Species sensitivity of zeolite minerals for uptake of mercury solutes

The uptake of inorganic Hg2+ and organometallic CH3Hg+ from aqueous solutions by 11 different natural zeolites has been investigated using a batch distribution coefficient (Kd) method and supported by a preliminary voltammetric study. The effect of mercury concentration on theKd response is shown over an environmentally appropriate concentration range of 0.1-5 ppm inorganic and organometallic Hg using a batch factor of 100 ml g−1 and 20 h equilibration. Analcime and a Na-chabazite displayed the greatest methylmercury uptakes (Kd values at 1.5 ppm of 4023 and 3456, respectively), with mordenite as the smallest at 578. All uptake responses were greater for methylmercury than for the inorganic mercuric nitrate solutions, suggesting a distinctive sensitivity of zeolites to reaction with different types of solute species. It is likely that this sensitivity is attributable to the precise nature of the resultant Hg-zeolite bonds. Additionally, both the Si-Al ratio and the Na content of the initial natural zeolite samples are shown to influence the Kd responses, with positive correlations between Kd and Na content for all zeolites excluding mordenite

Uptake of caesium and strontium radioisotopes by natural zeolites from Mongolia

Mongolian clinoptilolite-rich tuffs were examined for their ability to take up 137-Cs and 90-Sr/90-Y in the presence of competing cations (Na+, K+, Cs+, Ca2+, Mg2+, Sr2+), as nitrate salts, in the concentration range 10−1–10−3 M. Experiments were carried out by the batch technique and expressed as distribution coefficients. Clear differences were seen in Sr and Cs uptakes and those for Sr did not follow the trends expected from simple ion exchange theory. Results are discussed in relationship to the Si/Al framework compositions and cation contents of the zeolites, and suggestions made for the anomalies observed. It is concluded that the presence of some cations, potentially present in aqueous nuclear wastes, cause effects which can affect the use of clinoptilolite in the treatment of these wastes