(290b) Statistical Evaluation of Mineral Carbonation of a Fly Ash/Brine System

¹Environmental Nano Sciences Group, Chemistry Department, University of the Western Cape,

South Africa.

²Department of Ecology and Resource Management, School of Environmental Studies,

University of Venda, South Africa.

³Industrial Mineralogy Laboratory, Council for Geoscience, Pretoria, South Africa.

Statistical evaluation of mineral carbonation of a fly ash/brine system

Abstract

As countries continue on their development path, coal is bound to play a vital role as the main source of energy especially in BRICS (Brazil, Russia, India, China and South Africa) where coal is available in considerable quantities. International regulations, specifically the 2^nd Kyoto agreement reached in Durban, South Africa (28^th November to 9^th December 2011) binds developing countries to reduce their carbon emissions even as they industrialize. Finding alternatives to reduce CO₂ emissions is going to be paramount to achieve the targets set. The effect of four parameters on the mineralization potential of class F fly ash and a NaSO₄ brine type was evaluated in a statistically designed protocol. Main effects of temperature, particle size and solid to liquid (S/L) ratio were the most significant while the interactions of temperature and particle size as well as temperature and S/L ratio were also significant. Between 2.75 % to 6.5 % conversion of the CaO in fly ash into CaCO₃ was achieved depending on the factor combinations. Mineral carbonation at 90 ⁰C and 4 Mpa using bulk ash and S/L ratio of 1 gave the highest degree of carbonation of 6.5 %.  Carbonation conducted at 30 ⁰C and 1 Mpa using the >150 µm particle size and S/L ratio of 0.1 gave the lowest degree of carbonation of 2.75 %. Application of brine instead of ultra-pure water resulted in higher carbonation efficiency due to the utilization of the additional Ca²⁺ and Mg²⁺ present in brine. Moreover the carbonation effluents after the experiments are cleaner with regards to most elements (Pb, Zn, Cu, NO₃, Na, SO₄, As, Se, K, Al, Mg, Ca, Si, Sr and Ni) while Mo, B, V and Cl increased with carbonation. McNemar’s test (p-value of 0.01) of the factor combinations reveals that carbonation carried out at 90 ⁰C and 4 Mpa using bulk ash and S/L ratio of 1 has the best factor combinations as the highest removal of contaminants was achieved (≥70 %).