Algal sorbents and prospects for their application in the sustainable recovery of rare earth elements from E-waste

Abstract

Efficient and sustainable secondary sourcing of Rare-Earth Elements (REE) is essential to counter supply bottlenecks and the impacts associated with primary mining. Recycled electronic waste (E-waste) is considered a promising REE source and hydrometallurgical methods followed by chemical separation techniques (usually solvent extraction) have been successfully applied to these wastes with high REE yields. However, the generation of acidic and organic waste streams is considered unsustainable and has led to the search for “greener” approaches. Sorption-based technologies using biomass such as bacteria, fungi and algae have been developed to sustainably recover REE from e-waste. Algae sorbents in particular have experienced growing research interest in recent years. Despite its high potential, sorption efficiency is strongly influenced by sorbent-specific parameters such as biomass type and state (fresh/dried, pre-treatment, functionalization) as well as solution parameters such as pH, REE concentration, and matrix complexity (ionic strength and competing ions). This review highlights differences in experimental conditions among published algal-based REE sorption studies and their impact on sorption efficiency. Since research into algal sorbents for REE recovery from real wastes is still in its infancy, aspects such as the economic viability of a realistic application are still unexplored. However, it has been proposed to integrate REE recovery into an algal biorefinery concept to increase the economics of the process (by providing a range of additional products), but also in the prospect of achieving carbon neutrality (as large-scale algae cultivation can act as a CO2 sink). Graphical abstract

Review of Methods for Obtaining Rare Earth Elements from Recycling and Their Impact on the Environment and Human Health

“…Despite these advantages, certain pyrometallurgical processes still necessitate chemical inputs and result in waste generation. While pyrometallurgical recycling enables scalability and involves fewer chemicals (flame retardants, furans, and phenolics) [16]), it does release harmful gases like dioxins, carbon dioxide, and volatile metals such as mercury [91]. Cui and Zhang demonstrated that polychlorinated biphenyls (PCBs) can generate a mixed oxide, primarily containing lead (Pb) and zinc (Zn), as slag through a top-blown reactor.…”

“…Various purification processes can be employed to recover precious metals present in the leachates. Solvent extraction, chemical precipitation, ion exchange, adsorption, electrochemical deposition, and more innovative eutectic freeze crystallization are among the most common separation methods [91,98]. Although precipitation and ionic liquid methods are highly efficient for metal recovery, the use of precipitation often results in the generation of secondary sludge, which can lead to pollution [40].…”

“…Although precipitation and ionic liquid methods are highly efficient for metal recovery, the use of precipitation often results in the generation of secondary sludge, which can lead to pollution [40]. Consequently, these methods face challenges hindering their widespread industrial application [91]. Generally, ion exchange and solvent extraction, although more intricate and costly, are employed for obtaining pure individual REE products, whereas selective precipitation, which is more cost-effective, is preferred for generating mixed REE products [117].…”

“…Utilizing acid leaching is a commonly employed method to extract REEs from diverse sources. Commonly used leaching agents include hydrochloric acid (HCl), nitric acid (HNO 3 ), sulfuric acid (H 2 SO 4 ), aqua regia (3 HCl: HNO 3 ), hydrogen peroxide, cyanide, iodine, thiourea, halides, and thiosulphate, among others [91]. The effectiveness of acid leaching may vary due to numerous factors, including the acid type and concentration, the mineral composition of the source material, and operational variables.…”

An Insight into Rees Recovery from Spent Fluorescent Lamps: Evaluation of the Affinity of an Nh4-13x Zeolite Towards CE, La, EU and Y

“…Solvent extraction, or liquid-liquid extraction is highly used and is commercially exploited to produce high purity single REEs; however, it is an inefficient, labour-intensive and time-consuming method (Opare et al, 2021). Adsorption of REEs can also be carried out with either organic or inorganic compounds, depending on the element considered; the effectiveness of this method is strongly related to contact time, adsorbent dose, initial concentration, solution pH and temperature (Anastopoulos et al, 2016;Iannicelli-Zubiani et al, 2015;Pinto et al, 2023). Ion exchange is another widely exploited method that is generally carried out exploiting different resins (Chen et al, 2017;Hérès et al, 2018) and MOFs.…”