Analcime geopolymers as sorbents in water treatment

Zeolite mineral, analcime [Na16(Al16Si32O96)·16H2O], is formed in mining industry as lithium carbonate is produced from spodumene (LiAlSi2O6) using sodium pressure leaching process (1). Zeolite structure possess aluminosilicate framework and pores occupied by water and exchangeable cations (2). Zeolites act as cation exchangers due to which they have been applied as sorbents in water treatment (2). Geopolymers (GP) consist of an anionic framework of corner-sharing SiO4 and AlO4, and the exchangeable cations are located in the voids in the same way as in zeolites (3). However, GP are x-ray amorphous unlike zeolites. Also, GP are excellent sorbent materials in water treatment for e.g. As3+, Cu2+, NH4+ Ni2+, Sb3+ (4-6). The ion-exchange capacity of analcime at room temperature is quite low (Querol et al. 2002) and therefore analcime was geopolymerized with a 1:1 mixture of 10 M sodium hydroxide (NaOH) and sodium silicate (SiO2:Na2O = 3.1-3.4) to improve the sorption properties of analcime. Then analcime GP were applied as sorbents in the removal of different anions and cations (e.g. ammonium, nitrate, potassium). Before sorption experiments, the GP were crushed and sieved to a particle size \u3c500 \u3eµm and washed with deionized water until pH was stable. Experiments were conducted in batch mode with synthetic wastewater. The effect of sorbent dosage, sorption time, temperature, and anion/cation solution concentration on the anion/cation removal efficiencies of analcime GP were studied. The results indicate that analcime GP could be used as sorbents in water treatment. The use of the analcime GP in water treatment could lead to cost savings in water treatment as a low-cost by-product based GP are used instead of the commercial ion exchange resins. Please click Additional Files below to see the full abstract