• Mineral and Industry
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• v.26
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• pp.1-12
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• 2013

In this study, an accelerated carbonation process was applied to stabilize hazardous heavy metals of industrial solid waste incineration (ISWI) bottom ash and fly ash, and to reduce $CO_2$ emissions. The most commonly used method to stabilize heavy metals is accelerated carbonation using a high water-to-solid ratio including oxidation and carbonation reactions as well as neutralization of the pH, dissolution, and precipitation and sorption. This process has been recognized as having a significant effect on the leaching of heavy metals in alkaline materials such as ISWI ash. The accelerated carbonation process with $CO_2$ absorption was investigated to confirm the leaching behavior of heavy metals contained in ISWI ash including fly and bottom ash. Only the temperature of the chamber at atmospheric pressure was varied and the $CO_2$ concentration was kept constant at 99% while the water-to-solid ratio (L/S) was set at 0.3 and $3.0dm^3/kg$. In the result, the concentration of leached heavy metals and pH value decreased with increasing carbonation reaction time whereas the bottom ash showed no effect. The mechanism of heavy metal-stabilization is supported by two findings during the carbonation reaction. First, the carbonation reaction is sufficient to decrease the pH and to form an insoluble heavy metal-material that contributes to a reduction of the leaching. Second, the adsorbent compound in the bottom ash controls the leaching of heavy metals; the calcite formed by the carbonation reaction has high affinity of heavy metals. In addition, approximately 5 kg/ton and 27 kg/ton $CO_2$ were sequestrated in ISWI bottom ash and fly ash after the carbonation reaction, respectively.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.4
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• pp.203-209
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• 1998

The quality of groundwater used for natural mineral water should be strictly regulated on international level by hydrogeology experts and officials because groundwater is greatly subjected to contaminations and its aquifer system may be easily destroyed by external reasons. A total of 18 natural mineral water plants exist in Precambrian metamorphic terrains of the Gyunggi massif and Yeungam massif. The g개undwater quality for the natural mineral water investigated in hydrochemical aspects shows that pH ranges from 6.85 to 8.02 with an average of 7.52. The electric conductivity (EC) and hardness average 134.1 $\mu$S/cm and 43.5, respectively, which are relatively low to the total average (151.4 $\mu$S/cm and 57.9). The contents of major cations and anions are in the order of $Ca^{2＋}$＞$Na^{＋}$＞Mg$^{2＋}$＞K$^{＋}$ and HCO$_3$$^{-}$ ＞SO$_4$$^{2－}$ ＞Cl$^{-}$ ＞F$^{-}$ , respectively. The dominant water types determined by Piper diagram are $Ca^{2＋}$－$Na^{＋}$－HCO$^{-}$ $_3$and $Ca^{2＋}$-HCO$^{-}$ $_3$, mainly due to the dissolution of plagioclase in the host rocks. Representative correlation coefficients between chemical species are $Ca^{2＋}$－HCO$^{-}$ $_3$(0.92), $Ca^{2＋}$－Cl$^{-}$ (0.63), $Na^{＋}$－F$^{-}$ (0.67), HCO$^{-}$ $_3$－Cl$^{-}$ (0.66), and $Na^{＋}$－HCO$^{-}$ $_3$(0.63). The determinative. coefficients between $Ca^{2＋}$ and HCO$^{-}$ $_3$, and (Ca$^{2＋}$＋$Na^{＋}$＋K$^{＋}$ and EC art highest among the elements. According to the saturation index, most chemical species are undersaturated with respect to major minerals, except for some silica phases. In viewpoint of phase equilibrium, the chemical evolution of the groundwater may continue to proceed with increasing pH because the groundwater is undersaturated with respect to feldspars.

• Journal of the Mineralogical Society of Korea
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• v.24 no.2
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• pp.63-71
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• 2011

The mineral phases precipitated in the swamp built for the treatment of the mine drainage of the Dalsung Mine were investigated to reveal the mineralogical changes from schwertmannite to goethite and related behavior of heavy metals. Our XRD results show that most schwertmannite were transformed to goethite except the small portions of the samples in the uppermost part. No significant morphological changes were observed in the samples during mineral transformation by SEM, indicating that this transformation process occurred not from dissolution-precipitation process, but in solid state. Among heavy metals sorbed or coprecipitated in the mineral phases, Pb and Cu concentrations were relatively higher compared with their concentrations in the mine drainage. The relative concentrations of other heavy metals show similar values. The heavy metal concentration in the minerals do not show noticeable differences from uppermost schwertmannite to lower goethite samples, indicating the transformation process without any leaching or additional sorption of heavy metals in the solid state.

