Cyanide Degradation Research Articles

Bacterial Degradation of Cyanide and Its Metal Complexes under Alkaline Conditions

A bacterial strain able to use cyanide as the sole nitrogen source under alkaline conditions has been isolated. The bacterium was classified as Pseudomonas pseudoalcaligenes by comparison of its 16S RNA gene sequence to those of existing strains and deposited in the Coleccion Espanola de Cultivos Tipo (Spanish Type Culture Collection) as strain CECT5344. Cyanide consumption is an assimilative process, since (i) bacterial growth was concomitant and proportional to cyanide degradation and (ii) the bacterium stoichiometrically converted cyanide into ammonium in the presence of l-methionine-d,l-sulfoximine, a glutamine synthetase inhibitor. The bacterium was able to grow in alkaline media, up to an initial pH of 11.5, and tolerated free cyanide in concentrations of up to 30 mM, which makes it a good candidate for the biological treatment of cyanide-contaminated residues. Both acetate and d,l-malate were suitable carbon sources for cyanotrophic growth, but no growth was detected in media with cyanide as the sole carbon source. In addition to cyanide, P. pseudoalcaligenes CECT5344 used other nitrogen sources, namely ammonium, nitrate, cyanate, cyanoacetamide, nitroferricyanide (nitroprusside), and a variety of cyanide-metal complexes. Cyanide and ammonium were assimilated simultaneously, whereas cyanide strongly inhibited nitrate and nitrite assimilation. Cyanase activity was induced during growth with cyanide or cyanate, but not with ammonium or nitrate as the nitrogen source. This result suggests that cyanate could be an intermediate in the cyanide degradation pathway, but alternative routes cannot be excluded.

Natural cyanide degradation and impact on Ili River drainage areas from a Goldmine in Xinjiang autonomous region, China

The Ili River is a very important river to the northwest of China and Kazakhstan. The Axi Goldmine is located in the upstream of a branch of the Ili River. The cyanide from the goldmine effluent is a threat to the downstream areas. According to our study, the natural degradation of cyanide conforms to a negative exponential equation in the tailings impoundment, second wastewater pond and even in the receiving streams if the dilution action from other streams were deducted. In the combined action of dilution and natural decomposing, the cyanide from the goldmine effluent does not pose a hazard to the trunk of the Ili River in the normal producing states. The equations of cyanide degradation in the streams and the hydrology parameters could be used to assess the environmental impact on the downstream areas if accidental discharges of cyanide occurred. The available way of decreasing the cyanide impact on the streams is to increase the rate of recycled water so that the lower the wastewater level in the tailing impoundment and the second wastewater pond, the lower is the amount of leakage of wastewater to the streams.

Alkaline cyanide biodegradation by Pseudomonas pseudoalcaligenes CECT5344

Pseudomonas pseudoalcaligenes CECT5344 uses cyanide, cyanate, beta-cyanoalanine, and other cyanoderivatives as nitrogen sources under alkaline conditions, which prevents volatile HCN (pK(a) 9.2) formation. The cyanide consumed by this strain is stoichiometrically converted into ammonium. In addition, this bacterium grows with the heavy metal, cyanide-containing waste water generated by the jewellery industry, and is also a cyanide-resistant strain which induces an alternative oxidase and a siderophore-based mechanism for iron acquisition in the presence of cyanide. The detection of cyanase and beta-cyanoalanine nitrilase activities in cyanide-induced cells suggests their implication in the cyanide degradation pathway.

Modeling Free and Copper-Complexed Cyanide Degradation in a Continuous Flow Completely Mixed Ozone Contactor

The objective of this study was the development of a fully mechanistic model for describing the degradation of free and copper-complexed cyanide and the evolution of degradation byproducts in a continuous flow completely mixed ozone contactor. The developed model incorporated mechanisms describing rate and extent of ozone mass transfer from gaseous to aqueous phases, comprehensive consideration of ozone self-decomposition reactions in the aqueous phase, and interactions of aqueous phase ozone and hydroxyl radicals with free and copper-complexed cyanide and byproducts of their degradation. Simulation of the effect of changes in influent gaseous ozone concentration, scavenger concentration, liquid flow rate, and influent pH on free and copper-complexed cyanide degradation was accompanied by explanation of simulation results based on the current understanding of aqueous ozone chemistry with respect to cyanide degradation. Experimental work included the operation of a laboratory-scale continuous-flow complete...

