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Naoki Hiroyoshi - One of the best experts on this subject based on the ideXlab platform.

  • Ammonium Thiosulfate extraction of gold from printed circuit boards pcbs of end of life mobile phones and its recovery from pregnant leach solution by cementation
    Hydrometallurgy, 2020
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Yoshito Nagata, Mayumi Ito, Naoki Hiroyoshi
    Abstract:

    Abstract In this study, the Ammonium Thiosulfate leaching of gold (Au) from printed circuit boards (PCBs) of end-of-life mobile phones and the subsequent recovery of dissolved metals from pregnant leach solution via cementation were elucidated under various conditions. Over 99% of Au was extracted from crushed PCBs (D50 = 85 μm) under the following conditions: 1 M of Na2S2O3, 10 mM of CuSO4, 1 M of ammonia/Ammonium concentration, 0.1 g/10 ml of solid-to-liquid ratio, and a 24-h of leaching time in the presence of oxygen. In contrast, the recovery of Au ions via cementation was more favorable in the absence of oxygen. Among the various cementation agents evaluated, copper (Cu) was the most selective and recovered around 95% of extracted Au from the pregnant leach solution even in the presence of various coexisting metal ions. The cementation of Au exhibited two distinct kinetic regions: (1) an initially rapid rate, and (2) a more gradual and constant rate. Finally, the use of Cu plates to recover Au ions from Ammonium Thiosulfate pregnant solution of crushed PCBs is proposed, which could selectively recover about 80% of dissolved Au and is easier to handle and reuse compared with Cu powder.

  • enhanced cementation of gold via galvanic interactions using activated carbon and zero valent aluminum a novel approach to recover gold ions from Ammonium Thiosulfate medium
    Hydrometallurgy, 2020
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Mayumi Ito, Hirotaka Takahashi, Naoki Hiroyoshi
    Abstract:

    Abstract In gold (Au) hydrometallurgy, Ammonium Thiosulfate is the most attractive and promising alternative to conventional lixiviants like cyanide or the halides because it is non-toxic, less corrosive and has high selectivity for Au. However, its industrial-scale application for Au extraction is still severely limited because the recovery of dissolved Au from pregnant solutions remains challenging. The present study proposes a novel, simple and effective technique to address this difficulty using zero-valent aluminum (ZVAl) and activated carbon. Gold recovery was investigated by mixing 0.15 g of ZVAl and/or activated carbon and 10 ml of a solution containing 1 M Na2S2O3, 0.5 M NH3, 0.25 M (NH4)2SO4 and 10 mM CuSO4 with 100 mg/l of dissolved Au in a constant temperature water bath shaker at 25 °C for 24 h. Gold recovery from the Ammonium Thiosulfate solution was negligible when only ZVAl or activated carbon was added. When ZVAl and activated carbon were both present in the Ammonium Thiosulfate solution, however, over 99% of Au ions were successfully recovered. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) observations of the solid residues indicate that Au was predominantly deposited on activated carbon attached to ZVAl. Based on the rest potentials of these two materials, their synergistic effect on Au recovery could be attributed to the formation of numerous galvanic cells in solution where ZVAl acted as anodes (i.e., primary electron donor) while activated carbon acted as the cathode onto which Au ions are reduced via cementation to elemental Au.

  • a physical separation scheme to improve Ammonium Thiosulfate leaching of gold by separation of base metals in crushed mobile phones
    Minerals Engineering, 2019
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Mayumi Ito, Rongrit Pongsumrankul, Shinya Tanaka, Naho Kitajima, Ayumu Saito, Naoki Hiroyoshi
    Abstract:

    Abstract As technology advances, consumers are looking to buy new phones. This phenomenon leads to decrease in life-cycle of mobile phones (ca. 2–3 years), resulting in increase of waste mobile phones. In waste mobile phones, it contains various components including display unit, battery, cases, and printed circuit boards (PCBs). PCBs alone contain variety of materials such as gold (Au), copper (Cu), and iron (Fe) as well as aluminum (Al) with plastics, which causes difficulty in recycling. The coexistence of Cu and Al in crushed mobile phones has been recently reported to cause very low Au extraction efficiency in Ammonium Thiosulfate medium due primarily to enhanced re-deposition of extracted Au ions via galvanically induced cementation. To limit this antagonistic effect of Cu and Al coexistence on Au extraction, Au-containing components were separated from Cu- and/or Al-bearing parts using a two-step crushing approach in tandem with various physical separation techniques (i.e. jig, hybrid jig, magnetic separation, flotation, and sink-float separation) that were applied on appropriate size fractions. The results showed that over 96% of PCBs, the primary Au-containing material in mobile phones, were recovered after jig separation. These concentrated PCBs were collected and further crushed to liberate Au-containing parts and then treated by diverse physical separation techniques such as magnetic separation, jig separation, hybrid jig separation, flotation, and sink-float separation depending on the crushed particle sizes. Ammonium Thiosulfate leaching of the mixed Au-concentrated products from various physical pretreatment techniques showed that Au extraction improved by about 15-fold, indicating that the physical separation scheme proposed in this study is very promising.

