Study on Gold (Ⅰ) Solvent Extraction from Alkaline Cyanide Solution by TBP with Addition of Surfactant

The new solvent extraction system for gold() from alkaline cyanide solution by TBP with addition of surfactant in aqueous phase was studied. The effect of various factors, such as equilibrium pH, constitution of organic phase, molar ratio of CPBAu(CN)2-, extraction time, aqueous/organic phase ratio, different initial gold concentration, equilibrium temperature, different diluent, different types of extractants and surfactants etc., was inspected. The results show that gold() can be extracted quantitatively by controlling the quantity of surfactant (CPB); both the equilibrium pH and diluent hardly influence percent extraction. Gold() percent extraction reaches more than 98% under the optimal experimental conditions. 30% vol TBP diluted by sulphonating kerosene can load gold() to rather high levels. Loading capacity is in excess of 38 g/L. The extraction mechanism is discussed and the overall extraction reaction is deduced.

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.

Granular activated carbons from palm nut shells for gold di-cyanide adsorption

Granular activated carbons were produced from palm nut shells by physical activation with steam. The proximate analysis of palm nut shells was investigated by thermogravimetric analysis, and the adsorption capacity of the activated carbons, produced as a result of shell pyrolysis at 600℃ followed by steam activation at 900℃ in varying activation times, was evaluated using nitrogen adsorption at 77 K. Applicability of the activated carbons for gold dicyanide adsorption was also investigated. Increasing the activation hold time with the attendant increase in the degree of carbon burn-off results in a progressive increase in the surface area of the activated carbons, reaching a value of 903.1 m2/g after activation for 6 h. The volumes of total pores, mieropores, and mesopores in the activated carbons also increase progressively with the increasing degree of carbon burn-off, resulting from increasing the activation hold time. The gold di-cyanide adsorption of the activated carbons increases with the rise of pore volume of the activated carbons. The gold di-cyanide adsorption of palm nut shell activated carbon obtained after 6-h activation at 900℃ is superior to that of a commercial activated carbon used for gold di-cyanide adsorption.

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.

Cyanide removal for ultrafine gold cyanide residues by chemical oxidation methods

Because of the highly toxic cyanide in the gold cyanide residues,cyanide must be removed for environmental protection.The process mineralogy of residues was studied firstly,and then cyanide removal was carried out by three chemical methods.The results showed that the residue mainly contained Si,S and Fe.Pyrite was the main metallic mineral,and the iron-complex cyanides make cyanide removal difficult.The minerals in residues were in ultrafine particle size with high monomer dissociation degrees.In H_(2)O_(2)oxidation process,the self-decomposition and side reactions resulted in high consumption of H_(2)O_(2).In Na_(2)S_(2)O_(5)-air oxidation process,the time for complete process was long because of the reactions between Na_(2)S_(2)O_(5)and O_(2).Na_(2)SO_(3)oxidation method was found to be a new method for cyanide removal without air inflation device.The cyanide content was reduced to the national standard level in 90 min at pH 9.0 with optimum Na_(2)SO_(3)dose of 2.0 g/L.

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.

Active and passive behaviors of gold in cyanide solutions

Active and passive behaviors of pure gold（Au） and roasted gold ore（RGO） electrodes were investigated at 25 °C in de-aerated agitated cyanide media.Cyclic voltammetry and potentiodynamic polarization with agitation at 100 r/min in 0.04 mol/L NaCN solution showed different peak positions and current densities.Potentiodynamic tests illustrate that the peak current densities increase greatly with increasing the cyanide concentration.Increasing the pH value from 10 to 11 resultes in a great decrease of current density,while it increases noticeably by decreasing the agitation from 100 to 60 r/min.In the presence of oxygen,Au and RGO electrodes show different characteristics of peak positions and corrosion rates.The potentiostatic studies show that increasing the potential from 1 to 1.4 V at pH value of 11 results in an 80% decrease of current density while decreasing the pH value from 11 to 10 at 1 V gives a 1.7 fold increase of current density,possibly due to more effective passive layer.Following polarization,electrochemical noise measurements（ENM） during decay periods show that Au results in more passive states at high potentials,showing pitting corrosion.The ENM results show that this technique can be a promising tool for a better understanding of gold leaching.The XPS studies prove the presence of passive oxides.

