The durability of slag and tannery sludge based geopolymer corroded by acid and base solutions

Abstract

The current treatment (landfill, composting, and incineration) of chromium-containing sludge can contaminate soil, surface water and groundwater. In this study, tannery sludge and granulated blast furnace slag was chosen to make a geopolymer and its ability to resist acid and alkali was investigated by immersing them in different solutions for 28 d. The experimental results showed that when pH value increased from 1.0 to 13.0, the compressive strength linearly increased from 36.7 MPa to 68.4 MPa while the porosity decreased from 4.37 % to 3.4 %. The results of NMR, SEM and FIR showed that the H+ in HCl acid solution depolymerized the three-dimensional network structure of the geopolymer and acicular product (CaCl2) was generated, which leaded to the increase in small pores and large pores. However, when immersed in alkaline solution the secondary polymerization occurred and more C-S-H appeared, making the geopolymer denser. In addition, the environmental benefits of the geopolymer were investigated and the results showed that the leaching concentration ranges of total chromium and Cr(VI) were 1.21–0.97 mg/L and 0.04–0.06 mg/L, both of which were far below the requirement of standards. The CO2 emission was 8.06 kg/(m3 Mpa), which was roughly half of the ordinary Portland cement (18 kg/(m³ MPa)). Therefore, the geopolymer could be a way to treat tannery sludge and the geopolymer made of tannery sludge and slag had the potential to be environmentally friendly building materials.