Electrokinetics of natural and synthetic calcite suspensions

Abstract

Electrophoretic mobilities u/m 2 s −1 V −1 of calcite particles suspended in different electrolytes (NaCl and natural sea water) were measured, and corresponding zeta potentials ζ/mV calculated. Calcite samples used in this work were synthetic calcite (Socal) and natural calcite (Polcarb). The difference in electrokinetic behaviour of these two samples was the main subject of this work. Synthetic calcite (Socal) suspended in 10 −3 mol dm −3 NaCl solution was positively charged and the resulting ζ potential at inherent pH 8.6 was +22 mV. This value, however, was influenced greatly by the addition of natural seawater or organic solutes. Two seawater samples originating from the northern Adriatic, as well as the solutions of fulvic and citric acid, changed the positive ζ potential of Socal calcite to negative. Natural calcite (Polcarb) when suspended in NaCl solution had a negative ζ potential of −18 mV at pH 8.6. This value was not affected significantly by any factors mentioned above-it remained negative under all experimental conditions. The main reason for such behaviour of natural calcite was concluded to be the organic coating attached to its surface which prevented calcite from reacting with ions and solutes from the solution.