Gold bioabsorption and reduction by Chilopsis linearis (desert willow): An alternative for in-situ gold extraction

Elena Rodriguez, University of Texas at El Paso

Abstract

Current processes for gold (Au) recovery are expensive and harmful to the environment because of the use of toxic compounds. In addition, mining residues or tailings regularly have high concentrations of contaminants such as As, Cd, Hg, Pb, and Tl, among others. Phytoremediation, the use of plants to extract, remove, transform, destroy, or immobilize contaminants from soil and water, has appeared as a feasible option to recover precious elements from ores containing valuable metals at low concentration. ^ This study reports on the feasibility of using Chilopsis linearis (Desert willow) to phytoextract Au and to phytoremediate mercury (Hg). Seedlings of C. linearis were cultivated in Au-enriched media under different growth conditions. Factors such as cultivation matrix, pH, and Au-chelating agents were studied. ^ The concentration-response experiments have shown that the plants grew better in a medium containing 40-80 mg Au L-1. X-ray Absorption Spectroscopy (XAS) studies showed that plants exposed to 160 mg Au L -1 formed Au nanoparticles of approximately 8, 35 and 18 Å in roots, stems and leaves, respectively. These results suggest that the average size of the Au nanoparticles formed within the plants is related to the portion of the plant and to the gold content. On the other hand, the pH experiment showed that hydroponically grown plants exposed for 15 days to 20 mg Au L -1 in a liquid medium adjusted at pH 6.0, had the highest gold absorption (100 and 44 mg Au kg-1 dry weight mass (DWM) in stems and leaves, respectively). ^ Hydroponically grown C. linearis plants treated with Au at 25 μM and different concentrations of thiocyanate or thiourea demonstrated that these chelating agents significantly increased (P < 0.05) the Au accumulation in plant tissues. The Au concentration in stems and leaves increased 3 and 4.5 times with 100 μM of thiourea and 5 and 5.6 times with thiocyanate, respectively. C. linearis seedlings grown in Au enriched soil (5 mg kg-1) and treated with thiocyanate and thiourea also demonstrated that these chelating agents increased the Au translocation to the leaves. ^ Seedlings of C. linearis were also exposed to gold-mercury spiked solutions to explore the Hg uptake and the Hg interaction in Au uptake. The plant concentrated Au and Hg mainly in the roots and had more selectivity for Hg. The microscopic analysis (SEM) showed that Hg induced structural changes mainly in the roots. (Abstract shortened by UMI.) ^

Subject Area

Chemistry, Analytical|Environmental Sciences

Recommended Citation

Rodriguez, Elena, "Gold bioabsorption and reduction by Chilopsis linearis (desert willow): An alternative for in-situ gold extraction" (2006). ETD Collection for University of Texas, El Paso. AAI3214898.
http://digitalcommons.utep.edu/dissertations/AAI3214898

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