Trattamento delle acque reflue del settore automobilistico con un approccio di economia circolare, riutilizzo dell'acqua e ZLD

This research addresses the critical challenge of sustainable wastewater treatment and management within the automotive sector, championing the principles of the circular economy (CE), water reuse, and Zero Liquid Discharge (ZLD). Industrial activities consume approximately 22% of global water, with 80% of generated effluent being directly discharged into water bodies, posing significant environmental and health risks. The imperative for treating and reusing industrial wastewater is therefore profound, directly contributing to United Nations Sustainable Development Goal 6 (SDG 6), "Clean Water and Sanitation," by focusing on innovative strategies for water-intensive recycling processes. The research encompasses four distinct case studies, each tackling wastewater generated from the hydrometallurgical recycling of key automotive components. For wastewater from spent Lithium-ion Batteries (LIBs) recycling, which presented a high Chemical Oxygen Demand (COD) of 5390 mg/L and basic pH (10.17), the Fenton process was optimized, achieving a maximum COD removal of 98.79%. An economically favorable condition, at a cost of 23.23 €/m3, achieved 94.79% COD reduction, rendering the treated water (COD 56.90 mg/L) suitable for recycling into subsequent hydrometallurgical processes, supporting lithium recovery and ZLD. Wastewater from spent Alkaline Batteries (SABs) recycling, characterized by a highly basic pH (11.7) and significant levels of barium, lead, strontium, and a COD of 9715 mg/L, underwent a crucial acidic precipitation pre-treatment at pH 1. This step effectively reduced Ba, Pb, and Sr concentrations to negligible levels (0.1-0.3 mg/L) and substantially reduced COD by 72% to 2727 mg/L. Subsequent Fenton treatment achieved up to 84.11% COD removal, with optimization via central composite design identifying optimal conditions (7.91% H₂O₂ and 1.5 g/L Fe2+) that yielded 81.37% COD removal with minimized cake generation and reagent consumption. The final treated water, primarily sodium sulfate (13.8 g/L), allows for its recovery via evaporation-crystallization, further enhancing circularity. In the case of In-Mold Structural Electronics (IMSEs) recycling, wastewater from silver extraction was acidic (pH 1.39) with high COD (14.48 g/L), iron (8.69 g/L), copper (117 mg/L), and thiourea. Direct Fenton treatment was applied without preliminary pH correction, achieving 93.6% COD removal and over 99% removal of both Fe and Cu without additional ferrous sulfate, leveraging the inherent iron content. UV-VIS analysis confirmed the effective decomposition of thiourea. This efficient treatment allows for a 90% reduction in water consumption, supporting a Minimal Liquid Discharge (MLD) approach, and offers a cost-effective alternative to wastewater disposal (81.60 €/m3 vs. 150 €/m3). Finally, for spent Permanent Magnets (NdFeB) recycling, wastewater from Rare Earth Element (REE) extraction was acidic (pH 3.04) and rich in iron (32366 mg/L), boron, and praseodymium. This study focused on iron recovery using oxalic acid. Optimal conditions were identified as 80% stoichiometric oxalic acid addition at 25 °C, achieving 85.3% iron recovery while simultaneously removing a significant portion of praseodymium (94%) and boron. A secondary lime precipitation step ensured the removal of residual iron and other elements. Thermal analysis confirmed the decomposition of precipitated iron oxalate into iron oxide at an optimal calcination temperature of 214.5 °C, contributing to resource recovery. Overall, this research consistently demonstrates that integrating advanced wastewater treatment technologies into hydrometallurgical recycling processes is not only technically feasible but also economically viable and environmentally essential for achieving sustainable industrial ecosystems within the circular economy model.