Sustainable hydrophobic terpene-based eutectic solvents for the extraction and separation of metals

Abstract

a Sustainable hydrophobic eutectic solvents, composed of low-priced and biodegradable terpenes and fatty acids, were used for the extraction and separation of Cu(II) from other transition metals in mildly acidic solutions. Multiple parameters were evaluated for metal extraction and the hydrophobic eutectic solvent was successfully recovered and reused.Metals represent an inherent source of both economic value and toxicity, with their consumption projected to increase in line with global economic standards. Furthermore, the starting compounds are biodegradable and approved for human consumption by various food and drug agencies, turning the resulting HES of interest for a wide range of industries. In this work, sustainable HES based on menthol or its aromatic counterpart thymol combined with long chain carboxylic acids (C n H (2n+1) OOH; n = 8, 10,12,14, 16, 18) (Fig. S1 in the ESI †), are evaluated for the extraction of Cu(II) and its separation from other transition metals, namely Co(II) and Ni(II). The solid-liquid phase diagrams of these HES were previously reported by us along with their physico-chemical properties at compositions close to the eutectic.10 These are summarised in

Quest for Green‐Solvent Design: From Hydrophilic to Hydrophobic (Deep) Eutectic Solvents

“…Contrary to hydrophilic DESs, hydrophobic (D)ESs exhibit similar and lower densitiest han water,v arying between 0.889 and 0.93 depending on the components.T he highest densities were observed for the thymol family ( % 0.93 gcm À3 ). [8] For all families of hydrophobic (D)ESs, density decreases with the increase of the alkyl chains, regardless of whether they are on HBD or HBA. Moreover,asignificant effect can be observedf or DESs containing as odium salt as HBAi nsteado fi ts homologous fatty acid, leading to alargeincrease in density values.…”

“…With regard to hydrophobic ESs,M arrucho's group [17a] proposed the first hydrophobic ES based on natural renewabler esourcesb yc ombining dl-menthol ands everaln atural carboxylic acids. In the same direction, Coutinho's group [8] proposed naturalh ydrophobic ESs based on terpenoids (l(À)-menthol and thymol) combined with severalc arboxylic acids. Other hydrophobic ESs based on lidocaine and decanoic acid at several molar ratios were also proposed.…”

“…Comparison of solid-liquid phase diagrams of aD ES composed of sodium dodecanoatea nd decanoic acid (* NaC 12 /C 10 ) [7] and an ES composed of an atural compound, l-menthol and decanoic acid (& l(À)-menthol/C 10 ). [8] The data refers to the liquid-to-solid-liquid phase transition. The linesare meant to guidet he eye.…”

“…The selectivee xtraction and separation of Cu II from other transition metals in mildly acidic aqueous solutionsu sing all natural hydrophobic (D)ESs based on low-price and biodegradable terpenes and fatty acids was also reported. [8] Furthermore, the hydrophobic (D)ESs could be successfully recovered and recycled using selected hydrophilic DESs. Persistent micropollutants,s uch as pesticides from the neonicotinoids family [9] and bisphenol-A (a plasticizer present in water bottles and simultaneously acting as an endocrine disruptor), [19] were successfully extracted using all natural hydrophobic (D)ESs with extraction efficiencies around7 0% and more than 90 %, respectively.R ecently,D ietz et al [16] reported the selectives eparation of furfural and hydroxymethylfurfural from an aqueous solution using as upported liquid membrane based on hydrophobic (D)ESs.…”

Electrodialytic removal of tungsten and arsenic from secondary mine resources — Deep eutectic solvents enhancement

“…Deep eutectic solvents (DES) have been considered the solvents of the XXI century, having successful results in the extraction of metals from various sources (Abbott et al, 2017;2011;Schaeffer et al, 2018;Söldner et al, 2019;Su et al, 2018). DES are now a feasible option for scale-up purposes, since they are composed by inexpensive and abundant raw materials, and their formulations are simple and reproducible (Smith et al, 2014;Zhang et al, 2012).…”