Application of cyanide hydrolase from Klebsiella sp. in a biosensor system for the detection of low-level cyanide

A partially purified preparation of cyanide hydrolase (cyanidase) from a bacterium, Klebsiella sp., was applied as a biocatalyst in a biosensor system for low-level cyanide detection. In the biosensor system cyanide hydrolase converts cyanide into formate and ammonia. The formate produced in the cyanide degradation was detected with a formate biosensor, in which formate dehydrogenase (FDH; E.C. 1.2.1.2) was co-immobilized with salicylate hydroxylase (SHL; E.C. 1.14.13.1) on a Clark electrode. The principle of the formate sensor is that FDH converts formate into carbon dioxide using beta-nicotinamide adenine dinucleotide hydrate (NAD(+)). The corresponding NADH produced is then oxidized to NAD(+) by SHL using salicylate and oxygen. The oxygen consumption is monitored with the Clark electrode. The optimum buffer pH and temperature for the enzymatic hydrolysis of potassium cyanide were studied. The preliminary experiments including the pretreatment of cyanide with cyanide hydrolase and then detection by the formate sensor gave a detection limit at 7.3 micromol l(-1) cyanide. The linear range of the calibration curve was between 30 micromol l(-1) and 300 micromol l(-1) cyanide.

Oxidation of cyanide in aqueous solution by chemical and photochemical process

Cyanide waste is found predominantly in industrial effluents generated from metallurgical operations. The toxicity of cyanide creates serious environmental problems. In this paper, oxidation of cyanide in aqueous solution was investigated using chemical and photochemical process. Chemical oxidation was studied at room temperature using H 2O 2 as oxidant and Cu 2+ as catalyst. Photochemical oxidation was studied in an annular type batch photoreactor of 1 l capacity using 25 W low-pressure (81.7% transmission at 254 nm wavelength) ultraviolet (UV) lamp along with H 2O 2 as oxidant. The effect of Cu 2+ catalysis was also studied. It was observed that in absence of UV source, the degradation of cyanide by H 2O 2 alone was very slow, whereas copper ions accelerated the rate of reaction thereby acting as catalyst. Copper formed a complex with cyanide ion, i.e. tetracyanocuprate which had greater affinity for H 2O 2. Cyanate hydrolysis was also favoured by copper ions. As Cu 2+ ion concentration was increased, rate of degradation also increased. Photochemical oxidation by H 2O 2 and Cu 2+ was found to be the best system for cyanide degradation. CN − (100 mg/l) was degraded to non-detectable level in 9 min at pH 10.0 with optimum H 2O 2 dose of 35.5 mM and Cu 2+ dose of 19 mg/l. Reaction kinetics of cyanide oxidation was found to be pseudo-first order and the rate constant has been determined for different processes.

Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

AbstractPhoto‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H2O2 as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H2O2 was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H2O2 concentration and the optimum dose of H2O2 was found to be 35.3 mmol dm−3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H2O2 process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H2O2 dose of 35.3 mmol dm−3, cyanide (100 mg dm−3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10−2min−1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry

Photocatalytic degradation of iron–cyanocomplexes by TiO2 based catalysts

The removal of iron–cyanocomplexes in industrial effluents is a difficult process, due to the resistance of these compounds to conventional treatments for cyanide wastewater detoxification. The mechanism of both the homogeneous photolysis of these compounds and their heterogeneous photocatalytic oxidation with Degussa P25 TiO2 and silica-supported TiO2 photocatalysts has been investigated. The activities of the tested catalysts for complexed cyanide degradation were found to be different from those observed for free cyanide photo-oxidation. The best activity was found for the photocatalyst synthesized by supporting 20wt.% of TiO2 on SBA-15 silica as compared with the commercial catalyst Degussa P25 and the other supported catalysts tested. On the basis of detected intermediate species, a mechanism for iron–cyanocomplexes photodegradation is suggested. The influence of the textural properties of the support and titania loading on the process is discussed. The results point out that the high activity observed, when SBA-15 is used as support of TiO2, seems to be related to the microporosity of the material acting as molecular sieve, which avoids the deactivation of the semiconductor. The porous structure of the SBA-15 material limits the access of the iron–cyanocomplexes to the TiO2 particles whereas the free cyanides homogeneously released can reach the semiconductor surface, being subsequently oxidized to cyanate.