  • interference of coexisting copper and aluminum on the Ammonium Thiosulfate leaching of gold from printed circuit boards of waste mobile phones
    Waste Management, 2018
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Mayumi Ito, Hirotaka Takahashi, Naoki Hiroyoshi
    Abstract:

    Ammonium Thiosulfate solution is an ideal lixiviant to extract gold (Au) from electronic wastes (E-wastes) because it is non-toxic, less corrosive, and more selective than conventional cyanide or halide solutions. It was reported recently, however, that Au leaching efficiency in Ammonium Thiosulfate medium dramatically decreased at high solid-to-liquid ratios (S/L), even though the amounts of reagents used were in excess. To understand how this occurred, leaching experiments were conducted using printed circuit boards (PCBs) from waste mobile phones, and Au distribution in the leaching residues was examined by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Significant amounts of Au were found together with copper (Cu) and aluminum (Al), implying that extracted Au ions were likely re-deposited during leaching onto Cu and Al found in PCBs via cementation (i.e., reductive deposition). A more detailed elucidation of this phenomenon by cementation experiments using pure Cu and/or Al powders indicates that these metals could only recover Au ions alone via cementation at very high amounts, however, this process became more extensive when Cu and Al powders were suspended together in solution even though the amounts of the individual metals were much lower. Electrochemical experiments (chronoamperometry) in Ammonium Thiosulfate solutions containing Au ions using an Al working electrode also showed that Au ion cementation was dramatically enhanced when Cu powder was present in solution, and the bulk of Au was cemented on Cu powder rather than on the Al electrode. These results suggest that coexistence of Cu and Al interfered with the extraction of Au in Ammonium Thiosulfate medium at high S/L because of the enhanced re-deposition of extracted Au via galvanic interaction.

  • gold recovery from shredder light fraction of e waste recycling plant by flotation Ammonium Thiosulfate leaching
    Waste Management, 2018
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Mayumi Ito, Rongrit Pongsumrankul, Naho Kitajima, Naoki Hiroyoshi
    Abstract:

    Abstract This paper describes the recovery of gold (Au) from shredder light fraction (SLF) of a recycling plant by flotation and leaching. SLF is typically sent to landfills as waste, but it still contains substantial amounts of Au, and other metals like Cu and Fe. The SLF sample used in this study contains 0.003% of Au, 12% of Cu, and 10% of Fe. Flotation results showed that over 99% of Au and 50% of combustibles were recovered in froth while most of the base metals were recovered in tailing. SEM-EDX of froth products indicates that Au floated via two mechanisms: (1) flotation of Au-plated plastic particles, and (2) agglomeration of fine Au particles together with plastic particles due to kerosene-induced hydrophobic-hydrophobic interactions followed by the flotation of these agglomerated particles. Combustibles in froth/tailing were analyzed by ATR-FTIR, and the results showed that plastics in the froth were mostly sulfonated polystyrene (PS) and acrylonitrile butadiene styrene (ABS) while those in tailing were polyurethane (PU) and polyethylene terephthalate (PET). Contact angle measurements of plastic particles suggest that PS and ABS are more hydrophobic than PU and PET. Most of the base metals in the tailing had either bent or twisted shapes because they were mostly made up of wires. In flotation, these large and heavy particles are unaffected by bubbles and simply sink. Leaching results using Ammonium Thiosulfate solutions showed that Au extraction increased from 33 to 51% after flotation.

Scott R Yates - One of the best experts on this subject based on the ideXlab platform.

  • effect of surface application of Ammonium Thiosulfate on field scale emissions of 1 3 dichloropropene
    Science of The Total Environment, 2017
    Co-Authors: Scott R Yates, Daniel J Ashworth, Q Zhang
    Abstract:

