Material Conversion of Waste Aluminoborosilicate Glass into Faujasite-type Zeolite using Alkali Fusion
Abstract
A large amount of liquid crystal display (LCD) television becomes popular for the last decades, and the amount of waste LCD panels will increase soon. LCD panels mainly consist of aluminoborosilicate glass, and it is difficult to recycle aluminoborosilicate glass using the same recycling method of soda-lime glass, due to the high strain point. Therefore, a novel recycling method for aluminoborosilicate is desired. In this study, we attempted to convert waste aluminoborosilicate glass powder into faujasite-type zeolite using alkali fusion method. Waste aluminoborosilicate glass powder (< 300 μm) were mixed with NaOH powder (the weight ratio of NaOH / aluminoborosilicate = 1.0 - 2.0), and then heated at 100 – 800 oC for 0.5 - 7 h to make a fused material with high solubility. This fused material was agitated in distilled water for one day, then heated at 80 oC for 24 hours to synthesize zeolite product. Most of the aluminoborosilicate glass were converted into soluble phases by alkali fusion with NaOH (NaOH / sample = 1.5) at 400 oC for 0.5 h, and could be transformed into faujasite-type zeolite. The cation exchange capacity (CEC) of the zeolite product is 1.9 mmol/g, which is 31 times higher than that of raw glass powder, and is 59% of CEC for commercial faujasite-type zeolite 13X (3.2 mmol/g). Zeolitization process from agitated material can be explained by theconcentrations of Si, Al and B in the product and the crystallinity of faujasite-typezeolite in the product.
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Introduction
In recent years, home appliance recycling law was established to promote the recycling society in Japan. Therefore, a novel recycling technology for typical home appliance, such as televisions (TVs), refrigerators and washing machines were developed to recycle. TV is a typical home appliance. In Japan, liquid crystal display (LCD) TVs began to popular since 2000, and demands for TV change from Cathode Ray Tube TV to LCD TV. LCD mainly consists of aluminoborosilicate glass. Therefore, in the future, a large amount of waste aluminoborosilicate glass will discharge in Japan [1-2]. Aluminoborosilicate glass mainly consists of SiO2 and Al2O3,and is difficult to recycle by the typical method of soda lime glass because strain point of aluminoborosilicate glass (650 oC) is higher than that of soda lime glass (550 oC). Aluminoborosilicate glass also has high heat and chemical-resistance, and has various composition in each product. Therefore, it is difficult to recycle LCD again. From these background, new utilization of waste LCD is desired. In recent years, researches have also been made to synthesize zeolite from industrial wastes, such as coal fly ash [3-6], papermaking sludge incineration ash [7-16], rice husk ash [17], waste ceramics [18, 19], stone cake [20, 21] and so on using hydrothermal reaction, andthere is possibility to convert a part of aluminoborosilicate glass waste into zeolite materialsby hydrothermal treatmentvia pretreatment, e.g. acid leaching [22-24]. Zeolite is microporous aluminoborosilicate minerals with regularly arrange pores, and can use as catalyst and ion-exchanger for cleaning polluted environment [25]. Zeolite has a structure in which tetrahedrons share the oxygen located at the apexes of the tetrahedral unit and are regularly bonded threedimensionally [26]. Furthermore, since aluminoborosilicate glass contains boron, it would be possible to synthesize a boroncontaining zeolite having high heat resistance and hydrophobicity by incorporating this boron into the structure of the zeolite [27-29].
In our previous studies,stable minerals, such as quartz, were converted into soluble alkali salts to synthesize zeolite using alkali fusion [30-35], and it would be possible to covert a large part of aluminoborosilicate to zeolite crystals via alkali fusion.
In this study, we tried to convert the aluminoborosilicate glass into zeolite using alkali fusion. For conversion of aluminoborosilicate into zeolite, alkali fusion was applied to convert insoluble oxide into soluble alkali salt to convert aluminoborsilicate glass powder into faujasite-type zeolite including boron.
Conclusion
We attempted to synthesize faujasite-type zeolite from waste aluminoborosilicate glass using alkali fusion. The processing conditions to obtain fused material with sufficiently high reactivity for zeolite formation was investigated. By alkali fusion, we converted waste aluminoborosilicate glass into fused materials with high reactivity on the condition that heating condition is above 400oC, the weight of NaOH/aluminoborosilicate glass is above 1.5 and heating time is above 0.5 h. Faujasite-type zeolite can be synthesized from aluminoborosilicate glass using alkali fusion, and the CEC of the product with 3 wt% boron content is CEC of 1.9 mmol/g and specific surface area of 201 m2 /g.