Interaction mechanism of cyanide with pyrite during the cyanidation of pyrite and the decyanation of pyrite cyanide residues by chemical oxidation

The toxic cyanides in cyanide residues produced from cyanidation process for gold extraction are harmful to the environment.Pyrite is one of the main minerals existing in cyanide residues.In this work,the interaction of cyanide with pyrite and the decyanation of pyrite cyanide residue were analyzed.Results revealed that high pH value,high cyanide concentration,and high pyrite dosage promoted the interaction of cyanide with pyrite.The cyanidation of pyrite was pseudo-second-order with respect to cyanide.The decyanation of pyrite cyanide residue by Na_(2)SO_(3)/air oxidation was performed.The cyanide removal efficiency was 83.9% after 1 h of reaction time under the optimal conditions of pH value of 11.2,SO_(3)^(2-) dosage of 22 mg·g^(-1),and air flow rate of 1.46 L·min^(-1).X-ray photoelectron spectroscopy analysis of the pyrite samples showed the formation of Fe(Ⅲ)and FeSO_(4) during the cyanidation process.The cyanide that adsorbed on the pyrite surface after cyanidation mainly existed in the forms of free cyanide(CN^(-))and ferrocyanide(Fe(CN)_(6)^(4-)),which were effectively removed by Na_(2)SO_(3)/air oxidation.During the decyanation process,air intake promoted pyrite oxidation and weakened cyanide adsorption on the pyrite surface.This study has practical significance for gold enterprises aiming to mitigate the environmental impact related to cyanide residues.

Beneficiation and Characterization of Gold from Itagunmodi Gold Ore by Cyanidation

This paper has reported the beneficiation and characterization of gold from Itagunmodi gold ore in Atakumosa West LGA in the State of Osun Nigeria using cyanide solution obtained from cassava and commercially available sodium cyanide analar grade. Cyanide solution extracted from cassava variety TMS 30572 leaves obtained from Obafemi Awolowo University (O.A.U) Research and Teaching Farm was discovered to have the highest free cyanide (CN-) among the ten different cassava varieties evaluated. The samples were exposed to varied concentrations from 0.25% to 2.00% CN at intervals of 0.25% CN from cyanide solution obtained from cassava and commercially available sodium cyanide analar grade. The result showed that after 24 hours of cyanidation and concentration of 2% CN- on 10 g gold ore concentrate, the analar grade sodium cyanide yielded 0.123 g of gold while the cassava based cyanide yielded 0.098 g. The cyanidation performance of analar grade sodium cyanide is greater than cassava based cyanide by a difference of 0.25%.

Copper and Cyanide Recovery in Cyanidation Effluents

Cyanidation is the main process for gold and silver recovery from its ores. In this study, a process is proposed to recover copper and cyanide from barren solutions from the Merrill-Crowe cementation process with zinc dust. This technology is based on inducing nucleated precipitation of copper and silver in a serpentine reactor, using sodium sulfide as the precipitator, and sulfuric acid for pH control. Results show that pH value has a significant effect on copper cyanide removal efficiency, and it was determined the optimal pH range to be 2.5 - 3. At this pH value, the copper cyanide removal efficiency achieved was up to 97 and 99%, when copper concentration in the influent was 636 and 900 ppm. respectively. In this process (sulphidization-acidification-thickening-HCN recycling), the cyanide associated with copper cyanide complexes, is released as HCN gas under weakly acidic conditions, allowing it to be recycled back to the cyanidation process as free cyanide. Cyanide recovery was 90%. Finally, this procedure was successfully run at Minera William in México.

Cyanidation of gold clay ore containing arsenic and manganese

The extraction process of gold and silver from the gold clay ore containing arsenic and manganese was investigated.With the conventional technique,the leaching rates of gold and silver are 78.23%and 49.02%,respectively.To eliminate the negative effects of arsenic and manganese on cyanidation and increase the gold and silver leaching rates,a novel catalyst was added.The content of the catalyst used in the process was 8 g per 500 g org sample,the sample size was 60μm and the pH value was kept between 10 and 11.Leaching with the catalyst for 3-5 h under certain conditions,the gold leaching rate increased to over 90%and the silver leaching rate increased to 80%-90%.The catalyst can effectively liberate gold and silver from the enclosure of arsenic and manganese and the industrial experiment has great significance to the development and utilization of the gold clay ore containing arsenic and manganese.

