Crystalline silica in compressed rice hull coke ash


  • T Okutani Rice Hulls Research Center
  • E Ichikawa Yokohama National University
  • H Nagai National Institute of Advanced Industrial Science and Technology
  • T Hashimoto Tromso Co., Ltd.
  • T Makihata Tromso Co., Ltd.


Compressed rice hull coke was produced by compressing rice hulls ground to less than 200 µm diameter at 1.22x106 N/m2 and 310˚C with an oxygen deficient atmosphere. The compressed rice hull coke had a 5 cm outer diameter, a 1.5 cm inner diameter and 35 cm length. The density of the coke is 1.2, and, the heat value is 16570 kJ·kg-1. In this study, 2 kg coke was combusted at the average temperature of 850˚C for 104 min with a maximum temperature of 860˚C. The ash was colored black-grey, and the form remained coke. The ash contained 95.4% silica with 9.2% cristobalite and 86.2% amorphous silica. The occupational exposure limits of respirable fraction of crystalline silica such as cristobalite and quartz in floating dust less than the diameter of 7 µm is 0.025 mg/m3; however, no respirable cristobalite was detected during combustion of the compressed rice hull coke. Cristobalite was not present in floating dust because it melted during the crystallization of amorphous silica to cristobalite.


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Author Biography

E Ichikawa, Yokohama National University

Graduate School of Environment & Information Sciences




How to Cite

T. Okutani, E. Ichikawa, H. Nagai, T. Hashimoto, and T. Makihata, “Crystalline silica in compressed rice hull coke ash”, J. Met. Mater. Miner., vol. 28, no. 1, Jun. 2018.



Original Research Articles