Iron Cyanide Research Articles

Photo induced dissociation of ferri and ferro cyanide in hydroponic solutions

The potential for photo-induced dissociation of ferri- and ferro-cyanide was investigated. The overall reactions followed first order kinetics, judged by the free cyanide analyzed in aqueous solution. The dissociation rates for ferri- and ferro-cyanide were mathematically described by the equations: C (CN,t) = C (CN,O)e1.3t and C (CN,t) = C (CN,O)e0.39t , respectively. In addition, photo-induced dissociation of both iron cyanides was enhanced under an alkaline environment than a neutral condition. Results from the temperature-dependent tests indicated that the dissociation rate of ferri- cyanide was significantly higher than that of ferro-cyanide at all treatment temperatures. The kinetic parameter, activation energy (E a ) was also experimentally determined to be 12.02 and 12.32 kJ/mol for ferri- and ferro-cyanide, respectively. The results obtained suggest that both iron cyanides are susceptible to photo-dissociation and the rates are positively correlated to the change of temperatures. The information collectively also has important implications for waste management of iron cyanides as well as for risk assessment in a field trial.

Cobalt–iron cyanide hollow cubes: Three-dimensional self-assembly and magnetic properties

Cobalt–iron cyanide hollow cubes have been synthesized via a poly(vinylpyrrolidone) assisted solvothermal route. A unique formation process: self-assembly followed by Ostwald ripening process, has been put forward to take account for the construction of hollow cubes. The rod-like nanocrystals first assemble as porous cubes via an oriented attachment process. Then, the porous cubes undergo an Ostwald-ripening process, which create interior spaces and result in the formation of hollow cubes. The magnetic property investigation reveals that K 0.22Co 0.58Fe 2.2(CN) 6 hollow cubes exhibit a ferromagnetic behavior.

Characterization of a Tricationic Trigonal Bipyramidal Iron(IV) Cyanide Complex, with a Very High Reduction Potential, and Its Iron(II) and Iron(III) Congeners

Currently, there are only a handful of synthetic S = 2 oxoiron(IV) complexes. These serve as models for the high-spin (S = 2) oxoiron(IV) species that have been postulated, and confirmed in several cases, as key intermediates in the catalytic cycles of a variety of nonheme oxygen activating enzymes. The trigonal bipyramidal complex [Fe(IV)(O)(TMG(3)tren)](2+) (1) was both the first S = 2 oxoiron(IV) model complex to be generated in high yield and the first to be crystallographically characterized. In this study, we demonstrate that the TMG(3)tren ligand is also capable of supporting a tricationic cyanoiron(IV) unit, [Fe(IV)(CN)(TMG(3)tren)](3+) (4). This complex was generated by electrolytic oxidation of the high-spin (S = 2) iron(II) complex [Fe(II)(CN)(TMG(3)tren)](+) (2), via the S = 5/2 complex [Fe(III)(CN)(TMG(3)tren)](2+) (3), the progress of which was conveniently monitored by using UV-vis spectroscopy to follow the growth of bathochromically shifting ligand-to-metal charge transfer (LMCT) bands. A combination of X-ray absorption spectroscopy (XAS), Mössbauer and NMR spectroscopies was used to establish that 4 has a S = 0 iron(IV) center. Consistent with its diamagnetic iron(IV) ground state, extended X-ray absorption fine structure (EXAFS) analysis of 4 indicated a significant contraction of the iron-donor atom bond lengths, relative to those of the crystallographically characterized complexes 2 and 3. Notably, 4 has an Fe(IV/III) reduction potential of ∼1.4 V vs Fc(+/o), the highest value yet observed for a monoiron complex. The relatively high stability of 4 (t(1/2) in CD(3)CN solution containing 0.1 M KPF(6) at 25 °C ≈ 15 min), as reflected by its high-yield accumulation via slow bulk electrolysis and amenability to (13)C NMR at -40 °C, highlights the ability of the sterically protecting, highly basic peralkylguanidyl donors of the TMG(3)tren ligand to support highly charged high-valent complexes.

