Incorporation of Al and Na in Hydrothermally Synthesized Tobermorite

Calcium silicate hydrate and its Al‐substituted form synthesized by a hydrothermal process were investigated by X‐ray diffraction, compositional analysis, and magic‐angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, in order to determine the mechanism of Al and Na incorporation in the tobermorite structure with varying molar ratios of Ca/Si and Al/Si. At a high molar ratio of Ca/Si, the silicate chains of tobermorite are ruptured, the degree of polymerization of the silicate chains is lowered, and the high calcium concentration lowers the content of Na₂O in the structure. Solid‐state ²⁹Si and ²⁷Al MAS NMR spectroscopy confirm that all Al atoms were incorporated in the silicate chains of tobermorite. The tetrahedrally coordinated Al (Al(IV)) could either act as the bridging tetrahedron () for the dreierketten chain of tobermorite, or be present in Q³ sites that link two dreierketten chains together. Therefore, the degree of polymerization of the silicate chains of tobermorite is increased at high molar ratio of Al/Si. Furthermore, the greater charge deficit due to the replacement of Si⁴⁺ by Al³⁺ ions is compensated by increased adsorption or binding of Na⁺.     

Combined Extraction of Cesium and Strontium from Alkaline Nitrate Solutions

Abstract

The combined extraction of cesium and strontium from caustic wastes can be achieved by adding a crown ether and a carboxylic acid to the Caustic‐Side Solvent Extraction (CSSX) solvent. The ligand 4,4′(5′)‐di(tert‐butyl)cyclohexano‐18‐crown‐6 and one of four different carboxylic acids were combined with the components of the CSSX solvent optimized for the extraction of cesium, allowing for the simultaneous extraction of cesium and strontium from alkaline nitrate media simulating alkaline high level wastes present at the U.S. Department of Energy Savannah River Site. Extraction and stripping experiments were conducted independently and exhibited adequate results for mimicking waste simulant processing through batch contacts. The promising results of these batch tests showed that the system could reasonably be tested on actual waste.     

Sorption of Cesium and Strontium Radionuclides by Synthetic Ivanyukite from Model and Process Solutions

Theoretical Foundations of Chemical Engineering - The sorption of 137Cs and 90Sr radionuclides from model and real solutions of various salt compositions has been studied on a synthetic powder and...     

碳热还原氮化粉煤灰的研究

以粉煤灰加入炭黑为主要原料,在氮气气氛下对粉煤灰进行了碳热还原氮化研究.研究了碳加入量、合成反应温度、保温时间和Fe2O3含量等因素对生成物物相的影响.实验结果表明:选用理论加入碳含量的样品,在反应温度为1350℃、保温9h条件下,产物中含有较多β-Sialon相;而且经磁选除铁后的粉煤灰较未除铁粉煤灰在反应温度为1400℃、保温9h条件下,碳化还原氮化产物中15R相含量明显增多.     

粉煤灰动态水热合成纳米复合托贝莫来石晶须及其表征

以山西某地普通粉煤灰为原料,采用动态水热法合成纳米复合托贝莫来石晶须,考察了CaO/SiO2摩尔比、反应温度、液固比、反应时间的影响. 结果表明,以预活化的普通粉煤灰为原料,控制CaO/SiO2摩尔比为1.0、液固比为25 mL/g,在220℃下水热反应10 h,可制备出晶须长/径比大于20的纳米复合托贝莫来石晶须,优化条件下晶须可相互缠绕成中空球形颗粒,纯度达80%以上.     

