Weak Acid Dissociable Cyanide Research Articles

Monitoring WAD cyanide concentration in river waters with a glassy carbon electrode modified with 9,10‐Phenanthroquinone

AbstractHeavy metal‐containing industrial effluent streams from electroplating and metalworking industries represent a major environmental issue. They contain metal cyanide complexes ([Ni(CN)4]2− and [Cu(CN)3]2−) referred to as weak acid dissociable cyanide (CN‐WAD), which require continuous in situ monitoring. In this scenario, a glassy carbon (GC) electrode superficially decorated with 9,10‐phenanthroquinone (FNQ) is manufactured and employed for the simultaneous electrochemical monitoring of cyanide WAD complexes. The interaction between GC and FNQ was characterized by Raman and electrochemical impedance spectroscopies, cyclic voltammetry, and chronocoulometry. The electrochemical evaluation was conducted by differential pulse voltammetry (DPV) and CV. The GC/FNQ electrochemical sensor simultaneously detected cyanide complexes with an average linear range of 9–93 μmol L−1, and a detection limit of 0.15±0.04 μmol L−1 and 1.2±0.6 μmol L−1 for [Ni(CN)4]2− and [Cu(CN)3]2−, respectively. The sensor demonstrated remarkable selectivity in the presence of multiple interfering species with a percentage variation range of 89.2–109.4 %. Moreover, a computational DFT study provided valuable insights into the electrode/electrolyte interface. Finally, the developed sensor was applied for the electrochemical detection of WAD cyanide in river water samples.

INCO Cyanide destruction insights from plant reviews and laboratory evaluations

ABSTRACTInsights from a number of INCO cyanide destruction process reviews and studies are presented and discussed. In particular, the performance of three plants are discussed in terms of reagent (sulfite and oxygen) stoichiometry and utilisation, and the impact of process design, control, reagent addition points and slurry properties. Discussed also is the effectiveness of hydrogen peroxide use (supplementary oxygen source) in two of the plants reviewed.Oxygen mass transfer often limits the capacity of an INCO process. Hydrogen peroxide addition can improve the capacity, though process design improvements could provide a better economic outcome. Optimisation of the INCO process requires constant monitoring of feed and discharge weak acid dissociable cyanide concentrations and maintaining low but measurable dissolved oxygen in the reactor (e.g. 2–5 mg L−1). Changing solids properties over time requires adjustment to the sodium metabisulfate-to-weak acid dissociable cyanide weight ratio used for the destruction process control.

A composable module-type cyanide microfluidic sensor based on polydimethylsiloxane membrane pervaporative sampling with sodium bicarbonate internal-pressure regulation and dual fluorescence/potentiometric monitoring

This paper demonstrates a reliable and safe microfluidic sensor on the monitoring of weak-acid dissociable cyanide (WAD-CN−) from environmental waters. The sensor chip consists of three parts: a pervaporative membrane sampling module, a fluorescence labelling/detection module and a cyanide ion selective-electrode (CN−-ISE) potential detection module. Cyanide pervaporation was achieved by in situ sample acidification to produce hydrogen cyanide (HCN) through a gas-diffusing polydimethylsiloxane (PDMS, 4–5 μm thickness) membrane. HCN was recovered using a lye solution and subsequently split into two streams for the dual fluorescence/potentiometric monitoring. Dual fluorescence and CN−-ISE potential monitoring were performed by applying two indispensable treatment to the split streams with naphthalene-2,3-dicarboxaldehyde (NDA)-glycine (Gly) and total-ionic-strength-adjustment buffer solution (TISAB), respectively. The parameters in the pervaporation process and both detections were optimized. To increase the sensitivity at low concentrations, a sodium bicarbonate solution was introduced into the sample stream as a chemical pressure regulator, which maintained a constant pressure in the channel by continuously producing CO2. To prevent the loss of produced gas, the channels, except for the membrane, were coated by a polyvinylsilazane (PVSZ) polymer solution and cured. Under an HCl donor stream (0.5 mol L−1; 15 μL min−1) and a sodium hydroxide acceptor stream (0.1 mol L−1; 20 μm/min), 65.7% of transmission rate (RSD = 0.86%; n = 3 for 0.1 mg L−1 CN−) was achieved. The pervaporative sampling method effectively minimized the interferences (except organic thiols) from the environmental matrices during the detection of cyanide in both detection modules. The validity and quality of the assay were assessed in terms of the linearity 5–500 μg L−1 (R2 = 0.9992) and limit of detection (cL) 0.015 μg L−1 with the fluorescence method and those are 2.6–1000 μg L−1 (R2 = 0.998), and 1.1 μg L−1 with the CN−-ISE potentiometric detection. The cyanide levels in waste waters were determined using the standard addition method and verified using the EPA method OIA-1677. Furthermore, a microchip electrophoresis (MCE) analysis was performed to investigate the systemic errors from the mercapto-interferences of the samples. The developed microfluidic sensor was applied to monitor WAD-CN− in waste waters. The sensor is a flexible, extensible, and environmentally friendly alternative for WAD-CN− monitoring.