Impact of silver sulphides on gold cyanidation with polymetal sulphides

Gold leaching was influenced in association with silver and polymetal sulphide minerals.A packed bed was adopted to single out the galvanic and passivation effects with four sets of minerals:pyrite?silica,chalcopyrite?silica,sphalerite?silica and stibnite?silica.Pyrargyrite enhanced Au recovery to 77.3%and 51.2%under galvanic and passivation effects from pyrite(vs 74.6%and 15.8%).Pyrargyrite in association with sphalerite also enhanced Au recovery to 6.6%and 51.9%(vs 1.6%and 15.6%)under galvanic and passivation effects from sphalerite.Pyrargyrite associated with chalcopyrite retarded gold recovery to 38.0%and 12.1%(vs 57%and 14.1%)under galvanic and passivation effects.Accumulative silver minerals enhanced Au recovery to 90.6%and 81.1%(vs 74.6%and 15.8%)under galvanic and passivation impacts from pyrite.Silver minerals with sphalerite under galvanic and passivation effects enhanced Au recovery to 71.1%and 80.5%(vs 1.6%and 15.6%).Silver minerals associated with chalcopyrite retarded Au recovery to 10.2%and 4.5%under galvanic and passivation impacts(vs 57%and 14.1%).Stibnite retarded Au dissolution with pyrargyrite and accumulative silver minerals.Pyrargyrite and accumulative silver enhanced gold dissolution for free gold and gold associated with pyrite and sphalerite.Gold dissolution was retarded for gold and silver minerals associated with chalcopyrite and stibnite.

DISSOLUTION KINETICS OF GOLD AND SILVER IN CYANIDATION

The dissolution kinetics of gold and silver cyanidation of Cu-Au sulfide concentrate has been investigated at ambient temperature in consideration of effects of various parameters,such as particle size of ores,hydrodyna.mics of the process and initial cyanide concentration as well as oxygen partial pressure.The experimental data are mathematically treated with an approach based on the shrinking core model.A phenomenological expression describing the rate and rate constants for cyanidation of the concentrate is developed from the treatment.The dissolution of gold and silver is explained by an electrochemical mechanism in which the rate determining step is,the diffusion of cyanide and dissolved molecular oxygen through a porous layer formed during the minerals dis-solutions.

Effect of Pretreatment of Sulfide Refractory Concentrate with Sodium Hypochlorite, Followed by Extraction of Gold by Pressure Cyanidation, on Gold Removal

The majority of the refractory gold and silver occurs in occlusion in sulphides, then precious metal dissolution is possible by first oxidizing auriferous sulfide concentrate using sodium hypochlorite-sodium-hydroxide solution followed of pressure cyanidation of the oxidized concentrate, for the extraction of precious metals. This process was conducted and evaluated under cyanide and oxygen pressure. This versatile approach offers many advantages, including low temperatures, low pressure and less costly materials of construction than conventional pressure oxidation. In this study, the effect of oxygen pressure, concentration of sodium hypochlorite, temperature, and initial pH, in precious metals recovery and As removal were evaluated using a 24 factorial design. Characterization of the ores showed that pyrite and arsenopyrite were the main minerals present on the concentrate. The best results for gold extraction were obtained with oxygen pressure of 80 psi, 10% (w/w) sodium hypochlorite, temperature of 80℃, at pH = 13, and a constant stirring speed of 600 rpm. These conditions allowed an approximated 60% of gold and 90% of silver extractions in 1 hr.

Clinical Case Report of Acute Heart Injury and Acute Rhabdomyolysis Due to Cyanide Poisoning

Cyanide poisoning is one of the most dangerous poisonings, and it can be absorbed into the body through the mouth, inhalation and through the skin. A 32-year-old female patient was admitted to our poison control center because of high fever, severe vomiting, and seizures. Physical examination found that the patient was drowsy, had a high fever of 40 degrees Celsius, pulse of 140 beats/minute, and increased tendon and bone reflexes. Exploiting the patient’s information, it was discovered that the patient bought Cyanide to drink with the intention of committing suicide. The patient was quickly treated with gastric lavage and activated charcoal. Echocardiography recorded EF: 35%, reduced movement of the entire myocardium. CK blood test: 4562 U/L. The patient’s condition rapidly deteriorated and the patient was made ECMO, IHD and CVVHDF. After 3 days of treatment, the patient’s condition did not improve, so the family asked for the patient to go home. This article aims to describe the rapidly progressing and severe damage to the heart and muscles of patients with cyanide poisoning.

