Inorganic polymer cement from Fe-Silicate glasses: Varying the activating solution to glass ratio

Large volumes of Fe-silicate glasses - slags - are produced as residues of metal production and waste treatment processes. It would be interesting if these materials could become an alternative group of precursors for the synthesis of inorganic polymer (IP) cements. This paper investigates the polymerisation of Fe-silicate glasses of composition (in wt%) SiO2: 40; FeO: 30; CaO: 15; Al2O3: 8 and an activating solution of composition (in wt%) Na2O: 15; SiO2: 13; H2O: 72. The mass ratio of the activating solution to the glass (L/S) was varied from 0.3 to 1.0 and the effect on the IP chemistry, microstructure and properties was investigated. Despite the high Fe and low Al contents of the glass, an IP cement could be synthesised, resistant to water dissolution and delivering mortars of compressive strength >52 MPa after 28 days curing at room temperature when using a L/S ratio of 0.45. Lowering the ratio from 1.00 to 0.45 results in a significant improvement in compressive strength, a lower porosity and when immersed in water, Na dissolution is decreased and water pH is lower. Microstructural investigation indicates that when the amount of activating solution is decreased, the degree of glass dissolution is lower resulting in less IP formation and a more homogeneous IP chemistry. Compared to higher L/S ratios, the IP mortar has a more densely packed microstructure of partially dissolved glass and sand aggregates bound by the IP matrix. At lower L/S ratios, the formation of micro scale shrinkage cracks in the IP matrix is strongly reduced, while at higher L/S ratios, shrinkage cracking is more pronounced and individual micro-cracks connect to form more pronounced large scale cracks. At a L/S ratio of 0.45, the IP cement is composed of 90 wt% Fe-silicate glass and only 10 wt% Na-silicate (% of powder mix) and it is indicated that this percentage can still be reduced. As 90 wt% of this IP cement is composed of a waste material and as curing is performed at ambient temperatures, its production is expected to have important ecological and economic benefits.status: publishe

Robert J. Baczuk v. Salt Lake Regional Medical Center and Dr. Brian Moench : Reply Brief

APPEAL FROM A FINAL JUDGMENT OF THE THIRD DISTRICT COURT THE HONORABLE HOMER F. WILKINSO

Quantification of the Fe3+ concentration in lead silicate glasses using X-band CW-EPR

The majority of the existing experimental techniques for determining the fractions of Fe3+ and Fe2+ in silicate glasses are based on X-ray or gamma-ray absorption. Materials with a high lead content are not suitable for these techniques because they strongly absorb such high-energy radiation. This work investigates the feasibility and precision of X-band CW-EPR as an alternative technique for the quantification of the concentration of Fe3+ in iron containing lead silicate glasses. This could be a viable alternative since it is based on the absorption of microwaves, which are not heavily influenced by the presence of lead. A practical and robust method using standards is proposed, based on the empirical relation between the concentration of Fe3+ species and the occurrence of two distinct features in the collected EPR spectra. It was found that EPR can indeed be used for the quantification of Fe3+ concentration in lead silicate glasses up until about 8 wt.% Fe2O3, depending on the lead content of the glass. A precision of about +/- 0.10 wt.% (2 sigma) was observed for two tested experimental set-ups. The quantification method proposed requires standards of known composition

Effect of Accelerated Carbonation on AOD Stainless Steel Slag for Its Valorisation as a CO2-sequestering Construction Material

Non-stabilized Argon Oxygen Decarburisation (AODNS) slag in powdered form was examined for its carbon dioxide sequestration capacity and for its potential utilization in the fabrication of high value building materials. The curing of the sample was carried out in two accelerated carbonation environments: i) in a carbonation chamber, maintained at atmospheric pressure, 22 °C, 5 vol.% CO2 and 80% RH; and ii) in a carbonation reactor, where the CO2 partial pressure (pCO2) and temperature could be further increased. In the carbonation chamber, an average compressive strength of over 20 MPa, on a 64 cm3 cubic specimen, was obtained after one week of curing, which is sufficient for many construction applications. Further carbonation resulted in a linear increase of strength up ~30 MPa after three weeks. The CO2 uptake followed a similar trend, reaching a maximum of 4.3 wt.%. In the reactor, the compressive strength improved with an increase in pCO2 up to 8 bar, temperature up to 80 °C, and duration up to 15 h where the maximum CO2 uptake was 8.1 wt%. The reduction in porosity in the carbonated specimens was approximately in line with the strength gain in the samples. Phase analysis by X-ray powder diffraction and inspection by scanning electron microscopy showed the precipitation of calcite and formation of significant amounts of amorphous material after carbonation. Infrared spectroscopy also pointed to the presence of aragonite and vaterite. In the carbonation chamber, the calcite morphology was uniform throughout the specimen. In the reactor, however, the calcite crystals near the outer edges of the cubes had different morphology than those near the core. Carbonation of the slag resulted in the reduction of basicity by up to one pH unit, and contributed to controlling the leaching of several heavy metals and metalloids

Stabilization of Basic Oxygen Furnace Slag by Hot-stage Carbonation Treatment.

Treatment and disposal of Basic Oxygen Furnace (BOF) slag, a residue of the steel production process characterized by high basicity and propensity for heavy metal leaching, is a costly burden on metallurgical plants; a sustainable valorization route is desired. The stabilization of BOF slag utilizing hot-stage carbonation treatment was investigated; this approach envisions carbonation during the hot-to-cold pathway followed by the material after the molten slag is poured and solidified. Three experimental methodologies were employed: (i) in-situ thermogravimetric analyzer (TGA) carbonation was used to assess carbonation reaction kinetics and thermodynamic equilibrium at high temperatures; (ii) pressurized basket reaction carbonation was used to assess the effects of pressurization, steam addition and slag particle size; and (iii) atmospheric furnace carbonation was used to assess the effect of carbonation on the mineralogy, basicity and heavy metal leaching properties of the slag. Free lime was found to be the primary mineral participating in direct carbonation of BOF slag. Initial carbonation kinetics were comparable at temperatures ranging from 500 to 800 oC, but higher temperatures aided in solid state diffusion of CO2 into the unreacted particle core, thus increasing overall CO2 uptake. The optimum carbonation temperature of both BOF slag and pure lime lies just below the transition temperature between carbonation stability and carbonate decomposition: 830-850 oC and 750-770 oC at 1 atm and 0.2 atm CO2 partial pressures, respectively. Pressurization and steam addition contribute marginally to CO2 uptake. CO2 uptake progressively decreases with increasing particle size, but basicity reduction is similar independent of particle size. The solubility of some heavy metals reduced after carbonation (barium, cobalt and nickel), but vanadium and chromium leaching increased