Kinetics and mechanism of sphalerite leaching by sodium nitrate in sulphuric acid solution

Interest for application of hydrometallurgical processes in a processing of complex sulphide ores and concentrates has increased in recent years. Their application provides better metal recoveries and reduced emission of gaseous and toxic ageneses in the environment. The kinetics and mechanism of sphalerite leaching from complex sulphide concentrate with sulphuric acid and sodium nitrate solution at standard conditions was presented in this paper. The influences of temperature and time on the leaching degree of zinc were investigated and kinetic analysis of the process was accomplished. With temperature increasing from 60 to 90°C, the zinc leaching increased from 25.23% to 71.66% after 2 hours, i.e. from 59.40% to 99.83% after 4 hours. The selected kinetic model indicated that the diffusion through the product layer was the rate-controlling step during the sphalerite leaching. The activation energy was determined to be 55 kJ/mol in the temperature range 60-90°C. XRD, light microscopy and SEM/EDX analyses of the complex concentrate and leach residue confirmed formation of elemental sulphur and diffusion-controlled leaching mechanism

Kinetics and mechanism of synthetic CoS oxidation process

The results of investigation of kinetics and mechanism for synthetic a-CoS oxidation process are presented in this paper. Based on experimental data obtained using DTA and XRD analysis and constructed PSD diagrams for Co-S-O system, mechanism of synthetic a-CoS oxidation process is suggested. Characteristic kinetic parameters were obtained for experimental isothermal investigations of desulfurization degree using Sharp method

EXAMPLES OF LCA METHODOLOGY IMPLEMENTATION IN STEEL INDUSTRY

Steel industry kept pace with actual trends for environmental protection in many ways – through different technological improvements considering environment protection, important share of recycling in the steel production, design of so called “eco-steels”, materials designed according to recent environmental directives and legislatives, etc. In the frame of steel production monitoring, LCA methodology is very important for obtaining an accurate environmental picture of a process, due to the fact that the process should be evaluated over its entire life cycle. A number of tools and methodologies have been developed in recent years to assess the potential environmental impacts associated with a product, process or activity during its entire life cycle. The examples of Life Cycle Assessment (LCA) are used by large steel industrial companies as potentially helpful tool for improving the production processes, efficiency of resource utilization and significantly reduction of waste generation and emissions are presented in this paper

Thermal analysis and kinetics of the chalcopyrite-pyrite concentrate oxidation process

The paper presents the results of experimental investigation of the chalcopyrite-pyrite concentrate oxidation in the air. Characterisation of the initial sample and oxidation products was done by ICP-AES, XRD, EDXRF methods. Phase stability diagrams were constructed for Cu-Fe-S-O system at 25, 450, 650 and 900 °C. Equilibrium composition of the charge for the optimal oxidation process was calculated. DTA-TG analysis was used for monitoring the oxidation process. Kinetic parameters in non-isothermal conditions were determined, based on Kissinger and Ozawa methods.Values of activation energies showed that all stages of the oxidation process occur in the kinetic field

A water quality assessment based on benthic diatoms of the timok river basin (Eastern Serbia) under multiple anthropogenic pressures

The study is focused on diatom communities as indicators of the water quality of aquatic ecosystems. The study included watercourses of the Timok River Basin in eastern Serbia. Sampling of algological material and physicochemical measurements were conducted at 30 locations in September 2016. Non-metric multidimensional scaling (NMDS) showed that conductivity had an effect on the spatial variability of the diatom communities. At locations under influence of acid mine drainage along the Borska river, its tributaries and the Timok river, the diversity of benthic diatoms decreased and the abundance of metal tolerant taxa Achnanthidium minutissimum, Nitzschia capitellata and Nitzschia palea increased. Our study revealed that the combined effect of different pollutants significantly impacted on diatom assemblages; diatoms are good bioindicators of multiple pressures; and diatom indices with different types of pollution, may show an unreliable picture of the actual state, therefore, biological and physico-chemical parameters should also be observed when interpreting the results of a solely diatom-based assessment of the ecological condition of freshwaters

Oxygen reduction reaction features in neutral media on glassy carbon electrode functionalized by chemically prepared gold nanoparticles

Gold nanoparticles (AuNPs) were prepared by chemical route using 4 different protocols by varying reducer, stabilizing agent and solvent mixture. The obtained AuNPs were characterized by transmission electronic microscopy (TEM), UV-Visible and zeta potential measurements. From these latter surface charge densities were calculated to evidence the effect of the solvent mixture on AuNPs stability. The AuNPs were then deposited onto glassy carbon (GC) electrodes by drop-casting and the resulting deposits were characterized by cyclic voltammetry (CV) in H2SO4 and field emission gun scanning electron microscopy (FEG-SEM). The electrochemical kinetic parameters of the 4 different modified electrodes towards oxygen reduction reaction (ORR) in neutral NaCl-NaHCO3 media (0.15 M / 0.028 M, pH 7.4) were evaluated by rotating disk electrode voltammetry and subsequent Koutecky-Levich treatment. Contrary to what we previously obtained with electrodeposited AuNPs [Gotti et al., Electrochim. Acta 2014], the highest cathodic transfer coefficients were not obtained on the smallest particles, highlighting the influence of the stabilizing ligand together with the deposits morphology on the ORR kinetics

A THERMODYNAMIC ASPECTS OF METALLIC SECONDARY RAW MATERIALS RECYCLING POSSIBILITY

Industrial products are made from different materials, therefore existing metallurgical plants are not always able to adequately process them. Knowing the thermodynamic parameters, possibility and degree of removal of contamininats from the base metal in the recycling process can be predicted. Such approach facilitates a decisions about products design, selection of recycling technology, reduces contamination and increases the system resources. In addition, recycling process becomes more profitable, reducing energy costs and increasing environmental protection. In this way, the use of resources becomes more sustainabl

A THERMODYNAMIC ASPECTS OF METALLIC SECONDARY RAW MATERIALS RECYCLING POSSIBILITY

Industrial products are made from different materials, therefore existing metallurgical plants are not always able to adequately process them. Knowing the thermodynamic parameters, possibility and degree of removal of contamininats from the base metal in the recycling process can be predicted. Such approach facilitates a decisions about products design, selection of recycling technology, reduces contamination and increases the system resources. In addition, recycling process becomes more profitable, reducing energy costs and increasing environmental protection. In this way, the use of resources becomes more sustainable

Scanning tunneling spectroscopy of nanostructured Zn surfaces

Scanning tunneling spectroscopy investigations involving the I-V characteristics and the conductance of nanostructured mirror bright Zn coatings have been performed. Those characteristics have shown the decreasing values with the increase of the nanograins size.Conference on Applied Physics in Serbia, May 27-29, 2002, Belgrade, Yugoslavi