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.

Indirect mineral carbonation of blast furnace slag with(NH4)2SO4 as a recyclable extractant

Large quantities of COand blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial COemission reduction and comprehensive utilisation of the solid waste. In this study, a recyclable extractant,（NH）SO, was used to extract calcium and magnesium from blast furnace slag（main phases of gehlenite and akermanite） by using low-temperature roasting to fix COthrough aqueous carbonation. The process parameters and efficiency of the roasting extraction, mineralisation, and Al recovery were investigated in detail. The results showed that the extractions of Ca, Mg, and Al can reach almost 100% at an（NH4）SO-to-slag mass ratio of 3:1 and at 370°C in 1 h. Adjusting the p H value of the leaching solution of the roasted slag to 5.5 with the NHreleased during the roasting resulted in 99% Al precipitation, while co-precipitation of Mg was lower than 2%. The Mg-rich leachate after the depletion of Al and the leaching residue（main phases of CaSOand SiO） were carbonated using（NH）COand NHHCOsolutions, respectively, under mild conditions. Approximately 99% of Ca and 89% of Mg in the blast furnace slag were converted into CaCOand（NH）Mg（CO）·4 HO,respectively. The latter can be selectively decomposed to magnesium carbonate at 100-200 °C to recover the NHfor reuse. In the present route, the total COsequestration capacity per tonne of blast furnace slag reached up to 316 kg, and 313 kg of Al-rich precipitate, 1000 kg of carbonated product containing CaCOand SiO, and 304 kg of carbonated product containing calcium carbonate and magnesium carbonate were recovered simultaneously. These products can be used, respectively, as raw materials for the production of electrolytic aluminium, cement, and light magnesium carbonate to replace natural resources.

Simultaneous preparation of TiO2 and ammonium alum,and microporous SiO2 during the mineral carbonation of titanium-bearing blast furnace slag

In this study,a route for simultaneous mineralization of CO2 and production of titanium dioxide and ammonium alum,and microporous silicon dioxide from titanium-bearing blast furnace slag(TBBF slag)was proposed,which is comprised of(NH4)2 S04 roasting,acid leaching,ammonium alum crystallization,silicic acid flocculation and Ti hydrolysis.The effects of relevant process parameters were systematically investigated.The re sults showed that under the optimal roasting and leaching conditions about 85%of titanium and 84.6%of aluminum could be extracted while only 30%of silicon entered the leachate.84%of Al^3+was crystallized from the leachate in the form of ammonium aluminum sulfate dodecahydrate with a purity up to 99.5 wt%.About 85%of the soluble silicic acid was flocculated with the aid of secondary alcohol polyoxyethylene ether 9(AEO-9)to yield a microporous SiO2 material(97.4 wt%)from the crystallized mother liquor.The Al-and Si-depleted solution was then hydrolyzed to generate a titanium dioxide(99.1 wt%)with uniform particle size distribution.It was figured out that approximately 146 kg TiO2 could be produced from 1000 kg of TBBF slag.Therefore,the improved process is a promising method for industrial application.

Indirect mineral carbonation of titanium-bearing blast furnace slag coupled with recovery of TiO_2 and Al_2O_3

Large quantities of CO2 and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO2 emission reduction and comprehensive utilization of the solid waste. This paper describes a novel route for indirect mineral carbonation of titanium-bearing blast furnace （TBBF） slag, in which the TBBF slag is roasted with recyclable （NH4）2SO4 （AS） at low temperatures and converted into the sulphates of various valuable metals, including calcium, magnesium, aluminium and titanium. High value added Ti-and Al-rich products can be obtained through stepwise precipitation of the leaching solution from the roasted slag. The NH3 produced during the roasting is used to capture CO2 from flue gases. The NH4HCO3 and （NH4）2CO3 thus obtained are used to carbonate the CaSO4-containing leaching residue and MgSO4-rich leaching solution, respectively. In this study, the process parameters and efficiency for the roasting, carbonation and Ti and Al recovery were investigated in detail. The results showed that the sulfation ratios of calcium, magnesium, titanium and aluminium reached 92.6%, 87% and 84.4%, respectively, after roasting at an AS-to-TBBF slag mass ratio of 2：1 and 350℃ for 2 h. The leaching solution was subjected to hydrolysis at 102℃ for 4 h with a Ti hydrolysis ratio of 95.7%and the purity of TiO2 in the calcined hydrolysate reached 98 wt%. 99.7% of aluminium in the Ti-depleted leaching solution was precipitated by using NH3. The carbonation products of Ca and Mg were CaCO3 and （NH4）2Mg（CO3）2·4H2O, respectively. The latter can be decomposed into MgCO3 at 100-200℃ with simultaneous recovery of the NH3 for reuse. In this process, approximately 82.1% of Ca and 84.2% of Mg in the TBBF slag were transformed into stable carbonates and the total CO2 sequestration capacity per ton of TBBF slag reached up to 239.7 kg. The TiO2 obtained can be used directly as an end product, while the Al-rich precipitate and the two carbonation products can act, respectively, as raw materials for electrolytic aluminium, cement and light magnesium carbonate production for the replacement of natural resources.

Extraction of valuable metals from Ti-bearing blast furnace slag using ammonium sulfate pressurized pyrolysis−acid leaching processes

A novel method of extracting valuable metals from Ti-bearing blast furnace slag(TBBF slag)via pressure pyrolysis of recyclable ammonium sulfate(AS)−acid leaching process was proposed.The results show that when pressurized roasting at an AS-to-slag mass ratio 3:1 and 370℃for 90 min,the extraction rates of titanium,aluminum and magnesium reached 94.5%,91.9%and 97.4%,respectively.The acid leaching solution was subjected to re-crystallization in a boiling state to obtain a titanium product having a TiO2 content of 94.1%.The above crystallization mother liquor was adjusted to pH=6 and pH≥12.2,respectively,and then qualified Al2O3 and MgO products were obtained.The analysis through XRD and SEM−EDS proves that the main phases in roasted samples were NH4AlSO4,CaSO4 and TiOSO4.The thermodynamic analysis presents that the main minerals of perovskite,spinel and diopside in raw ore could spontaneously react with the intermediate produced by AS under optimal conditions.

Effect of content of Al_2O_3 and MgO on crystallization of blast furnace slag during fiber formation

The simulation of blast furnace slag was prepared by pure chemical reagents.Test methods like DSC,XRD and SEM were used to study the effect of Al2O3 and MgO content on crystallization of blast furnace slag during fiber formation.The results show that as Al2O3 and MgO contents in the sample changed,blast furnace slag was crystallized at the average temperature below 1232 K.When the ratio of Mg/Al in the samples is 0.6 calculated by Kissinger equation,crystallization activation energy is at the maximum value and the system is in the most stable condition.The sample crystallization phases are mainly calcium akermanite(2CaO?MgO?2SiO2)and gehlenite(2CaO?Al2O3?SiO2).Secondary crystallization phases are anorthite(CaAl2Si2O8),wollastonite minerals(WOLLA)and pyroxene minerals(cPyrA).Meanwhile,the principal crystallization phases of the samples are different types and have different contents,and the microstructures of the sample sections are different due to the difference between MgO/Al2O3 ratio.

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.

INFLUENCE OF MnO ON REDUCTION OF TiO_2 IN BLAST FURNACE TYPE SLAG

A study was carried out on the formation of Ti(C,N) during smelting vanadium-bearing titanomagnetite in blast furnace and the influence of MnO content on reduction of TiO_2 in the slag containing high titania. The reduction of TiO_2 is restricted by MnOpredominantly at the slag-metal interface and no more at the slag-coke one. The formation of Ti(C,N) is remarkably restricted by MnO in the slag when the MnO content is about 4% and the basicity from 0.6 to 1.2 in the slag. MnO may also retards the reduction of SiO_2 and accelerates the desulphidation under certain condition.

ACTIVITY OF TiO_2 IN MOLTEN BLAST FURNACE SLAG

Activity of TiO_2 in the molten blast furnace slag containing TiO_2 has been examined at 1500℃ by means of “molten slag-Sn” chemical equilibrium method,using metallic Sn as flux and graphite as deoxidizer,together with phase diagram caIculation.In the pentary slag system CaO-MgO-SiO_2-TiO_2-Al_2O_3,a_(TiO_2)=0.01—0.05 or 0.02—0.10 with pure liquid or solid TiO_2 as standard state,respectively.The activity and activity coefficient of TiO_2 in relation to concentration of TiO_2 have been discussed.

Preparation of high acidity coefficient slag wool fiber with blast furnace slag and modifying agents

Preparation of high acidity coefficient slag wool fiber with molten slag and modifying agents is considered to be a positive approach for value-added utilization of blast furnace slag. In order to achieve the multi-purposes of fiber-forming, energy saving, and waste heat recovery, the modifying agents that can improve the acidity coefficient of slag effectively, economically, and environmentally were investigated. Three agents with different acidity coefficients were adopted to modify slag and manufacture wool fibers. The effect of agent and slag proportion on the melting temperature and viscosity of molten slag was studied at a fixed acidity coefficient of 1.8 and 2.0. The results indicate that the sample modified with high acidity coefficient agent and high slag proportion has lower melting temperature and viscosity. The effect of agent and slag temperature on the fiber diameter was also investigated when the acidity coefficient of slag is 2.0. At a fixed slag proportion of 50 wt.%, the mean diameter decreases with increasing temperature and decreasing viscosity coefficient. Besides, the temperature drops caused by the addition of agents and energy consumption of samples for heating the slag were also analyzed.

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。

钢渣粉对高强混凝土力学性能和耐久性的影响

超细矿渣是制备高强混凝土的优质矿物掺合料,但是超细矿渣水化放热量较大、凝结较快,不利于高强混凝土的强度和耐久性发展。而钢渣粉具有延缓水泥水化、降低水化放热的作用,可以充当“缓凝剂”。通过在高强混凝土中复掺钢渣粉和超细矿渣,研究了钢渣粉对高强混凝土性能的影响。结果表明复掺15%钢渣粉时初凝时间和终凝时间分别比纯水泥组延长53.0%和35.9%。同时早期强度降低,但与超细矿渣复掺后28 d和90 d强度分别为77.3 MPa和84.6 MPa,比对照组高4.3%和8.6%。此外,钢渣粉有效降低了高强混凝土的绝热温升和自收缩率。单掺15%超细矿渣时7 d自收缩率为1189.63×10^(-6),约为纯水泥组的2.5倍;复掺15%钢渣粉时自收缩率为211.62×10^(-6),比纯水泥组降低了52%。复掺钢渣粉的高强混凝土与纯水泥制备的混凝土的抗氯离子渗透性等级均为“低”。

水淬高炉矿渣还原性对高硫尾砂氧化过程的影响探索研究

尾砂是选矿厂在特定的经济技术条件下,将矿石磨细,选取有用成分后排放的废弃物,是我国排放量最大的工业固废。尾砂的大量堆存不仅会形成安全隐患,还会引起占用土地、污染土地和水体等问题。利用尾砂进行矿山充填是实现尾砂大宗量消纳处置的有效途径。高硫尾砂一般指硫元素含量大于8%的尾砂,由于高硫尾砂氧化生成的硫酸根达到一定浓度后就会对水泥的硬化过程有破坏作用,导致高硫尾砂在矿山充填中的利用率较低。找到抑制高硫尾砂氧化的方法是降低高硫尾砂环境污染、提高高硫尾砂充填利用率的途径之一。本文通过开展高硫尾砂氧化试验,对水淬高炉矿渣的还原性对高硫尾砂氧化过程的影响开展了探索研究,通过观察试验结果,结合理论分析和其他学者的研究成果,可以得出结论:①高硫尾砂在水中可以发生氧化反应,主要反应过程为黄铁矿(FeS2)等硫化物与水和水中的溶氧反应生成硫酸根和氢离子;②矿渣微粉对高硫尾砂的氧化过程有抑制作用,可以显著减缓水中高硫尾砂的氧化速率;③矿渣微粉具有还原性,还原性来源是高炉中的还原性气氛,还原性的物质承担者是其中低价态的硫;④矿渣微粉抑制高硫尾砂氧化速率的原因是矿渣中低价态的硫优先与水中的溶氧发生反应,降低了高硫尾砂中硫化物的氧化速率。

工业废渣在湖相软土固化改良中的应用研究

为改善湖相软土承载力小、易压缩变形、含水率大的工程特性,提出采用粒化高炉矿渣(GGBS)作为主固化材料,电石渣和Na_(2)SO_(4)作为激发剂材料对湖相软土进行复配固化改良,并与水泥固化方案进行了工程性能对比试验。结果表明:单掺GGBS、电石渣或者Na_(2)SO_(4)均能提升软土强度,分别在12%、2.5%和4%掺量时达到强度最大值,但对于强度的提升程度较小;当采用GGBS(12.18%)+电石渣(2.3%)+Na_(2)SO_(4)(5.31%)的复配方案时,强度提升较为显著,28d龄期强度可以达到1107kPa,是原状软土的24.6倍,其强度改善效果与掺入13%水泥的固化改良效果相当;采用GGBS+电石渣+Na_(2)SO_(4)进行复配固化的软土稳定性强于采用水泥固化的软土,在经历9次干湿循环后,强度仅降低7kPa,而水泥固化组则降低了86kPa,复配固化改良软土具有更优越的工程力学性能。

粒化高炉矿渣粉沥青混合料路用性能研究

为了拓宽废弃粒化高炉矿渣的利用途径,文中采用不同比例的粒化高炉矿渣粉代替矿粉后,进行AC-13C沥青混合料配合比设计,并对其高温稳定性、水稳定性和低温抗裂性等路用性能进行对比分析。结果表明,将粒化高炉矿渣粉作为填料应用于沥青混合料中,提高了沥青混合料的高温稳定性和高温水稳定性,但降低了其低温水稳定性。当粒化高炉矿渣粉替代率不超过50%时,沥青混合料的低温抗裂性可以得到提高,而当粒化高炉矿渣粉替代率超过75%时,沥青混合料的低温抗裂性降低。综合分析结论得出,AC-13C沥青混合料的粒化高炉矿渣粉替代率不超过50%。

炉渣成分对含钛高铝型高炉渣结构及黏度的影响

为了保证含钛高铝型铁矿石高炉冶炼的稳态顺行,围绕含钛高铝型高炉渣系,解析了炉渣成分、炉渣结构和炉渣黏度之间的内在作用机制.结果表明:当w(TiO_(2))=0~10%时,TiO_(2)呈现酸性氧化物的特性,故随着w(TiO_(2))的增加,炉渣发生聚合反应,黏度增大;当w(TiO_(2))=10%~25%时,随着w(TiO_(2))的增加,(SiO_(4)^(4-)+TiO_(4)^(4-))和AlO_(4)^(5-)的峰谱强度逐渐降低,且(SiO_(4)^(4-)+TiO_(4)^(4-))峰左移,这说明此时TiO_(2)呈现碱性氧化物的特性,炉渣中网状结构被破坏,炉渣发生解聚反应,黏度减小;随着w(Al_(2)O_(3))的增加,AlO_(4)^(5-)的峰谱强度逐渐升高,炉渣中AlO_(4)^(5-)网状结构增加,炉渣发生聚合反应,黏度逐渐增大;随着w(MgO)/w(Al_(2)O_(3))和w(CaO)/w(SiO_(2))的增大,AlO_(4)^(5-)和SiO_(4)^(4-)的峰谱强度降低,炉渣中AlO_(4)^(5-)和SiO_(4)^(4-)网状结构减少,炉渣发生解聚反应,黏度逐渐减小.

唐钢新区3号高炉两段式炉身生产操作浅析

唐钢新区3号高炉针对高球比炉料结构及冶炼特点,炉型设计采用两段式炉身结构,上段炉身角为79.56°,下段炉身角为82.58°。两段式炉身结构具有能适应高球比冶治炼、有利于发展边沿气流、削弱上部调剂效果、降低上部压差等冶炼特点。3号高炉现阶段入炉球团矿比例在40%左右,生产实践表明:炉型采用两段式炉身结构,能有效缓解高球比冶炼时,因球团矿还原膨胀导致的透气性差的问题;但是对大矿批冶炼不利,应选择合适的布料矩阵,随着入炉球团矿比例的提升,需加强对煤气流的控制,尤其是边沿气流的控制。

莱钢3 800 m^(3)高炉经济炉料下的生产实践

分析了3800 m^(3)高炉在面对新的钢铁生产形势,采用经济炉料冶炼。通过创新建立气流指数模型,实现布料加权角度系统的研判。通过对风口面积、火焰温度科学选取和冶炼过程中造渣制度与炉身静压的管理,高炉实现低碳降耗,工序能耗降低至350.43 kgce/t。

细粒级钢渣在混凝土掺合料中的应用

将钢渣粉(0~10mm)通过破碎、筛分、磁选获得85%的细粒级钢渣(≤4.75mm),并将细粒级钢渣粉、细粒级铁渣粉(≤4.75mm)和石灰按照45∶45∶10的比例混合后共同粉磨时台时产量提高1t。将其用于混凝土C30、C40和C50掺和料试验,和易性均较好,坍落度均相近,C40和C50相比提高3.23%和2.37%。针对细粒级钢渣的加工工艺应通过预筛分将全部的颗粒料送入破碎工序,可提高颗粒物料的破碎率。同时,将筛下物料一同经过弱磁脱铁(1 000高斯),可获得高品位磁选料和回收率大于90%的细粒级钢渣。

中南股份6号高炉高铝渣低燃料比冶炼生产实践

阐述了中南股份6号高炉在高w(Al2O3)≥16.5%条件下,通过合理调整烧结矿的镁铝比,调整优化布料制度、热制度,保持炉缸热量充沛,控制好炉内压差,保持高富氧率≥6.5%,强化炉前出铁等关键技术措施,取得煤比达到170 kg/t、燃料比≤510 kg/t的优秀技术经济指标。