire assay by salt-roasting

The aim of this study was to investigate the effect of a simple and economical salt-roasting method on the gold recovery of a conventional lead fire assay. An enhanced gold recovery of 30.99 g/ton (16.82%) was obtained by roasting a gold concentrate at 750°C, but this was further enhanced to 40.44 g/ton (21.95%) at the same temperature with the addition of 20% salt. The fact that the maximum recovery was obtained at a roasting temperature of 750°C was attributed to the fact that pyrites within the concentrate contained invisible gold, with the addition of salt enhancing the decomposition of these pyrites. Thus, by treating the gold concentrate with a combination of conventional and salt roasting, its gold content was increased and the loss of gold to the glass slag was reduced. Finally, it was also observed that the amount of gold loss with an amorphous specimen was less than that of samples containing galena.

The Characteristic of Te Recovery in Gold Concentrate Using Electrolysis

Department of Rural Systems Engineering/Research Institute for Agriculture and Life Science, Seoul NationalUniversity, Seoul, Korea In order to obtain pure metallic Te from gold concentrate, roasting treatment, hypochlorite leaching, Fe removaland electrolysis experiments were carried out. The contents of Au, Ag and Te from the concentrate sample androasted sample were much more soluble in the hypochlorite solution than in aqua regia digestion, whereas the met-als Pb, Zn, Fe and Cu were easier to leach with the aqua regia than the hypochlorite. With the addition of NaOHin the hypochlorite leaching solution prior to electrolysis, the Fe removal rate achieved was only 96% in the con-centrate sample, while it reached 98% in the roasted sample. The results of electrolysis for 240 min, 98% of themetallic copper was recovered from the concentrate sample, while 99% was obtained from the roasted sample dueto the removal of S by roasting. The amount of anode slime was also greater in the electrolytic solution with theroasted sample than with the concentrate sample. The results on the anode slime after the magnetic separation pro-cess showed the amount of metallic pure native tellurium recovered was greater in the roasted sample than in theconcentrate sample.