Ultrasound-assisted extraction of rare-earth elements from carbonatite rocks

Lisarb O Diehl; Thais L Gatiboni; Paola A Mello; Edson I Muller; Fabio A Duarte; Erico M M Flores

doi:10.1016/j.ultsonch.2017.04.012

Ultrasound-assisted extraction of rare-earth elements from carbonatite rocks

Ultrason Sonochem. 2018 Jan;40(Pt B):24-29. doi: 10.1016/j.ultsonch.2017.04.012. Epub 2017 Apr 12.

Authors

Lisarb O Diehl¹, Thais L Gatiboni¹, Paola A Mello¹, Edson I Muller¹, Fabio A Duarte¹, Erico M M Flores²

Affiliations

¹ Departamento de Química, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brazil.
² Departamento de Química, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brazil. Electronic address: ericommf@gmail.com.

PMID: 28434880
DOI: 10.1016/j.ultsonch.2017.04.012

Abstract

In view of the increasing demand for rare-earth elements (REE) in many areas of high technology, alternative methods for the extraction of these elements have been developed. In this work, a process based on the use of ultrasound for the extraction of REE from carbonatite (an igneous rock) is proposed to avoid the use of concentrated reagents, high temperature and excessive extraction time. In this pioneer work for REE extraction from carbonatite rocks in a preliminary investigation, ultrasonic baths, cup horn systems or ultrasound probes operating at different frequencies and power were evaluated. In addition, the power released to the extraction medium and the ultrasound amplitude were also investigated and the temperature and carbonatite mass/volume of extraction solution ratio were optimized to 70°C and 20mg/mL, respectively. Better extraction efficiencies (82%) were obtained employing an ultrasound probe operating at 20kHz for 15min, ultrasound amplitude of 40% (692Wdm^-3) and using a diluted extraction solution (3% v/v HNO₃+2% v/v HCl). It is important to mention that high extraction efficiency was obtained even using a diluted acid mixture and relatively low temperature in comparison to conventional extraction methods for REE. A comparison of results with those obtained by mechanical stirring (500rpm) using the same conditions (time, temperature and extraction solution) was carried out, showing that the use of ultrasound increased the extraction efficiency up to 35%. Therefore, the proposed ultrasound-assisted procedure can be considered as a suitable alternative for high efficiency extraction of REE from carbonatite rocks.

Keywords: Analysis of carbonatite rocks; Carbonatite; Green extraction; Process intensification; Rare-earth elements extraction; Ultrasound extraction.