Removal of refractory organics from saline concentrate produced by electrodialysis in petroleum industry using bone char

Development of novel sericin and alginate-based biosorbents for precious metal removal from wastewater

In this study, two novel low water-soluble sericin and alginate-based biosorbents were successfully developed for precious metal removal from wastewater: sericin and alginate particles chemically crosslinked by proantocyanidins (SAPAs) and sericin, alginate and polyvinyl alcohol particles (SAPVA). The proportions of proantocynidins (PAs) or polyvinyl alcohol (PVA) added to sericin (2.5% w/v) and alginate (2.0% w/v) blend were 0.5, 1.5, 2.5 and 3.5% w/v. Among these concentrations, particles produced with 0.5% w/v of PVA or 2.5% w/v of PAs presented the lowest water solubility percentages (3.74 ± 0.05 and 3.56 ± 0.21%, respectively) and the following metallic affinity order: AuCl₄^- > PdCl₄^2- > PtCl₆^2- > Ag⁺. Then, gold biosorption kinetics by SAPAs was evaluated at three gold initial concentrations (72.88, 187.12, and 273.79 mg/L), and its performance was compared to activated carbon adsorbent uptake. The data modeling revealed that the process follows pseudo-first-order kinetics and is mainly controlled by external diffusion. SAPAs before and after gold biosorption (SAPAs-gold) were characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, optical microscopy, helium pycnometry, mercury porosimetry, N₂ physisorption, and Fourier-transform infrared spectroscopy.

Use of bentonite calcined clay as an adsorbent: equilibrium and thermodynamic study of Rhodamine B adsorption in aqueous solution

The Rhodamine B adsorption was realized in batch using calcined bentonite clay. The effects of Rhodamine B initial concentration, pH, and temperature were evaluated and the conditions where the adsorption was favored were in 500 mg L^-1, pH 3, and 35 °C. The equilibrium isotherms studied were from Langmuir and Freundlich. The coefficients of determination (R² > 0.99) were found to confirm the best fitted to Langmuir isotherm, with a monolayer adsorption capacity (q_max) of 552.49 mg g^-1. The kinetic data agreed well with the pseudo-second order model (R² > 0.99). The in natura and calcined clay were characterized by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ physisorption (BET), and scanning electron microscopy (SEM). Thermodynamic parameters including Gibbs free energy (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were calculated to estimate the nature of Rhodamine B adsorption in clay. The results suggested that the adsorption was endothermic and spontaneous, with the enthalpy adsorption increasing with the increase of temperature. Therefore, calcined bentonite can be used as an efficient adsorbent for discoloration of large volume of residual water, presenting low-cost and high adsorptive capacity.