粉煤灰合成沸石对重金属铅与镍的吸附性能研究

利用粉煤灰合成的沸石吸附混合重金属Ni~(2+)与Pb~(2+),考察吸附剂量、初始p H、反应温度与反应时间对其竞争吸附效果的影响,探讨沸石吸附Ni~(2+)与Pb~(2+)的吸附动力学。结果表明:随着吸附剂量的逐渐增大,沸石对Ni~(2+)与Pb~(2+)的吸附去除率不断提高,而单位质量吸附剂对Ni~(2+)与Pb~(2+)的吸附容量不断下降。在整个吸附过程中两种离子竞争吸附去除顺序是PbNi。初始p H值对沸石吸附Ni~(2+)与Pb~(2+)去除效果影响显著。酸性环境中沸石对混合重金属中Pb~(2+)的吸附抑制了其对Ni~(2+)的吸附。随着反应温度的上升与反应时间的延长,沸石对Ni~(2+)与Pb~(2+)的吸附去除率不断提高。沸石对Pb~(2+)的吸附去除率在各个反应温度均高于其对Ni~(2+)的去除率。沸石对混合重金属Ni~(2+)与Pb~(2+)的吸附动力学均符合准二级动力学模型。     

利用粉煤灰和氧化铝粉末合成莫来石材料的性能特性研究

本文的主要目的是论证利用精选型粉煤灰和氧化铝粉末合成莫来石材料的可行性。F级和C级标准型及精选型粉煤灰都能用于合成莫来石材料,其中F级精选型粉煤灰能成功地转变为与市场出售的质量等级相同的莫来石材料,但F级及C级标准型粉煤灰不适宜于合成低膨胀系数的莫来石材料。     

由飞灰合成的沸石吸附废水中染料的动态平衡

The removal performance of a basic dye, methylene blue (MB), in aqueous solution was investigated by adsorption process on single-phase and high-crystalline zeolite A (FA-ZA) and X (FA-ZX). Both adsorbents FA-ZA and FA-ZX were synthesized from fly ash prepared aluminosilicate gel followed by the hydrothermal treatment at 100°C with the control of Si/Al molar ratio, respectively. The properties of the synthetic zeolites and commercial grade zeolites, such as thermal stability, elemental composition, and cation exchange capacity, were investigated for comparison. Batch method was used to study the influential parameters, such as initial pH value of the solution, temperatures, and adsorbents dosage, on the adsorption process. The experimental data were well fitted by Ho’ pseudo-second-order model and liquid film diffusion model. The suitability of Langmuir and Freundlich isotherms to the equilibrium data was investigated in the solid-liquid system while the Langmuir model produces the best re-sults. Thermodynamic data (ΔH, ΔS, and ΔG) corresponding to the MB uptake were evaluated from the Langmuir model. In all the adsorption experiments, the adsorption capacity followed the order as follows: FA-ZX > FA-ZA. In addition, attempts were also made to regenerate the adsorbents.     

粉煤灰合成沸石对混合重金属离子的吸附研究

利用粉煤灰合成沸石吸附混合重金属离子Cu^2＋、Ni^2＋、Pb^2＋、Zn^2＋,考察初始浓度对沸石吸附4种混合重金属离子的吸附效果影响。结果表明：初始浓度对沸石吸附重金属离子的效果影响显著,当混合重金属离子初始浓度不同时,沸石对其去除率也不同。当初始浓度为50mg／L与100mg／L时,重金属离子去除顺序为Cu〉Pb〉Ni〉Zn。当初始浓度提高为200mg／L与300mg／L时,去除顺序变为Cu≈Pb〉Zn〉Ni。沸石对Pb^2＋与Cu^2＋两种重金属离子的吸附性能较强,而对Zn^2＋与Ni^2＋两种重金属离子的吸附能力较弱。     

Immobilization of Cesium and Strontium Radionuclides in Framework Aluminosilicates with the Use of Porous Glass-Ceramic Matrices Based on Coal Fly Ash Cenospheres

The possibility of solidifying liquid radioactive wastes containing cesium and strontium radionuclides into framework aluminosilicates of the feldspar (anorthite) and feldspathoid (nepheline) types with the use of porous glass-ceramic matrices based on coal fly ash cenospheres is demonstrated. Cesium and strontium are immobilized through solid-phase crystallization at temperatures below the softening point of the matrix material (at 700–900° C). The technique for solidifying liquid radioactive wastes in mineral-like forms with the use of matrices based on coal fly ash cenospheres is a sufficiently simple and energy-efficient procedure due to the combination of the calcination and solid-phase crystallization stages. The chemical durability of the matrices satisfies the requirements of the GOST (State Standard) R 50926-96 for solidified high-level wastes.     

