Sulfide Salts Research Articles

Evaluation of toxicity, bioavailability and speciation of lead, zinc and cadmium in mine/mill wastewaters

The toxicity of common compounds of lead, cadmium and zinc was evaluated in waters similar to that found in the world’s largest lead producing area in Missouri. Static, acute toxicity tests were performed using fathead minnows (Pimephales promelas) and water fleas (Daphnia magna) respectively. Test organisms were subjected to varying amounts of sulfide, carbonate, chloride and sulfate salts of lead, zinc and cadmium mixed in hard, alkaline waters typical to this region. Median lethal concentrations were calculated using nominal versus measured metal concentrations. Measured metal concentrations included four different metal fractionation (extraction/filtration) techniques at different pH levels which included “dissolved”, “available”, “easily dissolved” and “total” metals. Most consistent correlations between mortality and metal concentrations were found with the “Total” or “Nominal” values. The “Easily Dissolved” metals which corresponded to acid soluble criteria did not effectively represent toxicity and bioavailability of metals. A metal speciation model, MINTEQA2, was used to predict the concentrations of the dissolved metal species at the pH levels commonly seen in the toxicity test vessels. MINTEQ model results suggested that analysis of metals in aqueous environment is better understood when examining speciation characteristics and would likewise be a better mechanism to develop site-specific water quality criteria for metals.

The determination of sulfide in seawater by flow-analysis with voltammetric detection

Abstract Preliminary measurements of sulfide in seawater using cathodic stripping voltammetry and a hanging mercury drop electrode (HMDE) in batch-mode showed that the sulfide peak decreased rapidly with time. This decrease was not caused by O 2 , H 2 O 2 or IO 3 − , and the sulfide peak was not stabilised by trace metal additions. A home-made flow-cell was constructed to enable the determination of sulfide in seawater using voltammetry with an HMDE. A stable sulfide peak was obtained by flow-analysis with voltammetric detection, with a precision of 2.8% and detection limit of 0.5 nM at a 60 s adsorption time. Several thiol compounds were found to produce a peak at, or very close to, the peak potential for sulfide. Their interference was evaluated by allowing the sulfide peak in conventional (batch) voltammetry to decay. Comparative experiments showed that waste metallic mercury is responsible for removal of sulfide in batch-mode analysis due to formation of insoluble mercuric sulfide salts causing the rapid decay of the sulfide peak. The problem is circumvented by using flow-analysis to determine sulfide.

Reaction of 4-aryl-3-thiosemicarbazides with carbon disulfide: A facile synthesis of 2,3-dihydrothiazoles and their fused derivatives

The reaction of 3-aryl-3-thiosemicarbazides 1a-d with carbon disulfide in alkaline medium affords the non-isolable sulfide salts 2a-d. The latter undergo in situ heterocyclization with some α-halogenated compounds, e.g., 3a,b and 13, to afford polyfunctionally substituted 2,3-dihydrothiazoles 4a-e and thiazolidine 14, respectively, which, in turn, could be annelated into fused heterocyclic systems. Chemical and spectroscopic evidence for the new compounds are described. © 1997 John Wiley & Sons, Inc.

Inhibition of Anaerobic Digestion Caused by Heavy Metals

The severity of heavy metal inhibition on anaerobic digestion is dependent on the metal species and their dissolved concentration in the digester. The general sequence of inhibition on anaerobic digestion of municipal sewage sludge was found with Ni > Cu > Cd > Cr > Pb. Metal immobilization affinity in the sludge followed the reverse sequence. Due to sulfide production during digestion high quantities of heavy metals are precipitating as highly insoluble sulfide salts. Nickel was immobilized to 94 % in the digester and indicated the most dramatic effect on anaerobic digestion. At a concentration of 250 to 300 g Ni m-3 toxicity occurred. Lower nickel concentrations resulted in reversible process inhibition. Copper up to 1000 g Cu m-3 caused reversible inhibition of acid producing, fermentative, and methanogenic bacteria. The time necessary for recovery of the process was dependent on the initial copper concentration in the digester. The organisms indicated capability of adaptation to copper. The copper uptake in the digester was 97 %. Cadmium inhibited digestion of sewage sludge up to approximately 50 % at 650 g Cd m-3. For long durations of acclimation a tendency toward recovery was observed. The cadmium uptake in the digested sludge was 99 %. Chromium and lead were uptaken at 99.9 % during digestion. Hence, the addition of these metals up to 1000 mg Cr/l and 600 mg Pb/l showed only little effect on anaerobic digestion.

