Decomposition Of Cyanide Research Articles

Photoelectrocatalytic Degradation of Cyanide Using TiO2 on Conducting Glass and Polarographic Analysis of the Products

Cyanide used in gold mines is collected in tailing dams and has a high risk of contaminating the surrounding environment. Cyanide contaminations in the atmosphere, as well as in water and soil are insufficiently studied so far. The lack of interest, the complexity of the reaction mechanisms and the challenging analysis of the products are major reasons for this deficiency. The circumstance that a prominent part of cyanide is volatilsed during and after the gold extraction is often neglected; volatalised HCN is said to be sufficiently destroyed by the sunlight and the oxygen of the atmosphere which can easily be disproved by analysis of the cyanide content in the contaminated atmosphere. The investigation of the products of cyanide decomposition is an essential part in the evaluation of the toxicity originating from effluents of gold processing. In this work, spray pyrolysed TiO2 on conducting glass is used for the photoelectrocatalytic treatment of cyanide. In UV-A irradiating the catalyst and applying an external bias for the separation of the charge carriers, the cyanide is oxidised in solutions of different pH. The cyanide content after the process as well as the quantity of the products is analysed via polarography. Besides the oxidation, hydrolysis was detected as well, correlating to the pH of the solutions. The proposed method allows the evaluation of the level of environmental contamination of gold processing as well as the analysis of products that result from decontamination processes in gold mines. Furthermore the photocatalytic capability of TiO2 for the decontamination of cyanide wastewaters is determined.

Experimental analysis on cyanide removal of gold tailings under medium-temperature roasting

The cyanide content of gold tailings exceeds the standard seriously due to the cyanide extraction process. In order to improve the resource utilization efficiency of gold tailings, a medium-temperature roasting experiment was carried out on the stock tailings of Paishanlou gold mine after washing and pressing filtration treatment. The thermal decomposition rule of cyanide in gold tailings was analyzed, and the effects of different roasting temperatures and roasting durations on cyanide removal efficiency were compared. The results show that when the roasting temperature reaches 150 °C, the weak cyanide compound and free cyanide in the tailings begin to decompose. When the calcination temperature reached 300 °C, the complex cyanide compound began to decompose. When the roasting temperature reaches the initial temperature of cyanide decomposition, the cyanide removal efficiency can be improved by prolonging the roasting time. After roasting at 250–300 °C for 30–40 min, the total cyanide content in the toxic leachate decreased from 3.27 to 0.01 mg/L, which met the water quality standard of III class in China. The research results provide a low-cost and efficient way for cyanide treatment, which is of great significance for promoting the resource utilization of gold tailings and other cyanide-containing wastes.

Study on ultrasonic enhanced ozone oxidation of cyanide-containing wastewater

Gold smelting wastewater contains cyanide ions and copper ions, which may cause potential risks to the environment. In this study, a new ultrasonic enhanced ozone (US/O3) oxidation method was developed for the comprehensive treatment of cyanide-containing wastewater, destruction of cyanide and further recovery of copper. The cyanide removal rate and copper recovery rate reached 99.96 % and 99.3 % under the optimum conditions of ozone flow rate of 80 L/h, temperature of 25 °C, reaction time of 15 min and ultrasonic power density of 80 W/L, respectively. The dried sediment was characterized by XRD, SEM and particle size analysis, the results showed that the dry sediment was Cu slag. The experimental results were in accordance with the pseudofirst-order kinetic model with apparent rate constants of 0.1662 L/(mg·min) and 0.2056 L/(mg·min) for ozone oxidation and ultrasonic enhanced ozone (US/O3) oxidation, respectively. The mechanism of ultrasonic enhanced ozone was studied by FT-Raman, FT-IR, EPR and Gas chromatography. Ultrasonic enhanced ozone (US/O3) oxidation process for treatment of cyanide containing wastewater is characterized by rapid and complete decomposition of cyanide in wastewater and efficient recovery of valuable element copper.

Solidification/stabilization of spent cathode carbon from aluminum electrolysis by vitric, kaolin and calcification agent: fluorides immobilization and cyanides decomposition.

