Cyanide Concentration Research Articles

A biginelli-azophenol based robust sensor for rapid diagnosis of cyanide in real samples

The self-aggregation of multifunctional Biginelli-azophenol (Ligand1) in water (ONPs) led to sensitive and selective detection of toxic pollutant cyanide in an aqueous medium and solid matrix. The origin behind the excellent sensing performance of Ligand1 is assessed by 1H NMR spectroscopy which confirmed the deprotonation of OH and simultaneous H-bond formation by cyanide with NH of Ligand1. Furthermore, the UV–Visible absorption titration studies resulted in two isosbestic points at λmax 399 nm and 314 nm, which also confirmed the complex formation between Ligand1 and CN− with the detection of the lowest concentration of cyanide at 14.5 nM. Additionally, the colorimetric detection was supported by RGB color quantification as well as a thin column impregnated with Ligand1, which gives high-performance on-site cyanide detection in real water samples. Remarkably, such a cost-effective, robust colorimetric sensor having several key features, offered novel opportunities for real-time cyanide monitoring in polluted water and hence, this makes it unique among the other reported sensors for the same.

Ion Chromatography with Pulsed Amperometric Detection for Determining Cyanide in Urine and Meconium Samples.

The parents’ addictions and eating habits have a significant influence on the child’s growth. The first stool of a newborn baby provides a large amount of information about xenobiotics transmitted by the mother’s body. The analytical technique used in the study is ion chromatography with pulsed amperometric detection (IC-PAD). The biological samples, which were obtained from women staying in a maternity ward and their partners, revealed cyanide concentrations in urine samples spanning 1.30–25.3 μg L−1. Meanwhile, the results of the meconium samples were in the range of 1.54 μg L−1 to 24.9 μg L−1. Under the optimized chromatographic conditions, the IC-PAD system exhibited satisfactory repeatability (R < 3%, n = 3) and good linearity in the range of 1–100 μg L−1. Thus, it proved to be an effective tool for monitoring trace cyanide concentration in a series of human body fluid matrices, including meconium. Based on the literature review, this is the first application of the IC-PAD analytical technique for the determination of cyanide ions in meconium samples.

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.

Nitrogen Fixation at Early Mars.

The Mars Science Laboratory (MSL) recently discovered nitrates in Gale Crater (e.g., Stern et al., 2015; Sutter et al., 2017). One possible mechanism for ancient nitrate deposition on Mars is through HNOx formation and rain out in the atmosphere, for which lightning-induced NO is likely the fundamental source. This study investigates nitrogen (N2) fixation in early Mars' atmosphere, with implications for early Mars' habitability. We consider a 1 bar atmosphere of background CO2, with abundance of N2, hydrogen, and methane varied from 1% to 10% to explore a swath of potential early Mars climates. We derive lightning-induced thermochemical equilibrium fluxes of NO and HCN by coupling the lightning-rate parametrization from the study of Romps et al. (2014) with chemical equilibrium with applications, and we use a Geant4 simulation platform to estimate the effect of solar energetic particle events. These fluxes are used as input into KINETICS, the Caltech/JPL coupled photochemistry and transport code, which models the chemistry of 50 species linked by 495 reactions to derive rain-out fluxes of HNOx and HCN. We compute equilibrium concentrations of cyanide and nitrate in a putative northern ocean at early Mars, assuming hydrothermal vent circulation and photoreduction act as the dominant loss mechanisms. We find average oceanic concentrations of ∼0.1-2 nM nitrate and ∼0.01-2 mM cyanide. HCN is critical for protein synthesis at concentrations >0.01 M (e.g., Holm and Neubeck, 2009), and our result is astrobiologically significant if secondary local concentration mechanisms occurred. Nitrates may act as high-potential electron acceptors for early metabolisms, although the minimum concentration required is unknown. Our study derives concentrations that will be useful for future laboratory studies to investigate the habitability at early Mars. The aqueous nitrate concentrations correspond to surface nitrate precipitates of ∼1-8 × 10-4 wt % that may have formed after the evaporation of surface waters, and these values roughly agree with recent MSL measurements.

