Esperanza López

A systematic experimental study on gold recovery from electronic waste using selective ammonium persulfate oxidation

This paper presents a systematic approach on gold recovery from electronic waste (e-waste) using ammonium persulfate. This process was developed as a response to the lack of hydrometallurgical systems capable of separating gold from its metallic substrate without material grinding, with minimum formation of pollutants, and achieving a lower reaction time. Computer memory boards, electronic processors and electronic pins and contacts were analyzed to determinate base metals (Ni, Fe, Cu) and gold (Au) using microwave plasma atomic emission spectroscopy (MP-AES). An aqueous commercial grade ammonium persulfate with oxygen and pressure was used to produce the persulfate anion (S2O8 2) and the oxidative sulfate ion (SO4 2), which partially oxidized and leached the base metals breaking the Au-Ni-Fe-Cu bonds and allowing gold to be recovered in its original non-leaching state. The influence of the oxidative parameters was evaluated using full factorial (FF) and central composite designs (CCD) with response surface methodology (RSM) and first and second order models were developed. Using RSM allowed to obtain a faster recovery of gold, minimizing the agent consumption. The findings presented suggest that optimized quantities of ammonium persulfate, oxygen, pressure, temperature and liquid solid ratio could be used for selective oxidization of the base metals and to extract more than 96% of gold from e-waste.

Microestructura y propiedades mecánicas por microindentación y nanoindentación de un recubrimiento de circona estabilizada con itria (4,5% en mol) elaborado por plasma atmosférico a partir de suspensiones

espanolEn este trabajo se analizo la relacion entre la microestructura de un recubrimiento de 4,5% en mol de circona estabilizada con itria (4.5YSZ) con sus propiedades mecanicas medidas por nanoindentacion y microindentacion. Los recubrimientos fueron elaborados por la tecnica de proyeccion termica por plasma atmosferico a partir de una suspension de etanol y dos tipos de polvos (3 y 8% en mol de YSZ) con particulas de tamano nanometrico. El analisis de la microestructura de la seccion trasversal del recubrimiento de 4.5 YSZ revelo una estructura bimodal, la que estaba compuesta de una zona con particulas semifundidas (ZS) y otra zona compuesta de lamelas con un alto grado de fusion (ZF). Los ensayos de nanoindentacion mostraron una distribucion Weibull bimodal para la dureza y monomodal para el modulo de elasticidad, lo que esta relacionada con su estructura. Los ensayos microindentacion (microdureza Vickers y modulo de elasticidad: E) presentaron una distribucion Weibull monomodal. Estos resultados de microindentacion estuvieron influenciados por el area de contacto de las zonas indentadas, ya que estas tomaban las dos zonas microestructurales (ZF y ZS) del recubrimiento de 4.5YSZ revelando una medicion global de sus propiedades mecanicas. EnglishIn this paper the microstructure of 4.5 mol% Yttria-Stabilized-Zirconia (4.5YSZ) coating and its mechanical properties measured by nanoindentation and microhardness was analyzed. The coatings were elaborated by suspension plasma spraying (SPS) from a suspension of ethanol and two types of powders (3 and 8 mol% YSZ) with nanosized particles. The analysis of the microstructure of the cross section of the 4.5 wt. YSZ coating revealed a bimodal structure, which was composed of a zone with semi-molten particles (ZS) and another zone consisting of lamellae with a high degree of fusion (ZF). Nanoindentation tests showed a bimodal Weibull distribution for hardness and monomodal Weibull distribution for elastic modulus (E), which is related to its structure. Microhardness tests (hardness Vickers and E) had a monomodal Weibull distribution. These results of microindentation were influenced by the contact area of the indentation zones, as they took the two zones (ZF and ZS) of the microstructure of 4.5YSZ coating revealing global measurement of their mechanical properties

Study of thermal shock resistance of flame sprayed coatings manufactured to protect molds used in glass containers industry

espanolLos moldes usados en la manufactura de vidrio estan sujetos a continuos ciclos de calentamiento y enfriamiento, lo que resulta en fallas prematuras por fatiga termica. Con la idea de proteger estos moldes, una aleacion de niquel (Eutectic Castolin CPM1205™) fue depositada por proyeccion termica de llama bajo condiciones de combustion neutras como capa base sobre sustratos de hierro gris. Posteriormente, con la misma tecnica de proyeccion, y bajo condiciones oxidantes y superoxidantes, fueron aplicados como recubrimientos superiores polvos de: Al2O3-40 wt. % TiO2, ZrO2-36 wt. % Al2O3 y Al2O3, asi como el cermet: Ni-WC, esto con el fin de evaluar la influencia del tipo de llama y el tipo de recubrimiento sobre la resistencia al choque termico. Los resultados indican que los recubrimientos de Ni-WC manufacturados desde polvos de Eutectic Castolin 10112™ en condiciones oxidantes, asi como recubrimientos de ZrO2-Al2O3 fabricados desde polvos nanoaglomerados de Eutectic Castolin 25088™ en condiciones superoxidantes, mostraron los mejores desempenos. La naturaleza del Ni-WC permitio incrementar la resistencia al choque termico debido al comportamiento termoelastico de la matriz de niquel, asi como a la capacidad de contrarrestar las grietas caracteristica de los materiales compuestos. Por su lado, para los recubrimientos de ZrO2-Al2O3, la microestructura bimodal que esta clase de materiales muestra fue la que contribuyo a incrementar la resistencia al choque termico. Por ultimo, es de notar que los mejores desempenos para ambos tipos de recubrimientos fueron obtenidos en niveles de porosidad entre 20% y 40%. EnglishMolds used in glass manufacturing are subjected to continuous heating and cooling cycles, which result in their premature failure by thermal fatigue. In order to protect these molds a nickel alloy (Eutectic Castolin CPM 1205TM) was deposited as bond coat by flame spraying onto compacted graphite iron substrates and then, Al2O3-40 wt. % TiO2, ZrO2-36 wt. % Al2O3 and Al2O3, as well as a Ni-WC cermet, were sprayed as a top coatings using super oxidized and slightly oxidized flames. The effect of the flame type and the thickness of coatings on thermal shock resistance were evaluated. The results obtained indicate that coatings of Ni-WC sprayed from Eutectic Castolin 10112TM powders using a slightly oxidized flame, and ZrO2-Al2O3 coatings manufactured from nano-agglomerated Eutectic Castolin 25088TM powders with an super oxidized flame showed the best performances. The nature of Ni-WC cermets allowed increasing the thermal shock resistance due to the thermo-elastic behavior of nickel matrix and the arrest crack effect characteristic of composite materials. Likewise, in ZrO2-Al2O3 coatings, the bimodal microstructure that this kind of coatings shows contributed to increase the thermal shock resistance. The better performances of both coatings were obtained with a porosity level between 20% and 40%.