Spent cathode carbon (SCC) is a hazardous waste containing fluorides and cyanides from aluminum electrolysis. Many literatures have focused on SCC leaching; however, SCC hazard-free treatment remains understudied. This article used 10.0 g raw SCC sample to explore the vitric/kaolin solidification and calcium stabilization of SCC, and analyze their hazard-free mechanisms by the methods of XRD and SEM. The leached fluorides were all below the Chinese identification standard for hazardous wastes (GB5085.3-2007), whether at 750/950 °C for 60 min above 8.0 g vitric, or at 1200 °C for 120 min with above 8.0 g kaolin, or above 700 °C for more than 30 min with above 0.5 g CaCO3. Kaolin/vitric solidification relied on the massive addition of vitric and kaolin to produce glassy or glass-like material (K2O·Al2O3·6SiO2) which may retain fluoride. Calcium stabilization converted soluble fluoride NaF in raw SCC sample into insoluble CaF2. Heating 60 min at 500-1200 °C at oxygen atmosphere decomposed almost of cyanides, with leached cyanides meeting Chinese standard GB5085.3-2007. Mass-loss rates of kaolin addition came from a large amount of adsorbed water and structural water in kaolinite and illite wai lost, and that of CaCO3/CaSO4 addition was attributed to their decomposition into volatile CO2/SO2, while that of CaO was a little negative due to its absorption of water vapor and CO2. In brief, as the effective hazard-free manner of SCC, both kaolin/vitric solidification and calcium stabilization successfully have achieved fluoride immobilization and cyanide decomposition.

Efficient separation of fluoride and graphite carbon in spent cathode carbon from aluminum electrolysis by mechanical activation assisted alkali fusion treatment

Spent cathode carbon (SCC) is the largest and most inevitable hazardous solid waste continuously discharged from the aluminum electrolysis industry. In this study, mechanical activation was used to assist alkali fusion treatment in dissociating toxic substances and recovering graphite carbon from SCC. The effect of mechanical activation (i.e., milling speed, ball-to-material mass ratio, and milling time) on the alkali fusion treatment was investigated. Its effect on the physicochemical properties of SCC–Na2CO3 mixtures was also analyzed through particle size distribution, Brunauer-Emmett-Teller surface area analysis, scanning electron microscopy, X–ray diffraction and thermogravimetric analysis–differential scanning calorimetry. Results showed that mechanical activation enhanced the alkali fusion treatment by improving the physical separation of fluoride, the mixing uniformity and reaction contact area of SCC and Na2CO3, and promoting the conversion of Na2CO3 to Na2O. The formation of agglomerates was the main reason that the carbon content of recovered graphite carbon and the fluoride ion leaching rate increased initially then decreased with the increment in mechanical activation conditions. Under optimal mechanical activation conditions, the carbon content of recovered graphite carbon and the fluoride ion leaching rate increased from 89.35% and 76.50% (non-activated sample) to 93.93% and 95.02%, respectively, indicating that mechanical activation assisted alkali fusion treatment effectively enhanced the separation efficiency of fluoride and graphite carbon. In addition, thermodynamic analysis of the alkali fusion treatment and characterization of recovered graphite carbon (under the optimal mechanical activation conditions) were performed. Results demonstrated that the simultaneous conversion of multiple fluorides (i.e., Na3AlF6 and CaF2) and oxidative decomposition of cyanide in SCC can be achieved via mechanical activation assisted alkali fusion treatment. These findings indicate that mechanical activation–assisted alkali fusion treatment is a promising method for the detoxification and utilization of SCC.