Adsorption of iron cyanide complexes onto clay minerals, manganese oxide, and soil

The adsorption characteristics of an iron cyanide complex, soluble Prussian blue KFe(III)[Fe(II)(CN)6], were evaluated for representative soil minerals and soil at pH 3.7, 6.4 and 9.7. Three specimen clay minerals (kaolinite, montmorillonite, and illite), two synthesized manganese oxides (birnessite and cryptomelane), and a Drummer soil from Indiana were used as the adsorbents. Surface protonation of variable charge sites increased with decreasing pH yielding positively charged sites on crystal edges and enhancing the attractive force between minerals and iron cyanide complexes. Anion adsorption on clays often is correlated to the metal content of the adsorbent, and a positive relationship was observed between iron or aluminum content and Prussian blue adsorption. Illite had high extractable iron and adsorbed more ferro-ferricyande anion, while kaolinite and montmorillonite had lower extractable iron and adsorbed less. However, less pH effect was observed on the adsorption of iron cyanide to manganese oxides. This may due to the manganese oxide mediated oxidation of ferrocyanide [FeII(CN)6 4−], to ferricyanide [FeIII(CN)6 3−], which has a low affinity for manganese oxides.

X-ray structure of the metcyano form of dehaloperoxidase fromAmphitrite ornata: evidence for photoreductive dissociation of the iron–cyanide bond

X-ray crystal structures of the metcyano form of dehaloperoxidase-hemoglobin (DHP A) from Amphitrite ornata (DHPCN) and the C73S mutant of DHP A (C73SCN) were determined using synchrotron radiation in order to further investigate the geometry of diatomic ligands coordinated to the heme iron. The DHPCN structure was also determined using a rotating-anode source. The structures show evidence of photoreduction of the iron accompanied by dissociation of bound cyanide ion (CN(-)) that depend on the intensity of the X-ray radiation and the exposure time. The electron density is consistent with diatomic molecules located in two sites in the distal pocket of DHPCN. However, the identities of the diatomic ligands at these two sites are not uniquely determined by the electron-density map. Consequently, density functional theory calculations were conducted in order to determine whether the bond lengths, angles and dissociation energies are consistent with bound CN(-) or O(2) in the iron-bound site. In addition, molecular-dynamics simulations were carried out in order to determine whether the dynamics are consistent with trapped CN(-) or O(2) in the second site of the distal pocket. Based on these calculations and comparison with a previously determined X-ray crystal structure of the C73S-O(2) form of DHP [de Serrano et al. (2007), Acta Cryst. D63, 1094-1101], it is concluded that CN(-) is gradually replaced by O(2) as crystalline DHP is photoreduced at 100 K. The ease of photoreduction of DHP A is consistent with the reduction potential, but suggests an alternative activation mechanism for DHP A compared with other peroxidases, which typically have reduction potentials that are 0.5 V more negative. The lability of CN(-) at 100 K suggests that the distal pocket of DHP A has greater flexibility than most other hemoglobins.

Copper Solvent Extraction from Waste Cyanide Solution with LIX 7820

The use of a solvent mixture of a quaternary amine and nonylphenol (LIX 7820) to extract copper cyanide from waste cyanide solution has been studied. Copper extraction is favorable at low pH, whereas a high cyanide‐to‐copper ratio tends to suppress copper loading. The preferential extraction of Cu(CN)3 2− over Cu(CN)4 3− and CN− has been confirmed by the examination of both the extraction of copper and cyanide by the solvent mixture under different experimental conditions. The solvent mixture also strongly extracted zinc and nickel from the cyanide solution, but it exhibits weak affinity for iron cyanide complex and free cyanide. The important findings suggested the potential application of the solvent mixture for the recovery of copper and cyanide from waste cyanide solutions, by which copper can be extracted and concentrated into a small volume of solution and the barren cyanide solution recycled to the cyanidation process.

