Cyanide Complex Ions Research Articles

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.

Study on electrosorption behavior of weak metal cyanide complex ions based on coal-based electrode

Using the electrosorption technology treatment the cyanide wastewater has a good treatment effect, but the mechanism is not completely clear. In this paper, we conducted electrosorption experiments using simulated cyanide solutions to study the adsorption kinetics, thermodynamics, adsorption isotherms and analyze the reaction mechanism of zinc-cyanide and copper–cyanide complex ions. The results show that the electrosorption process of weak metals cyanide complexes treated by coal-based (CB) electrode conforms to the second-order kinetic model and follow the Langmuir model, affected by the dipole force and exchange of coordination groups. The equilibrium adsorption amounts of the two species at 2 V were 1.53 and 1.74 times higher than those at open circuit, respectively. During the electrosorption process, affected by the pseudo-capacitance, pore structure of CB electrodes and the charges of complex ions, the zinc-cyanide complex is bound in the double electric layer on the anode surface by the electric field, but partly decomposed to produce zinc ions and forms Zn(OH)2 in alkaline solution then generates ZnO precipitates, a small amount of Zn2+ were electrostatically adsorbed on the cathode surface for reduction deposition. However, the majority of the copper–cyanide complexes were purified by electrostatic adsorption to the double layer near the anode, while a small amount of decomposition occurred to produce Cu(OH)2 in the alkaline system, and almost no copper was deposited by reduction. This research results can enable us to better understand the removal characteristics of the weak metal cyanide complex ions in the process of electrosorption by CB electrode, and have great significance for the application of electrosorption technology to the treatment of cyanide wastewater.

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.

Study on Removal Mechanism for Copper Cyanide Complex Ions in Water: Ion Species Differences and Evolution Process.

A large amount of cyanide-containing wastewater is discharged during electrode material synthesis. Among them, cyanides will form metal-cyanide complex ions which possess high stability, making it challenging to separate them from these wastewaters. Therefore, it is imperative to understand the complexation mechanism of cyanide ions and heavy metal ions from wastewater in order to obtain a deep insight into the process of cyanide removal. This study employs Density Functional Theory (DFT) calculations to reveal the complexation mechanism of metal-cyanide complex ions formed by the interaction of Cu+ and CN- in copper cyanide systems and its transformation patterns. Quantum chemical calculations show that the precipitation properties of Cu(CN)43- can assist in the removal of CN-. Therefore, transferring other metal-cyanide complex ions to Cu(CN)43- can achieve deep removal. OLI studio 11.0 analyzed the optimal process parameters of Cu(CN)43- under different conditions and determined the optimal process parameters of the removal depth of CN-. This work has the potential to contribute to the future preparation of related materials such as CN- removal adsorbents and catalysts and provide theoretical foundations for the development of more efficient, stable, and environmentally friendly next-generation energy storage electrode materials.

Removal of metal ions from cyanide gold extraction wastewater by alkaline ion-exchange fibers

The metal cyanide complex ions of gold extraction wastewater consume extra cyanide and compete with gold for adsorption on activated carbon during wastewater recycling. Therefore, the removal of metal cyanide complex ions from gold extraction wastewater is of great significance. In this study, polypropylene (PP) fibers were used to prepare strong acylated alkaline ion-exchange fibers (SAA-IEFs) using a polymer graft monomer method that achieved excellent adsorption of metal cyanide complex ions from gold extraction wastewater. The properties of the SAA-IEFs were characterized via scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). Adsorption experiments were conducted to study the adsorption performance and to verify the adsorption mechanism. The results show that the highest adsorption efficiencies of the SAA-IEFs for zinc and copper cyanide complex ions were 85.5% and 91.2%, respectively, and these performances were obtained when the SAA-IEF concentration was 50 g/L and pH was 10. The adsorption efficiency of the cyanide complexes in practical wastewater reached 92% at a concentration of 30 g/L. The desorption and regeneration results indicate that the adsorption capacity of the SAA-IEFs remained high after nine cycles. Moreover, an adsorption mechanism is proposed, and the adsorption process is best modeled using the Freundlich isotherm and pseudo-second-order kinetic model. These results indicate that chemisorption plays a dominant role in the adsorption process. Overall, SAA-IEFs are a promising, efficient, and cost-effective adsorbent for metal cyanide complex ion adsorption from gold extraction wastewater.

