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.

Preparation of High Activity Admixture from Steel Slag,Phosphate Slag and Limestone Powder

The problem of low disposal and utilization rate of bulk industrial solid waste needs to be solved.In this paper,a high-activity admixture composed of steel slag-phosphate slag-limestone powder was proposed for most of the solid waste with low activity and a negative impact on concrete workability,combining the characteristics of each solid waste.The paper demonstrates the feasibility and explains the principle of the composite system in terms of water requirement of standard consistency,setting time,workability,and mechanical properties,combined with the composition of the phases,hydration temperature,and microscopic morphology.The results showed that the steel slag:phosphate slag:limestone=5:2:3 gave the highest activity of the composite system,over 92%.Besides,the composite system had no significant effect on water demand and setting time compared to cement,and it could significantly increase the 7 and 28 d activity of the system.The composite system delayed the exothermic hydration of the cement and reduced the exothermic heat but had no effect on the hydration products.Therefore,the research in this paper dramatically improved the solid waste dissipation in concrete,reduced the amount of cement in concrete and positively responded to the national slogan of carbon neutral and peaking.

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.

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.

On the application of calcium carbide slag as CO_2 absorbent

Calcium carbide slag, generated in the hydrolysis process of calcium carbide, is an potential carbon capture reagent because its main ingredient is Ca(OH)_2. Calcium carbide slag, a by-product of a resin factory was used as carbon capture reagent. The change of p H and electrical conductivity(EC) of the calcium carbide slag slurry with different solid-to-liquid ratios, as well as the capture efficiency and dynamics under different temperatures and flow rates of CO_2 were studied. The properties of solid were characterized with XRD, TG-DTA, SEM and FT-IR before and after capturing carbon. The results show that the change of p H and EC were greater with low solid-to-liquid ratio than that with high solid-to-liquid ratio. The analysis of XRD and SEM show that the content of Ca CO_3 increased significantly, which improved that Ca(OH)_2 and free Ca O were reacted with CO_2. The results of TG-DTA and FT-IR show that the physicochemical properties and microstructure of the slag changed after capturing CO_2 because of the increase of Ca CO_3 content. All the results mentioned above improve the feasibility of utilizing calcium carbide slag to capture CO_2 and offer a practical way for carbon emission reduction and disposal of wasted calcium carbide slag.

Effective removal of phosphorus from high phosphorus steel slag using carbonized rice husk

High phosphorus steel slag and carbonized rice husk are two common wastes characterized by high generation and low secondary use values.Through the reduction of high phosphorus steel slag by biomass,both wastes were fully utilized,thus reducing the negative impact on the environment.In this study,variables such as temperature,time,and amount of reactants were changed to determine the optimal conditions for the reaction of steel slag with carbonized rice husk at high temperatures.The actual amount of reducing agent consumed during the reduction was significantly greater than that predicted by theoretical calculations.Adding three carbon equivalent of carbonized rice husk and maintaining at 1500℃ for 30 min could remove 79.25% of P_(2)O_(5) in the slag.By modeling the material cycle in which high phosphorus steel slag was treated with biomass,the product could be used for crop growth.Meanwhile,the reduced iron and residual steel slag can be used tomake steel again,thereby leading to a sharp reduction in fossil fuel usage and greenhouse gas emissions in this process.

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。

含生活垃圾焚烧炉渣的碱矿渣水泥耐高温机理

为探究生活垃圾焚烧炉渣(MSWI-BA)对碱矿渣净浆耐高温性能的影响机理,将6%的矿渣等质量替换为MSWI-BA,制备碱矿渣水泥净浆(AASBp),研究不同温度对AASBp的质量损失率、干燥收缩率和强度的影响.以普通硅酸盐水泥净浆作为对照组,结合多种微观手段,揭示AASBp的耐高温机理,并与未掺MSWI-BA的碱矿渣水泥(AASp)进行对比.结果表明:随着温度的升高,AASBp中水化硅铝酸钙的钙硅比(C/S)先降低后升高;在400℃时,水化硅铝酸钙的聚合度最高,C/S最低;Al—O键在600℃断裂,而Si—O键在1000℃断裂;MSWI-BA可提高基体孔隙的连通性,高温处理后孔隙压力得到释放,因此AASBp比AASp具有更高的归一化抗压强度和耐高温性能.