ERK activation increases nitroprusside induced apoptosis in human melanoma cells irrespective of p53 status: Role of superoxide dismutases

Constitutive ERK activation, superoxide dismutases (SOD) and p53 mutations are implicated in modulating tumor apoptotic response. We now investigated whether human melanoma survival in response to sodium nitroprusside (SNP) is modulated by: a) stable introduction of a DN- mutant p53 ; b) pharmacologically inhibiting ERK activation with UO126 ; c) addition of exogenous SOD. Nitroprusside releases nitric oxide (NO) when intact , or acts in a NO-independent manner via iron and residual cyanide after light exposure (lex-SNP) . When tested at 300 µM in 72 hour treatments by cytometric live-dead assays , intact SNP caused a 50 % lethality versus a 30 % lethality induced by lex-SNP. No protection from SNP toxicity was seen when inhibiting the PI3-kinase pathway with LY294002 or c-Jun NH(2) kinase signaling with SP600125. However , pretreatment with UO126 protected from SNP –mediated cell death including counteracting apoptosis-associated Bax expression and PARP cleavage, plus reversing loss of Cu,Zn-SOD. Moreover , addition of exogenous SOD also protected cells from SNP toxicity. In spite of the greater earlier effects of intact SNP, cells treated with single doses of either intact or lex-SNP, revealed about a 90 % mortality in longer 120 hour treatments, and these were also counteracted by UO126 or exogenous SOD. This report is the first to show that: constitutive ERK activation characteristic of cancer cells, increases a nitroprusside-induced apoptosis modulated by SOD.

Effect of temperature on removal of iron cyanides from solution by maize plants

Cyanide is commonly found in soils and groundwater complexed with iron as ferro- and ferri-cyanide. It is evident that plants are capable of tolerating, transporting, and assimilating iron cyanides. The objectives of this study were to investigate the influence of temperatures on the removal and bioaccumulation of two chemical forms of iron cyanides by maize seedlings. Maize (Zea mays L. var. ZN 304) seedlings were grown hydroponically and treated with ferro- or ferri-cyanide in solution for 5 days. Six different temperatures were tested ranging from 12 to 27 degrees C. Total cyanide in solution phase and plant tissues was analyzed spectrophotometrically. The temperature coefficient (Q (10)) was also determined for maize exposed to both iron cyanides. The dissociation of both iron cyanides to free cyanide in solution was below the detection limit. Maize seedlings showed a significantly higher removal potential for ferro-cyanide than ferri-cyanide at all treatment temperatures. Analysis of mass balance revealed that the majority of these iron cyanides taken up from the hydroponic solutions was assimilated by maize, and roots were the major sink for cyanide accumulation. The Q (10) values were determined for ferro- and ferri-cyanide to be 2.31 and 2.75, respectively. Due to the significant difference in the removal rate between the two species of iron cyanides by plant, the conversion of ferri- to ferro-cyanide in aqueous solution prior to uptake is unlikely. Compared to the treatments amended with ferro-cyanide, more cyanide was recovered in plant materials of maize when exposed to ferri-cyanide, implying that ferri-cyanide is less sensitive to degradation than ferro-cyanide. Although the velocity of botanical assimilation of ferro-cyanide was faster than that of ferri-cyanide at any of the treatment temperatures, the removal of ferri-cyanide by maize was more sensitive to changes in temperature than that of ferro-cyanide. Removal of both iron cyanides by maize seedlings was observed to be positive in response to temperatures. Changes in temperatures have a substantial influence on not only the uptake and assimilation of ferro- and ferri-cyanide by maize but also cyanide accumulation in plant tissues. As one of the crucial abiotic factors involved in phytoremediation, temperature shows a positive influence on the removal of iron cyanides by plants. Further investigation on the fate of ferro- and ferri-cyanide in plant tissues would have helped distinguish the differences in the botanical assimilation pathways between the two iron cyanides. The ability of maize to remove iron cyanides has important implications on the vegetation management of environmental contamination.

Bioremediation of a Cyanide-Contaminated Site Using E<sub>H</sub>-/PH-Controlled Conditions (ENA)

In the course of remedial investigations for a former gasworks site, high cyanide pollution of the soil (74.6 - 101.7 mg/kgDS total cyanide) and of the groundwater (3,840 µg/l total cyanide /approx. 300 µg/l free cyanides) were particularly problematic. Extensive investigations in the laboratory as well as in field studies finally resulted in a 2-step oxic/anoxic concept. Both the free cyanides as well as the complex bound cyanides could be biodegraded at more than 90% through a combination of H2O2-treatment (ISCO) and denitrification by in situ conditions. Furthermore a destruction of the iron cyanide complexes under fermentative conditions could be observed for the first time.

