The adsorption of gold on activated carbon in ammoniacal thiosulfate solution was studied. The variables affecting the adsorption of gold on the carbon included, among others, temperature, concentrations of ammonium hydroxide and thiosulfate, and those of accompanying cations and anions. The apparent activation energy for the adsorption process was estimated to be 19.4 kJ/mol, and this value indicates that the gold adsorption is film diffusion-controlled. It was also found that the rate of initial adsorption rate was fast, when compared to that of the overall adsorption process.
Background Prone positioning is currently applied in time-limited daily sessions up to 24 h which determines that most patients require several sessions. Although longer prone sessions have been reported, there is scarce evidence about the feasibility and safety of such approach. We analyzed feasibility and safety of a continuous prolonged prone positioning strategy implemented nationwide, in a large cohort of COVID-19 patients in Chile. Methods Retrospective cohort study of mechanically ventilated COVID-19 patients with moderate-to-severe acute respiratory distress syndrome (ARDS), conducted in 15 Intensive Care Units, which adhered to a national protocol of continuous prone sessions ≥ 48 h and until PaO2:FiO2 increased above 200 mm Hg. The number and extension of prone sessions were registered, along with relevant physiologic data and adverse events related to prone positioning. The cohort was stratified according to the first prone session duration: Group A, 2–3 days; Group B, 4–5 days; and Group C, > 5 days. Multivariable regression analyses were performed to assess whether the duration of prone sessions could impact safety. Results We included 417 patients who required a first prone session of 4 (3–5) days, of whom 318 (76.3%) received only one session. During the first prone session the main adverse event was grade 1–2 pressure sores in 97 (23.9%) patients; severe adverse events were infrequent with 17 non-scheduled extubations (4.2%). 90-day mortality was 36.2%. Ninety-eight patients (24%) were classified as group C; they exhibited a more severe ARDS at baseline, as reflected by lower PaO2:FiO2 ratio and higher ventilatory ratio, and had a higher rate of pressure sores (44%) and higher 90-day mortality (48%). However, after adjustment for severity and several relevant confounders, prone session duration was not associated with mortality or pressure sores. Conclusions Nationwide implementation of a continuous prolonged prone positioning strategy for COVID-19 ARDS patients was feasible. Minor pressure sores were frequent but within the ranges previously described, while severe adverse events were infrequent. The duration of prone session did not have an adverse effect on safety.
ResumenSe estudió el efecto de las propiedades físicas de un carbón activado, tales como distribución de tamaño de poros, superficie específica, diámetro promedio de poros, en la adsorción de oro desde disoluciones cianuradas, con el oro disuelto a la forma de Au (CN) -2 . Para cumplir con los objetivos planteados se trabajó con dos carbones activados: el carbón A, con superficie específica de 985 m 2 /g, 57 % de microporos y 3,8 nm como diámetro promedio de poros, y el carbón B, con superficie específica de 786 m 2 /g, 27 % de microporos y 11,6 nm como diámetro promedio de poros; ambos carbones, de forma granular, han sido fabricados a partir de cáscara de coco. Se realizaron ensayos de adsorción batch en un reactor de 500 ml de capacidad, con agitación mecánica a temperatura constante. Se estudiaron los efectos de cationes presentes, tales como Ca 2+ , Na + , K + y Li + , de la distribución de tamaño de poros, del diámetro promedio de poros y del área superficial, en la velocidad y cantidad de oro adsorbido en los carbones activados denominados como A y B. Se encontró que las propiedades físicas de un carbón activado constituyen un factor relevante en el proceso de adsorción de oro, en términos de velocidad y cantidad de oro adsorbido. El carbón B, con 786 m 2 /g de superficie específica, alcanzó una mayor carga por unidad de superficie (0,02 mg Au/m 2 ) en relación al carbón A, de 985 m 2 /g, el cual alcanzó una carga de 0,01 mg Au/m 2 , después de 6 h de contacto carbón-disolución. La velocidad de adsorción de oro en ambos carbones fue controlada por transferencia de masa en la película líquida que rodea a las partículas de carbón, a tiempos cortos o cargas pequeñas de oro en las partículas, lejos del equilibrio. Al aplicar un modelo cinético de primer orden, se obtuvo que la razón de las constantes cinéticas para los carbones A y B, es decir, (k B /k A ), fluctúa en un valor de 3 para los distintos cationes en estudio. En general, es posible afirmar que la velocidad de adsorción y la cantidad de oro adsorbido aumentan con el aumento de macroporos y con el aumento del diá-metro promedio de poros. La presencia de cationes favorece el proceso de adsorción de oro en medio cianuro, especialmente los de mayor valencia. Palabras clavePropiedades físicas; Carbón activado; Adsorción; Oro. Effect of the physical properites of activated carbon in the gold adsorption from cyanide media AbstractThe effect of the physical properties of an activated carbon such as pore size distribution, specific surface, pore average diameter, in the gold adsorption from cyanide solution with the gold to the Au (CN) -2 form, was studied. To meet the proposed objectives two carbons were studied: carbon A with specific surface of 985 m 2 / g, 57 % of micropores and 1.85 nm as average diameter of pores and carbon B with specific surface of 786 m 2 / g, 27 % and pores of 2.35 nm as average diameter of pores; both granular carbons made from coconut shell. Batch adsorption tests were performed in a reactor of 500 ml of capacity with mechanical...
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