NaOH和Na2CO3对磷渣水化过程的影响

采用NaOH和Na2CO3作为磷渣的激发剂。通过测定磷渣的凝结时间、化学结合水和反应率,研究碱激发剂对磷渣水化程度的影响。利用X射线衍射和扫描电镜分析,研究碱激发磷渣水化产物的物相组成和微观形貌。结果表明,这两种碱激发剂均能加快磷渣的水化速率,其中NaOH对磷渣的激发效果明显优于Na2CO3。NaOH和Na2CO3对磷渣水化过程的影响主要表现为促进磷渣玻璃体溶解,生成更多的C-S-H(B)和托贝莫来石,从而形成致密的结构。     

Influence of slag chemistry on the hydration of alkali-activated blast-furnace slag — Part I: Effect of MgO

The hydration and the microstructure of three alkali activated slags (AAS) with MgO contents between 8 and 13 wt.% are investigated. The slags were hydrated in the presence of two different alkaline activators, NaOH and Na₂SiO₃·5H₂O (WG). Higher MgO content of the slag resulted in a faster reaction and higher compressive strengths during the first days. The formation of C(− A)–S–H and of a hydrotalcite-like phase was observed in all samples by X-ray diffraction (XRD), thermal analysis (TGA) and scanning electron microscopy (SEM) techniques. Increasing the MgO content of the slag from 8 to 13% increased the amount of hydrotalcite and lowered the Al uptake by C–S–H resulting in 9% higher volume of the hydrates and a 50 to 80% increase of the compressive strength after 28 days and longer for WG activated slag pastes. For NaOH activated slags only a slight increase of the compressive strength was measured.     

X-ray microtomography shows pore structure and tortuosity in alkali-activated binders

Durability of alkali-activated binders is of vital importance in their commercial application, and depends strongly on microstructure and pore network characteristics. X-ray microtomography (μCT) offers, for the first time, direct insight into microstructural and pore structure characteristics in three dimensions. Here, μCT is performed on a set of sodium metasilicate-activated fly ash/slag blends, using a synchrotron beamline instrument. Segmentation of the samples into pore and solid regions is then conducted, and pore tortuosity is calculated by a random walker method. Segmented porosity and diffusion tortuosity are correlated, and vary as a function of slag content (slag addition reduces porosity and increases tortuosity), and sample age (extended curing gives lower porosity and higher tortuosity). This is particularly notable for samples with ≥ 50% slag content, where a space-filling calcium (alumino)silicate hydrate gel provides porosity reductions which are not observed for the sodium aluminosilicate (‘geopolymer’) gels which do not chemically bind water of hydration.     

Early hydration properties and microstructure evolutions of MgO-activated slag materials at different curing temperatures

This study reports on the early hydration properties and microstructure evolutions of MgO-activated slag at five curing temperatures (20 °C, 40 °C, 50 °C, 60 °C, and 80 °C) and three MgO types (S-MgO, M ? MgO, and R-MgO). The results indicated that high-temperature curing substantially increased the compressive strength of the specimens. Particularly, the highest strength was obtained at 40 °C and 60 °C for the S-MgO and M-MgO-activated slag specimens, respectively, and the high curing temperature for the R-MgO-activated slag specimen was 40 °C. We focused on the relationship between the mechanical properties, pore structure characteristics, and hydration products. The combination of calcium-silicate-hydrate (C-S-H) gel and Al increased under high-temperature curing conditions. XRD, FT-IR, TG-DTG, and ²⁷Al MAS-NMR results showed a high Al content in the formation of calcium silicate hydrate with Al in its structure (C-A-S-H gel) for the R-MgO-activated slag pastes under high-temperature curing; however, the microstructure was loose owing to the formation of excessive brucite. For the S-MgO-activated slag specimen, the Ca/Si ratio was high, with more Mg²⁺ penetrating the C-S-H gel interlayer, forming more hydrotalcite-like phases and increasing the chain length of the C-S-H gel. The microstructure showed good compatibility of the hydration products interweaving to form dense microstructures.     

