Direct reduction of lead sulfide with carbon and lime; Effect of catalysts:Part i. experimental

Rao, Y. K.; El-Rahaiby, S. K.

doi:10.1007/bf02654845

Cited by 12 publications

(13 citation statements)

References 24 publications

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“…Bars with different letters were significantly different in comparison with control or Cd stressed alone samples at P \ 0.05 according to Duncan's multiple range test c Cd could be derived from the chelation or direct reaction of Cd by NaHS. As expected (Wilson et al 1978;Rao and El-Rahaiby 1985), we also observed yellow crystals of CdS formed after the addition of the increasing concentrations of NaHS ? CdCl 2 (Online Resource, Fig.…”

Section: Nahs and Snp Alleviated Cd-induced Lipid Peroxidationsupporting

confidence: 86%

Roles of hydrogen sulfide and nitric oxide in the alleviation of cadmium-induced oxidative damage in alfalfa seedling roots

2012

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Despite hydrogen sulfide (H(2)S) and nitric oxide (NO) are important endogenous signals or bioregulators involved in many vital aspects of plant growth and responses against abiotic stresses, little information was known about their interaction. In the present study, we evaluated the effects of H(2)S and NO on alfalfa (Medicago sativa L.) plants exposed to cadmium (Cd) stress. Pretreatment with an H(2)S donor sodium hydrosulfide (NaHS) and well-known NO donor sodium nitroprusside (SNP) decreased the Cd toxicity. This conclusion was supported by the decreases of lipid peroxidation as well as the amelioration of seedling growth inhibition and Cd accumulation, in comparison with the Cd-stressed alone plants. Total activities and corresponding transcripts of antioxidant enzymes, including superoxide dismutase, peroxidase and ascorbate peroxidase were modulated differentially, thus leading to the alleviation of oxidative damage. Effects of H(2)S above were reversed by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO), the specific scavenger of NO. By using laser confocal scanning microscope combined with Greiss reagent method, further results showed that NO production increased significantly after the NaHS pretreatment regardless of whether Cd was applied or not, all of which were obviously inhibited by cPTIO. These decreases of NO production were consistent with the exaggerated syndromes associated with Cd toxicity. Together, above results suggested that NO was involved in the NaHS-induced alleviation of Cd toxicity in alfalfa seedlings, and also indicated that there exists a cross-talk between H(2)S and NO responsible for the increased abiotic stress tolerance.

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Section: Nahs and Snp Alleviated Cd-induced Lipid Peroxidationsupporting

confidence: 86%

Roles of hydrogen sulfide and nitric oxide in the alleviation of cadmium-induced oxidative damage in alfalfa seedling roots

2012

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“…[12,13,14] Consequently, it is conceivable that mixtures of MoS 2 -C can react at high temperatures forming gaseous species such as CS 2 and CS in equilibrium with condensed phases. In the temperature range of interest, 700 ЊC to 1400 ЊC, the stable molybdenum solid phases that can be found are MoS 2 , Mo 2 S 3 , Mo, MoC, and Mo 2 C. [15,16] Therefore, the direct reduction of molybdenite by carbon will be governed by the prevailing chemical equilibrium between these phases and the reaction kinetics.…”

Section: Mos 2 -C Systemmentioning

confidence: 99%

Reduction of molybdenite with carbon in the presence of lime

Padilla

Ruiz

Sohn

1997

Metall Mater Trans B

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The thermodynamics of the MoS 2 -C-CaO system has been studied in order to understand the carbothermic reduction of molybdenite in the presence of CaO. Kinetic studies were also conducted with mixtures of MoS 2 ϩ C ϩ CaO in the temperature range of 900 ЊC 1200 ЊC. The reduction of MoS 2 with carbon in the presence of lime proceeds through the direct oxidation of MoS 2 by CaO to form intermediate molybdenum oxidized species, MoO 2 and CaMoO 4 , which subsequently undergo reduction by CO to yield mixtures of Mo, Mo 2 C, and CaS. Complete conversion of MoS 2 can be obtained at 1200 ЊC in less than 20 minutes for molar concentrations of MoS 2 :C:CaO ϭ 1:2:2. The kinetic model ln (1 Ϫ X) ϭ kt was used to determine the rate constants. The activation energy found for the temperature range studied was 218.8 kJ/mol.

