Iron Cyanide Complexes Research Articles

High-efficiency degradation of Fe-CNs in SPL through microwave-activated persulfate

Cyanide in spent potlining (SPL) is primarily present as sodium cyanide (NaCN) and iron (II, III) cyanide complexes (Fe-CNs). NaCN is easy to degrade, while Fe-CNs is extremely difficult to degrade. In this work, a novel microwave-activated persulfate technology (MW-PS) was firstly proposed to degrade Fe-CNs promptly and efficiently. The removal rate of 99.88 % was achieved within 180 s under optimal conditions of pH = 10.15, [oxidant]:[Fe-CNs] molar ratio of 5:1, and microwave power of 300 W. The remaining total cyanide content was less than 0.04 mg·L−1. The degradation mechanism of ferrocyanide (II) and ferricyanide (III) in the MW-PS degradation system was systematically analyzed through electron paramagnetic resonance (EPR) and element identification techniques. The ROS (SO4−, HO, O2−, and 1O2) generated under microwave activation and first attacked the C-Fe complex bond in Fe-CNs, causing the bond to dissociate and release the free CN−, and then CN− was thoroughly oxidized. This work develops a simple and high-efficiency decyanation technology for complex cyanide contained industrial waste disposal.

Novel approach for removing iron-cyanide complex ions and cesium ions from solutions using hydrogel-like beads

In the process of recycling cyanide leaching solutions, the presence of iron-cyanide complex ions in gold leaching solutions leads to increased cyanide consumption and competition with gold for adsorption onto activated carbon. Consequently, the removal of iron- cyanide complex ions from cyanide leaching solutions is crucial. This study presents a novel strategy for the treatment of metal ions in leaching solutions, achieving effective waste treatment using hydrogel-like beads. To remove iron-cyanide complex ions from cyanide leaching solutions, we synthesized carboxymethyl cellulose‑iron (CMCFe) hydrogel through a crosslinking method. The adsorbent, carboxymethyl cellulose-Prussian blue (CMC-PB) hydrogel, obtained after iron-cyanide complex ion adsorption, can directly remove Cs+ ions from solution without the need for desorption and regeneration. Notably, the CMC-Fe hydrogel exhibits exceptional adsorption performance and high selectivity toward iron-cyanide complex ions. The adsorption process of the CMC-Fe hydrogel follows a pseudo-second-order kinetic model, while the Freundlich isotherm model is more suitable for describing the adsorption equilibrium. Additionally, the CMC-PB hydrogel efficiently adsorbs 83.1% of Cs+ ions at a dosage of 86.5 μg, and desorption and regeneration studies reveal that its adsorption efficiency remains high even after three cycles. Furthermore, the proposed adsorption mechanism of CMC-PB for Cs+ ions involves a combination of chemisorption (K+/Na+ exchange) and physisorption (hole channels of hydrogels).

A new strategy for extraction of copper cyanide complex ions from cyanide leach solutions by ionic liquids

Copper cyanide complexes in cyanide leach solutions deteriorate the recoveries of gold. Herein, five phosphonate-based [P204]− ionic liquids were synthesized, which were pioneered to apply to extraction of copper cyanide complex ions in cyanide leach solutions. In the extraction process, macroscopic layered solids rich in copper cyanide complex ions were formed at the aqueous-organic phase interface, which was driven by self-assembly of ionic liquids. Notably, the layered solids can be obtained by simple filtration. The extraction behaviors were systematically studied in the present work. The results show that the extraction efficiency in excess of 90 % can be achieved at higher pH (13.16) and enriched as self-assembly solids in the process of one-step extraction and solidification, based on the self-assembly extraction systems of [P4444][P204] IL. It is worthy of note that no self-assembly sample was observed when the extraction systems is applied to extraction zinc and iron cyanide complex ions. It indicates that the present self-assembly extraction systems could be applied in separation copper and zinc/iron cyanide complex ions. Meanwhile, the coordination mechanism was investigated detaily, and the covalent nature played a leading role in the binding interaction. Remarkably, [P4444][P204] can be repeatedly used without obvious loss in extraction capacity of copper cyanide complex ions after two cycles, indicating that the IL has a good recycling ability. In conclusion, it is possible to employ the self-assembly extraction systems to separate and recover various valuable metals from aqueous solutions by designing and developing ILs extractants in the future.

