High Cyanide Research Articles

Solvent Extraction of Silver and Gold From Alkaline Cyanide Solution with LIX 7950

The cyanidation process is still the dominant technique for gold ore treatment. In this study, the potential use of the guanidine extractant LIX 7950 for recovering silver and gold from alkaline cyanide solution was investigated. The results indicate that LIX 7950 can effectively and efficiently extract silver and gold from their cyanide solution. The extraction of silver and gold with the extractant is favorable at low pH. High cyanide to silver ratio tends to suppress silver loading while cyanide concentration exhibits insignificant effect on gold extraction. The extraction of the mixture solution of metal cyanide complexes with the extractant indicated an extraction sequence of Au >A g > Zn > Ni > Cu > Fe. The loaded silver and gold can be stripped off efficiently with moderate strong NaOH solutions at the presence of small amount of NaCN. The important findings in the research suggest that the extractant can be potentially used to recover silver and gold from alkaline cyanide leachate and the barren cyanide solution from the SX circuit can be recycled to the cyanidation process.

A novel process based on gas filled membrane absorption to recover cyanide in gold mining

In the last ten years, the operational costs in the gold and silver cyanidation processes have increased, fundamentally, due to the treatment of ores which contains high cyanide soluble metals, such as zinc, copper, and nickel, among others, increasing the cyanide consumption along with the increase in cyanide price. Additionally, the high cyanide consumptions in gold operations have increased the cyanide contents in leach tailings, forcing the inclusion of processes to recover or eliminate cyanide. For these reasons, a membrane contactor operation to recover cyanide from gold mining, using gas filled membrane absorption is proposed in this study, performing laboratory tests in order to determine the throughput of this process and the most relevant parameters, which affect the cyanide recovery. Gas Filled Membrane Absorption (GFMA) process can extract cyanide, using an absorption solution of NaOH. In this process, previously reported for wastewater treatment, a hydrophobic membrane with its pores filled with air separates an aqueous stream containing cyanide and receives a solution with a high pH value. These aqueous solutions cannot penetrate into the membrane pores, promoting the cyanide transfer from the cyanidation solution to the receiving solution. The experimental results show cyanide recoveries higher than 90% in extraction times of approximately 10min, achieving an average cyanide transfer rate of 0.01kgm−2h−1 and identifying the pH, feed flow rate and copper concentration as the most influential parameters on the performance of the process.Furthermore, a phenomenological transport model was developed in order to explain the critical steps of the cyanide transfer in the GFMA process. This model was validated by means of the comparison with the experimental results of cyanide extraction with the presence of Cu(I) and Zn(II) ions, obtaining a statistical error lower than 10%. Thus, the gas filled membrane absorption process can recover cyanide, with similar performance to the current cyanide recovery processes, and could involve a smaller size of the equipment due to the high transfer surface area per volume that membrane contactors have.

Copper cyanide removal by precipitation with quaternary ammonium salts

Cyanide is widely used in the mining industry to extract gold from ores. Some of the minerals processed for precious metals extraction contain copper species which may react with cyanide to form cuprocyanide complexes. The presence of these copper species affects adversely the process and causes high cyanide consumption. In order to overcome these limitations this laboratory work explores the feasibility of removing the copper–cyanide complexes by precipitation with quaternary ammonium salts, allowing the remaining solution, free of copper and containing free cyanide, to be recycled to the cyanidation process. The first part of the experimental work was performed with synthetic copper–cyanide solution simulating a high copper–cyanide solution (2700mg/L cyanide, 730mg/L copper and pH adjusted to 12 with CaO) and three quaternary ammonium salts: hexadecyl trimethyl ammonium chloride (HTA), octadecyl trimethyl ammonium chloride (OTA) and dioctadecyl dimethyl ammonium chloride (DDA). The results showed that it is possible to remove up to 90% of the copper in the precipitate when adding 12.32g OTA/g copper at pH 12. The free cyanide remains unreacted in the solution and could be recycled to the process. Results of tests performed at different pH values suggest that regardless the initial species distribution in the solution, the solid formed will contain mainly copper tricyanide and some of copper tetracyanide. The molar ratio CN/Cu in the solid is around 3 while the molar ratio OTA/Cu is around 2. This implies that some amount of copper tetracyanide is transformed into copper tricyanide while reacting with the amine and forming the precipitate. When zinc is also present in the cyanide solution, the ammonium salt will react first with the zinc–cyanide complexes before precipitating the copper cyanides. Tests performed with an industrial solution corroborated the results obtained with synthetic solutions: quaternary ammonium salts (e.g. OTA) react with copper and zinc cyanides (but not with free cyanide) to form a precipitated that can be separated from the solution by filtration. An analytic technique for measuring quaternary ammonium salts HTA and OTA in solution was developed.

