Decarbonation of geothermal waters by seeding with aragonite crystals coupled with air bubbling

During the cooling of the geothermal water of Chott El-Fejjej (Tunisia), considerable scaling occurred in the inlet to the tower. To attempt to resolve this problem, decarbonation (CaCO3 precipitation) induced by seeding, with aragonite crystals recovered on site, coupled with air bubbling has been studied. The advantage of this new technique is that no chemical addition is needed and a large volume of sludge is avoided. Attention is paid to seeding time, airflow rates and amount of seed added. Experimental results indicate that crystallisation takes place on seed crystals; consequently, precipitation on the wall of the reactor is prevented. The seeding which accelerates the precipitation, that is dependent on the physico-chemical properties of the water, should be curried out at the earliest possible stage for instantaneous precipitation. A threshold for air bubbling, beyond which no improvement appeared is observed. The kinetics of the secondary germination are dependent on supersaturation of water, the airflow rate and the amount of added seed.