Approximately 500,000 abandoned mines across the U.S. pose a considerable, pervasive risk to human health and the environment. World-wide the problem is even larger. Various materials can be added to metal contaminated mine soils to decrease metal availability and to promote the establishment of a stabilizing plant cover. Biochar, a charcoal-like material, is a relatively new soil amendment that in addition to tying up potentially toxic metals, can also be a source of plant nutrients, used to adjust soil pH, improve soil water holding characteristics, and increase soil carbon content. We developed a three step laboratory procedure for matching biochar beneficial properties with mine waste toxicities and deficiencies. In step 1, a slightly acidic extract of the mine spoil soil was produced, representing the potentially available metals, and used to identify metal removal properties of a library of 38 different biochars. Step 2 is an evaluation of how well these biochars retained previously sorbed metals. Step 3 is an evaluation of the performance of 1%, 2.5% and 5% biochar additions (by weight) for reduction of mine spoil soil metal bioavailability. Using this procedure we were able to identify specific biochar(s) and application rate(s) to reduce metal availability and aid in remediation of a metal contaminated soil from an abandoned Cu and Zn mine on the National Priorities List of Superfund Sites. Our recommendations are being tested in greenhouse and field trials. This study is being used to develop a generalized, but directed method for matching biochars to specific metal contaminated soils for the purpose of reducing metal availability. This abstract is a part of SHC Project 3.63

Description:

Approximately 500,000 abandoned mines across the U.S. pose a considerable, pervasive risk to human health and the environment. World-wide the problem is even larger. Lime, organic matter, biosolids and other amendments have been used to decrease metal bioavailability in contaminated mine wastes and to promote the development of a mine waste stabilizing plant cover. The demonstrated properties of biochar make it a viable candidate as an amendment for remediating metal contaminated mine soils. In addition to sequestering potentially toxic metals, biochar can also be a source of plant nutrients, used to adjust soil pH, improve soil water holding characteristics, and increase soil carbon content. However, methods are needed for matching biochar beneficial properties with mine waste toxicities and soil health deficiencies. In this presentation we will report on a study in which we used mine soil from an abandoned Cu and Zn mine to develop a three-step procedure for identifying biochars that are most effective at reducing heavy metal bioavailability. Step 1: a slightly acidic extract of the mine spoil soil was produced, representing the potentially available metals, and used to identify metal removal properties of a library of 38 different biochars (e.g., made from a variety of feedstocks and pyrolysis or gasification conditions). Step 2: evaluation of how well these biochars retained (i.e., did not desorb) previously sorbed metals. Step 3: laboratory evaluation of the performance of 1%, 2.5% and 5% biochar additions (by weight) for reduction of mine soil metal bioavailability. Investigation results were used to identify specific biochar(s) and application rate(s) to reduce metal availability and aid in remediation of a specific metal contaminated soil. Results from this study are used to develop a generalized, but directed method for matching biochars to specific metal contaminated soils for the purpose of reducing metal availability.