Mechanical and thermal activation of nickel-laterite mine waste as a precursor for geopolymer synthesis

Abstract

Geopolymer materials are increasing in scientific interest due to their flexibility in various applications. The geopolymer precursor is a mineral source with reactive Si and Al that is synthesized either mechanically or thermally to improve its cementitious activity. It was found out in previous literature that Nickel-laterite mine waste (NMW) is a prospective geopolymer precursor. However, this potentiality has not been explored in the Philippines, albeit the massive generation of NMW, which is merely dumped as a mining industry downstream process. This paper thus investigates the potential of the NMW as a raw material for geopolymer synthesis. Mechanical activation was performed using a ball mill with the following factors: ball-to-NMW ratio (4:1 and 10:1), mill speed (200 and 500 ​rpm), and grinding duration (30 and 120 minutes). Thermal activation was performed using a furnace treated at temperatures of 600, 700, and 800 ​°C. Response Surface Methodology (RSM) of the mechanical activation shows that a ball-to-NMW ratio of 10:1, mill speed of 443 ​rpm, and grinding duration of 120 minutes achieved optimized leachability of Si and Al. Thermal analysis results showed that NMW could be thermally activated from 600 to 800 ​°C. The results showed that both activation methods enhanced cementitious activity; hence, NMW could be utilized in geopolymer synthesis after thermal and mechanical activations.