Vermiculite samples were impregnated with different amounts of calcium oxide by the conventional thermal heating technique and subject to CO2 capture experiments in thermal analysis equipment. The amount of CO2 captured by calcium oxide increased from 13 g of CO2 per mol of CaO to 16.8 g of CO2 per mol of CaO when the experiments were carried out with pure calcium oxide and vermiculite impregnated with CaO (1:1), respectively. Integral isoconversional methods of Kissinger-Akahira-Sunose (KAS) and Osawa-Flynn-Wall (OFW) were used for the kinetic study of the process and good correlation coefficients were achieved. The apparent activation energy values showed that for low conversions (α < 0.3) the controlling step of the process is a mixed step where the chemical reaction and the diffusion of the reagents into the vermiculite have rates of the same order of magnitude (20 kJ < Ea < 40 kJ). For higher conversions values (α > 0.3) the apparent activation energy values suggest that the slow step is a chemical step (Ea> 40 kJ).
High precision and accuracy make Pb-Fire assay the method of choice for gold analysis in mineralogical samples. The second stage of this method, called cupellation, leaves the used container (cupel) highly contaminated with PbO. Since tons of cupel waste are generated annually from gold analysis worldwide, the disposal of such material constitutes a serious risk to the environment. In the present paper the recovery of the lead from cupel waste by means of an alkaline fusion in the presence of sulfur was evaluated considering the effects of the following variables: amount of NaOH and sulfur, time, and temperature. Gravimetric analyses indicated 81.3% (w/w) recovery of lead in the form of metallic lead from 5.00 g of cupel waste using 3.00 g of NaOH, 0.5 g of S8, after 15 min at 650 °C. During the process, sulfur promoted the reduction of lead oxide. After the process, both the cupel wastes and the resulting secondary wastes presented lead concentrations below the maximum limits determined by both Brazilian legislation and that followed by US Environmental Protection Agency, and can be considered safe for disposal. Furthermore, the proposed method allows cupel wastes to be converted from an environmental liability to a raw material for the production of metallic Pb.
Hydrogen reduction and thermal treatment experiments were carried out in the laboratory using a transition zone lateritic nickel ore. The products of the pyrometallurgical operations were subjected to magnetic separation. The ore and samples produced after the thermal processing (reduction and thermal treatment) were characterized by X-ray diffractometry (XRD), thermogravimetric analysis (TG), scanning electronic microscopy (SEM), and energy dispersive spectrometry (EDS). The qualitative identification of the main mineral transformations was performed and the influence of these thermal transformations in the magnetic properties of the sample was studied. When the reduction experiments were performed at 800 ° C, with a magnetic flux of 97.5 ± 10.6 mT, the nickel content increased by up to 33 % (recovery of ≈ 75 %) in the magnetic fraction. During the formation of magnetite in the reduction experiments, carried out at 400°C, the sample became very magnetic and, consequently, the unit operation of magnetic separation was not selective. It was possible to remove magnesium from all samples, regardless of the thermal treatment or reduction temperature used. The contents of this element were adjusted to the characteristic values of a limonitic ore.
Two of the main challenges presented by the implementation of nickel laterites atmospheric acid leaching are: (i) high acid consumption and (ii) high final iron concentrations in the PLS. In the current work, a novel process was devised by applying pyrometallurgical and bio-hydrometallurgical operations. The experimental set-up comprised the reduction of a nickel limonitic ore with hydrogen gas in a rotary kiln, at 900 °C, until all the goethite was converted to metallic iron. Subsequently, the reduced sample was bioleached by mesophilic microorganisms grown on Fe2+ (Acidithiobacillus ferrooxidans) at 5% solids, 32 °C, and pH < 3. The results showed that an increase in the Eh values, promoted by the bacteria, resulted in the leaching Fe, Ni and Co, therefore a dissolution of 92% of the nickel and 35% of the cobalt was observed in experiments carried out with 35 Kg H2SO4/(ton of the reduced ore). The iron concentration in the liquor generated under these experimental conditions was below 5 mg/L owing to the fact that Fe3+ precipitated as jarosite. The experimental conditions applied also resulted in low acid consumption and the final total iron concentration was also reduced in the leach liquor (< 200 mg/L), which were considerably lower than the values reported for the HPAL process.
