• Resources Recycling
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• v.7 no.5
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• pp.3-12
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• 1998

The most recent research in precious metal processing is found in the increasing use of heap leaching for the extraction of gold from low grade ores and tailing dumps because heap leaching has several advantages compared to traditional milling. They include simplicity, lower capital and operating costs, faster starter-up time and environmental safety. In this paper, an attempt has been made to provide an overview of important factors involved in the implementation of heap leaching technology as a vehicle for gold extraction from its low grade ores. Brief discussions of the various important elements to this process has been made to ascertain the heap leaching characteristics, such as heap leaching chemistry, natural factors, ore preparation, heap and pad construction, solution collection system, pond system, metal extraction, and economical consideration.

• Resources Recycling
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• v.29 no.2
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• pp.3-7
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• 2020

Recently, the gold leaching technologies draw much interest to recover gold from low grade ores. Current leaching processes mostly use cyanide as the leaching agent, due to its high leaching efficiencies and cost-effectiveness. However, use of cyanide is severely problematic, because of toxicity and thereby environmental risks, and requires strict regulations and environmental management. Especially, this issue becomes further apparent when cyanide should be applied for dump or heap leaching for low cost gold recovery along with recent trends. To resolve this issue, the alternative leaching processes using thiosulfate or halogen compounds, instead of cyanide, have been studied and developed but there have been lots of difficulties toward commercialization, and therefore further research should be conducted. The commercialization of dump or heap bioleaching technologies should be urgently required for effective direct biogenic gold recovery from low grade ores or tailings without use of cyanide.

• Journal of the Mineralogical Society of Korea
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• v.27 no.4
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• pp.207-222
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• 2014

In order to recover the metallic copper powder from the mine-waste rock, heap bioleaching, Fe removal and electrowinning experiments were carried out. The results of heap leaching with the mine-waste rock sample containing 0.034% Cu showed that, the leaching rate of Cu were 61% and 62% in the bacteria leaching and sulfuric acid leaching solution, respectively. Sodium hydroxide (NaOH), hydrogen peroxide ($H_2O_2$) and calcium hydroxide ($Ca(OH)_2$) were applied to effectively remov Fe from the heap leaching solution, and then $H_2O_2$ was selected for the most effective removing Fe agent. In order to prepare the electrolytic solution, $H_2O_2$ were again treated in the heap leaching, and Fe removal rates were 99% and 60%, whereas Cu removal rates were 5% and 7% in the bacteria and sulfuric acid leaching solutions, respectively. After electrowinning was examined in these leaching solution, the recovery rates of Cu were obtained 98% in bacteria and obtained 76% in the sulfuric leaching solution. The dendritic form of metallic copper powder was recovered in both leaching solutions.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2008.05a
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• pp.51-52
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• 2008

• School Mathematics
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• v.4 no.2
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• pp.297-316
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• 2002

In this paper, a teaching unit on series of number sentences with patterns is designed according to Wittmann's perspectives. In this paper, series of number sentences wish patterns means number sentences in which some patterns are contained. especially, seven kinds of number sentences wish patterns are offered as basic materials, and fifteen tasks based on these basic materials are offered. These tasks are for ninth grade students and higher grade students. These tasks heap students to recognize patterns, and to understand mechanism underlying in those patterns by looking for patterns and proving whether these patterns are generally hold. As working on these tasks, students can reinforce meaning of algebraic expression, its manipulation, and concept of number series. Students also can reinforce mathematical thinking such as analogical thinking, deductive thinking, etc. In this point, this teaching unit reveal important objectives, contents, and Principles of mathematics education. This teaching unit can also be rich sources for student's activities. Especially, for each task's level is different, each student's personal ability is considered fully. Since teachers can know mathematical facet, psychological facet, and didactical facet holistically, this teaching unit can offer broad possibilities for experimental studies. SD, this leaching unit can be said to be substantial. In this paper, this leaching unit is not applied in classroom directly. Actually such applying in classroom is suggested as follow-up studies. By appling this teaching unit in various classroom, some effective informations for teaching this teaching unit and some particular phenomenons in those teaching processes can be identified, and this teaching unit can be revised to be better one.

• Resources Recycling
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• v.20 no.2
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• pp.30-44
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• 2011

This review describes the involvement of different microorganisms for the recovery of uranium from the ore. Mainly Acidithiobacillus forrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans are found to be the most widely used bacteria in the bioleaching process of uranium. The bioleaching of uranium generally follows indirect mechanism in which bacteria provide the ferric iron required to oxidize $U^{4+}$. Commercial applications of bioleaching have been incorporated for extracting valuable metals, due to its favorable process economics and reduced environmental problems compared to conventional metal recovery processes such as smelting. At present the uranium is recovered through main bioleaching techniques employed by heap, dump and in situ leaching. Process development has included recognition of the importance of aeration of bioheaps, and improvements in stirred tank reactor design and operation. Concurrently, knowledge of the key microorganisms involved in these processes has advanced, aided by advances in molecular biology to characterize microbial populations.