Uptake of Copper and Zinc Ions by Georgian Natural Heulandite and Resulting Changes in Its Chemical Composition and Structure

Extraction of metal ions from polluted waters and immobilization of metals in contaminated soils can be conducted using zeolites—porous aluminosilicate ion exchangers. The uptake of copper and zinc ions by the Georgian natural heulandite was studied under conditions of interaction of the zeolite with solutions (“liquid-phase” ion exchange) and powders (“solid-state” ion exchange) of the corresponding salts. The aim of the study was to compare the effect of the two procedures on the chemical composition and structure of the zeolite. It was found that the “liquid-phase” procedure provides a higher degree of uptake, particularly of zinc ions. Ion-exchange causes slight dealumination without decationization. Uptake of divalent ions occurs mainly through the leaching of sodium ions. According to X-ray data of ion-exchanged samples, the uptake of copper and zinc does not change the crystal structure of the zeolite framework, but nitrogen adsorption measurements show that ion exchange affects the mesoporous structure: solution treatment reduces the specific total pore volume and leads to the appearance of pores with a diameter of 4 nm. The “solid-state” procedure leads to an increase in specific total pore volume mainly due to an increase in the number of relatively small nanosized pores.