• Environmental Engineering Research
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• v.10 no.6
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• pp.294-305
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• 2005

The effectiveness of fly ash-, quicklime-, and quicklime-fly ash-based stabilization/solidification(S/S) in chromium(Cr) contaminated soils was investigated using modified semi-dynamic leaching tests. Artificial soil samples composed of kaolinite or montmorillonite contaminated with chromium nitrate(4000 mg $Cr^{3+}\;kg^{-1}$ of solid) were prepared and then subjected to S/S treatment using quicklime, fly ash, or quick lime-fly ash. The effectiveness of the treatment was evaluated by assessing the cumulative fraction of leached $Cr^{3+}$ as well as, by computing the effective diffusivity ($D_e$) and the leachability index (LX) of the treated samples. The reduction in $Cr^{3+}$ release for the untreated samples was more pronounced in the presence of montmorillonite, which was attributed to sorption. Treatment with quicklime, fly ash, or quick lime-fly ash was significantly effective in reducing $Cr^{3+}$ release most probably due to the formation of pozzolanic reaction products and $Cr(OH)_3$ precipitation. The most effective treatment was observed in montmorillonite-sand soil samples treated with quicklime-fly ash (99.8% removal). The mean $D_e$ decreased significantly and the mean LX was greater than 9 for all treated samples, indicating that the treated soils were acceptable for "controlled utilization". The mechanism controlling $Cr^{3+}$ leaching from all treated samples during the first 5 days appeared to be diffusion.

• Resources Recycling
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• v.20 no.3
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• pp.48-54
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• 2011

Sulphuric acid leaching was conducted to extract the metal values from spent refinery catalyst. More than 95% of Ni and V and 30% of Mo could be leached out in 1 M sulphuric acid and 1 hr of leaching time. The decrease in Mo leaching was due to typical characteristic of Mo matrix. The activation energies of the leaching reactions showed the dissolution process follows a diffusion control mechanism. In order to leach out all Mo, further the leaching experiments were conducted with sulfur free spent refinery catalyst. For sulfur free spent refinery catalyst, a two step process of leaching with 1 M sulphuric acid followed by sodium carbonate washing showed better leaching than a two step leaching process with sodium carbonate followed by sulphuric acid washing, with almost 99% leaching of Ni, Mo and V. Solvent extraction using LIX 841 were conducted for a leach liquor containing Ni, 2 g/L; V, 9 g/L, Mo, 0.6 g/L. More than 98% of Mo was extracted from the leach liquor at A:O ratio of 5:2 in a 2 stage process. Similarly V was extracted at A:O ratio of 5:3 in a 2 stage process with 82% of total V extraction.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.526-531
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• 2001

LD slag, that is, a by-product of steel making process, has been mainly used as land construction materials. Recently, the seashore application of LD slag was tried in Japan and Korea tut the reaction between LD slag and seawater was not studied yet. We tried to clarify the leaching reaction and/or mechanism of LD slag and the reaction between seawater and LD slag. We tried to apply these results to the decarbonization of seawater for seawater magnesia process. At first, LD slag was milled and classified into 5 grades, that is, (ⅰ)45${\mu}{\textrm}{m}$ under, (ⅱ)0.25~0.5mm (ⅲ)0.5~1mm(ⅳ)1~2mm, (ⅴ)2.36~3.35mm. These slags were leached in the distilled water. In case of 45${\mu}{\textrm}{m}$ under, the pH of the leached solution was over 12. The chemical analysis of leached solution showed that the $Ca^{+}$$^2$was main component and the S $i^{+}$$^4$was very low. On the other hand, the content of S $i^{+}$$^4$in leached solution was decreased with the increase of pH of this solution. The nearly pure calcium solution was made and the ultra high purity MgO could be made with this calcium solution. The leaching behavior of LD slag was different between the fine particle and coarse particle. The calcium was leached by bulk dissolution in the coarse particle and by surface controlled reaction in fine particle. The leaching rate was slow in coarse particle and fast in fine particle. Therefore, the high pH solution, that is, over 12, was obtained in fine particle.cle.e.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1476-1484
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• 2023

Laboratory experiments and point monitoring of reservoir sediments have proven that stable sulfate reduction (SSR) can lower the concentrations of toxic metals and sulfate in acidic groundwater for a long time. Here, we hypothesize that SSR occurred during in situ leaching after uranium mining, which can impact the fate of acid groundwater in an entire region. To test this, we applied a sulfur isotope fractionation method to analyze the mechanism for natural attenuation of contaminated groundwater produced by acid in situ leaching of uranium (Xinjiang, China). The results showed that δ³⁴S increased over time after the cessation of uranium mining, and natural attenuation caused considerable, area-scale immobilization of sulfur corresponding to retention levels of 5.3%-48.3% while simultaneously decreasing the concentration of uranium. Isotopic evidence for SSR in the area, together with evidence for changes of pollutant concentrations, suggest that area-scale SSR is most likely also important at other acid mining sites for uranium, where retention of acid groundwater may be strengthened through natural attenuation. To recapitulate, the sulfur isotope fractionation method constitutes a relatively accurate tool for quantification of spatiotemporal trends for groundwater during migration and transformation resulting from acid in situ leaching of uranium in northern China.

