Organofilização da palygorskita de Guadalupe-PI/Brasil: elucidação do processo e mecanismo de interação com um surfactante catiônico

Abstract

Palygorskite is a hydrated aluminum and magnesium silicate clay mineral. It is a potential sorption agent for decontamination of aqueous effluent because it has a high cation exchange capacity (20 to 40 meq 100 g-1) and surface area (125 to 210 m2 g-1). However, it has a negative surface charge, so to be applied in the removal of anionic contaminants it is necessary to change its surface charge from negative to positive. It can be done through organophilization that consists modification of palygorskite using a cationic surfactant. The present study was aimed to characterize and processing a sample of palygorskite from Guadalupe (PI / Brazil) and, subsequently, the kinetic study of the process of organofilization of this sample. The ore dressing steps consisted of wet granulometric classification and wet magnetic separation. To perform the kinetic study of organophilization, 100 g of cetyltrimethyl ammonium (CTAB) were mixed with 100 g of ore dressed palygorskite in 1 L of deionized water, then the pH was adjusted to 8 and the system was kept under agitation mechanics for 4, 8, 16, 24 and 48 h. After this time, the sample was washed with deionized water, dried and classified granulometrically in a 106 µm sieve. All samples obtained were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), thermal analysis, determination of the cation exchange capacity (CTC), vibrational spectroscopy in the infrared with fourier transform (FTIR), scanning electron microscopy (SEM), surface charge measurements (PZ) and textural analysis. Molecular modeling was used to determine whether the CTAB molecule was able to be inserted into the palygorskite channels. The XRD results indicated that the palygorskite sample consists of smectite, quartz, goethite, kaolinite and palygorskite. After ore dressing process, there was a concentration of palygorskite in the fraction less than 20 µm, characterized by a decrease in the quartz peak and an increase in the peaks related to kaolinite, smectite and palygorskite clay minerals. The FRX analysis corroborated these results since the sample consists mainly of MgO, Al2O3, SiO2. According to the NMR and thermal analysis, the organophilized samples reached saturation with CTAB and morphological stability after 8 and 16 h, respectively. The analysis of the Zeta potential curves showed that all samples present a change in surface charge from negative to positive in the all range of pH (2 - 12). The results of the CTC analysis indicated a decrease in the cation removal capacity, presenting similar values, around 3 meq 100 g-1 after 8 h of organophilization. The results suggest that the modified palygorskite can be promising for the removal of anionic contaminants from aqueous effluents.