Decomposition of Cyanide from Gold Leaching Tailingsby Using Sodium Metabisulphite and Hydrogen Peroxide

Cyanidation is widely used by most gold mine worldwide and will remain prevail in years (or decades) to come, while cyanide is hazardous, toxic pollutants whose presence in wastewater and tailings can seriously affect human and its environment; hence, it is necessary to control these contaminants. The purpose of this study was to examine the effects through the investigation of changes in pH, concentration, and contact time, and the optimal conditions were obtained. It has been proven that the decomposition of cyanide in solution and tailings increased as the alkalinity in the presence of 0.5 g/L Na2S2O5. An increase in H2O2 (30%) concentration (from 1 to 4 mL/L) increased the decomposition in solution, while the effect on removing cyanide was better when pH was 9 than 8 and 10 in tailings. The cyanide in tailings decreased in the first 4 h and increased after 4 h. The effective and economic conditions for maximum decomposition of cyanide from leach tailings are first treated in 0.5 g/L Na2S2O5 at pH 10 for 3 hours and then 2 mL/L H2O2 (30%) is added to the tailings at pH 9 for 4 hours through comparative study. The findings provide the basis to optimize the decomposition of cyanide from gold leaching tailings in mining or backfilling by using the synergetic effect of Na2S2O5 and H2O2.

English

Cyanide is a very toxic substance, which occurs in various forms in environmental matrices and its determination requires a good extraction method. From the reference method of cyanide distillation by reflux heating under acidic conditions and entrainment of HCN gas collected as CN- ions with detection by UV-Visible spectrophotometry, an improved and complete procedure for total cyanide extraction in aqueous and solid matrices has been developed. The best conditions after optimization of complete recovery (≃ 100%) of total cyanide and elimination of interferences in natural waters and soils fortified are: heating at 181.75°C, saving of reflux time to 30 min, sulfuric acid concentration of 0.6 M, 2 to 4 times less acid, without catalyst and other special treatments of interferences relatively to existing techniques. Application to water samples (drinking, surface, underground) and effluents collected at the Samira gold mine (Niger) and its environs shows the impact of distillation extraction on total cyanide recovery. Waters, exempt of cyanide at the starting of mining activity, currently contain total cyanide contents of 1 to 5 μg L-1 and in effluents up to 37 times the discharge standard (1 mg L-1). Key words: Cyanide decomposition, distillation extraction, environmental matrices, Samira gold mine (Niger).

Degradation mechanism of cyanide in water using a UV-LED/H2O2/Cu2+ system

In this study, we developed a UV-LED/H2O2/Cu2+ system to remove cyanide, which is typically present in metal electroplating wastewater. The results showed the synergistic effects of UV-LED, H2O2, and Cu2+ ions on cyanide removal in comparison with UV-LED photolysis, H2O2 oxidation, UV-LED/H2O2, and H2O2/Cu2+ systems. Cyanide was removed completely in 30 min in the UV-LED/H2O2/Cu2+ system, and its loss followed pseudo-first order kinetics. Statistically, both H2O2 and Cu2+ ions showed positive effects on cyanide removal, but Cu2+ ions exhibited a greater effect. The highest cyanide removal rate constant (k = 0.179 min−1) was achieved at pH 11, but the lowest was achieved at pH 12.5 (k = 0.064 min−1) due to the hydrolysis of H2O2 (pKa of H2O2 = 11.75). The presence of dissolved organic matter (DOM) inhibited cyanide removal, and the removal rate constant exhibited a negative linear correlation with DOM (R2 = 0.987). The removal rate of cyanide was enhanced by the addition of Zn2+ ions (from 0.179 to 0.457 min−1), while the co-existence of Ni2+ or Cr+6 ion with Cu2+ ion reduced cyanide removal. The formation of OH radicals in the UV-LED/H2O2/Cu2+ system was verified using an aminophenyl fluorescence (APF) probe. Cyanate ions and ammonia were detected as the byproducts of cyanide decomposition. Finally, an acute toxicity reduction of 64.6% was achieved in the system within 1 h, despite a high initial cyanide concentration (100 mg/L). In terms of removal efficiency and toxicity reduction, the UV-LED/H2O2/Cu2+ system may be an alternative method of cyanide removal from wastewaters.