Modeling of an Automatic Optimization System of Cyanide Concentration in Carbon in Leach for Optimal Ore Processing in a Mining Company

The optimization system, which was the subject of our study, is an autonomous chain for the automatic management of cyanide consumption. It is in the phase of industrial automation which made it possible to use the machines in order to reduce the workload of the worker while keeping a high productivity and a quality in great demand. Furthermore, the use of cyanide in leaching tanks is a necessity in the gold recovery process. This consumption of cyanide must be optimal in these tanks in order to have a good recovery while controlling the concentration of cyanide. Cyanide is one of the most expensive products for mining companies. On a completely different note, we see huge variations during the addition of cyanide. Following a recommendation from the metallurgical and operations teams, the control team carried out an analysis of the problem while proposing a solution to reduce the variability around plus or minus 10% of the addition setpoint through automation. It should be noted that this automatic optimization by monitoring the concentration of cyanide, made use of industrial automation which is a technique which ensures the operation of the ore processing chain without human intervention. In other words, it made it possible to substitute a machine for man. So, this leads us to conduct a study on concentration levels in the real world. The results show that the analysis of the modeling of the cyanide consumption optimization system is an appropriate solution to eradicate failures in the mineral processing chain. The trend curves demonstrate this resolution perfectly.

Impact of Selected Processing Methods of High-Level Cyanide in Cassava on Optic Neuropathy in Wistar Albino Rats—An Experimental Study

Background: Cassava tuber crop is a staple food rich in carbohydrates and utilized in various forms by millions of Nigerians. The storage root of the cassava contains linamarin, a cyanogenic glycoside that is easily hydrolyzed to release cyanide salt compounds which is toxic to the nervous system especially the optic nerve, sometimes leading to optic neuropathy and visual impairment. Aim: The aim of this study is to find out the impact of selected processing methods of high-level cyanide in cassava on optic neuropathy in Wistar albino rats. Methodology: Twenty-four Wistar albino rats were fed with different concentration and duration of predetermined high-cyanide content cassava root cultivar which was processed using different processing methods adopted by various communities in Rivers State, Nigeria (for human consumption). A control group of 3 Wistar albino rats was fed with normal “Growth Mesh” meals. The pre and post weights of the animals and the fundoscopic optic nerve status of the rats were evaluated after 30 and 60 days. SPSS Version 25 was employed for descriptive and inferential statistical analyses. A p-value of ≤0.05 was considered statistically significant. Results: The Cassava species available in Rivers State have high cyanide content (2336.79 mg CN-/kg dry weight of cassava). There was statistically significant reduction in the cyanide content (p = 0.000) depending on the various common processing methods (into garri for human consumption): 24 hours, 48 hours, fermentation;with and without red palm oil additive. The individual weights as well as the mean weight of the 24 rats in the experimental group increased gradually from the first week to the 9th week with a slight weight reduction on the third and fourth weeks which was not statistically significant (p = 0.092). However, there was a steady increase in the weights of the animals in the control group throughout the 9 weeks. Varying degrees of optic neuropathy occurred, worse with the rats that had 24-hour fermented cassava twice daily for 60 days. The intra and inter group differences in the optic disc changes was statistically significant (p = 0.000). Conclusion: Longer duration of processing cassava roots into garri for human consumption reduces its cyanide content and minimizes the adverse impact on the optic nerve.

Fe extraction from high-silicon and aluminum cyanide tailings by pretreatment of water leaching before magnetic separation

Pretreatment of high content of Si- and Al-containing cyanide tailings by water leaching to remove some impurities, such as the major impurities minerals of Si and A1, as well as its effect on Fe extraction in the water leaching process was investigated. The effects of different parameters on iron recovery were studied, and the reaction parameters were proposed as follows： sodium carbonate content of 30%, water leaching at 60 ~C for 5 min, liquid/solid ratio of 15：1, and exciting current of 2 A. Under these optimal conditions, magnetic concentrate containing 59.11% total iron and a total iron recovery rate of 76.12% was obtained. In addition, the microstructure and phase transformation of the process of water leaching were studied by X-ray powder diffraction technique （XRD）, Electronic image of backscattering （BEI）, X-ray fluorescence （XRF）, and energy dispersive spectrometry （EDS）. The results indicate that the soluble compound impurities generated in the roasting process are washed out, and the dissoluble substances enter into nonmagnetic materials by water leaching, realizing the effective separation of impurities and Fe.

