The influence of pyrite pre-oxidation on gold recovery by cyanidation

The influence of pyrite pre-oxidation in alkaline solutions on gold recovery by cyanidation from Twin Creek refractory gold ore in which pyrite was identified as the major sulfide mineral has been investigated with the aid of electrochemical measurements, leaching experiments, and direct analysis of reaction products for selected residues. It was found that gold recovery by cyanidation in bottle roll experiments mainly depended on the extent of pyrite pre-oxidation. The rate of pyrite oxidation in alkaline solutions measured by electrochemical measurements, including chronoamperometry and linear sweep voltammetry, increased with an increase in pH, potential, and temperature. All alkaline reagents used for the electrochemical measurements, NaOH, NH₄OH, Na₂CO₃ and Ca(OH)₂, showed a similar effect on pyrite oxidation kinetics. However, the results of alkaline pre-oxidation for pyrite of the Twin Creek refractory gold ore suggested that NaOH and Na₂CO₃/Ca(OH)₂ were superior to Ca(OH)₂. Without pre-oxidation, cyanide leachable gold was found to be only 20% which could be increased to 70% under appropriate pre-oxidation conditions. At the same time, cyanide consumption decreased from 2.5 kg/t ore to 1.5 kg/t ore.Selected residues after pre-oxidation and cyanidation were examined by X-ray diffraction. Backscattered electron images of pyrite particles in these residues were taken. The reaction products at the surface of pyrite particles were found to be iron-, silicon-, and calcium-bearing compounds with variable amounts of sulfur as determined by X-ray energy dispersion analysis. Additionally, some mineral fines, such as aluminum and/or potassium-bearing minerals, were found to be present at the partially oxidized pyrite surface.     

Quantifying accidental activation. Part II. Cu activation of pyrite

As a case study to quantify the flotation response, Cu activation of pyrite was examined. Two particle sizes, 106/150 and 37/74 μm (surface area 304 and 901 cm²/g), were used. Micro-flotation was performed to determine the rate constant, k, as a function of surface concentration of copper, [Cu]_surf. The [Cu]_surf was determined by EDTA extraction and controlled by contact with Cu salt solution or with chalcopyrite and chalcocite particles. The rate constant relative to zero copper, k_Cu/k₀, followed the same trend against [Cu]_surf for both particle sizes. Chalcocite gave a surface concentration about 40 times higher than chalcopyrite, corresponding to their relative ion production (the b-values in Part I). An estimate of mineral grade likely to cause activation was made assuming the grade was inversely dependent on b and taking the critical grade of chalcocite as 0.1% (Petruk, 2000). This gave a critical chalcopyrite grade of ca. 2%.     

Cyanide oxidation by ozone in cyanidation tailings: Reaction kinetics

The treatment of cyanidation effluents is one of the main problems the gold mining industry faces. Different methods are available for the removal of cyanide but in most cases the consumption of reagents raises the cost to unaffordable levels, or there exists the formation of residual byproducts that are also toxic. Ozone gas is used in a new alternative approach that presents several advantages for oxidation of cyanide compounds. However, the lack of information on the reactions of cyanide compounds with ozone has limited its industrial application in cyanidation effluents.The oxidation of cyanide by ozone in aqueous solutions was studied using a bubble column reactor. The reactor was operated at different conditions of pH, ozone dosage rate, gas flow rate and cyanide concentration. Preliminary experiments were performed with synthetic cyanide solutions and the results :showed that the rate of cyanide oxidation may be described by an equation which is first order with respect to ozone concentration in the oxidizing gas, and zero order with respect to cyanide concentration in the aqueous solution. The rate constant obtained for the reaction was about 10⁻⁵ mol/L·s. The stoichiometry estimated for the reaction indicated one mole of cyanide reacts with one mole of ozone to form one mole of cyanate. These results were corroborated with industrial eff luents from two mines in Mexico.     

Dissolution of gold during pyrite oxidation reaction

Numerous papers discuss the mechanism of alkaline oxidation of pyrite but there is limited information available describing the actual kinetics of the pyrite sulphide to thiosulphate reaction. A previous investigation in this series determined the rate of sulphide sulphur oxidation and thiosulphate yield in the reaction of pyrite with sodium hydroxide under various testing conditions. The goal of the current study is to validate these rates using two different gold-containing pyrite concentrates. A further objective of the current work is to investigate the simultaneous dissolution of gold with in situ formed thiosulphate during pyrite oxidation.It was found that at 20 psi oxygen overpressure and a temperature of 80 °C, the initial rate of sulphide oxidation and thiosulphate yield were close to 0.08 mol/h and 0.0155 mol/h, respectively. These rates are in agreement with previously published data. However, a shift from linearity occurred when the pH decreased below 12. A rapid decay of thiosulphate was evidenced at pH 8.3–9.2 while E_H was in the range of 22–141 mV. Based on relevant thermodynamic analysis of metastable thiosalts system, such rapid decomposition is not expected at these pH and E_H values. It is believed that the presence of unreacted pyrite acting as a catalyst caused this behaviour. It appears that under mildly alkaline conditions, the rate of oxidation of sulphide to thiosulphate becomes slower than the rate of thiosulphate degradation, which causes a net loss of thiosulphate in the system. The maximum extraction of gold and silver (96% and 75% respectively) was achieved under conditions of pH < 12.     