Modelling of the kinetics adsorption of gold (I) cyanide complex ion by active carbons prepared from Parinari macrophylla shells

Nowadays, one of the sectors to valorization of waste is their transformation in nobler materials rather than in energy. This study is about the valorization of agricultural waste (Parinari Macrophylla shells) for the development of active carbons, the characterization of porous materials gotten and the kinetic study for adsorption of gold (I) cyanide complex ion. The development is made by impregnation in KOH followed of a pyrolysis under flux of N2 or CO2. The characteristics determined for adsorption are iodine index, methylene blue index, pH to point of zero charge (pHPZC) as well as the textures characteristics gotten by adsorption of nitrogen at 77 K. For adsorption of gold (I) cyanide complex ion , the kinetics model’s pseudo-order 1, pseudo-order 2, the model of Elovich and those diffusions of Boyd and Weber-Morris are studied. The results of the characterization showed that samples are basic (pHPZC > 7), present the specific surfaces of 1008 m2/g and 1063 m2/g with percentages in microporous surface more than 78% and for microporous volume more than 71%. The kinetics of adsorption of gold (I) cyanide complex ion (Au(CN)2-) obeys more to pseudo-order 2 model and a multi-linearity of the models of Elovich and diffusions during adsorption.

Modelling of the kinetics adsorption of gold (I) cyanide complex ion by active carbons prepared from Parinari macrophylla shells

Modelling of the kinetics adsorption of gold (I) cyanide complex ion by active carbons prepared from Parinari macrophylla shells

Kinetic study on extraction of metal-cyanide complex ions by the N263-TBP system

In this study, the extraction of metal-cyanide complex ions in gold-leaching, cyanide-containing wastewater by a trioctylmethylammonium chloride (N263)-tributyl phosphate (TBP)-n-octanol-sulfonated kerosene system was investigated. The effects of N263 and TBP concentrations, the aqueous phase pH, and phase ratio (O/A) on the extraction were investigated by adopting the response surface methodology, and the operating parameters were optimized. The optimal solution was obtained by solving the model optimally. A Cu ion concentration of 3,000 mg/L, an N263 concentration of 0.459 mol/L, a TBP concentration of 0.214 mol/L, an initial pH of the aqueous phase of 10.064, and O/A of 0.900 were determined to be optimal for realizing an extraction yield of 99%. The effects of column height, oil droplet volume, metal ion concentration, N263 and TBP concentrations, and temperature on the mass transfer rate were investigated using the single droplet method. Kinetic studies showed that the kinetic equation for the extraction system was Rf (Mass transfer rate) = 1.57 × 10-4·CCu·CTBP·CN263. The apparent activation energy of Cu(I) was 15.186 kJ/mol. The extraction process was controlled by the diffusion process. Furthermore, the chemical reaction occurred at the two-phase interface, where the copper cyanide complex ions preferentially bound to TBP at the interface between the two phases, and the bound anion cluster then reacted with the N263 cation to form the extractive complex, which then entered the organic phase from the interface.

Ag3PO4/Ag nanocomposite for selective and sensitive cyanide determination in food samples through catalytical colorimetry using a paper-based test kit

