Kinetic Mechanism of Desilicated Fly Ash Lime Consumption

  • Thabo FALAYI
  • Felix Ndubisi OKONTA University of Johannesburg
  • Freeman NTULI
Keywords: desilicated fly ash, modified Jander kinetics, toxicity


This paper presents study of the kinetic mechanism of lime consumption using desilicated fly ash (DFA). Desilicated fly ash (DFA) a residue from leaching of silica from fly ash was stabilised using lime at elevated temperatures. DFA and lime were mixed in different ratios at optimum moisture content and maximum dry density and then cured at 40 ºC, 80 ºC and 100 ºC for 4 days. 80 ºC was found to be the optimum curing temperature. The DFA: lime ratio of 70:30 was found to have an average UCS of 8.6 MPa. Lime consumption was found to follow modified Jander kinetics with activation energy of 16 kJ/mol and a reaction grade of 3 meaning that the reaction was controlled by diffusion of reactants through a dense layer of reaction products. The main hydration products were calcium silicate hydrate and tricalcium aluminate. Toxicity leaching tests showed a 79 % reduction in the leachability of trace and heavy metals. Therefore, DFA can successfully be stabilised using lime.


Author Biography

Felix Ndubisi OKONTA, University of Johannesburg
Senior Lecturer and Head of Department of Civil Engineering Science, University of Johannesburg