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Nhi Thi Pham,Long Dang Khuat 한국응용곤충학회 2019 Journal of Asia-Pacific Entomology Vol.22 No.3
Two new species Ishigakia curvicaudicula Pham & Long sp. nov., and Yezoceryx comaensis Pham sp. nov. are described and illustrated. An updated key to 15 known species of Ishigakia of the world fauna is also provided. The new species Yezoceryx comaensis Pham sp. nov. is inserted in a key to the Vietnamese species provided by Pham et al. (2017). In addition, Siphimedia nigriscuta Sheng and Sun, 2010 is recorded for the first time from Vietnam.
Treatment and Recovery of Valuable Materials from Aluminum Dross by Leaching
Thuy Nhi Nguyen Thi,이만승 한국자원리싸이클링학회 2017 資源 리싸이클링 Vol.26 No.5
White and black dross are resulted from the recycling of aluminum. There are no established processes to recover valuable materials from black dross. Hydrometallurgical processes seem to be suitable for the treatment of aluminum dross. The salts in the black dross are recovered by dissolving with water. The residues are treated by either alkaline or acid leaching. Although the leaching rate of alumina by NaOH is lower than that by acid, its intermediates are more suitable to the production of aluminabased materials. The future direction for the treatment and recovery of valuable materials from aluminum dross is discussed.
Atmospheric Corrosion of Hot Dip Zinc Coated Steel in Coastal and Rural Areas of Vietnam
( Nguyen Nhi Tru ),( Le Khac Duyen ),( Tran Mai Han ) 한국부식방식학회(구 한국부식학회) 2017 Corrosion Science and Technology Vol.16 No.5
The comparative results of corrosion testing in humid tropical atmosphere in rural and coastal areas for hot dipped zinc coatings are presented below. The test was conducted in outdoor conditions over a period of five years. The mass loss and other performance characteristics of two types of zinc coatings were evaluated, analysed and discussed in relation to the climatic and environmental parameters. The corrosion rates of the coatings exposed to coastal conditions were about three times higher than the corrosion rates appreciated in rural conditions. The data demonstrates that the corrosion process obeys an equation of the form M=At<sup>n</sup>, where M is the loss of metal and t is the time of exposure. A and n are constants which values depend on the environmental characteristics and the physicochemical behavior of the corrosion products respectively. Corrosion is strongly influenced by atmospheric time of wetness (TOW) and airborne salinity. The nature and composition of corrosion products are also considered. Simonkolleite, a major crystalline phase, was found in the zinc corrosion products exposed to coastal conditions, while zinc hydroxide and zinc hydrosulfate are easily found in rural settings.
Thi Thuy Nhi Nguyen,이만승 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.3
Aluminum dross results from the re-melting of used aluminum cans, and is a valuable resource containing alumina. In general, aluminum dross contains oxides of Al, Ca, Fe, Mg, Si and Ti and some salts. As a continuation of the previous work to recover pure alumina from the dross, the effect of employing ultrasound wave in the NaOH solution was investigated to improve the leaching percentage of alumina from the mechanically activated dross. The use of ultrasound improved the leaching percentage of alumina from 35% to 60% and resulted in a leaching solution where the purity of aluminate ion was 99%. Among the optimum conditions (5 M NaOH, 50 oC, 4 h, pulp density of 100 g/L and ultrasonic power 100 W), leaching time had a remarkable effect on the dissolution of alumina in the presence of ultrasound. The combined effect of ultrasound and the addition of CaCl2 and organic acids to the NaOH solution was also investigated. Roasting of the black dross with CaCl2 followed by ultrasound leaching did not improve the leaching percentage of alumina. The presence of organic acids in the NaOH solution increased the leaching percentage of alumina as well as silica, and thus was not favorable for recovering pure aluminate solution from the black dross.
Speciation of alumina in aqueous solution and its interaction with silicate ion
Thi Thuy Nhi Nguyen,이만승 한국자원공학회 2019 Geosystem engineering Vol.22 No.4
Several aluminum (Al) species can be formed by the dissolution of Al-containing minerals. The distribution of Al-containing species depends on the total concentration of aluminum, solution pH, and the presence of complex-forming ligands. Polymeric species exists as Al-3(OH)(4)(5+), Al-13(OH)(32)(7+) when solution pH is 3-5. The mole fraction of these species is proportional to the concentration of Al (III). Al3+ exists at pH < 4 and Al(OH)(2+) exists in the pH range between 4 and 6, while Al(OH)(4)(-) is predominant at pH > 8. The reaction between Al (III) and impurity (silica) results in the formation of some new species. These data might be employed to develop a hydrometallurgical process for recovery of alumina from primary and secondary resources containing alumina.
Recovery of Alumina from Sodium Hydroxide Leaching Solution by Precipitation with Hydrogen Peroxide
Thi Thuy Nhi Nguyen,이만승 한국자원리싸이클링학회 2019 資源 리싸이클링 Vol.28 No.4
In order to recover pure alumina from balck dross, precipiatation experiments were done to the NaOH leaching solution of mechanically activated black dross. In this work, hydrogen peroxide was added to the synthic solution as a precipitating agent. Among some variables, the concentration of H2O2 and the volume ratio of H2O2 to solution showed a remarkable effect on the precipitation of aluminum hydroxide. At the optimum conditions, most of the aluminate was precipitated. Calcination of the aluminum hydroxide at 1200o C led to the formation of θ and α-alumina. The charactistics of the synthesized activated alumina was measured by XRD and EDS. The average particles size of the alumina was 3.73 μm.
Optimal Capital Adequacy Ratios for Commercial Banks: Empirical Evidence from Vietnam
Thi Minh Nhi LUONG,Phuong Anh NGUYEN 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.10
It is unavoidable for businesses, especially commercial banks, to compete with other firms and financial institutions in a globalized and internationalized world. Basel I, II, and III were developed by the Basel Committee on Banking Supervision with the primary purpose of supporting banks in dealing with potential risks and enhancing their ability to absorb losses. Basel II and III require the minimum capital adequacy ratio (CAR) of 8% and 10.5%, respectively. This paper estimates the optimal CAR of 26 commercial banks in Vietnam from 2016 to 2020 using the two-stage DEA method. According to the empirical findings, banks with ideal CARs exceeding 8% (as defined by Basel II) and 10.5 percent (as defined by Basel III) account for approximately 98 percent and 88 percent of all banks, respectively. Furthermore, 75.83 percent of all banks need to boost their existing CAR to achieve the optimal level of CAR as well as obtain the best performance. On average, the optimal CAR of state-owned banks is higher than other joint-stock banks, respectively 26 percent and 19 percent. Consequently, it is recommended for Vietnam commercial banks to reach optimal CAR and comply with the new policy set by Basel III with the purpose of approaching the efficient frontier.
Leaching of Black Dross by Hydrochloric Acid Solutions
Thi Thuy Nhi Nguyen,Thi Hong Nguyen,이만승 한국자원리싸이클링학회 2017 資源 리싸이클링 Vol.26 No.6
Leaching of black dross with HCl solution was conducted to find a suitable process to recover valauble materials. In this work, the leaching behavior of the components was compared between black dross and the residues after water treatment. All the components except TiO2 in the black dross were dissolved by HCl solution in the experimental ranges. Treatment of the black dross with water to recover the salts has negative effect on the leaching of Al2O3, MgO and SiO2. The reactions occuring during the leaching were discussed. At an optimum leaching condition of 3 M HCl and 90oC, the leaching percentage of Al2O3, MgO and SiO2 was 85, 100 and 40%, respectively.