Investigations about the effect of aggregates on strength and microstructure of geopolymeric mine waste mud binders

Geopolymeric binders appear to be an alternative to traditional Portland cement, due to high mechanical performances and environmental advantages. Some aspects related to the effect of aggregates in the microstructure and mechanical behaviour of geopolymeric mine waste mud (GMWM) binders are reported in the present study. Compressive and tensile strength of mine waste mud binders were analyzed. The factors investigated were the aggregate/binder ratio, the aggregate dimension and aggregate type, schist, granite and limestone.Test results showed that GMWM binders have a very high strength at early ages and also possess a very high tensile strength. It's suggested that behaviour may be due to the dissolution of quartz and alumina in the presence of alkalis enhancing bonding between paste and aggregates.The aggregate dimension showed only significant effect on tensile strength. Limestone aggregates showed a chemical bond to the alkali-activated paste but presented higher shrinkage. It was also found that no traditional porous ITZ was detected in GMWM binders.     

Structural investigation relating to the cementitious activity of bauxite residue — Red mud

The cementitious behavior of red mud derived from Bauxite-Calcination method was investigated in this research. Red mud were calcined in the interval 400–900 °C to enhance their pozzolanic activity and then characterized in depth through XRD, FTIR and ²⁹Si MAS-NMR techniques with the aim to correlate phase transitions and structural features with the cementitious activity. The cementitious activity of calcined red mud was evaluated through testing the compressive strength of blended cement mortars. The results indicate that red mud calcined at 600 °C has good cementitious activity due to the formation of poorly-crystallized Ca₂SiO₄. The poorly-crystallized Ca₂SiO₄ is a metastable phase which will transform into highly-crystallized Ca₂SiO₄ with the increase of calcination temperature from 700 °C moving to 900 °C. It is the metastable phase that mainly contributes to the good cementitious activity of red mud. This paper points out another promising direction for the proper utilization of red mud.     

Determining the Reactivity of a Fly Ash for Production of Geopolymer

A Western Australian fly ash has been analyzed by various techniques in order to quantify the reactive component that can be utilized in geopolymerization. Once the reactive amorphous aluminosilicate material was determined an estimate was made on how much material was left to act as filler material. Two approaches were used, the first a combination of XRD and XRF and the second an alkaline dissolution of fly ash. XRD/XRF results show that approximately 52 wt% of the fly ash is amorphous aluminosilicate material while the dissolution experiment provided a lower value of 39 wt%. Quantitative evaluation of minerals by scanning electron microscopy results showed an increase of iron oxide concentration in the undissolved component with increase in dissolution time leading to the conclusion that the amorphous iron does not participate in the geopolymerization process.     

Zirconium Oxide Coating on Anodized Aluminum by the Sol-Gel Process Combined with Ultraviolet Irradiation at Ambient Temperature

Instead of the conventional sol-gel process in which heat treatment is used to form a dense composite film after dipping/withdrawing a substrate into/from the sol, a new sol-gel process incorporating ultraviolet (UV) irradiation at ambient temperature has been attempted to improve the alkaline corrosion resistance of aluminum. A sol-gel film prepared by UV irradiation at ambient temperature indicated that alkaline corrosion resistance is superior in the range of 2.4 times to 2.6 times that of the conventional composite film heated at 573 K. The densification of the coating layer due to the elimination of residual organics induced by photoexcitation was responsible for the improvement in alkaline corrosion resistance. The high alkaline corrosion resistance of the irradiated film may be attributed to the formation of a dense coating layer and the self-repairing action caused by repetition for preparation and dissolution of the reactant in the penetrating path of NaOH solution into the composite film.     

