# Sustainable Ultrasound-Assisted Extraction and Recovery of Rare Earth Elements from Oil and Gas Drill Cuttings

## TL;DR

This paper explores a sustainable method to extract rare earth elements from oil and gas drill cuttings using ultrasound, achieving high recovery rates for elements like lanthanum and cerium.

## Contribution

The study introduces a sustainable ultrasound-assisted extraction method for rare earth elements from drill cuttings with high efficiency and recovery rates.

## Key findings

- Optimal extraction was achieved using 7.0 mol/L HNO3 with ultrasound at 80°C for 60 minutes.
- Extraction efficiency for lanthanum and cerium exceeded 82%, with recovery rates over 90% after precipitation.

## Abstract

Drill cuttings (DC) are mainly composed of fragmented
rocks that
are produced during the drilling of oil and natural gas wells. The
rocks and minerals present in DC are sources of several chemical elements,
including economically valuable elements, such as rare earth elements
(REEs). In this paper the sustainability and advantages of the ultrasound-assisted
extraction were applied for the extraction and recovery of REEs from
DC. To determine the optimal extraction conditions, a full factorial
and Doehlert matrix design was employed. The DC were characterized
by XRD and EDXRF, and the REEs concentrations were determined by ICP-MS.
The REEs recovery was performed by precipitation with oxalic acid.
The analyzed DC samples were primarily composed of aluminosilicate
minerals, the α-quartz, calcite, albite, and muscovite being
the most common phases. The EDXRF analysis confirms the predominance
of silicate and aluminosilicate rock-forming minerals and accounts
for the significant content of Fe, Ca, Na, and Mg. The optimal extraction
condition was achieved using HNO3 at 7.0 mol L–1 as extractor and ultrasound-assisted extraction at 80 °C for
60 min. The efficiency of extraction in the DC analyzed was high (for
La and Ce, >82%), and after precipitation, good recoveries were
achieved,
especially for La and Ce (>90%). Thus, the proposed ultrasound-assisted
extraction process proved to be suitable for the recovery of these
elements from DC, contributing to sustainable development and the
circular economy.