Low Concentrations Of Cyanide Research Articles

An innovative fluorescent probe for the detection of cyanide - enhanced sensitivity by controlling its electrostatic potential and suitable for applications such as cell imaging and food analysis

As cyanide is a huge hazard to the environment and human health, the study of the method of detecting low concentrations of cyanide is of great significance. In general, materials with strong positive electrostatic properties can use electrostatic attraction to enrich anions in the water near the materials, then realize rapid detection of low concentration anions by fluorescent probes. In this paper, fluorescent probes PI-S, PI-I and PI-N with cyanide-specific recognition and different charges were synthesized to study the relationship between the charge effect of probes and the sensing sensitivity. Through the zeta potential test and the calculation of the surface electrostatic potential, the positive electricity of PI-S, PI-I and PI-N gradually increased, the ΔG < 0 of the adsorption process gradually decreased, CN– could be aggregated to the vicinity of probes. As a result, the detection limit of the probe was gradually reduced from 1.07 × 10−6 to 5.03 × 10−8 M, the sensitivity was significantly enhanced. Therefore, this is expected to be a new strategy to improve the sensitivity of anion probes by increasing the positive electricity of molecules. In addition, PI-N has good anti-interference ability, short response time and certain application value in cell imaging and identification of endogenous cyanide in food.

Enhanced copper cyanide complex precipitation using polymer-surfactant aggregates

Precipitation of metal cyanide complexes using quaternary ammonium salts has been used in cyanidation solutions after gold leaching. Due to the high residual load of metal cyanide complexes and ammonium salts, this method does not apply to effluents containing moderate or low cyanide concentrations. To overcome these limitations, in this study, we introduce poly(sodium 4-styrenesulfonate) (PSS) into a solution containing cetyltrimethylammonium bromide Sinpharm (CTAB), to form polymer-surfactant aggregates (PSAs) and enhance the removal efficiency of Cu and TCN. 93.8% and 97.0% of Cu and TCN, respectively, were removed from the synthetic solution (Cu 0.5 mM and CN 1.5 mM) under optimum dosage of 150 ppm PSS and 0.8 mM CTAB, resulting in 92.2% of substrate usage. The addition of 3.0 mM CTAB without PSS resulted in only 46.3% of substrate usage, even though the removals of Cu and TCN were 92.2 and 93.6%, respectively. The presence of thiocyanate ions significantly reduced the removal efficiency due to the competitive interaction with PSAs, whereas the pH of the solution and the temperature did not have any noticeable impact. Tests performed with an industrial effluent corroborated the results obtained with synthetic solutions: PSAs react with copper cyanide to form a precipitate that can be separated from the solution.

Determination of cyanide concentration by chronoamperometry, cyclic voltammetry and fast Fourier transform electrochemical impedance spectroscopy

In this research electroanalytical methods based on chronoamperometry, cyclic voltammetry and fast Fourier transform electrochemical impedance spectroscopy (FFT-EIS) were adapted for the determination of cyanide ion concentration in the range between 2 mmol l−1 and 1 mol l−1. The widest range of linearly detectable concentration of cyanide ions was obtained by cyclic voltammetry-based method that allowed to quantify concentration of cyanide ions in the range from 10 mmol l−1 to 1 mol l−1 (R2 = 0.993). Chronoamperometry-based method showed the highest sensitivity to the low concentrations of cyanide enabling to detect cyanide ion in the linear range from 2 mmol l−1 to 50 mmol l−1 (R2 = 0.995). The FFT-EIS-based method exhibited linear range from 100 mmol l−1 to 700 mmol l−1 (R2 = 0.975) showing suitability of this method for the quantification of cyanide ion concentration in highly concentrated cyanide solutions. Moreover, the FFT-EIS-based method allows to carry out quantification of cyanide very fast, by registering the impedance spectrum within 0.5 s. Therefore, all three cyanide quantification methods presented in this research are convenient for the estimation of cyanide concentration in the relevant concentration ranges.

