Reaction mechanism and kinetics of sulfide copper concentrate oxidation at elevated temperatures

Sulfide copper concentrate from domestic ore deposit (Bor, Serbia) was subjected to oxidation in the air atmosphere due to a better understanding of reaction mechanism and oxidation of various sulfides present in the copper concentrate at elevated temperatures. Results of the initial sample characterization showed that concentrate is chalcopyrite–enargite-tennantite type, with an increased arsenic content. Characterization of the oxidation products showed the presence of sulfates, oxysulfates, and oxides. Based on predominance area diagrams for Me-S-O systems (Me = Cu, Fe, As) combined with thermal analysis results, the reaction mechanism of the oxidation process was proposed. The reactions which occur in the temperature range 25 – 1000 °C indicate that sulfides are unstable in the oxidative conditions. Sulfides from the initial sample decomposed into binary copper and iron sulfides and volatile arsenic oxides at lower temperatures. Further heating led to oxidation of sulfides into iron oxides and copper sulfates and oxysulfates. At higher temperatures sulfates and oxysulfates decomposed into oxides. Kinetic analysis of the oxidation process was done using Ozawa’s method in the non-isothermal conditions. The values for activation energies showed that the reactions are chemically controlled and the temperature is the most influential parameter on the reaction rates

Influence of the underground mining waste on the environmental tailings and wastewater characterization

In presented paper influence of the underground mining waste on the environmental was investigated. From that point tailings and wastewater characterization was performed on samples taken from lead and zinc mine Grot, Serbia. In order to obtain experiments necessary for characterization, representative samples were taken from three different parts of the tailings: outlet pipe of the flotation facility (JOF), hydro cyclone overflow (JHC) and crest of dam (JKB). Characterization of the tailing samples include: thermal (differential thermal analysis and thermo gravimetric analysis (DTA/TGA) and infrared analysis (FTIR), determination of the chemical composition and content of the heavy metals and qualitative roentgen analysis (XRPD). Also, wastewater samples have been taken from the tailings and concentrations of heavy metals in the taken samples were determined by using inductively coupled plasma mass spectrometry (ICPMS)

Development of a new system of solid ionic conductors based on multi-doped ceria for application in IT-SOFCs

Nanosized multi-doped ceria with composition Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-δ (CNSGDY) as perspective solid ionic conductor was obtained by modified glycine-nitrate procedure (MGNP) and room temperature self-propagating reaction (SPRT). The pressed pellets of both powders were sintered at 1550°C for 2 h in an air atmosphere. The obtained sintered samples were characterized by XRPD, Raman spectroscopy, FESEM, EDS and EIS methods. Despite a high temperature of sintering, XRPD and FESEM analyses of the samples confirmed appropriate dimensions of grains with fluorite structure. Overall concentration of introduced dopants (x = 0.2) in the structure of CeO2 after the sintering process was confirmed by EDS analysis. After sintering, Raman spectroscopy confirmed retention of the oxygen vacancies in the ceria lattice, which is in accordance with the improvement of ionic conductivity of solid ionic conductors. The highest value of total conductivity was obtained for the sintered MGNP sample at 700°C (4.22 × 10−2 S cm−1), with the corresponding activation energy of 0.26 eV

Heavy Metals Content in Selected Medicinal Plants Produced and Consumed in Serbia and Their Daily Intake in Herbal Infusions

The heavy metals content (HMs) was investigated in 14 different medicinal plants collected from the three regions in Central Serbia, Zlatar, Sokobanja, and Kopaonik. The concentrations of Cd, Cr, Ni, Hg and Pb were determined: Cd (<0.03–2.72 mg/kg); Cr (<0.08–12.1 mg/kg); Ni (<0.08–12.2 mg/kg); Pb (0.6–49.0 mg/kg); the Hg concentration was below the detection limit of 0.06 mg/kg in all samples. The daily intake of HMs due to ingestion of 200 mL of herbal infusion was in all cases below the recommended limit prescribed by the World Health Organization. The estimated daily intake values were below the values for the oral reference dose regulated by the U.S. Environmental Protection Agency (USA EPA). The target hazard quotient and hazard index for Cd, Cr Ni, and Pb were below 1. Nevertheless, due to the tendency of heavy metals to accumulate in the organism, attention should be paid to the daily intake of herbal infusion during long-term usage. Specifically, it is recommended to consume not more than one cup (200 mL) of infusion per day made from thyme (Mt. Zlatar) and blueberry (Mt. Kopaonik), and not more than two cups per day for other herbs

