MgO-based Binder Research Articles

Impacts of biochar and slag on carbon sequestration potential and sustainability assessment of MgO-stabilized marine soils: insights from MIP analysis

MgO-based binders enhance soil stability and CO2 sequestration. This study examines soft dredged marine soils treated with MgO, integrated with biochar or slag, demonstrating significant improvements in soil properties and environmental benefits.

MgO-based binders with different formulations for solidifying Pb and Cd in MSWI fly ash: Solidification effect and related mechanisms

The MgO-based binder is a novel and effective material for solidifying municipal solid waste incineration fly ash (MSWI FA). In this study, the effect of MgO-based binders with different MgO contents on the solidification and stabilization of MSWI FA was investigated by adjusting the proportions of MgO, silica fume, and MSWI FA in the solidified system. The leaching behavior and immobilization mechanisms of Cd and Pb in the solidified bodies were focused on. The hydration products generated were characterized by XRD, FTIR, and TG analysis. The results demonstrated that the compressive strength of the solidified bodies and the immobilization efficiencies of heavy metals improved with the increase in MgO addition. The MSWI FA solidified by MgO-based binders could maintain low leaching toxicity over a wider pH range. The generated Mg-containing hydration products, including Mg(OH)2 and M-C-S-H gels, were believed to contribute to the reduction of the leaching concentrations of heavy metals. The immobilization mechanisms of Pb and Cd were different: the immobilization of Pb came from chemical chelation, and Cd was stabilized from alkaline precipitation. In conclusion, this work provides new insights into applying MgO-based binders in MSWI FA solidification.

Advances in the carbonation of MgO-based binder and CO2 utilization in the construction industry

Advances in the carbonation of MgO-based binder and CO2 utilization in the construction industry

Use of kaolinite clays in development of a low carbon MgO-clay binder system

Magnesium oxide based cements may provide a promising alternative to the conventional Portland cement in many applications. This study investigates the feasibility of using calcined kaolinitic clay to produce an MgO binder. The MgO-based binder were prepared using a low kaolinite content clay and metakaolin and were compared with a silica fume system. Implications of the addition of magnesium carbonate in the binder were also investigated. Isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) were used to study the hydration characteristics of the binder system whereas compressive strength and porosity were measured to determine mechanical and durability attributes. The economic and environmental aspects of the binder system is also discussed. Hydrotalcite like phases were clearly produced on hydration in the clay mixes containing carbonate additions. The compressive strength of clay mixes was at par or better compared to systems containing silica fume, and the clay systems had significantly lower porosity levels. The presence of magnesium carbonate further enhanced the physical properties of the clay mixes.

Influence of cellulose pulp on the hydration followed by fast carbonation of MgO-based binders

This study aims at assessing the potential use of cellulose pulp in MgO-water slurries with potential for precast composites. These systems for composites applications envisage encapsulating CO2 when exposed to fast carbonation. The effect of cellulose fibers was evaluated on samples after the drainage of MgO-cellulose-water slurries. Different cellulose mass fractions were added into MgO-water suspensions – up to 30 wt% – to study the MgO hydration during the first 96 h. Afterward, the carbonation of the hydrated products for 6 and 12 h was evaluated. The addition of cellulose, after hydration, increases the sample porosity, where Mg(OH)2 is the main crystalline phase and only minor traces of unreacted MgO are found. MgO-H2O systems after hydration do not present any binding capacity given the low density and high apparent porosity of the clusters. However, XRD and TG analyses show that exposing samples to a rich CO2 environment promotes the formation of nesquehonite (MgCO3·3H20), which significantly reduces the porosity induced by the cellulose hygroscopy. This reduction in porosity is greater for samples with cellulose fibers because of the greater content of nesquehonite produced in samples with cellulose. Besides, cellulose fibers are covered with nesquehonite nanocrystals after carbonation. By adding cellulose to water-MgO suspensions yields lighter products with promising potential for fiber-cement applications. Moreover, the addition of cellulose contributes to the encapsulation of CO2 in building materials through the Mg(OH)2 carbonation.