    Soil fumigation is important for food production but has the potential to discharge toxic chemicals into the environment, which may adversely affect human and ecosystem health. A field experiment was conducted to evaluate the effect of applying Ammonium Thiosulfate fertilizer to the soil surface prior to fumigating with 1,3-dichloropropene (1,3-D). The Ammonium Thiosulfate solution was applied as a spray with minimal water to minimize the effect on emissions from saturating (e.g. sealing) the soil pores with water. Two independent data sets were collected for determining the emission rate. One data set was used with three micrometeorological approaches: aerodynamic, integrated horizontal flux and theoretical profile shape; the other dataset with two indirect, back calculation methods that used the CALPUFF and ISCST3 dispersion models. Using the five methodologies, the 1,3-D emission rate was obtained for 16days. The maximum emission rates ranged from 7 to 20μgm-2s-1, the maximum 24-hour averaged emission rates ranged from 5 to 13μgm-2s-1, and the total 1,3-D emissions ranged from 12 to 26%. Comparing to fumigation without Ammonium Thiosulfate spray revealed that emissions were reduced from 3% (CALPUFF) to 29% (ADM). Using a simulation model, Ammonium Thiosulfate spray would be expected to reduce emissions by almost 21%. These data provide evidence that emissions of 1,3-D can be reduced by spraying Ammonium Thiosulfate fertilizer on the soil surface prior to soil fumigation, and provides another emission-reduction strategy to those recently reported (e.g., deep injection, water seals and organic amendments).

  • mitigating 1 3 dichloropropene chloropicrin and methyl iodide emissions from fumigated soil with reactive film
    Environmental Science & Technology, 2012
    Co-Authors: Richeng Xuan, Scott R Yates, Daniel J Ashworth
    Abstract:

    Implicated as a stratospheric ozone-depleting compound, methyl bromide (MeBr) is being phased out despite being considered to be the most effective soil fumigant. Its alternatives, i.e., 1,3-dichloropropene (1,3-D, which includes cis and trans isomers), chloropicrin (CP), and methyl iodide (MeI), have been widely used. High emissions of MeI from fumigated soil likely put farm workers and other bystanders at risk of adverse health effects. In this study, two types of constructed reactive film were tested for their ability to mitigate emissions of 1,3-D, CP, and MeI using laboratory permeability cells. Before activation, these films act as a physical barrier to trap fumigants leaving soil. After activation of the reactive layer containing Ammonium Thiosulfate solution, the films also act as a sink for the fumigants. Over 97% of trans-1,3-D and 99% of the cis-1,3-D, CP and MeI were depleted when they passed into the reactive film. Half-lives (t1/2 )o fcis-, trans-1,3-D, CP and MeI under activated reactive film were 1.2, 1.4, 1.6, and 2.0 h respectively at 40 °C.

  • laboratory assessment of emission reduction strategies for the agricultural fumigants 1 3 dichloropropene and chloropicrin
    Environmental Science & Technology, 2009
    Co-Authors: Daniel J Ashworth, Richeng Xuan, F F Ernst, Scott R Yates
    Abstract:

    With the increased use of the agricultural fumigants 1,3-dichloropropene (1,3-D) and chloropicrin (CP), it is important that strategies to reduce emissions of these fumigant from soil to the air are assessed to protect air quality. Using an established soil column approach, the following emission reduction strategies were compared to a control: (1) spray application of Ammonium Thiosulfate to the soil surface; (2) deep injection at 46 cm depth; (3) high density polyethylene sealed over the soil surface; (4) virtually impermeable film sealed over the soil surface; and (5) irrigation with Ammonium Thiosulfate solution. Relative to the control, 1,3-D emissions were reduced by 26.1, 1.0, 0.01, 94.2, and 42.5%, for treatments 1 through 5, respectively. For CP the reductions were 41.6, 23.3, 94.6, 99.9, and 87.5% for treatments 1 through 5, respectively. Virtually impermeable film gave the greatest reductions for both fumigants, while HDPE was very effective only for CP. Despite offering less significant emissi...

  • Competitive Degradation between the Fumigants Chloropicrin and 1,3‐Dichloropropene in Unamended and Amended Soils
    Journal of environmental quality, 2003
    Co-Authors: Wei Zheng, Sharon K. Papiernik, Minxing Guo, Scott R Yates
    Abstract:

    The mixture of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) is used as a preplant soil fumigant. In comparison with individual fumigants, application of a mixture may affect the environmental dissipation and fate of each chemical, such as emission and degradation. We investigated the degradation of CP, 1,3-D, and their mixture in fresh soils and sterile soils, and evaluated the competitive characteristic of fumigants in the mixture. The degradation of low concentrations of CP in fresh soil was accelerated at early times in the presence of 1,3-D, whereas the addition of CP reduced the degradation rate of trans-1,3-D, possibly by inhibiting the activity of trans-1,3-D degrading microorganisms. The potential of applying amendments to the soil to increase the rate of CP and 1,3-D degradation was also illustrated. The degradation of both fumigants was significantly enhanced in soils amended with Ammonium Thiosulfate (ATS) and sodium diethyldithiocarbamate (Na-DEDTC) compared with unamended soil. Competitive degradation was observed for CP in amended soils in the presence of 1,3-D. The degradation of cis-1,3-D in amended soils spiked as a mixture of 1,3-D and CP was repressed compared with the rate of degradation in samples spiked with 1,3-D only. This implied that in abiotic degradation, CP and cis-1,3-D competed for a limited number of reaction sites in amended soil, resulting in decreased degradation rates. No significant influence of fumigant mixtures was observed for trans-1,3-D in amended soil.

