Effects of sintering atmosphere on cement clinkers produced from chromium-bearing sludge

Ying Liang Chen, Juu En Chang, Yi Chieh Lai, Ming Sheng Ko

研究成果: Article

4 引文 (Scopus)

摘要

The purpose of this study was to investigate the effects of sintering atmosphere (oxidizing and reducing) on the polymorphs of dicalcium silicates (Ca2SiO4, C2S) and on the chromium leaching of the belite-rich clinkers made from a chromium-bearing sludge. This sludge was generated in an electroplating factory, and in addition to chromium, it contained nickel, copper, and zinc. In the clinker production, airwas used as the oxidizing atmosphere, and carbon monoxide,whichwas produced by burning graphite with an insufficient amount of oxygen, was employed as the reducing atmosphere. Dicalciumsilicates were substantially formed under both kinds of sintering atmosphere, but there was some nonhydraulic γ-C2S in the clinkers produced under the oxidizing atmosphere. In addition, the amount of γ-C2S decreased with the chromium-bearing sludge addition, whereas that of β-C2S increased. The clinkers produced under the reducing atmosphere had less residual chromium, a finding that shows that more chromium was evaporated. However, the reducing atmosphere can decrease the proportion of hexavalent chromium (Cr(VI)) in the resulting clinkers. For other heavy metals, the residual amounts of nickel and copper generally increased with the sludge addition, but zinc was absent in most of the clinkers produced under the reducing atmosphere. This implies that the evaporation of zinc is much more significant than that of the other heavy metals under a reducing atmosphere. In the leaching tests, the concentrations of nickel, copper, and zinc were below the detection limits in all the leachates. In terms of chromium, the total leaching concentration was highly related to Cr(VI). The clinkers produced under the oxidizing atmosphere had high leaching concentrations of chromium, and thus failed to meet the regulatory limit. In contrast, the reducing atmosphere was effective in decreasing the chromium leaching, and it therefore makes the resulting cement clinkers more environmentally sound. Implications: This study presents the effects of oxidizing/reducing atmosphere on the polymorphs of C2S and on the oxidation states of chromium in the clinkers. The chromium-bearing sludge from an electroplating factory was employed as a cement raw material. The reducing atmosphere was used to prevent the chromium from oxidizing to Cr(VI) during the sintering process, thus decreasing the chromium leaching concentrations of the resulting clinkers.

原文English
頁(從 - 到)587-593
頁數7
期刊Journal of the Air and Waste Management Association
62
發行號5
DOIs
出版狀態Published - 2012 一月 1

指紋

chromium
cement
sludge
atmosphere
leaching
zinc
nickel
copper
sintering
effect
heavy metal
carbon monoxide
graphite
leachate
silicate
evaporation
oxidation
oxygen

All Science Journal Classification (ASJC) codes

  • Waste Management and Disposal
  • Management, Monitoring, Policy and Law

引用此文

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abstract = "The purpose of this study was to investigate the effects of sintering atmosphere (oxidizing and reducing) on the polymorphs of dicalcium silicates (Ca2SiO4, C2S) and on the chromium leaching of the belite-rich clinkers made from a chromium-bearing sludge. This sludge was generated in an electroplating factory, and in addition to chromium, it contained nickel, copper, and zinc. In the clinker production, airwas used as the oxidizing atmosphere, and carbon monoxide,whichwas produced by burning graphite with an insufficient amount of oxygen, was employed as the reducing atmosphere. Dicalciumsilicates were substantially formed under both kinds of sintering atmosphere, but there was some nonhydraulic γ-C2S in the clinkers produced under the oxidizing atmosphere. In addition, the amount of γ-C2S decreased with the chromium-bearing sludge addition, whereas that of β-C2S increased. The clinkers produced under the reducing atmosphere had less residual chromium, a finding that shows that more chromium was evaporated. However, the reducing atmosphere can decrease the proportion of hexavalent chromium (Cr(VI)) in the resulting clinkers. For other heavy metals, the residual amounts of nickel and copper generally increased with the sludge addition, but zinc was absent in most of the clinkers produced under the reducing atmosphere. This implies that the evaporation of zinc is much more significant than that of the other heavy metals under a reducing atmosphere. In the leaching tests, the concentrations of nickel, copper, and zinc were below the detection limits in all the leachates. In terms of chromium, the total leaching concentration was highly related to Cr(VI). The clinkers produced under the oxidizing atmosphere had high leaching concentrations of chromium, and thus failed to meet the regulatory limit. In contrast, the reducing atmosphere was effective in decreasing the chromium leaching, and it therefore makes the resulting cement clinkers more environmentally sound. Implications: This study presents the effects of oxidizing/reducing atmosphere on the polymorphs of C2S and on the oxidation states of chromium in the clinkers. The chromium-bearing sludge from an electroplating factory was employed as a cement raw material. The reducing atmosphere was used to prevent the chromium from oxidizing to Cr(VI) during the sintering process, thus decreasing the chromium leaching concentrations of the resulting clinkers.",
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AU - Chen, Ying Liang

AU - Chang, Juu En

AU - Lai, Yi Chieh

AU - Ko, Ming Sheng

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N2 - The purpose of this study was to investigate the effects of sintering atmosphere (oxidizing and reducing) on the polymorphs of dicalcium silicates (Ca2SiO4, C2S) and on the chromium leaching of the belite-rich clinkers made from a chromium-bearing sludge. This sludge was generated in an electroplating factory, and in addition to chromium, it contained nickel, copper, and zinc. In the clinker production, airwas used as the oxidizing atmosphere, and carbon monoxide,whichwas produced by burning graphite with an insufficient amount of oxygen, was employed as the reducing atmosphere. Dicalciumsilicates were substantially formed under both kinds of sintering atmosphere, but there was some nonhydraulic γ-C2S in the clinkers produced under the oxidizing atmosphere. In addition, the amount of γ-C2S decreased with the chromium-bearing sludge addition, whereas that of β-C2S increased. The clinkers produced under the reducing atmosphere had less residual chromium, a finding that shows that more chromium was evaporated. However, the reducing atmosphere can decrease the proportion of hexavalent chromium (Cr(VI)) in the resulting clinkers. For other heavy metals, the residual amounts of nickel and copper generally increased with the sludge addition, but zinc was absent in most of the clinkers produced under the reducing atmosphere. This implies that the evaporation of zinc is much more significant than that of the other heavy metals under a reducing atmosphere. In the leaching tests, the concentrations of nickel, copper, and zinc were below the detection limits in all the leachates. In terms of chromium, the total leaching concentration was highly related to Cr(VI). The clinkers produced under the oxidizing atmosphere had high leaching concentrations of chromium, and thus failed to meet the regulatory limit. In contrast, the reducing atmosphere was effective in decreasing the chromium leaching, and it therefore makes the resulting cement clinkers more environmentally sound. Implications: This study presents the effects of oxidizing/reducing atmosphere on the polymorphs of C2S and on the oxidation states of chromium in the clinkers. The chromium-bearing sludge from an electroplating factory was employed as a cement raw material. The reducing atmosphere was used to prevent the chromium from oxidizing to Cr(VI) during the sintering process, thus decreasing the chromium leaching concentrations of the resulting clinkers.

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