Hydration and Crystallization Behavior of MgO in Cold-Bonded Pellets Containing Basic Oxygen Furnace Dust

Basic oxygen furnace (BOF) dust is a kind of solid waste in the metallurgical steelmaking process, which contains more than 50 pct total iron and a certain amount of overburned MgO and CaO. Based on the nonhydraulic cementitious property of MgO in BOF dust, MgCl2 is added together as a binder to prepare cold-bonded pellets returning to BOF, which is the most economical route to recycle secondary resources. In this study, we investigated the hydration and crystallization behavior of MgO-based binder prepared by MgO superheated at 1500 °C and MgCl2 in cold-bonded BOF dust pellets, to solve the problem of whether the overburned MgO can be hydrated with MgCl2 to form crystalline phases, and generated nonhydraulic cementitious structure with high strength to consolidate the pellets. The results show that the overburned MgO prepared at 1500 °C and MgCl2 can form adhesive gels to absorb BOF dust particles by hydration reaction. The gels develop to 5Mg(OH)2·MgCl2·8H2O crystalline phase with a reticular structure after solidification, and the crystalline phase produces pellet mechanical strength by wrapping and connecting bridge. The hydration reaction produced by overburned MgO is incomplete, and the hydration reaction degree is 50 to 65 pct.

PC-based and MgO-based binders stabilised/solidified heavy metal-contaminated model soil: strength and heavy metal speciation in early stage

An investigation into using Portland cement (PC)-based and magnesia (MgO)-based binders for treating contaminated model soil was carried out to study the benefit of novel binders over conventional ones in stabilisation/solidification systems (S/S), as well as the binding mechanism involved. Binders used in this study include PC, ground granulated blast-furnace slag, pulverised fly ash and magnesia. The strength and the leaching properties of S/S treated samples by way of unconfined compressive strength and sequential extraction tests are presented. The results show that the early-age strength of these mixes is influenced by the reactivity of binders; heavy metals were principally distributed in the carbonate and the iron/manganese (Fe/Mn) oxide fractions in all mixes after 28 days of curing time; the speciation distribution characteristics are not the same among zinc (Zn), copper (Cu), nickel (Ni) and lead (Pb), and the stability of Zn, Cu, Ni and Pb benefits from a longer curing time and the use of magnesia.

Assessing long-term stability of cadmium and lead in a soil washing residue amended with MgO-based binders using quantitative accelerated ageing

A soil washing residue (SWR) (containing 90% clay, cadmium (Cd2+) of 132 mg/kg, lead (Pb2+) of 3410 mg/kg) was stabilized with MgO (M) and MgO + bioapatite (MB) respectively at a dosage of 5% in w/w. The stability of the metals in original and amended SWRs was assessed after immediate treatment and using a laboratory accelerated ageing method simulating 26, 52, 78 and 104 years in field conditions. The dissolved Cd2+ and Pb2+ from the SWR in Toxicity Characteristic Leaching Procedure (TCLP) leachates significantly reduced (by 96.84-99.06%) by both amendments after immediate treatment. The stabilization remained effective within simulated 26 years as the TCLP leached Cd2+ and Pb2+ kept below regulatory levels. This immobilization was mainly due to the increased non-bioavailable Cd2+ and Pb2+ from sequential extraction tests in SWR by the amendments. At simulated 52 years, the TCLP leached Cd2+ from M and MB exceeded regulatory level by 106% and 1% respectively. Large amounts of Cd2+ and Pb2+ were leached out by 36.74-48.18% regardless of the treatments at simulated 104 years. Although bioapatite can significantly aid the stabilization of metals by MgO, the stabilization effectiveness for both treatments diminished at simulated 52 years and from 52 to 104 years.

Effect of CO2 concentration on strength development and carbonation of a MgO-based binder for treating fine sediment.