A paper-based test kit for selective and sensitive determination of cyanide was successfully developed using a Ag3PO4/Ag nanocomposite for catalytic colorimetry. The Ag3PO4/Ag nanocomposite synthesized via a one-step chemical bath method could instantly oxidize the chromogenic substrate ABTS for the color development under acidic conditions without the requirement of H2O2. During the detection step, cyanide in the sample was converted into gaseous hydrogen cyanide (HCN) using sulfuric acid. The HCN species then reacted with the generated Ag+ species via coordinate covalent bonding to form silver cyanide complex ions [Ag (CN2)]-. The amount of Ag+ species used for oxidizing ABTS subsequently decreased and so did the color intensity on the paper-based test kit. Specifically, the color intensity decreased with increasing cyanide concentrations in the range of 2.50–20.0 mg L−1. The limit of detection (LOD) and limit of quantification (LOQ) were 0.48 mg L−1 and 1.59 mg L−1, respectively. The developed test kit showed relatively high selectivity towards cyanide and high tolerance towards other cations and anions present in real samples. When applied to real samples including fruit juices and food products, the performance of the rapid and low-cost test kit was well validated by a conventional precipitation titration method.

Recycling of residual valuable metals in cyanide-leached gold wastewater using the N263-TBP system

In this study, the synergistic extraction system of trioctylmethyl ammonium chloride (N263)-tributyl phosphate (TBP)-n-octanol-sulfonated kerosene was used to enrich and recover valuable metals from cyanide gold extraction of wastewater. The effects of the proportion of N263 and TBP, contact time, initial pH of water phase, temperature, and phase ratio (O/A) on the extraction percentage of metal cyanide complex ions and the synergistic extraction reaction mechanism were mainly investigated. Results showed that the single-stage extraction percentages of Cu, Zn, and Fe ions in wastewater were 99.87%, 99.8%, and 96.2%, respectively, and the saturated extraction capacity was 4356.4 mg/L under the conditions of N263 (20 vol%)-TBP (20 vol%)-n-octanol (10 vol%)-sulfonated kerosene system at 25 °C, O/A of 1:1, pH of 10, and contact time of 5 min. Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS) analyses showed that metals entered the organic phase in the form of metal cyanide complex ions during extraction. Metal cyanide complex ions preferentially combined with TBP to lose hydrophilicity and then reacted with N263 cations to enter the organic phase. The saturated organic phase was stripped by NaOH and NaSCN mixed solution, and the total concentration of metal ions in the stripping solution reached 11,996.6 mg/L.

Efficient adsorption of Au(CN)2− from gold cyanidation with graphene oxide-polyethylenimine hydrogel as adsorbent

Abstract The adsorption of gold cyanide complex ion (Au(CN)2−) on graphene oxide-polyethylenimine hydrogel (GO/PEI hydrogel) from gold cyanidation has been studied to explore the possibility of the application of GO/PEI hydrogel in gold cyanidation process for extracting gold from ores. The adsorption was carried out in artificial Au(CN)2− aqueous solution with GO/PEI hydrogel as adsorbent. The experimental results, as well as IR, XPS and SEM−EDS, have shown that GO/PEI hydrogel exhibited a high adsorption capacity and a fast adsorption rate of Au(CN)2−, suggesting that GO/PEI hydrogel might be a good adsorbent for the recovery of Au(CN)2−. The adsorption of Au(CN)2− on GO/PEI hydrogel obeyed the Langmuir isotherm model and fitted well with the pseudo second order model. The good recovery of Au(CN)2− was largely related to the porous structure, large specific surface area, as well as the oxygenous functional groups on the surface of GO/PEI hydrogel.

Use of vetiver (Vetiveria zizanoides) in remediation of cyanide soil contamination

purpose of this greenhouse study was to assess the vetiver (Vetiveria zizanoides) in terms of the capacity to tolerate and accumulate cyanide (KCN) from contaminated soils of varying physicochemical properties. The toxicity of potassium cyanide (KCN) to grass vetiver (Vetiveria zizonioides) was tested. At the end of test, almost all cyanides had vanished from soils. Also, the in vivo capacity of Vetiveria zizonioides to remove cyanide was evaluated. For cyanide adsorption onto Vetiveria zizonioides, various parameters, affecting the removal rate, such as pH (6-8), and contact time (3-9months) were evaluated. The effect of pH on cyanide complex ion uptake rate and capacity of Vetiveria zizonioides was studied at 4-8 mg kg-1 initial cyanide concentration. Cyanide adsorption was increased with increasing soil pH, water content and contact time. At an optimum pH of 8, over 85% removal of 8 mg kg-1 cyanide was obtained for Vetiveria zizonioides after 9 months of contact time. Data from the experiment were analyzed with statistical software SPSS. The removal of cyanide by vetiver might be useful in cleanup of soil from gold and silver mining.