Assessing the Impact of an Operating Tailings Storage Facility on Catchment Surface and Groundwater Quality in the Ellembele District of the Western Region of Ghana

<p>The study assessed the impact of an operating Tailings Storage Facility (TSF) of Adamus Resources Limited (Nzema Gold Mine) in the Ellembele District of the Western of Ghana on catchment surface and groundwater quality. Water samples were collected between June and December 2014 from seventeen (17) sampling sites including the TSF decant water (TSF-DW), three (3) streams, a water storage dam, a pond and eleven (11) groundwater monitoring boreholes within 500 m radius of the mine’s Tailings Storage Facility. Samples were analyzed for pH, true colour, electrical conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS), biological oxygen demand (BOD), dissolved metals (arsenic, cadmium, copper, mercury) and cyanide (weak acid dissociable cyanide (WAD), free cyanide and total cyanide) using standard procedures. The TSF-DW reported elevated arsenic, free cyanide and TSS concentrations above GHEPA guideline for effluent discharge. Elevated TSS and arsenic concentrations above GHEPA limits were reported in PWSD which is a pond uphill of the TSF and a receptor to effluents from illegal mining sites on the mine’s concession. All other parameters recorded in surface and groundwater bodies studied were within WHO guideline limit for potable water. Results of the study suggest that the quality of surface and groundwater around the TSF has not been adversely affected even though the TSF is contaminated. Study findings suggest that well-engineered tailings dam ofARLwith its effective liner and management systems may have provided a safe structure and prevented contamination of water resources within its catchment.</p>

Characterization and speciation modelling of cyanide in effluent from an active slimes dam

The utilization of cyanide in the process of gold extraction is an environmental concern as this pollutant is discharged with the tailings. The distribution and fate of cyanide in the environment upon release from the tailings dumps depends on its physical-chemical speciation. The present study was conducted to assess the presence of cyanide species in drainage water from an active slimes dam that receives effluent from a gold reprocessing plant in the Central Rand goldfield (south of Johannesburg, South Africa). Water samples were collected from decant pipes draining water from the top of the slimes dam as well as from a solution trench constructed around the dam. Efflorescent salt crusts and algae were also sampled along the solution trench to assess the extent of cyanide contamination and its promulgation from the slimes. Water samples presented varying chemistry with samples collected from the pipes recording low pH (between 2 and 4) with concentrations of weak acid dissociable cyanide (CNWAD) varying between 5.635 mg L-1 and 8.525 mg L-1. Water samples from the trench were less acidic (pH ranged between 5 and 7) with an average concentration of CNWAD of 21.72 mg L-1. These values are far greater than the limit of 0.50 mg L-1 set by the authorities through the 'Best Practice guidelines' for any effluent exiting a metallurgical treatment facility. Copper and iron cyanide complexes were the most abundant cyanide complexes in the water samples. The pH and conductivity of the solution prepared by the dissolution of the salt crusts (10 g in 50 mL of deionized water) were 3.44 and 1.611 mScm-1, respectively. High concentrations (198.4mg kg-1) of CNT were obtained in the crusts and these were predominantly strong acid dissociable cyanides (CNSAD) of Fe and Co. The presence of iron cyanides was evident from the bluish-green crusts (Prussian blue) observed around the site, indicating the extent of cyanide contamination. A very low pH (2.39) was recorded for the algae, with elevated concentrations of SCN- and OCN- that are byproducts of chemical conversion of cyanide. The Visual MINTEQ geochemical modelling code was used to complement the analytical methods in characterizing the speciation of cyanide. The simulations predicted the presence of the following metal-cyanide complexes in water samples as well as in the solid materials: Fe(CN)63-, Fe(CN)6(aq), NaFe(CN)62-, KFe(CN)62-, Ni(CN)42-, Zn(CN)42-, CaFe(CN)6-, NiH(CN)4- and NiH3(CN)4+. This study revealed that cyanide remains persistent in its immediate environment following its release from slimes dams, an issue of concern as some residential areas have developed in the proximity of such facilities. The major highlight of this work has been the comprehensive characterization of cyanide speciation by using geochemical modelling to complement analytical techniques. This is important in understanding the potential risk posed by this pollutant.