We previously described a MgO-based binder for treating fine sediment and simultaneously store CO2. Here, we describe a study of the physical/mechanical characteristics and carbonation reactions of the MgO-based binder used to solidify/stabilize fine sediment in atmospheres containing different CO2 concentrations. Carbonation of the sediment treated with the MgO-based binder at the atmospheric CO2 concentration markedly improved the compressive strength of the product. The compressive strength was 4.78MPa after 365days of curing, 1.3 times higher than the compressive strength of sediment treated with portland cement. This improvement was caused by the formation of carbonation products, such as hydromagnesite, nesquehonite, and lansfordite, and the constant high pH (~ 12) of the specimen, which favored the growth of hydration products such as calcium silicate hydrates and portlandite. Very low compressive strengths were found when 50 and 100% CO2 atmospheres were used because of excessive formation of carbonation products, which occupied 78% of the specimen depth. Abundant carbonation products increased the specimen volume and decreased the pH to 10.2, slowing the growth of hydration products. The absence of brucite in specimens produced in a 100% CO2 atmosphere indicated that MgO carbonation is favored over hydration at high CO2 concentrations.

An evaluation of stabilised/solidified contaminated model soil using PC-based and MgO-based binders under semi-dynamic leaching conditions.

The leaching performance of stabilised/solidified contaminated model soil was studied to investigate the benefit of stabilisation/solidification treatment using novel binders over conventional binders. Different combinations of Portland cement (PC), ground granulated blast-furnace slag (GGBS), pulverised fly ash (PFA), and magnesia (MgO) were used and grouped into PC-based and MgO-based binders. A semi-dynamic leaching test was used, where the cumulative releases of Zn, Cu, Ni, Pb, Ca, and Mg were measured and the effective diffusion coefficients (De) and the leachability indices (LX) were calculated. The effects of different binders and water/cement ratios (w/c) on the migration of different metals after treatment were also discussed. The results showed that w/c ratio has a significant impact on the cumulative leachability of heavy metals. The diffusion coefficients of Pb and Zn are higher than those of Cu and Ni. In addition, mixes (w/c at 0.5:1) showed better performance in immobilising heavy metals than mixes (w/c at 1:1), especially in the case of Cu, Ni, and Pb.

Investigation of the accelerated carbonation of a MgO-based binder used to treat contaminated sediment

A MgO-based binder developed to simultaneously solidify/stabilize contaminated sediment and store CO2 has been described previously. The objectives of the study presented here were to investigate the kinetics of the carbonation reactions of the binder and the extent to which carbonation occurred and to identify the optimal conditions for using the binder. The carbonation reaction was clearly faster and the degree of carbonation higher at CO2 concentrations of 50 and 100% than in the ambient atmosphere (which contains 0.04% CO2). A modified unreactive core model adequately described the kinetics. The rate constants were 0.0217–0.319 h−1 and were proportional to the degree of carbonation. A high degree of carbonation, 93.8%, was achieved at a CO2 concentration of 100%. The water to sediment ratio strongly affected carbonation, the optimal ratio being around 0.7. The relative humidity did not strongly affect the carbonation performance. The carbonation products were magnesite (MgCO3) and nesquehonite (MgCO3·3H2O). X-ray diffraction analysis showed that brucite (Mg(OH)2) was not present, suggesting that brucite was very quickly transformed into magnesium carbonates, the presence of which was confirmed by thermal gravimetric analysis. The results indicated that, in 7 d, 1 kg of binder could sequester up to 0.507 kg of CO2 in a 100% CO2 atmosphere. The results indicate that the MgO-based binder has great potential to be used to sequester CO2 under accelerated carbonation conditions.

촉진탄산염화에 의한 마그네슘계 고화제의 강도 향상 특성

촉진탄산염화에 의한 마그네슘계 고화제의 강도 향상 특성

Development of an MgO-based binder for stabilizing fine sediments and storing CO2.