  • surface application of Ammonium Thiosulfate fertilizer to reduce volatilization of 1 3 dichloropropene from soil
    Pest Management Science, 2000
    Co-Authors: Jianying Gan, Ole J Becker, Frederick F Ernst, Chad M Hutchinson, J A Knuteson, Scott R Yates
    Abstract:

    Atmospheric emission of the soil fumigant 1,3-dichloropropene (1,3-D) is of environmental concern because of its toxicity and carcinogenicity. Thiosulfate fertilizers have been found to rapidly transform 1,3-D in soil to non-volatile ions which are less toxic. We investigated the use of surface application of Ammonium Thiosulfate (ATS) for reducing 1,3-D volatilization. In packed soil columns, emission of 1,3-D applied by sub-surface injection decreased with increasing ATS application rate and the amount of water used for delivering ATS. When ATS was applied in 9 mm water at 64g m ˇ2 , total 1,3-D emission was reduced by 61%. The reduction was 89% when ATS was applied at 193 g m ˇ2 . Bioassays showed that ATS application did not affect the effectiveness of 1,3-D for controlling citrus nematodes. In field plots where a 1,3-D emulsified formulation was applied via sub-surface drip, surface spray of ATS reduced 1,3-D emissions by 50%, and by 71% when the surface was also covered with polyethylene film. ATS application had no effect on the efficacy of root-knot nematode control or tomato yields. These results suggest that surface application of Thiosulfate fertilizers may be a feasible and effective strategy for minimizing 1,3-D emissions. # 2000 Society of Chemical Industry

Jianguo Wang - One of the best experts on this subject based on the ideXlab platform.

  • presulfidation of como and nimop catalysts by Ammonium Thiosulfate
    Chinese Journal of Catalysis, 2010
    Co-Authors: G E Hui, L I Xuekuan, Zhangfeng Qin, L U Zhanjun, Guofu Wang, Jianguo Wang
    Abstract:

    Ammonium Thiosulfate ((NH4)2S2O3) was used as a sulfiding agent for presulfiding CoMo and NiMoP catalysts. The effect of the amount of (NH4)2S2O3 on hydrodesulfurization (HDS) activity was investigated. For the CoMo series, the use of a proper amount of (NH4)2S2O3 gave a higher HDS activity than when the catalyst was sulfided by H2S. SO42- formed during presulfidation modified the Al2O3 support and decreased the interaction between the active phase and support, and the activity was enhanced. However, a smaller amount of (NH4)2S2O3 used for the presulfidation would result in insufficient sulfidation, while a larger amount of (NH4)2S2O3 increased the particle size of the active phases, and both were harmful to HDS activity. For the NiMoP series, the presulfided catalysts were less active than those sulfided by H2S. This was ascribed to the high metal content and the addition of P to the catalyst.

  • study on hydrodesulfurization of thiophene over mo al2o3 catalyst presulfided by Thiosulfate Ammonium
    Journal of Fuel Chemistry and Technology, 2009
    Co-Authors: G E Hui, L I Xuekuan, Jianguo Wang, Zhangfeng Qin, L U Zhanjun, Ligong Zhou
    Abstract:

    Abstract Ammonium Thiosulfate as a novel sulfiding agent was used for presulfidation of hydrodesulfurization (HDS) catalysts. The presulfided Mo/Al 2 O 3 catalysts with different molar ratios of S/Mo were prepared by impregnating Mo/Al 2 O 3 catalysts with an aqueous solution of Ammonium Thiosulfate, followed by drying. Their characteristics of crystal phases, activation, and surface compositions were examined by X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The S 2− and S 6+ in Ammonium Thiosulfate play different roles during the activation of presulfided catalysts. The S 2− sulfides Mo and S 6+ reacts with Al 2 O 3 support, decreasing the interaction of support with the active metal. The collaboration between S 2− and S 6+ ions improves the sulfidation of MoO 3 . The best HDS performance was observed for the presulfided catalyst with S/Mo = 3. Its thiophene HDS activity is 17% higher than that of Mo/Al 2 O 3 catalyst sulfided with H 2 S.