Synthesis,Structure and Luminescence of a 1-D Chain of Copper(Ⅰ) Cyanide Decorated by Triphenylphosphine

A new wave-like infinite chain coordination polymer [Cu3（CN）3（PPh3）4]n（1,PPh3=triphenylphosphine） has been synthesized by solution reaction and characterized by X-ray single-crystal structure diffraction analysis.The complex crystallizes in space group P1 with a=13.343（6）,b=13.429（7）,c=20.694（10）A,α=103.163（4）,β=96.704（5）,γ=101.981（6）o,V=3479（3）A^3,Z=2,C75H60Cu3N3P4,Mr=1317.76,Dc=1.258 g/cm^3,F（000）=1356,μ=1.043 mm^-1,the final R=0.0680 and wR=0.1305 for 9232 observed reflections with I〉2σ（I）.The infinite chain is linked by C-H…π H bonding interactions to form a 2-D supramolecular network.Luminescent study reveals that the complex has green-light emission.

Recovery of Gold and Silver and Removal of Copper, Zinc and Lead Ions in Pregnant and Barren Cyanide Solutions

Over the past decade the concern about toxic metals in freshwater has increased. Environmental laws such as the Clean Water Act have forced industries that produce metal containing wastewater to treat their wastewater prior to discharge. The purpose of this study was to investigate the use of a novel method for the minimization of heavy metals in the wastewater from the mining industry. A very promising electrochemical treatment technique that does not require chemical additions is electrocoagulation (EC) and sulphide precipitation. The present study has been done for the recovery of gold and silver contained in pregnant solution from the cyanidation process using the electrocoagulation technology with iron electrodes;that is a developed alternative technology for the Merril-Crowe process. The average gold and silver content in pregnant solution was 4.27 and 283 ppm respectively and the recoveries were 92% for gold and 95% for silver, with optimum operating parameters of pH 10, residence time of 20 minutes and addition of sodium chloride of 4 gr/L. The results of precipitation process show that the elimination of lead, zinc, cooper and iron ions from the barren solution was successful, with optimum operating parameters of pH 3 and residence time of 15 minutes, and the recoveries were 99% of these ions. Finally the characterization of the solid products of gold and silver formed during the EC process with Scanning Electronic Microscope was performed. Results suggest that magnetite particles and amorphous iron oxyhydroxides (lepidocrocite) were present.

Use of ferricyanide for gold and silver cyanidation

Low gold and silver leaching kinetics has been commonly observed in traditional gold-silver cyanidation process, especially in heap leaching and in situ leaching operations. The different mineralogy of gold and silver in the ores is suspected to be the main reason, e.g., the occurrence of low solubility acanthite (Ag2S) typically results in low overall silver extraction. Due to the low solubility of oxygen in cyanide solution, the reactivity and availability of oxidant is believed to be the critical limitation for gold and silver dissolution. The use of ferricyanide as the auxiliary oxidant for gold and silver cyanidation has been examined. The rotating disc test results prove the assistant effect of ferricyanide on increasing the dissolution rate of gold and silver. The potential use of ferricyanide in gold/silver cyanidation process is proposed based on the leaching results of actual ores.

Dissolution of gold in chalcopyrite-containing cyanide solutions

The gold dissolution in anoxic cyanide solution in the presence of chalcopyrite was studied with a rotating disc electrode.It was found that the presence of chalcopyrite reduced and enhanced the dissolution activity of pure gold in the low and high potential regions,respectively.The dissolution of gold was diffusion-controlled at low potentials(≤177 mV)and low cyanide concentrations(≤980 mg/L);however,above the cyanide concentration of 980 mg/L,the current density of gold decreased and the dissolution of gold changed from diffusion-control to electrochemical reaction-control.At high potentials(>177 mV),gold dissolution was always controlled by diffusion.In cyanide solution containing chalcopyrite,appropriate increase of pH value and temperature could accelerate the dissolution of gold,but high pH value would promote the generation of passivation,which was harmful for the dissolution of gold in cyanide solution.

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.