Differences of cyanide leaching between calcine and dust from refractory gold concentrates

Differences of cyanide leaching between the calcine and the dust from a refractory gold concentrate were investigated by comparative method. Results showed that gold leaching efficiencies of the calcine and the dust were 85.31% and 54.30%, respectively, with direct cyanidation. Contents and existing forms of arsenic and carbon were the main reasons for those differences. The maximum gold leaching efficiencies of the calcine and the dust were 87.70% and 58.60%, respectively, with cyanidation after NaOH pre-leaching. Harmful elements removal, gold loss in NaOH pre-leaching and iron oxides hindrance codetermined gold leaching efficiencies of the calcine and the dust. After H2SO4 pre-leaching, the maximum gold leaching efficiencies of the calcine and the dust achieved 94.96% and 80.40%, respectively. The effect of carbonaceous matter was the main reason for differences for leaching efficiencies of the calcine and the dust. Based on those differences, two proper gold extraction processes were put forward, and gold leaching efficiencies for the calcine and the dust achieved 94.91% and 91.90%, respectively.

Co-intensification of gold leaching with heavy metals and hydrogen peroxide

Co-intensification was researched to accelerate gold leaching with regards to its electrochemical nature by using anodic intensifiers of heavy metal ions (Pb2+,Bi3+,Tl+,Hg2+ and Ag+) on the basis of hydrogen peroxide assistant leaching on three different types of materials which were classified as a refractory sulphide gold concentrate,an easily leachable sulphide gold concentrate,and a low grade oxide gold ore according to their leaching characteristics.The results showed that,favorable co-intensification effects on the three materials were obtained and leaching time of gold was effectively shortened to no longer than 12 h from 16 to 24 h for hydrogen peroxide assistant leaching.For the five tested heavy metal ions,Bi3+and Tl+ presented co-intensifying effect on all the three materials,and Hg2+ caused co-intensifying effect on both refractory and easily leachable sulphide gold concentrates,and Pb2+ and Ag+ only had co-intensifying effect on the easily leachable sulphide gold concentrate.

Artificial neural network modeling of gold dissolution in cyanide media

The effects of cyanidation conditions on gold dissolution were studied by artificial neural network （ANN） modeling. Eighty-five datasets were used to estimate the gold dissolution. Six input parameters, time, solid percentage, P50 of particle, NaCN content in cyanide media, temperature of solution and pH value were used. For selecting the best model, the outputs of models were compared with measured data. A fourth-layer ANN is found to be optimum with architecture of twenty, fifteen, ten and five neurons in the first, second, third and fourth hidden layers, respectively, and one neuron in output layer. The results of artificial neural network show that the square correlation coefficients （R2） of training, testing and validating data achieve 0.999 1, 0.996 4 and 0.9981, respectively. Sensitivity analysis shows that the highest and lowest effects on the gold dissolution rise from time and pH, respectively It is verified that the predicted values of ANN coincide well with the experimental results.

A Comprehensive Utilization Process for Black Manganese-silver Ores by Pyrite Reducing Method

On a 5 kg bench scale, the separating of Mn-Ag from black manganese-silver ores by pyrite reducing method was investigated. Leached Mn content of 98.3% (mass fraction) along with silver loss of 1.5% is achieved. The purification of solution by the precipitation method was effectively used. Chemical grade gamma -MnO2 with TMn content of 60.13% (mass fraction) and MnO2 content of 92.28% (mass fraction) is obtained. Mn recovery efficiency is 94.04%. The residues from leaching Mn process of black Mn-Ag ores was employed for silver extraction by cyanidation with leached silver content of 92.17% (mass fraction), displacement ratio of 99.5%, recovery efficiency of 90.79%. Therefore, the present study provides a feasible process for making full use of black manganese-silver ore resources.