Studies on solvent extraction of copper and cyanide from waste cyanide solution

The recovery of copper and cyanide from waste cyanide solution with the guanidine extractant (LIX 7950) and the modified amine extractant (LIX 7820) has been investigated. Copper can be effectively extracted from alkaline cyanide solutions by both extractants. The free cyanide remains in the aqueous phase due to the preferential extraction of Cu(CN) 3 2− over Cu(CN) 4 3− and CN − by the extractants. The selectivity of the metals with the extractants under different cyanide levels has been examined. High cyanide levels tend to depress extraction of copper and silver cyanides, but exhibit insignificant effect on extraction of gold, zinc, nickel and iron cyanides. A possible solution to the separation of copper cyanides and free cyanide in cyanide effluents has been suggested, by which copper can be concentrated into a small volume of solution and the barren cyanide solution recycled to the cyanidation process.

Treatment of Cyanide Bearing Water/Wastewater by Plain and Biological Activated Carbon

Comparative study of biodegradation and adsorption alone with simultaneous adsorption and biodegradation (SAB) process was carried out along with a brief review of the processes. Adsorption and SAB studies were carried out in plain and Pseudomonas putida immobilized granular activated carbon (GAC), whereas biodegradation was conducted with suspended cultures of P. putida. P. putida used iron cyanide as the sole source of nitrogen at an initial pH of 7.0 and temperature of 30 °C. At an initial iron(II) cyanide concentration of 100 mg/L, removal efficiencies of cyanide by adsorption, biodegradation, and SAB were found to be 81.5%, 78.2%, and 96.7%, respectively. The initial ferrocyanide concentrations of 50−350 mg CN−/L were taken for the study. The microbes adopted to grow at maximum cyanide concentration were harvested, and their ability to degrade cyanide were measured in both biodegradation and SAB. The removal efficiency of biologically activated granular activated carbon (BAC) was found better as compared to that of plain GAC. It was also found that the SAB process is more effective than adsorption and biodegradation alone.

Removal of metal cyanides from aqueous solutions by suspended and immobilized cells of Rhizopus oryzae (MTCC 2541)

AbstractThis paper presents a study on biodegradation and simultaneous adsorption and biodegradation (SAB) of zinc and iron cyanides by Rhizopus oryzae (MTCC 2541), with a brief process review. Granular activated carbon was used for the immobilization of Rhizopus oryzae (MTCC 2541) for the SAB study. pH and temperature were optimized at an initial cyanide concentration of 100 mg/L for biodegradation and SAB. The microbes adapted to grow at maximum cyanide concentration were harvested and their ability to degrade cyanide was measured in both biodegradation and SAB. The removal efficiency of the SAB process was found to be better as compared to the biodegradation process. In the case of biodegradation, removal was found up to a maximum cyanide concentration of 250 mg CN−/L for zinc cyanide and 200 mg CN−/L for iron cyanide, whereas in the case of SAB, about 50% removal of cyanide at 400 mg CN−/L zinc cyanide and 300 mg CN–/L iron cyanide was possible. It was found that the SAB process is more effective than biodegradation.

Removal of Cyanide Contaminants from Rhizosphere Soil

ABSTRACT Cyanide and cyanide-containing compounds from anthropogenic sources can be an environmental threat because of their potential toxicity. A remediation option for cyanide-contaminated soil may be through the use of plants and associated rhizosphere microorganimsms that have the ability to degrade cyanide compounds. Cyanogenic plant species are known to produce cyanide, but they also have the ability to degrade these compounds. In addition, the presence of these plants in soil may result in an increase in cyanide degrading microorganisms in the rhizosphere. Two cyanogenic species (Sorghum bicolor and Linum usitassium) and a noncyanogenic species (Panicum virgatum) were selected for a 200-day phytoremediation study to assess their potential use for removal of cyanide from soil. For both cyanogenic species, approximately 85% of the iron cyanide in soil was removed, whereas very little iron cyanide was removed in the unvegetated control or in the presence of Panicum virgatum. In addition, the activity of microbial communities in the rhizosphere of cyanogenic plants was higher than in cyanide-contaminated soil from unvegetated soil.

