Date of Award
Doctor of Philosophy
Major impacts of current and pre-regulatory mining activities on the environment include the generation of acid mine drainage (AMD) and metal(loid)-laden acid sulfate soils. Current remediation techniques are mostly cost prohibitive due to high energy, material, and labor requirement. This study investigated two complementary low-cost methods that harnessed the metal(loid)-removing and acid-neutralizing properties of drinking water treatment residuals (WTRs) and the uptake (phytoremediation) potential of vetiver (Vetiviera zizanioides L.) and pokeweed (Phytolacca americana L.) to attenuate and immobilize metal(loid)s from natural AMD and metal(loid)-contaminated soil. Metals were removed from AMD by using a reverse flow fluidized column filter and hydroponic phytoremediation with vetiver and pokeweed. Metals were immobilized in soil through the amendment with Fe and Ca-WTR complimented by the uptake and translocation of metals by vetiver and pokeweed. Experiments were performed under controlled greenhouse conditions as well as under natural Illinois environment in simulated field conditions. Furthermore, the integrated effects of WTR application and the growth of vetiver on soil erosion were also studied. Physicochemical analysis of AMD and soil samples from the Tab-Simco abandoned mine in the Illinois Coal Basin, U.S.A, showed significant concentrations of major metals and metalloids such as Fe, Al, Mn, Zn, Ni, Cu and As at acidic pH levels. The degree of soil contamination at the site was spatially variable with respect to the location of the main AMD seep. Physical, chemical, agronomic and mineralogical characterization of locally acquired water treatment residuals (WTR) showed that the silty and alkaline (pH ≈ 7.0-9.1) materials also contained significant amounts of plant required micronutrients. The presence of amorphous phases of mostly metal (oxy)hydroxides, alkalinity, and porosity of the WTRs suggested the potential to neutralize acidity and capability to remove metal(loid)s in contaminated soils and AMD. Recorded metal removal (%MR) rate by WTR was rapid in the first 80 min in a batch agitation study, except for Mn. Thus, high metal removal ranging from 99.8% to 84.9% at selectivity sequence of Al>Fe>Cu>Zn and Mn (9.6%) was obtained at equilibrium. The pH of the AMD was also increased from 2.6 to 6.7. Analysis of leachate samples from gravity-drained columns following simulated rain events in a greenhouse study showed reduced concentrations of Al, Fe, Mn, Zn, Cu, As and Pb at sustained neutral pH compared with unamended control columns during the 12 weeks study period. Metal immobilization in soil by the lower amendment rates of WTR was comparable to the higher application rates and also showed lower oxalate extractability of metals. Tissue analysis of pokeweed and vetiver hyperaccumulators showed appreciable uptake of relevant elements although translocation was relatively low in both. The analytical results at the greenhouse scale was reproducible in a simulated field scale study under natural Illinois environmental condition where the best amendment rate including 50 g/kg Fe-WTR and 15 g/kg of Ca-WTR and manure helped to improve metal(loid) retention, soil structure and enhanced vetiver growth which subsequently aided in reducing the rate of erosion to levels comparable to bermudagrass which was used as control. The developed integrated WTR fluidized column and phytoremediation technique with vetiver and pokeweed under hydroponic conditions sequentially removed significant quantities of most heavy metals from AMD. Thus, the overall findings showed that the locally collected WTRs - the otherwise waste materials, showed high metal-removing and acidity-reducing capabilities in AMD and contaminated soil treatment applications. The similarity between the results obtained from the laboratory and simulated field study also showed that laboratory/greenhouse experiments may serve as reliable proxies for field responses in applications such as soil and water conservation in agricultural environments, remediation of abandoned mine lands, as well as wastewater treatment systems.
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