A Hybrid Experimental and Theoretical Approach to Optimize Recovery of Rare Earth Elements from Acid Mine Drainage Precipitates by Oxalic Acid Precipitation

Abstract

The development of processing techniques for the extraction of rare earth elements and critical minerals (REE/CM) from acid mine drainage precipitates (AMDp) has attracted increased interest in recent years. Processes under development often utilize a standard hydrometallurgical approach that includes leaching and solvent extraction followed by oxalic acid precipitation and calcination to produce a final rare earth oxide product. Impurities such as Ca, Al, Mn, Fe and Mg can be detrimental in the oxalate precipitation step and a survey of the literature showed limited data pertaining to the REE precipitation efficiency in solutions with high impurity concentrations. As such, a systematic laboratory-scale precipitation study was performed on a strip solution generated by the acid leaching and solvent extraction of an AMDp feedstock to identify the optimal processing conditions that maximize REE precipitation efficiency and product purity while minimizing the oxalic acid dosage. Given the unique chemical characteristics of AMDp, the feed solution utilized in this study contained a moderate concentration of REEs (440 mg/L) as well a significant concentration (>7,000 mg/L total) of non-REE contaminants such as Ca, Al, Mn, Fe and Mg. Initially, a theoretical basis for the required oxalic acid dose, optimal pH and predicted precipitation efficiency was established by solution equilibrium calculations. Following the solution chemistry calculations, bench-scale precipitation experiments were conducted and these test results indicate that a pH of 1.5 to 2, a reaction time of more than 2 h and an oxalic acid dosage of 30 to 40 g/L optimized the REEs recovery of at ~95% to nearly 100% for individual REE species. The test results validated the optimal pH predicted by the solution chemistry calculations (1.5 to 5); however, the predicted dosage needed for complete REE recovery (10 g/L) was significantly lower than the experimentally-determined dosage of 30 to 40 g/L. The reason for this discrepancy was determined to be due to the large concentration of impurities and large number of potential metal complexes that cause inaccuracies in the solution equilibrium calculations. Based on these findings, a hybrid experimental and theoretical approach is proposed for future oxalic acid precipitation optimization studies.

Optimization of Iron Removal in the Recovery of Rare-Earth Elements from Coal Fly Ash Using a Recyclable Ionic Liquid

“…In our previous study on [Hbet]­[Tf 2 N], we found that iron is a significant contaminant . Moreover, Fe has been described as a dominant contaminant in the literature investigating other extraction methods for REE recovery from CFA, as well as from other REE-containing materials, including NdFeB magnets, ,− acid mine drainage sludge, bauxite mining residues, and ores of monazite, bastnasite, and xenotime. , The ubiquity of Fe across materials and its interesting behavior with [Hbet]­[Tf 2 N] made it the top priority for optimization.…”

Extraction of platinum group metals from catalytic converters

“…Various techniques are applied to extract PGMs from catalytic converters [ 114 , [125] , [126] , [127] , [128] ], including pyrometallurgical and hydrometallurgical methods with subsequent element recovery [ 55 , 106 , 110 , [129] , [130] , [131] , [132] , [133] , [134] , [135] , [136] , [137] , [138] ], biological methods [ 139 , 140 ], leaching methods [ 109 , [141] , [142] , [143] , [144] , [145] , [146] ], solvometallurgical methods [ [147] , [148] , [149] , [150] , [151] ], molecular recognition technology [ [152] , [153] , [154] , [155] , [156] , [157] ] and biometallurgical methods [ [158] , [159] , [160] , [161] , [162] , [163] , [164] , [165] , [166] ]. These methods collectively ensure effective and eco-friendly processing of PGMs.…”

“…In a study [ 166 ] an experimental investigation aimed at recovering platinum via the bioleaching method was conducted. Within this study, various bioleaching approaches were explored, encompassing both direct (including one-step and two-step processes) and indirect methods (involving spent medium bioleaching with and without pH control).…”

Selective Capacitive Recovery of Rare-Earth Ions from Wastewater over Phosphorus-Modified TiO2 Cathodes via an Electro-Adsorption Process

“…In recent years, various traditional technologies have been applied for the recovery of REIs from wastewater, including ion exchange, − chemical precipitation, − membrane separation, − and adsorption. − For example, Heres et al . reported that Amberlite IRC-747 and Lewatit TP-260 ion exchange resins showed excellent adsorption properties (1.8 mequiv/g) for dysprosium (Dy), lanthanum (La), gadolinium (Gd), erbium (Er), neodymium (Nd), and ytterbium (Yb).…”