Braking performance is dependent on friction materials of tribological components, generally metal and pad. The pad consists of a composite of thermosetting resin and reinforcement material that exhibits mechanical and wear resistant, heat conduction, lubricant, and others. Slate is a natural rock composed of extremely fine materials that brings interesting tribological properties, in addition, its industrial current activity generates a significant amount of mineral waste, which is a problem for the environment. The objective of this work was to propose a technological alternative as a new friction element based on slate particulate as tribological reinforcement in composite based on phenolic resin as a matrix, besides that, minimize the environmental impact due to the inadequate disposal of these slate tailings and add value to the mineral, classifying it as a residue to be used industrially and no longer as waste. In this sense, the effect of the amount of slate on the friction properties of the brake pads made was investigated. As the brake pad material, four different slate containing formulations were proposed, manufactured and analyzed, and as the brake wheel gray iron was chosen. The friction and wear characteristics were determined by Pin-on-Disk type tribological tests, the pair was composed by disk (pad formulations) and pin of gray iron, representing the brake wheel. The coefficients of friction of the composites were shown to be regular and stable, with an average of 0.44 between the samples. Among the results obtained, the formulation containing 40 % of slate and 35 % of phenolic resin, presented the most satisfactory parameters compared to commercial friction materials in current use.
A sample of limonitic nickel ore was characterized by XRD, SEM-EDS, and ICP-OES techniques. The Rietveld refinement method showed that the main mineral constituent of this sample is goethite (55.8 pct). Thermal analysis experiments were performed and the determination of the goethite content in the sample could be confirmed by the mass loss associated to the dehydroxylation of this mineral at temperature of ≈ 150 °C. After thermal decomposition, the sample was reduced in a rotary kiln using hydrogen and subsequent characterization showed that for low temperatures (400 °C ≤ T < 550 °C) the main chemical reaction is the reduction of hematite to magnetite. At high temperatures (500 °C ≤ T < 800 °C), metallic iron could be identified in the solid product of the reaction by XRD technique and reduction of hematite to metallic iron was the main chemical reaction identified at this temperature. In addition to metallic iron, tetrataenite was identified and quantified in the reduced sample at high temperature (T > 600 °C) and the results suggest that most of the nickel is in this mineral phase. The shrinking core model was used for the kinetic studies of the reduction process and for the reduction of hematite to magnetite at low temperature (T ≤ 550 °C). The slow step was diffusion of reagent (H2) or product (H2O) through the reduced solid product layer on the particle surface, the apparent activation energy calculated for the reaction was 46.2 kJ. For the reduction of hematite to metallic iron at high temperature (T ≥ 550 °C), the slow step was the reaction of hydrogen with hematite at the reaction surface of the particle, and the apparent activation energy achieved by the chemical reaction was 29.5 kJ.
The reduction by hydrogen and the thermal decomposition of a siliceous nickel laterite ore in the presence of NaCl were studied using thermogravimetric analysis (TGA). Reduction tests on H2 atmosphere in rotary kiln were performed in the presence of NaCl and the product of the reaction was leached in ammoniacal solution. The presence of only 1 pct of NaCl in the furnace increased the nickel extraction values from ≈ 3 to ≈ 90 pct when the experiment was carried out at 850 °C. According to the results of X-ray diffractometry and TGA, the presence of NaCl in the system and the reducing atmosphere of H2 promote the segregation of nickel according to the following steps: (1) Nickel oxide reduction by hydrogen: NiO + H2(g) → Ni + H2O(g). (2) Formation of HCl: Al2SiO5 + 2NaCl + SiO2 + H2O → 2HCl(g) + 2NaAlSiO4. (3) Chlorination of metallic nickel by HCl: Ni + 2HCl(g) → NiCl2 + H2(g). (4) Reduction of nickel chloride by hydrogen: NiCl2 + H2(g) → Ni + 2HCl(g).
