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METAL cyanides, THIOUREA, CYANIDES, SUSTAINABLE chemistry, SPECTROPHOTOMETERS, DIFFUSION, and IMPELLERS

In this work, the effect of the agitation speed on the thiourea kinetics with thiourea of gold-floated minerals, the concentration of thiourea (TU) that achieved the greatest recovery of gold from its floated concentrates compared with cyanide was determined, along with the kinetic model that controls leaching with thiourea. For this, a "Suction tube" type Baffled reactor is used with mechanical agitation by means of a vane type impeller. The parameters analyzed were: percentage of solids (15%); TU concentration (1, 3, 6, 9, 12 g / L); stirring speed (420, 490, 560, 700 rpm); reaction time (4 hours); effective reactor capacity (27.1 L). An atomic absorption spectrophotometer is estimated to determine the gold concentration. It was determined that the thiourea concentration of 9 g / L was the one that produced the best gold recovery results. The thiourea leaching process adapts to the kinetic diffusion model through the ash layer as a controlling stage. Thiourea, as a leaching agent of the Au concentrate, has a lower percentage (1.74% less) of recovery of this metal than with cyanide during the leaching process at 240 minutes of stirring at a stirring speed of 700 rpm. [ABSTRACT FROM AUTHOR]

ENGINEERING, MULTIDISCIPLINARY, adsorption, biosorption, chrome, kinetics, removal., adsorción, bioadsorción, cinética, cromo, and remoción.

Resumen En esta investigación se utilizó cáscara de yuca (Manihot esculenta) para remover cromo (VI) de disoluciones acuosas simulando efluentes in dustriales. Se utilizó un esquema de operación por lotes y se realizaron pruebas variando la concentración inicial de cromo (30, 40 y 50 ppm) y la temperatura (25, 30 y 35 °C), manteniendo fija la concentración del adsorbente (3,33 g/l), el tiempo de contacto 40 minutos y el pH 2, el cual se ajustó con ácido sulfúrico (H2SO4). Los datos obtenidos fueron ajusta dos a cuatro modelos cinéticos: primer orden reversible, pseudosegundo orden, Elovich y difusión intrapartícula. Los datos se ajustaron mejor al modelo de pseudosegundo orden. También se realizaron pruebas usando una concentración inicial de 50 ppm y tiempo de contacto de 120 minutos, variando la concentración del adsorbente (2, 4, 20 y 25 g/l). Se determinó que a mayor concentración de bioadsorbente se presenta mayor porcentaje de remoción.
In this research, cassava peel (Manihot esculenta) was used to remove chromium (VI) from aqueous solution simulating industrial effluents. Batch adsorption operation was used and tests were performed by vary ing the initial concentration of chromium solution (30, 40 and 50 ppm) and temperature (25, 30 and 35 °C), keeping fixed the adsorbent dosage (3.33 g/l), the contact time 40 minutos and pH 2, which was adjusted with sulfuric acid (H2SO4). Data were fitted to four kinetic models: reversible first-order, pseudo second-order, Elovich and intraparticle diffusion models. Pseudo second-order model fits best to most experimental data. Tests were also performed using an initial concentration of 50 ppm and contact time of 120 minutos, varying the adsorbent dosage (2, 4, 20 and 25 g/l). The higher adsorbent dosage is, the higher percent removal of Cr(VI) is observed.

Residue of roast and ground coffee as a lignocellulosic adsorbent material was investigated, in the removal of methyl orange dye from aqueous solutions by batch adsorption experiments. The effects of experimental parameters such as initial dye concentration, biosorbent dose, initial pH and temperature on dye biosorption were studied. The adsorption amount of methyl orange decreased with increasing pH and temperature. The experimental data fitted very well to the pseudo second-order kinetic Lagergren model. A maximum adsorption capacity of 1,3 mg of methyl orange per gram of biosorbent through an adjustment to the Langmuir model was calculated. It was found that the biosorption of methyl orange in the analyzed biosorbent is of exothermic nature. It was found that the roasted and ground coffee residue is viable for the primary treatment of wastewater contaminated with azoic compounds. [ABSTRACT FROM AUTHOR]