Waste Slag from Heating Plants as a Partial Replacement for Cement in Mortar and Concrete Production. Part I—Physical–Chemical and Physical–Mechanical Characterization of Slag

Numerous factors influence the complexity of environmental and waste management problems, and the most significant goal is the reuse of materials that have completed their “life cycle” and the reduction in the use of new resources. In order to reduce impact of waste slag on the environment, in the present study, waste slag, generated in heating plants after lignite combustion, was characterized in detail and tested for application as a replacement for cement in mortar or concrete production. For physical–chemical characterization of slag, different experimental and instrumental techniques were used such as chemical composition and determination of the content of heavy metals, investigation of morphological and textural properties, thermal analysis, X-ray, and infrared spectroscopy. Physical–mechanical characterization of slag was also performed and included determination of activity index, water requirement, setting time and soundness. A leaching test was also performed. Presented results show that waste slag may be used in mortar and concrete production as a partial cement replacement, but after additional combustion at 650 °C and partial replacement of slag with silica fume in the minimal amount of 12%. The maximal obtained cement replacement was 20% (17.8% slag and 2.2% of silica fume)

Mineralogical Characterization of the Grot Lead and Zinc Mine Tailings from Aspects of Their Further Use as Raw Material

The possibility of using waste tailings produced by flotation in the lead and zinc mine of Grot, Serbia as a potential source of secondary mineral raw materials was examined. The aim of the research was primarily to carry out a detailed characterization in order to determine the dominant minerals, and, for the first time, to trace the changes occurring in the unit cells of the minerals present in that deposit. There was also a need to determine the exact proportions of the present mineral phases for their further application and utilization as natural resources in environmental protection. Samples were taken from three different sections of tailings: the crest of dam (JKB), outlet pipe of the flotation facility (JOF) and hydrocyclone overflow (JHC). Granulometric separation was performed to facilitate the extraction of certain minerals from waste. The results showed that all samples mainly contained quartz, clinochlore, calcite, albite, pyrite and biotite, but their ratios in each sample varied significantly. After characterization, samples were separated into different fractions and their mineralogical compositions were determined. Depending on the fraction, the mineralogical compositions also changed. Mineralogy and geochemical analysis indicate that waste tailings can be used as a secondary mineral raw materials source applicable in various industries

Removal of Ethyl Xanthate Anions from Contaminated Aqueous Solutions Using Hazardous Waste Slag Generated by Lignite Combustion

This paper presents the results of the application of hazardous waste slag generated by lignite combustion for the adsorption of ethyl xanthate anions (EX) from aqueous solutions. The starting material (RWS) was washed (WWS) and modified (MWS) and then characterized in detail by using different chemical and physical–chemical techniques (determination of chemical composition and content of heavy metals, X-ray diffraction (XRD), infrared spectroscopy (FTIR), determination of textural properties and point of zero charge). Besides the chemical stability of EX, the influence of the initial pH, mass of the adsorbent, initial concentration, and time on the EX anion removal was tested. The characterization results showed that applied waste slag is a hazardous material with complex mineral and structural properties but with good buffer properties and pH stability, which is also characteristic of the MWS sample. The adsorption experiments showed that modification with Cu(NO3)2 and Fe(NO3)3 significantly increases the adsorption capacity of the starting slag. Under applied experimental conditions, the maximal adsorbed amount of EX anions on the MWS was 210 mg/g, while equilibrium was obtained after 700 min. The Freundlich model and pseudo-second-order model best fit the results, suggesting the complex mechanism of EX removal by the MWS sample

Sustainable Application of Waste Sludges from the Wastewater Treatment Plant Generated during the Production of Heating Devices in the Construction Industry