Assessing levels of hydrogen cyanide in fire experiments using a generalized correlation

A generalized relationship between the normalized yields of carbon monoxide and hydrogen cyanide for nitrogen-containing materials has recently been derived. This correlation is used in the current study to analyze experimentally derived hydrogen cyanide data from three sets of fire tests. For a reduced-scale compartment fire test, the yields of hydrogen cyanide with varied equivalence ratios and the transient hydrogen cyanide concentrations are estimated; for a series of room-corridor sofa fire tests, the extremely high hydrogen cyanide level observed is demonstrated to be a realistic result and a hydrogen cyanide yield value of 0.047 g/g is suggested for this sofa in post-flashover fires for fire safety assessments; and finally, for a series of smoke chamber tests with polyurethane, possible causes for the failure to detect hydrogen cyanide are suggested. Language: en

Total cyanide content of cassava food products in Australia

Cassava products obtained in two major Australian cities, Melbourne and Canberra, were analysed for total cyanide content using the picrate method. In Melbourne in 2010, ready to eat cassava chips were found to contain large amounts of cyanide with a mean value of 91mg HCN equivalents/kg fresh weight=ppm. In Canberra, similar values were found over a six-year study with cassava chip samples, except for one sample that gave 7ppm, which was obtained in 2011 after the introduction by Food Standards Australia and New Zealand of a 10ppm maximum limit. In Melbourne, the highest value obtained was 262ppm. A calculation based on this very high cyanide sample and using the lethal dose of cyanide for humans, shows that a child of 20kg body weight would only need to eat 40–270g of these chips to reach the lethal dose. Frozen cassava roots gave a mean value of 52ppm total cyanide, which is also a cause for concern. In contrast, more highly processed foods contained<1ppm total cyanide.

Strategies for elimination of cyanogens from cassava for reducing toxicity and improving food safety

Toxicity of cassava arises due to the presence of the cyanoglucosides linamarin and lotaustralin which are hydrolysed by endogenous enzyme linamarase to acetonecyanohydrin (ACN) and cyanide (CN) which are toxic. Major research efforts to eliminate/reduce cyanoglucosides have focused on (i) development of acyanogenic cassava varieties by breeding; (ii) controlling its metabolism; and (iii) processing to remove cyanogens. The cyanoglucoside (CNG) content in cassava is genetically controlled and cultivars may be classified as low (<50 μg/g), medium (50–100 μg/g) and high CN (>100 μg CN eq./g) varieties. Molecular techniques for reducing tuber CNG have focused on development of transgenic plants with reduced expression of cyt P 450 in leaves, or increased expression of hydroxynitrilelyase in tuber. For immediate solution, CNG content can be reduced using several processing methods. Traditional methods used for processing include boiling, drying, parboiling and drying, baking, steaming, frying and preparation of flour. These processes result in CN losses ranging from 25% to 98%. The cyanogen level in the final product is influenced both by the tuber CNG and the method of processing. In order to achieve safe levels of 10 μg/g in cassava products, new methods of processing, especially for cassava containing more than 250 μg CN eq./g, remains a challenging problem.

Dynamic rheological and physicochemical properties of annealed starches from two cultivars of cassava

Starch from tubers of “sweet” (low cyanide) and “bitter” (high cyanide) cassava ( Manihot esculentum Crantz) crops was isolated and subjected to annealing treatment at 50 °C for 24,96,144 and 192 h in 1:5 starch to water ratio. Annealing generally reduced the swelling power and solubility of the starches. Storage modulus ( G′) and loss modulus ( G″) increased with decrease in complex viscosity (Eta*) as a function of angular frequency ( ω). The magnitudes of G′ reported were greater than those of G″ revealing frequency dependency except sweet starch cultivar annealed at 192 h. The tan δ (ratio of G″/ G′) of annealed starches were within the ranges of 0.31–0.39 and 0.23–0.45 for sweet and bitter cultivars, respectively. The tan δ values of the starches were lower than one, indicating that the samples are elastic in nature than viscous. The X-ray patterns of the A-type starches were not altered on annealing denoting that the double helices in the amorphous region were not disrupted. Annealing as revealed by scanning electron micrographs changed the structure of the sweet cultivar, while there was no change in the size and shape of the bitter cultivar.