Preventing oxidation of iron sulfide minerals by polyethylene polyamines

This paper presents some important findings on the passivation of pyrite and pyrrhotite minerals. Polyethylene polyamines, such as triethylenetetramine (TETA), diethylenetriamine (DETA), used alone in dilute solutions or combined with potassium amyl xanthate (p.a.x.) can provide an effective protective layer for sulfidic ores and significantly reduce the penetration of atmospheric oxygen and the oxidation of these ores. Experimental studies were carried out systematically on both small particles and coarse samples using both diluted hydrogen peroxide solutions and atmospheric oxygen as oxidants. In all cases, a remarkable diminution of oxidation of the coated samples was observed. The study also demonstrates that solutions of polyethylene polyamines such as DETA and TETA are relatively strong reducing agents while showing good buffering capacities as well because of their nucleophilic functional groups. These properties give them additional advantages over other coating agents. The presence of these compounds also prevents the proliferation of the bacterium Acidithiobacillus ferrooxidans that plays an important catalyzing role in the oxidation of sulfides and acid mine generation. Polyethylene polyamines are effective coating agents to prevent surface oxidation of sulfidic minerals.     

Effects of high magnesium ion concentration on KCl flotation: Part II – Plant research

There appears to be several mechanisms affecting the recovery of coarse KCl particles as they flow through the flotation circuit of the Taquari Vassouras mine (Companhia Vale do Rio Doce; CVRD), Aracaju, Brazil in the presence of continually increasing concentrations of carnallite. The increase in carnallite assists in the deposition of fine NaCl and KCl crystals on the surface of the coarse KCl particles. The effect seems to be a slight net improvement in the surface hydrophobicity and therefore flotation recovery of the coarse KCl particles. As the concentration of Mg²⁺ ions increase, the precipitation of fine crystals of NaCl and KCl starts to increase. These NaCl crystals appear to have fine inclusions of KCl on the surface (and vice versa) which appear to attract collector, thus reducing hydrophobicity and flotation recovery of the coarse KCl feed. It is at this stage that the removal of fine precipitates appears to become critical in order to provide enough collector coverage of the coarse KCl particles to keep them floating.     

Investigation of the kinetics of pyrite oxidation by hydrogen peroxide in hydrochloric acid solutions

The kinetics of pyrite oxidation by hydrogen peroxide in hydrochloric acid solutions were investigated. The effects of stirring, temperature, particle size as well as hydrogen peroxide and hydrochloric acid concentrations were studied. The effects of H⁺ and Cl⁻ additions were also examined. The oxidation kinetics were found to follow a shrinking core model, with the surface chemical reaction as the rate-controlling step. This is in accord with an activation energy of 65 kJ/mol and a linear relationship between the rate constant and the reciprocal of the particle radius. The reaction order with respect to hydrogen peroxide concentration was found to be 1.32. The rate of pyrite oxidation was found to decrease as the hydrochloric acid concentration increases, most likely owing to the adsorption of chloride ions onto the surface of the pyrite particles. H⁺ ions had no effect on the rate, whereas Cl⁻ ions had an effect similar to that of the hydrochloric acid.     

Problems of Nonlinear Geomechanics. Part II

The most important results are presented in complex for experimental and theoretical researches on nonlinear wave processes. It is shown that problems, concerning these processes, are governed for the most part by the phenomenon of the alternating-sign reaction of rocks to dynamic effects and the base characteristics of block-hierarchically modeled geomedia. Elements of the theory of deformation/ waves, which have made it possible to bring together a number of empirical relationships not previously explained within the framework of traditional theoretical concepts, are stated.     

CaCO3存在下高铁硫化锌矿氧化焙烧的相变机理研究

针对目前湿法炼锌工艺处理高铁硫化锌矿存在浸出率偏低的缺点,本文提出添加一定量CaCO3的方式预先氧化焙烧矿样,使ZnS矿相转变为易于浸出的ZnO。结果表明：当高铁硫化锌矿中未添加CaCO3时,矿石中的ZnS在700℃和1h的焙烧条件下不能被完全氧化为ZnO,焙烧产物中有难以浸出的ZnFe2O4生成;当添加一定量的CaCO3（Ca:S =1:1）时,矿石中的ZnS在相同焙烧条件下可以完全氧化为易浸出的ZnO,在焙烧产物中未检测到ZnFe2O4,但发现有Ca2Fe2O5生成,同时添加的CaCO3在氧化焙烧过程中会转化成了CaSO4。因此,高铁硫化锌矿中加入适量的CaCO3,既能促进闪锌矿（ZnS）和黄铁矿（FeS2）在氧化焙烧过程中的物相转变,又能通过形成Ca2Fe2O5来抑制ZnFe2O4的生成,并通过形成CaSO4来固硫。同时实验结果与热力学分析相吻合。     

Pietra Serena Mining in Fiesole. Part II: Geological Situation

The results are presented for the investigations into the geological estimate of Macigno formation representing an Oligocene-Miocene turbiditic sequence of the Northern Apennines, from the coarse-graded beds of which the Pietra Serena quarry stone was mined. It is shown that the sedimentological features, the physico-mechanical properties, and the mineralogical composition of rocks govern the distinctions in the operating performances.     

