Removal of hexavalent chromium from electroplating wastewaters using marine macroalga Pelvetia canaliculata as natural electron donor

This paper reports a treatment strategy for an electroplating wastewater containing high amounts of hexavalent and trivalent chromium and zinc, and residual iron. The brown macroalga Pelvetia canaliculata was used as a natural electron donor for the reduction of Cr(VI) to Cr(III) at acidic pH, and as a natural cation exchanger for zinc, iron and trivalent chromium sequestration. The strategy adopted for the wastewater treatment involves: (i) the reduction of Cr(VI) to Cr(III) using the macroalga as electron donor; (ii) trivalent chromium, zinc and iron precipitation at pH 8.5; and (iii) the removal of residual zinc ions (13 mg/L) by cation exchange at pH 8.5, using the negatively charged functional groups present at the surface of P. canaliculata. The Cr(VI) reduction was evaluated as a function of the biomass and Cr(VI) concentration, pH and temperature. The reaction was promoted through biomass oxidation in acidic medium. The Cr(VI) reduction capacities of raw and protonated P. canaliculata were around 1.8 and 2.3 mmol/g and the values for the Cr (III) uptake capacity of the oxidized biomass were 0.8 and 1.9 mmol/g, respectively. The results suggest that the oxidation of the biomass during Cr(VI) reduction generates new negatively charged active sites for cation binding. The continuous treatment of the wastewater containing Cr(VI) was evaluated in a column packed with raw P. canaliculata, and a maximum Cr(VI) reduction capacity of around 2.1 mmol/g was achieved. After the Cr(VI) removal step, 100% (below the detection limit) and 95% of the remaining trivalent chromium and zinc, respectively, can be eliminated by precipitation at pH 8.5

Marine macroalgae Pelvetia canaliculata (Phaeophyceae) as a natural cation exchanger for cadmium and lead ions separation in aqueous solutions

This work aims to add value to marine brown macro-algae Pelvetia canaliculata (Linnaeus) Decaisne and Thuret through its use as cation exchanger for separation and recovery of cadmium and lead ions in aqueous solution, as a cost effective and environmental friendly process. Raw algae was established as a cation exchanger, in which cadmium and lead ions present in the solution exchange with Na+, K+, Ca2+ and Mg2+, bound to the negatively functional groups existing on the algae surface, with a stoichiometric ratio of 1:1 between ions of the same charge and 2:1 between monovalent and divalent ions. Batch equilibrium and kinetic experiments were conducted at different pH values using Na-loaded algae. The main functional groups present on the surface of the algae responsible for binding metals, as determined by Fourier Transform Infrared (FTIR) analysis, are weakly acidic carboxylic groups and strongly acidic sulfonic groups. Considering the potentiometric titration and biomass esterification results, the amount of sulfonic and carboxylic groups is 1.0 mmol/g and 1.5 mmol/g, respectively, which is in agreement with the total amount of Na+ present at the surface of Na-loaded biomass (2.5 mEq/g) and total amount of light metals present at the surface of raw biomass (2.5 mEq/g). Maximum biosorption capacity of Pb2+ at pH 4.0 was 1.25 mmol/g (2.5 mEq/g; 259 mg/g) and for Cd2+ at pH 4.5 was 1.25 mmol/g (2.5 mEq/g; 140 mg/g). The mass action law for the ternary mixture was able to predict the equilibrium data, with the selectivity coefficients alpha(Cd)(Na) = 337 and alpha(Pb)(Na) = 941 for carboxylic and alpha(Cd)(Na) = 38 and alpha(Pb)(Na) = 1695 for sulfonic groups, revealing a higher affinity of the biomass towards lead ions. A mass transfer model, considering equilibrium given by the mass action law, and a linear driving force model for intraparticle diffusion, was able to fit well the batch kinetic data

Use of cork granules as an effective sustainable material to clean-up spills of crude oil and derivatives

The use of cork granules for cleaning up crude oil or oil derivative spills and further oil recovery appears as a promising option due to their unique properties, which allow a high oil sorption capacity, low water pickup and excellent reuse. The present work reports the effect of oil viscosity on cork sorption capacity by using five types of oils (lubricating oil, 5.7 goil gcork-1; heavy oil, 4.2 goil gcork-1; light oil, 3.0 goil gcork-1; biodiesel, 2.6 goil gcork-1; and diesel, 2.0 goil gcork-1). The cork sorption capacity for light petroleum was also evaluated as a function of temperature and sorbent particle size. Additionally, improvements on oil recovery from cork sorbents by a mechanical compression process have been achieved as a result of a design of experiments (DOE) using the response surface methodology. Such statistical technique provided remarkable results in terms of cork sorbent reusability, as the oil sorption capacity was preserved after 30 cycles of sorption-squeezing steps. The sorbed oils could be removed from the sorbent surface, collected simply by squeezing the cork granules and further reused. The best operational region yielded near 80% oil recovery, using a cork mass of 8.85 g (particle size of 2.0-4.0 mm) loaded with 43.5 mL of lubricating oil, at 5.4 bar, utilising two compressions with a duration of 2 min each. Graphical abstract.publishe

Copper‑exchanged Y zeolites for gasoline deep‑desulfurization

Adsorptive desulfurization is one of the most efficient methods to remove recalcitrant sulfur compounds from transportation fuels. Two π-complexation-based sorbents were studied for desulfurization of synthetic gasoline. The sorbents were obtained by ion exchanging Y zeolites with copper cations using different techniques, which includes liquid phase ion exchange (CuY1) and vapor phase ion exchange (CuY2). Preliminary kinetic and equilibrium experiments for sulfur adsorption in batch system showed that CuY1 has the greatest desulfurization capacity and selectivity. The best adsorbent, CuY1 pellet, had a dynamic adsorption and equilibrium capacity of 2.97 and 4.14 mg S/g for fixed bed column assays, respectively. Experimental data obtained to batch reactor and packed bed column have been interpreted by means of a pore diffusion model in which the mass balance to the pellets are emphasized. The model proposed was able to fit well to the experimental data. After the first thermal regeneration, the copper ion-exchanged zeolite presented a maximum recovery of 91.5%. The copper-exchanged zeolite (in pellet form) has shown good uptake rate and regenerability for desulfurization of synthetic gasoline.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)#2019/07659-