固体碱激发矿粉/粉煤灰注浆材料性能及机理研究

以矿粉和粉煤灰为主要原料,NaOH和Na₂SiO₃·5H₂O为固体碱激发剂,制备地聚合物注浆材料,考察激发剂的模数、掺量及养护条件对材料性能的影响。当固体碱激发剂模数为1.0,掺入量为8%(质量分数)时,注浆材料初凝时间为120 min,工作时间可达50 min,经28 d养护后抗折和抗压强度分别可达7.1 MPa和42.7 MPa。相较于非密闭养护,密闭养护有利于早期强度形成,1 d、3 d、7 d抗压强度分别提高了38.0%、38.2%和19.3%。XRD、FT-IR、SEM/EDS测试结果表明,原料水化完全,最终产物包含无定形水化产物、钙沸石、水合铝硅酸钠钙矿和C-S-H凝胶等组分。反应过程中原料的Si—O—Al、Si—O—Si发生重组生成凝胶物质,并团聚成钙沸石类球形产物,提高材料强度。     

热活化铅锌尾矿基碱激发胶凝材料的制备及性能

以铅锌尾矿为主要原料,添加由矿渣、钢渣、氟石膏混合而成的辅助胶凝材料,以水玻璃和氢氧化钠为碱激发剂制备铅锌尾矿基碱激发胶凝材料。通过正交试验,探讨了水玻璃模数、水玻璃掺量及尾矿与辅助胶凝材料质量比对胶凝材料抗压强度的影响,并得出最佳原料配比。通过800 ℃、1 000 ℃、1 200 ℃的热处理,制备热活化铅锌尾矿基碱激发胶凝材料,并测试其性能。采用X射线衍射谱、傅里叶红外光谱和扫描电子显微镜对热活化前后尾矿和胶凝材料进行分析表征。结果表明,当水玻璃模数为1.8,水玻璃质量掺比为0.15,尾矿与辅助胶凝材料质量比为7 ∶3时,胶凝材料28 d抗压强度可达到20.68 MPa。胶凝材料内部形成大量水化硅酸钙(C-S-H)与硅铝多聚物构成三维网状结构,覆盖在尾矿晶体表面形成致密整体。当热活化温度为1 000 ℃时,胶凝材料28 d抗压强度达到28.05 MPa。热活化后的尾矿内部结构疏松,利于硅铝质在碱性条件下解聚,同时使得反应体系中生成了更多硅铝多聚体,取代了二聚体为主的C-S-H凝胶,为胶凝材料提供了更优良的抗压强度和早硬特性。此外胶凝材料对Pb、Zn重金属的固定作用极好,大幅降低了尾矿重金属Pb、Zn的毒性浸出浓度,有效解决了尾矿中重金属对周围环境的危害问题。     

Influence of activator type on hydration kinetics, hydrate assemblage and microstructural development of alkali activated blast-furnace slags

The hydration of two slags with different Al₂O₃ contents activated with sodium hydroxide and hydrous sodium metasilicate (commonly named water glass) is studied using a multi-method approach. In all systems, C-S-H incorporating aluminium and a hydrotalcite-like phase with Mg/Al ratio ~ 2 are the main hydration products. The C-S-H gels present in NaOH activated pastes are more crystalline and contain less water; a calcium silicate hydrate (C-S-H) and a sodium rich C-N-S-H with a similar Ca content are observed at longer hydration times. The activation using NaOH results in high early strength, but strength at 7 days and longer is lower than for the sodium metasilicate systems. The drastic difference in C-S-H structure leads to a coarser capillary porosity and to lower compressive strength for the NaOH activated than for the sodium metasilicate activated slags at the same degree of slag reaction.     

