Synthesis of Analcime Crystals and Simultaneous Potassium Extraction from Natrolite Syenite

Jian Chen,Changjiang Liu,Hongwen Ma,Jiangyan Yuan

doi:10.1155/2017/2617597

Abstract

Analcime single crystals were successfully synthesized from natrolite syenite powder (K2O 10.89%) and 92.6% of potassium was extracted simultaneously by means of soda roasting followed by alkali-hydrothermal method. Effects of NaOH concentration, reaction temperature, and holding period on the analcime formation and potassium extraction were investigated systemically. The results indicated that NaOH concentration plays an important role in determining the chemical composition of zeolites and size distribution; by turning the NaOH concentrations, three different pure zeolites (i.e., the phillipsite-Na, the analcime, and the sodalite) were prepared. Besides, a higher temperature could accelerate the dissolution of K+ions and enhance the crystallinity degree of zeolite. The reactions involved in the analcime synthesis can be summarized as follows: sodium aluminum silicate dissolution→precipitation and dissolution of metastable zeolite-P→analcime nucleation→analcime growth. The extraction ratio of K+is associated with the types of synthesized zeolites, among which analcime is the most effective to promote potassium leaching out from zeolite lattice position. The optimal condition for analcime crystallization and K+leaching is found to be as follows: 175°C for 4 h in 0.5 mol/L NaOH solution.

Highlights

Analcime (NaAlSi2O6⋅H2O) is a hydrated aluminosilicate mineral, the complex framework of which builds by cornersharing [SiO4] and [AlO4] tetrahedron resulting irregular channels and some cavities occupied by the exchangeable Naions in the crystal lattice [1, 2]
We report a simple and economic method to convert natrolite syenite into pure analcime and potassium salts
The results indicated that NaOH concentration plays an important role in determining the chemical composition of synthesized zeolite

Summary

Introduction

Analcime (NaAlSi2O6⋅H2O) is a hydrated aluminosilicate mineral, the complex framework of which builds by cornersharing [SiO4] and [AlO4] tetrahedron resulting irregular channels and some cavities occupied by the exchangeable Naions in the crystal lattice [1, 2]. Ma et al [16] firstly proposed an idea to utilize quartz syenite (one kind of potassium-rich rocks) as raw material to synthesize analcime via an alkali-hydrothermal reaction (treated at 240∘C for 4 h) This approach takes full use of the aluminosilicate and alkali metal source for analcime preparation; at the same time, it can extract potassium ions (K+) which can be used to prepare potassium fertilizer, the most rare fertilizers in China and India [21,22,23,24]. We report a simple and economic method (i.e., the soda roasting followed by alkalihydrothermal approach) to convert natrolite syenite (an important potassium-rich rock in China) into pure analcime and potassium salts In this reaction, the effects of the NaOH concentration, crystallization temperature, and time on the formation of analcime zeolite and the extraction of K+ were studied in detail. The reaction mechanism of analcime synthesis and dissolution of K+ ions was discussed

Experimental

Results and Discussion

Results

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Conclusions