Assimilation and physiological effects of ferrocyanide on weeping willows

Uptake, assimilation, and toxicity of exogenous iron cyanide complexes in plants were investigated. Pre-rooted young weeping willows ( Salix babylonica L.) were exposed to hydroponic solutions spiked with potassium ferrocyanide at 24.0±1 °C for 192 h. Transpiration rates, chlorophyll contents, soluble protein, and activities of superoxide dismutases (SOD), catalase (CAT), and peroxidase (POD) of the plants were monitored to determine toxicity to the cuttings. Of all selected parameters, POD activity in leaves was the most sensitive bioindicator to the increase of ferrocyanide concentrations. Between 11% and 19% of applied ferrocyanide in the solutions was removed by willows at the end of the incubation period. Only small amounts of ferrocyanide were recovered in different parts of the plant materials. Mass balance analysis showed that more than 90% of the ferrocyanide taken up from the hydroponic solutions was assimilated by plants. The assimilation of ferrocyanide by plants showed a dose-dependent manner. These findings suggest that phytoremediation of ferrocyanide-contaminating wastewater and soils can be possible for the environmental cleaning up.

Transport of Ferrocyanide by Two Eucalypt Species and Sorghum

The wastes from some industrial processes and the tailings from gold mining contain elevated concentrations of cyanide, which reacts with iron in the media to form iron cyanide complexes. This research examined the transport and possible metabolism of ferrocyanide by two native Australian trees, blue mallee and sugar gum, and by sorghum. Hydroponic studies using 15N-labeled ferrocyanide showed that both tree species transported ferrocyanide into roots and displayed significant increases in 15N enrichment and concentration with no evidence of phytotoxicity. A subsequent experiment with blue mallee and membrane-transport inhibitors showed that 15N enrichment was significantly inhibited in the presence of the protonophore carbonyl cyanide m-chlorophenylhydrazone, suggesting that ferrocyanide uptake is mediated partly by H+-symporters. A study of the time dependence of 15N translocation showed a rapid equilibration of 15N from ferrocyanide in the root of blue mallee, accompanied by a slow increase in shoot 15N, suggestive of the metabolism of ferrocyanide in plant roots. A similar experiment with sorghum showed a more rapid translocation of 15N, suggesting that the transport and/or metabolism of ferrocyanide by roots of this species may differ. The results offer additional incentive for the use of these species as vegetative cover over cyanidation wastes and for cyanide phytoremediation.

Removal of cyanide from water and wastewater using granular activated carbon

Abstract Cyanide is used extensively in the electroplating and mining industries due to its strong affinity to metal cations. Commercial granular activated carbon (GAC) was used as adsorbent for the adsorptive study of sodium, zinc and iron, cyanide complexes in the present study. The effect of process parameters such as pH, temperature, adsorbent size and dose, contact time on the performance of adsorption was investigated. Optimum pH was found to be 9, 7 and 5 for sodium, zinc and iron cyanides respectively. In the higher temperature range more percentage removal was observed for iron cyanides, whereas, sodium and zinc cyanides were removed optimally at 25–35 °C. Although particle size did not show any major influence on the percentage removal, but optimum size was taken as 2–4 mm. The percentage removal of cyanide compounds increased with the increase in adsorbent (GAC) concentration. However, specific uptake did not increase at GAC concentration above 20–25 g/L. Hence 20 g/L was considered as the optimum dose of adsorbent. Higher removal efficiency was achieved for metal cyanides as compared to sodium cyanide at optimal conditions.

Plant germination and growth after exposure to iron cyanide complexes

Phytoremediation has been proposed for treatment of cyanide-contaminated soil. This study was conducted to identify plants with the highest potential for phytoremediation of iron cyanide contaminated soil. Multiple cultivars of two cyanogenic species, sorghum (Sorghum bicolor) and flax (Linum usitatissimum), and one non-cyanogenic species, switchgrass (Panicum virgatum L), were selected for evaluation. The cultivars were screened by quantifying germination and root elongation. Differences in germination emerged among the cultivars (P < 0.05), but these differences appeared to be unrelated to cyanide concentration. The presence of 1000 mg/kg Prussian blue tended to suppress root growth parameters of flax and switchgrass but did not affect sorghum similarly.