Photocatalytic decomposition of cyanide in pure water by biphasic titanium dioxide nanoparticles

Cyanide found in industrial wastes is among the critical environmental issues. The purpose of this research was to investigate the effects of various operating parameters, such as cyanide initial concentration, hydrogen peroxide dosage, amount of catalyst, UV light intensity and acidity on the photocatalytic degradation of cyanide using TiO2 nanoparticles. The characterization of synthesized nanoparticles was also conducted using X-ray diffraction, and transmission electron microscopy techniques. Biphasic form of TiO2 nanoparticles indicated the maximum removal yield and complete degradation of cyanide. Increase in initial concentration of cyanide causes decrease in removal yield. The complete removal of cyanide was achieved with dose of 3 mg L−1 in 45 min, while lasting for 90 min without H2O2 degradation process. In addition, at pH 11 and catalyst content of 1 g L−1, the maximum cyanide removal was observed. The efficiency of cyanide removal can be affected by various operating parameters. Increasing cyanide concentration resulted in decreasing removal rate of cyanide, as for concentrations 15 and 100 ppm cyanide was completely degraded during 10 and 90 min, respectively. Moreover, for cyanide degradation, the optimum TiO2 content and pH were determined as 1 g L−1 and 11, respectively. Furthermore, the efficiency of removal process corresponds with the increased UV lamp irradiation and H2O2 dosage.

Wet oxidation characteristics of metal cyanide complexes below 423 K

In the present study, the wet oxidation of zinc and copper cyanide complexes (cyanide concentration of 1,000 mg dm-3) was conducted in a hydrothermal reactor, under oxygen atmosphere of which the pressure was set to 1 MPa. The pH of the reaction solution was kept in the range of 11 to 12 and the reaction temperature was changed from 383 K to 423 K. In the experiments, mainly the effect of reaction time on the cyanide decomposition was investigated. As a result, it was found that cyanide decomposition increased with an increase in the temperature and cyanide decompositions of 99.9 % and 96.1 % were achieved after 8 hours at 423 K for Na2[Zn(CN)4] and Na3[Cu(CN)4], respectively. In the case of Na2[Zn(CN)4], mainly HCOO- and NH4+ were identified as the decomposition products. By contrast, in the case of Na3[Cu(CN)4], carbon of CN- was transformed either to H2CO3 or HCOO-, and nitrogen was converted to NH4+, N2 or NO2-. Based on these results, the decomposition mechanisms of Na2[Zn(CN)4] and Na3[Cu(CN)4] at a temperature of 423 K and pressure of 1 MPa were discussed.

Decomposition of gaseous HCN in the presence of Ni-containing catalysts

This work is devoted to the decomposition of gaseous HCN by oxidation with air catalyzed by different nickel containing catalysts. The presence of metallic nickel does not cause the decomposition of cyanide at 400 °C, but NiO, electrochemical prepared nickel oxides Ni2O3·xH2O and (β,γ)-NiOOH exhibit distinctly high catalytic activity at this temperature. The effect of HCN decomposition for electrochemically prepared nickel oxides was over 90 %. Nickel deposited on activated carbon also demonstrated catalytic behavior during the destruction of HCN with an air mixture at the temperature 400 °C. Nickel oxide mixed with activated carbon showed a small increase of catalytic activity in the destruction of HCN in comparison with NiO.

Mechanism and Kinetics of Cyanide Decomposition by Ferrate

Abstract The mechanism of cyanide oxidation by ferrate in water is discussed using DFT computations in the framework of the polarizable continuum model. The reactivity of three oxidants, nonprotonated, monoprotonated, and diprotonated ferrates is evaluated. This reaction is initiated by a direct attack of an oxo group of ferrate to the carbon atom of cyanide, followed by an H-atom transfer from cyanide to another oxo group to lead to an intermediate having cyanate (NCO−) as a ligand. The produced cyanate is oxidized by an oxo ligand of ferrate and exogenous oxygen molecule to CO2 and NO2−. The initial C–O bond formation is found to be the rate-determining step in this reaction. The activation energy for the C–O bond formation is 51.9 kJ mol−1 for nonprotonated ferrate, 44.4 kJ mol−1 for monoprotonated ferrate, and 41.4 kJ mol−1 for diprotonated ferrate, which indicates that the oxidizing power of the three oxidants is in the order of nonprotonated ferrate < monoprotonated ferrate < diprotonated ferrate. The general energy profile for cyanide oxidation by ferrate is downhill toward the product direction after the C–O bond formation, so cyanide is readily converted to the final products in water. The reaction kinetics of this reaction are analyzed from the calculated energy profile and experimentally determined pKa values.

