title: Effect of ammonium compounds on dissolution rate of South African calcium-based material.
abstract: The rate at which limestone dissolves is very important in wet flue gas desulphurisation process (FGD). High dissolution rates provide better alkalinity that is important for sulphur dioxide (SO(2)) absorption. The dissolution characteristics have been studied by using a pH-Stat method at 60 degrees C, at pH value of 5, stirrer speed of 100 rpm and particle size of 44 microm. This paper examines the use of ammonium compound as the possible additives that will enhance the dissolution rate of limestone. The dissolution rates were measured according to the shrinking core model with surface control, i.e. (1-(1-X)(1/3))=k(r)t. It was found that the dissolution rate increases in the presence of ammonium compounds. Upon addition of 0.5 g of ammonium nitrate, the dissolution rate constants increased by 170%. As the pH is increased the dissolution rate decreases. The dissolution reaction follows a shrinking core model with the chemical reaction control as the rate-controlling step.
authors.affiliation: Department of Mechanical Engineering, Pretoria Campus, Tshwane University of Technology, Private Bag X680, 0001 Pretoria, South Africa.
authors.forename: Hillary
authors.initials: H
authors.lastname: Rutto
authors.forename: Zachariah
authors.initials: Z
authors.lastname: Siagi
authors.forename: M
authors.initials: M
authors.lastname: Mbarawa
mesh_terms: D002118:Calcium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D010316:Particle Size; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012995:Solubility
chemical_list: D000644:Quaternary Ammonium Compounds; D002118:Calcium