Zero liquid discharge recovery system for maximized tailings water reuse

The copper industry anticipates increased water consumption and generation of tailings due to declining copper ore grades and increased copper demand for energy transition. The strategy adopted in Chile to address the growing water demand is to transition from continental water sources to seawater, which is desalinated and transported from the coast to high altitudes, at high energy expenditures. We developed an alternative water management strategy, that involves maximizing water recovery from tailings through filtration, followed by treating the tailings water to restore water quality using an innovative recovery system with zero liquid discharge (ZLD). We evaluated our water management solution for three large copper mining operations. The ZLD recovery system integrates bipolar membrane electrodialysis (BMED) with established technologies such as reverse osmosis (RO), chemical precipitation (CP), ion exchange (IX), calcium carbonate calcination, and membrane contactors (MC) for CO₂ capture. The system recovers chemicals, produces freshwater, generates acids and bases, and captures CO₂, all within a chemically self-sufficient, integrated process. The system shows strong potential as an effective, environmentally friendly alternative to traditional ZLD methods. The ZLD recovery system proves to be technically feasible, based on the modeling of three key stages (CP, IX and RO) and experimental results for a fourth key stage (BMED). The ZLD recovery system also demonstrates economic feasibility when compared to a scenario in which mining companies use desalted seawater. The total cost of implementing the proposed ZLD recovery system ranges between 2.08 and 2.15 USD/m³ of inlet water, with an average energy consumption of 8.68 kWh/m³ for the most energy-intensive steps. For greenfield projects, even when the marginal cost increase of 0.47 USD/dry metric ton for filtering tailings is included, the proposed water management solution remains cost competitive. We also assessed the cost of adopting the new water management solution for brownfield projects, based on the average copper price in 2024 of 4.15 USD/pound. The normalized cost per pound of copper of the proposed water management system represents on average less than 5 % of the copper price. Furthermore, the proposed recovery system allows for obtaining high-quality permeate, maximizing water recovery, recovering products used in mining processes such as lime and sulfuric acid, while minimizing the carbon footprint and reducing the environmental risks associated with wet tailings disposal.