Metalurgia Extractiva

Los polvos de acería, residuos obtenidos de las corrientes gaseosas de los hornos de fusión y afino del acero, están constituidos principalmente por óxidos de zinc, óxidos de hierro y cantidades menores de metales pesados como el plomo y cadmio. Estos materiales catalogados como residuos tóxicos y peligrosos, podrían ser valorizados mediante la extracción de zinc.
Se caracterizaron polvos de acería mediante espectrofotometría de absorción atómica (AA), difracción de rayos X (DRX) y fluorescencia de rayos X (FRX), obteniéndose contenidos de Zn 33%; Fe 18%; Cd 0,03%; en forma de zincita (ZnO) 39% y magnetita (Fe3O4) 33%. Se realizaron ensayos de lixiviación con ácidos: sulfúrico, clorhídrico, nítrico, acético, tartárico, además con: cianuro de sodio, sosa caústica, carbonato de sodio y amoníaco. Operando con H2SO4 150 [g/L] al 30%, de sólidos se logra recuperar Zn 63%; Fe 15% y Cd 1% a las 8 horas de proceso y con las soluciones sulfúricas, mediante electrólisis y fusión se obtiene zinc en forma metálica.

A particular environmental problem is the growing generation and the difficulties in the disposal of waste tires. The European Union, USA, and Japan produce around 6 million tons of scrap tires per year; while in the entire world generate 1 billion of waste tires. Commonly, landfill zones are the primary destiny of tires, where they represents hazards such diseases and accidental fires. Tires are bulky, recalcitrant to natural degradation and difficult to compact. Actual treatments such as energy recovery in cement kilns and recycling process do not offer an integral way to benefit the end life tires (ELT). However, pyrolysis has shown to be an alternative treatment, and an attractive way to recover valuable products such as combustible gases, fuel and carbon. The last one is of interest in this research because it is the precursor in the production of activated carbon.

The main purpose of the present work was to prepare activated carbon from waste tires, which is suitable as an adsorbent of relatively large molecules. Small pieces of rubber (2-3 cm) from the sidewall of tires were used into the experimentation. The pyrolysis tests were developed into laboratory and pilot scales under temperatures between 450-550 °C. The physical activation of the char was carried under CO2 atmosphere and temperatures between 850-900 °C. The methods of iodine index, blue-methylene adsorption, and sugar index were used to determinate the specific area, and the adsorption capacity of activated carbon.

Pyrolysis results demonstrated that residence times superior to 45 min were necessary to get a char with a high content of fixed carbon with an overall weight loss constant of 67%. Activated carbon with specific area over 800 m2/g has been produced under certain conditions. The activation with CO2 shown a linear relation between time residence and specific surface for burnoff less to 70%.

Resumen: Este trabajo compara 2 agentes lixiviantes, H2SO4 y HCl con sus respectivos procesos de purificación y electrodeposición para recuperar Zn metálico a partir de residuos de polvos de acería. Estos polvos se generan en la producción de acero en hornos de arco eléctrico y tienen una alta concentración de Zn (20-50%). Mediante lixiviación con 150 g/L de H2SO4 se recupero 75,6 % de Zn en 8 h mientras que con 150 g/L de HCl se recuperó 70,9% de Zn en 2 h. Se logró eliminar alrededor del 99% de Fe, Cd y Pb de las soluciones obtenidas de la lixiviación, previo a la electrodeposición en la que se recuperó 50,6 % de Zn a partir de la solución de H2SO4 y 44,3 % de la solución obtenida del proceso de lixiviación con HCl.
Palabras clave: Polvos de acería, lixiviación, H2SO4, HCl, electrolisis bi-electrolítica.
Abstract: This work compares 2 leaching agents, H2SO4 and HCl with their processes of purification and electro-deposition to recover metallic Zn from electric arc furnace dust (EAFD). EAFD is generated in electric arc furnaces for steel production and has an important Zn content (20-50%) By leaching with 150 g/L of H2SO4, Zn recovery reached 75,5 % in 8 h of operation, meanwhile with 150 g/L of HCl Zn recovery reached 70,9% in 2 h. Purification processes reached eliminations near to 99 % for Fe, Cd and Pb. Electrodeposition process recovered 50,6 % of Zn from H2SO4 solution and 44,3 % of HCl solution
Keywords: Electric arc furnace dust, leaching, H2SO4, HCl, bi-electrolytic electrolysis.

