Cyanide Solutions Research Articles

The cyanidation of sub microscopic gold: An experimental and molecular modeling study

Sub microscopic refractory gold ore is an important resource of gold with the depletion of free-milling gold deposits in this century. It has been generally accepted that submicroscopic gold mainly in the form of solid-solution and colloidal particles are physically locked inside mineral phases and impervious to cyanide solution. However, some researches on synthetic nanoparticles show they have very different physical and chemical properties which can affect their dissolution behavior.This research has been conducted to investigate the dissolution behavior of gold sub microscopic particles experimentally and theoretically using density functional theory. For this purpose, 20 nm gold particles have been synthesized and dissolved in cyanide solution under controlled condition. The rate of dissolution has been monitored during cyanidation and compared with a gold disk. The results depict the rate of dissolution per surface area is significantly reduced in gold nanoparticles (30 times, the surface ratio of 14/9 m2/g and 0.006 m2/g in samples is 2500 times smaller while the dissolution rate in nanoparticles is 83 times faster). Also, the smaller nanoparticles have much slower dissolution kinetics than large nanoparticles (5.485 × 10−5 and 4.280 × 10−6 g/m2.s for 16 and 2 nm particles, respectively). Two different dissolution regimes can be identified for >3 nm and < 3 nm nanoparticles. In larger particles, by increasing the number of surface atoms with weaker bond energy and also lower oxidation potential, the dissolution rate increases compared to bulk gold. In nanoparticles smaller than 3 nm, the electrochemical reaction in the cyanide medium is disrupted by the reduction of oxidation potential and decreasing the conductivity as the requirement for electrochemical dissolution of gold in cyanide.The molecular modeling study on the gold clusters of 1 to 20 atom confirm that the oxidation of small clusters of gold is more difficult than bulk gold due to the high ionization energy (9.66 vs. 5.4 eV). Also, the monoatomic gold has a much weaker interaction with cyanide (−4.36 vs. -1.6 eV) and higher interaction with oxygen (−0.64 vs. -0.15 eV) compared to the bulk gold. The HOMO of monoatomic and bulk gold (−9.22 and − 4.5 eV) as well as LUMO of cyanide and oxygen (1.734 and − 4.657 eV), as two reactants in cyanidation process confirm the results based on HSAB theory. As a result, oxygen competes with cyanide for adsorption on the surface of gold nanoparticles, disrupting the first step of electrochemical dissolution of gold, as the adsorption of cyanide and the formation of the Au-CN− complex. This is possible by deactivating the surface by creating a resistant layer of gold oxide or electrostatic adsorption of oxygen on the gold surface and passivating the surface. The modeling data are very well in agreement with the experimental results indicating the inherent inactivity of free surface gold sub microscopic particles during the cyanidation process.

Quantification of hydrogen cyanide in fire effluent

Hydrogen cyanide is often the most toxicologically significant component in fire effluents from nitrogen-containing materials. Unlike the other major asphyxiant, carbon monoxide, sensors for continuous hydrogen cyanide quantification, at and above dangerous concentrations, are not commercially available. This article investigates the analysis of fire effluent captured in bubbler solutions, by colorimetric quantification of hydrogen cyanide using chloramine-T/isonicotinic acid. The bubbler samples were mixed with colorimetric reagents to give a blue dye in response to cyanide ions. A novel reaction scheme accounting for the formation of the blue dye from cyanide ions is presented. Dilute, standard cyanide solutions were found to be stable after storage for up to 1 year. Alkaline bubbler solutions, through which the fire effluent has passed, showed consistent cyanide concentrations, for samples stored between 5°C and 21°C, for up to 31 days after sampling. The effect of other common ions likely to be present in fire effluent solution samples (CO32−, SO32−, SO42−, NO2− and NO3−) was investigated for their potential interference. The most significant interference was sulphite which reduced the apparent cyanide concentration by 13% at 10 mg L−1SO32− concentration.

