On the foaming kinetics for the synthesis of porous inorganic polymers

status: publishe

Use of boron wastes in the production of heavy clay ceramics

Colemanite, ulexite and tincal are the main boron ores found in Turkey and account to 63% of the world estimated reserves. The production route of boron products results in significant amounts of different types of Boron Wastes, BW. Their open field disposal raises substantial environmental concerns in fear of leaching and groundwater pollution. The heavy clay ceramic industry can potentially absorb substantial quantities of BW. In the present study, BW produced from Kirka borax plants in Turkey, with 12.6 wt.% B2O3 was introduced in 0 wt.%, 5 wt.% and 15 wt.% in a heavy clay body mixture. Four peak temperatures, 800 degrees C, 850 degrees C, 900 degrees C and 950 degrees C, were examined for the dry pressed samples. The thermal behaviour analyzed by dilatometry and TGA shows that major loss in weight starts about 600 degrees C and continues to 700 degrees C approximately. For 5 wt.% BW addition and firing at 900-950 degrees C, the sintered bodies present comparable or improved physical and mechanical properties with respect to the reference formulation. The microstructure was analyzed by SEM whereas the main crystalline phases were identified by XRD. Samples fired at 900 degrees C with 5 wt.% BW present comparable properties with the reference ones. At 950 degrees C, the obtained properties were improved. Deformation occurs for samples with 15 wt.% BW when fired at >900 degrees C.status: publishe

Transformation of stainless steel slag toward a reactive cementitious binder

Argon oxygen decarburization (AOD) slag represents more than 50 wt% of the slag from stainless steel production. Although some applications are available,e.g., as aggregates for road constructions or fertilizers, they are characterized by low economic value and limited applicability. In order to increase the economic value of AOD slag, alternative applications have been proposed, e.g., as partial or full replacement for Ordinary Portland Cement (OPC). The work presented here investigates whether the adaptation of the AOD slag chemistry within a high temperature process leads to an improvement of its hydraulic properties and thereby can demonstrate its potential to be converted into a hydraulic binder suit able for OPC replacement. For this purpose, three synthetic AOD slags with basicities(CaO/SiO2) of 2.0, 2.2, and 2.4 were synthesized, and the effect of the CaO/SiO2 ratio on the material stability, the amount of tri-calcium silicate formed, and their hydraulic properties investigated. X-ray diffraction, scanning electron microscope(SEM), and isothermal calorimetry analysis were used to characterize the microstructure and the hydraulic activity. The results show that the proposed method is indeed a promising way to stabilize a stainless steel AOD slag and con-vert it into a hydraulic binder.status: publishe

Experimental and Mathematical Simulation Study on the Granulation of a Modified Basic Oxygen Furnace Steel Slag

Basic oxygen furnace (BOF) steel slag is a major waste of the steelmaking industry. Utilization of BOF slag contributes to the sustainability of the steel industry by alleviating its environmental impact. Vitrification during cooling is an effective method to promote the cementitious activity of slags with the aim to apply slags in high value-added applications. In the present study, an Al2O3- and SiO2-modified BOF slag was water granulated at a pilot scale. The amorphous and mineral fractions were measured quantitatively. The critical cooling rate to vitrify the modified slag was calculated through the Time-Temperature-Transformation diagrams constructed using in situ confocal scanning laser microscopy. To provide an insight into the crystallization behavior during the granulation process, a mathematical model was developed. The model was validated by comparing the amorphous fraction obtained from experiments with that from simulation. Temperature profiles of the slag particles with varied sizes were calculated with the aid of COMSOL Multiphysics software. The effect of particle size on the vitrified fraction was discussed in detail and the temperature gradient from surface to center of the particle was identified. The results provide novel fundamental understanding of the vitrification process regarding to the slag valorization, which will help the industrial implementation of granulation for pollution remediation and other engineered environmental systems such as chemical industry and pharmaceutical industry

Enhanced landfill mining in view of multiple resource recovery: a critical review