Photocatalytic oxidation of cyanide in aqueous titanium dioxide suspensions: Effect of ethylenediaminetetraacetate

The kinetics of the photocatalytic oxidation of cyanide in aqueous TiO 2 suspensions was investigated as a function of catalyst loading (0.1–5.0 g l −1), air-flow rate (0.2–1.1 l min −1), and the concentration of ethylenediaminetetraacetate, EDTA (0.4–40 mM) at pH 13.0. The cyanide oxidation rate did not vary with the TiO 2 loading while a slight increase in the degradation rate with an increase in the air-flow rate was found. Cyanate (NCO −) was the only product of the cyanide decomposition. The effect of EDTA on the photocatalytic oxidation of cyanide was examined at different molar ratios of EDTA to cyanide (0.1–10.5) by keeping the initial cyanide concentration at 3.85 mM. EDTA retarded the photocatalytic oxidation of cyanide and the decrease in the oxidation rate was not proportional to the molar ratio of EDTA to cyanide. The first-order rate constant, k (min −1) for the oxidation of cyanide in the presence of EDTA may be expressed as k = 3.38 × 10 −3 × ([EDTA]/[CN −]) −0.23. A mechanism of the oxidation of cyanide by a photocatalytic process in absence and presence of EDTA is presented.

Mechanistic studies on the decomposition of sodium cyanide in aqueous solution and in the solid state

The mechanism of the spontaneous decomposition of sodium cyanide in aqueous solution and in the solid state was studied by ion chromatography (IC), FT–Raman spectroscopy, gas chromatography/mass spectrometry (GC/MS), and carbon-13 nuclear magnetic resonance spectroscopy ( 13C NMR). In the aqueous solution, gradual decomposition of the cyanide to carbonate by a displacement reaction was observed. In the solid state, sodium cyanide was found to be stable when kept in dry air, however, it decomposed by the same mechanism as that in aqueous solution under non-dry conditions.

Synthesis of Tetraoctylammonium-Protected Gold Nanoparticles with Improved Stability

This paper shows that an introduction of thiosulfate anions in place of bromide anions greatly improves both chemical and thermal stability of tetraoctylammonium-protected gold nanoparticles. Tetraoctylammonium thiosulfate [(Oct)4N+-O3SS]-protected gold nanoparticles are synthesized by the reduction of (Oct)4N+-AuCl4 to Au(I)-SSO3-, followed by the addition of sodium borohydride. The presence of thiosulfate anions instead of bromide anions on the surface of gold nanoparticles results in a significant dampening of the surface plasmon band of gold at 526 nm due to the strong interaction between thiosulfate and the gold nanoparticle surface. Cyanide decomposition and heating treatment studies suggest that (Oct)4N+-O3SS-protected nanoparticles have much higher overall stability compared to (Oct)4N+-Br-protected gold nanoparticles.

Elution and decomposition of cyanide in soil contaminated with various cyanocompounds

Standard soil samples contaminated with various standard cyanocompounds were prepared. Column elution experiments and analyses were conducted. Compounds with an easy capacity for dissociation to ions, such as KCN and potassium hexacyanoferrate(III), were found to be eluted by forming free cyanide even in fresh water. Hexacyanoferrate(II) salts, such as potassium hexacyanoferrate(II) and iron(III) hexacyanoferrate(II), were found not to be dissociated in water, but were dissociated and diffused under alkaline conditions (pH >13). Hexacyanoferrate(II) ion was found to be more easily dissociated in water with a higher pH. Column tests as above were also conducted for soil samples taken from a former paint ink factory using iron(III) hexacyanoferrate(II), cyanogen chloride, potassium cyanate, copper cyanide, as well as potassium cyanide, as raw materials. It was demonstrate that iron(III) hexacyanoferrate(II) was dissociated and eluted under alkaline conditions. The elution rate was reduced when the contaminated soil was sandwiched with standard soil layers. Further, it was found that the Fe(CN) 6 4− ion eluted with NaOH from hexacyanoferrate acid in soil, were easily decomposed into cyanic acid or other byproducts by UV with the addition of ozone and H 2O 2.