Studies on the Extraction of Gold (I) Cyanide by Quaternary Ammonium Salt Using ^(198)Au as Tracer

The solvent extraction of KAu(CN)2 from alkaline solution by quaternary ammonium salts (trialkyl-methylammonium chloride or cetyltrimethylammonium bromide) was investigated by means of 198Au radioactive tracer method. Various parameters, such as the gold (I) concentration in aqueous phase, the modifier, emulsification at the interface of two phases, and phase ratio used in the extraction of gold (I) were studied. The results demonstrate that almost all gold (I) in the aqueous phase was practically extracted into the organic phase. The water content in the organic phase decreased significantly with increase of gold (I) concentration using long chain alcohol as modifier, in contrast with the system with tributyl phosphate (TBP) as modifier. Emulsification at the interface of two phases decreases with an increase of modifier concentration in the organic phase or with the addition of a small amount of lysozyme into the aqueous phase. The method with 198Au tracer can be directly used to determine the Au(I) concentration both in aqueous and organic phases, which is especially suitable for the low concentration of Au(I).

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%.

An SCF－MS－Xα Study of the Electronic Structures of Binuclear and Trinuclear Gold（Ⅰ） Compounds

The SCF-Xα-SW molecular orbital calculations were carried out on the modelcompounds of binuclear and trinuclear gold(Ⅰ)using starting potential of Au atom and the Watson sphere.The energy level order of the frontier orbital of a binuclear gold model compound is in agreement with the experimental result.The calculated ionization potential of the binuclear model compound is consistent well with the photoelectron spectrum of Au (Me)(PMe_3).The metal-metal interactions are discussed.The calculated electronic absorption spectra of binuclear and trinuclear gold(Ⅰ)are basically in agreement with experimental results.

Structure and Luminescence Property of a Linear Tetranuclear Gold(Ⅰ)-thiolate Complex through Au-Au Interaction

The synthesis,structure and luminescent property of a tetranuclear gold（Ⅰ）complex with doubly bridging diethyldithiocarbamate（Et2dtc）and 1,1-bis（diphenylphosphino）ethene（（Ph2P）2C=CH2）are described.The complex crystallizes in monoclinic space group C2/c with a=26.785（7）,b=25.654（6）,c=12.277（3）A,β=106.879（5）°,V=8073（4）A^3,Z=8,C31H32Au2F6NO3P2S2Sb,Mr=1222.32,Dc=2.011 g/cm^3,F（000）=4592,Rint=0.0529,T=293（2）K,μ=8.157 mm^（-1）,the final R=0.0464 and wR=0.1444 for 5804 observed reflections with I〉2σ（Ⅰ）.The intramolecular and intermolecular Au¨Au distances are 2.8670（9）and 3.2367（9）A,respectively.Weak emission appears at 517 nm at room temperature in the solid state.

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.

Ab Initio Molecular Orbital Calculation on Dinuclear Gold(Ⅰ) Complexes──Metal-Metal Interaction and Electronic Structure of Binuclear Gold(Ⅰ) Complexes with Bridging Bidentate Ligands

The electronic structure and electronic absorption spectra of binuclear Au(Ⅰ) complexes with bidentate phophines and a bidentate ylid ligand have been studied using quasirelativistic pseudopotential ab initio calculations at the HF and MP2 levels by the LANL2DZ basis sets. The electronic properties of the spectral transition and Au(Ⅰ)—Au(Ⅰ) interaction were also discussed.

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.

Isolation and Assessment of Cyanide Biodegradation Potential of Indigenous Bacteria from Contaminated Soil

Eight effective bacterial strains were isolated from cyanide-contaminated soil, from which, two (S11 and S13) were tested to determine their minimum inhibitory concentration using potassium cyanide (KCN) and potassium tetracyano nickelate (K2Ni(CN) 4). The isolates were tested for their KCN biodegradation potential (by measuring ammonia production) at neutral and alkaline pHs (7.0 and 9.0). Furthermore, the effect of the initial KCN concentration on biodegradation was evaluated at the optimal pH using nitrogen free M9 medium, supplemented with KCN as nitrogen source. The results showed that both strains tolerated cyanide concentrations of up to 10 × 10-3 mol⋅l-1 (0.651 g⋅l-1 KCN;2.409 g⋅l-1 K2Ni(CN)4) which makes them good candidates for cyanide bioremediation. For both strains, a change of initial pH from 7.0 to 9.0 significantly enhanced KCN degradation. S13 grown at pH 9.0 and S11 cultivated at pH 7.0 released the highest and lowest amounts of ammonia, respectively. For both strains, the release of ammonia increased when the initial KCN concentration increased from 10-3 to 5 × 10-3 mol⋅l-1. These findings open prospects for the application of these bacteria for remediation of cyanide-contaminated soils and wastewater at alkaline pH, alkaline pH being conditions that prevent cyanide volatilization.