The effect of zinc cyanide on the flotation of gold from pyritic ore

In gold processing plants, the process water contains a considerable amount of weak acid dissociable (WAD) cyanide species. The cyanide-containing water recycled to flotation circuits has a deleterious effect on mineral flotation. Zinc cyanide can be a major constituent of the process water due to the cyanide leaching of zinc minerals and the zinc cementation applied to precipitate gold and silver. In the present study, the effect of zinc cyanide on the flotation of gold from a pyritic ore was evaluated and the competitive adsorption between zinc cyanide species and the collector, potassium amyl xanthate (PAX) or Aerophine promoter (3418A), on gold was studied by surface enhanced Raman spectroscopy (SERS). It was found that free cyanide did not depress the flotation of liberated gold, but zinc cyanide with a CN/Zn ratio of 2 did. The depression of gold flotation by zinc cyanide was due to the preferential adsorption of Zn(CN)2 on gold surface over either 3418A or amyl xanthate in the solution, rendering gold surface hydrophilic.

Gold dissolution and copper suppression during leaching of copper–gold gravity concentrates in caustic soda-low free cyanide solutions

In the cyanidation process, copper–gold deposits containing significant amounts of cyanide soluble copper can lead to high cyanide consumption with low gold extraction. The significant levels of weak acid dissociable (WAD) cyanide must then be destroyed prior to tailings disposal. This increases the cost to the gold mining companies to cover both the extra cyanide consumption in the leaching stage and the additional cost for cyanide recovery/destruction. Therefore, in this study, a selective cyanide leaching process of gold over copper from copper–gold concentrate (also see Oraby and Eksteen, 2014) containing 490g/t Au and 0.97% Cu present as metallic copper, oxides and sulfides has been investigated. To decrease the cyanide consumption, cyanide is added into the leach solutions to maintain a ratio of cyanide to total reactive copper (CN/Cu) below 2. At low CN/Cu ratio, increasing the pH of solution can lead to the precipitation of solubilized copper as CuO/Cu(OH)2, releasing cyanide ions for further both gold and copper dissolution. A comparison of leaching gold in cyanide–caustic, cyanide–ammonia and conventional cyanidation processes has been made. Higher gold extraction and lower copper concentration in the final leach was achieved in the cyanide–caustic system than in either the cyanide–ammonia or conventional cyanidation processes. The effects of the caustic soda (pH) concentration or cyanide concentration on gold extraction and copper suppression have also been studied. The results show that at high pH (>12), the gold dissolution rate increases significantly in solutions containing caustic soda and cyanide at zero, or very low free cyanide concentration.

