Geopolymerization mechanism of binder-free mine tailings by sodium silicate

Abstract

The geopolymerization of solid substances rich in calcium and aluminum including mine tailings by sodium silicate is mainly believed to be under the influence of alkali activation. However, mine tailings’ relative neutral condition can decrease sodium silicate's overall alkalinity to an unfavorable condition for alkaline reactivity. The decreased sodium silicate's alkalinity initiates the silica gel's precipitation leading to the overall mine tailings’ geopolymerization. This makes sodium silicate as an alternative binder similar to Portland cement in cemented paste backfill. Any changes in mine tailings’ chemical state can accelerate or decelerate geopolymerization bringing inadequate knowledge about strength development. Thus, mine tailings’ geopolymerization by sodium silicate was investigated at different pH values and compared with cementation by Portland cement. It was found that the elevation in sodium silicate content decreases the acidification influence of mine tailings and postpones the strength development. The setting time of geopolymerised and cemented mine tailings were comparable, but pre-acidification of sodium silicate considerably accelerated the geopolymerization process. This made sodium silicate more advantageous over Portland cement because of manageable curing behavior and strength development. The obtained experimental results were discussed through several mechanical, rheological, microstructural, mineralogical, and chemical tests and analyses. © 2020 Elsevier Ltd