Valorisation of hard metal wastes using organic acids in an eco-friendly process

Abstract

The manufacturing of Hard Metals (HMs) faces significant challenges due to the critical shortage of its primary feedstocks, tungsten (W) and cobalt (Co). The rising demand for these metals, particularly cobalt in lithium-ion battery technology, has led to increased market volatility and pricing concerns. To address these issues, leveraging metal-containing HM waste as secondary resources presents a sustainable solution, aligning with the circular economy model advocated by European Directives. This study introduces a novel hydrometallurgical process utilizing low-cost, biodegradable organic acids for the recovery of critical metals from HM scraps, particularly focusing on materials derived from the pyrometallurgical oxidation, reduction, and carburization (ORC) process. Organic acids, obtainable from agro-industrial waste through cost-effective biological methods, have demonstrated effectiveness as selective leaching agents for cobalt from WC-Co materials.

In this paper the use of lactic acid leaching solutions on oxidized powders, predominantly composed of CoWO₄ and WO₃, generated in the first ORC stage, is discussed. The findings reveal that these solutions facilitate the dissolution of critical metals under eco-friendly conditions, highlighting the potential of the Bio-derived Chemicals Recycling (BioCR) process. An empirical model for predicting the Co content in the recycled HM, is here proposed and applied for validation. This approach not only valorises organic waste but also yields high-quality materials suitable for reintegration into the HM manufacturing chain. Our results support the development of integrated systems that enhance resource recovery and mitigate waste management issues, fostering sustainability and circular economy principles while allowing for tailored W:Co ratios in recycled materials.