Gold leaching in cyanide-starved copper solutions in the presence of glycine

In the cyanidation of copper–gold ores, the presence of copper minerals can lead to soluble gold losses, the production of weak acid dissociable (WAD) cyanide, as well as a number of operational challenges in CIP/CIL circuits with regard to competitive adsorption, and subsequent difficulties associated with elution, electrowinning and smelting. In addition, copper minerals are significant cyanide consumers, leading to higher cost in ore treatment. This paper presents a process to enhance the dissolution of gold using copper–cyanide solutions in the presence of glycine where the solution is cyanide starved. The effect of glycine addition on gold leaching kinetics in copper–cyanide solutions under different leaching conditions was studied. The results show that, in the presence of glycine, gold dissolution rate increases significantly in solutions containing copper–cyanide species at a very low, or zero, free cyanide concentration. In the presence and absence of glycine, gold dissolution rates in solutions containing 10mM Cu(CN)32− were 11.1μmol/m2·s and 0.65μmol/m2·s, respectively. It is shown that the average gold dissolution rate in a Cu–CN−-glycine system is about 6.5 times higher than the gold dissolution rate in the conventional cyanidation, the presence of cyanide being similar in each system. Kinetic and electrochemical studies were conducted to evaluate the effects of glycine concentration, pH, CN/Cu ratio, and initial copper concentrations on the dissolution of gold. It has also been shown that the gold dissolution rate increases by increasing the glycine concentration up to 1g/L and any further glycine addition has a negative effect on the dissolution of gold. Increasing leaching pH up to 12 enhances gold dissolution in the copper–cyanide–glycine solutions. However, increasing leaching pH to 13 has an adverse effect on the dissolution of gold.

Natural Cyanide Attenuation in a Tailings Dam in South-Western Ghana

The aim of this study was to investigate the viability of light and aeration (oxygen) in cyanide attenuation of gold tailings material in a tropical environment. It was established that under aeration conditions free cyanide (CN_F) concentration reduced from 200 mg/dm³ to below 0.03 mg/dm³ in 60 h weak acid dissociable cyanide (WAD_CN) concentration reduced from 200 mg/dm³ to 6 mg/dm³ after 60 h. Under non-aeration conditions CN_F concentrations reduced from 200 mg/dm³ to 60 mg/dm³ within 108 h, the pH reduced from 10.80 to 9.41. WAD_CN concentration decreased from 200 mg/dm³ to 73 mg/dm³ within 48 h. It then increased to 150 mg/dm³ after 60 h and then gradually decreased to 100 mg/dm³ after 144 h. It was inferred that volatilisation of HCN was the dominant mechanism accounting for degradation of CN_F Degradation of complex cyanide species and this was enhanced by sunlight and aeration. It was concluded that natural cyanide attenuation is possible but the rate of degradation particularly for WAD_CN is not as fast as free cyanide. Hence it is not a suitable process for cyanide degradation in tropical environment.

A fundamental investigation of the Caro's acid cyanide destruction process

Cyanide destruction by Caro's acid is a process commonly employed by gold operations to meet regulatory requirements and/or the International Cyanide Management Code compliance for weak acid dissociable (WAD) cyanide concentrations in cyanidation tails or waste water from such operations. Typically small-scale bench tests to evaluate and assess the suitability of the Caro's acid destruction process are conducted before implementation. Additionally, the experimental procedure used during these preliminary investigations may also differ from that implemented at the full scale. This paper presents the results from a fundamental investigation of the Caro's acid process to establish a more detailed understanding of the impact that the Caro's acid source, alkali used and experimental procedure has on the destruction of cyanide. In particular, it was found that the control of pH was important to avoid additional (greater than stoichiometry) cyanide and copper loss (most likely as copper(I) cyanide precipitation) at low pH and maximise WAD cyanide destruction. Residual peroxide in the preparation of Caro's acid has the potential for subsequent cyanide destruction and could be exploited.