Gold losses by cementation and thermal reduction in the gold recovery circuits

In this study, gold losses in a carbon-in-pulp (CIP) cyanidation gold recovery process and potential sources of these losses were investigated. Gold was found in samples from different streams through the CIP-cyanidation process, pointing to incidental losses. Mineralogical studies showed that gold losses occurred in two main forms, either as attached to larger entities or in the form of dendritic precipitates. SEM and EDS studies revealed that iron bearing minerals acted as the major media in cases when gold associations were observed as losses. The highly alkaline pH (≈13), elevated process temperature (≈145°C), and high cyanide concentration (≥250ppm) in the elution column along with a fine iron bearing material implied that gold attachment occurred through an electrochemical cementation mechanism. It was anticipated that the presence of iron in the process, which facilitated gold cementation, relied on the oxidative breakdown of the iron bearing minerals in the ore and/or due to the formation of porous iron oxides due to the roasting of iron sulfides in the regeneration kiln. In the elution column some part of the auro–cyanide complexes would remain non-eluted and be discharged into the carbon generation kiln and the carbon generation kiln was another section promoting gold losses. The high temperature condition in the carbon regeneration kiln (>500°C) caused thermal reduction of the non-eluted auro–cyanide complexes to metallic gold, leading to the formation of dendritic gold precipitates and their eventual loss.

Etiology of Konzo, epidemic spastic paraparesis associated with cyanogenic glycosides in cassava: Role of thiamine deficiency?

Konzo is a syndrome of symmetrical, non-progressive, non-remitting spastic paraparesis occurring in epidemic and endemic forms in several countries in Africa, invariably associated with monotonous consumption of inadequately processed bitter cassava roots (Manihot esculenta) with very minimal protein supplementation.Despite numerous epidemiological, clinical and biochemical studies by authors in several countries aimed at elucidating the etiological mechanisms of Konzo, the etiology remains unknown. High cyanide consumption with low dietary sulfur intake due to almost exclusive consumption of insufficiently processed bitter cassava roots was proposed as the cause of Konzo, but there has been no evidence of a causal association between cyanide consumption and Konzo.In this paper a new etiological mechanism of thiamine deficiency is presented, based on detailed review of the epidemiological, clinical and biochemical features of Konzo. It is postulated that in Konzo patients, a severe exacerbation of thiamine deficiency results from the inactivation of thiamine that occurs when, in the absence of dietary sulfur-containing amino acids; the sulfur in thiamine is utilized for the detoxification of cyanide consumed in improperly processed bitter cassava. Thiamine is known to be rendered inactive when the sulfur in its thiazole moiety is combined with hydrogen cyanide.This hypothesis may stimulate studies examining the role of thiamine in the etiology of Konzo, and may lead to the formulation of strategies for the prevention and treatment of this debilitating disease.

Effect of biooxidation conditions on cyanide consumption and gold recovery from a refractory gold concentrate

This study investigates the biooxidation of a refractory gold concentrate using a mixed culture of acidophilic mesophiles, moderate thermophiles and extreme thermophiles and their effect on the subsequent cyanidation and gold recovery. The experiments with high % solids using mixed mesophiles showed better oxidation potential compared to moderate thermophiles and extreme thermophiles. However, the extreme thermophiles performed better than mesophiles and moderate thermophiles during the biooxidation with < 5% solids (w/v). The biooxidized residues obtained from the experiments with extremophiles, gave a maximum gold recovery of 92% after cyanidation. The NaCN consumption during cyanidation of the biooxidized residues obtained from experiments with extremophiles was lower than bioresidues obtained from experiments with mesophiles and moderate thermophiles. The highest consumption of NaCN of 17.5 kg/ton was from the experiment with 10% solids (w/v) using mesophiles. X-ray diffraction studies and chemical analysis of the biooxidized residues confirms the precipitation of jarosites at high redox potential which produces some ferricyanide, thereby explaining the reason for high cyanide consumption during cyanidation.