Adsorption of the complex ion Au [formula omitted] onto sulfur-impregnated activated carbon in aqueous solutions

The adsorption of the gold–cyanide complex ion (Au ( CN ) 2 - ) on sulfur-impregnated activated carbon in aqueous solution has been studied in order to find a better adsorbent for the gold cyanidation process for extracting gold from ores. This study was performed using sulfur-impregnated activated carbon (SIAC 8.0) made from high-sulfur petroleum coke and an artificial aqueous solution of Au ( CN ) 2 - . The experimental results have shown that Au ( CN ) 2 - strongly adsorbed onto the SIAC 8.0, leading the gold adsorption capacity of the SIAC 8.0 to be 2.25× that on conventional activated carbon. It has been also found that the adsorption fit the Langmuir isotherm well, and the adsorption density of Au ( CN ) 2 - on the SIAC 8.0 in aqueous solution increased with increasing temperature, suggesting chemical adsorption. The chemical adsorption might be attributed to the formation of S–Au–CN on SIAC 8.0 surfaces through the covalent bond between the gold atom of the ion and the sulfur in the molecular structure of the SIAC 8.0. In addition, the desorption test has demonstrated that the majority of the adsorption was irreversible, which depended on the density of the adsorption sites on the SIAC.

Biosorption of hexacyanoferrate(III) complex anion to dead biomass of the basidiomycete Pleurotus mutilus: Biosorbent characterization and batch experiments

This work is a contribution to the use of natural, cost-effective biosorbants in industrial wastewater treatment processes, addressing more particularly to the effluents resulting from surface treatment and mining industries. A dead fungal biomass (i.e., Pleurotus mutilus) collected as a waste from an antibiotic production plant was tested as a biosorbent for iron(III)–cyanide complex ions. A physicochemical characterization of this biomass was followed by batch biosorption experiments. Potentiometric titration confirmed by FTIR analysis indicated a variety of functionalities on the biomass surface, primarily carboxylic and amine groups which conferred to the biosorbent a positive charge in acid medium and a negative charge in alkaline medium. Biomass pre-treatment with acetic acid slightly improved its biosorption efficiency which was also affected by the initial pH of the test solution, the size and concentration of biosorbent particles, and the stirring speed of the particle suspension. In particular, the best performance was obtained at strongly alkaline pH (around 12) even though the overall electrical charge of the biomass was negative in this pH range. The sorption kinetics obeyed both pseudo-first-order and pseudo-second-order models and intraparticle diffusion was the main limiting step in the biosorption kinetics. Applying the Langmuir isotherm modelling, the highest biosorption efficiency, i.e., the maximum solid phase concentration of complex ions (forming a complete monolayer coverage on the sorbent surface) was over 620 mg g−1. Continuous fixed-bed sorption–desorption experiments are in progress to confirm these promising results.

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.

Binary biosorption of iron(III) and iron(III)-cyanide complex ions on Rhizopus arrhizus: modelling of synergistic interaction