Se presentan algunos resultados de la gestión del Departamento de Metalurgia Extractiva (DEMEX) que se ha fundamentado en cinco criterios claves: definición de metas y objetivos muy claros; planificación estratégica coherente, participativa y orientada al mercado; administración por procesos; mercadeo estratégico y operacional sistemático de productos y servicios; y gestión del recurso humano. Se cita que lo realmente valioso de una organización es “su conocimiento” (savoir faire) y éste está en su personal, el éxito depende exclusivamente de su personal y de su actitud. Evolucionar de una normatividad a una cultura organizacional, esta es la mejor ventaja competitiva.

Steel dusts, considered as toxic wastes, are made of metal oxides (ZnO, PbO, Fe3O4), which can be valued by techniques like leaching with HCl o H2SO4, that are not selective with iron. Leachates have a pH between 1-2, therefore, it is necessary to add NaOHfor the solution to reach a pH of 4-5 that let theelectrodeposition of Zn. Organic acids (citric, oxalic, tartaric and acetic)permits the leaching of Zn at this pH with less dissolution of Fe. The results of this research show recoveries with: citric acid Zn- 68% Fe- 12%; oxalic acid  Zn-0,2%, Fe- 75%; tartaric acid Zn- 56%, Fe- 12% and acetic acid Zn- 70%, Fe- 5%, working with pulps with 10% of solids at a concentration of 100 g/L of organic acids. A bioelectrolitic cell was used for zinc´s recovery, which has two sections divided by a cation exchange membrane. Inside one of such sections, the leached solution is placed with Al cathode, for zinc´s recovery; in the other section, 1M sulfuric acid is added with lead anode and a current density of 300 A/m2. The function of the membrane is to permit the transfer of only hydronium ions from the sulfuric acid to trigger the formation of the first carboxylic acids. For this reason, the pH of the solution decreases. This research presents good economic perspectives for industrial application.

Carbon reactivation is a strategy to reduce waste and cost in many industrial processes, for example, effluent treatment, food industry, and hydrometallurgy. In this work, the effect of physical and chemical reactivation of granular activated carbon (AC) was studied. Spent activated carbon (SAC) was obtained from a carbon in pulp (CIP) leaching process for gold extraction. Chemical and physical reactivations were evaluated using several acid-wash procedures (HCl, HNO 3 , H 2 SO 4) and thermal treatment (650-950 • C) methods, respectively. The effect of the reactivation processes on the mechanical properties was evaluated determining ball pan hardness and normal abrasion in pulp resistance. The effect on the adsorptive properties was evaluated via the iodine number, the gold adsorption value (k expressed in mg Au/g AC), and Brunauer-Emmett-Teller (BET) surface area. Initial characterization of the SAC showed an iodine number of 734 mg I 2 /g AC, a k value of 1.37 mg Au/g AC, and a BET surface area of 869 m 2 /g. The best reactivation results of the SAC were achieved via acid washing with HNO 3 at 20% v/v and 50 • C over 30 min, and a subsequent thermal reactivation at 850 • C over 1 h. The final reactivated carbon had an iodine number of 1199 mg I 2 /g AC, a k value of 14.9 mg Au/g AC, and a BET surface area of 1079 m 2 /g. Acid wash prior to thermal treatment was critical to reactivate the SAC. The reactivation process had a minor impact (<1% change) on the mechanical properties of the AC.

The influence of the carbonization conditions of palm kernel in the hardnessof the produced char was established. attrition process was tested with differentchars evaluating the increase of hardness and carbon loss. active carbon-phe-nolic or epoxy resins composites were produced by impregnation and polyme-rization of resins on active carbon surface. an attritioned active carbon andphenolic resins composites with 99% hardness are obtained. such productscan adsorb a 100% of the soluble gold cyanide complex in the cyanidation -carbon in pulp (ciP) process, tested with a gold sulfide ore (9 g/ton au, 19%pyrite, 75% quartz) from the Portovelo deposit, Ecuador.

Nowadays, mining effluents have several contaminants that produce great damage to the environment, cyanide chief among them. Ferrites synthesized from transition metals have oxidative properties that can be used for cyanide oxidation due to their low solubility. In this study, cobalt and copper ferrites were synthesized via the precipitation method, using cobalt nitrate, copper nitrate, and iron nitrate as precursors in a molar ratio of Co or Cu:Fe = 1:2 and NaOH as the precipitating agent. The synthesized ferrites were impregnated in specific areas on active carbon. These composites were characterized using X-Ray Diffraction (XRD) and Scanning Electron Spectroscopy (SEM). The XRD results revealed a cubic spinel structure of ferrites with a single phase of cobalt ferrite and two phases (copper ferrite and copper oxides) for copper. The CoFe2O4 impregnated on active carbon reached a cyanide oxidation of 98% after 8 h of agitation; the composite could be recycled five times with an 18...

