Coal bottom ash processing for capitalization according to circular economy concept

•Coal bottom ash processing for capitalization according to circular economy concept.•Metals recovery by sequential precipitation at different pH.•Metals recovery by successive microemulsion assisted extractions.•Metals recycle as their oxides synthesized into microemulsion templates.•Bottom ash residue recycle as raw materials for different industrial applications. This work reports the semiquantitative laboratory chemical procedures developed for some Rare Earth Elements (REE) extraction and concentration from coal bottom ash (BA), including recycling the recovered valuable components. This preliminary assessment applied in case of 25 coal BA samples of Ceplea Valley landfill of Romania describes the chemical methods by using digestion with nitric acid coupled with microemulsion assisted extraction procedure. The enrichment of REE by concentrated nitric acid followed by water washing proved to be an adequate approach since water recovers 29.42% of metals comparing to that extracted by the total phase (ac + aq). The REE concentration process achieved by precipitation with NaOH, at different pH values, shows to be almost completely in the fraction at pH ≈ 0 and 3. The statistical outlook coefficient Coutl shows that evaluation of REE concentration in acid/aqueous solution falls into the “promising” field for their recovery by chemical procedures. Optimal microextraction was obtained by coupling microemulsion Winsor II ternary system consisting in Brij 30/AcOEt:AcOBu/metal ions solution, with citric acid as complexing agent. Results confirm that recovery of lanthanides as nanoparticles from microemulsion system yields over 85%. Optical characterization of oxide nanoparticles suggested applications such as for energy efficient buildings, photo-catalysts for water remediation or thin films for photonic optical devices. The ash residue can be also recycled as an alternative raw material for building materials production.