Sequential valorisation of Galdieria daedala biomass for C-phycocyanin extraction and rare earth elements recovery from waste of electric and electronic equipment leachates

Rare Earth Elements (REEs) recovery from Waste Electrical and Electronic Equipment (WEEE) requires sustainable alternatives to conventional, energy-intensive extraction processes. This study proposes an integrated biorefinery strategy based on the extremophilic red microalga Galdieria daedala for sequential C-phycocyanin (C-PC) extraction and subsequent REEs recovery from fluorescent-lamp leachates. Freeze-dried whole-cell biomass was used to assess biosorption potential and binding-site behaviour, whereas post-extraction cell debris was evaluated as a residual biosorbent in WEEE-derived leachates. Metal uptake was quantified by ICP-MS. At the highest tested leachate concentration (500 mg L −1 ), whole-cell biomass reached maximum uptake values of 320.6 ± 3.5 μmol g −1 for Y, 16.8 ± 0.1 μmol g −1 for Eu, and 2.90 ± 0.07 μmol g −1 for Ce. Binding-site analysis under sub-saturating conditions indicated element-specific interactions, showing that uptake depended not only on metal abundance in solution but also on apparent metal-specific surface interactions and competitive site occupation.. C-PC extraction yielded 25.7 ± 1.6 mg g −1 dry biomass, corresponding to 2.6 ± 0.1% dry weight, with a purity ratio of 2.4 ± 0.1. In time-course assays at 500 mg L −1 , post-extraction debris reached 102.3 ± 2.4 μmol g −1 Y after 3 min, while freeze-dried biomass reached 89.8 ± 8.0 μmol g −1 after 60 min, indicating retention of biosorption functionality after pigment extraction. Overall, these results demonstrate the sequential valorisation of G. daedala biomass for high-value bioproduct production and low-impact recovery of secondary critical raw materials from WEEE.