Syntesis of amine and thiol silica modified: used of removal Ag(I) of aqueous system

The recovery of Au from rich cyanidation solutions is usually carried out by adsorption on activated carbon, a process that presents as its main disadvantage the formation of fines in the classifying screens, these fines represent a considerable loss of values in the process, which is why The search for alternatives that allow the recovery of gold and silver from rich cyanidation solutions is of interest to hydrometallurgy. In this sense, magnetic pre-concentration could be an alternative for said process. the present work shows the study of the removal of AgNO3 and [Ag(CN)2]- in synthetic aqueous systems with mesoporous amino and/or thiol silicas modified with magnetite (MS-NH2-Fe3O4 and MSNH2-SH-Fe3O4) . It is observed that the presence of ligands of a softer nature favors the removal of Ag in AgCN systems, showing low removal capacity for amine materials.

Separation of Palladium from Alkaline Cyanide Solutions through Microemulsion Extraction Using Imidazolium Ionic Liquids.

In this paper, three imidazolium-based ionic liquids, viz., 1-butyl-3-undecyl imidazolium bromide ([BUIm]Br), 1-butyl-3-octyl imidazolium bromide ([BOIm]Br), and 1-butyl-3-hexadecyl imidazolium bromide ([BCIm]Br), were synthesized. Three novel microemulsions systems were constructed and then were used to recover Pd (II) from cyanide media. Key extraction parameters such as the concentration of ionic liquids (ILs), equilibration time, phase ratio (RA/O), and pH were evaluated. The [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system exhibited a higher extraction percentage of Pd (II) than the [BOIm]Br/n-heptane/n-pentanol/sodium chloride and [BCIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion systems. Under the optimal conditions (equilibrium time of 10 min and pH 10), the extraction percentages of these metals were all higher than 98.5% when using the [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system. Pd(CN)42- was separated through a two-step stripping procedure, in which Fe (III) and Co (III) were first separated using KCl solution, then Pd(CN)42- was stripped using KSCN solution (separation factors of Pd from Fe and Co exceeded 103). After five extraction-recovery experiments, the recovery of Pd (II) through the microemulsion system remained over 90%. The Pd (II) extraction mechanism of the ionic liquid [BUIm]Br was determined to occur via anion exchange, as shown by spectral analysis (UV, FTIR), Job's method, and DFT calculations. The proposed process has potential applications for the comprehensive treatment of cyanide metallurgical wastewater.

Outstanding Performance of the Deep Eutectic Solvent-Based Aqueous Biphasic System Constructed with Sodium Citrate for a Green Gold Separation.

Aqueous biphasic systems (ABSs) that are based on deep eutectic solvents (DESs) are environmentally benign systems to use for metal ion separation. In this work, a series of DESs was synthesized for the first time with PEG 400 as hydrogen bond donors and tetrabutylphonium bromide (P4Br), tetrabutylammonium bromide (N4Br), or tetrabutylammonium chloride (N4Cl) as hydrogen bond acceptors, and then they were combined with citrate (Na3C6H5O7), which is eco-friendly, to construct an ABS for use in the separation of Au(I) from an aurocyanide solution. Phase diagrams of DESs + Na3C6H5O7 + H2O systems were constructed using the experimentally measured data. Multiple factors that affect the efficiency of the gold extraction were studied; these factors were the species of salt or DES and their content, the equilibrium pH, the oscillation time, and the initial gold concentration. Gold(I) is preferentially retained in the DES-rich phase, and the P4Br:PEG 1:2 + Na3C6H5O7 + H2O system has a high extraction efficiency of 100.0% under optimized conditions. FT-IR, NMR, and TEM characterizations and DFT calculations show that the migration of Au(I) from the salt-rich to the DES-rich phase follows an ion exchange mechanism. Specifically, Au(CN)2- replaces Br- in the original P4Br and generates a stable ion pair with the quaternary phosphonium salt cation, P+, and this replacement is driven by electrostatic attractions. A new strong hydrogen bond network simultaneously forms between the anionic Au(CN)2- and the -OH group in the PEG 400 component. Finally, the gold of Au(I)-loaded P4Br:PEG 1:2 can be successfully reduced by sodium borohydride with an efficiency of 100.0%. The strategy to extract gold(I) from alkaline cyanide solutions using an ABS based on DESs as proposed in this work provides a potential platform for developing green technology for recovering gold.