Phytoremediation potential of water hyacinth (Eichhornia crassipes) for phenol and cyanide elimination from synthetic/simulated wastewater

Water pollution is increasing due to urbanization and industrialization. Waste water pollution raised concern because of its influence on plants and humans. Water hyacinth (Eichhornia crassipes) is used for the removal of pollutants because of its phytoremediation efficiency. In this study, water hyacinth (Eichhornia crassipes) has been tested for simultaneous elimination of phenol and cyanide from mono and binary component aqueous solution in batch systems. The plant was grown at six concentrations of phenol and cyanide in the ratio of (10:1), i.e. 100:10, 200:20, 300:30, 500:50, 700:70 and 1000:100 mg/L in aqueous solution. The effect of process parameters such as initial concentration of phenol and cyanide and pH was evaluated. The plant was found capable of eliminating up to 96.42% of phenol (300 mg/L) and 92.66% of cyanide (30 mg/L) during the 13 days cultivation time at pH 8. The calculated Km of the root length elongation for phenol was 5.20 mm and the Vmax was 12.52 μg phenol/g root/h. However, the calculated Km of the root length elongation for cyanide was 0.39 mm and the Vmax was 14.99 μg cyanide/ g root/h. In the Eichhornia crassipes plant, the biochemical parameters such as chlorophyll, protein and sugar content have been indicated a decreasing trend due to uptake of phenol and cyanide throughout cultivation. Toxicity to 100–1000 mg/L of phenol and 10–100 mg/L of cyanide was measured by measuring the relative transpiration over 13 days. At 100 mg/L of phenol and 10 mg/L of cyanide, only a small reduction in transpiration but no morphological changes were noticed. Both pollutants are absorbed through the root of the Eichhornia crassipes plant by plasmalemma and become accumulated into the root cells and stem of a plant. Thus, this study will be beneficial for the decontamination of highly polluted waste water.

Application of the Fe3O4/ alginate/ diatomite nano-adsorbent for the adsorption of palladium and cyanide from wastewater: optimisation, kinetic and equilibrium studies

ABSTRACT In this research, the adsorption rates of cyanide and palladium onto Fe3O4/alginate/diatomite nano-adsorbent (FADA) were evaluated. The co-precipitation technique was applied to synthesis of FADA. The response surface methodology (RSM) was employed to investigate the relation between input-independent factors (initial pollutant concentration, contact time, FADA dosage and pH) and one dependent output response (removal efficiency). The best model was selected based on the results of the ANOVA analysis.SO model due to R2 of 0.929 and the insignificant lack of fit (0.12) for cyanide and also R2 of 0.98 and the insignificant lack of fit (0.12) for palladium was selected as an appropriate model for adsorption of both pollutants. Therefore, prediction and optimisation of the adsorption of the pollutants onto FADAwere done based on SO model. The best conditions for the adsorption of cyanide (95.65%) and palladium (92.66%) onto FADA were obtainedat (pH, 5.45; palladium concentration, 15.13 mg L−1; contact time, 104.8 min and FADA dosage, 0.98 g L−1) and (pH,7.0; cyanide concentration, 4.88 mg L−1; contact time, 91.06 min and FADA dosage, 2.05 g L−1), respectively. Investigation of the non-linear isotherm models indicated adsorptions of cyanide (R2 = 0.995) and palladium (R2 = 0.999) ontoFADA have reasonably fit to the Sips model.The maximum adsorption capacities of cyanide and palladium per mass unit of FADA were 208.55 mg g−1 and 60.2 mg g−1, respectively.The pseudo-first-order (R2 = 0.99) and the intra-particle diffusion (R2 = 0.96) were found to agreement well with the adsorption experimental data obtained for cyanide and palladium, respectively. Results indicated the sorption reactions of cyanide and palladium onto FADA were endothermic and exothermic, respectively.The present study indicated diatomite magnano composite boosted with alginate polymer beads due to high operating groups and also a high surface-to-volume ratio and porosity can be applied as an efficient adsorbent for the removal of cyanide and palladium from aqueous solutions.

