Enhanced removal of rare earth elements from aqueous media: exploring the potential of AM-3 and AM-4 titanosilicates.

This study investigates the impact of three key variables on the performance of nanoporous AM-3 and layered AM-4 titanosilicates in removing nine REEs (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, and Dy) from natural mineral water and identifies optimal operational conditions using Response Surface Methodology (RSM). The experimental conditions were determined by a Box-Behnken Design of 3 factors-3 levels (pH 4, 6, and 8; sorbent dose 20, 100, and 180 mg/L; and element concentration 1, 3, and 5 µmol/L). Three-dimensional response surfaces were used to assess the linear, quadratic, and interaction influences of each factor on the REEs' removal percentage. The pH was the most significant factor in the removal process using AM-3, while the sorbent dose was more important for AM-4. The results highlighted the sorbents' strong capacity for REE removal. The optimal operating conditions obtained by RSM were applied to aqueous solutions with salinity 10 (common in coastal and transitional systems) and 30 (average seawater salinity). The results showed that AM-3 has a strong potential for removing REEs in solutions with salinity 10 and 30, while AM-4 was less efficient due to competition between REEs and other ions present in the solution.

Removal of chromium(III) from contaminated waters using cobalt ferrite: how safe is remediated water to aquatic wildlife?

The release of hazardous elements by industrial effluents to aquatic ecosystems is a potential threat to the environment. Chromium (Cr) is one of the elements whose levels in several freshwater ecosystems should be reduced to promote water reuse. In recent years, magnetic materials have gained increasing interest as sorbents because of their easy removal from treated water through magnetic separation. In this study, colloidal cobalt ferrite (CoFe2O4) particles were investigated as magnetic sorbents for chromium-aqueous chemical species. The oxidative stress responses of Mytilus galloprovincialis mussels exposed to 200 µg/L of Cr, resembling remediated water, were evaluated. More than 95% of Cr was removed from contaminated solutions by CoFe2O4 aqueous suspensions at pH 6 and pH 10. The kinetics of sorption experiments were examined using pseudo-1st order, pseudo-2nd order and Elovich models to evaluate which mathematical model has a better adjustment to the experimental data. The present study revealed that the levels of Cr that remained in remediated water induced limited biochemical changes in mussels, being considered safe for aquatic systems. Overall, the use of cobalt ferrite-based sorbents may constitute a promising approach to remediate contaminated water.

Spinel-type ferrite nanoparticles for removal of arsenic(V) from water.

Spinel ferrite particles (Fe3O4, MnFe2O4, and CoFe2O4) were investigated as magnetic nanosorbents for removing arsenic from spiked water samples. The nanosorbents were collected via magnetic separation from aqueous solutions spiked with an arsenic concentration that mimics the amount of this contaminant in real water samples. This research shows that using amounts of CoFe2O4 or MnFe2O4 as low as 40 mg/L, the arsenic content in the contaminated water decreased for levels below the maximum admitted value by the World Health Organization for drinking waters (10 µg/L). Moreover, these magnetic nanosorbents also showed good performance for As(V) sorption, when applied to aqueous matrices with variable ionic strength and in the mixtures of other several hazardous contaminants. The good performance observed for the MnFe2O4 and CoFe2O4 ferrites contrasts with the one observed for Fe3O4 nanosorbent, whose efficiency is lower in the removal of As(V) from water, nevertheless increased with the presence of other elements in solution.

Recovery of Rare Earth Elements by Carbon-Based Nanomaterials-A Review.

Modern societies depend strongly on electronic and electric equipment (EEE) which has a side effect result on the large production of electronic wastes (e-waste). This has been regarded as a worldwide issue, because of its environmental impact-namely due to non-adequate treatment and storage limitations. In particular, EEE is dependent on the availability of rare earth elements (REEs), considered as the "vitamins" of modern industry, due to their crucial role in the development of new cutting-edge technologies. High demand and limited resources of REEs in Europe, combined with potential environmental problems, enforce the development of innovative low-cost techniques and materials to recover these elements from e-waste and wastewaters. In this context, sorption methods have shown advantages to pre-concentrate REEs from wastewaters and several studies have reported the use of diverse nanomaterials for these purposes, although mostly describing the sorption of REEs from synthetic and mono-elemental solutions at unrealistic metal concentrations. This review is a one-stop-reference by bringing together recent research works in the scope of the application of carbon nanomaterials for the recovery of REEs from water.