In situ immobilization of metals using soil amendment processes is increasingly being considered as an effective and low cost remediation alternative (Mench et al. 2007, Kumpiene et al. 2008, Fellet et al. 2011). Leonardite is a carbon-rich material derived from the oxidation of Lignite and is rich in humic acid, whereas biochar is a product that results from the oxygen limited, pyrolysis of various biological ingredients, such as wood, fish or animal bone. Several studies have found biochar amendments result in significant decreases in the bioavailability of heavy metals associated with mining impacted soils (Namgay et al. 2006, Fellet et al. 2011, Beesley et al. 2010) and simultaneously improve physical, chemical and biological soil properties (Laird et al. 2010). Leonardite is known to improve soil conditions (Lao et al. 2005, Zeledόn- Torunõ et al. 2005, Madejόn et al. 2010) and has potential to significantly reduce metal bioavailability due to high metal adsorption capacity (Lao et al. 2005, Zeledόn- Torunõ et al. 2005).
