Understanding the deterioration mechanism of geopolymers for application in acidic systems used for in situ recovery (ISR)

Geopolymer-based barriers, synthesised from mine tailings, show promise for use in acidic in-situ recovery well fields, where conventional Portland cement barriers degrade rapidly. This study investigates the long-term performance of geopolymers, cast as cylinders and subjected to ferric sulphate-sulphuric acid and ferric chloride-hydrochloric acid lixiviants for 300 days. During this time, degradation progressed from the exposed surface inwards, resulting in three clearly identifiable concentric zones: (1) a deteriorated region, (2) an intermediate region and (3) the unreacted core. In Zones 1 and 2, dealumination of the aluminosilicate binder phases was significant, generating (secondary) residual phases with a higher Si/Al ratio that appear more resistant to ongoing acid attack. When combined with strong leaching of sodium and calcium from these phases, this resulted in enhancement in the porosity of these zones, the formation of channels/cracks, and reduced the resistance of the impacted regions to mechanical deformation. However, the formation of other secondary phases such as (i) gypsum and hydronium/natrojarosite for the ferric sulphate-sulphuric acid system and (ii) akagenéite for the ferric chloride-hydrochloric acid system, countered the development of porosity and the reduction in mechanical resistance. The key outcome from these combined findings was demonstration of the formation of deteriorated, yet competent outer zones that slowed the unreacted core deterioration rate. While further work is required to assess the prolonged behaviour of these protective layers and in turn, the lifetime of these geopolymers under in-situ recovery conditions, this study indicates that these materials may be suitable for application as barrier materials in these settings.