Effect Of Thiosulphate Research Articles

Thiosulphate leaching of silver from an arsenical refractory ore

Thiosulphate leaching has received particular attention in recent years as an environmentally benign alternative to cyanide leaching. In this study, thiosulphate leaching combined with ultra-fine grinding (UFG) was studied for silver extraction from an arsenical refractory ore. Direct cyanidation of the ore (d80: 50 µm) led to a low silver extraction of ≤ 70% over 24 h. leaching period. Extraction of silver in cyanide leaching was improved to 85% after ultra-fine grinding. In comparison, up to 98% of silver extraction was achieved in thiosulphate leaching system after ultra-fine grinding of the ore down to 5 μm (d80) in a stirred mill. Furthermore, thiosulphate leaching is more selective than cyanide leaching with only negligible leaching of arsenic, antimony and other metals observed in this study. This is of particular importance considering the environmental concern for the presence of arsenic in cyanide leaching solutions and effluents. Effects of thiosulphate (0.2–0.6 M Na2S2O3), ammonia (0.04–0.52 M NH3) and copper (0.02–0.11 M CuSO4) on the extraction of silver were investigated using a Box-Behnken design. Statistical analysis of the experimental data (%Ag extraction at 8 h.) confirmed that all the parameters have quadratic effects in that the extraction of silver tends to improve with increasing their concentration up to a critical level above which a reverse trend occurs. The addition of a small amount (0.1 M EDTA, 50 mg/L CMC) of ethylenediaminetetraacetic acid (EDTA) and carboxymethyl cellulose (CMC) improved (by ∼20–30%) silver extraction and reduced thiosulphate consumption by ∼20%. Using nickel sulphate in place of CuSO4 also improved silver extraction with concurrent decrease in thiosulphate consumption. Recovery of silver from real pregnant leach solutions using sodium borohydride (NaBH4) as the precipitating agent was also investigated in detail. A high silver recovery of ≥98% was achieved under suitable conditions. These findings highlight that ammoniacal thiosulphate leaching in combination with ultra-fine grinding can be used as a suitable and environmentally sound alternative to cyanide leaching and the additives such as EDTA and CMC, and nickel in place of copper can improve the extraction of silver from refractory silver ores.

The Effect of Thiosulphate on Arsenic Bioavailability in a Multi Contaminated Soil. A Novel Contribution to Phytoextraction

In this study it was evaluated on a laboratory scale (microcosm), the possibility of using ammonium thiosulphate in assisted phytoextraction for the simultaneous removal of mercury and arsenic from multi- contaminated industrial soil. The species selected were Brassica juncea and Lupinus albus the addition of thiosulfate to the soil greatly promoted the uptake and translocation of both contaminants in the aerial parts of the plants. Mercury concentration in the aerial parts reached in B. juncea 120 mg/kg approximately 40 times the value of the control). The concentration of arsenic also increased significantly in the shoots of B. juncea (14.3 mg/kg), where the value in the control was negligible. Similar trends were obtained for L. albus The results confirmed the known positive effects of thiosulphate in increasing mercury bioavailability for plants, moreover they showed the ability of thiosulphate to mobilize arsenic and significantly to promote its uptake by plants. The increase of arsenic bioavailability, promoted by thiosulfate addition, could be attributed to the competition between arsenate and sulphate ions for the same active sites in the soil surfaces, with the release of arsenic in the soil solution. The use of thiosulfate appears to have great potential since it is a common fertilizer used to promote plant growth and is able to increase the uptake by plants of mercury and arsenic. The simultaneous increase of both contaminants uptake by plants, using a single additive, will provide new insights into the phytoextraction technology in terms of cost and time reduction.

The Electrochemistry of the Leaching Reactions in the Caron Process. I. Anodic Processes

The Caron process involves the oxidative dissolution of pre-reduced iron alloys containing nickel, cobalt and copper in ammoniacal carbonate solutions. This study has demonstrated that passivation is exhibited by nickel and cobalt at higher potentials than previously established for iron. It is shown that alloys of iron with nickel and cobalt also undergo passivation at low potentials resulting in inhibition of the dissolution of the valuable metals. The potential regions of active dissolution of each of these metals in ammonia-ammonium carbonate solutions have been established. The effect of thiosulphate and cobaltammine complex ions on the dissolution of iron and nickel was found to be significant in that thiosulphate appears to partially prevent the passivation of nickel while the presence of cobaltammine ions leads to lower apparent anodic current densities. Possible mechanisms for the passivation processes and for the effects of thiosulfate and cobaltammines on the dissolution are presented.

