Valorization of steel slag by a combined carbonation and granulation treatment

Abstract

This work reports the results of a combined accelerated carbonation and wet granulation treatment applied to Basic Oxygen Furnace (BOF) steel slag with the aim of producing secondary aggregates for civil engineering applications and of storing CO2 in a solid and thermodynamically stable form. The tests were carried out in a laboratory scale granulation device equipped with a lid and CO2 feeding system. In each test, humidified slag (liquid/solid ratio of 0.12 l/kg) was treated for reaction times varying between 30 and 120 min under either atmospheric air or 100% CO2. Under both conditions, the particle size of the treatment product was observed to increase progressively with reaction time; specifically, the d(50) values obtained for the products of the combined granulation and carbonation treatment increased from 0.4 mm to 4 mm after 30 min and to 10 mm after 120 min. Significant CO2 uptake values (between 120 and 144 g CO2/kg) were measured even after short reaction times for granules with diameters below 10 mm and for the coarser particle size fractions after reaction times of 90 min. The density, mineralogical composition and leaching behavior of the obtained granules were also investigated, showing that the combined granulation-carbonation process may be a promising option for BOF slag valorization, particularly in terms of decreasing the Ca hydroxide content of the slag. Another interesting finding was that the leaching behavior of the product of the combined treatment appeared to be significantly modified with respect to that of the untreated slag only for coarse uncrushed granules, an indication that the carbonation reaction occurs mainly on the outer layer of the formed granules. (C) 2013 Elsevier Ltd. All rights reserved

Carbonation of BOF Slag in a Rotary Kiln Reactor in View of the Scale‐Up of the Wet Route Process

“…Ca, K, Mg, and Na release decreased compared to the fresh slag, in accordance with the pH values measured after the treatment. In particular, the decrease in the Ca concentration, from 1500 mg/L to around 700 mg/L (for Z3) and 800 mg/L (for Z1 and Z2), was linked to the formation of CaCO 3 , less soluble than CaO and Ca(OH) 2 , in accordance to what reported in our previous study and with the results of Morone et al , where Ca concentrations in the eluates decreased of at least one order of magnitude compared to the untreated material.…”

Accelerated Carbonation of Steel Slags Using CO2 Diluted Sources: CO2 Uptakes and Energy Requirements

“…The thin-film route carbonation tests were carried out on BOF slag samples c and d in a pressurized stainless steel reactor placed in a water bath for temperature control. The operating conditions selected for this route based on previous investigations (Baciocchi et al, 2011(Baciocchi et al, , 2015Morone et al, 2014) were a L/S of 0.3 l/kg, a temperature of 50°C, and a total pressure of 7-10 bar. For both types of routes, different reaction times (ranging from 0.5 to 24 h) and CO2 concentrations in the gas flow were tested.…”

“…Several studies have shown that a number of different types of steel slag present a significant reactivity with CO2, allowing to achieve, for specific process routes and operating conditions, relevant CO2 uptakes (Huijgen et al, 2005;Baciocchi et al, 2010Baciocchi et al, , 2015Uibu et al, 2011;Chang et al, 2012;Santos et al, 2013a,b). Furthermore, several types of residues generated in steel manufacturing plants, such as Basic Oxygen Furnace (BOF), Electric Arc Furnace (EAF), and argon oxygen decarburization (AOD) slag, are typically not valorized and generally landfilled, or employed only for low-end applications, owing for their significant content of free calcium and magnesium (hydr)oxides that may result in poor volumetric stability and hence in a low technical performance in construction applications (Morone et al, 2014). Therefore, accelerated carbonation of these types of materials may also represent a treatment strategy to improve their properties in view of valorization.…”

“…It should be noted, however, that in a recent study, milder operating conditions were shown to be effective employing a proper lixiviant (ammonium chloride) to enhance calcium dissolution (Mattila et al, 2014). Besides, promising results in terms of CO2 uptake (even if lower than those attained through the former route) have been achieved also via the thin-film (or wet) route (Baciocchi et al, 2011(Baciocchi et al, , 2015Santos et al, 2013b;Morone et al, 2014), which is operated at lower temperature and CO2 pressure and also presents the advantage of not generating a liquid by-product that necessitates suitable management and treatment.…”

Carbonate-bonded construction materials from alkaline residues

“…The production of carbonate-bonded aggregates from Basic Oxygen Furnace (BOF) steel slags was investigated by Morone et al [48] in a lab-scale granulation device and more recently by the same group also in a pilot-scale rotating drum [49]. Operating at lab-scale at 40% CO 2 concentration and ambient temperature and pressure, allowed to obtain a CO 2 uptake of 2.5% immediately at the end of the test (30 min) and of 5.5% after 28 days curing in a moist atmosphere.…”