贫镁和富镁坡缕石的热变化规律研究

A study of thermal behaviors of magnesium-poor and magnesium-rich palygorskite

贫镁和富镁坡缕石受热时表现出不同的热变化规律。物相分析表明,将提纯样品加热到设定温度并保温2h后,贫镁坡缕石经历了失水和玻璃相阶段：300℃以下晶体结构基本没变,350℃开始发生＂折叠作用＂,400℃以上晶体结构被完全破坏,生成玻璃相;富镁坡缕石经历了失水、玻璃相和新晶相（顽火辉石）阶段：300℃以下晶体结构基本没变,350~500℃发生＂折叠作用＂,600~950℃生成玻璃相,950℃以上生成顽火辉石雏晶。富镁坡缕石保持热稳定性的温度低于600℃,贫镁坡缕石的低于400℃。

The MgO concentration in the magnesium-rich palygorskite is 16.23,which is almost twice its concentration in the magnesium-poor palygorskite,whereas the Fe2O3 concentration in magnesium-poor palygorskite is almost twice its concentration in magnesium-rich palygorskite.The thermal behaviors vary with the chemical composition of the palygorskite.The results of phase analysis,which was carried out with the purified samples which had been heated and kept at a certain temperature for 2h,show that magnesium-poor palygorskite experienced water depletion and glassy phase.The crystal structure was complete below 300℃,began to folding when the temperature reached 350℃,and was completely destroyed and formed glassy phase above 400℃.Magnesium-rich palygorskite expererienced water depletion,glassy phase and new crystalline phase（enstatite）.The crystal structure was complete below 300℃,began to folding when the temperature rose from 350℃ to 500℃,and formed glassy phase from 600℃ to 950℃;enstatite began to form above 950℃.The temperatures for preserving thermal stability of magnesium-rich palygorskite and magnesium-poor palygorskite were about 600℃ and 400℃ respectively.The results of differential thermal analysis and XRD show the same regularity： the magnesium-rich palygorskite has better thermal stability than magnesium-poor palygorskite,which is probably attributed to the different ionic bonds.Mg（Ⅱ） and Fe（Ⅱ,Ⅲ） are the main coordination ions in the palygorskite and can form ionic bonds with the crystal water.Different bond energies in different bonds have an effect on the crystal structures of palygorskite.The content of Mg is low but the content of Fe is high in magnesium-deficient palygorskite,whereas things are just opposite for magnesium-rich palygorskite.With the same anions,the smaller the metal ion,the higher the lattice energy in the formed ionic bond.The ionic radius of Mg（Ⅱ） is between the radii of Fe（Ⅱ） and Fe（Ⅲ）.So the lattice energy of the ionic bond formed by Mg（Ⅱ） and crystal water is between the lattice energy of the ionic bond formed by Fe（Ⅱ） and that formed by Fe（Ⅲ）.With the combined action of Mg（Ⅱ）,Fe（Ⅱ） and Fe（Ⅲ）,the magnesium-rich palygorskite is destroyed above 500℃ while magnesium-deficient palygorskite is destroyed at 350℃.