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.

A Novel Analytical Method of Thallium Determination in Gold Electrodeposition

Thallium is used in both cyanide and sulfite-based gold plating bath solutions as an additive that modulates how gold deposits on the target substrate. The level of Tl in the plating solutions has a large effect on the properties of the gold being deposited, including its microstructure and hardness. Thus, especially in commercial process applications, it is critical to be able to measure the Tl content of plating solutions accurately, quickly, and facilely in order to ensure proper quality of the products being manufactured. The cyclic voltametric behavior of Tl-containing gold plating bath solutions has been investigated, but quantification of its Tl content is unsatisfactory, either expensive and time consuming, or not accurate in complexed matrices. Here, we present a proprietary, electroanalytical method of Tl measurement that is fast and gives excellent accuracy and sensitivity, even in the presence of common bath breakdown products.

Recovery of Au and Ag from the roasted calcine of a copper-rich pyritic refractory gold ore using ion exchange resins

The recovery of Au and Ag from a roasted copper-rich pyritic refractory gold ore (78 g/t Au, 6.8 g/t Ag, 1.38 % Cu and 3.09 % Fe was investigated. Cyanide leaching and adsorption tests were performed at different concentrations of cyanide (1.5 g/L and 5 g/L NaCN) and the adsorbent dosages ranged from 2 g/L to 10 g/L. In the cyanide leaching tests, those performed at a high cyanide level (i.e., 5 g/L) produced high gold and silver extractions from the roasted ore apparently due to the increased availability of cyanide for gold leaching. Adsorption tests (CIL/CIP, RIL/RIP) were performed to investigate the selective recovery of gold and silver from copper-laden pregnant leach solutions obtained from cyanide leaching of the roasted ore. Activated carbon (NORIT GAC 1240), strong base resin (Purogold A194) and weak base resin (Purogold S992) were tested as adsorbents in these tests. The practical importance of increasing cyanide concentration on the selectivity (gold/silver vs copper) of resins as well as activated carbon was demonstrated. Each adsorbent offered good selectivity for gold over copper, particularly at a high concentration of cyanide (5 g/L NaCN). Purogold S992 appeared to be the most selective adsorbent with the highest gold and the lowest copper loadings. This distinctive trait makes the resin preferable for gold recovery from cyanide solutions containing significant levels of copper. Comparative pore size distribution analysis of the adsorbents has shown that Purogold S992 has the smallest pores with uniform size distribution among the adsorbents used. This was concomitant with its superior selectivity for gold at high cyanide concentration, which is linked with the small-size and linear gold-cyanide complexes c.f. large size and non-linear copper–cyanide complexes (Cu(CN)32– and Cu(CN)43-).

Enhanced copper cyanide complex precipitation using polymer-surfactant aggregates

Precipitation of metal cyanide complexes using quaternary ammonium salts has been used in cyanidation solutions after gold leaching. Due to the high residual load of metal cyanide complexes and ammonium salts, this method does not apply to effluents containing moderate or low cyanide concentrations. To overcome these limitations, in this study, we introduce poly(sodium 4-styrenesulfonate) (PSS) into a solution containing cetyltrimethylammonium bromide Sinpharm (CTAB), to form polymer-surfactant aggregates (PSAs) and enhance the removal efficiency of Cu and TCN. 93.8% and 97.0% of Cu and TCN, respectively, were removed from the synthetic solution (Cu 0.5 mM and CN 1.5 mM) under optimum dosage of 150 ppm PSS and 0.8 mM CTAB, resulting in 92.2% of substrate usage. The addition of 3.0 mM CTAB without PSS resulted in only 46.3% of substrate usage, even though the removals of Cu and TCN were 92.2 and 93.6%, respectively. The presence of thiocyanate ions significantly reduced the removal efficiency due to the competitive interaction with PSAs, whereas the pH of the solution and the temperature did not have any noticeable impact. Tests performed with an industrial effluent corroborated the results obtained with synthetic solutions: PSAs react with copper cyanide to form a precipitate that can be separated from the solution.