Aqueous phase catalytic oxidation of cyanides over iron-modified cobalt oxide system

The catalytic oxidation of cyanide ions was carried out in an aqueous aerated suspension containing modified with iron Co-oxide system. The dependence of both cyanide oxidation rate and selectivity of the process on the initial pH and the catalyst amount was investigated. The results obtained show that the cyanide degradation proceeds most effectively and with high selectivity to the environmentally harmless carbon dioxide at pH≤9.5. The increase of the alkalinity (with other constant parameters) causes both a decrease in the cyanide conversion degree and lowering the selectivity in respect to complete oxidation products. The activity of Co–Fe-oxide system was compared to that of an individual Co-oxide. The observed high activity of the doped sample is explained by the influence of Fe as a modifying additive, which leads to the appearance of new active sites in the fresh samples—Fe(III)-ions in octahedral coordination and to increasing the mobility of the reactive oxygen.

Accelerated removal of cyanides from industrial effluents by supported TiO2 photo-catalysts

This study presents novel supported TiO2 catalysts able to mediate the photo-oxidation of cyanides with an acceptable kinetics. The catalyst preparation was optimized towards cyanide degradation using different TiO2 colloids on glass Raschig rings. The TiO2 during the photo-degradation of cyanides was activated by two different sources of UV light (366nm). The catalyst used showed long-term stability and was able to degrade the cyanide solution within minutes in a repetitive fashion. The dependence of the cyanides oxidation rate was investigated as a function of: (1) catalyst preparation, (2) cyanide initial concentration, (3) applied light intensity, and (4) nature and concentration of the oxidant (O2 or/and H2O2). The Langmuir–Hinshelwood mechanistic model was used to fit the experimental data. The by-products observed in solution during the cyanide degradation were identified as cyanates and nitrites. The catalytic efficiency of the best catalyst was tested on real wastewater from the galvanic industry containing ∼400mg/l of cyanides and 60–70mg/l of Cu-ions.

Oxidative Treatment of Cyanide in Wastewater Using Hydrogen Peroxide and Homogeneous Catalyst

Batch kinetic tests were conducted to determine the effects of experimental conditions and catalysts on cyanide degradation. Cyanide degradation by hydrogen peroxide was found to follow first-order kinetics. Reaction rates increased with increasing pH and decreasing temperature. The activation energy for cyanide degradation by hydrogen peroxide was found to be −13.81 kJ/mol. The addition of Cu2+ or Cd2+ as catalysts resulted in increasing reaction rates. In alkaline conditions, the catalytic effects of Cu2+ or Cd2+ were accelerated and Cu2+ was found to be a more effective catalyst than Cd2+. The practical relevance of the laboratory oxidation method of cyanide was demonstrated for actual industrial wastewater.

Advanced oxidation processes for destruction of cyanide from thermoelectric power station waste waters

AbstractSeveral advanced oxidation processes for the destruction of cyanide contained in waste waters from thermoelectric power stations of combined‐cycle were studied. Thus, oxidation processes involving ozonation at basic pH, ozone/hydrogen peroxide, ozone/ultraviolet radiation and ozone/hydrogen peroxide/ultraviolet radiation have been carried out in a semi‐batch reactor. All these methods showed that total cyanide can be successfully degraded but with different reaction rates, and the decrease in the total cyanide concentration can be described by pseudo‐first order kinetics. The influence of pH and initial concentration of hydrogen peroxide was studied to find the optimal conditions of the oxidation process. Experimental results of the single ozone treatment indicated that total cyanide is destroyed more rapidly at higher pH (12), while ozonation combined with H2O2 and/or UV is faster at pH 9.5. The optimum concentration of H2O2 was 20.58 × 10−2 M because an excess of peroxide decreases the reaction rate, acting as a radical scavenger. The total cyanide degradation rate in the O3/H2O2(20.58 × 10−2 M) treatment was the highest among all the combinations studied. However, COD reduction, in the processes using UV radiation such as O3/UV or O3/H2O2/UV was about 75%, while in the processes with H2O2 and/or O3/H2O2 was lower than 57% and was insignificant, when using ozone alone. Copyright © 2003 Society of Chemical Industry

