Physicomechanical properties, stabilization mechanism, and antifungal activity of alkali-activated slag mixed with Cr6+ and Ni2+ rich industrial wastewater

An eco-sustainable approach applied to full disposal of Ni and Cr (VI) wastewater through the fabrication of alkali-activated slag (AAS). The impact of activator type (NaOH, Na2SiO3, and NaAlO2), heavy metal-containing-wastewater (Ni or Cr), and curing time (1-90-day) on the compressive strength, drying shrinkage, and immobilization efficiency have been addressed. Both compressive strength gain and loss were detected when Cr- and Ni-wastewater was mixed with AAS, depending on the type of alkali-activator. Nevertheless, all activated mixtures with wastewater demonstrated drying shrinkage values lower than that of the control sample (mixed with tap water). Ni and Cr have stabilized inside AAS-microstructure through the cationic exchange between Mg/Ni and Cr/Al within hydrotalcite phase or their localization on a negative charge of tetrahedral Al atom inside activated aluminosilicate skeleton. All the fabricated samples showed Ni and Cr concentrations in leachates lower than the regularity limits of toxicity characteristic leaching procedure (TCLP) and solubility threshold limit concentration (STLC) after 28-day of curing. The proposed strategy not only successfully applied for the safe disposal of heavy metals but also led to the fabrication of cementitious materials with high resistivity to detrimental sulfur oxidizing Aspergillus Niger fungal strain, which makes such cement effectively applied in microorganisms-rich-media.