Determination of low environmental free cyanide concentrations in freshwaters

Cyanide compounds are naturally emitted into the environment in low levels by degradation processes or emitted from anthropogenic sources. In surface water, complex cyanide compounds as well as “free cyanide” are present. The latter term covers hydrogen cyanide and cyanide compounds which easily liberate hydrogen cyanide under slightly acidic conditions. Especially free cyanide may cause adverse effects in the environment. To exclude negative impacts on freshwater systems, in the context of the European Water Framework Directive (WFD), preventive regulatory activities for free cyanide are currently under discussion. However, established analytical methods for quantification of free cyanide only obtain limits of quantification (LOQs) in the range of 1 μg L−1. Thus, these methods are not sufficiently sensitive for a potential environmental quality standard (EQS) compliance monitoring at water concentrations below the current predicted no effect concentration (PNEC) level of free cyanide. In the present study, a standardized continuous flow analysis (CFA) method for quantification of low free cyanide concentrations was adapted by applying a special system which allows an ultra-sensitive photometric detection of a colored cyanide derivative. By this means, LOQs in a range of one magnitude below the PNEC are achievable. The method was validated according to ISO/IEC 17025 requirements. Free cyanide concentrations in tested surface water samples from a small river and a barrier lake with low anthropogenic influences were very low and clearly below the PNEC. The results prove that the adapted CFA method is suitable for the analysis of low concentration free cyanide in freshwaters and appropriate for a possible EQS compliance monitoring.

Dissolution of gold in chalcopyrite-containing cyanide solutions

The gold dissolution in anoxic cyanide solution in the presence of chalcopyrite was studied with a rotating disc electrode. It was found that the presence of chalcopyrite reduced and enhanced the dissolution activity of pure gold in the low and high potential regions, respectively. The dissolution of gold was diffusion-controlled at low potentials (≤177 mV) and low cyanide concentrations (≤980 mg/L); however, above the cyanide concentration of 980 mg/L, the current density of gold decreased and the dissolution of gold changed from diffusion-control to electrochemical reaction-control. At high potentials (>177 mV), gold dissolution was always controlled by diffusion. In cyanide solution containing chalcopyrite, appropriate increase of pH value and temperature could accelerate the dissolution of gold, but high pH value would promote the generation of passivation, which was harmful for the dissolution of gold in cyanide solution.

Cu adsorption behaviours onto chelating resins from glycine-cyanide solutions: Isotherms, kinetics and regeneration studies

A method is presented to remove and recover copper from copper-gold glycinate solutions using an iminodiacetic functionalized resin with subsequent regeneration. The adsorption/desorption approach was evaluated for a glycine leaching process which was shown to be effective for the dissolution of gold and copper from different gold-copper ores and concentrates. In this process, glycine is the lixiviant in the presence of very low cyanide concentration as a synergistic reagent. The copper species in glycine-cyanide process are mainly present as cupric glycinate and a low concentration of cuprous dicyanide and no free cyanide. While cupric glycinate does not load well onto activated carbon, cuprous dicyanide is problematic due to its high carbon affinity and co-loading with gold onto activated carbon, thereby requiring the removal of most of the copper prior to the gold recovery. In this study, the use of ion-exchange resins as one of the possible downstream recovery processes for gold and copper from glycine-cyanide solutions was tested. The isotherms and kinetics of gold and copper (cupric copper (Cu2+)) adsorb onto the chelating resin (Puromet MTS9300) from their alkaline glycinate and cyanide complexes were studied. Results show that the [CNT−]: [CuT] molar ratio has significant effects on the adsorption of CuT, due to the change in Cu2+/Cu+ ratio in the solutions, where [CN−T] is the total cyanide in the system (free cyanide being zero). The results show that the chelating resin is selectively adsorbed cupric (Cu2+) over cuprous (Cu+) ions. The adsorption results were fitted to both the Freundlich and Langmuir isotherm models, while the Langmuir model shows a better correlation. The adsorption kinetic data of Cu2+ is well fitted to the pseudo-second-order model. Alkaline glycine solutions in the presence of NaCl was selected as the main eluent for the resin elution study. The multi-cycle adsorption/desorption tests showed that the resin adsorption and regeneration efficiencies are not significantly changed after five cycles of adsorption/desorption. Microscopic visual analysis by using scanning electron microscopy (SEM) showed that there is no significant change in shape and size of the resins, although more cracks were observed after the 5 cycles of adsorption/desorption.

