Treatment of manganese-contaminated soil using lime-activated ground granulated blastfurnace slag

Abstract

Manganese (Mn)-contaminated soils poses certain risks and threats to human health and the environment. Lime-activated ground granulated blast-furnace slag (GGBS) has been commonly used in the soil stabilization, but few studies are conducted to use this stabilizer to treat the Mn-contaminated soil. Therefore, this study is to examine the effectiveness of lime-activated GGBS in the treatment of the Mn-contaminated soil. A series of laboratory tests were conducted to examine the properties of lime-activated GGBS to treat Mn-contaminated soil mixture which includes unconfined compressive strength (UCS) test, leaching test, X-ray diffraction (XRD) test and field emission scanning electron microscopy (FESEM) test. It is found that with increasing lime content, there is an increasing trend of increase strength for the treated Mn-contaminated soil. The strength of the treated Mn-contaminated soil also continued to increase with increasing curing ages tested at 28 days and 56 days. However, during the leaching test, the lime-activated GGBS is effective in immobilizing Mn (16000 ppm) presences in soil mixture as shown in the Mn leachability results but the strength gain is not as significant as compared to Mn (8000 ppm) which shows higher unconfined strength of soil with no heavy-metal contaminants. The leachate pH is also found to increases with higher lime content due to the alkalinity nature of lime. With the use of lime-activated GGBS in the soil, the Mn (8000 ppm) at both 28 days and 56 days leachability has been significantly reduced to values that is less than 0.4mg/kg which is acceptable by Public Utilities Board, Singapore (PUB). However, the Mn (16000 ppm) at 28 days, even at increasing lime concentration, the Mn leachability is still at unacceptable level set by PUB. Mn (16000 ppm) at 56 days, however, has lower Mn leachability which is acceptable by PUB after 0.5% lime. The XRD results of Mn (16000 ppm), 56 days, show the C-S-H and Mn(OH)2 present in Mn-contaminated soils. The formation of these two minerals reduces the Mn leachability in lime-activated GGBS-treated Mn-contaminated soil. The SEM result confirms the formation of CSH.