  • effect of thermal treatment under nitrogen on the Ammonium Thiosulfate presulfidized mo al2o3 catalyst
    Chinese Journal of Catalysis, 2009
    Co-Authors: G E Hui, L I Xuekuan, Zhangfeng Qin, L U Zhanjun, Weibin Fan, Jianguo Wang
    Abstract:

    Abstract A series of Mo/Al 2 O 3 catalysts were presulfidized with (NH 4 ) 2 S 2 O 3 aqueous solution, dried at ambient temperature, and thermally treated in N 2 flow. The catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry-mass spectrometry, and sulfur analysis. Thermal pretreatment in N 2 had a significant effect on the catalytic performance of the (NH 4 ) 2 S 2 O 3 -presulfidized Mo/Al 2 O 3 for the hydrodesulfurization (HDS) of thiophene. The sample pretreated at 80 °C in N 2 flow and activated at 200 °C in H 2 gave the highest thiophene conversion. This is due to that the modification of the Al 2 O 3 support by sulfate ions weakened the interaction of Mo species with the support, which increased its sulfidization to form a highly active multilayer Type II MoS 2 structure. In contrast, N 2 thermal treatment obove 200 °C led to the decomposition of (NH 4 ) 2 S 2 O 3 and decreased the sulfiding degree, which resulted in the formation of a less active single layer Type I MoS 2 structure with a low activity for thiophene HDS.

  • highly active mo al2o3 hydrodesulfurization catalyst presulfided with Ammonium Thiosulfate
    Catalysis Communications, 2008
    Co-Authors: Zhangfeng Qin, Jianguo Wang
    Abstract:

    Abstract Ammonium Thiosulfate ((NH 4 ) 2 S 2 O 3 ) was used as an ex situ sulfiding agent to pretreat Mo/Al 2 O 3 catalyst through impregnation. After H 2 activation, Mo/Al 2 O 3 presulfided with (NH 4 ) 2 S 2 O 3 exhibits much higher catalytic activity in thiophene hydrodesulfurization (HDS) than Mo/Al 2 O 3 in situ sulfided by dimethyl disulfide. Through (NH 4 ) 2 S 2 O 3 presulfidation, Al 2 O 3 support is modified by sulfate groups, leading to a decrease of interaction between Mo and support; this promotes the formation of multi-layer type II MoS 2 that contributes to the high HDS activity of the ex situ presulfided Mo/Al 2 O 3 catalyst.

  • activation and hydrodesulfurization activity of moo3 al2o3 catalyst presulfided by Ammonium Thiosulfate
    Chinese Journal of Catalysis, 2008
    Co-Authors: G E Hui, L I Xuekuan, Jianguo Wang, Zhangfeng Qin, L U Zhanjun, Ying Yang
    Abstract:

    Abstract MoO 3 / γ -Al 2 O 3 catalyst has been presulfided by Ammonium Thiosulfate. The effects of the presulfidation methods and the activation conditions on the hydrodesulfurization of thiophene were investigated. The results showed that the catalyst presulfided by Ammonium Thiosulfate (designated as Mo-ATS) exhibited higher activity than the one presulfided by dimethyldisulfide (denoted as Mo-DMDS). The former method gave a conversion of more than 99% in contrast to 92% obtained by the latter one under the same reaction conditions. The optimum temperature for the catalyst activation was in the range of 200–300 °C. An increase in the pressure was favorable for the activation and the enhancement in the HDS activity. In comparison to Mo-DMDS, the higher activity of Mo-ATS than that of Mo-DMDS was mainly attributed to the formation of an active type II MoS 2 phase as a result of suppressing the interaction of Mo with γ -Al 2 O 3 by modifying its surface with sulfate species. In addition, an increase in sulfidation degree (S 2− /Mo molar ratio) was observed after activation and supplemental sulfidation. This is also favorable for hydrodesulfurization.

G E Hui - One of the best experts on this subject based on the ideXlab platform.

  • hydrodesulfurization of thiophene over mo ac catalyst presulfided by Ammonium Thiosulfate
    Journal of Fuel Chemistry and Technology, 2015
    Co-Authors: Tengfei Wang, G E Hui, L U Zhanjun, Ye Zhang, Mingxing Tang, Ligong Zhou, L I Xuekuan
    Abstract:

    Through the impregnation of Mo/AC catalyst with an aqueous solution of Ammonium Thiosulfate (ATS), the ex-situ presulfided Mo/AC-ATS catalyst was prepared; the influence of activation temperature and time on the catalytic performance in the hydrodesulfurization (HDS) of thiophene as a probe reaction was investigated. The result indicated that under the optimized activation conditions, viz., 300°C and 0.5 h, the conversions of thiophene over the presulfided Mo/AC-ATS catalyst are 34% and 42% higher than those obtained over the Mo/AC catalysts sulfided with traditional DMDS and CS2 sulfiding agents, respectively. The XPS, TPR-MS and TEM results demonstrated that the presulfided Mo/AC-ATS has a high content of Mo4+, which may contribute to its high activity in HDS.