Reagent elution combined with positive pressure filtration: A zero-discharge method for cyanide tailings remediation

At present, the cyanide gold extraction process is still the main technology for gold production. Generated cyanide tailings containing highly toxic substances exhibit potential environmental risks. These tailings are in urgent need of purification treatment, especially after being classified as hazardous waste. In this study, the impacts of elution methods, operating time, tailings/water ratios, reagent types on the elution rates of cyanide were investigated. Furthermore, the composite elution method developed in this research was extended for engineering. Results showed that the optimum elution conditions were determined to be: stirring elution, tailings/water ratio (M/V; 1:1) and operating time (10-20 min). Besides, 4 reagents (sodium dodecyl benzene sulfonate, cyclodextrin, sodium silicate and calcium hydroxide) were selected from four categories of 21 reagents for further composite elution. The cyanide elution rate was the highest (90.7%±0.1%) while the molar ratio of these 4 reagents was 5:2:2:1. Moreover, the combination of reagent elution and positive pressure filtration improved the elution efficiency of cyanide (92.6%±0.8%). And the cyanide content in the toxic leaching solution was lower than the standard value (5.0 mg/L). Furthermore, the composite elution method developed in this study was also extended for engineering. The concentration of cyanide in the leachate was < 5.0 mg/L, and was stable during 189 days of detection. Notably, the effluent can be reused directly, or reused after further treatment. The zero discharge of effluents and solid wastes was realized in the processes. The above results provided supports for the engineering treatment of cyanide tailings.

An investigation for biogenic cyanide distillation for gold recovery and cyanide bioremediation by Bacillus megaterium

First time, we report the application of cyanide distillation process to selectively isolate biogenic cyanide (Bio-CN) generated by Bacillus megaterium for gold leaching, and to study the mechanism involved in the bioremediation of cyanide. We aimed to design a sustainable process for gold leaching that starts without chemical cyanide and ends with minimum hazardous waste. Results showed that Bio-CN generated by the bacteria reaches to 113 mg/L after 24 h. Baseline distillation experiments showed that almost entire cyanide from chemical solution (Chem-CN) is recoverable; however, only about 18% of the Bio-CN could be retrieved. Investigation about bioremediation property of B. megaterium at different ratios of Bio-CN and Chem-CN suggested that the presence of bacteria have negligible effect on cyanide conversion while the enzymes generated through bacteria activity play role in reducing the concentration of cyanide from expected concentration of 105 mg/L to less than 29 mg/L. Hydrolytic and substitution pathways are suggested as the main mechanisms of cyanide conversion/remediation by the bacteria. Potentiometric titration using AgNO3 was used to analyze the cyanide concentration and findings are also supported by UV–visible technique. Distillation experiments by using mixture of Bio-CN and Chem-CN solutions suggested that the partial recovery of cyanide could be associated with the complexation of CN with the organic materials in the biogenic solution, which needs further study. At similar cyanide concentration i.e., 15 mg/L, gold recovery from distilled cyanide (3.22 mg/L) was as high as from Chem-CN (3.15 mg/L), suggesting the successful functionality of distilled cyanide in gold leaching.

Spatial distribution, risk assessment, and source identification of pollutants around gold tailings ponds: a case study in Pinggu District, Beijing, China

This work investigated heavy metal and cyanide pollution in surface soils and edible plants around Yanzhuang gold tailings ponds in the region of Yanzhuang Village in Pinggu District, Beijing. Surface soil samples were collected from 33 sites around gold tailings ponds, and concentrations of seven heavy metals (i.e., Sb, As, Cd, Cu, Pb, Zn, and Hg) and cyanide were analyzed to determine their spatial distributions, pollution degrees, and sources. The potential ecological risks of As, Cd, Cu, Pb, Zn, and Hg were preliminarily assessed. The results showed that the mean cyanide, Sb, As, Cd, Cu, and Pb concentrations were higher than the standard values. The pollutant concentrations around the tailings ponds were high and decreased with increasing distance from the ponds. The single pollution index indicated that cyanide, As, and Cd were the main pollutants. The Nemerow pollution index revealed a large region and serious degree of heavy metal pollution in soils. The potential ecological risk level of the study area was moderate, with Cd and As posing the main risks. Multivariate statistical analysis suggested that the heavy metal and cyanide pollution present mainly derived from gold tailings, with agricultural pollution also had a certain effect. However, the 12 edible plants sampled were basically not polluted.