氧化铝厂赤泥剂的固硫反应动力学特性研究

采用热分析法研究了山东铝业公司赤泥和石灰石固硫反应过程,利用等效粒子模型计算分析了其固硫反应动力学参数,并在此基础上利用压汞仪、SEM分析了赤泥煅烧前后的微观结构,探讨了赤泥固硫机理,为利用氧化铝生产中排放的大量赤泥代替石灰石用作燃煤固硫剂提供了理论依据.结果表明,赤泥的钙利用率是相同条件下石灰石的2～3倍,赤泥煅烧后较石灰石具有更多的中孔和较大的比表面积,可提高化学反应速度和反应深度;另外,赤泥中较多的三氧化二铁和碱金属盐也可提高赤泥固硫反应速率常数和有效扩散系数,但温度过高会降低固体熔点而易导致烧结,削弱其固硫活性.     

Patterning of Lithium Niobate Thin Films Derived from Aqueous Solution

The micropatterning of lithium niobate (LiNbO₃) thin films was conducted by applying a photolithographic technique to an aqueous precursor solution that was derived from a double alkoxide. The neutralization process of the alkaline lithium niobium hydroxide solution was essential to avoid the dissolution of the aluminum masking pattern on the sapphire substrate. The acetic acid was a suitable neutralizer to form the stoichiometric and transparent gel film. The gel film that was prepared from a neutralized precursor solution at pH 6.4 gave high-quality crystalline LiNbO₃ films after heat treatment at 500°C.     

赤泥对玉米秸秆催化热解生物油的影响规律研究

将经过不同温度煅烧的赤泥与玉米秸秆按照一定质量比混合,在500℃下进行催化热解实验,研究赤泥对玉米秸秆生物油组成的影响规律。经TG-DTG和XRD分析发现：600℃煅烧后赤泥（RM600）中含水矿物失水,1 000℃煅烧后赤泥（RM1000）中碳酸盐类化合物分解完全,并且发生了烧结反应。对生物油进行GC/MS分析发现：经过干燥的赤泥（RM）和600℃煅烧的赤泥对羧酸酮基化反应具有明显促进作用,酸类的量降低,酮类的量相应增加,同时对呋喃类的生成也有促进作用。其中,干燥赤泥降酸作用更明显,玉米秸秆与赤泥质量比1：5时,生物油中酸类的量由未添加赤泥时的23.85%降至0.90%。此外,2种赤泥对糖类和醛类都有抑制作用,而1 000℃煅烧的赤泥发生烧结反应,催化作用大幅降低,对生物油组分影响较小。     

Mechanical and microstructural characterization of geopolymers synthesized from FCC waste catalyst and silica fume

A FCC waste catalyst-based geopolymer was synthesized from FCC waste catalyst and silica fume, which were used as the main silicon-aluminum raw material and correction material, respectively. Meanwhile, NaOH and water glass composite were used as alkaline activator in the preparation process. Herein, the effects of silicon correction materials, alkaline activator modulus, and silica fume content on the compressive strength performance of prepared geopolymers were discussed. The microstructure was comprehensively analyzed by X-ray diffraction, fourier infrared spectroscopy, nuclear magnetic resonance spectroscopy and scanning electron microscope. The results showed that the prepared geopolymer has good early property when the silica fume content is 50% and the water glass modulus is 1.2. The 3d compressive strength of the obtained sample reaches 23.77 MPa. Microstructure and geopolymerization process analysis indicate that the FCC waste catalyst and silica fume have a good synergistic effect, which confirms the feasibility of preparing the geopolymer by using these industrial waste materials.     

Bauxite ‘red mud’ in the ceramic industry. Part 2: production of clay-based ceramics

Some potential uses of red mud as a raw component in clay mixtures for ceramic bodies production are presented. The influence of increasing amounts of red mud on the forming procedure, sintering and final properties was analyzed. Samples were produced by uniaxial pressing and slip casting. Two different clays are used as basic materials, the former being currently employed for the production of bricks by extrusion, the second — almost pure Kaolin — for high quality ceramic manufacturing. In both cases the addition of red mud led to more deflocculated solid–water systems and an increase of the critical moisture content. Mixtures prepared with the first clay and red mud loads up to 50% were fired at 850°C. The red mud content did not influence the sample porosity while determining a strength decrease attributed to the inertness of red mud at the working temperature. Samples produced using the second clay and red mud (0 – 20%) were fired at 950 and 1050°C. The addition of red mud determined increases of density and flexural strength which can be accounted for by the formation of a larger amount of glassy phase at higher red mud contents. The results of this work indicate excellent perspectives for using ‘red mud’ as raw material in mixtures with clay for the production of ceramic bodies.     

