PARAMETERS DETERMINING THE DEPOSITION OF CALCIUM-CARBONATE INTO A GLASS-CAPILLARY

The deposition in situ of calcium carbonate inside glass capillaries w as studied as a function of the temperature, the flow rate of the solu tions, the concentration ratio of calcium and carbonate ions, the capi llary radii, and the solution volumes which flowed through the capilla ry. Calcium carbonate was precipitated just before the inlet to the ca pillary from sodium carbonate and calcium chloride solutions. Two seri es of experiments were conducted in two separate laboratories, and des pite the difference in relative depositions, some common features of t he deposition process were found. Thus, maximum deposition occurred ar ound 65-degrees-C. There were optimum flow rates, 0.60-0.80 ml/s, of t he solutions for maximum deposition to occur. The deposition was very sensitive to the concentration ratio of calcium and carbonate ions. Fo r example, the deposition at a ratio 5:1 (calcium to carbonate ion con centration) was more than twice that for an equimolar 1:1 ratio of the ions. The results indicate that the deposition of calcium carbonate i s determined by the balance of attractive and repulsive forces. The fo rces are of Lifshitz-van der Waals, acid-base (hydrogen bonding), and electrostatic nature. It seems that the electrostatic forces between t he glass surface and calcium carbonate particle, as well as between ca lcium carbonate particles, play an important role in the deposition pr ocess. The maximum deposition occurring around 65-degrees-C coincides with a change of the precipitate crystallographic structure, from calc ite into aragonite, at this temperature.