Toward sustainable electroplating of decorative silver for SMEs in Indonesia

Decorative silver electroplating has been a long time conducted by small and medium enterprises (SMEs) in Indonesia. Environmental pollution associated with the electroplating SMEs activities has created serious problems. For example SMEs of silver electroplating has contaminated groundwater which is no longer fit for domestic consumption due to its high level of cyanide contamination. Inefficient process and the use of high concentration of cyanide based electrolyte have been claimed to be the root cause. Therefore, the process of decorative silver electrodeposition in SMEs would be improved by developing an electrolyte with low cyanide concentration, determining onset potential and current densities, and modifying the process and the electrochemical cell so that the process would be more efficient and sustainable. A new electrolyte composed of AgNO3 and KCN with a ratio of 5:39 were chosen for the experimentation. For this electrolyte, silver would possibly be electrodeposited at potentials ranging from -2.2 V to -2.8 V. Corresponding current densities for silver electrodeposition would be between -2 and 7 mA/cm2. To improve the process, a new design of electrochemical reactor has been developed which ensure improvement of the observed electrochemical parameters i.e. the uniform current density distribution, the larger area of anode, and the stability of electrodes distance and position.

Acetic acid application as an activating reagent in the intensive cyanidation of gravity concentrates

The well-known technology of intensive cyanide leaching of gravity concentrates, which allows to bring part of gold into commercial products with obtaining high-purity Dore alloy, requires the use of expensive reagents and high temperature (80 °С) leaching. Studies have been carried out on intensive leaching of gold-containing gravity concentrate in a drum-type apparatus at low concentrations of sodium cyanide with the addition of a new reagent-activator. It is proposed to conduct intensive cyanidation of enriched gravity concentrate using acetic acid as an effective activator reagent. Improving the efficiency of cyanide leaching by introducing activators into the reagent system is achieved by dissolving passivating films on the surface of gold grains. Studies on the intensive leaching of gold in the enlarged laboratory tests. The results of the large-scale laboratory tests on the intensive cyanide leaching of the gravity concentrate using acetic acid as an activating agent activator were fully confirmed by the data of laboratory studies.

Intensive leaching of gold from gravity concentrate at low concentration of sodium cyanide

Studies on the intensive leaching of gold gravity concentrate in the drum and conical types at low concentration of sodium cyanide laced with reagent-activator. As a reagent-used organic acid activator with 1.5 and 3.0 kg/t. List the parameters of both devices intensive cyanidation. Tests conducted in comparison with well-known methods of intensive leaching of gold in similar devices with a high concentration of sodium cyanide, in which gold extraction reaches high results. However, there is significant consumption of sodium cyanide, which is an expensive reagent. Similar results can be achieved with a low concentration of sodium cyanide using a reagent-activator, with significant reduction in the consumption of sodium cyanide. It is shown that the use of reagent-activator on the basis of an aliphatic acid significantly intensifies the leaching process. Found that the gold content in the tails of the intensive cyanidation by using reagent-activator on the basis of an aliphatic acids in both vehicles lower than without the use of this reagent. As a result of study of dissolution rate of gold in rolling the unit higher than that of the conical, but for intensive cyanidation gravity concentrates may use both types of machines, drum and conical.

Myeloperoxidase-catalyzed oxidation of cyanide to cyanate: A potential carbamylation route involved in the formation of atherosclerotic plaques?

