Producing soil conditioner pellets from waste coal tailings for sustainable tomato production

Coal tailings (CT) are fine-grained waste products generated from washing run-of-mine (unprocessed) coal, and their accumulation poses ample challenges to storage facilities. However, CT are rich in organic carbon and comprise essential macro- and micro-nutrients for plant growth. This study proposed a novel approach to produce CT-based soil conditioner (CTSC) pellets for plants using a pelletiser. The pH value of raw CT was first adjusted to 6.16 to fall into the optimal range of 5.5–6.8 before adding supplementary nutrients to the feedstock for pelletisation. Various pellet production parameters (i.e., feedstock moisture content, speed and tilt angle of the pelletiser, and binder type and dosage) were optimised to produce pellets with suitable size (1.18−6.7 mm) and particle strength (1.11 MPa). A greenhouse test indicated a significant improvement in tomato growth by using the formulated CTSC pellets, whereas further field trials with CTSC treatment resulted in a marked increase of 11.1 % in tomato fruit yield and a significant improvement in soil properties. An economic and carbon footprint analysis was finally conducted to study the feasibility of the mass production of CTSC pellets. It confirmed that CTSC production is an economically viable and environmentally friendly way to manage waste CT, which can help to address the United Nations Sustainable Development Goals and achieve long-term sustainable waste management and food production. • 0.8 wt% of iron sulphate can reduce the pH of coal tailings (>8) to 6.16. • A coal tailings-based soil conditioner (CTSC) was formulated. • CTSC pellet production parameters were optimised. • CTSC improved plant growth and soil properties in both greenhouse and field tests. • Producing CTSC onsite is feasible and can lower coal mining's environmental impact.