Zeolites Synthesized from Class F Fly Ash and Sodium Aluminate Slurry

A Class F fly ash was combined with a sodium aluminate slurry (3:1 Na:Al) in an attempt to synthesize zeolites from a highly alkaline waste stream. The reaction was studied as a function of composition (3:2, 1:1, and 1:2 fly ash:slurry), time (1, 3, and 7 days), and temperature (80°, 130°, and 180°C). X-ray diffraction analyses of the products indicated that the fly ash and sodium aluminate had combined to form Zeolite A at 80°C, and NaP₁ (a gismondene-type) and an unnamed hydroxysodalite-type at 130° and 180°C. The fact that the pH of the reactants decreased from initial values in excess of 13 to near neutral (7–9) after reaction signifies that the bulk of the sodium had been incorporated into zeolitic phases. Because of the unique adsorptive and cation exchange capabilities of zeolites and the fact that some samples formed reasonably hard monoliths, zeolitic materials formed in this way might make excellent waste forms for "mixed wastes" which contain both radioactive and hazardous chemical species.     

粉煤灰改性吸附材料及其吸附机理

粉煤灰的主要成分为 Si O2 和 Al2 O3,属硅铝酸盐 ,还含有不同量的 Fe2 O3、Ca O、Mg O和未燃尽炭等。粉煤灰具有较大的比表面积和固体吸附剂性能。其吸附机制主要有吸附机理 (包括物理吸附、化学吸附和离子交换吸附等 )、接触凝聚机理 (污染物通过与粉煤灰发生接触凝聚而被去除 )、沉淀机理 (污染物由于沉降作用及共沉作用而被去除 )和过滤机理 (污染物通过粉煤灰滤层时被过滤截留去除 ) ,其中物理、化学吸附和离子交换吸附占主导地位。利用粉煤灰吸附工业废水中的磷酸盐、重铬酸盐和氟化物以及众多有害气体等 ,国内外文献已有报道 ,但…     

Fast-Sintered Gehlenite Glass–Ceramics from Plasma-Vitrified Municipal Solid Waste Incinerator Fly Ashes

Plasma heating is a highly efficient industrial treatment for municipal solid waste incinerator fly ashes, converted into leach-resistant glass. The viscous flow sintering of glass powders appears a very promising way for the subsequent conversion of the vitrified waste, not refined and available as glass flakes, into valuable glass–ceramics. Because of the particular glass composition, the densification of glass–ceramics was much hindered by the strong tendency of glass toward surface crystallization. The crystallization of glass was successfully coupled to a low porosity, thus yielding strong gehlenite-based glass–ceramics (with a bending strength exceeding 100 MPa), by adopting a fast sintering treatment (direct insertion of glass compacts at 1050°C, with an holding time of 1 h).     

利用粉煤灰制备分子筛及对水体中六价铬的吸附研究

以粉煤灰为原料,采用湿法加碱煅烧法合成了4A分子筛,研究了粉煤灰与烧碱配比、煅烧温度、煅烧时间对合成4A分子筛的影响,结果表明粉煤灰与烧碱配比1.0:0.8,煅烧温度700℃,煅烧时间1 h有利于4A分子筛的合成.利用合成的4A分子筛对水体中六价铬进行了吸附研究,实验确定的最佳吸附条件为:分子筛投加量为0.3 g,溶液pH值为6～7,吸附时间为30 min,吸附温度为10～25℃.最佳吸附条件下分子筛对六价铬有较好的去除效果.吸附以物理吸附为主,符合Freundlich等温吸附式.同时对4A分子筛的再生性进行了研究,2次循环使用后其吸附能力仍能保持初次吸附能力的90.0％以上.     