Cyanide detoxification and iron mineral recycle of cyanide tailings by the sustainable utilization technology of oxidation-reduction roasting: Process optimization and mechanism study

The novel cyanide detoxification and resource utilization of cyanide tailings were treated sequentially by the oxidation-reduction roasting. Through a series of conditional experiments, the oxidation roasting realized the content of cyanide decrease to < 0.04 mg/kg (detection limit) with the removal rate reached to 99.99% at the optimum conditions. The reduction roasting realized the main mineral hematite transformed to magnetite and recycled the iron concentrate from the cyanide tailings with iron grade of 59.21% and iron recovery of 89.57%. The migration and transformation paths and decomposition products of cyanide during oxidative degradation process were investigated by the hexacyanoferrate reagents decomposition with the real-time concentration of CO2, XRD and FT-IR. The hexacyanoferrate decomposition reactions were complex, and divided into three stages, such as the room temperature-350 ℃, 350 ℃− 550 ℃, 550 ℃− 800 ℃ respectively. The transformation paths and decomposition products iron-cyanide complex were mainly as follows: K4Fe(CN)6 or K3Fe(CN)6 was oxidized and decomposed into CNO-, and further decomposed into CO3- by the roasting temperature increasing.

Capture of copper cyanide complex ions based on self-assembly of ionic liquids actuation and application to cyanide wastewater

The tetrabutylammonium bis (2-ethylhexyl) phosphate [N4444][P204] ionic liquid (IL) was synthesized, which was applied to extract copper cyanide complex ions in cyanide tailing liquid stream pressure filtration. In the extraction process, macroscopic layered solids rich in copper cyanide complex ions were formed at the phase interface, which was based on self-assembly of ionic liquids actuation. The solid samples can be obtained by simple filtration. Meanwhile, the extraction behaviors were investigated in detail. The [N4444][P204] ionic liquid exhibited excellent extraction efficiency for copper cyanide complex ions. More than 90% of copper cyanide complex ions were extracted at pH 13.4 and enriched as self-assembly solids in the process of one-step extraction and solidification. Notably, the extraction efficiency of copper cyanide complex ions can still reach more than 75% after three cycles of organic phase with fresh aqueous phase. Furthermore, the analyses of the SEM, EDS, XPS, FTIR, and ESI-MS for self-assembly sample implied that the potential mechanism of extraction for copper cyanide complex ions is coordination reaction. It is worthy of note that the extraction system of [N4444][P204] IL has no extraction effect on iron cyanide complex ions. In the end, the proposed strategy may be further expanded to the separation of other metal cyanide complex ions by designing the ionic liquids.

Effectiveness and mechanism of cyanide remediation from contaminated soils using thermally activated persulfate

Persulfate (PS)-based advanced oxidation processes have been frequently employed for contaminant remediation, but the effectiveness of PS oxidation for the elimination of cyanide-bearing contaminants from soil, and the underlying mechanisms, have rarely been explored. This study investigated the degradation of two iron-cyanide (Fe–CN) complexes (ferricyanide and ferrocyanide) with thermally activated PS via two remediation strategies, namely one-step oxidation (direct PS oxidation) and two-step oxidation (alkaline extraction followed by PS oxidation). The two-step oxidation process was more effective for the elimination of cyanide pollutants from soil, reaching >94% remediation efficiency for both Fe–CN complexes studied. The presence of dissolved soil components, especially soil organic matter, increased consumption of PS during the remediation process. A combined analysis based on electron paramagnetic resonance (EPR), free radical scavenging, and degradation product identification revealed that SO4- and HO were the principal reactive radicals responsible for Fe–CN degradation. Based on the determination of radical species and identification of decomposition products, a transformation pathway for Fe–CN complexes during thermally activated PS oxidation is proposed. Overall, this study demonstrates the effectiveness of the thermally activated PS oxidation technique for cyanide elimination from polluted soil. Further study is required to verify the feasibility of this method for field applications.

