Biochars Ability to Sequester Heavy Metals in a Mine Impacted Soil.

The Tri-State Mining District (Southwestern Missouri, USA) has a century-long history of lead (Pb) and copper (Cu) extraction and milling processes. The ore milling process produced large amounts of waste mine tailings called chats. The chat material was disposed on the soil surface in large piles. Over the years, Cu and Zn along with cadmium (Cd) moved into the soil profile. Ensuing remediation strategies consisted of removing the mine spoil piles along with metal-enriched topsoil layers. After clean up, this strategy resulted in surface exposure of the infertile subsoil, which was then planted with grasses/trees to phytostabilize the site. Unfortunately, plant growth was less than satisfactory because of lingering heavy metal concentrations and/or poor soil health conditions.

Biochar has received attention as an amendment to improve soil health conditions and it has recently been proposed as a supplement for reclaiming spoil and mine-impacted soil. Thus, we tested the ability of a biochar pyrolyzed from beef cattle manure, along with a manure compost to improve soil health characteristics and reduce Cd, Cu, and Zn concentrations in mine impacted soil from the Tri-State site. We furthered evaluated improvements in soil:plant relations by planting two warm season-grasses (Blue Grama and Indian grass) and monitoring their plant growth and metal uptake potentials. The beef cattle manure biochar and compost were mixed into the soil material at 0, 2.5 and 5% rates along with fertilizer and allowed to pre-equilibrate for one week. Afterwards, the two grasses were mixed into treated and untreated (control) soil and were placed in a greenhouse. At the end of the study, we plan on measuring above ground grass biomass, soil enzymes activity, pH, and extracting the soil using water, salt, and DPTA-TEA (diethylenetriamepentenaacetic acid + triethanolamine) for Cd, Cu, and Zn availability. The above ground portion of the grasses will be digested using concentrated nitric acid and plant metal uptake along with other critical plant nutrients will be quantified. Our results will be discussed.