  • presulfidation of como and nimop catalysts by Ammonium Thiosulfate
    Chinese Journal of Catalysis, 2010
    Co-Authors: G E Hui, L I Xuekuan, Zhangfeng Qin, L U Zhanjun, Guofu Wang, Jianguo Wang
    Abstract:

    Ammonium Thiosulfate ((NH4)2S2O3) was used as a sulfiding agent for presulfiding CoMo and NiMoP catalysts. The effect of the amount of (NH4)2S2O3 on hydrodesulfurization (HDS) activity was investigated. For the CoMo series, the use of a proper amount of (NH4)2S2O3 gave a higher HDS activity than when the catalyst was sulfided by H2S. SO42- formed during presulfidation modified the Al2O3 support and decreased the interaction between the active phase and support, and the activity was enhanced. However, a smaller amount of (NH4)2S2O3 used for the presulfidation would result in insufficient sulfidation, while a larger amount of (NH4)2S2O3 increased the particle size of the active phases, and both were harmful to HDS activity. For the NiMoP series, the presulfided catalysts were less active than those sulfided by H2S. This was ascribed to the high metal content and the addition of P to the catalyst.

  • study on hydrodesulfurization of thiophene over mo al2o3 catalyst presulfided by Thiosulfate Ammonium
    Journal of Fuel Chemistry and Technology, 2009
    Co-Authors: G E Hui, L I Xuekuan, Jianguo Wang, Zhangfeng Qin, L U Zhanjun, Ligong Zhou
    Abstract:

    Abstract Ammonium Thiosulfate as a novel sulfiding agent was used for presulfidation of hydrodesulfurization (HDS) catalysts. The presulfided Mo/Al 2 O 3 catalysts with different molar ratios of S/Mo were prepared by impregnating Mo/Al 2 O 3 catalysts with an aqueous solution of Ammonium Thiosulfate, followed by drying. Their characteristics of crystal phases, activation, and surface compositions were examined by X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The S 2− and S 6+ in Ammonium Thiosulfate play different roles during the activation of presulfided catalysts. The S 2− sulfides Mo and S 6+ reacts with Al 2 O 3 support, decreasing the interaction of support with the active metal. The collaboration between S 2− and S 6+ ions improves the sulfidation of MoO 3 . The best HDS performance was observed for the presulfided catalyst with S/Mo = 3. Its thiophene HDS activity is 17% higher than that of Mo/Al 2 O 3 catalyst sulfided with H 2 S.

  • effect of thermal treatment under nitrogen on the Ammonium Thiosulfate presulfidized mo al2o3 catalyst
    Chinese Journal of Catalysis, 2009
    Co-Authors: G E Hui, L I Xuekuan, Zhangfeng Qin, L U Zhanjun, Weibin Fan, Jianguo Wang
    Abstract:

    Abstract A series of Mo/Al 2 O 3 catalysts were presulfidized with (NH 4 ) 2 S 2 O 3 aqueous solution, dried at ambient temperature, and thermally treated in N 2 flow. The catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry-mass spectrometry, and sulfur analysis. Thermal pretreatment in N 2 had a significant effect on the catalytic performance of the (NH 4 ) 2 S 2 O 3 -presulfidized Mo/Al 2 O 3 for the hydrodesulfurization (HDS) of thiophene. The sample pretreated at 80 °C in N 2 flow and activated at 200 °C in H 2 gave the highest thiophene conversion. This is due to that the modification of the Al 2 O 3 support by sulfate ions weakened the interaction of Mo species with the support, which increased its sulfidization to form a highly active multilayer Type II MoS 2 structure. In contrast, N 2 thermal treatment obove 200 °C led to the decomposition of (NH 4 ) 2 S 2 O 3 and decreased the sulfiding degree, which resulted in the formation of a less active single layer Type I MoS 2 structure with a low activity for thiophene HDS.

