Evaporation Crystallization Of Hydrochloric Acid Leachate Of Coal Chemical Ash

Coal chemical ash (CCA) is an inert aluminosilicate waste produced in modern coal gasification process. It is not suitable for construction materials and civil engineering application due to its high carbon content. As the total weight percent of aluminum oxide, iron oxide and calcium oxide in CCA are higher than 60% the utilization of CCA shows potential economic value. However, the separation of Al3+ from Fe3+ and Ca2+ is a big obstacle to utilization due to poor fundamental data base.In order to separate Al3+ from Fe3+ and Ca2+ through evaporation crystallization technology, this research investigated the phase equilibrium of Al3+ -Fe3+-Ca2+‖ Cl-—H2O quaternary system and its subsystems using static equilibrium method. Base on salt-water system phase equilibrium data the evaporation character of CCA hydrochloric acid leachate was found out and the composition variation of liquid and solid phase at different evaporation stage can be calculated. After taking requirements for integrated utilization of CCA into account, the best endpoint temperature of evaporation crystallization was 333.15 K.Evaporation crystallization kinetics of aluminum chloride in aqueous solution was investigated through batch method and nucleation and growth rate equations of crystal were deduced. The influence of supersaturation, suspension density, stirring intensity, temperature, crystal seed and impurities on the crystallization kinetics was also analyzed.Based on phase equilibrium of Al3+-Fe3+-Ca2+‖ Cl-—H2O system, the evaporation crystallization of CCA hydrochloric acid leachate was designed conceptually. The heat transfer area of each unit of three effect evaporator was 19.18m2. The heat transfer area of crystallizer was 2.61 m2. The consumption of saturated water vapor at 160℃ was1.48 tons per ton of AICl3·6H2O.