Synthesis of High Purity ZSM-5 Zeolite from Lignite Fly Ash via Two-stage Process

Abstract

Lignite fly ash and rice husk were used as raw materials to synthesize the high purity zeolite. The preparation of high purity silica and alumina from ligmte fly ash was focused. The iron oxides; Fe₂O₃ and Fe₃ O₄ in lignite fly ash were separated used various acids. The effects of period of time ranging 20-80 min. temperatures ranging 40-80ºC and acid type concentration (HCI₂ HNO₃ and H₂SO₄ of 0.5 – 5.0 M) on the separation of iron oxides were investigated. Hematite was firstly removed by magnetic separation and the results show that 32.1 wt% of Fe could be separated, After that, fly ash was treated with acid solution. The resultant Fe in fly ash can be reduced 16.7 wt% of amount of Fe by treatment with 3.5 M HCI 60 min at 70 ºC 15.9 wt% of amount of Fe by treatment with 2.5 M H₂SO₄ 50 min at 70 ºC and 13.9 wt% of amount of Fe by uneaten with 3.5 M HNO₃ 50 min at 70 ºC . Therefore, the order of separation capacity of acid were as follows: HCI > H₂SO₄> HNO₅. The high purity silica and aloumina obtained from the first rice husk was added to the mixture in order to adjust the Si/Al mole ratio in fly ash. The maximum yield of ZSM-5 Zeolite approximately 87.6 wt% was obtained by treatment of lignite fly ash with HCI