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The bulk material of six dioctahedral and two trioctahedral swellable clay minerals was leached in H2SO4 and HCl at concentrations of 1.0, 5.0 and 10.0 M at 80 °C for several hours. Alteration of the clay mineral structures was dependent on the individual character of each mineral (chemical composition and initial particle size). Acid attack dissolved the octahedral sheets by interlayer and edge attack. The number of substitutions by Mg or Fe in the octahedral sheet of the clay minerals promoted the dissolution of these layers and the formation of a silica phase. The dissolution of the octahedral cations occurred in the following order: Mg > Fe > Al. The dioctahedral smectites were more stable than the trioctahedral smectites and vermiculites; the behavior of trioctahedral smectites against acid was similar to that of vermiculites. The acid activated smectites displayed still the ability to exchange cations. The obtained materials had a lower layer charge, lower CEC and higher specific surface area than the crude materials but still adsorbed very large organic cations like dodecylammonium ions. The reaction with the acid caused particle splitting within the octahedral sheet. A model of dissolution and particle splitting is proposed. © 2009 Elsevier B.V. All rights reserved.

The bulk material of three kaolins, a sepiolite, an illite and one magadiite were treated with 1, 5 and 10 M H2SO4 at 80 °C for several hours. The alteration of the non-swelling clay mineral structures was controlled by the individual character of each mineral (chemical composition and initial particle size). The reaction resulted in a successive dissolution of the octahedral sheets by edge attack. The number of substitutions by Mg or Fe in the octahedral sheet promoted the dissolution of these layers and the formation of a silica phase. High amounts of Al in the tetrahedral sheet of the clay minerals caused partial dissolution of these sheets. The dissolution of the octahedral cations occurred in the following order: Mg > Fe > Al. Thus, dioctahedral clay minerals were more stable against acid attack than trioctahedral clay minerals. The release of the octahedral cations caused the lightening of the material together with a development of micropores and an increasing specific surface. Dissolution and splitting of the particles required longer reaction times compared to swellable smectites and vermiculites. Acid activation of non-swelling clay minerals can be used to produce layered materials with simple chemical composition and high specific surface area. © 2009 Elsevier B.V. All rights reserved.

While selenium is applied as decolorizing agent for flint container glass or tableware glass, the retention of selenium in glass however is very low. Generally more than 75% of the total selenium input sublimes from the glass melt and leaves the clay minerals due to the high volatility of SeO2. Therefore, alternative selenium containing raw materials, which might offer a better retention of added selenium and therefore substantially reduce the emission of selenium, are needed. One possible option is to intercalate suitable ionic compounds containing selenium into clay minerals and using the intercalated compounds as a carrier for the selenium into the glass melt. The intercalation of saponite with a specially synthesized selenonium compound (triphenylselenonium) is described and their performance in the glass melt is partially characterized. Compared to glass batches with ZnSeO3 the release of selenium could be reduced by about 75% if the selenonium intercalates are used.

Hydrotalcites with different counterions were tested with respect to their ability to act as heat stabilizers in PVC. The stabilization activity results from the capacity of the layered double hydroxides (LDHs) to react with the HCl formed during degradation of PVC. The experiments described are heat stability tests and experiments for a determination of the capacity of the hydrotalcites to react with HCl gas. They show a linear relationship between HCl capacity of LDHs with different counterions and their action as (heat) stabilizer. The reaction between the LDHs and the HCl occurs in a two-step process, firstly (if possible), the counterions between the LDH layers tend to react with the HCl gas, and, secondly, the LDHs themselves react with the HCl under complete destruction of the LDH structure and formation of metal chlorides.