Model of pulmonary fluid traffic homeostasis based on respiratory cycle pressure, bidirectional bronchiolo-pulmonar shunting and water evaporation

The main puzzle of the pulmonary circulation is how the alveolar spaces remain dry over a wide range of pulmonary vascular pressures and blood flows. Although normal hydrostatic pressure in pulmonary capillaries is probably always below 10 mmHg, well bellow plasma colloid pressure of 25 mmHg, most textbooks state that some fluid filtration through capillary walls does occur, while the increased lymph drainage prevents alveolar fluid accumulation. The lack of a measurable pressure drop along pulmonary capillaries makes the classic description of Starling forces unsuitable to the low pressure, low resistance pulmonary circulation. Here presented model of pulmonary fluid traffic describes lungs as a matrix of small vascular units, each consisting of alveoli whose capillaries are anastomotically linked to the bronchiolar capillaries perfused by a single bronchiolar arteriole. It proposes that filtration and absorption in pulmonary and in bronchiolar capillaries happen as alternating periods of low and of increased perfusion pressures. The model is based on three levels of filtration control: short filtration phases due to respiratory cycle of the whole lung are modulated by bidirectional bronchiolo-pulmonar shunting independently in each small vascular unit, while fluid evaporation from alveolar groups further tunes local filtration. These mechanisms are used to describe a self-sustaining regulator that allows optimal fluid traffic in different settings. The proposed concept is used to describe development of pulmonary edema in several clinical entities (exercise in wet or dry climate, left heart failure, people who rapidly move to high altitudes, acute cyanide and carbon monoxide poisoning, large pulmonary embolisms).

Sulfonium Boranes for the Selective Capture of Cyanide Ions in Water

Going fishing! The sulfonium borane [1](+) complexes cyanide in pure water at the maximum allowable concentration of 50 ppb recommended by the European Union. The high cyanide ion affinity displayed by this compound arises from favorable Coulombic effects augmented by a direct bonding interaction between the cyano and sulfonio groups.

Bioremediation of a Cyanide-Contaminated Site Using E&lt;sub&gt;H&lt;/sub&gt;-/PH-Controlled Conditions (ENA)

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

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

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

Copper Electrowinning from Gold Plant Cyanide-Containing Solution

The electrowinning method for treating high copper cyanide solution was investigated by thermodynamics analysis and experiment. The influences of copper concentration, solution temperature, electrolysis time, current density and flow rate on copper recovery and current efficiency was studied in detail and the suitable operation parameters were chosen. Copper electrowinning from the industrial barren solution with copper concentration of 12.40g/L was performed under the condition of current density of 75 mA/cm2, flow rate of 30mL/min and 50°C for 8 hours. An alloy with copper concentration of 99.87% was obtained at the cathode with total energy consumption 2938KWh/t. The used electrolysis solution added with some fresh cyanide sodium solution can be recycled to leaching process.

Catalytic oxidation of cyanides in an aqueous phase over individual and manganese-modified cobalt oxide systems

The possibility for purification of wastewaters containing free cyanides by applying of a new method based on cyanides catalytic oxidation with air to CO 2 and N 2 at low temperature and atmospheric pressure was investigated. On this purpose, individual and modified with manganese Co-oxide systems as active phase of environmental catalysts were synthesized. The applied method of synthesis favours the preparation of oxide catalytic systems with high active oxygen content (total-O* and surface-O* s) possessing high mobility, and the metal ions being in a high oxidation state and in an octahedral coordination-factors determining high activity in reactions of complete oxidation. The catalysts employed were characterized by powder X-ray diffraction, Infrared spectroscopy, and chemical analysis. The effect of pH of the medium and catalyst loading on the effectiveness of the cyanide oxidation process, expressed by the degree of conversion ( α, %), by the rate constant ( k, min −1), and COD was studied. The results obtained reveal that using catalysts investigated a high cyanide removal efficiency could be achieved even in strong alkaline medium. The higher activity of the manganese promoted catalytic sample could be explained on the basis of higher total active oxygen content and its higher mobility both depending on the conditions, under which the synthesis of catalyst is being carried out.

Rising African cassava production, diseases due to high cyanide intake and control measures

AbstractCassava is the staple food of tropical Africa and its production, averaged over 24 countries, has increased more than threefold from 1980 to 2005, and the population has more than doubled over that time compared with a 1.5 times increase worldwide. Agriculturally, cassava performs very well but the roots and leaves contain cyanogenic glucosides that are dangerous to human health. These cyanogens sometimes produce acute intoxication leading to death, they exacerbate goitre and cretinism in iodine‐deficient regions, cause konzo and are implicated in the occurrence of tropical ataxic neuropathy and stunting of children. Konzo is an irreversible paralysis of the legs with many thousands of cases, mainly amongst children, in Mozambique, Tanzania, Democratic Republic of Congo, Cameroon, Central African Republic and probably other tropical African countries. Attempts to alleviate cassava cyanide toxicity have included the development of an information network and distribution in developing countries of picrate kits, which measure total cyanide in cassava and urinary thiocyanate. A simple wetting method that reduces total cyanide in cassava flour three‐ to sixfold has been successfully field tested and is being introduced in Mozambique. Transgenic technology shows promise in increasing the rate of loss of cyanide from roots during processing. World health and agricultural bodies should pay more attention to emerging health problems associated with toxicity of cyanogens in cassava. Copyright © 2008 Society of Chemical Industry