Conditioning of POX slurry and its effect on pressure oxidation performance of refractory gold sulphide ore

This paper describes the results of a laboratory study that looked at the conditioning of POX slurries produced by pressure oxidation (225 oC) of refractory gold flotation concentrates. The authors used a case study of sulphide concentrates produced as a result of flotation of refractory gold ores of the Malomyr and Pioner deposits to define the conditioning parameters applicable to POX slurries: i.e. temperature &mdash; 95 oC, duration &mdash; 2 to 4 hours. The above conditions help improve the quality of POX cakes before cyanidation so that the POX residue contained less sulphate sulphur and the cake weight could be lowered by 40&ndash;70%. The authors looked at the relationship between the conditioning parameters (60&ndash;95 oC with the duration of up to 7 hours) and the solids yield. They also examined how the above parameters influenced the transfer of the key components (i.e. iron, sulphur and arsenic) into liquid phase. In particular, the authors examined the process of conditioning POX cakes obtained from concentrates with the minimum (up to 2%) and high (8&ndash;10%) concentration of arsenic. The paper examines how the material composition of POX products tends to change after conditioning when dealing with sulphide concentrates. Conditioning was found to benefit the recovery of gold from POX cakes when dealing with high-arsenic concentrates. The gold particles in cakes can be encapsulated by mixed arsenate/sulphates of iron(III), which get dissolved during atmospheric conditioning, and the gold surface becomes available for cyanide solution. After conditioning, the share of cyanidable gold in POX cakes increases by 3.0 to 5.5%.

Analysis of the Behavior of As and Pb during the Pretreatments Applied to a Jarosite Residue for the Recovery of Gold and Silver

The recovery of valuable metals from jarosites is a topic of great relevance regarding the implementation of the circular economy; however, these materials also contain metals such as arsenic and lead, which are harmful to health and the environment. Considering these factors, it is important to monitor these metals at each stage of treatment used to recover the valuable metals. In the present work, the behavior of As and Pb was assessed during the pretreatment conducted on a jarositic residue using direct zinc leaching (DLR), as well as leaching in cyanide and cyanide media with glycine. It was found that when no DLR pretreatment was performed, As and Pb naturally dissolved in the cyanide-leaching medium at concentrations of 34.08 mg/L and 99.12 mg/L, respectively. When an alkaline treatment was conducted on the residue (DLR-AH), it was found that there was no presence of As and Pb in the cyanidation solution, while in the case of the cyanide solution with glycine, we observed 83.35 mg/L of As and 213.63 mg/L of Pb. During the oxidizing alkaline hydrothermal treatment (DLR-AHO), 27.5 mg/L of As and 106.78 mg/L of Pb were detected in the cyanide solution. In the cyanide solution with glycine, there was less dissolution of As and Pb (11.68 and 66.75 mg/L), respectively. Finally, when desulfurization of the DLR was conducted prior to the DLR-AHO treatment, the dissolution of As and Pb increased due to the elemental sulfur covering the arsenopyrite and galena particles, so that, when removed, these were more susceptible to pretreatment and cyanidation.