Sodium silicate-based, alkali-activated slag mortars: Part I. Strength, hydration and microstructure

Alkali activation of ground granulated blast furnace slag (GGBFS) with sodium silicate gave clinker-free binders, with high strength and early strength development, although set times were short and somewhat variable. Isothermal calorimetry detected three heat evolution peaks (wetting, gelation of activator and bulk reaction of slag). X-ray diffraction (XRD) showed no crystalline products. Hydration was investigated by scanning electron microscopy (SEM; with quantitative image analysis) and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS NMR). From early age, a uniform gel filled the initially water-filled space, and gradually densified as reaction proceeded. Microanalysis of outer product (OP) showed an Al-substituted C-S-H gel phase of widely variable (0.5-1.0) Ca/Si ratio. NMR showed long-chain substituted C-S-H with Al/Si ratio rising to 0.19 at 1 year, and also cross-linked material, consistent with a Ca- or Al-modified silica gel. Inner product (IP) regions around slag grains probably also contained hydrotalcite. Activation with KOH gave more rapid reaction of slag than for silicate activation, a less homogeneous microstructure, and lower strengths. The hydrates contained a substituted C-S-H gel of low Ca/Si ratio probably mixed with hydrotalcite, and occasional higher Al regions in the OP regions.     

钢渣对矿渣基高水充填材料性能的影响及强度预测

采用钢渣、矿渣和铁尾砂等固体废弃物制备矿渣基高水充填材料,通过对其正交试验样本建立BP神经网络强度预测模型,并结合实测强度预测出不同龄期15%和25%钢渣掺量高水充填材料的抗压强度,分析了钢渣掺量对高水充填材料物理力学性能的影响,不同龄期高水充填材料水化产物的变化规律.研究表明:通过对正交试验样本建立的BP神经网络强度预测模型,可实现对各龄期不同钢渣掺量的高水充填材料抗压强度的预测;随着钢渣掺量的升高,高水充填材料的强度逐渐下降,吸水率逐渐增大,膨胀收缩率先减小后升高;随着养护龄期的延长,水化产物中的石英、氢氧化钙和斜硅钙石的衍射峰逐渐钝化,方解石、水化硅酸钙、C-S-H(I)和羟镁铝石晶相的衍射峰逐渐锐利.     

掺减水剂钼尾矿胶砂的力学性能和水化产物

将钼尾矿、矿渣、熟料、石膏进行机械力粉磨,制备胶凝材料,研究了减水剂种类和掺量对胶砂力学性能的影响,并对掺钼尾矿胶凝材料的水化产物进行了分析.结果表明,在相同流动度条件下制备胶砂试块,PC减水剂对掺钼尾矿胶砂的强度提高幅度最大,FDN次之,UNF-5最小.当PC高效减水剂掺量为0.4%时,大掺量尾矿胶砂试块28 d的抗压强度可以达到48.8 MPa.粉磨后的钼尾矿表现出一定的火山灰反应活性.掺钼尾矿胶凝材料的水化产物主要是钙矾石和水化硅酸钙凝胶.     

Slags with a high Al and Fe content as precursors for inorganic polymers

Slags from non-ferrous metallurgy are Fe rich, with Si as a minor constituent, and with low levels of Al. Due to variations in the slag cooling practice, they can exist as semi-amorphous or as crystalline solids. Considering that both higher Al in the slag and a higher cooling rate during solidification would have an impact on the availability of Al and ultimately on the formation of linkages in the inorganic polymer, we study the microstructure and reactivity of a Fe and Al rich slag cooled in different ways. Results show that high cooling rates lead to a predominantly amorphous material. For lower cooling rates the content of amorphous phase varies from 52 wt.% to 12 wt.%. Spinel is the primary phase precipitating, whereas, for the lowest cooling rate investigated, pyroxenes form as well. Dissolution tests in a 10 M NaOH solution for 96 h reveal that approx. 54 wt.% of Al and 33 wt.% of Si of the total content become available for the highly amorphous slag. On the contrary, the dissolved Al and Si are below 5 wt.% when slag pot cooling is applied. The above strongly influence the resulting inorganic polymers with the ones originating from the amorphous slag being superior in mechanical properties.     

