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Heavy Metal Removal and Neutralization of Acid Mine Waste Water ‐ Kinetic Study
Author(s) -
Ghirişan Adina L.,
Drǎgan Simion,
Pop Alexandru,
Simihǎian Marinela,
Miclǎuş Vasile
Publication year - 2007
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.5450850611
Subject(s) - activation energy , chemistry , metal , nuclear chemistry , neutralization , apatite , ball mill , kinetic energy , adsorption , mineralogy , materials science , metallurgy , organic chemistry , physics , quantum mechanics , antibody , immunology , biology
The influence of the apatite on the efficiency of neutralization and on heavy metal removal of acid mine waste water has been studied. The analysis of the treated waste water samples with apatite has shown an advanced purification, the concentration of the heavy metals after the treatment of the waste water with apatite being 25 to 1000 times less than the Maximum Concentration Limits admitted by European Norms (NTPA 001/2005). In order to establish the macro‐kinetic mechanism in the neutralization process, the activation energy, Ea, and the kinetic parameters, rate coefficient of reaction, k r , and k t were determined from the experimental results obtained in “ceramic ball‐mill” reactor. The obtained values of the activation energy Ea >> 42 kJ mol −1 (e.g. Ea = 115.50 ± 7.50 kJ mol −1 for a conversion of sulphuric acid η H2SO4 = 0.05, Ea = 60.90 ± 9.50 kJ mol −1 for η H2SO4 = 0.10 and Ea = 55.75 ± 10.45 kJ mol ‐1 for η H2SO4 = 0.15) suggest that up to a conversion of H2SO4 equal 0.15 the global process is controlled by the transformation process, adsorption followed by reaction, which means surface‐controlled reactions. At a conversion of sulphuric acid η H2SO4 > 0.15, the obtained values of activation energy Ea < 42 kJ mol ‐1 (e.g. Ea = 37.55 ± 4.05 kJ mol ‐1 for η H2SO4 = 0.2, Ea = 37.54 ± 2.54 kJ mol ‐1 for η H2SO4 = 0.3 and Ea = 37.44 ± 2.90 kJ mol ‐1 for η H2SO4 = 0.4) indicate diffusion‐controlled processes. This means a combined process model, which involves the transfer in the liquid phase followed by the chemical reaction at the surface of the solid. Kinetic parameters as rate coefficient of reaction, kr with values ranging from (5.02 ± 1.62) 10‐4 to (8.00 ± 1.55) 10‐4 (s ‐1 ) and transfer coefficient, kt, ranging from (8.40 ± 0.50) 10‐5 to (10.42 ± 0.65) 10‐5 (m s ‐1 ) were determined.