Protein carbamylation by cyanate is a post-translational modification associated with several (patho)physiological conditions, including cardiovascular disorders. However, the biochemical pathways leading to protein carbamylation are incompletely characterized. This work demonstrates that the heme protein myeloperoxidase (MPO), which is secreted at high concentrations at inflammatory sites from stimulated neutrophils and monocytes, is able to catalyze the two-electron oxidation of cyanide to cyanate and promote the carbamylation of taurine, lysine, and low-density lipoproteins. We probed the role of cyanide as both electron donor and low-spin ligand by pre-steady-state and steady-state kinetic analyses and analyzed reaction products by MS. Moreover, we present two further pathways of carbamylation that involve reaction products of MPO, namely oxidation of cyanide by hypochlorous acid and reaction of thiocyanate with chloramines. Finally, using an in vivo approach with mice on a high-fat diet and carrying the human MPO gene, we found that during chronic exposure to cyanide, mimicking exposure to pollution and smoking, MPO promotes protein-bound accumulation of carbamyllysine (homocitrulline) in atheroma plaque, demonstrating a link between cyanide exposure and atheroma. In summary, our findings indicate that cyanide is a substrate for MPO and suggest an additional pathway for in vivo cyanate formation and protein carbamylation that involves MPO either directly or via its reaction products hypochlorous acid or chloramines. They also suggest that chronic cyanide exposure could promote the accumulation of carbamylated proteins in atherosclerotic plaques.

Isolation and identification of endophytic bacteria with plant growth promoting and biocontrol potential from oak trees

SummarySamples of roots, leaves and stems of healthy oak trees were collected from various locations in the Baneh and Marivan regions, Iran. In total, 63 endophytic bacteria were isolated and grouped according to phenotypic properties. Seven selected isolates were further identified by partial sequencing of the 16S rRNA gene. Isolates Pp54, Pp88, Pp95 and Pp177 were Pseudomonas spp., isolates Sm59 and Sm79 were Stenotrophomonas spp., and isolate Bf 172 was a Bacillus sp. The ability of these isolates for plant hormone production such as auxin and gibberellin was evaluated, along with siderophore production, phosphate solubilization, atmospheric nitrogen fixation, protease and hydrogen cyanide production. All strains produced auxin and gibberellin in different amounts. Atmospheric nitrogen fixation ability was positive for strains Sm79, Pp54, Pp88 and Pp95. All strains except Sm79 solubilized phosphate. Strains Sm59, SM79, Pp88, Pp177 and Bf172 produced protease. Pp88, Pp95, Bf172 and Pp177 were able to produce siderophore. Strains Sm79 and Pp95 released low concentrations of hydrogen cyanide. Amongst the strains tested, Pp95, Pp88, Pp177 and Sm79 had different inhibitory effects on the bacterial plant pathogen, Pseudomonas syringae pv. syringae under in vitro conditions. This is the first reported case of endophytic Bacillus, Pseudomonas and Stenotrophomonas strains from oak trees in Iran.

Gold and copper leaching from gold-copper ores and concentrates using a synergistic lixiviant mixture of glycine and cyanide

The presence of cyanide soluble copper in the cyanidation of gold-copper ores and concentrates significantly increases the cyanide consumption in order to achieve sufficient gold recovery. In addition, cyanide recovery or cyanide detoxification/destruction processes are also required which adds extra cost to the process. This research introduces a leaching approach to extract gold, silver and copper from gold-copper ores and concentrates using a synergistic lixiviant leaching process using glycine in the presence of low concentrations of cyanide. The effects of glycine and cyanide concentrations on gold, silver and copper leaching kinetics and recovery were studied. It is shown that, in the presence of glycine, gold, silver and copper extraction increase significantly in solutions containing copper-cyanide species at a very low, or zero, free cyanide concentration. It has also been shown that the gold dissolution rate in glycine-cyanide system is almost three times higher than the gold dissolution rate in the conventional cyanidation. Kinetic studies were conducted to evaluate the effects of glycine concentration, pH, and CN/Cu ratio on the dissolution of gold and silver. It has also been shown that the gold dissolution rate increases by increasing the glycine concentration up to 2.0g/L (Gly:Cu molar ratio of 2.2:1) and any further glycine addition has no significant effect on the dissolution of gold. It is shown that the presence of glycine in solutions containing copper (I)-cyanide species can significantly enhance the dissolution of precious and base metals. The proposed leaching approach significantly reduces the cyanide consumption by at least 75% and most of the copper is present as cupric glycinate in the final leach solution. In addition, gold, silver and copper extraction was higher than the conventional cyanidation process utilising similar cyanide dosages for all the gold-copper sources studied.

