Improving gold phytoextraction in desert willow (Chilopsis linearis) using thiourea: a spectroscopic investigation

Abstract

Environmental context. The conventional methods used for the extraction of gold from mine tailings and runoff are costly and often require harsh chemical treatment. Using plants to extract gold is more environmentally friendly and economically feasible. Plants are especially appealing because they can uptake low levels of gold and accumulate them in their tissues, whereas conventional methods are less effective at extracting gold at low levels. Thiourea has been proposed as an alternative gold chelator that could help in gold phytomining. It is less toxic than cyanide, which is the chemical commonly used to dissolve gold from mine ores.Abstract. Phytomining, the use of plants to recover noble metals, is developing as a feasible option to extract gold from mine tailings. In this study, thiourea (TU) was used to increase gold availability and to enhance gold accumulation by the desert plant Chilopsis linearis. Seedlings of C. linearis were grown in a hydroponic solution containing 25 µM Au and TU at 25, 50, 100, 200, and 400 µM. After two weeks of growth, the concentration of Au, micro-and macronutrients was determined using inductively coupled plasma-optical emission spectroscopy. In addition, X-ray absorption spectroscopy was used to determine the oxidation state and the coordination of the Au atom within the plant tissues. The effect of TU on plant growth was determined as well. The results of the present study demonstrated that TU at 25 µM was able to increase the Au uptake by C. linearis plants grown in hydroponics without any toxic effect. However, the translocation to stem and leaves was better at 100 and 200 µM of TU, respectively. The addition of TU to hydroponic solutions did not affect the uptake of Ca, Mg, P, and K. However, TU induced an increase in uptake of S, Fe, Cu, and Zn and a decrease in Mn uptake. When Au was chelated with TU, the plant transformed 64% of the Au-TU complex to Au(0) and the other 36% remained in the ionic form.

Synchrotron-based techniques for plant and soil science: opportunities, challenges and future perspectives

“…These particles, which could be used in nanotechnology applications, have been shown to be produced by plants. Various studies (Gardea-Torresdey et al 2002Sharma et al 2007;Rodriguez et al 2007) have demonstrated, using XAS, that gold was present as Au(0) in the plants which confirmed the nature of the nanoparticles observed by TEM.…”

Synthesis and characterization of nano-gold composite using Cylindrocladium floridanum and its heterogeneous catalysis in the degradation of 4-nitrophenol

“…This is a cost-effective way of phytomining gold in nanosize from mine ores and leachates. Rodriguez et al [3] reported that the seedlings of Chilopsis linearsis (desert willow) in hydroponic solution with gold and thiourea can transform 64% of the uptaken gold-thiourea complex into metallic gold and accumulated in stem and leaves with an average size of 1.1 nm. Similarly, Sharma et al [4] reported the accumulation of AuNPs inside Sesbania drummondii.…”

Phytoremediation of Soil Trace Elements

“…Economic Au phytomining first requires standard ore mining and grinding, then placing the ground ore over plastic membranes to prevent leachate loss so that cyanide, thiocyanate or thiourea used to induce phytoextraction can be irrigated on the soil to promote Au uptake by growing plants [176][177][178]. Others have looked for formation of gold nanoparticles in the plant biomass because the nanoparticles may have higher value for use as catalysts, and other uses, than the gold content alone [179] and tested diverse plants to phytoextract soil Au [180,181]. Australian researchers estimated that Au phytomining could make more return per hecatre than Ni phytomining [182], so this research topic remains active.…”