Abstract
Nowadays, solving the problem of rational, integrated use of the mined raw materials, the transition to waste-free technologies for its processing is a crucial task. The sulfuric acid technology used for the processing of apatite concentrates on a large industrial scale does not provide the associated extraction of accompanying valuable components—rare earth metals (REM). During apatite concentrate processing, rare-earth metals are affected by the technology-related dispersion, being distributed between the insoluble leaching residue and phosphoric acid solution sent to the production of fertilizers. The necessity of a cost-effective method development for the extraction of rare earth metals is quite obvious already in connection with the indicated significance of the problem. Phosphoric acid solutions that simulate the composition of industrial phosphoric acid solutions of the following composition 4.5 mol/L H3PO4, 0.19 mol/L H2SO4 and 0.10–0.12% REM were selected as the object of research. The extraction of rare earth metals was carried out using polymers containing a fixed layer of an extractant—di-2-ethylhexylphosphoric acid (D2EHPA). Fixed layer was obtained by impregnation-saturation (solvent-impregnated resin (SIR)) or by the introduction of an extractant at the stage of polymer matrix synthesis (extractant-resin extraction (ERE)). The work determined the thermodynamic and technological characteristics of the solid-phase extraction of rare earth elements from phosphoric acid solutions with polymers impregnated with D2EHPA and containing a rigidly fixed extractant in a styrene-divinylbenzene resin matrix. The possibility of effective multiple use of polymeric resins containing D2EHPA, regenerated with a solution of 1 mol/L sodium citrate, was revealed.
Highlights
The most demanded heavy lanthanides group mainly goes into solutions, which determines the expediency of organizing the associated extraction of rare-earth metals
The results of this study demonstrate the potential of using diethylenetriaminepentaacetic acid (DTPA)-functionalized silica particles in the chromatographic process for the recovery and separation of rare earth elements (REE) from waste as an environmentally friendly alternative to standard processes
Comparison of the IR spectra of organic phases impregnated (SIR) and immobilized (ERE) into the polymer matrix shows the polarization of the P=O bond during the rareearth metals extraction, due to the participation of the di-2-ethylhexylphosphoric acid (D2EHPA) phosphoryl group, which is weakly fixed in the polymer matrix
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. During the apatite concentrates processing by the most common sulfuric acid technology, 20–40% of REM are transferred into solutions of phosphoric acid, which is used for the production of phosphoric fertilizers In this case, the most demanded heavy lanthanides group mainly goes into solutions, which determines the expediency of organizing the associated extraction of rare-earth metals. The use of sorbents modified with substances exhibiting a high capability to form complex compounds with rare earth metals in aqueous media is ineffective in phosphoric acid solutions. This work was carried out in order to reveal the thermodynamic and technological features of solid-phase extraction of rare-earth metals and its difference from liquid extraction and the process characteristics of extracting lanthanides of light, medium and heavy groups from phosphoric acid by polymeric materials containing the organophosphorus extractant D2EHPA
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