Presence of Critical Materials in Select U.S. Municipal Solid Waste Landfill Leachates

Abstract

This study detected and quantified a broad array of critical materials and other elements in U.S. municipal solid waste (MSW) landfill leachates in both the aqueous (i.e., supernatant) and wet solid fractions. A total of 59 elements were measured in 37 landfill leachate samples obtained from six MSW landfills across five U.S. states. Samples were collected from different aged cells, combined leachate streams, or after being treated by a membrane bioreactor (MBR) followed by reverse osmosis (RO). Results found that 24 elements classified as critical materials and eight other elements were independently quantified in at least one leachate sample. Concentrations ranged in the low to high mg/L and mg/kg of wet solids for the supernatant and wet solids fractions, which made up to >98 wt % and <2 wt % of the total leachate sample, respectively. Critical materials not detected included several rare-earth elements (REEs) and several platinum-group metals (e.g., Pt, Pd, and Ru) among others. Most elements were detected in both the supernatant and wet solids phases. Concentrations of several elements (Li, Ni, Co, Cr, Ti, and Al) increased linearly or exponentially with time when cells opened at later years or when the waste age decreased. MBR and RO treatment lead two elements (Ni and Mn) to be effectively concentrated without incurring mass losses, whereas all other elements incurred significant mass losses. Overall, this study provides a foundational step in understanding the critical materials composition of U.S. MSW landfill leachates and highlights key opportunities and challenges for resource recovery.