Rate Of Thiosulfate Oxidation Research Articles

English

Biological desulfurization is a novel technology for the removal of hydrogen sulfide from some biogas or sour gas, in which there are always a certain amounts of carbon disulfide together with much hydrogen sulfide. Nowadays, carbon disulfide is found to have negative effect on the biological desulfurization, but seldom research is afforded to investigate how carbon disulfide inhibits the process of biological desulfurization. In this paper, we investigated the effect of carbon disulfide both on the growth of Thiobacillus thioparus and the resting cells under various concentrations, including 0.01, 0.05, 0.10, 0.15 and 0.20%. In this process, the rate of the cell growth was characterized by the rate of nitrogen consumption in order to solve the problem that the adsorption of cells to sulfur granules have on the accuracy of biomass test. Under the cell density of 23.92 mg N/L, which is lower than the maximum of cell density 36.13 mg N/L, the average rate of thiosulfate oxidation reached the maximum (26.50 S 2 O 3 2- mg/L-h). Carbon disulfide at titers of 0.01% significantly inhibited the growth of cells, but hardly affected the biological desulfurization of resting cells. Although carbon disulfide at titers of 0.05% had negative effect on the biological desulfurization of resting cells, the effect of inhibition could be relieved by the increased density of resting cells. For the resting cells, the parameters of Michaelis-Menten equation were calculated by the method of Lineweaver-Burk. The V max of biological desulfurization was decreased from 27.93 to 14.0 S 2 O 3 2- mg/L-h, and the K m was increased from 0.264 to 0.884 mM, with the concentration of carbon disulfide rising up from 0.0 to 0.1%. These results show that the growth of cells was sensitive to carbon disulfide, and the resting cells had resistance to the low level of carbon disulfide (0.05%). Thus, the inhibition of carbon disulfide to biological desulfurization should be attributed to T. thioparus growth suppression function. Keywords: Carbon disulfide, bio-desulfurization, inhibition, Thiobacillus thioparus , resting cell, gases purification African Journal of Biotechnology , Vol 13(16), 1739-1744

Effect of thiourea on the rate of anodic processes at gold and graphite electrodes in thiosulfate solutions

Dependencies of the anode current on the potential were measured by means of voltammetry on the fresh surface of gold and graphite electrodes in the solutions of 0.01M sodium thiosulfate with the addition of thiourea (1×10−5–1×10−3M). Using EQCM measurements, we studied the partial currents of gold dissolution in the indicated solutions. The results give us ground to state that small amounts of thiourea (Tu) added cause a substantial increase both in the rate of thiosulfate oxidation and in the rate of gold dissolution. On graphite, the addition of Tu causes a decrease in the electrode polarization and is likely to lead to the change of the mechanism of the electrode reaction of thiosulfate oxidation. On the gold electrode, the addition of Tu has a multivariable effect on the anode process in thiosulfate solutions. On one hand, Tu functions as a depassivating agent with respect to the reaction of thiosulfate oxidation. On the other hand, it acts as an accelerating agent for the reaction of gold dissolution. After the addition of a small amount of Tu, the rate of gold dissolution becomes comparable with the rate of thiosulfate oxidation. Results show that no indices of gold passivation by polysulfides are observed with the solutions with Tu addition. At the same time, gold depassivation by Tu additive is seems not to be the reason of an increase in the rate of gold dissolution.

The Role of Malate Dehydrogenase Isoforms in the Regulation of Anabolic and Catabolic Processes in the Colorless Sulfur Bacterium Beggiatoa leptomitiformis D-402

The functional role of tetrameric and dimeric isoforms of malate dehydrogenase in the carbon metabolism of the colorless sulfur bacterium Beggiatoa leptomitiformis, strain D-402, was studied. This strain can grow both lithotrophically and organotrophically. By using the inhibition analysis, the tetrameric isoenzyme was shown to operate in the glyoxylate cycle and the dimeric one was found to be involved in the TCA cycle. The dynamics of the dimeric isoenzyme conversion to the tetrameric isoform was found to be determined by the rate of thiosulfate oxidation. The regulation of the carbon metabolism in Beggiatoa leptomitiformis is supposed to be accomplished by means of structural and functional changes in the protein molecule of malate dehydrogenase.

Copper catalysed oxidation of thiosulfate by oxygen in gold leach solutions

The environmental and public concern over the continued use of cyanide in the recovery of gold has grown in recent times due to a number of recently publicised environmental incidents. Of the alternative lixiviants, thiosulfate appears to be the most promising, though the considerable amount of research conducted on thiosulfate leaching of gold over the last three decades has not resulted in its commercial introduction. Perhaps the largest contributing factor to this is the poor understanding of the thiosulfate leach solution chemistry, especially the oxidation of thiosulfate in the presence of copper(II) and oxygen. It has been shown in this research that the oxidation of thiosulfate in the presence of copper(II) and oxygen is very complex with the rates of copper(II) reduction and thiosulfate oxidation being significantly faster in the presence of oxygen. The higher initial rate of copper(II) reduction indicated that oxygen increases the rate of copper(II) reduction to copper(I) by thiosulfate, though the mechanism for this remains unclear. The rates of thiosulfate oxidation and copper(II) reduction were also shown to be affected differently by the presence of anions. This is consistent with thiosulfate oxidation occurring via two mechanisms, with one of these mechanisms involving the oxidation of thiosulfate by copper(II) and the other involving the oxidation of thiosulfate by the intermediate superoxide and hydroxide radicals formed as a result of copper(I) oxidation by oxygen. The effect of various parameters on the rate of thiosulfate oxidation and the copper(II) concentration are also shown.