Recovery of copper cyanide from waste cyanide solution by LIX 7950

The use of the guanidine extractant, LIX 7950, to extract copper cyanide from waste cyanide solution has been investigated. Copper extraction is favorable at low pH while a high cyanide to copper molar ratio tends to suppress copper loading. The extractant also strongly extracted zinc and nickel from cyanide solution, but the extraction of iron was poor. The presence of thiocyanate ion significantly depressed copper extraction, but thiosulfate ion produced negligible impact on copper extraction. The preferential extraction of metal cyanide species to free cyanide has been noticed. The potential application of the recovery technique as a pre-concentration step for the treatment of cyanide effluent has been suggested, by which copper can be extracted and concentrated into a small volume of solution and the barren cyanide solution recycled to the cyanidation process.

Biogenic sulphide for cyanide recycle and copper recovery in gold–copper ore processing

Many complex-ore gold deposits with cyanide-soluble copper minerals such as chalcocite, covellite, bornite, cuprite, malachite and azurite are now being considered for processing. In some cases the ore is not currently being mined largely due to the various issues associated with the cyanide-soluble copper minerals in the ore, which results in low gold recoveries and high cyanide consumption and detoxification costs. Moreover, the presence of copper in tailings supernatant tends to stabilize weak-acid dissociable cyanide in a form toxic to wildlife. In the SART process (sulphidization–acidification–recycle–thickening), the cyanide associated with the copper cyanide complexes is released by NaHS dosing to precipitate copper and convert cyanide to HCN gas under weakly acidic conditions, allowing it to be recycled back to the leach process as free cyanide. Copper is also recovered as a valuable, high-grade (∼70% Cu) Cu 2S by-product. Cyanide recycling allows the leach circuit to be operated at higher cyanide levels, maximizing leach efficiency and minimizing copper deportment to gold electrowinning. The first commercial plant is at Telfer in Western Australia. Biogenically-produced hydrogen sulphide can be used to replace chemical sulphide at significantly lower cost and with the added advantage of lowering the acid demand substantially. While the capital cost of a biogenic SART plant will be higher than a cyanide detoxification plant, this will be more than offset by the revenues generated by copper recovery and the savings realized by cyanide recycle, allowing for a short payback time on the incremental capital. BioteQ is currently working with Columbia Metals Corporation Ltd., Canada, to apply its sulphide generating and precipitation technology in a SART circuit at both of Columbia’s gold projects (La Jojoba and Lluvia de Oro) in Northern Mexico. Processing of ores from both mines has presented challenges resulting from the presence of cyanide-soluble copper. This paper reviews the BioteQ biogenic SART process technology, economics and commercial status as well as environmental and operating outcomes.

Cyanide Produced by Human Isolates ofPseudomonas aeruginosaContributes to Lethality inDrosophila melanogaster

Some Pseudomonas aeruginosa strains are cyanogenic, and cyanide may contribute to the bacterium's virulence. Using human isolates of P. aeruginosa, we have shown that Drosophila melanogaster suspended above cyanogenic strains become motionless and develop bradycardia and that flies injected with cyanogenic bacterial strains die more rapidly than those injected with noncyanogenic strains. Flies exposed to cyanogenic strains had high cyanide and low adenosine triphosphate (ATP) concentrations in body extracts, and treatment with a cyanide antidote equalized survival of flies injected with cyanogenic and noncyanogenic strains. P. aeruginosa PAO1 strain with a mutation in the hydrogen cyanide synthase gene cluster was much less toxic to flies than the parental cyanogenic strain or 2 knock-in strains. Transgenic flies overexpressing rhodanese, which detoxifies cyanide by converting it to thiocyanate, were resistant to cyanide and the increased virulence of cyanogenic strains. We conclude that D. melanogaster is a good model for studying cyanide produced by P. aeruginosa.