Effect of potassium silicate and aluminate on the stabilisation of gold mine tailings

Abstract

In this study, acidic gold mine tailings were alkali activated using potassium hydroxide (KOH). The effect of potassium silicate (KS) and potassium aluminate (KA) on the strength and durability of the synthesised geopolymers was investigated. An optimisation experimental programme of various conditions was used to get the best geopolymers in terms of strength and metal leachability. A 1·1 mass/mass (m/m) potassium silicate : potassium hydroxide activation solution yielded a geopolymer with an unconfined compressive strength (UCS) of 9·94 MPa after curing for 5 d at 80ºC. A 2·8 m/m potassium aluminate : potassium hydroxide activation solution yielded a geopolymer with a UCS of 18·10 MPa after curing for 5 d at 100ºC. The potassium aluminate-based geopolymer was more durable for use as a backfill material as, after 10 wet and dry cycles, it had a UCS of 4·8 MPa whereas the potassium silicate-based geopolymer had a UCS of 1·23 MPa. The potassium aluminate-based geopolymer resulted in over 85% reduction in leachability of heavy metals from the cured geopolymer. This study showed that potassium aluminate activation of acidic gold mine tailings is an attractive route to stabilise/solidify hazardous material. The use of elevated temperature to achieve high strength for the geopolymer pales in comparison to the energy requirements of cement production.