This research presented, for the first time, the results of the successful application of the waste press sludges, WSLP (plant for lacquer and paint) and WSEP (powdery enamel plant), from a wastewater treatment plant generated during heating device production in the construction industry. The results of WSEP characterization and its influence on cement paste, mortar, and concrete properties showed that this material could be used as a cement replacement (with a maximum replacement amount of 20%) in producing mortar and concrete. Although waste WSLP sludge does not possess pozzolanic properties and does not meet the criteria prescribed by the standards for application in mortar and concrete due to its chemical inertness and fineness, as well as its extended setting time, it can be used as a replacement for stone filler or other powdered mineral admixture in the production of self-compacting concrete (SCC) in amounts up to 100%, with a maximum quantity of up to 100 kg/m3. The obtained results indicate that with the appropriate conversion, waste sludges, despite representing hazardous waste, can be used as safe products in the construction industry; i.e., the waste material can become a useful and valuable raw material by applying (respecting) all of the principles of the green economy

Application of Lignite Combustion Waste Slag Generated in Heating Plants as a Partial Replacement for Cement. Part II: Physical–Mechanical and Physical–Chemical Characterization of Mortar and Concrete

The presented study is a continuation of the research with the aim of finding a useful value of hazardous waste slag generated by the combustion of lignite in heating plants and its application in the construction industry. The different amounts of cement (10%, 15%, 20% and 25%) were replaced with waste slag and silica fumes in mortars and concrete production. Detailed physical–mechanical characterization was performed on the mortar and concrete samples according to standard procedures. Test results indicated that the replacement of cement with slag and silica fumes reduces the physical and mechanical properties of mortar and concrete, but cement composites retained the required structural properties. If 15–20% is considered an acceptable level of compressive strength decrease, then it can be concluded that waste slag can be implemented in practice and be used as a construction material, with cement replacement in the maximal amount of 20% (17.8% of slag and 2.2% of silica fumes). On hardened mortar samples with maximal possible cement replacement (20%), physical–chemical characterizations were performed and included X-ray and infrared spectrophotometry, scanning electron microscopy, and thermal analysis. Results showed the absence of new phases and the presence of only those which were characteristic for starting samples, predominantly portlandite, quartz, calcite and calcium silicate-oxid

Novel Glass-Ceramic Sealant With Addition of Alumosilicate-Based Waste Material for Application in IT-SOFC

In the present paper, possible application of novel concept synthesis method of glass-ceramic sealant with implementation of alumosilicate-based waste material in intermediate temperature solid oxide fuel cells (IT-SOFC) was investigated. Besides basic components for glass-ceramic sealant (sample GC0), for this purpose four additional sealant compositions with certain waste content, designated as GC1, GC2, GC3, GC4, were prepared for a comparative study. Waste was added in the basic sealant composition in such a way that certain percent of alumosilicate clay was substituted with alumosilicate-based waste material, with proper amount of water as a solvent. Waste share in compositions was 5, 10, 15 and 20% of total amout of alumosilicate clay as a replacement, respectively.A total of five different joint specimens were assembled by placing a sealant paste of 10mm thickness between two bricks to form brick/glass–ceramic/brick sandwich specimens appropriate for further heat treatments. Such formed ‘green’ joints were initially air-dried for 24h at room temperature, which was required for solvent to evaporate and cause initial bonding. Heating cycle in the period of four weeks was carried out in a chamber furnace. First day samples were heated to 200 ̊C for 2 h. Each day heating temperature was raised for 100 °C while dwelling time was prolonged for one hour, so by the end of the first week samples were heated to 600 °C for 6 hours. Next three weeks annealing of the samples was performed at 600 °C for 6 hours, 700 °C for 7 hours and 800 °C for 8 h, respectively, after what the thermal cycle was completed. The heating rate of the furnace at each heating step in the given joining process was 5 °C/min,while cooling was at natural speed. Mentioned firing temperatures were selected in accordance to common operating temperature range of IT-SOFC so as to simulate real working conditions. After the completion of the cycle, it was observed that all variants of the sealant withstood high temperatures without significant cracks or damage. Moreover, after detailed chemical, physical, mechanical and optical properties examination it was determined that compositions remained unaltered, which clearly indicates to their stability and reliability that is required for their application as sealants for IT-SOFC components. In addition, this research shows the possibility of forming a cost-effective, environmentally-friendly and high- efficient sealant for application in IT-SOFC by incorporating waste materials in its composition, without significant negative effects on its performance and main properties.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad