Dry Mix Slag—High-Calcium Fly Ash Binder. Part Two: Durability

This work investigates durability of cement-free mortars with a binder comprised of ground granulated blast furnace slag (GGBFS) activated by high-calcium fly ash (HCFA) and sodium carbonate (Na2CO3): the soundness, sulfate resistance, alkali-silica reactivity and efflorescence factors are considered. Results of tests show that such mortars are resistant to alkali-silica expansion. Mortars are also sulfate-resistant when the amount of HCFA in the complex binder is within a limit of 10 wt%. The fineness of fly ash determines its’ ability to activate GGBFS hydration, and influence soundness of the binder, early strength development, sulfate resistance and efflorescence behavior. The present article is a continuation of authors’ work, previously published in MSA, Vol. 14, 240-254.

Dry Mix Slag—High-Calcium Fly Ash Binder. Part One: Hydration and Mechanical Properties

High-calcium fly ash (HCFA)—a residue of high-temperature coal combustion at thermal power plants, in combination with sodium carbonate presents an effective hardening activator of ground granulated blast-furnace slag (GGBFS). Substitution of 10% - 30% of GGBFS by HCFA and premixing of 1% - 3% Na2CO3 to this dry binary binder was discovered to give mortar compression strength of 10 - 30 to 30 - 45 MPa at 7 and 28 days when moist cured at ambient temperature. High-calcium fly ash produced from low-temperature combustion of fuel, like in circulating fluidized bed technology, reacts with water readily and is itself a good hardening activator for GGBFS, so introduction of Na2CO3 into such mix has no noticeable effect on the mortar strength. However, low-temperature HCFA has higher water demand, and the strength of mortar is compromised by this factor. As of today, our research is still ongoing, and we expect to publish more data on different aspects of durability of proposed GGBFS-HCFA binder later.

Green evaluation of microwave-assisted leaching process of high titanium slag on life cycle assessment

A greenness evaluation index and system of microwave-assisted leaching method were established.The effects of the life cycle assessment variables,such as the resource consumption,environment impact,cost,time and quality,were investigated,and the concept of green degree was applied in the production of synthetic rutile.An analytic hierarchy process was utilized to assess matrix of greenness evaluation.The Gauss-Seidel iterative matrix method was employed to solve the assessment matrix and obtain the weights and membership functions of all evaluation indexes.A fuzzy decision-making method was applied to build the greenness evaluation model,and then the scores of green degree in microwave-assisted leaching process was obtained.The greenness evaluation model was applied to the life cycle assessment of the microwave-assisted leaching process.The results show that the microwave-assisted leaching process has advantages over the conventional ones,with respect to energy-consumption,processing time and environmental protection.

Roasting and leaching behaviors of vanadium and chromium in calcification roasting–acid leaching of high-chromium vanadium slag

Calcification roasting–acid leaching of high-chromium vanadium slag(HCVS)was conducted to elucidate the roasting and leaching behaviors of vanadium and chromium.The effects of the purity of Ca O,molar ratio between Ca O and V_2O_5(n(Ca O)/n(V_2O_5)),roasting temperature,holding time,and the heating rate used in the oxidation–calcification processes were investigated.The roasting process and mechanism were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM),and thermogravimetry–differential scanning calorimetry(TG–DSC).The results show that most of vanadium reacted with Ca O to generate calcium vanadates and transferred into the leaching liquid,whereas almost all of the chromium remained in the leaching residue in the form of(Fe_(0.6)Cr_(0.4))_2O_3.Variation trends of the vanadium and chromium leaching ratios were always opposite because of the competitive reactions of oxidation and calcification between vanadium and chromium with Ca O.Moreover,Ca O was more likely to combine with vanadium,as further confirmed by thermodynamic analysis.When the HCVS with Ca O added in an n(Ca O)/n(V_2O_5)ratio of 0.5 was roasted in an air atmosphere at a heating rate of 10°C/min from room temperature to 950°C and maintained at this temperature for 60 min,the leaching ratios of vanadium and chromium reached91.14%and 0.49%,respectively;thus,efficient extraction of vanadium from HCVS was achieved and the leaching residue could be used as a new raw material for the extraction of chromium.Furthermore,the oxidation and calcification reactions of the spinel phases occurred at 592and 630°C for n(Ca O)/n(V_2O_5)ratios of 0.5 and 5,respectively.

Study on non-metallic inclusions in Al killed high strength alloy steel refined by high basicity and high Al_2O_3 content slag

Laboratory and industrial studies were carried out to investigate non-metallic inclusions in high strength alloy steel refined by high basicity and high Al_2O_3 slag.It was found that the steel/slag reaction time largely affected non-metallic inclusions.With the reaction time increased from 30 min to 90 min in laboratory study,MgO-Al_2O_3 spinels were gradually changed into CaO-MgO-Al_2O_3 system inclusions surrounded by softer CaO-Al_2O_3 surface layers.By using high basicity slag which contained as much as 41%Al_2O_3 in the laboratory study,ratio of low melting temperature CaO-MgO-Al_2O_3 system inclusions was remarkably increased to above 80%.In the industrial experiment,during the secondary refining,the inclusions changed in order of 'Al_2O_3→MgO-Al_2O_3→CaO-MgO-Al_2O_3'.Through the LF and RH refining,most inclusions could be transferred to lower melting temperature CaO-Al_2O_3 and CaO-MgO-Al_2O_3 system inclusions.

Influence of TiO2 on the melting property and viscosity of Cr-containing high-Ti melting slag

A study on the melting and viscosity properties of the chromium-containing high-titanium melting slag(CaO–SiO2–MgO–Al2O3–TiO2–Cr2O3) with TiO2 contents ranging from 38.63 wt% to 42.63 wt% was conducted. The melting properties were investigated with a meltingpoint apparatus, and viscosity was measured using the rotating cylinder method. The FactSage 7.1 software and X-ray diffraction, in combination with scanning electron microscopy–energy-dispersive spectroscopy(SEM–EDS), were used to characterize the phase equilibrium and microstructure of chromium-containing high-titanium melting slags. The results indicated that an increase in the TiO2 content led to a decrease in the viscosity of the chromium-containing high-titanium melting slag. In addition, the softening temperature, hemispheric temperature, and flowing temperature decreased with increasing TiO2 content. The amount of crystallized anosovite and sphene phases gradually increased with increasing TiO2 content, whereas the amount of perovskite phase decreased. SEM observations revealed that the distribution of the anosovite phase was dominantly influenced by TiO2.

Lowering ash slagging and fouling tendency of high-alkali coal by hydrothermal pretreatment

High-alkali species in coal are notorious for causing ash slagging and fouling incidents.In this paper,four high-alkali coals were individually subject to hydrothermal pretreatment(HTP),within a batch-type autoclave at 300 -C for 1 h,and the treated coals were analyzed,along with the oxygen-containing functional groups determined by Fourier transform infrared spectrometer(FT-IR).Then the alkali species and other components in the coal ash were quantified by X-ray fluorescence(XRF)for evaluating the ash slagging and fouling tendency.Apart from this,FactSage was adopted to simulate the occurrence and transformation of alkali species during coal thermal conversion ending at various temperatures.The findings indicate that the treated coals are superior to the parent ones in terms of certain remarkable changes via HTP.The moisture,oxygen and sulfur of the hydrothermally treated coals decline obviously,while the calorific value rises sharply.HTP could reduce the alkali species to less than 2%(%,by weight,equivalent to Na2O in dry ash),with a maximum removal ratio of 88.9%,lowering the ash slagging and fouling tendency.The proposed mechanism of HTP was that the alkali species in coal matrix became released due to the breakage of the coal functional groups and micropores during HTP.

Microwave absorbing properties of high titanium slag

Microwave absorbing properties of high titanium slag were investigated by using microwave cavity perturbation technique. High titanium slag containing more than 90% TiO2 was prepared by carbothermal reduction of ilmenite. The temperature rise curve of high titanium slag in microwave heating process was obtained. Crystalline compounds of high titanium slag before and after microwave irradiation were obtained and characterized by X-ray diffractometry (XRD). Effects of particle size of high titanium slag and mixtures of high titanium slag with different mass fractions of V2O5 on microwave absorbing properties were investigated systematically. The results show that high titanium slag has good microwave absorption property; untreated high titanium slag mainly consists of crystalline compounds of anatase and iron titanium oxide, while the microwave-irradiation treated one is mainly composed of crystalline compounds of rutile and iron titanium oxide. Synthetic anatase is transformed completely into rutile at about 1 050 ℃ for 20 min under microwave irradiation. High frequency shift and low amplitude of voltage make high titanium slag an ideal microwave absorbent. 180 μm of particle size and 10% mass fraction of V2O5 are found to be the optimum conditions for microwave absorption.

Study of the Corrosion of High Alumina Refractories by Al_2O_3-CaO Slag as a Reactive Impregnation Mechanism

The corrosion of refractories results from reactive transport,namely,transport of agents and chemical reactions of these agents with impregnated medium. On one hand,the transport involves either diffusion or impregnation depending on the state of the corrosive agents and the microstructure of the host media. On the other hand,chemical reactions may be very numerous and complex.This study focused on the reactive impregnation of Al2O3- CaO slag into porous high alumina refractory. The transport properties of the refractory material were identified by means of a dedicated capillary rising test. Chemical reactions between the solid high alumina skeleton and Al2O3- CaO slag involve successive dissolution / precipitation mechanisms forming aluminates of lime. Contrary to the thermodynamic properties of the binary system,the kinetics of these solid / liquid reactions is not well known.Corrosion tests associated with the quenching method,XRD analyses were performed for a better understanding of the kinetics. The results of this study open up a coupling approach for predicting the corrosion wear of refractory.

Analysis of Spent High Chrome Brick in Slagging Gasifier

Wear of the spent high chrome brick in slagging gasifier was studied. The result shows that erosion and spalling are the m, ain wear mechanism of high chrome brick and the CaO content of coal slag is crucial to wear of high chrome brick.

Early Intervention on the Properties of Steel Slag at High Temperature by Modifier Compound with Tailings: A Feasible Way for Comprehensive Utilization of Solid Wastes

Steel slag, a by-product of the steel production industry reaches 10%–15% of crude steel output (Motz and Geiseler, 2001). Their main application lies in the field of building materials due to some containing cementitious components, such as dicalcium silicate (C2S) and tricalcium silicate (C3S) (Waligora et al., 2010). However, blended cements with steelmaking slag show low early hydration activity, low compressive strength and bad durability because steel slag generates above 1600 ℃ with the tense and large grain size crystals, consisting of low content of C2S and C3S and high proportions of f-CaO and f-MgO compared with cement clinker.

高温改性钢渣活化过硫酸盐降解甲基橙和苯酚的反应机制

采用高温改性钢渣活化过硫酸盐(peroxymonosulfate,PMS)降解甲基橙(methyl orange,MO)和苯酚(phenol,AR)。考察了改性钢渣投加量、PMS浓度、初始pH值、反应温度对MO和AR降解效果的影响。在改性钢渣质量浓度为9.0 g/L、PMS物质的量浓度为12.0 mmol/L、初始pH值为7.0、反应温度为25℃的条件下,反应90 min,30 mg/L MO和15 mg/L AR的降解率分别达到90.5%和100%。材料表征分析结果表明,高温改性钢渣比表面积增大、孔隙率高、催化氧化PMS性能好,且重复利用仍有较好的原位恢复性能。自由基淬灭和电子顺磁共振波谱实验说明,高温改性钢渣/PMS反应体系存在非自由基(1 O 2)和自由基(SO_(4)^(-)·和·OH),发挥了碱活化PMS和铁氧化物活化PMS的共同作用,最终将MO和AR降解为小分子物质。

基于有限时间ADP的微波加热高钛渣温度跟踪控制

针对常规控制方法对微波加热过程控制效果不够理想的问题,提出一种基于数据驱动模型的有限时间自适应动态规划微波加热温度跟踪算法。算法包含模型网络、评价网络和执行网络,这3个网络的实现依赖于神经网络。模型网络实现微波加热过程的数据驱动建模,评价网络和执行网络实现最优性能指标函数和控制功率的逼近。最后将温度跟踪转化为误差的镇定。通过理论推导证明了算法的收敛性及最优性,并进一步开展了微波加热高钛渣温度跟踪实验和仿真研究。结果表明,算法能有效地跟踪高钛渣的加热过程,基于ELMAN神经网络的模型预测误差小于1℃,温度跟踪误差小于0.2℃,在工业微波加热中具有潜在的应用价值。

钢-PVA混杂纤维高性能混凝土抗渗性能试验研究

为探究钢纤维掺量、聚乙烯醇(PVA)纤维掺量和矿粉掺量对钢-PVA混杂纤维高性能混凝土(HFHPC)抗渗性能的影响,本文开展了钢-PVA HFHPC抗渗性能试验,并对试验结果进行了极差分析、方差分析和回归分析。结果表明:对HFHPC抗渗性能的影响程度从高到低依次为钢纤维、矿粉和PVA纤维。在试验水平范围内,得出混凝土试件抗渗性能最佳水平组合:钢纤维体积掺量1.0%、PVA纤维体积掺量0.7%、矿粉质量取代率20%。当钢纤维掺量超1.0%时,HFHPC抗渗性能略有下降,但仍高于基准素混凝土。最后采用多元回归分析,建立了HFHPC渗透系数与钢纤维、PVA纤维和矿粉的预测模型。

高碳铬铁渣微表处混合料路用性能研究

针对道路养护工程优质石料资源匮乏,高碳铬铁渣大多采用堆存处理且利用率低等问题,将高碳铬铁渣分别以0%、20%、30%、40%、50%、60%的掺量替换常规微表处混合料,通过湿轮磨耗试验、车辙试验、黏聚力试验和构造深度试验研究不同高碳铬铁渣掺量下的微表处混合料的路用性能。试验结果表明:高碳铬铁渣掺量为20%时,混合料的耐磨耗性能和水稳定性与常规微表处混合料相近,抗车辙性能略有下降,早期强度和抗滑性能均优于常规微表处混合料。

多固废超高性能混凝土性能及微观结构研究

为了提高锂渣、磷渣等固体废弃物的综合利用率,以锂渣和磷渣为复合掺和料替代部分水泥制备超高性能混凝土(UHPC),通过改变复合掺和料掺量,研究其对UHPC抗压强度和微观结构的影响规律。结果表明,与基准组相比,随着复合掺和料掺量的增加,UHPC的3 d抗压强度逐渐降低,复合掺和料对UHPC早期强度不利,但能显著增强后期抗压强度。当复合掺和料掺量为25%时,UHPC的28 d抗压强度达到最大值,为145.78 MPa。微观分析表明,随着龄期的增加,复合掺和料的活性得到充分发挥,其活性SiO_(2)和Al_(2)O_(3)会与Ca(OH)_(2)反应生成大量水化硅酸钙(C-S-H)、水化硫铝酸钙(AFt)等水化产物,Ca^(2+)消耗进一步促进磷渣水化,固废协同耦合水化,促进UHPC后期强度增加。

电石渣和煤矸石对型煤固硫性能的影响及作用机制研究

研制高效低成本的耐高温固硫剂和添加剂有助于解决型煤高温燃烧环境下钙基固硫产物的分解问题。电石渣和煤矸石属于典型的工业固体废弃物,利用固废作为添加剂制备固硫型煤有助于降低固硫型煤成本和挖掘固废资源价值,发挥这两种固废中矿物组分协同作用可改善高温条件下型煤固硫效果。开展了电石渣和煤矸石分别作为固硫剂和添加剂制备环保型煤的研究,考察了固硫剂种类(碳酸钙、氧化钙、氢氧化钙和电石渣)、钙硫物质的量比(1.5~4.0)、燃烧温度(900℃~1300℃)、煤矸石用量(2%~7%)对型煤固硫效果的影响。通过型煤燃烧评价实验发现,仅用电石渣作为固硫剂,在钙硫物质的量比为3.0时制得的型煤在燃烧温度低于1000℃时固硫率能达到80%以上,燃烧温度提高到1300℃时型煤固硫率下降40%,结合分析表征数据发现主要原因是固硫产物硫酸钙的高温分解。添加的煤矸石在高温条件下被电石渣组分活化后起到辅助固硫作用,当添加的煤矸石的质量分数达到5%时型煤的固硫率能维持在60%以上,在此基础上增加煤矸石用量并不能明显提升型煤固硫率。通过固硫产物热稳定性研究并结合分析表征数据发现,高铝煤矸石灰渣活性组分发生高温反应生成硫铝酸钙、钙黄长石、硅酸三钙等耐高温稳定物相,在一定程度上抑制了CaSO_(4)的分解,从而提高了型煤的高温固硫率。

循环流化床高碱煤气化技术研发及应用进展

系统回顾了循环流化床高碱煤气化技术的研发及应用历程,重点概况了在高碱煤基础理化特性、气化反应特性及碱金属的迁移特性、防结渣技术研究及循环流化床高碱煤气化工程应用四个方面的进展与成果。梳理了高碱煤的煤质特征、碱金属的赋存形态和含量、前处理方法对碱金属含量测定的影响,以及高碱煤的燃烧和成灰特性。总结了煤种、反应进程、气化温度、氧碳摩尔比、反应气氛等对高碱煤气化性能指标和气化灰结渣特性的影响。阐述了配煤、添加剂及更换床料等方法对预防高碱煤气化结渣的作用和反应机理,采用刚玉做床料实现了循环流化床高碱煤气化中试装置稳定运行。评述了循环流化床高碱煤气化技术的自主创新以及在工业燃气、合成气领域的成功应用。最后,从建立高碱煤气化用煤数据库、开发纯用高碱煤的气化技术、开发高效脱碱及原位耦合利用革新技术、探索高碱煤与其他物料协同利用技术并制备高性能材料四个方面展望了未来高碱煤气化技术的发展方向。

高密度电阻率法在建筑渣土填埋范围勘察中的应用

地势较低区域、洼地、河堤或河道中间经常有建筑渣土堆积,造成环境污染。对建筑渣土填埋的治理,首先查明建筑渣土填埋范围,经过现场勘察,采用高密度电阻率法对建筑渣土填埋进行地球物理勘探,通过野外数据采集、数据转换、地形矫正、二维反演和成果解释,完成对建筑渣土填埋范围的探测,为计算建筑渣土储量提供依据。

钛渣熔体结构及传输性质分子动力学模拟研究进展

高品位钛渣(TiO_(2)含量≥90%)的高效制备不仅是高品质钛产品生产的关键,而且已成为我国钛冶金行业发展的迫切需要。钛铁矿还原熔炼过程钛渣熔体传输性质的调控是实现高品位钛渣高效制备的关键。国内外学者采用分子动力学模拟的方法,开展钛渣熔体结构演变及传输性质的研究,取得了显著的进展,证实了分子动力学模拟的方法在钛渣熔体研究中的有效性。分子动力学模拟的方法在研究钛渣熔体结构和性质方面具有显著的优势,不但能考察钛渣熔体结构参数、传输性质及相关微观细节,而且不受试验条件(高温、高腐蚀性、高化学活性)的限制。通过分子动力学模拟能够获取钛渣熔体丰富的结构信息和重要的传输性质,避免了钛渣熔体结构及物理性质试验测试中存在的难题。最后,结合冶金熔体成分和结构的复杂性,总结存在的问题,对分子动力学模拟在熔体结构及传输性质研究中的应用进行了展望。