Many heavy metal-bearing wastewaters also contain their metal cyanide complex ions. Although the biosorption of single or multi-metal ions to various microorganisms has been extensively studied, very little attention has been given to the bioremoval and the expression of the adsorption equilibrium and kinetics of metal–metal cyanide complex ion systems. In this study, the simultaneous biosorption of iron(III) (ferric) cations and iron(III)-cyanide complex (ferricyanide) anions to Rhizopus arrhizus from binary mixtures was studied and compared with single metal and metal cyanide complex ion situation in a batch stirred system. The effects of initial pH and single and dual-component concentrations on the biosorption kinetics and equilibrium uptake of each component, both singly and in mixture were investigated. The working pH value for both species was determined as 2.0. Multi-component biosorption studies were also performed at this pH value. The biosorption rates and equilibrium uptakes of iron(III) or iron(III)-cyanide complex ions increased by the presence of increasing concentrations of the other ion up to 200 mg l −1 for iron(III) and up to 1000 mg l −1 for iron(III)-cyanide complex ions. This situation showed a synergistic interaction between these ions. The Freundlich, Langmuir and Redlich–Peterson adsorption models were used to predict the mono-component equilibrium uptake and model parameters were estimated by the non-linear regression. It was seen that the mono-component adsorption equilibrium data fitted very well to the mono-component Langmuir and Redlich–Peterson models for both the components at moderate ranges of concentration. A modified synergistic Langmuir model was proposed for dual-component system and model parameters were also estimated by the non-linear regression. The pseudo second-order kinetic model was applied to single and multi-component experimental data assuming that the external mass transfer limitations in the system can be neglected and biosorption is sorption controlled.

Effect of internal diffusivity of ferrous(II) cyanide complex ions in Ca-alginate immobilized Pseudomonas fluorescens gel beads on the biodegradation rate

Combined biodegradation and internal diffusion effects on the biodegradation rate of ferrous(II) cyanide complex (ferrocyanide) ions by Ca-alginate gel immobilized Pseudomonas fluorescens beads were investigated as a function of initial ferrocyanide concentration and particle size in a batch system. Assuming first-order biodegradation kinetics ( ν= kC), first-order biodegradation rate constants for free and different sized immobilized particles were predicted and at 100 mg l −1 bulk ferrocyanide ion concentration experimental effectiveness factors ( η) were determined for each particle size. Then using these data, the Thiele modulus ( φ) was evaluated for each particle size. Finally effective diffusion coefficient ( D e) was calculated from the Thiele modulus equation, which is a function of particle size, effective diffusion coefficient and first-order biodegradation rate constant. The results showed that the intraparticle diffusion resistance has a significant effect on the observed biodegradation rate.

Biodegradation kinetics of ferrous(II) cyanide complex ions by immobilized Pseudomonas fluorescens in a packed bed column reactor

Combined external mass transfer and intrinsic biodegradation effects on the observed biodegradation rate were investigated for ferrous (II) cyanide complex (ferrocyanide) ions removal with calcium–alginate gel immobilized Pseudomonas fluorescens in a packed bed column reactor. Assuming first-order biodegradation kinetics, observed first-order biodegradation rate constants ( k p) were calculated at different flow rates. To investigate the effect of external film diffusion on the observed biodegradation rate, several external mass transfer correlation models of the type J D= KN Re −(1− n) were tested and the mass transfer coefficients ( k l) were calculated as a function of the mass flux ( G) and the Reynolds number ( N Re) at different K and n values. The intrinsic first-order biodegradation rate constants ( k) and the surface areas per unit weight of dried cells for mass transfer ( a m) were determined from 1/ k p versus 1/ G n plots at the same n values. Combining the k and k l a m values, the observed first-order biodegradation rate constants ( k p) were calculated again at the same n values and compared with the k p values determined from experimental data. The mass transfer correlation J D=1.625 N Re −0.507 predicted accurately the experimental data.

Adsorption of iron(III)‐cyanide complex ions to granular activated carbon

The adsorption of iron(III)‐cyanide complex anions to granular activated carbon was investigated. The iron(III)‐cyanide complex ion binding capacity of the adsorbent was shown as a function of initial pH, initial iron(III)‐cyanide complex ion and adsorbent concentrations. The results indicated that a significant reduction of iron(III)‐cyanide complex ions was achieved at pH 13.0, a highly alkaline condition. The equilibrium loading capacity of adsorbent was 410.0 mg/g at 1255.0 mg/l initial iron(III)‐cyanide complex ion concentration at this initial pH value. The Freundlich, Langmuir and Redlich‐Peterson adsorption models were fitted to the equilibrium data at pH 3.0, 7.0 and 13.0. The equilibrium data could be best fitted to the Langmuir and Redlich‐Peterson adsorption models over the entire concentration range at all the studied initial pH values.