Solidification/Stabilization of Heavy Metal-Loaded Red Muds and Fly Ashes

Red muds and fly ashes, used as immobilization agents for heavy metal ions in aqueous solution, were loaded to saturation with Pb(II), Cd(II) and Cu(II), and solidified by cement-based CFS technology to hard concrete blocks which should not pose any risk to the environment. The setting and hardening characteristics of mortars as well as the flexural and mechanical strengths of the solidified specimens were optimized with respect to the dosage of natural and metal-loaded solid wastes. The fixed metals essentially did not leach out into water over extended periods. The matrix-disrupting effect of lead was eliminated by adding NaAlO₂, Ca₃(PO₄)₂ or Ca₃(PO₄)₂+CaCl₂ at optimal dosages so as to improve the setting, hardening and mechanical properties of the final concrete block. © 1997 SCI.     

粉煤灰合成莫来石晶须过程中的相变特征

采用循环流化床(CFB)高铝粉煤灰和煤粉炉(OF)高铝粉煤灰为原料,以AlF_3·3H_2O为导向剂,V_2O_5为催化剂,通过固相反应制备莫来石晶须。利用XRD和SEM等手段,分析了产物的物相,对产物的形貌进行了表征。探讨了原料结晶程度、合成温度及保温时间、导向剂含量等工艺条件对产物的影响,优选出合理的制备工艺参数,分析了莫来石晶须的合成反应机制。     

上海地区不同商品粉煤灰的化学活性

对上海地区多种商品粉煤灰的化学活性作了研究与比较。测试结果表明 ,常温下不同灰样在FA Ca(OH) 2 H2 O系统中的反应率有一定差别 ,随龄期延长 ,差别逐渐减小 ,在 180天差值不超过 3 5 %。Ⅱ级磨细灰的化学活性优于Ⅱ级分选灰和Ⅰ级分选灰。但在高温 (80℃ )下 ,分选灰的反应速率常数大于磨细灰。酸溶法不适用于高钙灰反应率的测定。强度测试表明商品高钙灰的活性不低于低钙灰 ,Ⅰ级混烧高钙灰活性最高。     

Solvent Extraction of Strontium and Cesium: A Review of Recent Progress

Radioactive isotopes ¹³⁷Cs and ⁹⁰Sr, two significant fission products that are usually carried into High Level Waste (HLW) during spent nuclear fuel reprocessing are suggested to be removed from HLW in order to reduce the volume of HLW and then make nuclear energy more clean and sustainable. A variety of separation techniques, including solvent extraction, have been developed for the removal of ¹³⁷Cs and ⁹⁰Sr from HLW. Among those developed separation techniques, solvent extraction is more applicable and promising, particularly for acidic HLW. This article reviews the scientific progress as well as application developments of the solvent extraction method for the separation of strontium and cesium from HLW in the last decade.     

熔融-水热合成法制备超微4A沸石

以粉煤灰为原料,采用加碱熔融-水热合成法制备超微4A沸石,并采用XRD、SEM和激光粒度分析等手段将合成结果与常规4A沸石进行了对比.结果表明,该法不仅可以有效地减小沸石的结晶粒度和粒径分布范围,而且可降低沸石原料煅烧活化温度和时间.     

粉煤灰合成P型沸石及其对氨氮吸附性能研究

以粉煤灰为主要原料,采用碱熔融-水热法改型合成沸石,利用XRD、SEM、TEM等检测手段对产物进行性能检测并进行氨氮吸附性能研究.实验结果表明:采用碱熔融-水热法合成的粉煤灰沸石主要以P型沸石为主,晶粒尺寸分布均匀、孔道结构排列规则,沸石颗粒的比表面积可达148.81 m2/g,平均孔径为3.82 nm,沸石对氨氮的吸附能力随溶液浓度的升高呈上升趋势,pH值为6～8,吸附30 min后,其去除率可达68.2％.