Red mud-metakaolin based cementitious material for remediation of arsenic pollution: Stabilization mechanism and leaching behavior of arsenic in lollingite.

The proper treatment of lollingite is of great significance due to its rapid oxidation leading to release of arsenic into the environment. Herein, a green multi-solid waste geopolymer, consisting of red mud, metakaolin, blast furnace slag, and flue gas desulfurization gypsum, was developed. The obtained red mud-metakaolin-based (RMM) geopolymer demonstrated good arsenic retention capability. The results showed that the replacement of SO 4 2− in ettringite with AsO 4 2− via ion exchange, formation of Ca-As and Fe-As precipitates, and physical encapsulation with aluminosilicate gel were the main mechanisms that prevented the release of arsenic. Further dissolution of ettringite in RMM was alleviated by adding a suitable amount of Ca(OH) 2 and controlling the pH of the leachate. TCLP results verified that RMM materials possessed an outstanding ability to stabilize arsenic, with a leaching rate below the permitted value of 5 mg/L for safe disposal. The low leachability of the RMM geopolymers (<0.50 mg/L) is potentially related to the pH buffering capacity of the hydration products at a pH range of 2–5. RMM geopolymers showed a high compressive strength (>15 MPa) and low arsenic leaching concentration (<2.66 mg/L) after 28 days of curing. These results demonstrate the potential of RMM geopolymers to be utilized as an environmentally friendly backfilling cementitious material for sustainable remediation of arsenic pollution. • The evolution pathways of arsenic from lollingite to RMM samples was investigated. • The dissolution of ettringite is correlated with the increase of As leachability. • Arsenic-bearing phases in RMM samples were demonstrated to be stable at pH 2–5. • RMM can be used as environmentally multi-solid waste cementitious material. [ABSTRACT FROM AUTHOR]