Title |
Hydration of dicalcium silicate and diffusion through neo-formed calcium-silicate-hydrates at weathered surfaces control the long-term leaching behaviour of basic oxygen furnace (BOF) steelmaking slag
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Published in |
Environmental Science and Pollution Research, January 2018
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DOI | 10.1007/s11356-018-1260-7 |
Pubmed ID | |
Authors |
Douglas I. Stewart, Andrew W. Bray, Gideon Udoma, Andrew J. Hobson, William M. Mayes, Mike Rogerson, Ian T. Burke |
Abstract |
Alkalinity generation and toxic trace metal (such as vanadium) leaching from basic oxygen furnace (BOF) steel slag particles must be properly understood and managed by pre-conditioning if beneficial reuse of slag is to be maximised. Water leaching under aerated conditions was investigated using fresh BOF slag at three different particle sizes (0.5-1.0, 2-5 and 10 × 10 × 20 mm blocks) and a 6-month pre-weathered block. There were several distinct leaching stages observed over time associated with different phases controlling the solution chemistry: (1) free-lime (CaO) dissolution (days 0-2); (2) dicalcium silicate (Ca2SiO4) dissolution (days 2-14) and (3) Ca-Si-H and CaCO3 formation and subsequent dissolution (days 14-73). Experiments with the smallest size fraction resulted in the highest Ca, Si and V concentrations, highlighting the role of surface area in controlling initial leaching. After ~2 weeks, the solution Ca/Si ratio (0.7-0.9) evolved to equal those found within a Ca-Si-H phase that replaced dicalcium silicate and free-lime phases in a 30- to 150-μm altered surface region. V release was a two-stage process; initially, V was released by dicalcium silicate dissolution, but V also isomorphically substituted for Si into the neo-formed Ca-Si-H in the alteration zone. Therefore, on longer timescales, the release of V to solution was primarily controlled by considerably slower Ca-Si-H dissolution rates, which decreased the rate of V release by an order of magnitude. Overall, the results indicate that the BOF slag leaching mechanism evolves from a situation initially dominated by rapid hydration and dissolution of primary dicalcium silicate/free-lime phases, to a slow diffusion limited process controlled by the solubility of secondary Ca-Si-H and CaCO3 phases that replace and cover more reactive primary slag phases at particle surfaces. |
Mendeley readers
Geographical breakdown
Country | Count | As % |
---|---|---|
Unknown | 28 | 100% |
Demographic breakdown
Readers by professional status | Count | As % |
---|---|---|
Student > Ph. D. Student | 10 | 36% |
Student > Bachelor | 2 | 7% |
Student > Doctoral Student | 2 | 7% |
Researcher | 2 | 7% |
Professor | 2 | 7% |
Other | 4 | 14% |
Unknown | 6 | 21% |
Readers by discipline | Count | As % |
---|---|---|
Engineering | 6 | 21% |
Materials Science | 6 | 21% |
Earth and Planetary Sciences | 3 | 11% |
Environmental Science | 3 | 11% |
Pharmacology, Toxicology and Pharmaceutical Science | 1 | 4% |
Other | 2 | 7% |
Unknown | 7 | 25% |