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Title: Changes in mineralogical and leaching properties of converter steel slag resulting from accelerated carbonation at low CO{sub 2} pressure

Highlights: > Accelerated carbonation studied to improve environmental properties of steel slag. > Carbonation found to occur predominantly at surface of the steel slag grains. > Combined geochemical modelling and mineral analysis revealed controlling processes. > Enhanced V-leaching with di-Ca silicate (C2S) dissolution identified as major source. > Identified mineral transformations provide guidance for further quality improvement. - Abstract: Steel slag can be applied as substitute for natural aggregates in construction applications. The material imposes a high pH (typically 12.5) and low redox potential (Eh), which may lead to environmental problems in specific application scenarios. The aim of this study is to investigate the potential of accelerated steel slag carbonation, at relatively low pCO{sub 2} pressure (0.2 bar), to improve the environmental pH and the leaching properties of steel slag, with specific focus on the leaching of vanadium. Carbonation experiments are performed in laboratory columns with steel slag under water-saturated and -unsaturated conditions and temperatures between 5 and 90 {sup o}C. Two types of steel slag are tested; free lime containing (K3) slag and K1 slag with a very low free lime content. The fresh and carbonated slag samples are investigated using a combination of leaching experiments, geochemical modelling ofmore » leaching mechanisms and microscopic/mineralogical analysis, in order to identify the major processes that control the slag pH and resulting V leaching. The major changes in the amount of sequestered CO{sub 2} and the resulting pH reduction occurred within 24 h, the free lime containing slag (K3-slag) being more prone to carbonation than the slag with lower free lime content (K1-slag). While carbonation at these conditions was found to occur predominantly at the surface of the slag grains, the formation of cracks was observed in carbonated K3 slag, suggesting that free lime in the interior of slag grains had also reacted. The pH of the K3 slag (originally pH {+-} 12.5) was reduced by about 1.5 units, while the K1 slag showed a smaller decrease in pH from about 11.7 to 11.1. However, the pH reduction after carbonation of the K3 slag was observed to lead to an increased V-leaching. Vanadium leaching from the K1 slag resulted in levels above the limit values of the Dutch Soil Quality Decree, for both the untreated and carbonated slag. V-leaching from the carbonated K3 slag remained below these limit values at the relatively high pH that remained after carbonation. The V-bearing di-Ca silicate (C2S) phase has been identified as the major source of the V-leaching. It is shown that the dissolution of this mineral is limited in fresh steel slag, but strongly enhanced by carbonation, which causes the observed enhanced release of V from the K3 slag. The obtained insights in the mineral transformation reactions and their effect on pH and V-leaching provide guidance for further improvement of an accelerated carbonation technology.« less
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [1] ;  [4]
  1. Energy Research Centre of the Netherlands (ECN), P.O. Box 1, 1755 ZG Petten (Netherlands)
  2. Tata Steel RD and T, Ceramics Research Centre, P.O. Box 10000, 1970 CA IJmuiden (Netherlands)
  3. Tata Steel Strip Products, OSF2, P.O. Box 10000, 1970 CA IJmuiden (Netherlands)
  4. (Netherlands)
Publication Date:
OSTI Identifier:
21578433
Resource Type:
Journal Article
Resource Relation:
Journal Name: Waste Management; Journal Volume: 31; Journal Issue: 11; Other Information: DOI: 10.1016/j.wasman.2011.05.022; PII: S0956-053X(11)00264-9; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; CALCIUM SILICATES; CARBON DIOXIDE; CARBONIZATION; CRACKS; GEOCHEMISTRY; LEACHING; MINERALS; PH VALUE; REDOX POTENTIAL; SIMULATION; SLAGS; SOILS; STEELS; SURFACES; VANADIUM; WATER ALKALINE EARTH METAL COMPOUNDS; ALLOYS; CALCIUM COMPOUNDS; CARBON ADDITIONS; CARBON COMPOUNDS; CARBON OXIDES; CHALCOGENIDES; CHEMICAL REACTIONS; CHEMISTRY; DECOMPOSITION; DISSOLUTION; ELEMENTS; HYDROGEN COMPOUNDS; IRON ALLOYS; IRON BASE ALLOYS; METALS; OXIDES; OXYGEN COMPOUNDS; SEPARATION PROCESSES; SILICATES; SILICON COMPOUNDS; TRANSITION ELEMENT ALLOYS; TRANSITION ELEMENTS