Optimization of an Operational Waste Valorization Investment Portfolio in Copper Mining: An ε-Constraint Approach

The mining industry generates substantial volumes of operational waste, including lubricant oils, lead-acid batteries, steel scrap, and end-of-life tires (ELTs). Their valorization is increasingly required under Extended Producer Responsibility (EPR) frameworks, but Centre for Innovation in Technology and Design of Materials for the Built Environment—CIMAC_ANID CTI250005 investment decisions are constrained by limited capital and competing sustainability objectives. This study proposes a dynamic Mixed-Integer Linear Programming (MILP) model to optimize a multi-waste valorization investment portfolio for the copper industry. The model maximizes Net Present Value (NPV) over a multi-period horizon while satisfying EPR targets, capital constraints, and sustainability requirements. Using the ε-constraint method, it quantifies trade-offs between economic performance and social value by incorporating permanent local employment as a binding constraint. Applied to a single case study of a Chilean SX–EW plant, the model selects an Oil Filtration Plant, a Scrap Recycling Yard, and an ELT Pyrolysis Plant, achieving a maximum NPV of USD 5.363 million. Sensitivity analysis of the employment target identifies three decision zones: up to 18 jobs, the target is not binding and the NVP-optimal portfolio is unchanged; between 19 and 26 jobs, the Battery Processing Plant must also be built, reducing NPV by approximately USD 0.49 million (9%); above 26 jobs, the problem becomes infeasible. The framework integrates economic, environmental, and social dimensions, providing a decision-support tool for EPR compliance and sustainable waste valorization planning.