Comparing cyanidation with amalgamation of a Colombian artisanal gold mining sample: Suggestion of a simplified zinc precipitation process

We highlight the inefficiency of whole ore amalgamation practices used by artisanal gold miners. Cyanide is an alternative to mercury, but cleaner (cyanidation) plants are expensive and demand certain skills to operate. The main costs associated with operating a standard cyanidation plant using gold precipitation with zinc are linked to filtration, which can be costly for artisanal producers to deploy. To overcome the cost barrier, we call for the adoption of a Modified Merrill-Crowe Process (MMCP), which simplifies gold precipitation from cyanide solutions because it eliminates the need for filtration and vacuum system. Under this setup, zinc shavings in a fabric bag are introduced into the pulp of the leaching tanks with very low agitation. Lab results from a Colombian ore sample revealed that 84% of the gold was leached in 24 h with 1 g/L of CN, and over 99% of gold was precipitated in two hours. By comparison, lab amalgamation tests on the same ore using 28 times more mercury used by artisanal miners yielded less than 19% gold recovery.

Selection of a leaching system for the extraction of gold from the ore of the Byn’govskoye deposit

A theoretical substantiation of an environmentally friendly technology for extracting gold from mineral raw materials is presented. In terms of an alternative to conventional cyanide, the authors propose chlorine-bearing derivatives of organic isocyanuric acid (C3H3N3O3). In the studied process, this reagent combines the roles of a long-acting oxidant and complexing agent due to the resulting Cl– ion. For experimental purposes, the rotating disc technique was applied. Experimental results were evaluated by measuring the concentration of gold in solutions using the atomic adsorption method. The theoretical characteristics of gold dissolution using the proposed reagent were studied. In order to evaluate the applicability of the revealed regularities for practical purposes, comparative indicators for leaching gold from the ore of the Byn’govskoye deposit (Sverdlovsk Oblast) using the proposed reagent, cyanide and CYCAD cyanide substitute (China) were evaluated. The dependence of the gold disc dissolution rate on temperature, as well as leaching reagent and hydrochloric acid concentrations, were studied. In disc sample experiments, the exponential dependence of the dissolution rate on the concentration of the studied reagent was established. In this case, the maximum intensity of the process is achieved at a concentration higher than 50 g/dm3. The optimum acidity level comprises 0.3–0.4 g ion/dm3 of hydrochloric acid. Despite an increase in temperature being shown to accelerate the dissolution process, this appears to be technologically unjustified. Under optimal conditions, the gold disc dissolution rate reaches 0.5•10-3 g ion/(cm2•min), which is approximately one hundred times higher than during the dissolution by the cyanic solutions in conventional modes. Close gold extraction values were achieved in the solutions of cyanides and chlorine-bearing derivatives of isocyanuric acid during the leaching of gold from the ore under the comparable conditions. For CYCAD solutions, the same indicator is two times lower. The results of the performed studies demonstrate the high dissolution rate of gold using the proposed reagent along with the technological possibility of leaching gold from ores using this environmentally friendly reagent.

The properties of electric double layer at activated carbon surface and their effect on gold and silver adsorption from cyanide solutions

This paper looks at the properties of electric double layer (EDL) found at the surface of activated carbons. The study relied on the electrical conductivity method, which is based on simultaneous use of polarization dependences at direct current and conductometric measurements at alternating current. It was found that the adsorption of gold and silver intensifies in the anode region of carbon surface polarization. Two regions with peak adsorption were identified in the following ranges of potentials: +0.2&divide;+0.25 and +0.6&divide;+0.8 V. EDL diffusion helps improve the environment for the adsorption of cyanide complexes of gold and silver by active centres of the adsorbent surface. The authors believe that an increased mass transfer in the first range of potentials can be attributed to a decreased diffusion resistance caused by changed zero charge polarity, while in the second range of potentials it can be attributed to the cyan-ion oxidation reaction and an easier access of the negatively charged cyanide complexes of gold and silver to the positively charged surface of the carbon adsorbent. The polarization dependences by direct current in the anode region tend to monotonously rise, which is indicative of a lower EDL density, an increased conductivity at the adsorbent surface/solution boundary and improved adsorption conditions. Graphs showing a relationship between alternating current and carbon adsorbent potential helped determine maximum conducti vity values, which almost match the peak values of gold and silver adsorption. The authors established that the adsorbent&rsquo;s potential has a significant effect on the activated carbon adsorption of cyanide complexes of gold and silver. The use of the electrical conductivity method for examining the EDL helps explain certain features typical of the activated carbon adsorption of gold and silver from cyanide solutions.

