A process of carbon enrichment of bottom slag ash for value-added applications

  • Priyanka P. Jatav
  • Sonali P. TajaneEmail author
  • S. A. Mandavgane
  • S. B. Gaidhani


Coal is the primary source of energy in India. Coal ash obtained after coal combustion is considered a waste and dumped near the plant. Storage of coal ash close to thermal and other plants has now become a serious problem and creates environmental pollution. Coal ash contains an appreciable amount of unburned carbon, which can be recovered and reused as a source of energy; whereas the carbon-free ash can be utilized in cement, refractory, and fertilizer industries. Thus, there is a need to apply an effective separation technology to recover unburned carbon from coal ashes. In this study, a froth flotation technique was used to recover unburned carbon from a boiler bottom slag. The effect of particle size, conditioning time, and collector combination was studied to achieve maximum selectivity. The optimum liberation size of bottom slag was found to be around 150 µm (100 mesh size) with a conditioning time of 2 min. Furthermore, it was observed that a collector with a 1:1 proportion of kerosene and fuel oil with methyl isobutyl carbinol as the frother provides significant results. The carbon content in the concentrate was increased from 17% (7283.3 kJ/kg) in the feed to 40% (17990.6 kJ/kg) in the final concentrate and can be recycled as fuel, whereas the tailing fraction with carbon content less than 6% can be used in cement, concrete, and refractory industries.


Bottom ash Unburned carbon Flotation Recovery and calorific value 



American Society for Testing and Materials


Loss on ignition


Methyl isobutyl carbinol


Combustible recovery


Ash rejection


Maharashtra Industrial Development Corporation


X-ray fluorescence



Authors are thankful to IBM and Womika coal and minerals Technologies Pvt. limited, Nagpur, for providing analysis and characterization facilities.


  1. 1.
    World Coal Association (2016) Sustainable energy development: opportunities and innovation for indian coal conference proceedings. India Habitat Centre, New DelhiGoogle Scholar
  2. 2.
    World Coal Association (2015) Energy in India, pp 1–2. Accessed 2 Oct 2017
  3. 3.
    International Energy Agency (2017) Key world energy statistics 2017. International Energy Agency, Paris, pp 1–97Google Scholar
  4. 4.
    Mandal A, Sinha O (2014) Review on current research status on bottom ash: an Indian prospective. J Inst Eng India Ser A 95(4):277–297. CrossRefGoogle Scholar
  5. 5.
    Michalski S, Gray R (2001) Ash disposal—mine fires—environment: an Indian dilemma. Bull Eng Geol Env 60(1):0023–0029. CrossRefGoogle Scholar
  6. 6.
    Mishra U (2004) Environmental impact of coal industry and thermal power plants in India. J Environ Radioact 72(1–2):35–40. CrossRefGoogle Scholar
  7. 7.
    Eisele T, Kawatra S (2002) Use of froth flotation to remove unburned carbon from fly ash. Miner Process Extract Metall Rev Int J 23:1–10CrossRefGoogle Scholar
  8. 8.
    Oz D, Koca S, Koca H (2009) Recycling of coal combustion wastes. Waste Manag Res 27:267–273. CrossRefGoogle Scholar
  9. 9.
    Gray M, Champagne K, Soong Y et al (2002) Physical cleaning of high carbon fly ash. Fuel Process Technol 76:11–21. CrossRefGoogle Scholar
  10. 10.
    Gray M, Champagne K, Soong Y, Finseth D (2001) Parametric study of the column oil agglomeration of fly ash. Fuel 80:867–871. CrossRefGoogle Scholar
  11. 11.
    Harris T, Wheelock T (2008) Process conditions for the separation of carbon from fly ash by froth flotation. Int J Coal Prep Util 28:133–152. CrossRefGoogle Scholar
  12. 12.
    Walker A, Wheelock T (2006) Separation of carbon from fly ash using froth flotation. Coal Prep 26:235–250. CrossRefGoogle Scholar
  13. 13.
    Yamik A, Altinkaya Y (2006) Recovery of unburned carbons from the seyitomer ashes by flotation, Turkey. J Ore Dress 8:43–53Google Scholar
  14. 14.
    Uçurum M (2009) Influences of Jameson flotation operation variables on the kinetics and recovery of unburned carbon. Powder Technol 191:240–246. CrossRefGoogle Scholar
  15. 15.
    Uçurum M, Toraman Ö, Depci T, Yoğurtçuoğlu E (2011) A study on characterization and use of flotation to separate unburned carbon in bottom ash from Çayirhan power plant. Energy Sour Part A Recov Utilization Environ Eff 33:562–574. CrossRefGoogle Scholar
  16. 16.
    Huang Y, Takaoka M, Takeda N (2003) Removal of unburned carbon from municipal solid waste fly ash by column flotation. Waste Manag 23:307–313. CrossRefGoogle Scholar
  17. 17.
    Cao Y, Li G, Liu J et al (2012) Removal of unburned carbon from fly ash using a cyclonic-static microbubble flotation column. J South Afr Inst Min Metall 112:891–896Google Scholar
  18. 18.
    Runge K, Tabosa E, Jankovic A (2013) Particle size distribution effects that should be considered when performing flotation geometallurgical testing. In: The second AusIMM international geometallurgy conferenceGoogle Scholar
  19. 19.
    Jain S (1987) Ore processing, 1st edn. Balkema, RotterdamGoogle Scholar
  20. 20.
    Aktas Z, Cilliers J, Banford A (2008) Dynamic froth stability: particle size, airflow rate, and conditioning time effects. Int J Miner Process 87:65–71. CrossRefGoogle Scholar
  21. 21.
    Naik P, Reddy P, Misra V (2005) Interpretation of interaction effects and optimization of reagent dosages for fine coal flotation. Int J Miner Process 75:83–90. CrossRefGoogle Scholar
  22. 22.
    Hwang J, Sun X, Li Z (2002) Unburned carbon from fly ash for mercury adsorption: I. separation and characterization of unburned carbon. J Miner Mater Char Eng 01:39–60. CrossRefGoogle Scholar

Copyright information

© Springer Japan KK, part of Springer Nature 2018

Authors and Affiliations

  • Priyanka P. Jatav
    • 1
  • Sonali P. Tajane
    • 1
    Email author
  • S. A. Mandavgane
    • 1
  • S. B. Gaidhani
    • 2
  1. 1.Department of Chemical EngineeringVNITNagpurIndia
  2. 2.Womika Coal and Minerals Technologies Pvt LimitedNagpurIndia

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