• Resources Recycling
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• v.14 no.6 s.68
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• pp.3-9
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• 2005

In this study, the separation and recovery of cerium hydroxide was investigated from the wasted cerium polishing powders. Waste cerium polishing powder contains $64.5\;wt\%$ of rare earth oxide and the content of cerium oxide is $36.5\;wt\%$. Since cerium oxide, $56.3\%$ of rare earths, is the most stable state in rare earth, the dissolution of cerium oxide in acid solution is not easy. Therefore the process of rare earth oxide by sulfation and water leaching was examined in order to increase the recovery of rare earth. Rare earth elements were recovered in the form of $\Re{\cdot}Na(SO_{4})_{2}$ by the addition of sodium sulfate to leached solution. The slurry of rare earth hydroxide was prepared by the addition of $\Re{\cdot}Na(SO_{4})_{2}$ to sodium hydroxide solution. After the oxidation of cerous hydroxide($CE(OH)_{3}$) to ceric hydroxide($CE(OH)_{3}$) by aeration, ceric hydroxide was separated from other rare earth hydroxides by controlling the acidity of solution.

• Journal of Soil and Groundwater Environment
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• v.11 no.1
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• pp.23-36
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• 2006

Experimental leaching of tailings was performed as a function of times (1, 2, 4, 7, 14, 21 and 30 days) in the laboratory using reaction solutions equilibrated to three different pH set-points (pHs 1,3 and 5). The initial pHs of 5 and 3 stabilized at either 4.6-6.1 or 2.8-3.5 in 2 days and decrease gradually with time afterwards. The results of the leaching tests indicate that the significant increase in the sulfate concentrations and in acidity after 7 days of leaching results from the oxidation of sulfide minerals. There were no significant variations in the extractable Pb found in the leach solutions of pH 5 and 3 within the reaction time (1-30 days), while Zn, Cd and Cu concentrations tend to significantly increase with time. In tailings leaching at an initial pH=1, two trends were observed: i) The 'Zn-type' (Zn, Cd and Cu), with increasing concentrations between days 1 and 30, corresponding to the expected trend when continuous dissolution is the dominant process, ii) the 'Pb-type' (Pb), with decreasing concentrations over time, suggesting rapid dissolution of a Pb source followed by the precipitation of 'anglesite' in relation to the large increase in dissolved sulfates. The high sulfate concentrations were coupled with high concentrations of released Fe, Zn and Cd. Release of Zn and Cd and acidity from these leaching experiments can potentially pose adverse impact to surface and groundwater qualities in the surrounding environment. The kinetic problems could be the important factor which leads to increasing concentrations of trace metals in the runoff water.

• Economic and Environmental Geology
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• v.45 no.6
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• pp.661-672
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• 2012

Lab scale experiments to investigate the dissolution reaction among supercritical $CO_2$-sandstone-groundwater by using sandstones from Gyeongsang basin were performed. High pressurized cell system (100 bar and $50^{\circ}C$) was designed to create supercritical $CO_2$ in the cell, simulating the sub-surface $CO_2$ storage site. The first-order dissolution coefficient ($k_d$) of the sandstone was calculated by measuring the change of the weight of thin section or the concentration of ions dissolved in groundwater at the reaction time intervals. For 30 days of the supercritical $CO_2$-sandstone-groundwater reaction, physical properties of sandstone cores in Gyeongsang basin were measured to investigate the effect of supercritical $CO_2$ on the sandstone. The weight change of sandstone cores was also measured to calculate the dissolution coefficient and the dissolution time of 1 g per unit area (1 $cm^2$) of each sandstone was quantitatively predicted. For the experiment using thin sections, mass of $Ca^{2+}$ and $Na^+$ dissolved in groundwater increased, suggesting that plagioclase and calcite of the sandstone would be significantly dissolved when it contacts with supercritical $CO_2$ and groundwater at $CO_2$ sequestration sites. 0.66% of the original thin sec-tion mass for the sandstone were dissolved after 30 days reaction. The average porosity for C sandstones was 8.183% and it increased to 8.789% after 30 days of the reaction. The average dry density, seismic velocity, and 1-D compression strength of sandstones decreased and these results were dependent on the porosity increase by the dissolution during the reaction. By using the first-order dissolution coefficient, the average time to dissolve 1 g of B and C sandstones per unit area (1 $cm^2$) was calculated as 1,532 years and 329 years, respectively. From results, it was investigated that the physical property change of sandstones at Gyeongsang basin would rapidly occur when the supercritical $CO_2$ was injected into $CO_2$ sequestration sites.