Conductometric analysis of the second acid dissociation constant of H 2S in highly concentrated aqueous media

Discrepancies by a factor of 10 5 have been reported for the fundamental S 2− aqueous acid equilibrium constant which acts as a cornerstone for the foundation of aqueous metal sulphide thermochemistry. We report the conductometric determination of the Gibbs free energy and the acid equilibrium constant for S 2− aq, K 2: ▪ Uncertainty in K 2 directly affects solubility, thermodynamic and redox potential values of each of the metal sulphides. Unlike previous investigations, the conductometric measurements determine the extent of free OH − in solution directly. This study is performed in unusually concentrated media, and makes conventional use of the anomalously high equivalent conductance of hydroxide compared with other anions. The differential conductometric measurements and conductometric titrations reported here demonstrate that hydroxide resists dehydrolysis in solutions containing less than 3 M hydrosulphide and hydroxide, and the equilibrium: ▪ lies substantially to the left, confirming that p K 2 > 16. As the concentration is increased from 3 to 7 M, the relative conductivity diminishes, and free OH − is consumed increasingly. A solution containing 6.4 M KHS and 6.4 M KOH, a solution with a pH of approximately 17, is shown (i) to contain comparable concentrations of free S 2−, HS − and OH − species, (ii) to have an ionic conductance for free sulphide of λ 1 2 s 2−= 0.87 λ HS − , and (iii) to affirm that aqueous sulphide salt thermodynamics, solubilities and rest potentials are limited by HS − and not S 2− chemistry.

Synthesis of β‐lactosyl 1‐thioceramide

Abstract3‐O‐Benzoyl‐azidosphingosine 3 was transformed into the corresponding 1‐thio derivative 6. Its sodium sulfide salt 6A was treated with hepta‐O‐acetyl‐α‐lactosyl bromide 8 to provide after complete O‐deprotection the β‐connected thioglycoside 9. Azido group reduction and N‐palmitoylation led to the desired β‐lactosyl thioceramide 1; for structural assignments it was converted into the per‐O‐acetyl derivative 2.

Aqueous Solubilities, Solubility Products and Standard Oxidation‐Reduction Potentials of the Metal Sulfides

Available thermodynamic data, incorporating a new free energy of formation for aqueous S2− of 111 (±2) kJ/mol at 25°C, indicate that solubility products of the insoluble metal sulfide salts are several orders of magnitude smaller than previously considered. Thermodynamic characterization for a variety of soluble and insoluble aqueous metal sulfide systems is reported. Trends in the aqueous solubilities of the alkali salts solubilities are compared and discussed. New aqueous solubility products, , and standard redox potentials, , for over forty metal sulfides are determined. The new values of and at 25°C include: , and . Significant free S2− occurs only in extremely alkaline media. The suitability of , rather than , based solubility products and redox potentials is discussed and these alternate values determined.

A comparative pitting corrosion study of mild steel in different alkaline solutions containing salts with sulphur-containing anions

The localized corrosion of mild steel in alkaline solutions containing a salt with a sulphurcontaining anion (sodium sulphate, sodium sulphite, sodium thiosulphate, potassium thiocyanate and sodium sulphide) is studied by using potentiostatic and potentiodynamic techniques complemented with scanning electron microscopy. Alkaline solutions containing one of those salts produce pitting of mild steel at potential values more positive than those of the active-passive transition of iron in base. In the presence of either thiocyanate or thiosulphate anion iron pitting takes place through sulphide formation which reacts at the electrode surface yielding poorly protective ferrous sulphide. At potential more positive than the breakdown potential the kinetic behaviour fits a competitive surface reaction mechanism involving the formation of the passive film and the nucleation and growth of a ferrous sulphide salt layer. The proposed reaction model reproduces the corresponding experimental current-transients.

