Avaliação da adsorção de corante artificial em resíduo de laranja

Abstract

A large amount of artificial coloring is used by the food industries. This represents the generation of polluting-colored effluents, as they are discarded into the environment without proper treatment or require expensive and time-consuming treatments. The need to remove these materials before incorporation into the environment, makes techniques such as adsorption to be developed, when solid particles, the adsorbents, concentrate diluted substances on their surface. The most common adsorbent material is activated carbon, but in recent years, by-products from the food industry have been tested as substitutes, such as orange residue. Thus, this study aimed to evaluate the use of orange residue as an adsorbent for artificial dye Red 40. Dried bagasse and orange peel were used as adsorbent material. The process conditions were: 300 mg of orange residue in contact with 50 mL of dye solution (50.6 mg/L) in an incubator at 100 rpm, at two temperatures (25 ºC and 35 ºC). For equilibrium analysis, samples were taken at time intervals until the adsorption equilibrium, verified through spectrophotometric measurements. Equilibrium parameters were obtained through mass balance calculations. For the adsorption isotherms, five different dilutions were used under the same conditions of equilibrium test up to 60 minutes. The equilibrium isotherm data were analyzed by fitting the Langmuir model. The fraction of material chosen to be used in the experiments was the one with an average diameter of 0.71 mm. In equilibrium kinetics, the dye adsorption by the adsorbent decreased with increasing temperature. Dye removal was faster in the initial periods of contact and gradually decreased to equilibrium. After 60 minutes, a trend towards equilibrium in the adsorbed dye mass was observed. The maximum amount of dye adsorbed was 1.49 mg/g at 25 °C at 180 minutes and 1.34 mg/g at 35 °C at 120 minutes. Regarding to isotherms, it was found that the adsorption capacity decreased with increasing temperature. The maximum adsorption capacity decreased from 8.36 mg/g at 25 ºC to 7.57 mg/g at 35 ºC. The analyzed parameters indicated a favorable adsorption process. Therefore, it appears that the orange residue is a material with the potential for adsorption of the Red 40 dye in aqueous solutions.