Avaliação da capacidade de adsorção da borra de café e da casca de café na remoção de 2,4-D em amostras de água

Abstract

Contamination of water resources for human supplying by micro pollutants is a difficulty that conventional water treatments do not solve effectively. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a micro-contaminant fouling pesticide that has high toxicity to the aquatic ecosystem and to humans, requiring its removal from this environment. The most widely used method for the removal of these compounds is adsorption on activated carbon, where the substance interacts with clusters present on the coal surface, so that, after filtration, the compound is removed. In the attempt to develop new materials for the adsorption of 2,4-D, Coffee grounds (CG) and Coffee husks (CH), in natura and carbonized, were used in adsorption studies, as they are highly available materials in Brazil and have lower cost of obtaining when compared to activated charcoal. This study evaluated the surface characteristics of these materials by Analysis of Specific Surface Area (BET), Scanning Electron Microscopy (SEM), Thermogravimetry (TG) and Point Zero Charge (PZC). Studies were carried out to set equilibrium time and the adsorbent mass to be used, but it was not possible to determine any adsorption of 2,4- D using CG and CH in natura. Thus, adsorption studies varying the initial 2,4-D concentration and the pH of the solution were conducted only for activated carbon AC and carbonized CG and CH. To the isotherms, generated from the adsorption study, the Langmuir and Freundlich models were applied to obtain parameters of the adsorption process. In general, carbonized CG presented higher adsorption in relation to carbonized CH, presenting qA MÁX values of 23.4 and 4.4 mg/g, respectively. However, both had lower performance than AC (qA MÁX = 94.0 mg/g). Among the studied pH, it was observed that in acid pH's, 2,4-D removal was higher for all studied adsorbents.