Silver(I) recovery on thiomorpholine - modified functional polymer

The functional polymer containing heterocyclic ligands was synthesized by microwave modification of a crosslinked poly(vinylbenzyl chloride–divinylbenzene) matrix with thiomorpholine. The modification yield was 89.3%. The sorbent was used to recover Ag(I) from the synthetic and real chloride solutions. The maximum sorption capacity of Ag(I) was approximately 180 mg Ag/g. The sorption kinetic data were well-fitted to the pseudo-first-order kinetic model. The degree of silver desorption was approximately 50.0% using a 1.0% potassium cyanide solution in a 0.50% hydrogen peroxide solution. The resin retained its capacity toward Ag(I) in five consecutive sorption/desorption cycles. The thiomorpholine modified resin was highly selective toward Ag(I) in relation to Cu(II), Pb(II), Co(II), Ni(II), and Zn(II) from the real chloride leaching solution.

Low-temperature crystallization of LaFeO3 perovskite with inherent catalytically surface for the enhanced oxygen evolution reaction

This study reports a facile and economic method for LaFeO3 perovskite crystallization process at low temperature range from 300 °C to 500 °C and an outstanding oxygen evolution reaction (OER) catalyst based on inherent catalytically surface. As a key material for low temperature synthesis, cyanogel-peroxo-complex as a metastable molecular precursor was synthesized via ligand exchange using potassium cyanide solution to provide superoxo (O2–) ligand to Fe-CN-La gel structure, leading to a high degree of crystallinity with ideal ABO3 stoichiometry at low temperatures (400 ∼ 500 °C). Electrocatalysts based on LaFeO3 nanoparticles were fabricated, showing an outstanding OER performance with low overpotential of ∼ 438 mV at 100 mA/cm2 and small Tafel slope of 61 mV·dec–1 under alkaline conditions, better than commercialized available IrOx/C catalysts. Its OER performance is attributed to the inherent oxygen-deficient layer at the surface created at low temperature (300 °C). Long-term stability test shows no significant change (< 1%) in the potential during 50 h, indicating a high stability of such catalysts.

Nickel-Catalyzed Cyanation of (Hetero)aryl Bromides Using DABAL-Me3 as a Soluble Reductant.

A nickel-catalyzed cyanation of (hetero)aryl halides using air-stable bis(trimethylaluminum)-1,4-diazabicyclo[2.2.2]octane (DABAL-Me3) as a soluble reductant has been developed. The reaction uses readily available and inexpensive Ni(dppf)Cl2 as a precatalyst, a substoichiometric amount of Zn(CN)2, and DABAL-Me3 as an alternative to commonly prescribed insoluble reductants. We found the addition of catalytic tetrabutylammonium bromide (TBABr) to be beneficial, due to facilitating dissolution of low levels of the cyanide salt (confirmed via a control study). Similarly, slow addition of a tetrabutylammonium cyanide (TBACN) solution is effective and results in a completely homogeneous reaction mixture.

Comparative study of oxidants in gold cyanidation: A molecular picture

Oxygen plays a crucial role in the oxidation of gold in cyanidation. However, gold can be dissolved in oxygen free solutions by other oxidants. Here, the oxidizing potential of two other oxidants including peroxide (H2O2) and iron hydroxide (Fe(OH)4-) as the dominant Fe specie in alkaline cyanide solutions has been compared with oxygen. For this purpose, a computational modelling method using DFT has been used with BLYP functional. The interaction energy of O2,H2O2 and Fe(OH)4- with the 111 surface of Au is calculated and compared in absence and presence of cyanide ion. Oxygen adsorption energy was higher than the other species with energy values of −50. The H2O2 and the Fe(OH)4-, like oxygen, had a positive effect on the interaction of cyanide with 111 surface as well.