流化床锅炉温度条件下钙基工业废弃物的固硫反应性能

在流化床锅炉温度条件下研究了赤泥、电石渣等钙基工业废弃物煅烧后的固硫特性,并与石灰石比较,同时研究了吸收剂在反应过程中的物相变化、微观结构特性。结果表明,在相同反应条件下,随反应时间增加,赤泥的钙转化率高于电石渣和石灰石,石灰石的钙转化率最小。赤泥和电石渣的最佳固硫温度分别为850～900℃和950～1000℃。随SO2浓度增加,在相同反应时间内赤泥的钙转化率和硫化反应速率也相应增大。粒径对赤泥的固硫性能影响不大。赤泥和电石渣中钙的主要化合物分别为Ca2SiO4和Ca(OH)2。它们煅烧后孔径主要分布在5～20nm内,这正是最有利于固硫的孔径区域,石灰石煅烧后孔径主要分布于45～420nm。钙基废弃物具有优良的孔隙结构,因而它们在流化床锅炉温度条件下具有良好的固硫性能。     

Dissolution kinetics of calcined kaolinite and montmorillonite in alkaline conditions: Evidence for reactive Al(V) sites

Calcined clays are attracting significant research attention because of their potential to partially replace CO₂-intensive portland cement. This potential depends largely on their reactivity, especially dissolution under alkaline conditions. Identification and characterization of reactive sites in these amorphous calcined clays has so far not been reported. Here, we investigate kaolinite (1:1 clay) and montmorillonite (2:1 clay) calcined at different temperatures under alkaline conditions (0.1 mol/L NaOH). Solution compositions are determined in batch dissolution experiments, whereas ²⁷Al and ²⁹Si MAS and CP/MAS NMR are used to investigate the structure of the undissolved residues to identify sites that are reactive and undergo preferential dissolution. The highest Si and Al dissolution rates for kaolinite are observed for calcination at 700°C, corresponding to the temperature of optimum reactivity, whereas the rates decrease and become increasingly incongruent at higher temperatures. The Si and Al dissolution rates for optimally calcined kaolinite are 4 and 12 times larger than the corresponding rates for optimally calcined montmorillonite, in accord with the much higher reactivity of calcined kaolinite compared to calcined 2:1 clays. This superior performance of kaolinite is explained by novel ²⁷Al NMR results, which show strong evidence for preferential dissolution of highly reactive pentahedral aluminum sites.     

粉煤灰中玻璃体含量的化学物相分析

为快速评判粉煤灰的火山灰反应活性和分析其加工过程中技术特征,需准确测定粉煤灰中玻璃体含量.通过分析粉煤灰中各种矿物相在碱、酸溶液中溶解反应特征,提出碱-酸两段溶解来测定粉煤灰中玻璃体含量的化学物相分析法.粉煤灰中莫来石、石英、磁铁矿、赤铁矿和未燃尽碳粒,在碱、酸溶液中是稳定相;玻璃体和f-CaO在碱溶液中反应形成凝胶,凝胶在酸溶液中完全溶解,两者含量为溶解过程的质量缩减率,减去f-CaO含量即为玻璃体含量.测定操作要点,-20μm粉煤灰在90℃20%NaOH溶液溶解2.5 h,溶解1.5 h时湿磨至-12μm.碱溶解后滤渣在30℃10%的HNO3溶液溶解1.0 h.试样与试剂比例为5 g粉煤灰、500 mL NaOH溶液、200 mL HNO3溶液.     