• Proceedings of the Korean Nuclear Society Conference
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• 2005.05a
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• pp.229-230
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• 2005

• Economic and Environmental Geology
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• v.53 no.2
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• pp.159-166
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• 2020

In this research, we investigate the effect of microwave pretreatment on the recovery of gold from the gold concentrates by thiourea leaching. The changes in mineral phases by decomposition of pyrites in the gold concentrates using microwave were observed, and the result of microwave irradiation showed that the temperature of the irradiated sample increases with increasing irradiation time. With the reaction of temperature increases, Sulfur (S) in pyrites was converted to sulfur dioxide (SO₂), and then the content of S in the sample was reduced. The analytical results of XRD and SEM-EDS showed that pyrites are converted to magnetite and hematite, and its surfaces are changed to a porous shape where micro-cracks are developed. The Au leaching efficiency from the irradiated gold concentrates using thiourea-mixed solvent increased with the increases of irradiation time and solvent concentration. The experimental results considering leaching parameters indicate that the mechanism of microwave irradiation increases the maximum leaching efficiency and leaching rate of the gold concentrates, and the solvent does a role for the increasing of leaching rate constant.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.419-424
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• 2007

The contents were investigated by the monitoring survey from the soils and tailings caused by numerous abandoned mines in Korea. Cause heavy metals due to abandoned metal mines are raising significant environmental problems. But it is an important key such as a leaching and a transfer mechanism to evaluate contamination levels caused by abandoned mines. In this study the column test was carried in order to calculate a leaching level from soils and tailings. It was demonstrated that the leaching of Pb, Cd and Mn was expressed with similar behaviors and that of As and Cu was expressed with similar behaviors. For Zn, the leaching behavior was shown a serious leaching level with 40 mg/kg during the 45days. This was explained by Zn high contents of soils Zn in a natural world and ORP conditions where the leaching of Zn was occurred easily. Hence it was necessary that the survey of ORP was a key as well as total contents for the management of abandoned metal mines. We could estimate the chemical forms of heavy metals using the physical index such as ORP and pH and reduce the risk from heavy metals caused by abandoned metal mines.

• Nuclear Engineering and Technology
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• v.20 no.3
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• pp.155-164
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• 1988

A rate equation for UO$_2$ pellet leaching has been derived and compared with some experimental results. The leach rate model comprises the processes of oxygen penetration into UO$_2$ pellets and the dissolution and transport of oxidized UO$_2$ depending on the penetration depth of oxygen. The model may be analyzed with two regions of transient and steady state behaviors, which should depend on the initial oxidation state of pellets. Also this model can be utilized in the analyses of general leach processes if the oxidation reaction of UO$_2$ is replaced with similar mechanism of those processes.

• Economic and Environmental Geology
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• v.38 no.5 s.174
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• pp.587-597
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• 2005

This review deals with arsenic chemistry and its occurrence in groundwater. Specifically, the paper gives an overview regarding chemical and physical properties of arsenic species, oxidation of As(III), geochemical processes related to the fate and transport of arsenic, arsenic leaching from soil, and mechanism of arsenic leaching from arsenic-containing minerals.

• Membrane Journal
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• v.6 no.4
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• pp.189-195
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• 1996

It is concluded from this study that human consumption of very low TDS water does not leach minerals from the body that cause ill health effects because; -The human body's own control mechanism of homeostasis and internal body secretions keep tight controls on body fluid composition regardless of drinking water TDS for a normal person under normal csonditions. -The unofficial WHO document's proposed guideline of a 100m/l lower limit for drinking water due to mineral leaching and subsequent ill health was not found to be scientifically or physiologically credible. Leaching of minerals from the body is not officially recognized by WHO. -The experience of the U.S. Navy, Army, NASA and dommunity demonstrations do not support ill health symptoms caused by consumption of low TDS drinking water. -Millions of people regularly consume maturally occurring low TDS water without symptoms of ill health.