The potential of phytomining and bioenergy integration for sustainable rehabilitation of nickel mined-out areas in the Caraga region, Philippines

Abstract

This study investigates the potential of phytomining combined with bioenergy production as a sustainable post-mining land use strategy in a nickel laterite mine site in the Caraga Region, Philippines. Focusing on naturally thriving and site-adapted plant species, the research identified four significant hyperaccumulators—Leucaena leucocephala, Casuarina cunninghamiana, Pennisetum polystachion, and Mimosa pudica—based on their capacity to accumulate nickel (Ni). Metal accumulation was assessed using heavy metal concentration in shoot, leaf-to-root ratio, translocation factors, and bioaccumulation coefficients. While conventional phytomining offers limited economic viability due to slow metal uptake and biomass yield, integrating bioenergy production significantly enhances its feasibility. Leucaena and Casuarina, in particular, exhibit high biomass productivity and energy generation potential, capable of producing up to 293 MWh/month per hectare. This dual-purpose system not only extracts residual metals but also provides renewable energy, aligning with circular economy principles. The study advocates for phytomining-bioenergy systems as a transitional strategy towards safer, productive post-mining land uses.