Heavy Metal Removel and Neutralization of Acid Mine Waste Water - Kinetic Study

• Published in: Canadian journal of chemical engineering 2007-12, Vol.85 (6), p.900-905
• Main Authors: Ghirisan, AL, Dragan, S, Pop, A, Simihaian, M, Miclaus, V
• Format: Article
• Language: English
• ISSN: 0008-4034

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 sub(r), and k sub(t) were determined from the experimental results obtained in "ceramic ball-mill" reactor. The obtained values of the activation energy Ea >> 42 kJ mol super(-1) (e.g. Ea = 115.50 plus or minus 7.50 kJ mol super(-1) for a conversion of sulphuric acid eta sub(H2SO4) = 0.05, Ea = 60.90 plus or minus 9.50 kJ mol super(-1) for eta sub(H2SO4) = 0.10 and Ea =55.75 plus or minus 10.45 kJ mol0 for eta sub(h2SO4) =0.15) suggest that up to a conversion of H sub(2)SO sub(4) 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 eta sub(H2SO4) > 0.15, the obtained values of activation energy Ea < 42 kJ mol super(-1) (e.g. Ea = 37.55 plus or minus 4.05 kJ mol super(-1) for eta sub(h2SO4) = 0.2 Ea = 37.54 plus or minus 2.54 kJ mol super(-1) for eta sub(H2SO4) = 0.3 and Ea = 37.44 plus or minus 2.90 kJ mol super(-1) for eta sub(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, k sub(r) with values ranging from (5.02 plus or minus 1.62) 10 super(-4) to (8.00 plus or minus 1.55) 10 super(-4) (s super(-1)) and transfer coefficient, k sub(t), ranging from (8.40 plus or minus 0.50) 10 super(-5) to (10.42 plus or minus 0.65) 10 super(-5) (m s super(-1)) were determined.