Proteína do solo relacionada à glomalina de solos tropicais para remover cádmio em solução aquosa

Abstract

Cadmium (Cd) is one of the most dangerous substances and needs to be immobilized/removed in scenarios of imminent increase in its concentration. Evaluating ecological alternatives, such as glomalin-related soil protein (GRSP), for Cd (II) immobilization becomes relevant. Characterizations and adsorption experiments with GRSP of two soils, oxidic and organic, were carried out with the aim of evaluating the ability to immobilize Cd in aqueous solutions. The hypotheses tested were i) the structure and elemental composition of GRSP differs according to the type of pedosystem; ii) the interaction between GRSP-Cd is regulated by surface complexation; and iii) the ability of Cd adsorption by GRSP is strongly modulated by pH, contact time and concentration. The thesis was divided into two chapters: in chapter 1 the characterizations by FTIR, XRF, XRD, SEM, TGA and electrical charges (pHZPC) of GRSP were carried out. The GRSP of the two soils, in general, dominant functional groups (CH, NH2, OH, COOH (carboxyl), CO-NH (amide), C=O (carbonyl), which contribute to the sequestration and immobilization of Cd (II There is a marked presence of goethite and gibbsite in the GRSP of both soils. The surface morphology showed that the GRSP were flocculent solids, light weight, amorphous in appearance and with a typical color of the soil from which they were extracted. TGA demonstrated that GRSP-Org has a solid residual mass of 33.2%, while GRSP LV, 58.3%, after heating up to 900 oC. In chapter 2, the adsorption capacity of Cd (II) in aqueous solutions was evaluated. Adsorption tests to evaluate the effect of pH and contact time were performed to obtain optimized parameters for the isotherms. In the isotherms, two adsorbents and 7 concentrations were studied, 0.0625-3.0 mmol L-1

of Cd (II). Removal efficiency (RE) and qe (adsorption capacity) for Cd (II) in both GRSP reached a maximum at pH 7 and at 24 h, respectively. In the isotherms, RE for GRSP Org was, on average, 98%, and for GRSP LV, 94%. With increasing concentration (up to 3 mmol L-1

), RE decreases to 92 and 88%. The isothermal models tested to evaluate the GRSP-Cd interaction were from Langmuir, Freundlich, Sips and Temkin. The adsorption of Cd (II) follows the order of Sips > Freundlich > Langmuir, that is, the Sips isothermal model at room temperature is the best fit. Our hypotheses are that the mechanisms of Cd (II) adsorption by glomalin-related soil protein are electrostatic attraction and surface complexation. GRSP from tropical soils becomes an excellent alternative for Cd (II) immobilization.