Chemical basis synthesis of phosphate binders from inorganic salts of elements of Groups I and II

Abstract

Industrial production generates millions of tonnes of phosphate-rich by-products that burden ecosystems; converting them into binders for foundry cores and moulds remains underexplored, despite the urgency of recovering value from waste streams globally. This study targets Groups I and II phosphates. We aimed to develop and validate a thermodynamically guided synthesis yielding stable binders from reactive salts and orthophosphoric acid. We computed Gibbs free-energy changes for reactions of Li, Na, K, Mg, and Ca carbonates, chlorides, bromides, sulphates, and nitrates with H₃PO₄ from 20 to 300 °C, then verified by laboratory synthesis, phase analysis, and compressive tests of quartz-sand composites. Predictions matched transformations and, for the first time, showed phosphate formation from salts of stronger acids. Binders cured at 150–300 °C. Na and K systems achieved 2.0–3.5 MPa (94% sand); Mg, Ca, and Li were <1.0 MPa. These findings define feasible synthesis maps and performance benchmarks, enabling circular use of phosphate wastes in casting.