Directly upcycling copper mining wastewater into a source of mixing water for the preparation of alkali-activated slag materials

Mining wastewater (MWw) in tailing ponds is one of the major obstacles in reusing tailings in practice and should be disposed preferentially. This paper investigated the feasibility of exploring MWw from copper mining as a source of mixing water to prepare activators for alkali-activated slag materials (AASM). Four MWws with different concentrations were prepared by using MWw to replace all, 1/2, 1/3, and 1/4 of tap water. The in-fluences of different MWws on the setting time, hydration kinetics, hydration products, compressive strength, nano-mechanical properties, pore structure of AASM were investigated. Experimental results confirmed that MWw can be upcycled as the partial or total mixing water for alkali-activated slag materials. The influence of MWw on the properties of AASM was related to its concentration. MWw with low concentrations accelerated the hydration of slag at early ages, nevertheless raw MWw without dilution slightly impeded the hydration process. Although no new hydration product is induced by adding MWw, both NMR pore analysis and nanoindentation testing suggested that the addition of MWw densified the hydration products, which is beneficial for mechanical properties of AASM. As a result, the 28d compressive strengths of AASM increased with increased concentrations of MWw by -0.8 to 19.9%. Through this paper, a low-cost, green and practical method was developed as an option for the disposal and recycle of MWw.