  • activation and hydrodesulfurization activity of moo3 al2o3 catalyst presulfided by Ammonium Thiosulfate
    Chinese Journal of Catalysis, 2008
    Co-Authors: G E Hui, L I Xuekuan, Jianguo Wang, Zhangfeng Qin, L U Zhanjun, Ying Yang
    Abstract:

    Abstract MoO 3 / γ -Al 2 O 3 catalyst has been presulfided by Ammonium Thiosulfate. The effects of the presulfidation methods and the activation conditions on the hydrodesulfurization of thiophene were investigated. The results showed that the catalyst presulfided by Ammonium Thiosulfate (designated as Mo-ATS) exhibited higher activity than the one presulfided by dimethyldisulfide (denoted as Mo-DMDS). The former method gave a conversion of more than 99% in contrast to 92% obtained by the latter one under the same reaction conditions. The optimum temperature for the catalyst activation was in the range of 200–300 °C. An increase in the pressure was favorable for the activation and the enhancement in the HDS activity. In comparison to Mo-DMDS, the higher activity of Mo-ATS than that of Mo-DMDS was mainly attributed to the formation of an active type II MoS 2 phase as a result of suppressing the interaction of Mo with γ -Al 2 O 3 by modifying its surface with sulfate species. In addition, an increase in sulfidation degree (S 2− /Mo molar ratio) was observed after activation and supplemental sulfidation. This is also favorable for hydrodesulfurization.

Sanghee Jeon - One of the best experts on this subject based on the ideXlab platform.

  • Ammonium Thiosulfate extraction of gold from printed circuit boards pcbs of end of life mobile phones and its recovery from pregnant leach solution by cementation
    Hydrometallurgy, 2020
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Yoshito Nagata, Mayumi Ito, Naoki Hiroyoshi
    Abstract:

    Abstract In this study, the Ammonium Thiosulfate leaching of gold (Au) from printed circuit boards (PCBs) of end-of-life mobile phones and the subsequent recovery of dissolved metals from pregnant leach solution via cementation were elucidated under various conditions. Over 99% of Au was extracted from crushed PCBs (D50 = 85 μm) under the following conditions: 1 M of Na2S2O3, 10 mM of CuSO4, 1 M of ammonia/Ammonium concentration, 0.1 g/10 ml of solid-to-liquid ratio, and a 24-h of leaching time in the presence of oxygen. In contrast, the recovery of Au ions via cementation was more favorable in the absence of oxygen. Among the various cementation agents evaluated, copper (Cu) was the most selective and recovered around 95% of extracted Au from the pregnant leach solution even in the presence of various coexisting metal ions. The cementation of Au exhibited two distinct kinetic regions: (1) an initially rapid rate, and (2) a more gradual and constant rate. Finally, the use of Cu plates to recover Au ions from Ammonium Thiosulfate pregnant solution of crushed PCBs is proposed, which could selectively recover about 80% of dissolved Au and is easier to handle and reuse compared with Cu powder.

  • enhanced cementation of gold via galvanic interactions using activated carbon and zero valent aluminum a novel approach to recover gold ions from Ammonium Thiosulfate medium
    Hydrometallurgy, 2020
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Mayumi Ito, Hirotaka Takahashi, Naoki Hiroyoshi
    Abstract:

    Abstract In gold (Au) hydrometallurgy, Ammonium Thiosulfate is the most attractive and promising alternative to conventional lixiviants like cyanide or the halides because it is non-toxic, less corrosive and has high selectivity for Au. However, its industrial-scale application for Au extraction is still severely limited because the recovery of dissolved Au from pregnant solutions remains challenging. The present study proposes a novel, simple and effective technique to address this difficulty using zero-valent aluminum (ZVAl) and activated carbon. Gold recovery was investigated by mixing 0.15 g of ZVAl and/or activated carbon and 10 ml of a solution containing 1 M Na2S2O3, 0.5 M NH3, 0.25 M (NH4)2SO4 and 10 mM CuSO4 with 100 mg/l of dissolved Au in a constant temperature water bath shaker at 25 °C for 24 h. Gold recovery from the Ammonium Thiosulfate solution was negligible when only ZVAl or activated carbon was added. When ZVAl and activated carbon were both present in the Ammonium Thiosulfate solution, however, over 99% of Au ions were successfully recovered. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) observations of the solid residues indicate that Au was predominantly deposited on activated carbon attached to ZVAl. Based on the rest potentials of these two materials, their synergistic effect on Au recovery could be attributed to the formation of numerous galvanic cells in solution where ZVAl acted as anodes (i.e., primary electron donor) while activated carbon acted as the cathode onto which Au ions are reduced via cementation to elemental Au.

