Argilas organofílicas aplicadas à remoção de carbamazepina visando a remediação de águas subterrâneas contaminadas

Abstract

In recent years there has been growing concern about the contamination of water by emerging contaminants, such as pharmaceuticals. Carbamazepine (CBZ) is a psychotropic drug widely used throughout the world and has been frequently detected in water bodies, including groundwater. Organoclays have been used as efficient adsorbents for pharmaceutical pollutants. In this study, four types of organoclays were prepared from the modification of national bentonite clay with two cationic surfactants: hexadecyltrimethylammonium bromide (HDTMA) and octadecyltrimethylammonium bromide (ODTMA). X-ray diffraction analyzes showed that the basal spacing of organoclays varied from 1.54 to 2.93 nm, suggesting the intercalation of organic cations in the interlayer space of montmorillonite. Initially, the synthesized clays were evaluated as adsorbents for the sorption of CBZ through batch equilibrium experiments, under variation of the pH, contact time, dosage of adsorbent, and initial drug concentration. pH variation showed no adsorption influence. CBZ sorption by the organoclays followed a pseudo-second-order kinetics. The best sorption performance was obtained for the BCN1-HDTMA100 clay, with a capacity of 34.34 ± 1.41 mg/g, about ten times greater than the unmodified bentonite under the same conditions. This may be attributed to the higher surfactant content. The adsorption isotherm at 25 ºC showed linear behavior. FTIR and TG analyzes on organoclay-CBZ hybrids confirmed the incorporation of the drug. Hydrophobic interaction was the dominant contribution evaluated to the adsorption of CBZ. Furthermore, toxicity tests were carried out on organoclays and the medium in the presence of CBZ before and after treatment. This is a novelty report. Most of the organoclays had no toxicity against Artemia salina. The toxicity of the medium after adsorptive treatment was eliminated. After batch study, two synthesized organoclays (BCN1-HDTMA100 and BCN1-ODTMA100) were selected for the study of continuous adsorption of CBZ through tests in a fixed bed column filled with a mixture of sand and organoclay aiming at application as a medium reactive Permeable Reactive Barriers (PRB) for groundwater remediation. At this stage, the performance of the synthesized clays was compared to that of a commercial organoclay, Spectrogel Type C. The adsorption performance was evaluated using breakthrough curves. The effects of the initial drug concentration, quantity and type of clay in the fixed bed were evaluated. In general, the synthesized clays performed better than Spectrogel Type C. The lower adsorption capacity of CBZ by commercial clay may be associated with effects related to the packing density of organic cations in the interlayer space. Under the conditions of 1.0g of clay in the bed, 95 mg/L of initial CBZ concentration and flow rate of 1.0 mL/min, the clays BCN1HDTMA100 and BCN1-ODTMA100 presented breakthrough times of 505 and 525 min and adsorption capacities of 46.6 and 50.1 mg/g, respectively. Therefore, organoclays have demonstrated promising potential for use in groundwater remediation applications.