• Journal of the Korean Electrochemical Society
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• v.15 no.3
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• pp.135-148
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• 2012

Ionic liquids are steadily attracting interests throughout a recent decade and their application is expanding into various fields including electrochemistry due to their unique properties such as non-volatility, inflammability, low toxicity, good ionic conductivity, wide electrochemical potential window and so on. These features make ionic liquids become an alternative solution for electrodeposition of metals that cannot be electroplated in aqueous electrolytes. In this review, we classify investigated metals into three categories, which are light (Li, Mg), refractory (Ti, Ta) and noble (Pd, Pt, Au) metals, rather than covering the exhaustive list of metals and try to update the recent development in this area. In electrodeposition of light metals, granular fine Li particles were successfully obtained while the passivation of electrodeposited Mg layers is an obstacle to reversible deposition-dissolution process of Mg. In the case of refractory metals, the quality of Ta and Ti deposit particles was effectively improved with addition of LiF and pyrrole, respectively. In noble metal category, EMIM TFSA ionic liquid as an electrolyte for Au electrodeposition was proven to be effective and BMP TFSA ionic liquid developed a smooth Pd deposit. Pt nanoparticle production from ionic liquid droplet in aqueous solution can be cost-effective and display an excellent electrocatalytic activity.

• Economic and Environmental Geology
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• v.33 no.5
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• pp.353-365
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• 2000

After their first appearance on Earth, bacteria have exerted significant influence on geochemical behavior of elements. Numerous evidence of their control on geochemistry through geologic history has been observed in a variety of natural environments. They have mediated weathering rate, formation of secondary minerals, redox transformation of metals and metalloids, and thus global cycling of elements. Such ability of bacteria receives so considerable attention from microbiologists, mineralogists, geologists, soil scientists, limnologists, oceanographers, and atmospheric scientists as well as geochemists that a new and interdisciplinary field of research called 'geomicrobiology' is currently expanding. Some recent subjects of geomicrobiology which are studied extensively are as follows: 1) Functional groups distributed on bacterial cell walls adsorb dissolved cations onto cell surfaces by electrostatic surface complexation, which is followed by hydrous mineral formation. 2) Dissimilatory metal reducing bacteria conserve energy to support growth by oxidation of organic matter coupled to reduction of some oxidized metals and/or metalloids. They can be effectively used in remediating environments contaminated with U, As, Se, and Cr. 3) Bacteria increase the rate of mineral dissolution by excreting proton and ligands such as organic acids into aqueous system. 4) Thorough investigation on the effects of biofilm on geochemical processes is needed, because most bacteria are adsorbed on solid substrates and form biofilms in natural settings.

• Journal of Soil and Groundwater Environment
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• v.21 no.1
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• pp.40-48
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• 2016

A siderophore-producing bacterium (i.e., Pseudomonas aeruginosa) capable of chelating Fe³⁺ from its mineral form (i.e., iron oxides) was used to enhance As uptake by plants. Since As in soil is mainly associated with iron oxides, siderophore can play an important role in As mobilization through the dissolution of As-bearing iron oxides. A series of pot experiment using Pteris cretica showed that As removal by P. cretica with siderophore-producing bacteria addition increased more than three times compared to that without bacteria addition. Competition between indigenous bacteria and introduced bacteria (i.e., P. aeruginosa) was also observed, but such competition seemed not to be significant. This study suggests that enhanced-phytoremediation by siderophore-producing bacteria addition could be a visible option for longterm As removal in the forest area at the former Janghang smelter site.

• Korean Journal of Metals and Materials
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• v.47 no.3
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• pp.188-194
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• 2009

Recently, new extraction technology for manganese nodule has been developed as alternative noble metallic resources. It is important to understand thermodynamic behaviors of phosphorus in low basic slag system from the viewpoint of the refining processing optimization. Thermodynamic behaviors of phosphorus in the $FeO-MnO-CaO-SiO_2-MgO_{satd.}$ slag system were investigated at 1723 K with various oxygen potential and slag composition of low basicity. The experimental results for dependence of phosphorus on oxygen potential and slag basicity indicated that the dissolution mechanism of phosphorus into slag of low basicity could be derived as follows; $[P]+5/4O_2+(O^{2-})=({PO_{3.5}}^{2-})$ Present experimental results implied that stability of phosphorus in slag would be depended on both of $O^{2-}$ (basicity) and content of $Ca^{2+}$ in molten slag. The thermodynamic effect of FeO, MnO and $Na_2O$ on low basicity on phosphate capacity was discussed.