One‐Part Geopolymers Based on Thermally Treated Red Mud/NaOH Blends

In this study, one‐part “just add water” geopolymer binders are synthesized through the alkali‐thermal activation of the red mud which is relatively rich in both alumina and calcium. Calcination of the red mud with sodium hydroxide pellets at 800°C leads to decomposition of the original silicate and aluminosilicate phases present in the red mud, which promotes the formation of new compounds with hydraulic character, including a partially ordered peralkaline aluminosilicate phase and the calcium‐rich phases C₃A and α‐C₂S. The hydration of the “one‐part geopolymer” leads to the formation of zeolites and a disordered binder gel as the main reaction products, and the consequent development of compressive strengths of up to 10 MPa after 7 d of curing. These results demonstrate that red mud is an effective precursor to produce one‐part geopolymer binders, via thermal and alkali‐activation processes.     

Mullite/SiAlON/Alumina Composites by Infiltration Processing

The formation of mullite/SiAlON/alumina composites was studied by infiltrating a SiAlON/alumina-base composite with two different solutions, followed by thermal treatment. The base composite was prepared from a mixture of tabular Al₂O₃ grains, fume SiO₂, and aluminum powders. The mixture was pressed into test bars and nitrided in a nitrogen-gas (N₂) atmosphere at 1480°C. The infiltrants were prehydrolyzed ethyl polysilicate solution and ethyl polysilicatealuminum nitrate solution. The composites were infiltrated under vacuum, cured at 100°C, and precalcined in air at 700°C. This infiltration process was repeated several times to produce bars that had been subjected to multiple infiltrations, then the bars were calcined in a N₂ atmosphere at 1480°C to obtain mullite/SiAlON/alumina composites. The infiltration process increased the percentage of nitrogenous crystalline and mullite phases in the matrix; therefore, a decrease of the composite microporosity was observed. The infiltration increased the mechanical strength of the composites. Of the two composites, the one produced using prehydrolyzed ethyl polysilicate as the infiltrant had a higher mechanical strength, before and after being subjected to a severe thermal shock.     

赤泥/木质素共热解制备复合吸附材料及其性能

炼铝工业产生的赤泥废渣以不合理的方式处置,会造成严重的环境污染和资源浪费。赤泥中富含的铁元素以Fe₂O₃的形式存在,不利于铁资源回收,可通过还原方式制取磁性材料用于重金属离子的去除。基于此,本研究采用碳热还原法耦合赤泥与木质素制备一种复合吸附材料。系统探究还原温度、还原时间、还原剂用量对还原效果的影响,并开展铅离子吸附实验。研究表明,通过与烟煤还原赤泥对比得出木质素还原赤泥最佳工艺参数：还原温度625℃、还原时间30min、木质素与赤泥质量比为1∶1;GC对共热解气体产物进行分析得出赤泥的引入能够提高氢气产量;GC-MS对共热解液体产物进行分析得出木质素/赤泥共热解能够提升芳烃类化合物产量;吸附实验得出制备的复合材料能够有效去除水溶液中的铅离子。通过耦合赤泥、木质素残渣两种废弃物制备复合吸附材料,能够响应国家环保政策,具备潜在的经济、能源、环境效益。     

Mechanical strengths of epoxy resin composites reinforced by calcined pearl shell powders

A series of epoxy resin (EP) composites were prepared using ground pearl shell powders, which had been calcined at various temperatures. The EP composite containing ～ 3% weight content of the calcined pearl shell powder had the highest impact strength and the presence of silane agent was found to be essential for the composite formulation. The impact strengths of the resultant EP composites were highly influenced by the specific surface area, surface morphological structure, and chemical composition of the calcined pearl shell powder. The highest mechanical improvement was obtained for the EP composite prepared with the pearl shell powder calcined at 700°C for 3 h. The layered biopolymeric materials were completely degraded for the pearl shell powder calcined at 700°C, resulting in “sponge‐like” or “net‐like” porous calcium carbonate powder. However, the degradation of the layered biopolymeric materials was not complete for the calcinations at lower temperatures (<600°C), while calcium carbonate decomposed to form calcium oxide at higher temperatures (>800°C). The mechanical improvements of the processed EP composites have been discussed along with the chemical compositions and surface microstructures of the incorporated pearl shell powders. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Bio-derived sodium silicate for the manufacture of alkali-activated binders: Use of bamboo leaf ash as silicate source

