A COMPARISON OF METHODS FOR THE EXTRACTION OF SMECTITES FROM CALCAREOUS ROCKS BY ACID DISSOLUTION TECHNIQUES

Four methods of extracting clays from calcite-rich samples were compared: (i) sodium acetate buffer solution; (ii) lithium acetate buffer solution; (iii) hydrochloric acid; (iv) liquid cation-exchange acid. The methods were tested on mixtures consisting of 80% calcite, 10% quartz and 10% hectorite. Potassium had previously been exchanged on to the interlayer sites of the clay. XRD traces of the extracted clays appeared identical with those of the original clays except for a sharpening of the 001 reflection. The bulk chemistry of the clay was unchanged except by the HCl extraction, which appeared to cause a stripping of the octahedral cations. With all of the methods the exchangeable cation content was altered; the sodium acetate method, for example, retained only 17% of the original exchangeable K+, the other methods all retaining < 10%.