A Simple Method for Investigations on the Chemotaxis of A. ferrooxidans and D. vulgaris

Acidithiobacillus ferrooxidans R 1 and Desulfovibrio vulgaris NCIMB 8457 were taken as test strains in a study for the development of a chemotaxis test using a modified capillary assay. 2.0-μl glass capillaries were filled with 1.6 μl of a solution containing chemotactic substances under vacuum. Thereby a better load of the capillaries with the chemotactic substances was ensured. This enabled a highly precise, direct microscopic enumeration of cells using a Thoma chamber.Attractants were characterised by a migration of cells into glass capillaries filled with chemotactic substances and consequently high cell numbers therein. Compared to a control, a low cell number in the glass capillaries indicated that the test substance was a repellent. A. ferrooxidans was attracted by Fe2+ ions and tetrathionate. The effect was dependent on the concentration: at a concentration of 100.0 mM Fe2+, 6.0 × 103 cells/capillary were enumerated, at a concentration of 1.0 mM Fe2+ , only 103 cells/capillary were counted. The effect of tetrathionate was not as significant as that of Fe2+ ions: at concentrations of 1.0 and 10.0 mM tetrathionate, 1.0 × 103 cells per capillary and at a concentration of 100.0 mM tetrathionate, 2.0 × 103 cells/capillary were determined. After the application of 0.1, 1.0 and 10 mM aspartate, low cell numbers in the glass capillaries were found. Consequently, aspartate acted as a repellent. Cells of D. vulgaris were attracted by lactate and thiosulphate. At a concentration of 10.0 mM lactate, the highest amount of bacterial cells (1.6 × 105 cells/capillary) was measurable. Between 8.0 × 104 and 1.0 × 105 cells/capillary were determined at concentrations of 100.0, 1.0, 0.1 and 0.01 mM lactate. The effect of thiosulphate was not as significant as the effect of lactate: at a concentration of 10.0 mM thiosulphate, 5.0 × 104 cells/capillary, at a concentration of 1.0 mM thiosulphate, 3.0 × 104 cells/capillary and at a concentration of 0.1 mM thiosulphate, 2.0 × 104 cells/capillary were determined. Finally, the effect of the highly toxic biocide tributyltin chloride was tested. The cell numbers of D. vulgaris were not affected by concentrations of 0.01 and 0.1% tributyltin chloride compared to the control assay (4.1 × 104 and 3.8 × 104 cells/capillary). This result is important for the application of tributyltin chloride compounds. Consequently, the use of the modified capillary assay enabled fast tests and yielded reproducible results for measurements of chemotactic activities of Acidithiobacillus ferrooxidans and Desulfovibrio vulgaris. Dependent on the concentration, the impact of biocides or inhibitory substances on the main bacteria involved in bioleaching and corrosion processes could be detected as a matter of routine.

Effect of thiosulphate as electron acceptor on glucose and xylose oxidation by Thermoanaerobacter finnii and a Thermoanaerobacter sp. isolated from oil field water

During glucose and xylose fermentation, Thermoanaerobacter finnii was observed to produce lactate, acetate, H 2 and CO 2, with ethanol being the major end product. Thermoanaerobacter strain SEBR 5268, an isolate from an oil field, also produced a similar range of end product from glucose and xylose fermentation, with the exception that both ethanol and lactate were the major products of sugar metabolism. Both these strains were able to reduce thiosulphate to sulphide in the presence of these two substrates, with acetate being the dominant metabolite in that case. In addition, a faster growth rate and increased cell yield were obtained in the presence of thiosulphate, than in its absence. The higher concentrations of acetate produced in the presence of thiosulphate rather than without any electron acceptor indicated that more ATP was generated from substrate-level phosphorylation. These results have implications for our understanding of the breakdown of carbohydrates present in organic matter found in the natural ecological niches of Thermoanaerobacter species (sulphide-, elemental sulphur- or sulphate-rich thermal hot springs and oil fields).

The effect of thiosulphate and other inhibitors of autotrophic nitrification on heterotrophic nitrifiers

It has been found that heterotrophic nitrification by Thiosphaera pantotropha can be inhibited by thiosulphate in batch and chemostat cultures. Allythiourea and nitrapyrin, both classically considered to be specific inhibitors of autotrophic nitrification, inhibited nitrification by Tsa. pantotropha in short-term experiments with resting cell suspensions. Hydroxylamine inhibited ammonia oxidation in chemostat cultures, but was itself fully oxidized. Thus the total nitrification rate for the culture remained the same. Heterotrophic nitrification by another organism, a strain of "Pseudomonas denitrificans" has also been shown to be inhibited by thiosulphate in short term experiments and in the chemostat. During these experiments it became evident that this strain is able to grow mixotrophically (with acetate) and autotrophically in a chemostat with thiosulphate as the energy source.