  • a physical separation scheme to improve Ammonium Thiosulfate leaching of gold by separation of base metals in crushed mobile phones
    Minerals Engineering, 2019
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Mayumi Ito, Rongrit Pongsumrankul, Shinya Tanaka, Naho Kitajima, Ayumu Saito, Naoki Hiroyoshi
    Abstract:

    Abstract As technology advances, consumers are looking to buy new phones. This phenomenon leads to decrease in life-cycle of mobile phones (ca. 2–3 years), resulting in increase of waste mobile phones. In waste mobile phones, it contains various components including display unit, battery, cases, and printed circuit boards (PCBs). PCBs alone contain variety of materials such as gold (Au), copper (Cu), and iron (Fe) as well as aluminum (Al) with plastics, which causes difficulty in recycling. The coexistence of Cu and Al in crushed mobile phones has been recently reported to cause very low Au extraction efficiency in Ammonium Thiosulfate medium due primarily to enhanced re-deposition of extracted Au ions via galvanically induced cementation. To limit this antagonistic effect of Cu and Al coexistence on Au extraction, Au-containing components were separated from Cu- and/or Al-bearing parts using a two-step crushing approach in tandem with various physical separation techniques (i.e. jig, hybrid jig, magnetic separation, flotation, and sink-float separation) that were applied on appropriate size fractions. The results showed that over 96% of PCBs, the primary Au-containing material in mobile phones, were recovered after jig separation. These concentrated PCBs were collected and further crushed to liberate Au-containing parts and then treated by diverse physical separation techniques such as magnetic separation, jig separation, hybrid jig separation, flotation, and sink-float separation depending on the crushed particle sizes. Ammonium Thiosulfate leaching of the mixed Au-concentrated products from various physical pretreatment techniques showed that Au extraction improved by about 15-fold, indicating that the physical separation scheme proposed in this study is very promising.

  • interference of coexisting copper and aluminum on the Ammonium Thiosulfate leaching of gold from printed circuit boards of waste mobile phones
    Waste Management, 2018
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Mayumi Ito, Hirotaka Takahashi, Naoki Hiroyoshi
    Abstract:

    Ammonium Thiosulfate solution is an ideal lixiviant to extract gold (Au) from electronic wastes (E-wastes) because it is non-toxic, less corrosive, and more selective than conventional cyanide or halide solutions. It was reported recently, however, that Au leaching efficiency in Ammonium Thiosulfate medium dramatically decreased at high solid-to-liquid ratios (S/L), even though the amounts of reagents used were in excess. To understand how this occurred, leaching experiments were conducted using printed circuit boards (PCBs) from waste mobile phones, and Au distribution in the leaching residues was examined by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Significant amounts of Au were found together with copper (Cu) and aluminum (Al), implying that extracted Au ions were likely re-deposited during leaching onto Cu and Al found in PCBs via cementation (i.e., reductive deposition). A more detailed elucidation of this phenomenon by cementation experiments using pure Cu and/or Al powders indicates that these metals could only recover Au ions alone via cementation at very high amounts, however, this process became more extensive when Cu and Al powders were suspended together in solution even though the amounts of the individual metals were much lower. Electrochemical experiments (chronoamperometry) in Ammonium Thiosulfate solutions containing Au ions using an Al working electrode also showed that Au ion cementation was dramatically enhanced when Cu powder was present in solution, and the bulk of Au was cemented on Cu powder rather than on the Al electrode. These results suggest that coexistence of Cu and Al interfered with the extraction of Au in Ammonium Thiosulfate medium at high S/L because of the enhanced re-deposition of extracted Au via galvanic interaction.

  • gold recovery from shredder light fraction of e waste recycling plant by flotation Ammonium Thiosulfate leaching
    Waste Management, 2018
    Co-Authors: Sanghee Jeon, Carlito Baltazar Tabelin, Ilhwan Park, Mayumi Ito, Rongrit Pongsumrankul, Naho Kitajima, Naoki Hiroyoshi
    Abstract:

    Abstract This paper describes the recovery of gold (Au) from shredder light fraction (SLF) of a recycling plant by flotation and leaching. SLF is typically sent to landfills as waste, but it still contains substantial amounts of Au, and other metals like Cu and Fe. The SLF sample used in this study contains 0.003% of Au, 12% of Cu, and 10% of Fe. Flotation results showed that over 99% of Au and 50% of combustibles were recovered in froth while most of the base metals were recovered in tailing. SEM-EDX of froth products indicates that Au floated via two mechanisms: (1) flotation of Au-plated plastic particles, and (2) agglomeration of fine Au particles together with plastic particles due to kerosene-induced hydrophobic-hydrophobic interactions followed by the flotation of these agglomerated particles. Combustibles in froth/tailing were analyzed by ATR-FTIR, and the results showed that plastics in the froth were mostly sulfonated polystyrene (PS) and acrylonitrile butadiene styrene (ABS) while those in tailing were polyurethane (PU) and polyethylene terephthalate (PET). Contact angle measurements of plastic particles suggest that PS and ABS are more hydrophobic than PU and PET. Most of the base metals in the tailing had either bent or twisted shapes because they were mostly made up of wires. In flotation, these large and heavy particles are unaffected by bubbles and simply sink. Leaching results using Ammonium Thiosulfate solutions showed that Au extraction increased from 33 to 51% after flotation.