Coal reverse flotation. Part II: Cleaning of a subbituminous coal

Reverse flotation of a subbituminous coal was investigated and it turned out that a large amount of DTAC was needed in this process. The application of the zero-conditioning time method along with the use of PAM significantly reduced DTAC consumption from over 6 kg/t down to 1.375 kg/t.Dextrin was necessary to improve the selectivity. The addition of a dispersant (tannic acid) improved further the quality of concentrate. The concentrate ash content of 16.7% at 50.4% yield was obtained for the feed ash content of 34.6%. Although this gives only about 64% combustible recovery, since the inherent ash content for this coal was determined to be 10% the room for further improvement is very limited.The best separation was obtained around a natural pH of 7.5–8.4 for this coal.     

Gold Mining by Geotechnological Methods. Part II: Practical Experience of Heap and Underground Gold Leaching

A review is given for the world practical experience of gold mining by heap and underground leaching methods with a brief characteristic of technological process at the concrete plants. The possibilities of geotechnology under conditions of negative temperatures are considered.     

Rock drillability classification. Part II: Canonical representation of rock properties in the rock classification by fracture resistance

A multifactor classification of rocks by drillability is proposed based on canonical representation of the mechanical and structural properties of rocks by the dimensionless characteristics of rock fracture resistance. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 6. pp. 86–104, November–December, 2008.     

Movement of Rock Blocks during Large-Scale Underground Explosions. Part II: Estimates by Analytical Models, Numerical Calculations, and Comparative Analysis of Theoretical and Experimental Data

The calculation results are cited for the parameters of block movement under the large-scale dynamic action. The estimates by analytical models and the results of numerical calculations are compared with the experimental data. This made it possible to interpret the data and determine the most probable mechanism of originating the movements along the interblock boundaries.     

Pendulum-type waves. Part II: Experimental methods and main results of physical modeling

Conclusions 1. Investigations of physical modeling of pulsed actions on models of block media (with different material composition and characteristic dimensions of the subblocks) by energy-calibrated impacts confirmed the hypothesis expressed earlier by the authors about the possibility of existence of pendulum-type waves, the elementary carriers of which are geoblocks of a different scale level (-waves).2. An analysis of the regularities of formation of the spectra of the wave packets and graphs of the absolute displacements of the blocks, determined by the optical method, permitted concluding a resonance mechanism of occurrence of -waves, underlying which is the canonical relationship of the spectral modes for wave packets with respect to factor (2)ⁱ, i=0, ±1, ±2, ±3, ... .3. The effect of the condition of canonical relationship of the spectrum in wave packets of -waves under certain conditions of energy actions can leads to the occurrence of the effect of anomalously low friction between interacting blocks (carriers of -waves) in directions orthogonal to the line of action of the external pulse.The work was performed with the financial support of the Russian basic research fund (grant No. 96-05-66052).Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 3–39, July–August, 1996.     

Numerical study into dynamics of self-oscillatory hydropercussion systems. Part II: Direct action systems

The paper presents mathematical model of a direct-acting self-oscillatory hydropercussion system. Output characteristics of the system are studied numerically in the space of the determined dynamic simulation criteria. Analysis of the results shown as isolines of the integral characteristics, theoretical oscillograms and phase curves has yielded a series of important behavioral features of the system in the basic simulation criteria space. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 2, pp. 78–94, March–April, 2008.     

Basis of borehole radiometric defectoscopy for rocks. Part II. Physical modeling

Conclusions We have shown that the distance between cracks can be determined from the distance between the maxima of radiometric logs. With a reduction in probe base there is an increase in the absolute maximum of the anomaly I_γmax with a simultaneous reduction in its width. The width of the maximum I_γmax of the anomaly equals the sum of the probe base and crack opening lengths. Physical and mathematical modeling demonstrates the identical qualitative dependence of recorded γ-radiation on crack parameters. However, in arranging problems of mathematical modeling it is necessary to carry out a laboratory experiment previously with the aim of eliminating unmonitored parameters. The possibility has been demonstrated of using hypotheses 1–4, which lie at the base of a theory for borehole geophysical defectoscopy, for interpreting gamma-gamma ray logging data. Institute of Mining, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk. Translated from Fiziko-tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 5, pp. 35–40, September–October, 1990.     

Towards prediction of oxidation during grinding I. Galena flotation

The degree of oxidation during grinding and its effect on galena flotation were studied using a specialised mill which permitted chemical conditions during grinding to be controlled. It was found that iron oxidation species derived from the grinding medium played a dominant role in galena flotation. The amount of hydroxide consumed to maintain the grinding pH at a constant value depended on the production of iron oxidation species. Linear relationships were obtained between the amount of hydroxide consumed to maintain a constant grinding pH and the production of iron oxidation species as well as galena recovery. These relationships should eventually permit oxidation during grinding and galena flotation to be predicted.