In a circular economy material loops are closed by recycling of pre-consumer manufacturing scrap/residues, urban mining of End-of-Life products and landfill mining of historic (and future) urban waste streams. However, in the past landfill mining was not performed with a focus on resource recovery. This paper addresses this gap by introducing the concept of Enhanced Landfill Mining, defined as the safe conditioning, excavation and integrated valorization of landfilled waste streams as both materials and energy, using innovative transformation technologies and respecting the most stringent social and ecological criteria. The feasibility of ELFM is studied by synthesizing the research on the Closing the Circle project, the first ELFM project targeting the 18 million metric ton landfill in Houthalen-Helchteren in the East of Belgium. It is argued that Environmental Impact Assessments of ELFM projects should be wide in scope and time. Embedded in a broad resource management perspective, the worldwide potential of ELFM is highlighted, in terms of climate gains, materials and energy utilization, job creation and land reclamation. The potential is quantified for the EU-27 with its 150,000-500,000 landfills. However, for ELFM to reach its full potential, strategic policy decisions and tailored support systems, including combined incentives for material recycling, energy utilization and nature restoration, are required.status: publishe

Feasibility of incorporating phosphogypsum in ettringite-based binder from ladle slag

Abstract Aiming to utilize phosphogypsum (PG) as a construction material, this study investigated the potential use of PG as a calcium sulfate source for the production of an ettringite-based binder (LSG). Six compositions with different percentages and PG’s of different origin were hydrated with ladle slag (LS) to form LSG. The hydration, mineralogy and compressive strength of all mixtures were investigated and compared with a reference LSG made of pure synthetic gypsum. The minor impurities in PG, the different particle size distribution as well as the mineralogy induced distinguishable effects on the heat of hydration, phase assemblage and morphology. The results showed that the use of side-stream PG instead of pure gypsum results in superior properties with a 60% increase in compressive strength. This investigation shows high potential to produce a completely by-product-based LSG by combining different sources of industrial side-streams with minimal chemical and energy use

Byproduct-based ettringite binder:a synergy between ladle slag and gypsum

Abstract Ladle slag (LS) is a byproduct from the steel industry that is usually reactive on its own and hydrates towards cementitious phases when mixed with water. However, these reaction products are often metastable, leading to micro-structural changes between 7 and 30 days after mixing. To address this issue, in this experimental investigation, a new binder was designed where LS was mixed with gypsum in order to deliver an ettringite-based binder (LSG). The experimental results revealed that the dominant crystalline phase of LSG was ettringite, which remained stable with no conversion at later stages. For better understanding of the ettringite-based binder, mortar characterization, mechanical properties, and durability of LSG were investigated. LSG showed good mechanical properties and excellent freeze-thaw resistance after 300 cycles, which is comparable to other calcium sulfoaluminate cements. Therefore, as a result, the byproduct-based ettringite binder synthesized herein could offer a solution to steelmaking byproducts with a low-CO2 binder, which could be used in a wide range of applications in the construction industry

Radiological and leaching assessment of an ettringite-based mortar from ladle slag and phosphogypsum

Abstract In this investigation, ettringite-based mortars were synthesized from ladle slag (LS) and phosphogypsum (PG), promoting the concept of a circular economy. However, the reuse of naturally occurring radioactive materials (NORM), such as PG, requires radiological investigation. Also, the immobilization degree for contaminants contained in PG should be evaluated. The former was investigated using gamma spectroscopy and radon exhalation/emanation tests, while the latter was assessed using an up-flow percolation column test according to the CEN/TS 16637‐3. The produced mortars comply with current legislation on naturally occurring radionuclides (NOR) in building materials, proving that they can be safely used for building purposes. The radon emanation decreased upon increasing the Polish PG content, which was mainly determined by the microporosity. The specific surface areas were 20‐30 times lower than conventional cement, and the immobilization degree for contaminants was generally high (>90%). This investigation demonstrates high potential for PG reuse in ettringite-based mortars