A Study of Residual Cyanides and Potential Stabilities in Tailings Storage Facility of Gold Mining Operation

The study aimed to investigate residual cyanides and their potential stabilities in tailings from a gold processing plant deposited in the Tailings Storage Facility (TSF) of a gold mining site. For this purpose, several samples of tailings were taken from the recently abandoned TSF to a depth of 2.5 meters, representing 1 to 2 years old tailings. The samples were analyzed for pH, metals, residual cyanides, and Net Acid Generation Test (NAG test). The results showed that, in all samples, pH values were neutral to slightly alkaline. Fe concentrations were relatively high (22,800-35,000 mg kg-1) indicating that Fe can readily react with free cyanide (CN-) to form iron cyanide complexes (strong metal cyanide complexes). The residual cyanide concentration in tailings was found to be very low; free cyanide (CNFree), weak acid dissociable cyanide (CNWAD), strong acid dissociable cyanide (CNSAD) and total cyanide (CNT) were in the range of 0.16-0.64, 0.37-1.06, 1.96-3.89 and 2.33-4.95 mg kg-1, respectively. Cyanides in the tailings were predominantly strong metal cyanide complexes being more stable to dissociate. Total cyanide (CNT) concentration was quite low compared with Thailand’s environmental regulations for soil quality standards andwere environmentally insignificant. The NAG test for all samples revealed that NAG pH was in the range of 5.02-6.10 and NAG was in the range of 0.08-0.31 kg H2SO4t-1indicating all samples have low or non-acid forming potentials. The findings indicated a potential to form a high proportion of strong metal cyanide complexes in the tailings, which is difficult to dissociate and releasehigh toxic cyanide to the environment.

Certification of a reference material for determination of total cyanide in soil to support implementation of the International Standard ISO 11262:2011.

Cyanides are among the most important inorganic pollutants to be tested and monitored in environmental compartments. They can be distinguished and determined as free cyanide, weak acid dissociable cyanide or as total cyanide. However, in any case obtained, measurement results are operationally defined referring to the applied analytical method. In 2011, the International Standard ISO 11262 has been published which specifies a normative analytical method for the determination of total cyanide in soil. The objective of the project described in this paper was to provide the first soil reference material (CRM) certified for its mass fraction of total cyanide on the basis of this standard. A total of 12 German laboratories with proven experience in the determination of cyanides in environmental samples participated in the certification study. Measurement results were evaluated in full compliance with the requirements of ISO Guide 35. Taking into account the results of the inter-laboratory comparison as well as the outcome of the homogeneity and stability studies, a certified mass fraction of total cyanide of 21.1mg/kg and an expanded uncertainty (k = 2) of 1.3mg/kg were assigned to the material. The reference material has been issued as CRM BAM-U114.

High levels of activity of bats at gold mining water bodies: implications for compliance with the International Cyanide Management Code

Wildlife and livestock are known to visit and interact with tailings dam and other wastewater impoundments at gold mines. When cyanide concentrations within these water bodies exceed a critical toxicity threshold, significant cyanide-related mortality events can occur in wildlife. Highly mobile taxa such as birds are particularly susceptible to cyanide toxicosis. Nocturnally active bats have similar access to uncovered wastewater impoundments as birds; however, cyanide toxicosis risks to bats remain ambiguous. This study investigated activity of bats in the airspace above two water bodies at an Australian gold mine, to assess the extent to which bats use these water bodies and hence are at potential risk of exposure to cyanide. Bat activity was present on most nights sampled during the 16-month survey period, although it was highly variable across nights and months. Therefore, despite the artificial nature of wastewater impoundments at gold mines, these structures present attractive habitats to bats. As tailings slurry and supernatant pooling within the tailings dam were consistently well below the industry protective concentration limit of 50mg/L weak acid dissociable (WAD) cyanide, wastewater solutions stored within the tailings dam posed a minimal risk of cyanide toxicosis for wildlife, including bats. This study showed that passively recorded bat echolocation call data provides evidence of the presence and relative activity of bats above water bodies at mine sites. Furthermore, echolocation buzz calls recorded in the airspace directly above water provide indirect evidence of foraging and/or drinking. Both echolocation monitoring and systematic sampling of cyanide concentration in open wastewater impoundments can be incorporated into a gold mine risk-assessment model in order to evaluate the risk of bat exposure to cyanide. In relation to risk minimisation management practices, the most effective mechanism for preventing cyanide toxicosis to wildlife, including bats, is capping the concentration of cyanide in tailings discharged to open impoundments at 50mg/L WAD.