Influence of copper minerals on cyanide leaching of gold

The paper thermodynamically examined the behavior of various copper minerals in cyanide solu tions and investigated the influence of copper minerals on cyanide leaching of gold. In elucidating the influence of copper minerals on cyanide leaching of gold, copper minerals were classified into two types according to their solubility in cyanide solutions by proposing two concepts, cyaniding easily soluble copper (E Cu ) and cyaniding insoluble copper. The former involves copper occurrence in metal, oxides and secondary sulfides, and the latter refers mainly to primary sulfides. Experimental results show that not all the total copper in an ore affected cyanide leaching of gold, while cyaniding easily soluble copper turns out to be the decisive factor that interferes with gold cyanidation by causing decrease in gold cyanidation recovery and increase in cyanide consumption. When cyaniding easily soluble copper content ( w E(Cu) ) lies in the range of 0 0.25%, it linearly affects gold cyanidation recovery ( R ) as well as cyanide consumption ( m c). The regression equations have been worked out to be R (%)=94.177 5-142.735 7 w E(Cu) with a correlation coefficient of -0.902 and m c=5.590 7+33.572 9 w E(Cu) with a correlation coefficient of 0.945, respectively.

BEHAVIOUR OF ELEMENTAL SULPHUR IN BIOOXIDATION OF GOLD-BEARING SULPHIDE ORES

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Leaching kinetics in cyanide media of Ag contained in the industrial mining-metallurgical wastes in the state of Hidalgo, Mexico

The leaching kinetics in cyanide media of the silver contained in the Dos Carlos waste tailings at the City of Pachuca de Soto, Hidalgo State, Mexico were carried out. The used material contained the following chemical composition: 56 10-6of Ag, 0.6 10 6of Au and 70.43%(by weight) of SiO2; 7.032%(by weight) of Al2O3; 2.69%(by weight) of Fe; 0.46%(by weight) of Mn; 3.98%(by weight) of K2O; 3.34%(by weight) of CaO; 2.50%(by weight) of Na2O; 0.04%(by weight) of Zn; 0.026%(by weight) of Pb. The mineralogical phases present were the following: Silica, albite, argentite, berlinite, orthoclase, potassium jarosite, and natrojarosite. In the leaching kinetics in cyanide media, and under the studied conditions,the effect of the CN concentration on the reaction rate has no effect on the whole process of alkaline cyanidation, of which the reaction order is n 0. Temperature has an effect on the cyanidation rate of the reaction, with an activation energy of 47.9 KJ/mol. At the same time, when the particle size decreases there is an increase in the reaction rate, which is inversely proportional to the particle diameter; when increasing the NaOH concentration there is an increase in the reaction rate Kexp, with a reaction order(n) of 0.215 under the studied ranges.

Kinetic Aspects of Gold and Silver Recovery in Cementation with Zinc Power and Electrocoagulation Iron Process

The Merrill-Crowe or Cementation process is used for concentration and purification of gold and silver from cyanide solutions. Among other available options for recovery of precious metals from cyanide solutions, Electrocoagulation (EC) is a very promising electrochemical technique for the recovery of this precious metals. In this work first, an introduction to the fundamentals of the Merrill Crowe and EC process are given, then Kinetic aspects conditions and results of the both process, for the removal of gold and silver from cyanide solutions are presented, and finally the characterization of the solid products formed during the EC process with X-ray Diffraction and SEM are shown. Results suggests that The cementation of both gold and silver by suspended zinc particles conforms to well-behaved fist order kinetics and for the EC process the results show that is an excellent option to remove Au and Ag from cyanide solution by using iron electrodes. Finally, 99.5% of gold and silver were removed in the experimental EC reactor, and it was achieved in 5 minutes or less.

LEACH OUT GOLD AND SILVER FROM SULFIDE CONCENTRATE CONTAINING COPPER WITH CYANIDE AND AMMONIA SOLUTIONS

A cyanidation leaching process for a sulfide concentrate containing gold and silver with ammonia and other complexes was investigated,and its potential in decrease of cyanide consumption was examined.The equilibria behaviors of copper and other metal ions in the CN-NH,-H_(2)0 system and the CN—NH,—EDTA-HjO system were analyzed by a microcomputer program.Experiments revealed that the leaching yield of gold in ammonia-cyanide solutions was raised from 86%to 99%from addition of EDTA in a certain concentration and its cooperative action with ammonia on the cyanidation of gold.Meanwhile,the leaching yield of silver was significantly increased from about 20%to 55%and the consumption of cyanide was decreased.