Performance of Full-Scale Thermophilic Membrane Bioreactor and Assessment of the Effect of the Aqueous Residue on Mesophilic Biological Activity

To date, the management of high-strength wastewater represents a serious problem. This work aims to evaluate the performance on chemical pollutants and on sludge production of one of the two full-scale thermophilic membrane bioreactors (ThMBRs) currently operational in Italy, based on monitoring data of the last two and a half years. Removal yields on COD, N-NOx, non-ionic and anionic surfactants (TAS and MBAS), increased with the input load up to 81.9%, 97.6%, 94.7%, and 98.4%, respectively. In the period of stability, a very low value of sludge production (0.052 kgVS kgCOD−1) was observed. Oxygen uptake rate (OUR) tests allowed us to exclude the possibility that mesophilic biomass generally exhibited any acute inhibition following contact with the aqueous residues (ARs), except for substrates that presented high concentrations of perfluoro alkyl substances (PFAS), cyanides and chlorides. In one case, nitrifying activity was partially inhibited by high chlorides and PFAS concentration, while in another the substrate determined a positive effect, stimulating the phenomenon of nitrification. Nitrogen uptake rate (NUR) tests highlighted the feasibility of reusing the organic carbon contained in the substrate as a source in denitrification, obtaining a value comparable with that obtained using the reference solution with methanol. Therefore, respirometric tests proved to be a valid tool to assess the acute effect of AR of ThMBR on the activity of mesophilic biomass in the case of recirculation.

Interfacing the enzyme multiheme cytochrome c nitrite reductase with pencil lead electrodes: Towards a disposable biosensor for cyanide surveillance in the environment

The present study reports a novel voltammetric biosensor for cyanide based on its inhibitory effect on cytochrome c nitrite reductase (ccNiR). Interestingly, the earlier development of a point-of-care test for nitrite based on the direct electrochemistry of ccNiR has shown that the cyanide inhibition depends on the type of carbon material employed as transducer (Monteiro et al., 2019). In this work, commercial graphite pencil leads were employed in the construction of both working and pseudo-reference electrodes, with ccNiR being simply drop casted onto the former. In this way, we produced a functional and fully integrated voltammetric biosensor for nitrite quantification that also allows to observe a decrease in the catalytic current due to cyanide addition. Under turnover conditions, the biosensor showed a linear response with the logarithm of cyanide concentration in the 5–76 μM (cyclic voltammetry) and 1–40 μM (square-wave voltammetry) ranges, with a sensitivity of 20–25% ln [cyanide μM]−1 and a detection limit of 0.86–4.4 μM. The application of the pencil lead as a putative pseudo-reference was very promising, since the potentials profile matched those observed with a true reference electrode (Ag/AgCl).Overall, the direct electron transfer between ccNiR and a pencil lead electrode was demonstrated for the first time, with cyanide-induced inhibition being easily monitored, paving the way for the employment of these low-cost bioelectrodes as cyanide probes for on-site surveillance of aquatic environments.

Aggregation-induced Fluorescent Response of Urea-bearing Polyphenyleneethynylenes toward Anion Sensing

A π-conjugated urea-bearing phenyleneethynylene polymer (Poly-2) was rationally designed by the Sonogashira coupling condensation reaction and had been demonstrated to have a unique fluorescent quenching effect for optical detection of all determined anions, especially for selectively probing cyanide anion (CN−). The fluorescent emission of Poly-2 was significantly quenched upon adding CN−, together accompanying with a continuous red-shift of the emission peak from 442 nm to 464 nm with the cyanide concentration increased from 0 to 1.0 mM. On the contrary, its precursor polymer, Poly-1, itself also displayed fluorescent responsibility with all selected anions, but had no obvious selectivity and tendency. For instance, the addition of highly basic CN−, N3 −, AcO−, or F− to Poly-1 solution in DMF/H2O (v/v = 1:1) led to the photoluminescence amplification, while the addition of weakly basic anions like Cl−, I−, and Br− showed a fluorescence quenching effect. Both polymers were in a seriously self-aggregated state in solution no matter in absence or presence of an anion. Interestingly, it was found that Poly-2 exhibited an aggregation-induced emission (AIE) behavior, while Poly-1 had an aggregation-caused quenching (ACQ) effect, based on the relationship between photoluminescence and polymer aggregation state. The structural characterizations of the polymers together with monomers were carried out by NMR spectroscopy and SEC measurements, the photoluminescence properties of Poly-1 and Poly-2 together with anion sensing properties were followed by fluorescence spectroscopy, and relationship between photoluminescence and aggregation behavior of both polymers in solution was investigated by dynamic light scattering (DLS) measurements. This study provided a novel π-conjugated polymer design bearing urea functional groups for anion sensing and especially selective for cyanide detection.

