Remoção de Imidacloprid de soluções aquosas por adsorção em casca do tamarindo (Tamarindus Indica L.)

Abstract

Brazil is considered one of the biggest consumers of pesticides, and the insecticide imidacloprid is among the ten best-selling pesticides. Due to its toxicity, onbiodegradability and bioaccumulation in river sources, it has become a major environmental concern. Among the various techniques that can be used to remove this contaminant is the adsorption process. With this in mind, there have been many studies into the development of adsorbents made from organic materials, showing satisfactory results in the removal of pesticides from aqueous solutions. Tamarind peel is a highly important agro-industrial waste due to its abundance and availability. In this context, the aim of this work was to evaluate the removal capacity of the insecticide imidacloprid by tamarind bark used as an adsorbent material. Initially, the tamarind bark was dried and an average particle diameter of 0.425 mm was selected for the study. It was then characterized in terms of scanning electron microscopy (SEM), specific area analysis by N2 physisorption (BET), zero charge point, infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Preliminary adsorption tests were carried out in a batch system, evaluating the influence of pH and adsorbent mass dosage. With the best conditions obtained in the preliminary tests, kinetics were studied for 24 hours and the adsorption equilibrium at temperatures of 30, 45 and 60ºC, and finally the regeneration capacity of the adsorbent was evaluated. The characterization of the adsorbent showed by SEM and BET that the shell is a low porosity material, with a low specific area (1.823 m2 g-1) and an average pore diameter (5.714 nm), being classified in the mesoporous region. The FTIR showed changes in the characteristic carbonyl and hydroxyl bands, indicating that adsorption may have occurred through hydrogen bonds and π-π interactions. The tamarind peel had a pHpcz of 5.10 ± 0.10. In the preliminary tests, it was observed that at pHs between 6.0 and 9.0 the greatest removals of imidacloprid were obtained. However, in a basic medium, the rate of hydrolysis of the insecticide increases. Neutral pH was therefore selected for the subsequent tests. The evaluation of the adsorbent mass showed the best removal at 60.00 mg L-1. In the kinetic study, the pseudo-second order kinetic model was the one that best fitted the experimental data with an equilibrium time of 780 min, with an adsorption capacity of 0.4070 mg g-1 at a temperature of 25±2 °C. All the isotherms were favorable, with the best result being at a temperature of 60 °C, reaching equilibrium at approximately 250.00 mg L-1, with a capacity of 39.37 mg g-1, with the Sips model having the best fit. The study of adsorbent regeneration showed that 94.38% of the adsorbent was recovered in the first cycle. Therefore, tamarind bark could be an alternative material for removing the insecticide imidacloprid.