The increasing generation of industrial waste sludge poses a serious worldwide problem with detrimental effects on the environment and the economy. Effective utilization of waste sludge in sustainable construction practices offers a universal solution to mitigate environmental impacts. As the mining industry continues to extract clay from clay mines, the demand for sustainable practices in both clay mineral extraction and brick production is growing. Bricks are fundamental in masonry construction, and current research is exploring the integration of industrial waste materials into fired clay bricks to enhance their properties and mitigate environmental impacts. This study investigates the incorporation of waste sludge in brick manufacturing to assess its potential for reducing environmental burdens while maintaining technical performance. X-ray Fluorescence Spectrometry (XRF) analysis reveals that both clay soil and mosaic sludge contain high levels of silicon dioxide (SiO2) and aluminum oxide (Al2O3), supporting their suitability as partial substitutes for clay soil. Incorporating up to 30% of body mill sludge (BS) and polishing sludge (PS) into the brick mix significantly enhances physical and mechanical properties, resulting in reduced shrinkage, increased porosity, and improved compressive strength, reaching up to 25 N/mm(2). Initial rate of suction tests shows values below 5 g/mm(2), indicating optimal water absorption characteristics. Various leachability assessments, including the Toxicity Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP), and Static Leachate Test (SLT), confirm that bricks containing up to 30% BS and PS comply with United States Environmental Protection Agency (USEPA) and Environment Protection Authority Victoria (EPAV) standards for heavy metals, making them environmentally safe for use. Additionally, indoor air quality assessments confirm that these bricks meet Industry Codes of Practice on Indoor Air Quality (ICOP-IAQ) guidelines. This study demonstrates that using BS and PS as alternative raw materials offers a sustainable, cost-effective solution aligned with Sustainable Development Goals (SDGs), promoting cleaner production practices in brick manufacturing.

Little was known about the leaching behavior of potentially toxic elements (PTEs) from soils under the interaction between freeze-thaw (F-T) cycle and the solutions of varying pH values. In this study, PTEs leachability from soils before and after F-T tests was evaluated using toxicity characteristics leaching procedure (TCLP) test. The microstructure and mineralogical evolution of soil mineral particles were conducted using pores (particles) and cracks analysis system (PCAS) and PHREEQC. The results indicated that during 30 F-T cycles, the maximum leaching concentrations of PTEs were 0.22 mg/L for As, 0.61 mg/L for Cd, 2.46 mg/L for Cu, 3.08 mg/L for Mn, 29.36 mg/L for Pb and 8.07 mg/L for Zn, respectively. Under the coupled effects of F-T cycle and acidification, the porosity of soil particles increased by 4.79%, as confirmed by the microstructure damage caused by the evolution of pores and cracks. The anisotropy of soil particles increased under F-T effects, whereas that decreased under the coupled effects of F-T cycle and acidification. The results from SEM-EDS, PCAS quantification and PHREEQC modeling indicated that the release mechanism of PTEs was not only associated with the microstructure change in mineral particles, but also affected by protonation, as well as the dissolution and precipitation of minerals. Overall, these results would provide an important reference for soil remediation assessments in seasonal frozen areas.

This study sheds light on the engineering and environmental performance of lime-activated incinerated sewage sludge ash (ISSA) and ground granulated blast furnace slag (GGBS) treated Hong Kong marine deposits (HKMD) slurry by stabilisation/solidification (S/S) technology, which is proposed using as fill materials in reclamation projects. The S/S performance of the treated HKMD with distilled water and seawater under different salinities was investigated. The results show that seawater could help S/S treated HKMD gain strength by using activated industrial wastes (ISSA and GGBS). The hydration and pozzolanic reactions between ISSA, GGBS, CaO and clayey compositions in HKMD make contributions to the strength development, porosity decrease and heavy metals stabilisation, which is supported by the characterization analysis including thermo-gravimetric (TG) analysis, mercury intrusion porosimetry (MIP) tests, nitrogen adsorption/desorption isotherms (NAI), scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS) and the leaching test of toxicity characteristic leaching procedure (TCLP). Seawater of 1.8% salinity (18 g/kg) is better than the distilled water and seawater of 3.6% salinity as a substrate solution in the S/S treated HKMD, because of the highest unconfined compressive strength and lowest porosity in the treated samples. The highest pH may account for its highest strength under the 1.8% salinity conditions. The S/S process could effectively stabilize the contaminants regardless of the curing time and the salinity of the mixing solution, and the leachates from the stabilized HKMD are environmentally safe and meet the requirement of standard in Hong Kong on the recycling treated soil. Therefore, recycling wastes-ISSA and GGBS with lime can be used as an appealing binder to stabilize/solidify marine deposits as environmental-friendly reusable materials in reclamation projects.

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.