Characterization of expanded vermiculite clay: an evaluation of the physical-chemical and mineralogical patterns for the application as adsorbent

ABSTRACT

Expanded vermiculite, in addition to being widely used in civil construction as acoustic insulation and flame retardant and in agriculture as carrier vehicles of fertilizers, has been explored as a possible adsorbent of contaminants in the environmental area. Thus, the objective was to characterize it by physical-chemical and mineralogical standards. For this, the following properties were determined: zero charge point (pH_zcp: 8.5), acid and basic sites (negative surface area with the presence of acid groups – carboxylic: 0.9680 m_Eq g^-1 and phenolics 0.0007 m_Eq g^-1 and basic groups: 1.5490 m_Eq g^-1), cation exchange capacity (CEC: 122 m_Eq of methylene blue per 100 g of expanded vermiculite), X-ray diffraction (XRD: high crystallinity and purity), Fourier transformation infrared spectrometry (FTIR: characteristic of filossilicate, axial and symmetrical angular deformation of O-H groups, asymmetric stretching Si-O-Si and Si-O-Al and stretching Al-O), scanning electronic microscopy (SEM: typical lamellar and vermiform structure) and adsorption of N₂ (BET/BJH: mesoporous solid - plate type, volume of surface area of 9 m² g^-1, pore volume and average pore diameter of 0.02 cm³ g^-1 and 19 Å, respectively). The results show that the expanded vermiculite clay is strongly adsorbent, possessing higher affinity with cations and cationic molecules and with adsorption capacity for molecules of different sizes.

Keywords
Adsorption; Clayey; Filossilicate; Lamellar; Mesoporous