The copper-molybdenum antagonism in ruminants. I. The formation of thiomolybdates in animal rumen

The formation of thiomolybdates, MoO xS 4−x 2− ( x = 0, 1, 2, or 3), from molybdate and sulphide salts in aqueous media has been studied under conditions which simulate the fluid phase in the rumen. The influences of the sulphide:molybdenum ratio, pH and phosphate levels on the nature of the species formed were investigated. The thiomolybdates, in particular the MoS 4 2− ion, have been implicated as the active intermediates in the widespread molybdenum induced copper deficiency that affects ruminants. The results presented here show that, under physiological conditions, di- and trithiomolybdates will form more readily than tetrathiomolybdate.

Effects of organic and inorganic binding on the volatilization of trace elements during coal pyrolysis

The volatility of bromine, chlorine, vanadium, managanese, selenium, arsenic, chromium, and cobalt during coal pyrolysis was determined. Volatility was determined for both hydrogenated and nonhydrogenated coal, and for coal spiked and unspiked with inorganic and organic forms of the trace elements. Volatilization of selenium and arsenic was higher when those elements were present as inorganic sulfide salts. The importance of chemical forms of elements to rates of volatilization during pyrolysis is established. (1 diagram, 9 references, 4 tables)

A New Field Method for the Quantitative Determination of Sulfides in Water-Base Drilling Fluids

This paper presents a new analysis method for measuring sulfides in water-base drilling fluids. The method is simple, accurate, and rapid. It can measure sulfide concentrations ranging from about 1 to 10,000 mg/liter. Laboratory, work to verify, the new method also is presented. Introduction A satisfactory method for analyzing sulfides in drilling muds and filtrates at the rig site has been a long-standing need in the drilling industry. The main requirements are speed, accuracy, reliability, and simplicity. The newly developed Garrett Gas Train procedure has been proven to meet these field requirements. The method has been tentatively adopted as an API procedure and was published recently. It is identified by the API as the Garrett published recently. It is identified by the API as the Garrett Gas Train Sulfide Analysis and is abbreviated here as GGT/S=. The old API Hach Paper method for sulfide determination has not shown sufficient accuracy nor wide enough analytical range to be acceptable for current H2S drilling situations. Quantitatively accurate laboratory sulfide methods are not fieldworthy, while simple methods are inaccurate and often respond falsely to components other than sulfides in a mud. The GGT/S= method does not respond falsely to other fluid components, primarily because it eliminates most of the interference problems by using a gas train to separate H2S gas from the complex liquid phase. The method's accuracy, reliability, and simplicity comes from using well known, commercially available, Drager H2S-detector tubes in conjunction with the gas train. Research has shown that this general gas train and detector tube principle of analysis can be applied to other volatilizable components in' drilling fluids. Two uses currently being applied experimentally in the laboratory and the field are analyses for filtrate carbonates, GGT/CO3=, and sulfites, GGT/SO3=. Sulfide Chemistry in Water-Base Muds Use of the chemical reactions between H2S and alkaline fluids is fundamental to how the GGT/S= method works and how its results can be applied at the rig to treat hazardous sulfides from a mud. H2S is a highly toxic and corrosive acidic gas having at low concentrations the distinctive odor of rotten eggs. If H2S enters a drilling fluid down hole, it reacts quickly as an acid with the alkaline mud. This neutralization at high pH converts the noxious H2S into the odorless, but not harmless, sulfide salts and water. From this di-basic acid, two salts in equilibrium are formed: bisulfides (HS-) and sulfides (S=). The hydroxyl ion (OH-) in the mud is the neutralizing agent, forming H2O as a byproduct. The process can be expressed as two separate neutralization reactions at equilibrium: H2S + OH- P H2O + HS-................... (1) HS- + OH- P H2O + S=.................... (2) The positive ion in this reaction is not indicated, but is Na+ in muds using caustic soda for pH control, or Ca++ when lime is used. For solutions in the pH range of 7 to 13 (most muds fall in this range), sulfides in solution would exist predominately in the form of HS-ions. If the pH is below about 7, the H2S gas becomes the predominant sulfide species, and above pH 13 the S= predominant sulfide species, and above pH 13 the S= predominates. predominates. The term "soluble sulfides," used frequently here, refers to the sum of all three sulfur-bearing components shown in Eqs. 1 and 2: HS- and S-ions plus any unreacted H2S that also might be present. JPT P. 1195

