Biochar selection methodology for remediating heavy metal contaminated mine tailings

Authors: Ducey, Thomas; IPPOLITO, JAMES - Colorado State University; Spokas, Kurt; Trippe, Kristin; JOHNSON, MARK - Us Environmental Protection Agency (EPA)

Submitted to: International Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2024
Publication Date: 4/15/2024
Citation: Ducey, T.F., Ippolito, J.A., Spokas, K.A., Trippe, K.M., Johnson, M.G. 2024. Biochar selection methodology for remediating heavy metal contaminated mine tailings. International Journal of Environmental Science and Technology [online]. https://doi.org/10.1007/s13762-024-05621-9.
DOI: https://doi.org/10.1007/s13762-024-05621-9

Interpretive Summary: There are close to a half million abandoned mines in the United States, many of which pose significant human and environmental hazards due to heavy metal contamination. To reduce the hazards these mines pose to human health and environmental damage, a number of management methods can be deployed. A newer management practice, utilizing biochar to bind heavy metals, shows significant promise. However, biochar properties are derived from the original feedstock (for example but not limited to the following organic materials: hard woods; grasses; and animal manures). In order to determine the best biochar design for a particular environment we developed a synthetic precipitation leaching procedure. This method mixes a solution carrying known concentrations of heavy metals with each designed biochar. We then measure how much heavy metal was pulled out of solution, and then look at the biochar to see how much heavy metal could subsequently pulled off the biochar and placed back into solution. This developed method can provide a low-cost, quick, initial screen of proposed biochars intended for environmental remediation purposes prior to field application.

Technical Abstract: Approximately 390,000 abandoned mines across the United States pose considerable, pervasive risks to human and environmental health; world-wide the problem is even greater. Lime, organic materials, and other amendments have been used to decrease metal bioavailability (for example; cadmium, copper, manganese, nickle and zinc) in contaminated mine wastes and to promote plant community establishment for tailings stabilization. Biochar properties (for example; alkaline pH, metal sorbing capabilities, available nutrients, improved soil water relations) make it a potential amendment for remediating metal contaminated mine tailings. A three-step procedure was developed to identify biochars that were most effective at reducing heavy metal availability as well as retaining metals: Step 1) a synthetic precipitation leaching procedure (SPLP) extract of mine tailings was produced, representing potentially available metals, and used to identify metal removal properties of 38 different biochars (for example; made from various feedstocks and pyrolysis or gasification conditions; 0.25 grams biochar:25 millilLiters of SPLP extract, shaken for 24 hours); Step 2) evaluate how well biochars retained previously sorbed metals (0.15 grams biochar:15 mililiters of 0.01 molar calcium chloride solution, shaken for 24 hours); and Step 3) laboratory evaluation of the most promising biochars, applied at 0, 1, 2.5, and 5% (by weight) to mine tailings for reducing metal bioavailability (3.00 grams total solid phase:30 milliliters of 0.01 molar calcium chloride solution, shaken for 2 hours). The reported methodology and results from this study could be used to identify specific biochars and application rates to reduce mine tailings metal availability and aid in future remediation of abandoned mine sites globally.