Predicting the capability of diatomite magnano composite boosted with polymer extracted from brown seaweeds for the adsorption of cyanide from water solutions using the response surface methodology: modelling and optimisation

ABSTRACT The rate of cyanide reduction in the aqueous solutions by adsorption onto the diatomite magnano composite boosted with alginate polymer beads (DMBA) was evaluated. The R software using RSM was used as an experimental technique to design a statistical equation. Based on statistical results obtained, second order model due to insignificant lack of fit (0.12) and the higher value of correlation coefficient (0.92) was selected as a suitable model to design of the adsorption process. Based on the stationary points, the maximum adsorption of cyanide (98.11%) was achieved under selected conditions (initial cyanide concentration, 4.88 mg L−1; contact time, 91.06 min and DMBA dosage, 2.05 g L−1). The Sips nonlinear model indicated the best compatibility with the experimental data. It was found to be a successful model for predicting the heterogeneity of surfaces. The maximum adsorption capacity of cyanide onto DMBA was determined 208.55 mg g−1. The pseudo-first-order model was found to agree well with the adsorption experimental data obtained for cyanide. The thermodynamic data revealed the spontaneous sorption and endothermic for the adsorption of cyanide onto DMBA.

Alkaline-extracted cyanide from cassava wastewater and its sole induction of chromosomal aberrations in Allium cepa L. root tips

ABSTRACT Cassava, a staple crop in Nigeria, processed by numerous factories in rural and suburban locations is known to contain some level of cyano compounds. Lack of stringent environmental regulations on the management of cassava wastewater (CWW) from cassava-processing factories had led to its indiscriminate discharge on the environment. CWW samples were obtained from cassava-processing factories from selected states (Lagos (A), Oyo (B), Ogun 1 (C1), Ogun 2 (C2) and Cross River (D)) in Nigeria to determine the cytotoxic and genotoxic effects of extracted cyanide from the wastewaters. The cyanide was hydrolysed via chemical degradation utilizing 1.25 M NaOH and subsequently titrated using silver nitrate with p-dimethylaminobenzalrhodamine as indicator. Further, in order to explore the potential toxicity of this pollutant present in the effluent, a battery of short-term biological assay (Allium cepa chromosomal aberration test) was used. Bulbs with roots of Allium cepa L. were treated with different concentrations (0.05%, 0.1%, 0.2%, 0.4% and 0.8%) of CWW, and after 48 h, the root tips were processed for cytological studies by the aceto-orcein squash procedure. The results revealed that cyanide concentrations on re-fluxing were in the range of 1.0 and 1.3 mg/L. All concentrations induced a number of chromosomal aberrations in the root tip cells. The mitotic index decreased significantly (p < 0.05) with increasing concentration. The cytotoxic effects showed strong concentration-dependent root growth inhibition with EC50 values of 30%, 20%, 37%, 43% and 22% for A, B, C1, C2 and D, after 72 h. The findings thus indicate that alkali treatment is very efficient in degrading the cyanide content of CWW and has shown that the combination of physico-chemical analysis along with the sole toxicity assessment could provide valuable information about the sole toxicity of cyanide as a chemical pollutant present in the cassava effluent.