Thermal decomposition of Hofmann-type complexes of di- and triethanolamine

Thermal behaviour of Hofmann-type complexes of di- and triethanolamine with cobalt, nickel, copper and cadmium was studied in dynamic nitrogen atmosphere by DTA, DTG and TG techniques. The first decomposition stage corresponds to dehydration. Kinetic analysis of dehydration data indicates that dehydration follows a low energetic process. Subsequently, release of di- or triethanolamine takes place to form bimetallic cyanides as intermediates and the final decomposition stage is the decomposition of cyanide to yield the respective metals.

4-Hydroxythiophenol-Protected Gold Nanoclusters in Aqueous Media

Gold nanoclusters protected by a monolayer of 4-hydroxythiophenol (HOPhSAu MPCs) were synthesized and characterized by various analytical techniques. The particles were found to be soluble in alkaline aqueous solutions, whereas at low pH, flocculation of particles started to occur. Acid/base titration of particle solutions indicated that the pKa of particle-bound phenol moieties was close to 10, about 1 unit higher than that of free monomers (ca. 8.9). Transmission electron microscopy (TEM) was employed to measure the average particle size (ca. 5 nm) and size dispersity (ca. 30%), where the resulting size histograms exhibited two major populations centered around 6 and 4 nm. Upon decreasing solution pH, partial fractionation was effected, with smaller particles showing a higher solubility at lower pH. UV−vis spectroscopic measurements showed a surface-plasmon band at about 530 nm in various organic media. The red-shift of this band, relative to that of alkanethiolate or arenethiolate MPCs, might be due to particle flocculation as well as the electronic interactions between the phenyl moiety and the gold core that were facilitated by the hydroxy functional groups. In aqueous solutions, the surface-plasmon band position shows a slight red-shift with decreasing solution pH, and the absorption intensity monitored at this position exhibited a titration-like pH-dependent feature. A cyanide decomposition study of these particles showed a rather rapid rate constant, which might be ascribed to the enhanced partition of cyanide into the aromatic monolayers. Electrochemical studies of an aqueous solution of HOPhSAu particles and self-assembled monolayers of HOPhSH on a gold electrode surface both exhibited a pair of (quasi)reversible voltammetric waves, where the peak position shifted cathodically with increasing solution pH. A reaction mechanism was proposed which involved the formation of a carbonium intermediate in the electro-oxidation of the phenol moieties.

Biodegradation of phenols and cyanides using membranes with immobilized microorganisms

The immobilization of microorganisms on ultrafiltration membranes made from polyacrylonitrile modified chemically with hydrazine hydrate and glutaraldehyde and their application to the biodegradation of phenol and cyanide contained in industrial wastewaters was examined. Three types of microorganism isolated from a mixed population of activated sludge adapted to phenol and cyanide decomposition were immobilized. Simulated phenol and phenol-cyanide wastewaters with a concentration of xenobiotics equal to their concentration in coke sewage were subject to ultrafiltration. The membranes were operated at a pressure ranging from 0·5 × 10 5 to 2·5 × 10 5 Pa, at a constant temperature of 298 K and a constant stirring rate in the bioreactor of 250 rpm. The results obtained were characteristic of each immobilized strain. The membrane with a mixture of microorganisms from the strains Agrobacterium radiobacter, Staphylococcus seiuri and Pseudomonas diminuta immobilized on its surface appeared to be the most effective. The coefficients of phenol and cyanide biodegradation were 36 and 20·3%, respectively.

Immobilized enzyme membranes for phenol and cyanide decomposition

An attempt at biodegradation of the most toxic substances (phenols and cyanides) formed in the coke industry is described. An ultrafiltration process was carried out in the batch mode of operation using a flat polyacrylonitrile membrane with an immobilized enzymatic fraction isolated from a bacterial strain of Pseudomonas. The optimal ultrafiltration process parameters, i.e. transmembrane pressure and stirring rate in the bioreactor, as well as the influence of the concentration of xenobiotics on the effectiveness of the process, are determined. The dynamics of the decomposition of phenol and cyanides has been found.