Optimization of acid flotation for quartz-feldspar separation from extractive waste

Quartz and feldspar are critical minerals for industries such as glass, ceramics, and photovoltaic cell production. The European Union classifies feldspar as a Critical Raw Material (CRM), while quartz is the main precursor for silicon metal production, also listed as a CRM. Conventionally, their separation relies on flotation with hydrofluoric acid (HF) under strongly acidic conditions (pH 2-3) to enhance the electronegativity and hydrophobicity of feldspar towards the quartz recovery. However, the use of HF poses severe environmental and safety risks and increases operational costs due to its high corrosivity, toxicity, and environmental restrictions posed by EU member states’ legislations. This study aims to improve the efficiency and sustainability of acid flotation for the separation of quartz and feldspar from Minerali Industriali’s extractive waste streams by minimizing or potentially eliminating HF consumption. This is pursued through the fine-tuning of key flotation parameters and the introduction of alternative reagents, such as sodium fluoride (NaF), sulphuric acid (H₂SO₄), organic acids and innovative chemical compounds, while preserving selectivity and high separation efficiency. In parallel, a sustainable wastewater treatment strategy is being developed to further reduce the environmental footprint of the process, including water recirculation, neutralization, and purification. A preliminary laboratory-scale protocol is currently under development and involves multiple conditioning and flotation stages using water, HF, and cationic collectors (e.g., CustAmine® by Arkema) to recover a high-purity feldspar concentrate from a pre-treated feldspathic sand in the 100-600 µm grain size range. The experimental study is being supported by a Design of Experiments (DoE) integrated with chemical and mineralogical characterization of the feed material and flotation products – both concentrates and tailings - to enable systematic process optimization. Semi-industrial testing through a pilot plant will validate the proposed solutions under real operating conditions. Environmental and economic aspects will be evaluated by Life Cycle Assessment (LCA) and Cost-Benefit Analysis (CBA), comparing conventional and innovative processing routes. Overall, this approach promotes circular economy strategies through by-product reuse, and contributes to safer and more sustainable mineral processing practices supporting the transition towards environmentally responsible industrial operations, while providing deeper insights into the flotation behaviour of quartz and feldspar under both conventional and innovative reagent schemes. The project is partially funded by the Italian Ministry of the Environment MASE (Ministero dell’Ambiente e della Sicurezza Energetica), and involves Minerali Industriali – R&D&I+QCLab Department - as the industrial partner and three different departments of the Università degli Studi di Torino – namely Department of Chemistry, Department of Earth Sciences, and Department of Management "Valter Cantino".