A Study on Ninhydrin Reaction with Weak Acid Dissociable Cyanide and Its Application for Toxic Cyanide Determination

Environmental Protection Agencies impose stringent limits for weak-acid dissociable metal-cyanide complexes (WAD) content in waters. The maximum contaminant level in drinking water is as low as 50 µg/L as CN-. Hence, sensitive methods for WAD cyanide determination are strongly required. Recently, ninhydrin reaction with free cyanide has been proven as a very sensitive at 485 nm (e = 1.2 105 L/mol.cm), fast (15 min), selective and with non-toxic reagents. In the presence of free cyanide the absorbance measurement was based on the formation of a red hydrindatin resulting from cyanide’s catalytic effect on ninhydrin at pH 10.8. This report presents the results from a study on the reaction between ninhydrin and complexed cyanide at ambient conditions. The WAD complexes: Hg(CN)42-; Ni(CN)42-; Cu(CN)43-; Ag(CN)2-; Zn(CN)42-; Cd(CN)42- are discussed. The reaction kinetic and standard curves are presented. Ligand exchange approach was applied without additional separation. Ninhydrin was showed to be selective and sensitive for direct cyanide quantification.

Online ligand exchange in the determination of weak acid dissociable cyanide by gas diffusion-flow injection analysis

A novel ligand exchange method for on-line gas-diffusion flow injection (GD-FI) determination of weak acid dissociable (WAD) cyanide has been successfully developed using a binary ligand combination of 0.10% thiourea and 0.10% pentaethylenehexamine. Complete WAD cyanide recovery with insignificant contribution from the dissociation of stable metal cyanide complexes (non-WAD complexes) has been achieved in the concentration range from 3μg L−1 to 10mgL−1 cyanide. The proposed GD-FI method offers considerable advantages over the existing standard methods for determining WAD cyanide, as it provides an analysis rate of 60 samples h−1 with a satisfactory reproducibility (average RSD=1.0% at n=3) and can be fully automated. A very good agreement between the proposed method and the standard distillation method has been observed when both methods have been applied to the determination of WAD cyanide in samples from the gold mining industry.

Cyanide detoxification of gold cyanidation tails and process streams

Cyanide detoxification by chemical means (sulphite, hydrogen peroxide or Caro’s acid) has typically been adopted by the gold industry to meet the International Cyanide Management Institute (ICMI) code and/or regulatory compliance for discharge into tailings storage facilities (TSFs), treatment of TSF return water or the discharge of excess water from the mining operation. This paper presents and discusses results from a number of different evaluations that have been conducted to reduce the cyanide concentration in cyanidation tails and process streams by chemical means. Preoxidation before cyanidation and the ore mineralogy were both found to potentially have a significant impact on reagent requirements in the treatment of cyanidation tails. The solution speciation provided important insights into the reagent consumption, which becomes very high in targeting residual weak acid dissociable (WAD) cyanide concentrations below 1 mg L−1. Preliminary evaluations of polishing and alternative processes for reducing the WAD cyanide showed potential to achieve these low concentrations and reduce the treatment costs.

Hydrological Evaluation of Gold Leach Pad Rinsing

Leach pad closure is a site and material specific consideration. This paper presents a summary of analytical and field studies conducted to determine the requirements for rinsing heap leach residue in conjunction with reclamation activities. An analytical model, based on simple dilution, was proposed for projecting changes in cyanide concentration following fresh water rinsing. A 23-month field test utilizing three test heaps verified that the weak acid dissociable cyanide concentration of effluent from the heaps was being reduced by half for each bed volume of fresh water applied to the pilot-scale test heaps. Whether rinsing is a valid part of closure depends on hydrogeologic and geochemical conditions within the heap and may not be appropriate in all cases.

Dissipation of cyanogenic glucosides and cyanide in soil amended with white clover ( Trifolium repens L.)