One of the main sources of activated carbon is biomass which can be transformed into char by pyrolysis. Apart from the obtaining coal, the pyrolysis of biomass can be used for the preparation of fuels, and this is why it is very important to determine its kinetic parameters for modelling. In the present research, the pyrolysis enthalpy of palm nut shells (Elaeis guineensis) was determined with the use of a differential scanning calorimetry study (DSC). To determine the kinetic parameters, the Not Reacted Core model was employed. This model considers that there is a heat and mass gradient between the furnace atmosphere and the interface formed during pyrolysis. To obtain the required data for the model, palm nut shells were submitted to pyrolysis in a Nichols furnace under reducing atmosphere. Samples were taken every 10 minutes to calculate char conversion. The experimental pyrolysis enthalpy resulted to be 301.81 J/g and then the monomeric units of cellulose, hemicellulose, and lig...

Waste electrical and electronic equipment (WEEE) has increased in recent decades due to the continuous advancement of technology in the modern world. These residues have various metals that are found in concentrations that make their recovery profitable. A group of metals of interest are the rare earths such as europium and yttrium, as well as semiconductors such as indium. Yttrium was recovered from cathode ray tubes that were manually dismantled. The resulted powder was leached with HNO3, and then the solution was submitted to solvent extraction with di-(2-ethylhexyl) phosphoric acid (DEHPA) using n-heptane as a diluent. For re-extraction, HNO3 was used again, and yttrium was precipitated by adding four times the stoichiometric amount of oxalic acid, reaching 68% yttrium purity. Indium was recovered from the liquid crystal display (LCD) screens for which the pulverized material was leached with H2SO4. Then, the indium sulfate was subjected to solvent extraction using DEHPA as an e...

Red gypsum, a waste material which derives from the production of titanium dioxide with a high content of CaSO 4 and Fe(OH) 2 , was evaluated as a low-cost adsorbent mixed with green compost. Red gypsum is becoming interesting because of the widespread TiO 2 industrial production in many industrialized countries. The aim of this work was to evaluate whether a mixture of red gypsum and compost could be used as an adsorbing material to decontaminate waters polluted with heavy metals. Batch adsorption experiments were carried out with Lead as representative of heavy metals in polluted waters. Lead adsorption was studied to test the performance of the composite material as a function of the composition of the mixture. The evaluation of the adsorption capacity of the compost plus red gypsum mixture was based on the Freundlich and Langmuir equations. The results indicate that the composite material has a high adsorption capacity for Pb from aqueous solutions. The adsorption capacity grew following the addition of increasing amounts of red gypsum due to the increase in negative charges, which promoted the attraction towards the positively charged Pb ions. Pb adsorption may occur as a result of different mechanisms such as ion exchange, surface complexation and electrostatic interaction. The mixture compost-red gypsum showed a considerable capacity to remove Pb from aqueous solutions over a wide range of concentrations.

The incorporation of titanium dioxide and copper onto activated carbon for phenol removal was evaluated. Based on catalyst contents and phenol degradation, four composites were selected and characterized. The results showed that both adsorption and photocatalytic activities were influenced by the presence and arrangement of the catalysts.

The photocatalytic oxidation of cyanide by titanium dioxide (TiO2) supported on activated carbon (AC) was evaluated in a continuous flow UV photo-reactor. The continuous photo-reactor was made of glass and covered with a wood box to isolate the fluid of external conditions. The TiO2-AC synthesized by the impregnation of TiO2 on granular AC composites was characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), Scanning Electron Microscopy (SEM), and nitrogen adsorption-desorption isotherms. Photocatalytic and adsorption tests were conducted separately and simultaneously. The results showed that 97% of CN− was degraded within 24 h due to combined photocatalytic oxidation and adsorption. To estimate the contribution of only adsorption, two-stage tests were performed. First, 74% cyanide ion degradation was reached in 24 h under dark conditions. This result was attributed to CN− adsorption and oxidation due to the generation of H2O2 on the surface of AC. Then...

