For the recovery of nuclear materials from the spent nuclear fuel by the sulfide process, fission products such as rare-earths are selectively sulfurized by CS2 at temperatures below 500 °C. However, sulfurization at lower temperatures would be favorable from the safety handling of CS2. In this paper, low temperature sulfurization of neodymiumu oxide Nd2O3 by mechanochemical method in the presence of CS2 was studied. When Nd2O3 powder was milled with CS2 by planetary mill in argon atmosphere followed by heatreatment in Ar, the broaden peaks for Nd2O2S phase were found by XRD analysis. These peaks for Nd2O2S became sharpened by the heat treatment at temperatures 500 — 600 °C in argon atmosphere. The relative intensity ratio of Nd2O2S peaks to Nd2O3 peaks increased with increasing milling time as well as the increasing CS2 amount . Finally, the experimental results were in good agreement with those of thermodynamic consideration.
The formation behavior of gadolinium and holmium sesquisulfides was examined by studying the sulfurization of their inorganic and organic salts such as nitrate, carbonates, oxalates, acetates and octanoate by carbon disulfide (CS2) gas. In previous studies, α-Gd2S3, which is low temperature phase, was produced by the sulfurization of the oxide at 1023 K. In the present study, single phase γ-Gd2S3, which is stable at relatively high temperature, was formed by the sulfurization of octanoate at 1073 K and oxalate at 873 K. It has also been found that gadolinium salts are thermally decomposed at temperatures higher than 500 K. The thermal decomposition leads to the formation of a gadolinium oxide via an oxycarbonate. In the case of holmium sesquisulfides, the sulfurization of holmium oxide and nitrate provide the mixture of δ-Ho2S3 and Ho2O2S impurity, while pure γ-Ho2S3 is exclusively formed from oxalates, acetates, or carbonates. These results reveal that the formation of oxycarbonate such as Gd2O2CO3 and Ho2O2CO3 play an important role in the formation of γ-phase. After sulfurization, the synthetic powder of γ-Ho2S3 was consolidated by pulse electric current sintering to investigate its high-temperature stability. Holmium sesquisulfide transformed from the γ-phase to the δ-phase at sintering temperatures above 1073 K while δ-phase was stable even at a high sintering temperature of 1773 K.
The purpose of this work is to present processing and function of the sulfide phosphor. Phosphors of rock salt structure such as SrS and CaS and alkaline earth thiogallates with the formula MIIGa2S4, where MII=Ca, Sr and Ba have been investigated for full-color inorganic thin film electroluminescence. More recently sulfide phosphors were used as phosphors in phosphor converted light emitting diodes for solid state lighting. Various Eu2+ doped phosphors were prepared by solid state reactions between alkaline earth carbonates and gallium oxides mixed in stoichiometric compositions. Phosphors were treated at 900°C for 5h under a H2S stream, then doped with Eu2+ luminescent center and retreated at 1100°C under similar conditions. The emission spectra of YAG:Ce3+, SrGa2S4:Eu2+ and CaS:Eu2+ are presented as a function of the temperature from 20°C to 100°C. The emission intensities of phosphors slightly decreased with increasing temperature.
Hydrogen gas can be effectively synthesized from the electrochemical and/or photochemical decomposition process of H2S because of its low electrochemical potential. However, decomposition rate was gradually decreased with increasing the amount of poly sulfide ion, such as S22-, which simultaneously synthesized as the by-product during the reaction. Thus, poly sulfide ion should be removed from the solution, nevertheless it could not be removed from the solution by without loss of basic solution and/or dissipation of metal ion. In this study, the idea based on the interaction between fullerenes and sulfur was introduced into the development of collection method for poly sulfide ions from basic solution. Fullerenes was dissolved into toluene, and mixed with aqueous solution contained S22- ion. After 6 hours agitation, the color of the aqueous phase was changed from yellow to transparent in the case of fullerene/toluene solution treatment. Additionally, during every treatment, elemental sulfur was produced in the aqueous phase, and fullerene-sulfur compounds, such as C60S16 and C70S16, were formed in the toluene phase after 4th treatment. Thus, extracting and separating of poly sulfide ion from aqueous solution was succeeded.
Photocatalytic decomposition of hydrogen sulfide (H2S) into hydrogen (H2) by using the stratified type photocatalyst is considered as efficient route for the conversion of natural energy (solar energy) into clean energy (H2) . This reaction obeyed to next formula; 2HS-→2H+ + S22- + 2e-→H2↑+ S22-. To construct the continuous system, effective conversion route from S22-ion into H2S gas should be developed. In other word, sulfur cycle system should be constructed. In this report, conversion route from sulfur compounds (elemental sulfur and Na2SO4) into H2S by utilizing biological reaction was studied. H2S gas was stably synthesized until c.a.5% in the case of elemental sulfur addition, while it was c.a. 2% in the case of Na2SO4. Rate of biological reaction was seriously decreased if concentration of H2S was over these values because of its toxicity. Conversion efficiency was higher in the case of elemental sulfur addition since impediment of sodium ion was not progressed.
This paper describes hydrogen sulfide generation, isolation and characterization of sulfate-reducing bacteria in the activated sludge obtained from wastewater treatment plant. The sludge, collected from aerobic treatment system, was used as inoculums for hydrogen sulfide generation and for isolation of sulfate-reducing bacteria. Hydrogen sulfide was generated when the sludge was inoculated into a pH controlled medium. Two strains G2 and G3 of sulfate-reducing bacteria were isolated from the sludge. The characteristics and identification of these isolates was based on culture of the experiments and molecular analysis. Reduced sulfate rates in G2 and G3 is 0.39 and 0.41 mmol/dm3 respectively. Two isolates located in the genus Desulfovibrio in the phylogenetic tree based. First one was 16S rRNA gene analysis with the highest homology, 96.6 %, as Desulfovibrio carbinoliphilus (DSM 17524T) . However, the branch of the isolates was separated from the relatives and no strain was recognized in this branch. Also the dsr gene of isolate G3 had the highest homology with Desulfovibrio fructosovorans (DSM 3604T) , 92.7 %. The isolates G2 and G3 belonged to the genus Desulfovibrio as confirmed by the results of these analyses, however, these isolates oxidized organic compounds to carbon dioxide completely although relative strain oxidized it completely. Therefore, these isolates have high possibility that they should be recognized as a new strain.