Autoclave-free ultra-early strength concrete preparation using an early strength agent and microstructure properties

Solidification and stabilization of Pb-Zn mine tailing with municipal solid waste incineration fly ash and ground granulated blast-furnace slag for unfired brick fabrication

The mismanaged and abandoned mine tailings are an important source of heavy metal pollution in the mining regions, and there is a significant need to develop technically, environmentally, and economically feasible and sustainable solutions to manage them. This study explored the solidification and stabilization of the tailing from an abandoned Pb-Zn mine using municipal solid waste incineration fly ash (MSWIFA) blended with ground granulated blast-furnace slag (GGBFS) for fabricating unfired bricks, and systematically characterized the products' mechanical and environmental performance. Various hydration products, such as ettringite, portlandite, and hydrotalcite, were formed in the unfired bricks in the solidification and stabilization process, which enhance the physical strength of unfired bricks and help immobilize the heavy metals. Slaking treatment of MSWIFA significantly increased the mechanical strength, reduced the water absorption, and improved the durability of unfired bricks, with the product prepared from MSWIFA with 7-day slaking exhibiting the highest unconfined compressive strength (12.3 MPa) after 56 days of curing. The concentrations of As (0.35-1.49 μg/L), Cd (0.35-0.70 μg/L), Cr (1.38-9.40 μg/L), Cu (2.28-5.87 μg/L), Ni (0.16-2.24 μg/L), Pb (0.16-59.80 μg/L), and Zn (1.60-10.80 μg/L) in the leachates of unfired bricks were below the relevant regulatory limits for surface water and groundwater. Converting the mine tailing (with MSWIFA and GGBFS) to different types of unfired bricks could yield economic payback in the range of 283.7-306.5 Yuan per ton. Replacing cement with MSWIFA blended with GGBFS in the solidification and stabilization treatment could save about 0.15 ton of cement per ton of mine tailing disposed, which avoids significant energy use and carbon dioxide emissions. These findings demonstrate that utilization of mine tailings and industrial wastes to fabricate unfired bricks is a promising way of reusing such wastes and controlling the associated pollution, which also brings significant economic benefit and improves environmental sustainability.