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“…To facilitate the interpretation of the experimental data, a mechanistic model was formulated (Rao and El-Rahaiby, 1984), only the barest details of which are given here. The model assumes that the mechanism of reduction consists of a sequence of heterogeneous reaction steps as follows:…”

Section: Discussionmentioning

confidence: 99%

“…With the He-rich He-NZ atmosphere, the reduction kinetics of catalyzed mixtures were determined at eight different temperatures. The investigation with pure Nz atmosphere was even more extensive; but only a limited portion of latter study will be considered here since a more detailed version is available elsewhere (Rao and El-Rahaiby, 1984). …”

Section: Methodsmentioning

confidence: 99%

Catalysis and synergism in the reduction smelting of lead sulfide with carbon and lime

Rao

El-Rahaiby

1985

AIChE Journal

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The catalyzed direct reduction of lead sulfide with carbon and lime was investigated at several temperatures and under two different inert gas atmospheres. The catalyzed reduction kinetics were determined both with a nitrogen atmosphere and a helium-rich helium-nitrogen atmosphere. The reduction kinetics under the latter were decidedly superior to those under the former. The differences were interpreted in terms of faster diffusion rates in a helium medium and synergistic effects. The catalyst used was a ternay eutectic mixture (K, Li, NahC03, which amounted to 2.5 wt. SCOPEThe effect of ambient atmosphere and the influence of temperature on the reduction smelting of lead sulfide with carbon and lime have been investigated in the temperature range 1,061 to 1,262 K. The experimental data are analyzed by means of a physicochemical model that envisions the Boudouard reaction (C + Cog -+ 2CO) as the rate-controlling step for the overall reduction process. The intrinsic rate constant values were derived by the application of the model. The rate constant values for reduction under helium-rich helium-nitrogen atmospheres are systematically higher than those for reduction under nitrogen atmospheres. These differences were reconciled in terms of synergistc effects arising from the presence of the catalyst. CONCLUSIONS AND SIGNIFICANCEThe addition of the ternary eutectic catalyst (K, Li, NahCOs proved to be quite effective in promoting the reduction rates in the PbS:4CaO:4C mixtures in the temperature range 1,061 to 1,262 K. The catalyst was added in modest amounts, i.e., 2.5 wt. %, and is known to exist in a molten state at all the temperatures investigated. The extent of catalysis was found to be significantly influenced by the nature of the inert ambient atmosphere used. The reaction mechanism consisted of reduction, carbon gasification, and PbS vaporization steps with the middle step constituting the rate-limiting phenomenon. The intrinsic rate constant values for carbon gasification were obtained for two different atmospheres: log 11 = 5.300 -8,480 T-' for heliumrich helium-nitrogen atmospheres and log 11 = 3.981 -7,790 T-' for nitrogen atmospheres. The catalyst addition in conjunction with the ambient atmosphere, eyen.though the latter is inert, produces a synergistic effect; that is, the catalyst is more effective in a helium-rich helium-nitrogen atmosphere as compared to a nitrogen atmosphere. This synergistic effect, expressed as a ratio of the intrinsic rate constants, has a value of 4.7 at 8OO0C, which rises to 6.0 at l,OOO°C.

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Direct reduction of lead sulfide with carbon and lime; Effect of catalysts:Part i. experimental

Cited by 12 publications

References 24 publications

Roles of hydrogen sulfide and nitric oxide in the alleviation of cadmium-induced oxidative damage in alfalfa seedling roots

Roles of hydrogen sulfide and nitric oxide in the alleviation of cadmium-induced oxidative damage in alfalfa seedling roots

Reduction of molybdenite with carbon in the presence of lime

Catalysis and synergism in the reduction smelting of lead sulfide with carbon and lime

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