Sol–gel synthesis of vanadia–silica for photocatalytic degradation of cyanide

Cyanides used in some chemical synthesis and metallurgical processes are highly toxic and must be destroyed or removed from wastewaters prior to discharge. Vanadia–silica xerogel as photocatalyst has been prepared via sol–gel technique by dissolving ammonium metavanadate (AMV) and tetraethylorthosilicate (TEOS) and applied for photodegradation of cyanide from solution. The optimum conditions for preparation of V2O5–SiO2 gel is 1:1 of vanadium/silicon (V/Si) molar ratio and TEOS:H2O:C2H5OH is 1:8:4 mole ratios at 30°C for 10min, at these conditions the photoactivity of V2O5–SiO2 was 98.5% at surface area 310m2/g. The calculated activation energy of the reaction between AMV and TEOS was found to be −10.81kcal/g. The optimum loading of vanadia–silica xerogel was 0.166wt.% that give 98.5% cyanide removal efficiency after 3h. The overall kinetics of photodegradation of cyanide using vanadia–silica photocatalyst was found to be of first order.

Biological treatment of cyanide by natural isolated bacteria ( Pseudomonas sp.)

Biological treatment is a proven process for the treatment of mining effluents such as tailings, wastewaters, acidic mine drainage etc. Several bacterial species ( Pseudomonas sp.) can effectively degrade cyanide into less toxic products. During metabolism, they use cyanide as a nitrogen and carbon source converting it to ammonia and carbonate, if appropriate conditions are maintained. In this study, nine strains of Pseudomonas sp. were isolated and identified from a copper mine. Two (CM5 and CMN2) of the nine bacteria strains were used in a cyanide solution. Some important parameters in the biological treatment process were tested and controlled: pH, cell population and CN − concentration. Tests were conducted to determine the effect of the type of bacterial strains on the treatment of cyanide. Laboratory results indicated that biological treatment with Pseudomonas sp. might be competitive with other chemical treatment processes. This paper presents the results of an investigation of a biological treatment system for cyanide degradation in a laboratory batch process.

SONOCHEMICAL ENHANCEMENT OF CYANIDE OXIDATION METHODS

This paper presents a short review of the classical methods for cyanide treatment, together with some potential applications of ultrasound irradiation for cyanide remediation. By the combination of ultrasound irradiation with usual oxidants like hydrogen peroxide or oxygen new and efficient methods of cyanide degradation can be obtained. This paper presents a short review of the classical methods for cyanide treatment, together with some potential applications of ultrasound irradiation for cyanide remediation. By the combination of ultrasound irradiation with usual oxidants like hydrogen peroxide or oxygen new and efficient methods of cyanide degradation can be obtained.

Biotransformation of cyanide to methane and ammonia by Klebsiella oxytoca

Klebsiella oxytoca, isolated from cyanide-containing industrial wastewater, was shown to be able to biodegrade cyanide to non-toxic endproducts using cyanide as the sole nitrogen source. In this study, ammonia was one of the detected endproduct of cyanide biodegradation by the concentrated resting cells of K. oxytoca. Moreover, cyanide has been shown to be biotransformed to methane through the actions of concentrated resting cells. Biodegradation of cyanide by cell-free extracts was not observed, which might be due to the inactivation of nitrogenase (an oxygen-labial enzyme) caused by the oxygen exposure after cell disruption. Results show that the cyanide consumption by resting cells of K. oxytoca was induced when the pretreatment of these cells with cyanide was conducted. However, the cyanide-degrading capability of resting cells pretreated with ammonia was inhibited. The inhibition of cyanide degradation by resting cells of K. oxytoca was affected by the ammonia concentration. This might result from the suppression of nitrogenase activity of K. oxytoca by ammonia since nitrogenase was suggested to be the sole cyanide-degrading enzyme during the cyanide degradation process. Results from this study also show that the processes of cyanide biodegradation and ammonia production by resting cells occurred simultaneously. This suggests that the utilization of cyanide as nitrogen source by K. oxytoca might proceed using ammonia as an assimilatory substrate.

