A Material Flow Model for Impurity Accumulation in Beverage Can Recycling Systems

Recycling of aluminum is beneficial due to reduced energy inputs, greenhouse gas emissions and raw material costs. Beverage cans are currently the second largest source of old scrap, and could become even larger with improved collection. However, impurities such as iron, titanium or lead may impede end-of-life recycling at higher levels, especially in closed-loop systems where they can accumulate over time. A generic material flow model for impurity accumulation in a simple recycling system is presented here. Sensitivity analysis was used to investigate the effect of key parameters on dynamics of accumulation and concentration at steady state. It was found that it takes longer to reach steady state at high collection rates, and that the steady state concentration is disproportionally higher. Increasing the U.S. beverage can collection rate from today’s 54% to the goal of 75% may cause more than a doubling of impurity concentrations unless better scrap treatment and remelting are developed in parallel or the scrap is used in other applications.