A TiO2 Nanotube-Based Sensor for the Detection of Cyanide in Water

Cyanide is an acutely toxic compound capable of reducing or eliminating oxygen utilization in living organisms on exposure. Natural and industrial processes contribute to the presence of cyanide in the environment. However, the concentrated nature of industrial-process-derived cyanide calls for greater attention. The ability to bind to other compounds makes cyanide capable of spreading to ground and surface waters more easily than other industrial contaminants. Cyanide concentrations in waste waters need monitoring to ensure that they are within permissible levels. Furthermore, cyanide is an essential reagent in some processes, and thus tracking of cyanide concentrations in the process line is essential. Real-time monitoring of cyanide concentrations calls for a robust and quick method for detection of cyanide concentrations in water. As such, this work focuses on the application of titanium dioxide (TiO2) nanotubes for the sensitive and selective electrochemical detection of cyanide in water. The TiO2 nanotubes were modified by the addition of iron (Fe) and sulfur (S) to the nanotube structures. Characterization of the prepared sensing electrode was carried out using X-ray diffraction and electron microscopy. Electrochemical sensing of the cyanide in water was performed using a three-electrode system with an Fe-S-TiO2 working electrode. Cyclic voltammetry was used to establish the sensing of the cyanide species as well as the response to cyanide concentration in water. Chronoamperometry was used to test the effect of interfering species as well as the sensor sensitivity, with an observed current response to a 0.1μM change in cyanide concentration. The sensor response indicated that an Fe-S-TiO2 sensing electrode could effectively be used for the sensing of cyanide concentrations lower than the recommended limits in water, and with good sensing electrode reusability.

TiO2 Nanotube-Based Sensor for the Detection of Cyanide in Water

Cyanide is an acutely toxic compound capable of spreading to ground and surface waters more easily than other industrial contaminants. Real-time monitoring of cyanide concentrations calls for a robust and quick method for cyanide detection in water. This work focuses on the application of anodized titanium dioxide (TiO2) nanotubes as a substrate, with suitable and relatively inexpensive additives, for the sensitive and selective electrochemical detection of cyanide in water. The TiO2 nanotubes were modified by the addition of iron (Fe) and sulfur (S) as sensing elements. Characterization of the prepared sensing platform was performed using X-ray diffraction and electron microscopy. Current-time measurements indicated that i) increasing cyanide concentration can perturb the current proportionally, ii) the differential in the current can be used as a calibration for quantitative detection of cyanide, and iii) the sensor is highly selective even in the presence of interfering species. A cyanide detection limit of 0.49 μM and a sensitivity of −13.8 mAcm−2 μM−1 were established. The sensor response indicated that an Fe-S-TiO2 nanotube sensing electrode could effectively and repeatedly be used over a period of several months for the sensing of cyanide concentrations lower than the recommended WHO and USEPA limits in water.

Hydrometallurgical Processing of Gold-Containing Ore and its Enrichment Products

This research focuses on the hydrometallurgical processing of auriferous ores and their processing products, namely, flotation and gravity concentrates. The main valuable component of an ore sample of any deposit is gold. The gold content should be in the range of 11.11–12.87 g/ton. The main rock-forming minerals of the original ore are quartz (60.1%), quartz–chlorite–micaceous aggregates (3.8%), and carbonates (7.1%). In this study, original ores of various sizes were treated by direct and sorption cyanidation under various leaching modes, and the results obtained were presented. The original ore was leached with various concentrations of sodium cyanide (NaCN) in solution to study the effect of the complexing agent concentration on gold recovery. Data on the dynamics of leaching revealed that a decrease in the concentration of NaCN in solution from 0.2% to 0.03% leads to a decrease in gold recovery in solution by 26.81%. Original ores could easily be processed using hydrometallurgical methods. The recovery of gold with a coarseness of 95% − 0.045 mm from the original ore averaged 97.77%. This work features a full range of studies on the hydrometallurgical processing of concentrates and gravity tailings, as well as the effects of flotation concentration of gold recovery. The gravity concentrate is resistant to intensive cyanidation (i.e., only 67.07% gold recovery into the solution). The use of 1% lead nitrate (PbNO3) during intensive cyanidation could reduce the refractoriness of the concentrate and increase the recovery of gold into the solution by up to 94.35%. The total gold recovery from gravity concentrate is 98.71%, and the recovery of gold by cyanidation of gravity tailings with a cyanide concentration of 0.2% averages 96.57%. The recovery of gold during leaching of the flotation concentrate at the original size (95.5% − 0.074 mm) and a cyanide concentration of 0.2% is 96.64%. A decrease in the size of the flotation concentrate from 95.5% − 0.074 mm to 95% − 0.02 mm leads to a decrease in gold recovery by 35.43% because of the strong chemical activation of the material during grinding.

Detecting Effects of Low Levels of FCCP on Stem Cell Micromotion and Wound-Healing Migration by Time-Series Capacitance Measurement.