Fate and toxicity of ferric ferrocyanide with cyanogenic and non-cyanogenic plant species

Iron cyanide complexes are common contaminants at former manufactured gas plant sites. Although combined forms of cyanide have low toxicity, iron cyanide complexes can be decomposed to HCN through photolysis. This experiment was designed to evaluate the efficiency of phytoremediation and investigate potential toxic effect for iron cyanide complexes (i.e., ferric ferrocyanide) using the cyanogenic and non-cyanogenic plants in soil. Results showed that Sorghum (a cyanogenic plant) had the highest cyanide degradation in the root zone with the removal of approximately 32% while Switchgrass (a non-cyanogenic plant) and Flax (a cyanogenic plant) had 21% and 17% removal, respectively, with 4% dissipation in unvegetated soil. It was found that roots had higher cyanide concentrations than plant shoots. Water-soluble cyanide and the weak acid dissociable (WAD) fraction in the soil had increased at the end of the experiment, suggesting that plant may enhance the mobility and bioavailability of cyanide by root exudation. The risk associated with the leaching of cyanide compounds was assessed with the toxicity assay (Microtox). However, results indicated that the leachate from the pots was not toxic.

Kinetics and mechanism of the reaction between dimethyl trisulfide and cyanide

Environmental context Dimethyl trisulfide (DMTS) is a malodorous compound formed from decomposing algal matter and can severely compromise the quality of drinking water. The reactivity of DMTS toward cyanide was studied in aqueous solutions at environmentally relevant conditions. It was found that the half-lives of DMTS in the presence of free cyanide varied from several months to several thousand years depending on environmental conditions. Abstract Organically bound sulfur in the form of mono-, di- and polysulfide bridges constitutes a significant fraction of this element in recent and ancient sediments. In water columns of lakes, the concentrations of organo-sulfur compounds are much lower, and they are present in the form of malodorous dimethyl polysulfides. Currently, information regarding reactivity of organic polysulfides towards nucleophiles that are stronger than hydroxyl anions is lacking. In this work, the reaction kinetics of dimethyl trisulfide (DMTS) with the strong nucleophile and important environmental pollutant cyanide as a function of concentrations of reactants, pH and temperature were studied. It was found that the reaction rate constant as well as the activation energy of the reaction strongly depend on pH. The experimental data agree well with the existence of two distinct pathways: slow reaction between protonated cyanide and DMTS under acidic and neutral conditions and fast reaction between cyanide anion and DMTS under highly alkaline conditions. However, reactions of DMTS with the iron cyanide complexes hexacyanoferrate(ii) and hexacyanoferrate(iii) have no environmental significance since they are slower than the rate of DMTS decomposition. Under environmentally relevant conditions, rates of reactions of free cyanide with DMTS will be lower than the reaction with inorganic polysulfides or tetrathionate, but faster than the reaction with thiosulfate. Examples of application of kinetic parameters for calculation of rates of cyanide consumption in industrial and non-polluted natural aquatic systems as well as a protocol for quantification of organic polysulfide sulfur based on reaction with cyanide are provided.

Density Functional Theory and XPS Studies of the Adsorption of Cyanide on Chalcopyrite Surfaces.

In this work, both the density functional theory (DFT) calculation and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the depression mechanisms of cyanide on the flotation performance of chalcopyrite. The density functional theory calculation results showed that cyanide could be adsorbed on a chalcopyrite (112) surface spontaneously, which preferably occurred on the surface Fe–Fe hollow site. Both C and N atoms of cyanide could bond with Fe atoms of the chalcopyrite (112) surface, while the interaction of Fe–C bond was more intense, where the Fe 3d orbital donated electrons to the hybrid sp orbital of a C atom forming a back-donating bond. XPS analysis indicated that the chemical interaction between cyanide and surface Fe atoms occurred, resulting in the generation of a hydrophilic iron–cyanide complex on the chalcopyrite surface, which deteriorated the flotation performance of chalcopyrite.

Heteroaggregation between Charged and Neutral Particles.