A oxidação do concentrado de esfalerita (ZnS) por oxigênio gasoso foi realizada por meio de análise termogravimétrica (TGA). Os produtos de oxidação foram analisados por difratometria de raios X e microscopia eletrônica de varredura (MEV/EDS) e a formação de sulfato de zinco foi detectada durante o processo de oxidação. A pirita presente no concentrado foi aquecida a uma temperatura mais baixa do que a esfalerita e o mecanismo de oxidação estava de acordo com o mecanismo proposto por Dunn J. G. et. al. (1989). A cinética da oxidação da esfalerita foi avaliada por meio do método de isoconversão de Linhas de Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS) e não-linear (MNL) e os resultados sugerem que o processo de oxidação segue um mecanismo complexo. Os valores de energia de ativação encontrados foram superiores a 40kJ/mol na gama completa de conversão sugerindo que a etapa de controle ocorre por meio de reação química.
The cementation of copper and cadmium by zinc powder was investigated in order to assess the influence of different parameters in the process. The results showed that the process follows a first order reaction with two stages in both systems. In the system Cu/Zn, the second stage is faster than the first while in the system Cd/Zn the second stage is slower than the first. In the system Cu/Zn, the variation on the surface area of copper cement followed a power law and a straight line was obtained by plotting –ln([Cu2+]/[Cu2+] 0 ) against t3/2, the activation energy was calculated as 16.3kJ. In the system Zn/Cd the surface area available for reaction decreased as a result of the cement agglomeration. On the experiments carried out with ions Cu2+ and Cd2+ in solution, purer copper cement was obtained when the experiments were carried out in the presence of less than stoichiometric amount of zinc powder and longer reaction times.
The kinetics of the thermal decomposition of a synthetic ettringite sample was studied between 298 and 820 K in an inert atmosphere for the present work. The ettringite and its thermal decomposition products were characterized using X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Four endothermic events were observed with thermogravimetry curves, the maxima of which occurred at 366, 397, 537, and 641 K. All events were associated with the loss of water molecules with different degrees of interaction within the ettringite structure. Chemical equations for each decomposition step were proposed based on the percentages of mass loss observed. In addition, for the first time, the activation energies of each ettringite decomposition events were determined by the isoconversional methods of Ozawa–Flynn–Wall, Friedman, and Kissinger–Akahira–Sunose. The modeling revealed that the activation energy varied from ~50 kJ mol−1, characteristic of mass transfer control steps, to ~150 kJ mol−1, which is typical of chemical control, as the temperature increased and the ettringite structure lost water. A total of 32 mol of water was released equivalent to 43.1 % of the initial sample mass.
This work describes the synthesis of hydrogels of cellulose acetate (AC) crosslinked with 1,2,4,5-benzenotetracarboxylic dianhydride (PMDA). The crosslinking reaction was monitored by FTIR. Analysis of aromatic fragments from the alkaline hydrolysis of the gels by UV spectroscopy indicated that an increase in the stoichiometric ratio of dianhydride resulted in higher degrees of crosslinking. The non-porous nature of the gels was confirmed by analysis of nitrogen adsorption. Water absorption isotherms showed that as the temperature and degree of crosslinking increased, the percentage of water absorbed at equilibrium (%Seq) also increased. The hydrogels presented second order swelling kinetics.