Alkali activated binders are a promising alternative to the use of Portland cement in the manufacture of concrete for curbing CO₂ emissions. Novel sources of silicates have been investigated in recent years for reducing cost and environmental impacts associated with the use of chemical activators. This study describes the production of solid sodium silicate (SS) activating powder from bamboo leaf ash (BLA). Bamboo leaves were calcined at 550–800°C, mixed with NaOH pellets, and heated in an oven at 300°C. The obtained silicate powder was used for activating blended fly ash/slag samples. Mechanical and microstructural properties of BLA-based samples were compared to those of samples made with commercially available chemicals. The strength of BLA-activated mortars matched the commercially-sourced activators, being 25–30 MPa at 7 days and exceeding 40 MPa at 28 days. The microstructural analysis suggested that BLA-based SS showed a lesser degree of dissolution of precursors at 7 days, but the quality of the matrix was higher than that of NaOH-activated samples. These results confirmed that the reactivity of BLA-silicate powder was similar to that of commercial SS solutions, and show the potential valorization of future biomass renewable waste in the production of low carbon, alkali-activated concretes.     

新型赤泥基充填材料的制备与性能研究

为弥补多数矿用充填材料因成本较高而在煤矿开采过程中存在的不足,并有效解决铝行业固废赤泥大量堆积、无法处理的现状,通过多种添加剂与主原料的有效掺和,开发出一种可用于煤矿井下沿空留巷充填工艺的新型赤泥基充填材料,并对其抗压强度、凝结时间、流动性以及稳定性等性能指标进行研究。结果表明:新型赤泥基充填材料单浆流动性好,凝结时间大于6 h;材料中的赤泥添加量可调控(质量分数在0%~50%);成型材料早强快硬,初凝时间仅为25 min,抗压强度1 d可达8.4 MPa,3 d可达10.3 MPa,7 d可达12.3 MPa;成型材料封膜浸渍长达14 d,浸出液pH值保持为6,赤泥组分中的碱性物质得到良好的固化,造成污染的概率低。     

Adsorption of Nickel from aqueous solution by the use of low-cost adsorbents

The removal of Ni(II) from aqueous solution by different adsorbents was investigated. Calcined phosphate, red mud, and clarified sludge (a steel industry waste material) were used for the adsorption studies. The influence of pH, contact time, initial metal concentration, adsorbent nature and concentration on the selectivity and sensitivity of the removal process was investigated. The adsorption process was found to follow a first-order rate mechanism and rate constant was evaluated at 30 °C. Langmuir and Freundlich adsorption isotherms fit well in the experimental data and their constants were evaluated. The thermodynamic equilibrium constant and the Gibbs free energy were calculated for each system. The adsorption capacity (q _max ) calculated from Langmuir isotherm and the values of Gibbs free energy obtained showed that calcined phosphate has a higher capacity and affinity for the removal of Ni(II) compared to the other adsorbents used in the study.     

聚氯乙烯/赤泥复合材料的制备与性能研究

制备了聚氯乙烯(PVC)/赤泥复合材料,研究了赤泥的不同表面处理方式对共混物的力学性能和耐温性能的影响。结果表明:湿法处理赤泥的效果最好,不做处理的效果最差;赤泥的含量在15份时,共混物的缺口冲击强度和拉伸强度最大;添加赤泥可以提高PVC材料的弯曲强度和弯曲模量,同时,耐温性能也有一定程度的提高。