Crystallization field and rate study for the formation of single phase sodium‐potassium and potassium clinoptilolite

Abstract

Reproducible synthesis of clinoptilolite as the single crystalline phase was achieved in the narrow crystallization field at or around the nominal batch composition of 2.1(Na 2 O+K 2 O):Al 2 O 3 :10SiO 2 :110H 2 O at 140 °C. Clinoptilolites of high purity were crystallized in the pure sodium or mixed sodium-potassium cation systems. Partial replacement of hydroxyl anions with the salts of carbonates or chlorides also yielded clinoptilolite as the single crystalline phase although at lower crystallization rates.

Synthesis and Modification of Clinoptilolite

“…The raw materials used in synthesizing of clinoptilolite include silica, alumina, and alkali sources. Silica source may be colloidal silica [ 19 , 21 , 24 , 26 , 28 , 29 , 30 ], silica gel [ 18 , 20 ], fumed silica [ 24 ], and amorphous silica [ 24 ], from among in which colloidal silica is the most frequently used. The influence of silica sources on the formation of clinoptilolite has not much been in question.…”

“…The raw materials providing alumina are varied. They can be aluminum hydroxide [ 18 , 21 , 23 , 27 , 28 , 29 , 30 , 32 ], sodium aluminate [ 20 , 22 , 23 , 29 , 30 ], aluminum [ 24 , 29 , 30 ], and aluminum salts [ 19 , 22 ]. The use of aluminum hydroxide was the most common way to produce pure clinoptilolite that could be obtained, while the use of aluminum salts was not preferred because it produced impurities.…”

“…In addition, clinoptilolite with good yield was obtained when Si/Al ratio was in a range from 5.0 to 6.0 [ 29 ]. When hydroxyl anions were partially replaced by chloride or carbonate ions, the crystallization rate was slowed down [ 30 ].…”

“…Consequently, there is a significant number of studies focused on the synthesis of clinoptilolite. Literature [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ] demonstrates the efforts to synthesize from various sources of chemicals and different techniques to obtain clinoptilolite with different compositions.…”