Scaling Up of a Lightweight Aggregates System Based on Recovery Raw Materials and With Fertilisation Capacity: From Laboratory Prototype to Semi-Industrial Production

This study evaluates the semi-industrial prototyping of a sustainable phosphorus-potassium (PK) fertiliser (ABVF) developed at laboratory scale, using red clay and waste-derived materials as biochar, spent coffee grounds, and cullet glass. A new fertiliser glass composition was developed to ensure industrial meltability, while enabling low-temperature processing. Micropellets were manufactured through semi-industrial cold extrusion and firing, yielding mechanically stable aggregates with controlled porosity. Chemical and physical characterisation showed that firing enhances structural integrity, porosity distribution, favouring water retention and gradual nutrient diffusion. Chemical analyses confirmed enrichment of P2O5 and K2O in fired aggregates, with leaching tests demonstrating a more sustained release of P and K in citric acid compared to raw aggregates, and high resistance to leaching under acetic acid conditions, indicating potential to minimise nutrient losses in field applications. Antimicrobial assays revealed that both raw and fired aggregates inhibited bacterial growth, suggesting additional benefits for storage stability. A 6-month field trial on turfgrass and photinia shrubs demonstrated that fired ABVF can match the performance of a conventional NPK fertiliser. By integrating materials processing, nutrient release control, and agronomic validation, this work demonstrates the feasibility of producing sustainable PK fertilisers at semi-industrial scale from recovered resources.