The use of white clover ( Trifolium repens L.) as green manure is common practice due to its high nitrogen content. White clover produces the two cyanogenic glucosides linamarin and lotaustralin, which release toxic hydrogen cyanide upon hydrolysis. The hydrolysis of cyanogenic glucosides and release of cyanide were studied in batch experiments with ground white clover added to soil at loadings of 75 g leaves per kg soil. Linamarin and lotaustralin were quickly hydrolysed with first-order rate constants of 0.026–0.0062 h −1 (corresponding to half lives of 11–27 h) in sandy and loamy soils at natural moisture contents and 11 °C. Experiments with addition of pure cyanogenic glucosides and with sterilized soil material as well as addition of white clover to inert quartz showed that hydrolysis by plant glucosidases is partly inhibited in the soil matrix, but also that soil glucosidases present in soil contribute to degradation of the cyanogenic glucosides, and more so for linamarin than for lotaustralin. Cyanide was produced during the hydrolysis of the cyanogenic glucosides as seen by formation of HCN(g) and WAD-CN ( Weak Acid Dissociable Cyanide) amounting to max. 5 and 50% of total-CN in the systems with white clover added to natural soils. However, the increase in WAD-CN was transient, due to subsequent dissipation of the compound caused by abiotic and microbial CN degradation. Due to WAD-CN dissipation in the top soils studied, long term effects of cyanide on sensitive microorganisms and plants are not expected. However, knowledge on the stability of WAD-CN in subsoil is lacking and warrants further investigations.

Factors influencing the risk of wildlife cyanide poisoning on a tailings storage facility in the Eastern Goldfields of Western Australia

Patterns of wildlife visitation and interaction with cyanide-bearing tailings slurry and solutions at the Fimiston tailings storage facility (TSF) have been reported in a previously published ecological study. The above-mentioned findings are extended in this paper by the examination of additional wildlife survey data, along with process water chemistry data collected during the same study period. Analysis of the combined results revealed that the primary wildlife protective mechanism in operation was effective management of tailings cyanide concentration. Nevertheless, tailings discharge concentration exceeded the industry standard wildlife protective limit of 50 mg/L weak acid dissociable (WAD) cyanide episodically during the study period. Wildlife that interacted with habitats close to the spigot outlet during brief periods of increased discharge concentration were likely to have been exposed to bioavailable cyanide at concentrations greater than the industry standard protective limit. However, no wildlife deaths were recorded. These results appear to support the hypothesis that hypersalinity of process solutions (unique to the Kalgoorlie district of Western Australia) and a lack of aquatic food resources represent secondary protective mechanisms that operated to prevent cyanide-related wildlife mortality during the project. The proposed protective mechanisms are discussed in the context of their potential application as proactive management procedures to minimise wildlife exposure to cyanide.

A green flow-based procedure for fluorimetric determination of acid-dissociable cyanide in natural waters exploiting multicommutation

A flow system designed with solenoid valves is proposed for determination of weak acid dissociable cyanide, based on the reaction with o-phthalaldehyde (OPA) and glycine yielding a highly fluorescent isoindole derivative. The proposed procedure minimizes the main drawbacks related to the reference batch procedure, based on reaction with barbituric acid and pyridine followed by spectrophotometric detection, i.e., use of toxic reagents, high reagent consumption and waste generation, low sampling rate, and poor sensitivity. Retention of the sample zone was exploited to increase the conversion rate of the analyte with minimized sample dispersion. Linear response (r = 0.999) was observed for cyanide concentrations in the range 1-200 microg L(-1), with a detection limit (99.7% confidence level) of 0.5 microg L(-1) (19 nmol L(-1)). The sampling rate and coefficient of variation (n = 10) were estimated as 22 measurements per hour and 1.4%, respectively. The results of determination of weak acid dissociable cyanide in natural water samples were in agreement with those achieved by the batch reference procedure at the 95% confidence level. Additionally to the improvement in the analytical features in comparison with those of the flow system with continuous reagent addition (sensitivity and sampling rate 90 and 83% higher, respectively), the consumption of OPA was 230-fold lower.