Modeling and optimization of Carbon in leach (CIL) circuit for gold recovery

Carbon in leach (CIL) is an important step in gold processing that involves simultaneous adsorption and leaching. While the mechanism of leaching and adsorption are well known, the effect of different operating and design parameters on the dynamics and performance of CIL circuit are not yet studied. The focus of this paper is to study the effect of operating parameters like cyanide concentration, oxygen concentration and mean particle diameter on the overall efficiency of CIL circuit. A dynamic model based on first principles is developed for the entire CIL circuit. Suitable kinetic models for both leaching and adsorption are adopted from the literature. Customizable simulator is written in MATLAB to simulate the model. Simulation results are first validated using previously published results. The validated model is then used to perform sensitivity studies on different parameters that affect the gold extraction process. The key parameters are optimized by conducting a multi-objective optimization study using elitist non-dominated sorting genetic algorithm of MATLAB. The percent recovery and net profit are maximized, while minimizing the cyanide used in the process. Four decision variables are used viz. particle diameter, oxygen concentration, cyanide concentration and ore volume fraction in tanks. A Pareto-optimal solution for the process parameters is provided such that all the objectives are improved to a value above which their improvement will result in degradation of other objectives. As a result, high recovery, high profit and low cyanide concentrations can be achieved simultaneously.

Bicinchoninic acid-based colorimetric chemosensor for detection of low concentrations of cyanide

Bicinchoninic acid (BCA) is reagent that is widely used to determine the concentration of proteins in solutions through the colored complex it forms with Cu(I) and the proteins. In this report, we present a new use for BCA, where a highly sensitive method for detection of cyanide ions in solutions by using Cu2+–BCA complex as the chemosensing agent is demonstrated. The detection of cyanide ions is achieved by taking advantage of the nucleophilic attack of the Cu2+–BCA complex by cyanide ions. Upon the addition of cyanide ions, the Cu2+–BCA complex undergoes transformations to free BCA via a series of equilibriums and, as a result, forms different Cu(II)–(BCA)x(CN)y species depending on the concentrations of cyanide ions in the solution. These different Cu(II)–(BCA)x(CN)y species, in turn, give different metal-to-ligand charge transfer electronic spectra and colors that are easily detectable both with naked eyes and UV–vis spectroscopy. As the cyanide ion concentration increases, the color of the solution containing the complexes changes from green to purple, red, yellow, and finally colorless, giving a corresponding blue shift in the absorption maxima on their UV–vis spectra. Through this process, the complexes enable detection of cyanide ions with a detection level of up to 0.06ppm in solutions. Thus, this colorimetric technique based on Cu2+–BCA can make low concentrations of cyanide detectable, well before the concentrations possibly reach lethal amounts. Furthermore, the method is shown to give fast detection response with no interference from other anionic and cationic species and has the potential to be adopted for accurate and convenient analysis of cyanide ions in drinking water sources as well as industrial effluents.

Colorimetric Cyanide Chemosensor Based on 1',3,3',4-Tetrahydrospiro[chromene-2,2'-indole

A new class of chemosensors based on the 1′,3,3′,4-tetrahydrospiro[chromene-2,2′-indole] ring system, which detects cyanide with high specificity, is described. These chemosensors show a distinct color change when treated with cyanide in acetonitrile solution buffered with sodium phosphate, and this procedure is not affected by the presence of other common anions. The chemisensors exhibit high sensitivity to low concentrations of cyanide, meeting the European Union water quality control criterion of sensitivity below 0.05 mg L−1, and show a very fast response within tens of seconds. The mechanism for detection is rationalized by the nucleophilic substitution of the phenolic oxygen atom at the indoline C-2 atom by the cyanide anion to form a stable indolylnitrile adduct and to generate the colored 4-nitrophenolate chromophore. These chemosensors can be synthesized by a simple procedure from commercially available starting materials.

