Palladium phytoremediation and phytomining potential of vetiver grass (Chrysopogon zizanioides)

Abstract

Levels of palladium in the environment are on the rise due to anthropogenic activities. There is a need to remediate contaminated environments, while also recovering the precious metal (Pd(II)) in a cost-effective and environmentally friendly manner. The leading contributor of Pd and other catalytic metal pollution in the environment is the automotive industry where platinum group metals (PGMs) are used in catalytic converters. Recently, there is renewed interest in platinum and other PGMs due to their use in the cathode of fuel cells for hydrogen generation. In this study, the phytomining and phytoremediation potential of vetiver grass (Chrysopogon zizanioides) was investigated by assessing its removal and accumulation of Pd, and its tolerance towards elevated Pd concentrations. Vetiver grass was grown in Pd solutions with concentrations ranging from 10 – 120 ppm. The grass was harvested after a period of 20 d and separated into roots and shoots. The removal efficiency of Pd ranged from 80 % at 10 ppm initial concentration to 20 % at 120 ppm. The removal of Pd from the solution and accumulation in the plant was influenced by the initial Pd concentration. The highest accumulation achieved was 0.4 mg g-1 dry weight (DW) in the roots at 120 ppm. Low translocation factors < 1 suggested that Pd was mainly kept in the roots of vetiver grass. The toxicity of Pd to vetiver grass was observed at concentrations 20 ppm as demonstrated by the reduced growth and drying up of the aerial biomass of the grass. The results revealed that vetiver grass may have potential in the phytoremediation and recovery of palladium for reuse by burning and reprocessing of ash.