Nitrification and sulphur oxidation by Aspergillus flavus growing in medium containing reduced nitrogen and sulphur

Aspergillus flavus oxidized elemental sulphur in vitro to thiosulphate, tetrathionate and sulphate, and mineralized peptone oxidizing the liberated ammonium to nitrite and nitrate. When elemental sulphur was added to peptone-containing medium the fungus oxidized sulphur but its ability to nitrify was inhibited. Such inhibition could have resulted from the reduction in medium pH following S-oxidation. Nitrification was still inhibited however, when S-oxidation occurred in medium buffered to pH 7.0, which suggests that pH was not the only factor inhibiting nitrification. Thiosulphate inhibited nitrification by A. flavus at concentrations similar to that produced by the fungus when oxidizing sulphur. Higher rates of nitrification by A. flavus occurred in medium containing ammonium sulphate and acetate, and in this medium thiosulphate (100 μg ml−1) prevented nitrification by A. flavus for one week, and reduced the rate of nitrification after three weeks. A. flavus appears to be incapable of simultaneously nitrifying and oxidizing sulphur due to the inhibitory effect of thiosulphate.

The immunopotentiating effect of thiosulphate in vivo.

Sodium thiosulphate injected i.v. into mice causes a marked increase in concentration of several serum proteins, particularly immunoglobulins. When given together with antigen, it significantly potentiates the T-dependent humoral responses.

COBALT COMPOUNDS AS ANTIDOTES FOR HYDROCYANIC ACID.

The antidotal potency of a cobalt salt (acetate), of dicobalt edetate, of hydroxocobalamin and of cobinamide against hydrocyanic acid was examined mainly on mice and rabbits. All the compounds were active antidotes for up to twice the LD50; under some conditions for larger doses. The most successful was cobalt acetate for rabbits (5xLD50), which was effective at a molar cyanide/cobalt (CN/Co) ratio of 5, but had as a side-effect intense purgation. Hydroxocobalamin was irregular in action, but on the whole was most effective for mice (4.5xLD50 at a molar ratio of 1), and had no apparent side effects. Dicobalt edetate, at molar ratios of up to 2, was more effective for rabbits (3xLD50) than for mice (2xLD50), but had fewer side effects than cobalt acetate. The effect of thiosulphate was to augment the efficacy of dicobalt edetate and, in mice, that of hydroxocobalamin; but, apparently, in rabbits, to reduce that of hydroxocobalamin. Cobinamide, at a molar ratio of 1, was slightly more effective than hydroxocobalamin on rabbits and also less irregular in its action. Cobalt acetate by mouth was effective against orally administered hydrocyanic acid. The oxygen uptake of the body, reduced by cyanide, is rapidly reinstated when one of the cobalt antidotes has been successfully administered.

The effects of thiosulphate and oxygen concentration on tetrathionate oxidation by Thiobacillus X and T. thioparus.

The effects of thiosulphate and oxygen concentration on tetrathionate oxidation by Thiobacillus X and T. thioparus.

Chromatographic studies on sulphur compounds : Part IV. The decomposition of acidified thiosulphate and polythionate solutions

Since many of the reactions involving thionic acids occur in acid media, it was felt that a qualitative study of the stability of these substance in various concentrations of hydrochloric acid was desirable. One of the main reactions in acid media is said to be: The effect of thiosulphate and formaldehyde (which removes bisulphite) was therefore observed. Results obtained agreed with the above equation and also showed that as the number of sulphur atoms in the thionates increases, the concentration of acid in which the thionate is stable increases. Experiments conducted to ascertain the primary thionate produced in the decompsition of acidified thiosulphate solution are described, this being trithionate; a possible mechanism is suggested for this reaction.

Selective Toxic Action of Thiosulphate on Plants

Investigations have been recently carried out on the effects of low concentrations of sodium thiosulphate on the germination and subsequent root growth of a number of plants. (These investigations were undertaken as a result of earlier work, not yet published, by Quastel, Hewitt arid Nicholas, on the effects of thiosulphate on growth of crops in soils.)