Experimentally determined heteroaggregation rates between charged and neutral colloidal particles are reported for the first time. Different positively and negatively charged polystyrene latex particles are investigated. The neutral particles are obtained through adsorption of an appropriate amount of oppositely charged additives, such as aliphatic oligoamines, iron cyanide complexes, or alkyl sulfates. Heteroaggregation rates were measured with time-resolved multiangle light scattering. One observes that heteroaggregation between charged and neutral particles is always fast and diffusion controlled. These experimental values are compared with calculations of the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, whereby one finds that this heteroaggregation process is highly sensitive to charge regulation conditions. The comparison with experiments shows unambiguously that the surface of the neutral particles regulates strongly and probably behaves close to a constant potential surface. This observation is in line with direct force measurements on similar systems and further agrees with the fact that for neutral surfaces the capacitance of the diffuse layer is expected to be much smaller than the one of the inner layer.

Treatment of mining wastewater polluted with cyanide by coagulation processes: A mechanistic study

In this work, coagulation and electrocoagulation for the removal of cyanide ions contained in synthetic mining wastewater were evaluated paying particular attention to the elucidation of the coagulation mechanisms. Iron and aluminum salts with concentrations ranging from 0.01 to 10 000 mg dm−3 metal were used in chemical coagulation. Experimental data were properly fitted to Freundlich isotherm to elucidate that the main mechanism to remove cyanide during chemical coagulation was adsorption onto coagulant flocs although a maximum cyanide removal percentage of only 25% was attained. Then, electrochemical coagulation with iron and aluminum electrodes was evaluated at 1, 10 and 100 A m−2, obtaining completely different results. Iron electrochemical coagulation leads to the complete cyanide removal regardless of the current density applied, although the TOC removal was much lower than expected. On the contrary, only 60% of cyanide removal was reached by aluminum electrochemical coagulation and its efficiency was found to be highly dependent on the current density applied. Furthermore, no cyanate or hazardous inorganic chlorine species were detected during both electrocoagulation processes. However, chloride was oxidized to hypochlorite and then, it reacted with ammonium ions (contained in mining wastewater or produced by chemical reduction of nitrate by aluminum) to form chloramines. A proposal of coagulation mechanisms during the electrochemical process that explains experimental results was developed which involved the formation of iron-cyanide complexes, charge neutralization, adsorption on a superficially charged metal precipitate and/or enmeshment into a sweep metal floc.

Kinetics of Thiocyanate Formation by Reaction of Cyanide and Its Iron Complexes with Thiosulfate

Reactions between cyanide and compounds, which contain S–S bonds, in aqueous media result in formation of thiocyanate. In this work, we studied the kinetics of reactions of thiosulfate with free cyanide and its complexes under environmental conditions. Rates of reactions between cyanide species and thiosulfate decrease in the following order: CN− > HCN > [Fe(CN)6]3− > [Fe(CN)6]4−. However, at neutral and slightly acidic pH range, reaction of thiosulfate with iron-cyanide complexes outcompetes its reaction with free cyanide, which exists in equilibrium with complexed cyanide. At environmentally relevant conditions, the characteristic time of reaction between free cyanide and thiosulfate was found to be tens of thousands of years, while for iron-cyanide complexes it was found to be hundreds to millions of years. Examples of application of kinetic parameters for calculation of rates of cyanide consumption in industrial (coke oven wastewater) and non-polluted natural aquatic system (Delaware Great Marsh) are provided.

Thermal remediation of cyanide-contaminated soils：process optimization and mechanistic study

Site soils with persistent cyanide compounds (primarily iron-cyanide complex) pose potential hazards to the environment and require remediation before redevelopment. This study evaluated the possibility of thermal treatment on remediation of cyanide-contaminated soils via batch heating experiments spanning a wide temperature range (200–500 °C). The change with operation variables of total cyanide and some reaction intermediates (e.g. CN−) was analyzed in order to elucidate the optimal variables that guarantee cyanide removal while generating no hazardous byproducts. Temperature, heating time and cyanide species have been found to be important parameters influencing removal/destruction of cyanide in soils. For soils bearing K3[Fe(CN)6] and K4[Fe(CN)6], a removal efficiency of >99.9% can be obtained with temperatures over 350 °C at 1 h, while for samples bearing Fe4[Fe(CN)6]3, a higher temperature (>450 °C) is needed to obtain an equivalent efficiency. During heating, the iron-cyanide complexes decomposed, releasing highly toxic free cyanides, which will subsequently be oxidized. However, a small percentage of free cyanide can always be detected as a result of incomplete oxidation, thus caution should be taken to minimize the accumulation of free cyanide during thermal treatment.

