NaA zeolite-clay composite membrane formulation and its use as cost-effective water softener

Abstract

The present study describes the exchange of calcium and magnesium ions through an active layer of zeolite Na-A deposited on flat porous support made from clay. Microfiltration membrane's supports are prepared by uniaxial pressing dry mixture of clay, and 3% w/w activated carbon then sintered to 1000 °C. The zeolite Na-A (LTA) layer is deposited on the clay support using the hydrothermal method. An increase in the specific surface area and the pore volume and a decrease in pore diameter after deposition of the zeolite Na-A on the support is observed. SEM analysis of the zeolite Na-A shows well-defined cubic crystals with sizes between 1.3 and 2.4 μm. The efficiency of the zeolite membrane for the exchange of calcium and magnesium ions with the sodium (Na) within the zeolite-A cavities was evaluated by filtration tests of solutions containing chlorides salts of the two metals using a flow loop adjusted for dead-end filtration. The obtained results show that the Na+ ions of Zeolite-A were completely exchanged with Ca2+ and Mg2+ and that the maximum retention on the zeolite membrane reached 93.3% and 72.1% for Ca2+ and Mg2+ ions, respectively after 30 min of filtration. The electrochemical impedance spectroscopy (EIS) has shown an electron transfer increase of the membrane paste electrode exchanged with Ca2+, Mg2+ as single ions or as mixture, with a preference for Ca2+ compared to Mg2+, indicating that a combination of exchange and size exclusion mechanisms must be used to explain the membrane behavior. These properties make the zeolite Na-A membrane a suitable material that could be used effectively in the softening of hard water.