Photocatalytic degradation of cyanide using titanium dioxide modified with copper oxide

Copper (II) oxide was loaded onto the surface of Degussa P25 TiO2 particles by photodeposition. The doped material was subsequently utilized as the photocatalyst for cyanide oxidation. The copper content on the TiO2 surface was varied from 0.05 to 10.0 at.% of Cu. It was found that nanosized CuO deposits were present on the surface of TiO2. Modifying TiO2 with CuO changed the optical properties of TiO2 and the onset of absorption was red shifted. The photocatalytic activity of the CuO loaded TiO2 catalysts was measured to determine their ability to oxidize cyanide. It was found that the rate of photooxidation of cyanide assisted with the doped catalyst was improved slightly at 0.10 at.% Cu. Any further increase of the copper dopant concentration decreased the oxidation rate markedly. The presence of Cu2+ ions (0.002–0.5 mM) in the solution also decreased the photocatalytic degradation of CN−. The decrease in the activity was explained in terms of the competition reaction of Cu(I) cyanide complex ions for surface hydroxyl radicals. In all cases cyanide was being oxidized to cyanate, the end product of cyanide photooxidation.

Ozone enhanced activity of aqueous titanium dioxide suspensions for photocatalytic oxidation of free cyanide ions

The ozonization and the heterogeneous photocatalytic method are contemporarily applied for the oxidation of free cyanide ions. A batch photoreactor with immersed lamp was used for treating aqueous suspensions containing polycrystalline TiO2 powders irradiated in the near-UV region. Air or ozone–air mixtures were used as oxidation reactants. At the used experimental conditions, the photoreaction proceeds at a measurable rate until low values of cyanide concentration. In the presence of ozone (O3) several parallel reaction routes are contributing to the overall cyanide degradation: (i) homogeneous oxidation by ozone; (ii) heterogeneous catalytic reaction by ozone; (iii) photocatalytic degradation with oxygen; and (iv) photocatalytic degradation with ozone. The rate of cyanide oxidation by heterogeneous photocatalytic mechanism is enhanced by ozone with respect to that observed in the presence of neat oxygen. A kinetic model based on Langmuir–Hinshelwood equations describes adequately the photoreactivity results and provides the values of the kinetic constants and equilibrium adsorption constants for the catalytic and photocatalytic reactions contributing to cyanide oxidation. In order to gain further information on the interaction of ozone with TiO2 surfaces, either in the dark or under UV-irradiation, an ESR study has been also carried out. The results indicate that ozone strongly interacts with TiO2, leading mainly to the formation of ozonide radicals.

ChemInform Abstract: UV Light Induced Photocatalytic Degradation of Cyanides in Aqueous Solution over Modified TiO2.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Substrate-regulated cyanide hydratase (chy) gene expression in Fusarium solani: the potential of a transcription-based assay for monitoring the biotransformation of cyanide complexes.

The fungus Fusarium solani detoxifies cyanide through induction of the cyanide hydratase gene activity (chy) in the presence of either KCN or the metal-complexed cyanides, K2Ni(CN)4 or K4Fe(CN)6, at pH 7.0 and 4.0 respectively. Sequence analysis of the chy gene identified primers for reverse transcriptase-polymerase chain reaction (RT-PCR)-directed analysis of mRNA transcripts, which demonstrated that activity correlated to the substrate-specific induction of gene expression. chy transcription was initiated 30-60 min after exposure of F. solani cultures to cyanide complexes. Maximum expression was detected within 4.5 h, after which chy mRNA synthesis declined below the limits of detection within 26 h. A lag period of approximately 2 h, following initial transcription, was recorded before cyanide complexes were converted to formamide. mRNA transcripts of chy were not detected in the absence of cyanide or cyanide complexes. The presence of introns within the gene resulted in a difference in size of 100 bp for DNA compared with mRNA of the corresponding 5' region. This size difference facilitated PCR detection of gene and transcript respectively. Comparisons of the predicted amino acid sequence of the F. solani chy gene and those of Gloeocerospora sorghi, Fusarium lateritium and Leptosphaeria maculans demonstrate that cyanide hydratase genes are highly conserved and of a similar evolutionary origin. These data predict that the functional assay described here to monitor the induction of chy gene expression and, potentially, cyanide degradation would be applicable to a variety of polluted environments.