Rare earth elements, sustainability, and ion-adsorption clay: A bibliometric study on global trends and Brazil's prominence

Abstract

Rare Earth Elements (REE) are critical minerals for the global energy transition and for fulfilling Sustainable Development Goals (SDGs), such as SDG 7 (Clean Energy). However, the traditional supply chain, focused on primary deposits, faces significant geopolitical and environmental challenges. In this context, ion-adsorption clay (IAC) deposits have emerged as the main research route for a more sustainable REE production, aligned with the 2030 Agenda. Despite this relevance, there has been no systematic analysis of the scientific production on this topic in an integrated manner, from the perspective of the entire 2030 Agenda. The objective of this study is to fill this gap by mapping the synergies and trade-offs between global REE-IAC research and the 17 SDGs, and contextualizing this trend with Brazil's emergence as a strategic industrial player. To this end, a bibliometric and systematic review analysis was conducted using the Scopus and Web of Science databases, covering the period from 1973 to 2024. Keyword co-occurrence analysis and thematic clustering were processed using VOSviewer. This analysis was supplemented by a survey of active exploration projects in Brazil, based on technical and governmental reports. The results demonstrate an exponential growth (R² = 0.98) in research starting from 2015, the year the SDGs were launched. This period accounts for 91.5% of all historical literature on the topic. The cluster analysis reveals that the intellectual structure of the field is dominated by two pillars: the demand for sustainability (Cluster 1, centered on sdg) and the geological solution (Cluster 2, centered on ion adsorption clay). The research field proves to be mature, actively addressing the challenges of water management (SDG 6, Cluster 8) and toxicity. On the global stage, Brazil stands out as the 5th largest publisher. More importantly, the practical survey identified 24 active IAC projects in the country, including the commercial operation of Serra Verde (GO) and the advanced projects in Poços de Caldas (MG), such as Caldeira and Colossus. It is concluded that the SDGs act as the main driver of innovation in IAC research. Brazil demonstrates a unique convergence between innovation policy (aligned with SDG 9), the global scientific trend, and industrial execution. The country is using IAC deposits as a strategic solution to overcome the environmental challenges of its traditional deposits (associated with Th/U), positioning the country as the main Western hub for REE-IAC production and a strategic supplier for the sustainable energy transition.