Ion exchange resins for the treatment of cyanidation tailings: Part 3 – Resin deterioration under oxidative acid conditions

Oxidative acid eluents comprising of H 2O 2 and H 2SO 4 have been proven to be effective in eluting base metal cyanide complexes from strong base resins. This study found that the repeated cycling between alkaline cyanide conditions and oxidative acid conditions does not affect the strong base or the total base capacity of strong base resins. However, it was found that a significant reduction of net operating capacity of the ion exchange resin bed, along with a small reduction of the total base capacity of the resin, takes place when this eluent is repeatedly used to elute resins loaded with a mixture of metal cyanide complexes. The reduction of the total base capacity is thought to be due to the oxidation of the resin by the oxidant in the presence of Cu 2+ ions. A precipitate of copper hexacyanoferrate was detected in resin loaded with a mixed copper and iron cyanide solution. While the formation of this precipitate did not appear to have an impact on the total base capacity of the resin, it affected the net operating capacity of resin beds. These two processes gave rise to an approximately 1–3% reduction of the net operating capacity of the ion exchange resin columns per loading/elution cycle.

Availability of Ferrocyanide and Ferricyanide Complexes as a Nitrogen Source to Cyanogenic Plants

The effects of additional nitrogen on the toxicity and removal of ferrocyanide and ferricyanide by cyanogenic plants were investigated. Maize (Zea mays L. var. ZN 304) seedlings were grown in the hydroponic solutions with or without additional nitrogen, and amended with either potassium ferrocyanide or potassium ferricyanide at 25.0 +/- 0.5 degrees C for 144 h. Various physiological parameters were monitored to determine the responses of the plant seedlings to the exposure of these two chemicals. A remarkable decrease in transpiration rate, biomass, shoot length, chlorophyll contents, and soluble proteins was evident for maize seedlings grown in the N-free hydroponic solutions spiked with either ferrocyanide or ferricyanide (P < 0.01), but slight changes were observed in the selective parameters in the N-containing hydroponic solutions spiked with either of these chemicals (P > 0.05). A higher removal of ferrocyanide than ferricyanide was registered in the N-free hydroponic solutions, but more ferricyanide than ferrocyanide was removed by maize grown in the N-containing nutrient solutions (P < 0.01). Although roots of maize accumulated iron cyanides, more cyanide was recovered in plant materials of those grown in the N-containing hydroponic solutions than the N-free nutrient solutions (P < 0.05). Mass balance analysis indicated that the majority of the iron cyanides removed from solution was assimilated by maize and additional nitrogen had a significantly negative impact on the uptake of both chemicals (P < 0.01). Results of this study suggest that uptake and assimilation mechanisms for ferrocyanide and ferricyanide might be quite different in maize and the application of the external nitrogen has a substantial influence on the removal of both iron cyanides by plants. None of the iron cyanide complexes can serve as a sole nitrogen source to support maize growth.

Effects of available nitrogen on the uptake and assimilation of ferrocyanide and ferricyanide complexes in weeping willows

The effects of different levels of external nitrogen on the uptake, distribution and assimilation of iron cyanide complexes were investigated. Pre-rooted weeping willows ( Salix babylonica L.) were grown in a hydroponic solution with or without nitrogen and amended with potassium ferrocyanide or potassium ferricyanide at 25.0 ± 0.5 °C for 144 h. Faster uptake of ferrocyanide than ferricyanide was observed in willows grown in the deionized water. Negligible difference in the removal rate between the two chemicals was detected for willows grown in nutrient soultions with or without amendment of nitrogen. The volatilization of ferro- and ferricyanide due to transpiration through plant aerial tissues was below detection level. Less then 20% of the ferrocyanide or ferricyanide taken up from the N-free nutrient solution was recovered in the biomass and majority was accumulated in the roots. In contrast, less than 9.0% of both iron cyanide compelxes taken up was detected in the plant materials of willows grwon in the N-containing nutrient solution and roots were the major sites for accumulation of both chemicals. A large fraction of the ferro- and ferricyanide taken up from the hydroponic solution was assimilated during the transport within plant materials. Willows grown in the N-containing nutrient solution showed a higher assimilation potential for both chemical forms than those grown in the N-free nutrient solution in general. The information collectively suggests that uptake and assimilation mechanisms for ferro- and ferricyanide are largely different in willows; the strength of external nitrogen had a negligible effect on the uptake of both chemicals, while assimilation of ferro- and ferricyanide in plant materials was strongly related to the presence of easily available nitrogen in the hydroponic solution.