Strength and leaching behavior of tailing-based paste backfill at high water content amended with lime activated ground granulated blast furnace slag and flocculant

Flocculent is commonly used in mining activities to improve the concentration of tailing slurry by enhancing the sedimentation process of small tailings particles. The presence of flocculent in thickened tailings is unavoidable, and it affects the heavy metal leaching performances and mechanical and rheological characteristics of tailing-based cemented paste backfill (CPB). This study is carried out to investigate the physicochemical and leachability of CPB amended with flocculants and lime-activated ground granulated blast-furnace slag (GGBS). The stabilized samples were subjected to a series of model tests, including toxicity characteristics leaching procedure (TCLP) and pH, unconfined compressive strength (UCS), scanning electron microscopy (SEM), and X-ray diffraction. Moreover, the CPB amended with anionic polyacrylamide (APAM) demonstrated better performance in terms of a decrease in heavy metal leachability besides higher mechanical strength than poly aluminum chloride (PAC) and poly ferric chloride (PFC) samples. Furthermore, the UCS results showed that increasing binder content up to 15% negatively influences strength improvement of all stabilized samples because of weak connections between soil particles and cementitious material, resulting in high leachability of heavy metals. The analysis of XRD and SEM showed that anionic polyacrylamide (APAM) cases exhibited more voluminous hydration products, resulting in a compact stabilized matrix and substantially reduced heavy metal leachability.

Mechanical, Leaching, and Microstructure Properties of Mine Waste Rock Reinforced and Stabilised with Waste Oyster Shell for Road Subgrade Use

Two waste materials, oyster shell (NCOS; non-calcined oyster shell as coarse aggregate and COSP; calcined oyster shell powder as total and partial cement replacement) are used to reinforce and stabilise poorly graded and heavy metal-contaminated mine waste rock (MWR) for pavement subgrade use. Mechanical, leaching, and microstructural tests and analysis were performed on reinforced and stabilised samples to evaluate the effectiveness of the reinforcement and stabilisation of the MWR. Experimental results revealed NCOS and COSP improved the mechanical, leaching, and microstructural properties of the stabilised composite, with a 5% cement–15% COSP–15% NCOS mix being optimal when compared to the control mixes of cement only and no- NCOS. Higher COSP contents beyond 10% reduced the heavy metal contents significantly, but with relatively lower unconfined compressive strengths. Microstructural test results revealed the formation of calcium silicate hydrate (CSH), calcium aluminium silicate hydrate (CASH), ettringite, and calcite as the stabilisation products. Heavy metal complexes in both the cement-only and cement–NCOS–COSP mixes were also found. It is concluded that NCOS reinforced and improved the grading of poorly graded MWR, and that COSP stabilised and immobilised heavy metals present in MWR, thereby improving strength and other engineering properties for subgrade use.