The removal mechanisms that govern Se concentrations in the Great Salt Lake are unknown despite this terminal lake being an avian habitat of hemispheric importance. However, the volatilization flux of Se from the Great Salt Lake has not been previously measured due to challenges of analysis in this hypersaline environment. This paper presents results from recent field studies examining the spatial distribution of dissolved volatile Se (areally and with depth) in the south arm (main body) of the Great Salt Lake. The analyses involved collection of dissolved volatile Se in a cryofocusing trap system via sparging with helium. The cryotrapped volatile Se was digested with nitric acid and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Results show concentrations of dissolved volatile Se that increase with depth in the shallow brine, suggesting that phytoplankton in the open waters and bioherms in shallow sites (<4 m in depth) may be responsible for volatile Se production. Volatile Se flux to the atmosphere was determined using mass transport models corrected to simulate the highly saline environment of the south arm of the Great Salt Lake. The estimated annual flux of volatile Se was 1455 kg/year within a range from 560 to 3780 kg Se/year for the 95% confidence interval and from 970 to 2180 kg Se/ year within the 68% confidence interval.

A mass balance for Se in the south arm of the Great Salt Lake was developed for September 2006 to August 2007 of monitoring for Se loads and removal flows. The combined removal flows (sedimentation and volatilization) totaled to a geometric mean value of 2079 kg Se/yr, with the estimated low value being 1255 kg Se/yr, and an estimated high value of 3143 kg Se/yr at the 68% confidence level. The total (particulates + dissolved) loads (via runoff) were about 1560 kg Se/yr, for which the error is expected to be ±15% for the measured loads.

The Great Salt Lake (GSL) is a unique ecosystem in which trace element activity cannot be characterized by standard geochemical parameters due to the high salinity. Movement of selenium and other trace elements present in the lake bed sediments of GSL may occur due to periodic stratification displacement events or lake bed exposure. The water column of GSL is complicated by the presence of a chemocline persistent over annual to decadal time scales. The water below the chemocline is referred to as the deep brine layer (DBL), has a high salinity (16.5 to 22.9%) and is anoxic. The upper brine layer (UBL) resides above the chemocline, has lower salinity (12.6 to 14.7%) and is oxic. Displacement of the DBL may involve trace element movement within the water column due to changes in redox potential. Evidence of stratification displacement in the water column has been observed at two fixed stations on the lake by monitoring vertical water temperature profiles with horizontal and vertical velocity profiles. Stratification displacement events occur over periods of 12 to 24 h and are associated with strong wind events that can produce seiches within the water column. In addition to displacement events, the DBL shrinks and expands in response to changes in the lake surface area over a period of months. Laboratory tests simulating the observed sediment re-suspension were conducted over daily, weekly and monthly time scales to understand the effect of placing anoxic bottom sediments in contact with oxic water, and the associated effect of trace element desorption and (or) dissolution. Results from the laboratory simulations indicate that a small percentage (1%) of selenium associated with anoxic bottom sediments is periodically solubilized into the UBL where it potentially can be incorporated into the biota utilizing the oxic part of GSL.

Mining and petroleum production are the source of many elements and base materials fundamental for our modern way of life. The flip side of these keystone industries is the environmental degradation they can cause if not properly managed. Metallic mining and petroleum production can contaminate the local ecosystem with sediments, chemicals used in the industrial processes and heavy metals, part of the metallic ore or oil reservoir. The objective of this project was to analyze the spatial distribution of the presence of different potentially hazardous elements that make up the metallic deposits and oil reservoirs in Ecuador, focused mainly on artisanal and small-scale gold mining (ASGM) districts. Additionally, we were interested in analyzing this information under the local political and administrative contexts which are key to determining how likely it is that mismanagement of the local mineral deposits and petroleum exploitation projects will end up causing environmental degradati...

In this paper, the effect of pre-injection timing on the combustion and emission performance of methanol/diesel high premixed charge compression ignition (HPCCI) combustion mode at low load was studied by three-dimensional numerical simulation. The simulation is carried out under the conditions of 1900 r/min and 25% load, and the pre-injection diesel mass remains constant and the pre-injection timing is changed under the conditions of 50% and 60% methanol ratio respectively. The results show that with the delay of preinjection timing, the evaporation of pre-injected fuel in cylinder becomes faster, the low temperature reaction is enhanced, and the peak value of heat release rate is higher. In addition, the distribution of pre-injected diesel in cylinder and the position of impact wall are the important factors affecting the combustion and emission performance in cylinder, and when the injection timing is-35 °CA ATDC, the combustion and emission characteristics of the engine are optimal. Finally, by comparing with the traditional RCCI combustion mode, the enhancement ability of HPCCI combustion mode on methanol combustion efficiency under low load is verified and analyzed.

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