Abstract
The proper disposal of Lead-Zinc Smelting Slag (LZSS) having toxic metals is a great challenge for a sustainable environment. In the present study, this challenge was overcome by its solidification/stabilization through alkali-activated cementitious material i.e., Blast Furnace Slag (BFS). The different parameters (water glass modulus, liquid-solid ratio and curing temperature) regarding strength development were optimized through single factor and orthogonal experiments. The LZSS was solidified in samples that had the highest compressive strength (after factor optimization) synthesized with (AASB) and without (AAS) bentonite as an adsorbent material. The results indicated that the highest compressive strength (AAS = 92.89MPa and AASB = 94.57MPa) was observed in samples which were prepared by using a water glass modulus of 1.4, liquid-solid ratio of 0.26 and a curing temperature of 25 °C. The leaching concentrations of Pb and Zn in both methods (sulfuric and nitric acid, and TCLP) had not exceeded the toxicity limits up to 70% addition of LZSS due to a higher compressive strength (>60 MPa) of AAS and AASB samples. While, leaching concentrations in AASB samples were lower than AAS. Conclusively, it was found that the solidification effect depends upon the composition of binder material, type of leaching extractant, nature and concentration of heavy metals in waste. The XRD, FTIR and SEM analyses confirmed that the solidification mechanism was carried out by both physical encapsulation and chemical fixation (dissolved into a crystal structure). Additionally, bentonite as an auxiliary additive significantly improved the solidification/stabilization of LZSS in AASB by enhancing the chemical adsorption capacity of heavy metals.
Highlights
Nowadays, the increase in hazardous wastes, which contains various heavy metals due to industrialization has attracted the attention of scientists regarding its proper disposal
The samples with the highest compressive strength were prepared by substituting different proportions of bentonite and a higher compressive strength were prepared by substituting different proportions of bentonite and a higher strength was observed with the 4% addition of bentonite
The decrease positive interaction of Blast Furnace Slag (BFS) and Lead-Zinc Smelting Slag (LZSS) resulted in an increase in the compressive strength of solidified in strength with the addition of LZSS (>40%) was due to less activity substance in cementitious material bodies
Summary
The increase in hazardous wastes, which contains various heavy metals due to industrialization has attracted the attention of scientists regarding its proper disposal. Smelting Slag (LZSS) is an industrial waste produced during the smelting of lead (Pb) and zinc (Zn) from their ores. It is considered hazardous waste as to it contains a number of heavy metals including Pb, Zn, Cu, Mn, Cr, Cd and Ni etc. This kind of waste having heavy metals. Res. Public Health 2019, 16, 1121; doi:10.3390/ijerph16071121 www.mdpi.com/journal/ijerph
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