(176d) Assessment of Combustion Residual Leachate: Treatment Standards, Wastewater Volumes and Critical Mineral Recovery

Combustion residuals and the resulting leachate from storage sites represent a large and variable volume of wastewater in the United States (U.S.). Constituents in this wastewater are regulated at the federal and local levels – federal emissions standards include total suspended solids (TSS), oil/grease, arsenic, and mercury for new and existing sources of leachate, whereas local emissions standards can include pH and a selection of 11 additional constituents, including copper, iron, selenium, mercury, and fluoride. Heterogenous regional standards and variable leachate volumes make quantifying treatment needs for leachate difficult. To address this issue, this work aggregates regional standards in the U.S. and assesses the treatment technologies necessary to meet these standards. Next, using data from the Environmental Protection Agency (EPA) and the Electric Power Research Institute (EPRI), the combustion residual leachate volume from landfills and impoundments is calculated on a national level. The annual wastewater discharge volume of a single landfill with combustion residual leachate can exceed 200 million gallons. In the U.S., landfill leachate is found to represent an annual volume of 7.1–11.3 billion gallons. Closing surface impoundments is a second source of leachate discharge that is determined to yield between 220 and 280 billion gallons of leachate in the U.S. over a three-year closure period.
While treatment of these large volumes of leachate will be costly, recovery of critical minerals offers an opportunity to offset treatment costs and improve critical mineral supply reliability. This work presents critical mineral recovery potential both as the available mass of a given mineral and the expected market value for 17 critical minerals available from EPRI’s Combustion Product Information (CPInfo) database. Of the available minerals, magnesium has by far the highest concentration, reaching up to 2,000 ppm in landfill leachate and 1,300 ppm in impoundment leachate. Magnesium recovery from water is an industrially established process that can be readily implemented. Applying average magnesium concentrations and leachate volumes, if magnesium was recovered from all landfills it would represent a $39.2 million market– from all impoundments, this would represent a $650 million market. This supply would account for 9.1% and 151%, respectively, of 2021 U.S. magnesium consumption.