Phytoremediation of cyanide and iron cyanide complexes and the mechanisms involved

This paper reviewed the physical and chemical properties of cyanide species - free cyanide and iron-cyanide complexes, and the potential of cyanide phytoremediation with reference to the phytotoxicity of free cyanide and iron-cyanide complexes in plants. There are three possible pathways, which are β-cyanoalanine synthase, sulfur transferase and formamide hydrolase pathways, for transforming and assimilating endogenous free cyanide in plants. Iron-cyanide complexes are generally resistant to microbial and fungal degradation. It is suggested that there may be undiscovered degradation pathways involved in assimilating iron-cyanide complexes in plants; however the detailed pathways of assimilation of iron-cyanides are still unknown. While uptake of free cyanide is mainly by simple diffusion, as iron-cyanide complexes are membrane-impermeable, it is suggested that the complexes may be transported into the plants through the mode of protein mediated uptake. Upon uptake, biological fates of cyanide species vary with different species of cyanide, depending on their chemical properties and concentrations. Phytotoxicity of free cyanide in plants is much higher than that of iron-cyanide complexes as plants could generally withstand a higher concentration of iron-cyanide complexes comparing with free cyanide. However, it is still unsure if the iron-cyanide complexes are toxic themselves or if they disrupt the metabolism of plants indirectly. It is known that endogenous cyanogenic compounds play a role in providing sources of nitrogen and acting as precursors in some biochemical processes in plants. Studies suggested that exogenous cyanide species, to a certain extent, could benefit the plants through providing nutrition to them. However, there is still no study conclusively indicates that there is a direct acquisition of exogenous cyanide species by plants as their alternative source of nitrogen. Further investigations on the degradation pathways of iron-cyanide complexes and the essential enzymes involved in phyto-assimilation of iron-cyanide complexes are required for better understanding of the degradation and assimilation pathways of cyanogenic compounds in plants.

Alkaline-assisted leaching of iron-cyanide complex from contaminated soils

Soils with persistent cyanide compounds (including ferricyanide and ferrocyanide) pose potential hazards to the environment and require remediation before utilization. This study investigated the alkaline-assisted leaching behavior of iron-cyanide complexes from five cyanide-contaminated soils via batch leaching experiments spanning a wide pH range (10–14). The results showed that the leaching ratio of iron-cyanide complex (R) was highly dependent on pH. Leaching with alkaline solution of pH < 12 resulted in a small desorption ratio (1%–5% for the laboratory-contaminated A type soils and 11% for B type soil), while alkaline solution with elevated pH (>13) significantly enhanced the desorption ratio, reaching 87%–100% within a reaction time of 0.5 h except one soil sample. The desorption kinetics of the cyanide complexes at different pHs indicated that time is another parameter closely related to R. The time-dependent leaching ratio at pH 12 only slightly increased from 0.5 h to 48 h, reaching a maximum desorption ratio of 24% and 31% for ferricyanide and ferrocyanide, respectively. Whereas, the desorption profiles of contaminated soils at pH 13 revealed a rapid desorption of iron-cyanide complexes within the first two hours followed by a plateau that corresponded to a complete desorption. The leaching characteristics of all cyanide contaminated soils revealed the fact that ferricyanide has a stronger affinity with soils than ferrocyanide, which implies a lower mobility of ferricyanide.

Matrix Infrared Spectra of Manganese and Iron Isocyanide Complexes.

Mono and diisocyanide complexes of manganese and iron were prepared via the reactions of laser-ablated manganese and iron atoms with (CN)2 in an argon matrix. Product identifications were performed based on the characteristic infrared absorptions from isotopically labeled (CN)2 experiments as compared with computed values for both cyanides and isocyanides. Manganese atoms reacted with (CN)2 to produce Mn(NC)2 upon λ > 220 nm irradiation, during which MnNC was formed mainly as a result of the photoinduced decomposition of Mn(NC)2. Similar reaction products FeNC and Fe(NC)2 were formed during the reactions of Fe and (CN)2. All the product molecules together with the unobserved cyanide isomers were predicted to have linear geometries at the B3LYP level of theory. The cyanide complexes of manganese and iron were computed to be more stable than the isocyanide isomers with energy differences between 0.4 and 4 kcal/mol at the CCSD(T) level. Although manganese and iron cyanide molecules are slightly more stable according to the theory, no absorption can be assigned to these isomers in the region above the isocyanides possibly due to their low infrared intensities.

