Stabilization/solidification of Mn-contaminated clay slurry by using CaO-GGBS: Effects of anions

Clay sediment is removed by dredging, resulting in the disposal of enormous waste sediment clay slurries that consumes land space, as well as risks the human health and the environment. Manganese (Mn) is often identified in clay slurries. Quicklime (CaO)-activated ground granulated blast-furnace slag (GGBS) can be used to stabilize/solidify (S/S) contaminated soils; nevertheless, few studies have been published on the S/S of Mn-contaminated clay slurries using CaO-GGBS. Moreover, the anions contained in clay slurries may affect the S/S efficiency of CaO-GGBS in treating Mn-contaminated clay slurries, but this effect has hardly been investigated. Therefore, this study investigated the S/S efficiency of CaO-GGBS in treating MnSO4-bearing and Mn(NO3)2-bearing clay slurries. The effect of anions (i.e. SO42- and NO3-) on the strength, leachability, mineralogy, and microstructure of Mn-contaminated clay slurries treated with CaO-GGBS was explored. Results showed that CaO-GGBS could improve the strength of both Mn-contaminated slurries to meet the strength requirement for landfill waste outlined by United States Environmental Protection Agency (USEPA). The Mn leachabilities of both Mn-contaminated slurries were decreased to be less than the Euro limit for drinking water after cured for 56 days. The MnSO4-bearing slurry generally produced higher UCS while lower Mn leachability than Mn(NO3)2-bearing slurry at the same CaO-GGBS addition. CSH and Mn(OH)2 were formed, thereby enhancing strength and reducing leachability of Mn. Ettringite in CaO-GGBS-treated MnSO4-bearing slurry, which was formed by the supply of SO42- from MnSO4, further contributed to the strength enhancement and the decrease of Mn leachability. Ettringite was the factor leading to the difference in strength and leaching properties between MnSO4-bearing and Mn(NO3)2-bearing clay slurries. Hence, anions contained in Mn-contaminated slurries significantly affected the strength and the Mn leachability, and need to be identified before CaO-GGBS was used to treat such slurries.