Siderite-calcite (FeCO3–CaCO3) series cement formation by accelerated carbonation of CO2(g)–H2O–Fe–Ca(OH)2 systems

Accelerated carbonation of steel slag monoliths at low CO2 pressure – microstructure and strength development

“…The role of dissolved-CO 2 in the release of Ca/Mg/Fe by primary-dissolution of the parent sources during accelerated carbonation is still underappreciated. However, a recent set of studies have shown that dissolved-CO 2 can even lead to significant primary-dissolution of metallic Fe(0) to produce FeCO 3 cement [38,41,42]. Extending onto this observation, this study also investigates whether accelerated carbonation of non-ferrous slags rich in Fe-minerals could also lead to the formation of clinker-free carbonate-bonded blocks in which hazardous metals are also immobilized.…”

“…In case of carbonate-bonded systems, the mechanical properties are known to depend simultaneously on the amount of the carbonate binders as well as on their spatial distribution, and crystal shape/size [38,41]. Higher temperature/CO 2pressure are generally known to result into higher amounts of carbonatebinder; however, for a given amount of carbonates formed, slower rates of carbonate formation at lower temperature/CO 2 -pressure result in well-formed carbonate crystals that connect precursor particles and provide higher mechanical strength than rapidly precipitated fine carbonates randomly distributed in the available pore space [38,41]. As such slower carbonation rates can result in higher compressive strength, in particular when the difference in carbonate amount is limited.…”

“…It must be noted that, when CO 2 is introduced in the green pellets, the CO 2 -speciation depends to a great extent on the pH of the pore solutions. To this end, based on the hydrolytic leaching behavior of uncarbonated FMS, the high pH in the pore solution of its green pellet means CO 2− 3 being the dominant CO 2 -species [37][38][39]. On the other hand, for the non-carbonated NFMS, while CO 2− 3 would still have been a major species (since pH > 9.4), HCO − 3 concentration is expected to increase considerably due to the relatively lower pH of the pore solutions.…”

“…5 (c-d)). Such simultaneous decreases in pH and Caleaching in FMS on carbonation are usually attributed to the formation of Ca-carbonates [37][38][39]. Since all the mixes contain FMS, its behavior is reported in all the figures (in Fig.…”

“…It must be noted that unlike the highly alkaline nature of ferrous slags, the native pH of the non-ferrous slags can even be below neutral [35,36]. It must further be noted that speciation and solubility of the dissolved-CO 2 itself is also dependent on the pH of the leaching solutions: in a solution with highly alkaline native pH, CO 2− 3 is the dominant species; while in a system with below-neutral pH acidic species (H + /H 2 CO 3 /HCO − 3 ) are the dominant species [37][38][39][40]. Therefore, mixing the lower-pH non-ferrous and higher-pH ferrous slags can have a significant influence on their behaviors, both during the primary dissolution of the slags (during carbonation), as well as during the secondary-dissolution of the carbonated blocks (during leaching).…”