高炉镍铁渣粉在水泥基复合胶凝材料中的水化特性研究

通过对不同高炉镍铁渣掺量的水泥-高炉镍铁渣粉复合胶凝材料水化放热速率、高炉镍铁渣粉的反应程度、硬化浆体化学结合水含量以及水化产物中C-S-H凝胶Ca/Si的测定,分别研究了水泥-高炉镍铁渣粉复合胶凝材料的早期、中长期水化进程、浆体微观形貌以及水化产物特点等水化特性.研究结果表明:高炉镍铁渣的掺入会降低水化放热速率,并推迟水化加速期放热峰的出现时间;在复合胶凝体系中,随着高炉镍铁渣粉掺量的增大,其反应程度和硬化浆体中化学结合水含量将降低.复合胶凝材料水化生成的C-S-H凝胶的Ca/Si低于水泥,且随着水化的进行呈降低趋势;高炉镍铁渣粉中的Al,在水化过程中会取代部分Si进入C-S-H凝胶中,形成C-A-S-H凝胶.     

Blast-furnace slag hydration. Surface analysis

X-ray photoelectron spectrometry (XPS) was used to determine the variation of the characteristic ratios Ca/Si, Al/Si and Mg/Si of two different slags (one in granulated, the other in pelletized form) during hydration. The results show that the slag surface is modified as soon as it becomes in contact with water or alkaline solution. The hydrated superficial layer is depleted of calcium but contains alkali ions if instead of water, NaOH or KOH solutions are used in mixing.     

Hydration Products and Reactivity of Blast-Furnace Slag Activated by Various Alkalis

Pastes of blast-furnace slag were cured for up to 90 d using sodium silicate (waterglass), NaOH, and three different mixtures of Na₂CO₃–Na₂SO₄–Ca(OH)₂ to activate reactions. The highest slag reactivity was observed for NaOH activation and the least for waterglass, although nonevaporable water indicated similar amounts of hydration products formed. The main hydration products found using X-ray diffractometry in all systems were calcium silicate hydrate (C-S-H) and a hydrotalcite-type phase. Microanalysis was performed on pastes activated using 50% Na₂CO₃·25% Na₂SO₄·25% Ca(OH)₂, NaOH, and waterglass; the chemical composition of the C-S-H in the waterglass case was different relative to the other two alkalis. For all alkaline agents used, the C-S-H seemed finely intermixed with a hydrotalcite-type phase of Mg/Al = 1.82, on average.     

氢氧化钠熔盐分解钛渣制备二氧化钛的热力学分析

针对我国钛资源特色,采用NaOH熔盐对钛渣进行分解制备二氧化钛是一种生产钛白的新工艺。以酸溶性钛渣（70%相似文献   

Immobilization of Cr, Cd, Zn and Pb in alkali-activated slag binders

Granulated blast furnace slag is the main component of alkali-activated slag cementitious materials (AASCs). Calcium silicate hydrates with a low Ca/Si ratio, hydrotalcite-type phase, some amounts of hydrogarnets and sodium zeolites form as main AASC hydration products. The microstructure of alkali-activated slag pastes shows a higher amount of gel pore content compared to OPC pastes and, simultaneously, significantly lower amount of capillary pores. The microstructure and phase composition of hydrated slag indicate that they can play an essential role in the immobilization of heavy metals. The properties of alkali-activated slag pastes in the presence of Zn, Cd, Cr and Pb ions were studied. The leaching TANK test was used to evaluate the level of immobilization of particular elements in mortars made containing these elements. It was found that the degree of Cd, Zn and Pb ion immobilization was very high (exceeding 99.9%). The values for Cr⁶⁺ were lower (ca. 99.0%). The strength development as well as microstructure observations are presented in the paper.     