Co-intensification of cyanide leaching gold by mercury ions and oxidant

The effects of mercury ions on gold cyanidation were studied. The results show that under low cyanide concentration, gold cyanide process is controlled by CN − transfer, while at higher cyanide concentration, there forms passivation on gold surface. Therefore, chemical oxidation of gold in cyanide solution of higher concentration is controlled by surface reaction. Small quantity of additions of mercury ions bring about great increases in anodic gold dissolution rate, decreases the passivation and reduces the equilibrium activated energy. In addition, they also markedly change the effect pattern of cyanide concentration. Mercury ions show positive effects on cathodic reduction of oxygen and raise the rate of electrochemical step of the cathodic reduction of oxygen. Addition of a certain amount of hydrogen peroxide is confirmed to be an effective way for intensification of cathodic process on gold electrode. Active potential range and current peak on anodic dissolution are enlarged when being co-intensified with Hg 2+ and hydrogen peroxide. Co-intensifying effect may be obtained and gold leaching rate is considerably increased on cyanide leaching of gold from gold concentrates.

Control of Respiration by Cytochrome c Oxidase in Intact Cells

Metabolic control analysis was applied to intact HepG2 cells. The effect on the control coefficient of cytochrome c oxidase (CcOX) over cell respiration of both the electrical (Delta psi) and chemical (Delta pH) component of the mitochondrial transmembrane proton electrochemical gradient (Delta mu(H(+))) was investigated. The overall O(2) consumption and specific CcOX activity of actively phosphorylating cells were titrated with cyanide under conditions in which Delta psi and Delta pH were selectively modulated by addition of ionophores. In the absence of ionophores, CcOX displayed a high control coefficient (C(IV) = 0.73), thus representing an important site of regulation of mitochondrial oxidative phosphorylation. A high control coefficient value (C(IV) = 0.85) was also measured in the presence of nigericin, i.e. when Delta psi is maximal, and in the presence of nigericin and valinomycin (C(IV) = 0.77), when Delta mu(H(+)) is abolished. In contrast, CcOX displayed a markedly lower control coefficient (C(IV) = 0.30) upon addition of valinomycin, when Delta psi is converted into Delta pH. These results show that Delta psi is responsible for the tight control of CcOX over respiration in actively phosphorylating cells.

Determination of the leaching parameters for a refractory gold ore containing aurostibite and antimony minerals: Part II — AD Zone

Following a successful investigation on the Central Zone sample, a cyanidation study was conducted on an ore sample from the AD-MW Zone of Clarence Stream Property, owned by Freewest Resources Canada, to develop a leaching strategy to extract gold. At a grade of 6.48 g/t, gold is present in the forms of aurostibite, free gold and electrum. The ore contains 4.3% berthierite/gudmundite, 1.3% pyrrhotite, 0.7% pyrite, 0.07% stibnite and 0.9% arsenopyrite. Similar to the Central Zone, the extraction of gold from the AD-MW Zone can be performed at atmospheric pressure, pH 10.5 and with a low concentration of cyanide. The grind size had no effect on gold extraction between a P80 of 28 to 71 μm. The oxygen and cyanide requirement significantly increased with a finer grind. Consequently, a very close control of cyanide addition is required to minimize passivation of gold. Lead nitrate, added in the pretreatment, increased the extraction of gold by 2.3%. Leaching at pH < 10 improved gold extraction but increased the cyanide consumption by 5%. Passivation of gold occurred when the pretreatment was longer than 2 hours. A longer pretreatment reduced the cyanide consumption by 5%. Mineralogical characterization of the leach residue with no gravity pretreatment prior to leaching indicated the presence of unleached gold grains and passivated gold grains. Removal of coarse gold by gravity increased the extraction by 2.8% (leach residue at 0.74 g/t Au). Increasing the DO to 16 ppm or the lead nitrate from 500 to 1,000 g/t increased the overall gold extraction to 90.4% (leach residue at 0.62 g/t), which is the maximum gold extraction obtained. The leaching parameters were 800 ppm NaCN, DO 16 ppm and pH 10.5 for a duration of 120 hours. The associated cyanide consumption was 4.0 kg/t. Gold leaching was not sensitive to cyanide concentration. Reducing the cyanide concentration to 250 ppm resulted in a gold extraction of 89.5% with a cyanide consumption of 2.6 kg/t.

