Use of zinc-rich extracts recovered from black mass of spent batteries as a sustainable and efficient alternative source of zinc for plants

This study explores the potential of glycine-based and glycine/NH 3 leaching of zinc (Zn) from pyrolyzed black mass (PBM) of spent Zn/C and alkaline batteries to obtain extracts with fertilizer properties. Zinc recovery was optimized under different extractant/black mass ratios, pH levels and particle size. The most effective extraction conditions were achieved using glycine solutions at pH 10, with a particle size < 50 µm, and a molar ratio of 1:8 (Zn:glycine). The effect of the extracts on germination and vigour of vetch, tomato, lettuce and mustard seedlings was evaluated, as well as their impact on Zn availability in the soil, plant nutrient uptake and microbial biomass after application in a lettuce crop. The results showed that the use of glycine at pH 10 (adjusted with NaOH) allowed the extraction of more than 95% by weight of Zn from PBM. The extracts showed no phytotoxicity, although their effect depended on the dose, pH and plant species. At doses up to 5 mg Zn L-¹, they improved the development of vetch, lettuce and mustard seedlings. Zn-glycine was as effective as ZnSO₄ in nutrient uptake by lettuce and in increasing Zn availability in the soil. No synergistic effects of Zn and glycine were detected. These findings support the potential of Zn-glycine extracts from battery waste as an alternative source of micronutrients in agriculture, promoting circular economy strategies and sustainable nutrient recycling. • Glycine-NaOH at pH 10 was the most effective treatment for selective Zn recovery • Zn extraction efficiency increased with decreasing particle size of the pyrolyzed black mass • Aqueous NH₃ was largely ineffective for Zn and Mn extraction from battery black mass • Zn-glycine extracts showed no inherent phytotoxicity in germination assays • Glycine showed high selectivity for Zn over Mn • Phytonutrient effects were observed at doses up to 5 mg Zn L⁻¹ in vetch, lettuce, and mustard • Zn-glycine extract matched ZnSO₄ in improving Zn availability and nutrient uptake in acidic soil.