The effect of temperature on nickel sulfide bioleaching was studied in the presence of mesophile (Acidithiobacillus ferrooxidans) and moderate thermophile (Sulfobacillus thermosulfidooxidans) strains and the results were discussed in terms of sulfide dissolution thermodynamics (Eh–pH diagrams) and kinetics (cyclic voltammetry). It was observed that in the pH range 1.8–2.0 the highest nickel dissolution was achieved which reached 50% for mesophiles and over 80% for moderate thermophiles. External ferrous iron addition had no effect on the metal dissolution at 34 °C, but adversely affected nickel leaching at higher temperatures. The best outcomes were accomplished with low FeSO4 additions (2.5 g/L) at 50 °C. Pyrrhotite dissolution avoided the need for external iron addition, providing Fe2+ concentrations as high as 7 g/L during bioleaching, which supports bacterial growth. Eh–pH diagrams for pentlandite and pyrrhotite show a negligible effect of temperature on the stability field of each sulfide whilst cyclic voltammetry indicated that temperature has the strongest influence on pyrrhotite oxidation. The latter along with a rapid increase in solution potential (Eh) explains the higher and faster extraction observed with S. thermosulfidooxidans.
The biological oxidation of ferrous iron is an important sub-process in the bioleaching of metal sulfides and other bioprocesses such as the removal of H2S from gases, the desulfurization of coal and the treatment of acid mine drainage (AMD). As a consequence, many Fe(II) oxidation kinetics studies have mostly been carried out with mesophilic microorganisms, but only a few with moderately thermophilic microorganisms. In this work, the ferrous iron oxidation kinetics in the presence of Sulfobacillus thermosulfidooxidans (DSMZ 9293) was studied. The experiments were carried out in batch mode (2L STR) and the effect of the initial ferrous iron concentration (2–20 g L−1) on both the substrate consumption and bacterial growth rate was assessed. The Monod equation was applied to describe the growth kinetics of this microorganism and values of μmax and Ks of 0.242 h−1 and 0.396 g L−1, respectively, were achieved. Due to the higher temperature oxidation, potential benefits on leaching kinetics are forecasted.
The alkaline leaching kinetics of a zinc silicate ore assaying 34.1% Zn, 11.1% Fe and 22.9% SiO2 is studied in sodium hydroxide solutions. Speciation diagrams indicate zinc dissolution as [Zn(OH)4]2− and SEM analysis showed a progressive reduction in particle size during leaching which supports the shrinking particle model. The process is chemically controlled with an activation energy of 67.8 ± 9.0 kJ/mol and reaction order with respect to NaOH determined as 1.44 ± 0.46.
This work describes the synthesis of hydrogels of cellulose acetate (AC), with a nominal degree of substitution DS = 2.5, cross-linked with 3,3’,4,4’ benzophenonetetracarboxylic dianhydride (BTDA). The raw materials were characterized by thermal analysis (TG/DTG) and by Fourier transform infrared spectroscopy (FTIR). DS of cellulose acetate was determined by titration with a known amount of standard NaOH solution. Hydrogels of BTDA were synthesized with 0.5, 0.75 and 1.0 mol of BTDA/mol of AC. FTIR proved to be a suitable method to monitor the course of reactions and the progress of purification. UV-vis spectroscopy and analysis confirmed the esterification of the free hydroxyl groups. Surface modification of AC structure after the cross-linking reaction was analyzed by Scanning Electron Microscope (SEM) and density and porosity of the hydrogels were determined by BET. The influence of the concentration of dianhydride on the time necessary for formation of the gel was investigated. The influence from the increase in the degree of cross-linking on the thermal behavior of the material was also documented. Water absorption isotherms were obtained for hydrogels with different reticulating agents and reticulation degrees at different temperatures. The Arrhenius equation was used to determine the diffusion coefficient of the different hydrogels at distinct temperatures and the threshold energy for the swelling process. The enthalpy of mixture was determined through the measurement of the maximum quantity of water absorbed at equilibrium at different temperatures, with the Gibbs/Helmholtz equation.
Universidade Federal de Ouro Preto - UfopEscola de Minas - EMDepartment of Metallurgical and Materials EngineeringPyrometallurgy and Thermal Analysis LaboratoryOuro Preto - Minas GeraisCEP 354000-000BrazilContac email - email@example.com<embed>