Thiosulfate oxidation by three soils as influenced by temperature

Ammonium thiosulfate (ATS) is a popular liquid fertilizer in North America, and potassium thiosulfate (KTS) is also gaining acceptance for specialty purposes. Thiosulfate is known to oxidize rapidly in soil to tetrathionate and then to sulfate, but little information is available on the effect of temperature on these reactions. The objective of this study was to compare the rates of thiosulfate oxidation at three temperatures (5, 15, 25°C) by three soils, an Enon loamy sand from North Carolina (soil NC), an O'Neill loamy sand from Nebraska (soil NE), and a Vang loam from North Dakota (soil ND). Ammonium thiosulfate, or KTS were added at a rate of 25 mg S kg−1. At 25°C, oxidation was very rapid, being complete after 1 or 2 weeks by all three soils. No apparent immobilization of the applied S was observed with any soil after 2 weeks of incubation. At 15°C, oxidation was slowed, but oxidation was still nearly complete after 2 or 3 weeks. There was some apparent S immobilization by soil NE, and to a lesser degree by soil ND at this temperature. At 5°C, the kinetics of oxidation and immobilization differed greatly between soils. With soil NC, oxidation was complete after 4 weeks, with no apparent immobilization. Soil NE exhibited a strong immobilization of the added S at 5°C, with most of the applied S remaining immobilized for 12 weeks. Soil ND was intermediate between these two soils, showing a temporary immobilization of applied thiosulfate for 2–6 weeks, with apparent mineralization from 6–12 weeks. The effect of temperature on immobilization of S fertilizers deserves further research.

Factors Affecting Oxidation of Thiosalts by Thiobacilli

The effects of temperature, initial pH, and the concentrations of ammonium, phosphate, and heavy metals on the oxidation of thiosalts by an authentic strain of Thiobacillus thiooxidans (ATCC 8085) and by a mixed culture isolated from a base metal-processing mill effluent pond were studied. The optimum temperature was 30 degrees C and the optimum initial pH was 3.75 for both cultures using thiosulfate and for the mixed culture using tetrathionate. T. thiooxidans ATCC 8085 did not oxidize tetrathionate. For a thiosalt concentration of 2,000 ppm (2,000 mg/liter), maximal rates of destruction occurred at concentrations of ammonium ion above 2 mg/liter and in the presence of 1 mg of phosphate per liter. Under optimal conditions, the rate of thiosulfate oxidation by the pure culture was 55 +/- 3 mg/liter per h; the mixed culture oxidized thiosulfate at the rate of 40 +/- 1 mg/liter per h and tetrathionate at the rate of 50 +/- 2 mg/liter per h. Metal ions caused normal inhibition kinetics in the oxidation of thiosulfate by T. thiooxidans ATCC 8085. K(i) values were calculated for cadmium (16 mg/liter), copper (0.46 mg/liter), lead (2 mg/liter), silver (3.1 mg/liter), and zinc (33 mg/liter). Only a slight additive effect was apparent in the presence of all of these metal ions. The mixed culture of thiosalt-oxidizing bacteria was less sensitive to heavy metal inhibition; the order of inhibition of thiosulfate oxidation was Cd < Zn < Pb < Ag < Cu, and that of tetrathionate oxidation was Zn < Cd < Pb < Ag < Cu.

Comparison of the kinetics of thiosulfate oxidation by three iron-sulfur oxidizers.

The sulfur metabolism of Thiobacillus ferrooxidans, Ferrobacillus ferrooxidans, and Ferrobacillus sulfooxidans was found to differ in the rate of utilization of thiosulfate and tetrathionate, with tetrathionate showing the most significant difference between the three organisms. The apparent Km values of the three organisms ranged from 2–5 × 10−2 M for T. ferrooxidans and F. sulfooxidans to 5–7 × 10−3 M for F. ferrooxidans. Increasing the temperature caused a greater effect on thiosulfate oxidation by F. ferrooxidans than with the other two as shown by the apparent Ea values (Ea′ for F. ferrooxidans, 18 000; F. sulfooxidans, 11 400; T. ferrooxidans, 11 000).The initial pH of the medium determined the rate of thiosulfate oxidation. If the initial pH was 4.0–4.5, a sharp break in oxygen uptake was shown by T. ferrooxidans and F. sulfooxidans after 20–30 min, but not with F. ferrooxidans.When the disappearance of thiosulfate and tetrathionate from the medium was used as an indicator of the affinity of the three test organisms for the sulfur compounds, F. ferrooxidans demonstrated the highest net loss of both compounds from the medium.