Eco-friendly collectors in apatite froth flotation: A review

Abstract

The global reliance on phosphate rock for agriculture and other industries, coupled with chemical regulations in developed countries, has driven the search for green alternatives in apatite flotation. This review investigates eco-friendly collectors’ effectiveness in promoting sustainable mineral processing, guiding future alternatives to traditional reagents. The manuscript discussed the surface properties of apatite and its interaction with eco-friendly collectors, assessing existing fundamental studies. This study sought to: (1) define, organize, and classify “eco-friendly” collectors; (2) evaluate their effect in IEP and contact angle; (3) provide a better understanding of the adsorption behavior of the different fatty acid chains into apatite surface; (4) assess their ability to reversely and directly float apatite; (5) address gaps to achieve selectivity and process optimization. Outcomes demonstrated that fatty acids are largely applied, but other renewable sources of these reagents have been promisingly evaluated. In addition, other natural reagents have been tested, and new green synthetics have demonstrated synergistic effects when combined with fatty acids, yielding significant improvements in grade and recovery. However, collector effectiveness varies with ore characteristics, like particle size and surface properties, which remain underexplored. Future research should design tailored collectors that align with mineralogical differences to enhance selectivity.

1. Introduction

The phosphate rock is one of the critical raw materials listed by the European Union (EU) in 2023, and there is no substitute for phosphorus in agriculture [1]. 82% of the phosphate rock in the EU are imported, and the sourcing countries are mostly Morocco, Russia, Finland, and Algeria [1]. In 2022, the global phosphate fertilizer market experienced impacting supply disruptions due to China’s restrictions on fertilizer exports and Russia’s conflicts with Ukraine [2]. Moreover, phosphates are one of the primary sources of rare earth elements [3]. In the EU, the export reductions of phosphate rock and fertilizers from Russia and Russian companies caused volatility in the market, high prices, and a lack of import reliance, increasing the urgency in establishing domestic sourcing for this raw material. Considering this situation, many countries (inside and outside the EU, such as Sweden, Brazil, Kazakhstan, Mexico, Morocco, Australia, Canada, Congo, Guinea-Bissau, and Senegal) with phosphate reserves started the feasibility studies of different projects, looking for apatite concentration alternatives [4]. These new projects represent an opportunity to develop new reagents and process routes.

Before being transferred to fertilizer production, the raw apatite is commonly concentrated via froth flotation beneficiation, a complex physicochemical process that works through the surface properties and the control over the hydrophobicity of the different materials [5,6]. Since most minerals are naturally hydrophilic, flotation reagents known as “collectors” are necessary to induce hydrophobicity in the mineral surfaces [6]. Collectors are amphiphilic molecules known as “surfactants”, which are the main players in the flotation process: their “head” adsorbs into the mineral surface, and the hydrophobic “tail” allows it to float once the air is injected into the system [7]. Fatty acids, in their salt forms, are the most applied eco-friendly anionic phosphate collector, and sodium oleate (SO)/oleic acid (HOl) is the main studied compound [8–10]. However, their disadvantages are that they are sensitive to lower temperatures and the presence of cations and slimes, require high collector dosage, lack selectivity, and present fluctuation in performance (as a natural source, it may vary their composition).