Preparation of hydro-sodalite from fly ash using a hydrothermal method with a submolten salt system and study of the phase transition process

Hydro-sodalites are zeolitic materials with a wide variety of applications.Fly ash is an abundant industrial solid waste,rich in silicon and aluminum,from which hydro-sodalite can be synthesized.However,traditional hydrothermal synthesis methods are complex and cannot produce high-purity products.Therefore,there is a demand for processing routes to obtain high-purity hydro-sodalites.In the present study,high-purity hydro-sodalite(90.2 wt%)was prepared from fly ash by applying a hydrothermal method to a submolten salt system.Samples were characterized by powder X-ray diffraction(XRD),scanning electron microscopy(SEM),thermogravimetry and differential thermal analysis(TG–DTA),and Fourier transform infrared spectroscopy(FTIR)to confirm and quantify conversion of the raw material into the product phase.Purity of the samples prepared with an H2O/Na OH mass ratio of 1.5 and an H2O/fly ash mass ratio of 10 was calculated and the conversion process of the product phase was studied.Crystallinity of the product was influenced more by the Na OH concentration,less by the H2O/fly ash mass ratio.The main reaction process of the system is that the Si O ions produced by dissolution of the vitreous body in the fly ash and Na+ions in the solution reacted on the destroyed mullite skeleton to produce hydro-sodalite.This processing route could help mitigate processing difficulties,while producing high-purity hydro-sodalite from fly ash.

Utilization of molten chloride salt derived from MSWI fly ash washing as energy storage material:thermophysical properties and corrosion behavior

Fly ash,as a byproduct of municipal solid waste incineration,contains several kinds of pollutants,especially dissolvable salts that cause a severe challenge for fly ash disposal.Washing combined with cement kiln co-processing for fly ash disposal has been applied in China.After washing,the wastewater was evaporated to produce fly ash salt(FAS).In this study,FAS was mixed the KCl and LiCl to be used as molten chloride salt for energy storage material.Twenty-three types of molten salts with various ratios of FAS-KCl-LiCl were evaluated.Thermophysical properties(melting point and latent heat)and thermal stability of these salts were characterized.The increase in FAS fraction decreased the latent heat of molten salts.Among the tested samples,the best compatibility ratio of FAS:KCl:LiCl was 10:50:40(%,in weight),with latent heat of 108.7 J/g and melting point of 333℃.This molten salt also showed good thermal stability after 1–13 h of thermal experiments,and the mass loss was less than 2%after 5 heating cycles at 600℃.By corrosion test,FAS-KCl-LiCl(10:50:40,%in weight)could be more safely used in vessels made of nickel-based alloy,but it might cause corrosion risk for stainless steel.

硫酸钠在亚熔盐介质中的过饱和性

采用激光浊度法对亚熔盐法粉煤灰提铝清洁工艺中硫酸钠在亚熔盐介质中的过饱和性进行了研究。结果表明:对亚熔盐介质进行真空蒸发时,其中的硫酸钠达到平衡浓度时即从体系中结晶析出,表明硫酸钠在亚熔盐介质中几乎无过饱和性。此外,杂质二氧化硅与碳酸钠对硫酸钠在铝酸钠溶液中的过饱和性具有一定影响,二氧化硅杂质会使硫酸钠析晶点碱浓度提高到20 g/L左右;碳酸钠会使硫酸钠析晶点碱浓度降低至15 g/L左右。同时,对析出晶体的物相分析表明:杂质二氧化硅的存在会使析出晶体向钠硅渣转变,而杂质碳酸钠的存在会使析出晶体向碳钠矾复盐转变。

以脱铝赤泥-脱铝粉煤灰为原料制备硬硅钙石

以脱铝赤泥和脱铝粉煤灰为原料，采用水热法制备硬硅钙石，考察原料配比、液固比及反应时间对硬硅钙石生成及形貌的影响。结果表明：在220℃、钙硅比为1．0时，脱铝粉煤灰掺入量的增加、液固比的提高和反应时间的延长均促进了硬硅钙石的生成。最佳反应条件为：脱铝粉煤灰加入量大于总质量40％、液固比35mL儋、反应时间9h。在该条件下获得了由直径为25～50nm，长径比大于20的硬硅钙石单晶晶须缠绕而成的球形粒子。通过扫描电镜（SEM）、透射电镜（TEM）和背散射电子图像（BSE）分析晶须生长、成球机理及粒子内部结构，证实了球形粒子的中空结构可能与反应初期形成的前驱体包裹晶态SiO_2有关。

循环流化床粉煤灰中金属元素的溶出

为实现固体废弃物循环流化床粉煤灰的综合利用,探寻铝土矿的替代资源,采用微波消解、亚熔盐法及直接酸溶法对循环流化床粉煤灰中含量高的金属元素铝、铁和钛进行了溶出实验,比较了不同条件对粉煤灰中上述元素溶出率的影响.结果表明:微波消解粉煤灰,消解剂为质量分数20%的NaOH溶液或HNO_(3)-HCl-HF混合酸,粉煤灰中的铝都全部溶出,但是钛和铁在碱性条件下消解,溶出率小于50%;用亚熔盐法和酸法溶出粉煤灰,粉煤灰中的铝、铁和钛的溶出率都小于50%,但亚熔盐溶出后再加酸浸出,铝和铁都全部溶出.本研究为循环流化床粉煤灰的综合利用提供理论参考.