Abstract
Acid waste waters are usually treated by means of lime in order to meet pH requirements for discharge. Considerable saving may be achieved using limestone in neutralization processes. The feasibility of limestone neutralization processes also in those cases where precipitates form both on the reactive surface and in the liquid bulk as pH rises has been evaluated. Experiments were carried out with a well mixed tank reactor contacting limestone with acid solutions containing iron (III) sulphate and sulphuric acid. Analyses for calcium and iron (III) concentrations as well as for CO 2 desorption rate for their changes with time and continuous recording of pH were carried out during each run. The results show that neutrality can be achieved within a few minutes providing the operation conditions ensure a continuous removal of precipitates from the reacting surface. A critical comparison with previous results concerning a similar system containing AlCl 3 and HCl emphasizes the phenomenological differences between the two systems. The kinetic model for limestone dissolution in acid solutions previously developed has been successfully applied to the system studied.
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