Leaching of chalcopyrite with hydrogen peroxide in hydrochloric acid solution

The aim of this work was to investigate the leaching of chalcopyrite concentrate in hydrochloric acid with hydrogen peroxide as a strong oxidizing agent. The effects of the leaching variables on metal extraction, such as stirring speed, solid-to-liquid ratio, temperature and HCl and H2O2 concentrations, were studied. The maximum final copper extraction of 33% was attained with 3.0 mol/L H2O2 in 0.5 mol/L HCl at room temperature after 180 min of the reaction. The results showed that the copper extraction was increased in the first 60 min of reaction, after which it essentially ceased due to the fast catalytic decomposition of hydrogen peroxide. Further, solid-to-liquid ratio affected the copper extraction significantly and the highest copper extraction was obtained in the most dilute suspension（i.e., S/L ratio of 1：100）. The dissolution process was described by the first order kinetics equation. The apparent activation energy of 19.6 k J/mol suggested that the dissolution process was under diffusion control. The reaction orders for HCl and H2O2 were established to be 0.30 and 0.53, respectively. The results of the XRD and SEM/EDS analysis of the leaching residue indicated the generation of the elemental sulphur on mineral surfaces which tended to inhibit the leaching rate.

Copper,zinc,and iron bioleaching from polymetallic sulphide concentrate

Bioleaching of low-grade complex Cu&ndash;Zn&ndash;Pb&ndash;Fe&ndash;Ag&ndash;Au sulphide concentrate (of Majdanpek ore body, RTB Bor, Serbia) was carried out in an aerated bioleach reactor in the presence of mesophilic mixed bacterial culture of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans. A mesophilic acidophiles culture was isolated from the acidic solution of the underground copper mine of Bor, Serbia. The nutrient medium was 9K at pH 1.6. 87% of the particles were <10 &micro;m in size, with a pulp density of 8% (w/v). Bioleaching efficiencies of 89% for zinc, 83% for copper, and 68% for iron can be achieved in the examined conditions. Kinetic analysis shows that the change in leaching corresponds to the Spencer-Topley kinetic model for diffusion-controlled topochemical reactions.

Identification and characterization of single crystal Bi_(2)Te_(3-x)Se_(x) alloy

The results of experimental investigation of n-type semiconductor based on Bi2Te3 alloy were presented. This material is used in manufacture of thermoelectric coolers and electrical power generation devices. BizTe2.88Se0.12 solid solution single crystal has been grown using the Czochralski method. Monitoring of structure changes of the sample was carried out by electron microscope. The elemental composition of the studied alloy was obtained by energy dispersive spectrometry （EDS） analysis and empirical formula of the compound was established. X-ray diffraction analysis confirmed that the Bi2Te2.88Se0.12 sample was a single phase with rhombohedral structure. The behavior upon heating was studied using differential thermal analysis （DTA） technique. Changes in physical and chemical properties of materials were measured as a function of increasing temperature by thermogravimetric analysis （TGA）. The lattice parameters values obtained by X-ray powder diffraction analyses of Bi2Te2.88Se0.12 are very similar to BizTe3 lattice constants, indicating that a small portion of tellurium is replaced with selenium. The obtained values for specific electrical and thermal conductivities are in correlation with available literature data. The Vickers microhardness values are in range between HV 187 and HV 39.02 and decrease with load increasing. It is shown that very complex process of infrared thermography can be applied for characterization of thermoelectric elements and modules.

Thermodynamics and characterization of shape memory Cu-Al-Zn alloys

The thermodynamic properties and the microstructure, hardness and electrical conductivity of shape memory alloys （SMAs） belonging to ternary Cu？Al？Zn system were studied by Muggianu model and experiment, respectively. The isothermal section of phase diagram at 293 K was calculated using Thermo-Calc software. Experiments were conducted by X-ray diffraction, light optic microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry, hardness and electrical conductivity measurements. The calculated values of thermodynamic properties indicate that Cu shows good miscibility with Al and Zn in all investigated alloys. The microstructural analysis of samples reveals that the structure consists of large and polygonal grains.

Prototype of highly efficient liquid electrode pulsating corona plasma reactor for degradation of organics in water

Prototype of atmospheric pressure non-thermal corona plasma reactor, developed for degradation of organics in water, operates at significantly higher frequency than other reactors for that purpose, and without sparks. Its construction provides the umbrella shaped, sustained pulsating corona discharge, with defined discharge oscillations on a given pulse frequency above the water surface. Dye degradation rate decreases with the decrease of discharge current density. Plasmaformed H2O2 is consumed in dye degradation. The energy yield of dye degradation is 2.45 g k Wh^-1 for 50 ppm solution, which is higher than in other publications for comparable experimental conditions.