An MgO-based binder was developed that could stabilize fine dredged sediments for reuse and store CO2. Initially, a binder consisting of fly ash (FA) and blast furnace slag (BFS) was developed by using alkaline activators such as KOH, NaOH, and lime. The FA0.4-BFS0.6 binder (mixed at a FA-to-BFS weight ratio of 4:6) showed the highest compressive strength of 10.7 MPa among FA/BFS binders when 5 M KOH was used. When lime (L) was tested as an alkaline activator, the strength was comparable with those obtained when KOH or NaOH was used. The L0.1-(FA0.4BFS0.6)0.9 binder (10 % lime mixed with the FA/BFS binder) showed the highest strength of 11.0 MPa. Finally, by amending this L0.1-(FA0.4BFS0.6)0.9 binder with MgO, a novel MgO-based binder (MgO0.5-(L0.1-(FA0.4BFS0.6)0.9) 0.5) was developed, which demonstrated the 28th day strength of 11.9 MPa. The MgO-based binder was successfully applied to stabilize a fine sediment to yield a compressive strength of 4.78 MPa in 365 days, which was higher than that obtained by the Portland cement (PC) system (3.22 MPa). Carbon dioxide sequestration was evidenced by three observations: (1) the decrease in pH of the treated sediment from 12.2 to 11.0; (2) the progress of the carbonation front inward the treated sediment; and (3) the presence of magnesium carbonates. The thermogravimetric analysis (TGA) results showed that 67.2 kg of CO2 per ton of the treated sediment could be stored under the atmospheric condition during 1 year.

Multiscale structure of calcium- and magnesium-silicate-hydrate gels

Concrete is the world's most widely used building material. However, the production of CaO-based cements generates large amounts of anthropogenic emissions of CO2. Among different strategies to reduce CO2 emissions, newly developed MgO-based cements, though currently suffering from inferior mechanical properties, are some of the most promising and attractive options. By combining wide- and small-angle X-ray scattering and electron microscopy, we identified differences in the multiscale structure of the two main binding phases: the calcium-silicate-hydrate (C-S-H) gel for CaO-based cements and the magnesium-silicate-hydrate (M-S-H) gel for MgO-based cements. We found the primary unit at the nanoscale level of C-S-H to be a multilayer disk-like globule, whereas for M-S-H it is a spherical globule. These prominent differences result in diverse microstructures, leading to disparities in mechanical properties and durability for the associated cements. Modulating the M-S-H structure and enhancing the compatibility between C-S-H and M-S-H will be the key to improve the robustness of eco-friendly MgO-based binders.

MgO 기반 고화제를 이용하여 처리한 중금속 오염 준설토의 고형화/탄산염화 특성

A novel MgO-based binder was developed and applied to treat the anoxic sediment that was collected from Seonakdong river, Korea and was contaminated with heavy metals. The treated sediment was evaluated by measuring compressive strength, expansion, leaching of heavy metals and storage characteristics for <TEX>$CO_2$</TEX>. Initially, an optimal blending ratio of lime (L)/fly ash (FA)/blast furnace slag (BFS) that was to be mixed with MgO was screened to be <TEX>$L_{0.3}-FA_{0.1}-BFS_{0.6}$</TEX>. Long-term strengths of the sediments that were treated by various mixtures of MgO and <TEX>$L_{0.3}-FA_{0.1}-BFS_{0.6}$</TEX> were then evaluated and the blending ratios between 4 : 6 and 6 : 4 were found optimal, which yielded a compressive strength of 4.09 MPa. On this basis, the optimal MgO-based binder was selected to be a 5 : 5 mixture of MgO and <TEX>$L_{0.3}-FA_{0.1}-BFS_{0.6}$</TEX>. The good performance of the MgO-based binder was believed to be due to the formation of Mg <TEX>$(OH)_2$</TEX>, which filled the micropores and also increased the density of the solidified matrices. The MgO-based binder exhibited an average stabilizing capacities for heavy metals of 92.9%, which was similar to or higher than that of Portland cement. It was found that 69.1 kg of carbon dioxide could be sequestrated after 365 days of curing when treating a ton of anoxic sediments.