EFFECT OF NON-SWELLING LAYERS ON THE DISSOLUTION OF REDUCED-CHARGE MONTMORILLONITE IN HYDROCHLORIC-ACID

A series of reduced-charge montmorillonites (RCM), prepared from the s ame parent Li-montmorillonite (Jelsovy Potok, Slovakia) by heating at various temperatures (105-210 degrees C) for 24 h, was treated with 6 M HCl at 95 degrees C for periods up to 30 h. Reaction solutions obtai ned were analysed for Al, Fe, Mg and Li and the solid reaction product s were investigated by FTIR spectroscopy. Both analyses provided evide nce that the extent of dissolution decreased with increased amounts of Li fixed within the montmorillonite structure, i.e. with increased he ating temperature. Differences in the acid dissolution process were re flected in the structural changes which occurred within the RCM sample s, due presumably to different positions of fixed Li. The ethylene gly col monoethyl ether (EGME) surface areas, and XRD and HRTEM analyses o f the RCM series revealed an increased amount of non-swelling layers i n the samples prepared at higher temperatures, which caused a substant ially slower decomposition of M7 and M8 in HCl. The calculated XRD pat terns of M6 and M7 confirmed the presence of 20% and 45% pyrophyllite- like layers, respectively, in these samples. Mixed-layer pyrophyllite- like-smectite and pyrophyllite-like crystals, containing only non-swel ling layers, were found in sample M8. The results confirmed that the a mount of swelling layers in RCM significantly affects their dissolutio n rate in HCl.