Evaluation of leaching parameters for a refractory gold ore containing aurostibite and antimony minerals: Part I – Central zone

A cyanidation study was conducted on a mild refractory gold ore sample from the Central zone of Clarence Stream Property, owned by Freewest Resources Canada, to develop a leaching strategy to extract gold. Gold, at a grade of 8.00 g/t, is present as native gold, electrum and aurostibite. The ore also contains 2.8% pyrrhotite, together with several antimony minerals (0.8% berthierite and gudmundite, 0.18% native antimony and stibnite). It also exhibits weak preg-robbing properties with 0.16% organic carbon. Aurostibite, a gold antimony compound, is particularly known to be insoluble in cyanide solution. The antimony dissolves in cyanide solution to form antimonates, which retards gold dissolution. Industrial practice of extracting gold from aurostibite generally consists of producing a flotation concentrate, which is leached in a pipe reactor at low alkalinity and high oxygen pressure with about 20 g/L cyanide. The proposed new approach is efficient and allows the extraction of gold directly from an ore at atmospheric pressure and a low cyanide concentration at pH 10.5. The effects of grinding, pre-treatment, lead nitrate, kerosene and cyanide concentrations have been investigated. The maximum gold extraction obtained on the ore was 87.9% using 800 ppm NaCN, 500 g/t lead nitrate, 30 g/t kerosene, DO (dissolved oxygen) 10 ppm and pH 10.5 in 168 h. The associated cyanide consumption was 1.3 kg/t. The additions of lead nitrate and kerosene increased gold extraction. In comparison to a P 80 of 74 μm, a P 80 of 30 μm significantly increased gold extraction. Gold in solid solution in gudmundite and arsenopyrite was believed to be responsible for the un-leached fraction until mineralogical analysis of hydroseparation concentrates of leach residues showed that most of the un-leached gold occurs as aurostibite, either as locked grains in sulphides/sulpharsenides or as grains with passivation rims of an Au–Sb–O phase. Coarse gold was also found. Gold extraction was not sensitive to cyanide concentration from 250 to 1200 ppm NaCN and high pH was detrimental. Decreasing the cyanide concentration reduced the cyanide consumption from 1.39 to 0.85 kg/t. The removal of coarse gold using a Knelson concentrator and a Mosley table prior to leaching increased the gold extraction to 90.4% (leach residue at 0.77 g/t).

Whole‐genome transcriptional and physiological responses of Nitrosomonas europaea to cyanide: Identification of cyanide stress response genes

Nitrosomonas europaea (ATCC 19718) is one of several nitrifying species that participate in the biological removal of nitrogen from wastewater by oxidizing ammonia to nitrite, the first step in nitrification. Because nitrification is quite sensitive to cyanide, a compound often encountered in wastewater treatment plants, we characterized the physiological and transcriptional responses of N. europaea cells to cyanide. The cells were extremely sensitive to low concentrations of cyanide, with NO-(2)production and ammonia-dependent oxygen uptake rates decreasing by 50% within 30 min of exposure to 1 microM NaCN. Whole-genome transcriptional responses of cells exposed to 1 microM NaCN were examined using Affymetrix microarrays to identify stress-induced genes. The transcript levels of 35 genes increased more than 2-fold while transcript levels of 29 genes decreased more than 20-fold. A gene cluster that included moeZ (NE2353), encoding a rhodanese homologue and thought to be involved in detoxification of cyanide, showed the highest up-regulation (7-fold). The down-regulated genes included genes encoding proteins involved in the sulfate reduction pathway, signal transduction mechanisms, carbohydrate transport, energy production, coenzyme metabolism, and amino acid transport.