Effect of Sulfuric Acid Baking and Caustic Digestion on Enhancing the Recovery of Rare Earth Elements from a Refractory Ore

Rina Kim,Sugyeong Lee,Ho-Sung Yoon,Chul-Joo Kim,Kyeong Woo Chung,Jihye Kim,Jinan Jeong,Heechan Cho

doi:10.3390/min10060532

Abstract

To improve the recovery of rare earth elements (REEs) from a refractory ore, this study investigated two different chemical decomposition methods, namely sulfuric acid baking and caustic digestion, with their respective leaching processes. The studied lateritic ore contained goethite (FeOOH) as a major constituent with REEs scattered around and forming submicron grains of phosphate minerals, such as apatite and monazite. Therefore, despite the substantially high content of REEs (3.4% total rare earth oxide), the normal acidic leaching efficiency of REEs reached only 60–70%. By introducing sulfuric acid baking and caustic digestion, the REE-leaching efficiency was significantly improved. After sulfuric acid baking at 2.0 acid/solid ratio and 200 °C for 2 h, the leaching efficiency reached 97–100% in the subsequent water-leaching. When the ore was digested with a solid/liquid ratio of 100 g/L in a 30 wt% NaOH solution at 115 °C and 300 rpm for 3 h, the REE-leaching efficiency of 99–100% was attained at 80 °C using a 3.0 M HCl solution. The correlation between the REE and the Fe-leaching was determined. The improvements in REE-leaching in both methods were mostly attributed to the mineral phase and crystallinity changes of Fe-bearing minerals due to the ore pretreatments. Such findings were also supported by X-ray diffraction and scanning electron microscopy analyses.

Highlights

The rare earth elements (REEs) comprise 17 elements in the periodic table, namely the 15 lanthanide elements (La–Lu) plus Sc and Y
This study investigated the enhancement in REE recovery from a refractory ore containing 3.4% total rare earth oxide (TREO) by applying two different chemical decomposition methods followed by leaching processes, i.e., sulfuric acid baking—water-leaching and caustic digestion–acid-leaching
The REE-containing particles were scattered throughout the ore, and some of them were even trapped in other minerals such as Fe oxide, the total REE concentration was relatively high at 3.4%

Summary

Introduction

The rare earth elements (REEs) comprise 17 elements in the periodic table, namely the 15 lanthanide elements (La–Lu) plus Sc and Y. The rare earth elements (REEs) comprise 17 elements, namely the 15 lanthanide elements (La–Lu) plus Sc and Y. These 17 elements are generally divided into two groups: La–Eu (Nos. 57–63) are light REEs (LREEs), whereas Gd–Lu (Nos. 64–71) and Y (No 39) are heavy REEs (HREEs). The REEs are used in various high-tech industries, e.g., the manufacturing of computers, cell phones, optical glasses, phosphors, hybrid cars and batteries, because of their unique electrical and magnetic properties [1,2,3,4]. More than 250 rare earth minerals have been discovered to date [1], and the representative minerals are monazite (REEPO4 ), bastnasite (REECO3 F)

Methods

Results

Conclusion