STABILITY OF SULFIDES OF MANGANESE, IRON, ZINC, COPPER, AND MERCURY IN FLOODED AND NONFLOODED SOIL

The stability of heavy metal sulfides (MnS, FeS, ZnS, CuS, and HgS tagged with 35S) in aerobic and anaerobic soil was studied. The sulfides are listed in decreasing order of solubility. Water extracts of each treated soil were made regularly during a 75-day incubation period. The radioactivity of the extracts was indicative of the stability of the water-soluble salts. For the aerobic soils, H2O-extractable 35S decreased with a decrease in solubility of the sulfide. The metal-sulfides were relatively stable in the anaerobic soil. The least soluble salt was the most stable. To study the oxidative capacity of rice (Oryza sativa L.) roots the 35S tagged metalsulfides were mixed with anaerobic soil to which rice was transplanted. The tagged soil was placed in the lower rooting zone and covered to a depth of 8 cm with unlabeled soil. The transplanted rice plants were grown for specific times and the aerial portions harvested. The uptake of 35S from the respective sulfide salt was determined. The apparent degree of stability and subsequent uptake of 35S was directly related to the solubility of the sulfide salt. No 35S was taken up from the Hg35S.

Copper and molybdenum in subcellular fractions of rat liver.

1. Black-hooded weanling rats were given a copper-deficient diet or diets providing 3 ppm Cu with or without supplements containing combinations of molybdate, sulphate and sulphide salts to provide 35 ppm molybdenum and 2μg atoms sulphur/g. Changes in weight and blood haemoglobin concentration were studied during 48 d of treatment. The subcellular distribution of Cu and Mo in the liver was subsequently determined.2. Rats fed on the Cu-deficient diet had a lower growth rate than animals receiving 3 ppm Cu and suffered a decline in blood haemoglobin concentration; Mo supplementation of the diet providing 3 ppm Cu produced similar adverse effects on growth but not on Hb. Effects of Mo on growth were exacerbated by a sulphide supplement which also decreased the rate of the gain in Hb concentration. This concentration of dietary sulphide was without effect when Mo was omitted from the diet.3. The Cu-deficient diet decreased both the Cu concentration and proportion of total liver Cu in mitochondria + microsome and supernatant fractions of liver.4. Mo-supplemented diets greatly increased both the Cu and Mo contents of all liver fractions. This phenomenon is considered in relation to previous suggestions that an unavailable Cu–Mo complex can form in tissues as a response to Mo accumulation.

The Origin of Calcareous Ooliths

ABSTRACT Laboratory studies were undertaken to discover mechanisms which might explain the origin of calcareous ooliths in nature. Calcium carbonate was precipitated from sea water by evaporation, by addition of precipitating agents and by the growth of sulfate-reducing bacteria. The effect of the major ions in sea water on the form of the calcium carbonate precipitate was also studied. These experiments showed that calcareous ooliths can be formed by chemical precipitation from sea water and by the growth of sulfate-reducing bacteria in sea water. The presence of magnesium ion in sea water causes calcium carbonate to precipitate as aragonite rather than calcite. An environment in which fresh waters high in carbonate ion flow into a shallow sea would reproduce the laboratory conditions for chemical precipitation of calcareous ooliths. Such a mechanism does not appear to be responsible for any large present day deposits. Environments where sulfate-reducing bacteria might be important in the origin of calcareous ooliths should be characterized by deficiency of oxygen, increased pH and presence of hydrogen sulfide or sulfide salts. Such environments might be highly localized.

The Blackening of Zinc Sulfide Phosphors

The process of blackening of zinc and cadmium sulfide phosphors is studied experimentally and theoretically. A survey of the principal experimental facts is given and several new experiments are described. It is suggested that the blackening of the sulfide salts is a two-quantum process in which both positive and negative charges are released from the interior; these charges move to the surface and there produce electrolysis in a film of moisture that is present on the surface when the specimen is in damp air. This picture will explain the known experimental facts concerning the blackening process. The important differences between the blackening of sulfides and the print-out effect in photographic emulsions are discussed.