Novel Synthetic Clays for Cation Exchange

This paper reviews synthesis, characterization and cation exchange properties of a novel swelleing mica "Na-4-mica" and their synthetic analogues with a high layer charge denisty. Na-4-mica (Na4Mg6Al4Si4O20F4) of a synthetic brittle mica has a very high Al(III) content and but exhibits unusual swelling behavior and selective cation exchange properties potentially useful in hazardous cation separations from solutions. Although normal brittle micas do not swell in water at all, this synthetic mica can readily become hydrated upon contact with water or even in moist air. This mica has a theoretical cation-exchange capacity of 468 milli-equivalents per 100 g on an anhydrous basis. The present authors found a simple and cost-effective preparation process of micro- or nano-crystallites of this mica from naturally occurring clay kaolinite. The fine mica is a selective exchanger for Sr, Ba, Ra, Pb, Cu, or Zn. The modified micas, such as "Na-3-mica" and "Na-2-mica" were also synthesized by the similar syntehtic processes. Na-3-mica improved the cation exchange kinetics and capacity for Sr. These micas also exhibited extremely low cation leachability once dehydrated at room temperature or moderate temperatures, and, hence, are expected to be useful for radioactive strontium or radium removal followed by its immobilization for safe disposal.

The brittle mica-like KNiAsO4 and its organic derivatives

The nickel arsenate KNiAsO4 has a mica-like layer structure with surface charge densities similar to brittle micas. In contrast to micas it easily exchanges alkylammonium ions. The interlayers have paraffin-type chain arrangements, as in alkylammonium vermiculites and alkylamine smectites and vermiculites, but the very regular chain packing causes a marked odd/even alternation of the basal spacings. The reactions of KNiAsO4 throw light on the exchange behaviour of micas.

Effects of structural order and disorder on the infrared spectra of brittle micas

SummaryComparison of the infrared spectra (4000-50 cm−1) of natural and synthetic samples of margarite, beryllian margaritc, ephesite, and clintonite indicates that the tetrahedral layers of margarite and ephcsite, containing Si and Al in equal atomic proportions, are ordered as the spectra are sharp and show no Al-O-Al vibrations. Clintonite of this tctrahedral composition is disordered. The hydroxyl-stretching frequencies are affected by ionic substitutions in both the octahedral and tetrahedral layers. The spectra permit the distinction of the different species of brittle mica. They also indicate the presence of beryllium in margarite, and allow an estimate of the tetrahedral composition of clintonites.