Analysis of Chromium Species in Synthesis Clinker and Cement from Co-Burning of Hazardous Wastes

Name: Suthatip Sinyoung

Name: สุธาทิพย์ สินยัง

keyword: Clinker

Abstract: The goal of this study is to investigate the behavior of chromium during each step of the cement-production pro cess, including clinkeri zation, hydration and leaching from the finished cement product and to inve stigate the speciation of chromium in all pro cesses. Several techniques such as XRD, XANES , SEM, OM, ESE/EDS, and TG/DTA were used for the investigation. The results showed that chromium was incorporated in the clinker phase and inhibits the reaction of C2S and CaO to form C3S. The formation of the chromium compounds CacAl4Cr2O15. Ca5Cr3O12, Ca5Cr2SiO 12. and CaCr2O7 with chromium oxidation states of +3, +4.6, +5, and +6, respectively, was detected in the clinker. The results from XANES spectra also show that all samples contain Cr+6 species which is more toxic to humans and the environment. After the hydration process, additional chromium compounds were identified in the mortar matrix, including Ca5(CrO4)3-OH, CaCrO4-2H2O, and Al2(OH)4CrO4, with chromium oxidation states of +4.6, +6, and +6, respectively. Additionally, some ionic chromium species such as Cr3+ from Ca6Al4Cr2O15 and Cr6+ from CaCr2O7, CaCrO4-2H2O, and Al2(OH)4CrO4, were leached out during the leaching tests, whereas the other species remained in the mortar. Chromium addition not only changed the clinker phase and formed new chromium compounds in each production process but also changed the contents of Ca(OH)2 and CSH in the mortar, affecting the compressive strength and setting time. Increasing the chromium content in the raw meal reduced the compressive strength and retarded the time for setting pr oportionally. The changes in the c linker phases C3S and C2S and hydration products Ca(OH)2 and CSH also directly affected the leaching behaviors of chromium from the cement. The concentrations of chromium more than 0.1 wt.% leached from the mortar following the EA NEN 7375:2004 leaching tests were higher than that allowed by the Environmental Agency, England and Wales standard. Moreover, the effective diffusion coefficient (De) and leachability index (LX) were used to explain the mechanisms of chromium in cement. These resul ts showed that the LX value was lower than 8. So, the amount of chromium in the samples can not control. Thus, waste containing chromium (> 0.1 wt.%) should not be allowed to mix with raw materials in the cement manufacturing process.

King Mongkut's University of Technology Thonburi. KMUTT Library

Address: BANGKOK

Email: info.lib@mail.kmutt.ac.th

Name: Suwimol Asavapisit

Role: Advisors

Created: 2010

Modified: 2017-09-20

Issued: 2011-09-17

วิทยานิพนธ์/Thesis

application/pdf

CallNumber: ENV676

eng

DegreeName: Doctor of Philosophy

Level: Doctoral Degree

Descipline: Environmental Engineering

Grantor: King Mongkut's University of Technology Thonburi

©copyrights King Mongkut's University of Technology Thonburi

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