Electric cell–substrate impedance sensing (ECIS) has been used as a real-time impedance-based method to quantify cell behavior in tissue culture. The method is capable of measuring both the resistance and capacitance of a cell-covered microelectrode at various AC frequencies. In this study, we demonstrate the application of high-frequency capacitance measurement (f = 40 or 64 kHz) for the sensitive detection of both the micromotion and wound-healing migration of human mesenchymal stem cells (hMSCs). Impedance measurements of cell-covered electrodes upon the challenge of various concentrations of carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), from 0.1 to 30 μM, were conducted using ECIS. FCCP is an uncoupler of mitochondrial oxidative phosphorylation (OXPHOS), thereby reducing mitochondrial ATP production. By numerically analyzing the time-series capacitance data, a dose-dependent decrease in hMSC micromotion and wound-healing migration was observed, and the effect was significantly detected at levels as low as 0.1 μM. While most reported works with ECIS use the resistance/impedance time series, our results suggest the potential use of high-frequency capacitance time series for assessing migratory cell behavior such as micromotion and wound-healing migration.

Old Poison, New Problem: Cyanide Fatal Intoxications Associated with Internet Shopping.

Widespread access to the Internet has an increasing influence on how suicides are committed. On websites such as eBay® or Amazon.com® highly toxic substances including cyanides are available for purchase. In the last 5 years, a few fatal intoxications associated with Internet shopping and buying "suicide kits" have been reported. Epidemiology of intoxications reported by American Association of Poison Control Centers between 2000-2018 shows that about 10% of all exposures to cyanide were related to suicide attempts and intentional ingestion of this substance. In order to determine the cyanide concentration in four fatal intoxication cases associated with Internet shopping, a headspace gas chromatography with dual column/dual flame ionization detector (HS-GC-FID/FID) method was validated and applied to casework. The method was linear in range, from 1 to 50 µg/mL, with a coefficient of determination of 0.999 (R2). The limit of quantification was 1.0 µg/mL; the detection limit was 0.5 µg/mL. Intra- and inter-day validation precision and accuracy did not exceed 10% and 15%, respectively. Recovery and matrix effect values ranged from 94.8- 103.8% and -5.2─3.8%, respectively. The cyanide concentrations were determined in biological fluids (blood, urine, bile, vitreous humor, gastric content) and postmortem tissue samples (spleen, kidney, liver, brain). The headspace gas chromatographic method, which is routinely used in clinical and forensic toxicology to quantify ethanol with its congeners (methanol, acetone, isopropanol, n-propanol and n-butanol), can be also applied to determine cyanide in intoxication cases. The global problem of a high number of suicides each year, requires increasing and more restrictive control of highly toxic substances available online as well as caution monitoring of human exposure to cyanide. This old and well known poison is being increasingly used nowadays for suicidal purposes, therefore determination of cyanide in biological samples is still important in terms of clinical and forensic toxicology.

Quantification of Active Site Density and Turnover Frequency: From Single-Atom Metal to Nanoparticle Electrocatalysts.

Single-atom catalysts (SACs) featuring atomically dispersed metal cations covalently embedded in a carbon matrix show significant potential to achieve high catalytic performance in various electrocatalytic reactions. Although considerable advances have been achieved in their syntheses and electrochemical applications, further development and fundamental understanding are limited by a lack of strategies that can allow the quantitative analyses of their intrinsic catalytic characteristics, that is, active site density (SD) and turnover frequency (TOF). Here we show an in situ SD quantification method using a cyanide anion as a probe molecule. The decrease in cyanide concentration triggered by irreversible adsorption on metal-based active sites of a model Fe–N–C catalyst is precisely measured by spectrophotometry, and it is correlated to the relative decrease in electrocatalytic activity in the model reaction of oxygen reduction reaction. The linear correlation verifies the surface-sensitive and metal-specific adsorption of cyanide on Fe–Nx sites, based on which the values of SD and TOF can be determined. Notably, this analytical strategy shows versatile applicability to a series of transition/noble metal SACs and Pt nanoparticles in a broad pH range (1–13). The SD and TOF quantification can afford an improved understanding of the structure–activity relationship for a broad range of electrocatalysts, in particular, the SACs, for which no general electrochemical method to determine the intrinsic catalytic characteristics is available.