Preparation of 15N-labeled Potassium Ferrocyanide for Tracer Studies

Isotopic labels are widely used to trace the fate and cycling of common environmental contaminants. Many of the labeled materials are not available commercially and, depending on the complexity of the substance, the label and the enrichment level, custom syntheses are costly. A simple, straightforward, and cost effective method for the preparation of a highly enriched, 15N-labeled potassium ferrocyanide (K4[Fe(C15N)6]*3H2O) has been developed to meet the requirements of related tracer experiments and minimize their costs. In this case, the 15N label was used to quantify iron cyanide detoxification (biodegradation and/or transformation) within soil-plant-systems. 15N-labeled potassium cyanide (KC15N) and a ferrous iron salt have been used for the synthesis. Extensive qualitative and quantitative analyses showed a product, entirely identical in its functional and elemental components to commercial non-labeled K4[Fe(CN)6]*3H2O and in its 15N enrichment to the KC15N used for its synthesis. To investigate their behavior and fate in various environmental compartments, other labeled iron or metal cyanide complexes might be synthesized in analogous manner.

Quick detection and quantification of iron-cyanide complexes using fourier transform infrared spectroscopy

The continuous release of persistent iron-cyanide (Fe-CN) complexes from various industrial sources poses a high hazard to the environment and indicates the necessity to analyze a considerable amount of samples. Conventional flow injection analysis (FIA) is a time and cost consuming method for cyanide (CN) determination. Thus, a rapid and economic alternative needs to be developed to quantify the Fe-CN complexes. 52 soil samples were collected at a former Manufactured Gas Plant (MGP) site in order to determine the feasibility of diffuse reflectance infrared Fourier spectroscopy (DRIFTS). Soil analysis revealed CN concentrations in a range from 8 to 14.809 mg kg−1, where 97% was in the solid form (Fe4[Fe(CN)6]3), which is characterized by a single symmetrical CN band in the range 2092–2084 cm−1. The partial least squares (PLS) calibration-validation model revealed IR response to CNtot which exceeds 2306 mg kg−1 (limit of detection, LOD). Leave-one-out cross-validation (LOO-CV) was performed on soil samples, which contained low CNtot (<900 mg kg−1). This improved the sensitivity of the model by reducing the LOD to 154 mg kg−1. Finally, the LOO-CV conducted on the samples with CNtot > 900 mg kg−1 resulted in LOD equal to 3751 mg kg−1. It was found that FTIR spectroscopy provides the information concerning different CN species in the soil samples. Additionally, it is suitable for quantifying Fe-CN species in matrixes with CNtot > 154 mg kg−1. Thus, FTIR spectroscopy, in combination with the statistical approach applied here seems to be a feasible and quick method for screening of contaminated sites.

Low Voltage Charge/Discharge Behavior of Manganese Hexacyanoferrate

Recently, Prussian blue analogues (PBAs) have been reported to exhibit a low voltage charge/discharge behavior with high capacity (300–545 mAh/g) in lithium-ion secondary batteries (LIBs) [...]

Proton‐Coupled Reduction of an Iron Cyanide Complex to Methane and Ammonia

AbstractNitrogenase enzymes mediate the six‐electron reductive cleavage of cyanide to CH4 and NH3. Herein we demonstrate for the first time the liberation of CH4 and NH3 from a well‐defined iron cyanide coordination complex, [SiPiPr3]Fe(CN) (where [SiPiPr3] represents a tris(phosphine)silyl ligand), on exposure to proton and electron equivalents. [SiPiPr3]Fe(CN) additionally serves as a useful entry point to rare examples of terminally‐bound Fe(CNH) and Fe(CNH2) species that, in accord with preliminary mechanistic studies, are plausible intermediates of the cyanide reductive protonation to generate CH4 and NH3. Comparative studies with a related [SiPiPr3]Fe(CNMe2) complex suggests the possibility of multiple, competing mechanisms for cyanide activation and reduction.