Industrial waste such as metal hydroxide sludge (in natura and calcined) from galvanic bath was evaluated as an adsorbent in the removal of brilliant blue synthetic dye (NB 180) in aqueous solution. The samples were characterised using X-ray fluorescence analysis (XRF), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), as well as the specific surface area (BET) and the point of zero charge (pHZCP). The effects of the conditions in relation to pH and adsorbent dosage were also investigated. For the conditions of 5 g.L-1 and pH of 4, the sludge in natura (LG-IN) reached equilibrium after 60 min, removing 78% of NB 180 dye, while the calcined sample at a temperature of 250°C (LG-250) removed 100% of dye in solution in 30 min. The effect of calcium salts and the leaching study showed that the presence of (Ca2+) ions in solution and metal oxides/hydroxides are the main factors responsible for the removal of colour. As for the study of kinetics and adsorption equilibrium, the experimental data were better adjusted to the pseudo-second order models and Freundlich model, respectively. The parameters of the kinetics, equilibrium and intraparticle diffusion models demonstrated a better performance of the sample LG-250 (qe = 4.09 mg.g-1), when compared to the sample LG-IN (qe = 2.76 mg.g-1). These results demonstrated that metal hydroxide sludge can be reused and applied in dye removal processes for the treatment of textile effluent.
Keywords: Adsorption; brilliant blue dye; galvanic sludge; metal hydroxide sludge; residue.