Extraction and separation of rare earth elements from hydrothermal metalliferous sediments

Abstract

Rare earth elements (REE) can be efficiently extracted from umbers, ferromanganese metalliferous sediments of the Troodos ophiolite (Cyprus) by simple leaching and selective precipitation, without accumulation of radioactive by-products. Umbers are dominantly composed of amorphous Fe and Mn oxides with minor goethite, quartz and zeolites, and contain 350-500 mg.kg-1 of rare earth elements and yttrium (REY), 200 times lower than many of the major REY source ores. To compensate for relatively low grades, a cost-effective extraction process was developed that utilises a weak lixiviant concentration (0.1-1.5 N) and short reaction times (5 min to 11 h). Acid solutions recover 70-85% of the initial sample REY content even at 20 °C. By contrast, extraction using ionic solutions of NaCl and ammonium sulphate proved ineffective. Acid recoveries of REY increase by nearly 10% at 70 °C and the use of different acids (HCl, HNO3, H2SO4) yields comparable results. The main impurities in the leachate include Ca and Na at even the weakest acid concentration (0.1 N). However, two-step leaching method greatly reduces concentrations of impurities in the REY-rich liquor, although with REY losses approaching 20%. Purification of the leach liquor via selective precipitation of REY as an oxalate is highly efficient although pH dependent. With maximum REY precipitation (96-99%) occurring between pH 1 and 2, the precise adjustment of pH allows separation of REY from other precipitating impurities (Ca). The maximum purity of the precipitate is achieved at pH 1.1 (> 65%). Strong and consistent fractionation along the lanthanide series observed during the precipitation experiments has been successfully explained using a speciation modelling software (PHREEQC). The uptake of REY by oxalate in the experiments closely follows the bell-shape distribution of REY-oxalate solid complexes stability constant (-log β (RE2Ox3.nH2O)) replicating the fractionation trends observed at pH < 1.1. In addition, the modelling demonstrates that at equivalent REE concentration in solution, oxalate precipitates fractionate REY in the following order: middle REE > light REE >> heavy REE. This ordering and the variable degrees of uptake reflects the interplay of aqueous REY-oxalate complexes (log HOxβ1, Oxβ1 and Oxβ2) with the natural fractionation induced by solid REY-oxalate stability constant distribution. Overall, the combined leaching process and selective oxalate precipitation produces a total enrichment factor ranging between 1400 and 2400 for REY from the sample to the oxalate precipitate in a simple twostep process forming a high-purity end-product of mixed REY.

Leaching and Recovery of Rare-Earth Elements from Neodymium Magnet Waste Using Organic Acids

“…Moreover, when using strong mineral acids, evolution of poisonous gasses is often a problem. Using organic acids or significantly more diluted mineral acids [21] could have advantages in this regard because of easier handling, less poisonous gas evolution due to lower acidities, and much easier degradability. Some researchers even claim that a more sustainable REE-leaching process could be achieved using some bacteria like Shewanella putrefaciens [22].…”

Sustainable Hydrometallurgical Recovery of Valuable Elements from Spent Nickel–Metal Hydride HEV Batteries

“…Many hydrometallurgical processes start with an almost complete leaching of the batteries [12,[17][18][19][20][21][22][23][24]. For example, leaching by sulfuric acid and hydrochloric acid has been investigated in different studies [17,18,[20][21][22][25][26][27]. The rare earth elements present in metallic form are oxidized into trivalent ions in contact with hydrochloric acid and sulfuric acid according to the following reactions: REE (s) + 3H 2 SO 4 + 1.5O 2 (g) = REE +3 + 3SO 4 −2 + 3H 2 O…”

“…In this study the temperature was kept constant and acid was dosed during the leaching to also keep the pH constant. For further processing, precipitation and solvent extraction can be used to recover Co, Ni, and the rare earth elements [17,25,[27][28][29][30][31][32][33]. The recovery of nickel and cobalt has an important role for the economics of the recycling processes.…”

Experiments on Rare-Earth Element Extractions from Umber Ores for Optimizing the Grinding Process

“…In this study, hydrochloric acid and sulfuric acid were used as a leachate solution with reference to previous studies on REE leaching for deep-sea sediments [37,38] and umber samples [9]. The acid concentration was set to 0.5 mol/L for hydrochloric acid and 0.25 mol/L for sulfuric acid, and the leaching temperature was set to 25 • C. The leaching time was set to 5, 30, 180, 720, and 1440 min.…”

“…Umber lies on basaltic lavas, some of which are accompanied by cherts and limestone at the top [34]. Although umber is largely exposed on land, its thickness is often less than 1 m [9,34]. This sample exhibited a homogenous brown color.…”