Composition and microstructure of 20-year-old ordinary Portland cement-ground granulated blast-furnace slag blends containing 0 to 100% slag

The morphology of outer-product (Op) C-S-H in 20-year-old slag-cement pastes appeared in most blends to be finer than at younger ages. The Ca/Si and Ca/(Si + Al) ratios of the Op C-S-H decreased with increasing slag content, and the Al/Si ratio increased. The Ca/Si ratio of C-S-H in the slag-containing pastes was lower at 20 years than at 14 months and the amount of Ca(OH)₂ was reduced indicating that additional slag must have reacted. The mean aluminosilicate chain length of the C-S-H was very long in all the samples and would be expected to have increased with age. The TEM-EDX and NMR data are consistent with nanostructural models for C-S-H. The Mg/Al ratio of the Mg-Al layered double hydroxide phase (LDH) was lower at 20 years than at 14 months in all cases except for the neat slag paste; aluminium hydroxide-based structure might be interstratified with those of the Mg-Al LDH.     

Preparation and performance of slag-based binders for the cementation of fine tailings

To achieve effective cementation of fine tailings, slag-based binders were prepared using Portland cement clinker stimulation, early strength activator (ESA, mixture of anhydrite and triethanolamine at 97:3 (w/w)) activation and slag pulverization methods. The compressive strength, hydration products, slag reaction degree and non-evaporable water content of the consolidated samples under different curing times were analyzed to clarify the application performance and early strength action mechanisms of this slag-based binder. The results showed that clinker alone was able to effectively stimulate the slag’s cementitious property, but the cementation strength was relatively low. The addition of ESA in the clinker activated slag promoted the conversion of C₄AH₁₃ into ettringite (AFt) and accelerated the consumption of Ca(OH)₂, all of which significantly improved the early cementation strength of fine tailings. Slag pulverization promoted the slag reaction degree and increased the yield of hydrated products, which led to a further increase in the early strength of the slag-based binder. Eventually, a more efficient and higher early strength slag-based binder was prepared with the composition of 27% clinker, 10% ESA and 63% pulverized slag, and the cementation strength at 3 curing days for the fine tailings sample was 231% more than that of P.O 42.5 Portland cement.     

Solution‐Controlled Dissolution of Supplementary Cementitious Material Glasses at pH 13: The Effect of Solution Composition on Glass Dissolution Rates

Supplementary cementitious materials (SCMs) are widely used to partially replace portland clinker in blended cements. Reducing clinker contents further without compromising the development of early strength necessitates a better assessment and enhancement of the reactivity of the available SCMs. To this purpose, the reactivity of synthesized calcium aluminosilicate glasses covering a compositional range from blast‐furnace slags (BFS) over fly ashes to silica fume was analyzed by dissolution experiments. Initial glass dissolution rates were measured at 20°C and pH 13, and with varying initial concentrations of aqueous Al, Ca, and Si. At pH 13, glass dissolution rates were observed to scale linearly with the glass Ca/(Al + Si) molar ratio. Ca‐rich blast‐furnace type glass dissolution was shown to be up to one order of magnitude faster than tectosilicate fly ash and silica fume type glass dissolution, supporting different pathways to dissolution. In solutions that are strongly undersaturated with respect to hydrous glass and hydration products, glass dissolution rates are independent of changes in solution undersaturation and aqueous Si activity. In contrast, dissolution rates decrease with aqueous Ca concentration for all glasses and with aqueous Al concentration for tectosilicate‐type glasses. The insights gained are instrumental in finding ways to enhance SCM reactivity.     

粉煤灰与炉底渣的蒸压反应活性研究

粉煤灰和炉底渣均为燃煤发电过程中产生的固体废弃物,但两者的反应活性有所区别。研究结果表明,炉底渣的玻璃相含量以及活性SiO2、Al2O3含量均高于粉煤灰,在蒸压条件下炉底渣的反应活性优于粉煤灰,有利于生成更多的水化产物。利用炉底渣部分或全部取代粉煤灰制备蒸压硅酸盐制品,有利于提高制品的强度。