The valorization of industrial waste in agriculture represents a key strategy within the circular economy framework. In this context, the present study aimed to assess the feasibility and potential of fertilizers derived from black mass, a by-product of alkaline battery recycling, as alternative sources of Zn and Mn in citrus cultivation, evaluating their effects on fruit quality and food safety. The experiment was conducted in Pedreguer (Alicante, Spain) in ‘Navelina’ cultivar using Carrizo and C-35 rootstocks, comparing conventional fertilization with black mass-based formulations applied as sulfates (BMSs) and lignosulfonates (BMLSs). The results showed that the evaluated micronutrient sources significantly increased foliar Zn concentrations up to 17.9 mg·kg−1 and Mn concentrations up to 28.1 mg·kg−1, values markedly higher than those observed in the Control treatment (15.20 mg·kg−1 Zn and 11.5 mg·kg−1 Mn). No adverse effects on yield or fruit quality were detected: Average fruit weight remained close to 200 g per fruit, and the proportion of non-marketable fruit did not exceed 2% in any treatment. Regarding food safety, Pb, Cr, and Ni concentrations in pulp and peel were below the maximum levels established by European Union regulations, with maximum values of 0.02 mg·kg−1 for Ni and 0.04 mg·kg−1 for Pb on a dry matter basis, while Cd, Co, and Hg were not detected. Overall, black mass-derived fertilizers enhanced Zn and Mn availability in plants without compromising plant physiology or fruit quality and maintained safe levels of heavy metals. These results support their use as a sustainable alternative for mineral fertilization in citrus orchards and reinforce their contribution to reducing the consumption of virgin raw materials and advancing toward more circular agricultural systems.
Escudero et al. (Tue,) studied this question.