The potential for using slags activated with near neutral salts as immobilisation matrices for nuclear wastes containing reactive metals

Bai, Yun; Collier, N.C.; Milestone, Neil B.; Yang, Chen

doi:10.1016/j.jnucmat.2011.04.011

Cited by 44 publications

(28 citation statements)

References 45 publications

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“…Alkali-activation of slags is also achievable using, as sole activator, mildly alkaline solutions based on sodium carbonate (Na 2 CO 3 ) or sodium sulfate (Na 2 SO 4 ) [22,23]. Sodium carbonate can be obtained from mined trona, and also via the Solvay process [24], while sodium sulfate is obtained from mined mirabilite, and as a by-product from HCl production or from processes where surplus sulfuric acid is neutralised by sodium hydroxide.…”

Section: Brief Overview Of Alkali-activated Slag Materialsmentioning

confidence: 99%

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Advances in near-neutral salts activation of blast furnace slags

Bernal

2016

RILEM Tech Lett

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The utilisation of near-neutral salts as activators to produce alkali-activated slag cements offers several technical advantages, including reduced alkalinity of the binders, minimising the risk associated with handling of highly alkaline materials, and better workability of the fresh paste compared to that of sodium silicate-activated slag cements. Despite these evident advantages, the delayed setting and slow early-age mechanical strength development of these cements have limited their adoption and commercialisation. Recent studies have demonstrated that these limitations can be overcome by selecting slags with chemistry, which is more prone to react with near-neutral salts, or by adding mineral additives. A brief overview of the most recent advances in alkali-activation of slags using either sodium carbonate or sodium sulfate as activators is reported, highlighting the role of material design parameters in the kinetics of reaction and phase evolution of these cements, as well as the perspectives for research and development of these materials.Keywords: Alkali-activation; Blast furnace slag; Sodium Carbonate; Sodium sulfate; Characterisation Brief overview of alkali-activated slag materialsAlkali-activated cements are materials produced via the chemical reaction of a poorly crystalline aluminosilicate powder, and a highly alkaline solution, to form a hardened solid. These materials have been studied for more than a century, and in the past decades one of the main drivers for their development has been the potential environmental benefits associated with their production [1]. Alkali activated cements are usually produced from industrial wastes or byproducts such as blast furnace slag derived from the ironmaking industry, fly ashes from the coal combustion process, among others [2], and are now commercialised in several places around the world [3]. These materials can develop desirable properties including high mechanical strength [4], good retention of integrity when exposed to high temperatures [5] and acidic media [6], if properly formulated and cured. Significant advances have been made over the past decade in understanding alkali-activated slag materials at micro-and macroscopic scales, as discussed in recent reviews [7,8], particularly for those materials produced with sodium silicate solutions as alkali-activator. The influence of formulation parameters such as chemistry of the slag [9, 10], type of activator [11], addition of metakaolin [12] or fly ashes [13], on the microstructural development and therefore performance of these materials have been the main focus of study in recent years. The application of advanced analytical techniques, including synchrotron X-ray diffraction [14] and X-ray fluorescence microscopy [15], along with thermodynamic modelling [16], have revealed detailed information about the chemistry and phase assemblage of these cements, allowing the development of descriptive models for the activation processes of slags (Fig. 1). Figure 1. Simplified schematic diagram of the alk...

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Section: Brief Overview Of Alkali-activated Slag Materialsmentioning

confidence: 99%

“…These are important questions that need to be resolved, as sodium sulfate activated cements are currently attracting interest, particularly for specialised applications such as the encapsulation of radioactive metals [23] and sulfate-bearing nuclear wastes [38,40] where long-term stability is imperative.…”

Section: Sodium Sulfate Activated Slag Cementsmentioning

confidence: 99%

Advances in near-neutral salts activation of blast furnace slags

Bernal

2016

RILEM Tech Lett

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“…Sodium carbonate has been identified as a suitable possibility to achieve comparable pH in the pore solution of alkaliactivated slag to that identified in Portland cements (Bai et al, 2011), and is significantly less expensive than most other possible activators. Sodium carbonate activation of blast-furnace slag has been applied for several decades, especially in eastern Europe (Krivenko, 1994;Xu et al, 2008), as a more costeffective and environmentally friendly alternative to the widely used activators for production of activated slag products; it is possible in many parts of the world to obtain sodium carbonate either as a secondary product from industrial processes or by mining alkali carbonate deposits followed by moderatetemperature thermal treatment (Provis et al, 2014a(Provis et al, , 2014b.…”

Section: Introductionmentioning

confidence: 99%

Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

Bernal¹,

Nicolas²,

Provis³

et al. 2015

Advances in Cement Research

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An alkali-activated slag cement produced with a blend of sodium carbonate/sodium silicate activator was characterised. This binder hardened within 12 h and achieved a compressive strength of 20 MPa after 24 h of curing under ambient conditions, which is associated with the formation of an aluminium substituted calcium silicate hydrate as the main reaction product. Carbonates including pirssonite, vaterite, aragonite and calcite were identified along with the zeolites hydroxysodalite and analcime at early times of reaction. The partial substitution of sodium carbonate by sodium silicate reduces the concentration of carbonate ions in the pore solution, increasing the alkalinity of the system compared with a solely carbonate-activated paste, accelerating the kinetics of reaction and supplying additional silicate species to react with the calcium dissolving from the slag as the reaction proceeds. These results demonstrate that this blend of activators can be used effectively for the production of high-strength alkali-activated slag cements, with a microstructure comparable to what has been identified in aged sodium-carbonate-activated slag cements but without the extended setting time reaction usually identified when using this salt as an alkali activator.

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“…Alkali-activated wasteforms are in some instances dewatered by thermal treatment after hardening to reduce radiolysis [ 161 , 162 ], although this may not be practical in all cases due to handling issues and the possibility of cracking of larger blocks during thermal treatment. In some cases, mixed nuclear wastes will include reactive metals (particularly Al used in cladding) which can corrode at the high pH prevailing within AAM (or OPC) binder systems, leading to hydrogen generation and potential cracking of wasteforms; special low-alkalinity binders are desirable in such instances [ 163 ]. In designing and constructing an underground waste repository, barriers of swelling clays are often used with the intention of providing additional protection against groundwater ingress, but are also potentially reactive with concentrated alkalis, and so a low-alkalinity binder system would be preferred under such conditions [ 164 ].…”

Section: Stabilisation/solidifi Cation Of Radioactive Wastesmentioning

confidence: 99%

Other Potential Applications for Alkali-Activated Materials

Bernal

Schroeyers

Provis

et al. 2013

Alkali Activated Materials

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The focus of this chapter is the discussion of a variety of niche applications (other than as a large-scale civil infrastructure material) in which alkali-activated binders and concretes have shown potential for commercial-scale development. The majority of these applications have not yet seen large-scale AAM utilisation, except as noted in the various sections of the chapter. However, there have been at least pilot-scale or demonstration projects in each of the areas listed, and each provides scope for future development and potentially profi table advances in science and technology. In addition to the applications specifi cally discussed in this chapter, there are also commercial and academic developments in alkali-activation for specifi c applications including a commercial product which is being marketed as a domestic tiling grout showing some self-cleaning properties [ 1 ], as well as

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The potential for using slags activated with near neutral salts as immobilisation matrices for nuclear wastes containing reactive metals

Cited by 44 publications

References 45 publications

Advances in near-neutral salts activation of blast furnace slags

Advances in near-neutral salts activation of blast furnace slags

Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

Other Potential Applications for Alkali-Activated Materials

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