Development of Solution‐ and Film‐Based Economical Sensors for Reversible Sensing of Fluoride and Cyanide Ions

AbstractThree Bisphenol based economical sensors were developed from readily available reagents with single synthetic step. The bisphenols were obtained from reaction of 2,6‐dimethylphenol with 4‐hydroxybenzaldehyde (BP‐1), 4‐bromobenzaldehyde (BP‐2) and 4‐nitrobenzaldehyde (BP‐3). The cyanide and fluoride ions induce visual colour changes which enabled their naked eye detection and distinguished them as well. All the three sensors were able to detect these anions upto a nano molar range. Selective detection of these two anions with paper strips experiments were demonstrate by taking the BP‐1 as representative case. Again, among the sensors BP‐1 was chosen to immobilize into the cellulose based hydrogel matrix. Resulting composite efficiently detect cyanide and fluoride ions in 100 % aqueous system which otherwise was not feasible owing to water insolubility of BP‐1. The 1 cm2 film containing 0.01 mmol of BP‐1 can absorb 2 ppm of fluoride ion from standard aqueous solution of KF. The morphology study reveals a smooth and miscible distribution of BP‐1 into the polymer matrix. Surface morphology of the composite changes upon treatment with cyanide solution. Both the solution and film based sensing of these anions were found to be reversible in nature. The substituent effect on anion binding ability of respective sensors were demonstrated experimentally and validated theoretically.

Study of the effect of high-temperature activation of quartz on the adsorption of gold cyanide

• Gold cyanide ions are chemically adsorbed onto the quartz surface after high-temperature activation. • After high-temperature activation, Au-Si is adsorbed together, and the valence state of Au is + 1. • The N-Si bonding is enhanced after high-temperature activation. • The Au-O interaction on the surface of Au(CN) 2 − and quartz is transformed into a Au-Si interaction. The leaching rates for gold in the roasting oxidation pretreatment-cyanidation gold leaching process are generally low. An adsorption experiment for quartz baking slag (roasting time of 3 h, roasting temperature of 650℃) and gold cyanide solution was carried out under different stirring time conditions. It is found that after high temperature activation of the quartz surface, gold cyanide can be adsorbed. When the stirring time reaches 50 min, the adsorption rate is 6.08%, and the unit adsorption amount is 0.05 mg·g −1 . The EDS spectrum clearly shows that the Au element is distributed among Si and O, and 0.02% Au is adsorbed on the surface of the quartz baking slag. To further prove the adsorption mechanism for the gold cyanide solution and quartz slag, infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of quartz slags. Infrared spectroscopy analysis shows that new peaks emerge at 1429 cm −1 , 1878 cm −1 , and 1996 cm −1 after the elution experiment, and the characteristic peaks for inorganic cyanide are observed at 1878 cm −1 and 1996 cm −1 . This shows that after high-temperature activation of the quartz baking slag, chemical adsorption of gold cyanide occurs. The results obtained from X-ray photoelectron spectroscopy (XPS) show that during the adsorption process, Au-Si is adsorbed together, and Au shows a valence of + 1, which indicates that Au(CN) 2− ions are adsorbed onto the quartz activated at high temperature. Density functional theory (DFT) was used to determine the adsorption mechanism for Au(CN) 2− ions and different sites on the surface of quartz (1 0 1) before and after high-temperature activation (three Au-O, Au-Si, and N-Si adsorption sites). During the high-temperature activation process, the Au-O bonds and interactions on the surface of gold cyanide and quartz gradually transform into Au-Si bonds and interactions, and the N-Si bonds are also enhanced. This shows that the adsorption of gold cyanide onto quartz baking slag is enhanced after high-temperature activation. The simulation calculation result is consistent with the experimental results.