GREEN REMEDIATION OF AMD- IMPACTED SOIL USING AN INDUSTRIAL BYPRODUCT AND VETIVER GRASS: INCUBATION AND GREENHOUSE STUDIES

While surface mining is an important revenue generating industry, several negative environmental consequences are associated with it. During surface mining, metal-rich acid solutions, called acid mine drainage (AMD) and acid sulfate soils are produced, which are responsible for habitat deterioration in adjacent ecosystems. Also, acid sulfate soils are structurally unstable and highly prone to erosion. Current AMD-impacted soil treatment technologies are time-intensive and very expensive. This study evaluated the potential of a cost effective and environment-friendly “green” technology in treating AMD-impacted soils that utilizes the metal binding and acid-neutralizing capacity of an industrial by-product, namely drinking water treatment residuals (WTRs), and the extensive root system of a metal hyper-accumulating, fast-growing, non-invasive, high biomass perennial grass, vetiver (Vetiviera zizanioides L.) to prevent soil erosion. Two types of WTRs were used, one generated by groundwater treated with lime (Ca-WTR) and the other by alum (Al-WTR). AMD-impacted soils were collected from the Tab Simco coal mine in Carbondale, IL. A 60 day soil incubation study was performed using 7 different Al- and Ca-WTR amendments: 2.5% Al-WTR, 5% Al-WTR, 10% Al-WTR, 2.5% WTR [1:1 Al & Ca], 5% WTR [1:1 Al & Ca], 10% WTR [1:1 Al & Ca], and soil control (no WTR). An increase of soil pH from 2.44 to 6.86 was observed for the optimal treatment. Decrease in exchangeable fractions of all metals was observed with increasing equilibration time, including a 95% decrease in exchangeable Fe concentration (6.8 mg/kg) after 60 days. Toxicity Characteristics Leaching Protocol (TCLP) tests of all treatments showed that RCRA (Resource Conservation and Recovery Act) 8 metal concentrations were well below the USEPA-prescribed limits. Noticeably, none of the treatments resulted in significant leaching of Al. Currently, a scaled up greenhouse study is ongoing where both WTRs and vetiver grass are being used for treatment of AMD-impacted soils. Preliminary results are promising, which showed that this “green” remediation technique has the potential to effectively treat AMD-impacted soils.