Comparative electrochemical behavior of Prussian blue analogues as a host electrode for rare earth element recovery

In this paper, electrodeposited films belonging to the Prussian Blue Analogues (PBAs) family, namely, nickel-hexacyanoferrate (NiHCF) and copper-hexacyanoferrate (CuHCF), were employed as a host material for rare earth elements (REE), and the reported insertion/release study reveals a recovery capability for such valuable metals. The ion insertion/release was accomplished by adopting an electrochemically-driven process. A reversible intercalation was observed while considering both heavy and ligth rare earth elements. The amount of REEs inserted/released over the process and its kinetic evolution during the process were also studied by a chemometric approach. For CuHCF, it was seen that the intercalation of heavy rare earth elements occurs easily respect to the light ones, suggesting a possible selectivity among these ions

Hydrometallurgical Molybdenum Recovery from Spent Catalyst Using Tartaric Acid Derived from Agrifood Waste

In this study, a green and sustainable hydrometallurgical process, based on soft acid derived from agrifood waste as a byproduct, is used to recover molybdenum from selective spent oxidation catalysts for formaldehyde production. Tartaric acid recovered from winery waste is used as a leaching and chelating agent. The spent catalyst was characterized by X-ray diffraction, scanning electron microscopy, and inductively coupled plasma optical emission spectroscopy. The last term was also used to study the leaching efficiency. Under optimized conditions, a molybdenum recovery of 87.36% +/- 2.94 wt % was achieved: 1.3 M tartaric acid, 75 g/L solid-liquid ratio, and 60 min at 25 degrees C. Moreover, the leaching kinetics were also investigated using the shrinking core model, which is correlated to each step of the leaching process, including chemical reaction, product layer diffusion, and film diffusion control. The step that exhibits the best agreement with the experimental kinetic data is considered as the rate-controlling step. The proposed hydrometallurgical process was found to be simple, efficient, and environmentally friendly. Using agrifood wastes, it becomes possible to process industrial waste to recover and reintegrate expensive metals for an efficient circular economy

Electrochemical synthesis of nano-cobalt hexacyanoferrate at a sol–gel-coated electrode templated with β-cyclodextrin

The paper describes the time-dependent evolution of the electrochemical deposition of cobalt hexacyanoferrate (CoHCFe) on graphite foil electrode modified with electrochemically formed sol–gel film doped with β-cyclodextrin to impart porosity. With short-time electrodeposition, cyclic voltammetry (CV) shows a single redox couple typical of nano-sized clusters of CoHCFe, while at longer deposition times the CV’s shape evolves to the classical form of a bulk compound in which there are present two redox couples. The electrode modified with β-cyclodextrin (CD) included in the sol–gel film has an active surface that corresponds to pores created by CD stacks normal to the surface. Hence, the electrochemical formation of CoHCFe starts in these conductive pores; only at long deposition times do the clusters overlap to form moieties with the voltammetric characteristics of bulk CoHCFe

Sustainable Chromium Encapsulation: Alkali Activation Route

This article highlights recent experimental advances in the use of inorganic substances in the encapsulation of pollutants and, in particular, discusses the potential applicability and constraints of the geopolymerization process for the treatment of wastewater containing chromium. A great percentage of waste containing chromium salts is produced by the leather industry during the tannery process. Such industrial waste is in the form of liquor containing almost 40% of the initial chromium combined with many other pollutants. The stabilization/solidification (S/S) treatment of this type of waste must be combined with chromium encapsulation in an economic, environmentally friendly and efficient process to be industrially feasible. Here we present a novel process in which the wastewater is used as a component of the formulation together with a clay by-product and with the addition of NaOH pellets with the goal of a no-water plus no-waste technology approach. The final solidified “ceramic-like” material successfully immobilized the heavy metal cations as well as anions and macromolecules of surfactants, avoiding environmental damages to soil and groundwater. The article is completed by mentioning other S/S processes where wastewater has been treated and the resulting sludge encapsulated. The future of the S/S technologies in the tannery industry should progress in the direction of significantly reducing the amount of wastewater directed to the treatment plants, with associated reductions in transport and their CO2 emissions. This article intends to be a contribution in the direction of preventing waste, aligning circular economy and waste management objectives

Structure of Fe/Co/Ni Hexacyanoferrate As Probed by Multiple Edge X-Ray Absorption Spectroscopy

The structural parameters in selected cobalt and mixed cobalt/nickel hexacyanoferrates have been determined by X-ray absorption spectroscopy. The presence of two or three metals in the sample requires the use of a highly efficient multiple edge analysis. The typical structure of mixed hexacyanoferrates coupled with a suitable data analysis program, GNXAS, allow us to determine structural parameters considering a very high number of experimental points. The first data analysis of three contiguous edges (Fe, Co, and Ni K-edges), the structural parameters of which are entirely correlated, is presented. The advantages and limitations of the multiple edge approach are underlined and placed in the context of the previous studies. The CN bond length has been determined with a statistical error of few thousandths of an angstrom

Structural studies of gel-based V2O5 cathodes for rechargeable lithium batteries

The aim of the project was to investigate the structural environment of the zinc and copper doped V2O5 aerogel. In particular we were interested on the mechanism of the ion insertion onto the host by studying the \u2018site\u2019 in which the guest ion is located. This objective could be achieved by using synchrotron radiation to collect x-ray absorption (XAS) spectra, either in the XANES and EXAFS region with a suitable signal to noise ratio in order to perform a reliable data analysis