Growth potential of kenaf on coal tailings in South Africa

Abstract

The extraction and processing of mineral resources, particularly coal mining, leads to significant degrading of surrounding ecosystems, necessitating effective rehabilitation strategies. Coal tailings, the waste material from coal mining, are typically characterized by high heavy metal content and low pH, which pose severe challenges to plant growth. However, particular plant species exhibit physiological adaptations that enable survival under such stressors. Kenaf (Hibiscus cannabinus), an industrial crop known for its high fibre content and tolerance to metalcontaminated environments, presents potential for use in phytoremediation.

This study investigated the feasibility of cultivating kenaf on coal tailings and assessed its physiological performance and heavy metal absorption capacity. Kenaf was grown for two months in five soil treatments: control soil, two distinct raw coal tailing samples (Coal A and Coal B), and mixtures of each coal tailing with soil at a 1:2 ratio. Physiological responses were evaluated using an MPea fluorimeter to measure prompt chlorophyll fluorescence and modulated 820 nm reflection, alongside chlorophyll content analysis. Upon harvest, plant and soil samples were analysed for heavy metal and rare earth element content.

Results indicated that kenaf maintained functional photochemical activity and chlorophyll synthesis across all treatments, except Coal B, which exhibited reduced PSII and PSI efficiency. Despite these reductions, physiological parameters remained within normal ranges, suggesting kenaf's capacity to tolerate and grow in harsh conditions. Moreover, kenaf demonstrated the ability to absorb heavy metals and rare earth elements from coal tailings. These findings support the potential use of kenaf for phytoremediation and mine rehabilitation in South Africa, highlighting its resilience and environmental value in metal-contaminated soils