Electrochemical Characteristics of Natural Mineral Covellite

Electrochemical characteristics of covellite (CuS) are of importance from flotation and metallurgical point of view, as well as due to its potential application in solid state solar cells and in photocatalytic reactions. Also, the compound CuS appears as an intermediary product or a final product in electrochemical oxidation reactions of chalcocite (Cu2S) which exhibits supercapacitor characteristics. Natural copper mineral covellite has been investigated in inorganic sulfate acid electrolytes, as well as in strong alkaline electrolyte. Physical properties of covellite were characterized by X-ray diffraction (XRD) and the active surface was examined by optical and electron microscopy (EM) before and after oxidation in galvanostatic regime. Different electrochemical methods (galvanostatic, potentiostatic, cyclic voltammetry and electrochemical impedance spectroscopy - EIS) have been used. The capacitance of around 21 Fcm-2 (geometric area), serial resistance of about 90 Ωcm2 and leakage resistance of about 1200 Ωcm2 have been measured in 1 M H2SO4. The addition of cupric ions in sulfate electrolyte leads to the significant increasing of the capacitance, but having the increase of self-discharge as a negative side phenomenon. The capacitance of around 6.7 Fcm-2 (geometric area), serial resistance of about 80 Ωcm2 and leakage resistance of about 380 Ωcm2 have been measured in 6 M KOH.

Theoretical and experimental assessment of a novel method to establish the complete measurement range of the calorimeter and its limit of detection and quantification

For determining the accuracy of a calorimeter over the instrument’s entire measuring range,a novel method has been established.For this new approach,(a)benzoic acid(C_(6)H_(5)CO_(2)H) as a certified reference material(CRM),(b)SiO_(2) and(c)a mixture of CRM benzoic acid and SiO_(2) have been used.To illustrate the essential difference between 1)the novel analytical method for control of the entire measurement range and 2)the calorimeter calibration,both applications of benzoic acid(BA)have been demonstrated.An experimental result showed that BA was successfully used to check the whole calorimeter measurement range.The results also showed that the same new method was successfully applied to determine the limit of detection and quantification.A new instrument testing process and a new measurement technique have thus been established.In this way,the cost of using CRM to control the accuracy of measuring the entire measuring range of the calorimeter,as shown in this paper,is minimized.The requirements of the ISO/IEC 17025:2017 standard are satisfied.ISO/IEC 17025:2017,together with ISO 9001:2015(quality management systems),ISO 14001:2015(relate to environmental protection)and ISO45001:2018(occupational safety),constitute an integrated quality system by which a testing laboratory may also accredit.

Properties improvement and microstructure changes during thermomechanical treatment in sintered Cu-Au alloy

The changes in hardness, microhardness, electrical conductivity and microstructure of the sintered Cu-4%Au （mole fraction） alloy during thermomechanical treatment were studied. Following the primary strain hardening, an annealing of rolled alloy in the temperature range of 60-350 ℃ provided additional strengthening due to the anneal hardening effect. An increase in properties took place in two stages, and the best combination of properties was achieved in the alloy pre-rolled with 40% reduction after annealing at 260 ℃. Significant microstructural changes followed the changes of properties in the course of the thermomechanical treatment.

Applying the Different Statistical Tests in Analysis of Electrical Breakdown Mechanisms in Nitrogen Filled Gas Diode

This paper presents the results of our investigations of breakdown mechanisms, as well as a description of their influence on the distributions of time delay distributions, for a gas tube filled with nitrogen at 4 mbar. The values of the time delay are measured for different voitages, and the values of the relaxation times and their distributions and probability plots are analyzed. The obtained density distributions have Gaussian distributions and exponential distributions for different values of relaxation times （Gaussian for small values and exponential for large values of relaxation time）. It is shown that for middle values of relaxation time the delay distributions have a shape between Caussian and exponential distributions, which is a result of the different influences of electrical breakdown.

Mechanism of Chalcopyrite Leaching in Oxidative Sulphuric Acid Solution

The mechanism of the leaching process of chalcopyrite concentrate with sodium nitrate in sulphuric acid solution were studied and discussed. Chemical reactions of leaching and their thermodynamic probabilities are predicted based on the calculated Gibbs energies and analysis of E-pH diagrams. Experimental data, thermodynamic analysis, chemical, XRD, and SEM/EDX analyses of concentrate and the leach residues, were performed to develop a better understanding of the chemical reactions that took place in the system. Elemental sulphur was formed as the main leaching product, precipitated at the particle surfaces and tended to inhibit the leaching rate.

Extended Approach to Water Flow Algorithm for Text Line Segmentation

This paper proposes a new approach to the water flow algorithm for text line segmentation. In the basic method the hypothetical water flows under few specified angles which have been defined by water flow angle as parameter. It is applied to the document image frame from left to right and vice versa. As a result, the unwetted and wetted areas are established. These areas separate text from non-text elements in each text line, respectively. Hence, they represent the control areas that are of major importance for text line segmentation. Primarily, an extended approach means extraction of the connected-components by bounding boxes over text. By this way, each connected component is mutually separated. Hence, the water flow angle, which defines the unwetted areas, is determined adaptively. By choosing appropriate water flow angle, the unwetted areas are lengthening which leads to the better text line segmentation. Results of this approach are encouraging due to the text line segmentation improvement which is the most challenging step in document image processing.