Adsorção de metais pesados de efluente de fosfatização industrial usando argila bentonita e casca de soja

Abstract

In the present work heavy metals removal from real phosphate effluent, a stage of the industrial painting process, was investigated. As adsorbents, bentonite clay and soybean hulls without previous treatments were evaluated. Initially, the effluent was characterized regarding the initial concentration of metals and COD. The characterization of the adsorbents included BET, FTIR, XRD and pHPZC analyses. Afterwards, the influence of the variables adsorbent dosage (0.5, 1.0 and 5.0 g), pH (3 and 4) and temperature (25, 40 and 50°C) was evaluated, the equilibrium isotherms were constructed, the adsorption kinetics were studied and the definition of the mathematical models that best described the process was carried out. The initial metals concentration in the effluent was 953.85 mg/L (Zn), 818.6 mg/L (Ni) and 343.45 mg/L (Mn). The average Sauter diameter of the adsorbents was 63.5 μm and 0.2705 mm, the BET specific surface area was 180.8504 m²/g and 0.3063 m²/g, the pHPZC found was 3.65 and 6.43 for clay and soybean hulls, respectively. As for the influencing variables, the maximum removals were with 5 g/100 mL of adsorbent for both materials tested and the highest values achieved were with soybean hulls being 16.5% (Mn), 24.5% (Ni) and 28 .6% (Zn). Increasing the temperature only resulted in increased metal removal up to 40°C when using bentonite clay as an adsorbent. Similarly, the pH variation also only influenced the removal of metals from the clay. For both adsorbents, the equilibrium isotherms revealed endothermic behavior and the maximum adsorption capacities were 14.13 mg/g (Zn), 7.80 mg/g (Mn) and 3.12 mg/g (Ni) using soybean hulls and 12.68 mg/g (Zn), 4.35 mg/g (Mn) and 3.03 mg/g (Ni) for bentonite clay. Finally, the kinetic curves grew rapidly in the first minutes and a good fit to the pseudo-first order and pseudo-second order kinetic models was found. From the results obtained, it is possible to state that both adsorbents showed potential for adsorption of heavy metals, composing a low-cost complementary effluent treatment option.