N235从高碳石煤脱碳渣酸浸液中萃取钒的工艺研究

以某地高碳石煤脱碳渣经空白焙烧-酸浸后的浸出液为原料,采用萃取剂N235和反萃剂Na_(2)CO_(3)对钒萃取工艺和反萃取工艺进行了研究。结果表明,最佳萃取工艺参数为:萃原液pH值2.3、有机相组成为15%N235+5%仲辛醇+80%磺化煤油、相比(O/A)1∶4、萃取时间4 min、氧化剂氯酸钠用量为萃原液V_(2)O_(5)质量的0.05倍、萃取级数五级,钒萃取率达99%;最佳反萃工艺参数为:反萃剂Na_(2)CO_(3)溶液浓度8%、反萃相比(O/A)4∶1、反萃时间10 min、反萃级数三级,钒反萃取率可达99.50%。在最佳萃取和反萃取工艺条件下,钒浓度由4.25 g/L富集到68.50 g/L,且pH值为8.5,无需中和处理。对富钒液进一步沉钒、煅烧得到的最终产品V_(2)O_(5)品位为98.95%,且杂质含量低,满足行业标准YB/T 5304—2017中98级V_(2)O_(5)的要求。

高抗折矿渣硫铝酸盐水泥混凝土抗疲劳性能研究

传统水泥混凝土公路路面面临的主要问题是路面易开裂劣化和抗疲劳性能较差,这些问题大大缩短了路面的使用寿命,严重制约了水泥混凝土路面的发展和推广应用。矿渣硫铝酸盐水泥(Slag-Calcium Sulfoaluminate Cement,S-CSA)是一种具有高抗折强度的新型胶凝材料,利用该水泥制备的混凝土路面具有解决现有路面抗疲劳性能差的潜力。通过三点弯曲疲劳试验和声发射试验,对比分析了高抗折S-CSA混凝土和普通硅酸盐水泥(Ordinary Portland Cement,OPC)混凝土的抗疲劳性能。研究结果表明:相同荷载作用下,高抗折S-CSA混凝土粗骨料断裂数量更多;不同强度等级下,高抗折S-CSA混凝土的疲劳寿命均高于OPC混凝土,且提升幅度随着强度等级的提高而显著增加,最高可达到约7.2倍;钙矾石的生成有效改善了界面过渡区,从而提升了高抗折S-CSA混凝土的抗疲劳性能。

密闭机械活化浸出电石渣制备高纯钙溶液

电石渣是工业生产过程产生的碱性危废,利用于CO_(2)固化,将有助于“碳达峰、碳中和”目标早日实现。在碱性环境中,用氯化铵浸出剂可选择性浸出Ca,使电石渣中的Ca与其他杂质分离开来,从而制备高纯度含钙溶液,之后将所得富钙液与CO_(2)反应制备高纯碳酸钙,从而实现固废资源化。以氯化铵为浸出剂,球磨机为浸出反应设备,采用密闭机械活化手段进行处理,探究了浸出剂用量、机械搅拌转速、反应时间和液固比等工艺参数对电石渣中Ca浸出率的影响。结果表明,在氯化铵用量为理论用量的1.1倍、球磨机转速500 r/min、反应时间10 min和液固比4∶1最佳反应条件下,Ca浸出率可达到89.76%,滤液Ca浓度高达79.4 g/L。相较于常规浸出,采用密闭机械活化手段可提高Ca浸出率3个百分点,且可大幅度降低氨气挥发,保证良好操作环境。

高纯五氧化二钒制备过程钒铬分离的研究进展

全钒液流电池因资源禀赋好、自给率高,有望成为我国大规模储能市场的主力军。全钒液流电池以高纯五氧化二钒为原料,对铬等杂质含量要求严格。目前,我国五氧化二钒主要从含钒钢渣中提取,但钒铬难以深度分离,导致产品中铬含量较高。因此,从含钒钢渣中提取并制备电池级五氧化二钒,以及钒铬深度分离问题亟待解决。本文综述了高纯五氧化二钒制备过程钒铬分离的研究进展,对化学沉淀法、溶剂萃取法、离子交换法、吸附法及结晶法分离钒铬进行比较,并通过绘制298 K下V-Cr-H_(2)O系电位(E)-pH图,获得钒铬选择性分离的热力学窗口。与其他方法相比,化学沉淀法具有成本低、操作简单等优势,可根据钒铬氧化还原的电位差异,通过选择性氧化或还原沉淀,实现钒铬的深度分离。

高铝钒土精炼造渣工艺研究

针对新余钢铁股份有限公司特钢厂造渣工艺存在化渣效果差、终渣成分与目标成分偏差大、渣中全铁含量高以及成本高等问题,本研究提出了一种高铝钒土精炼造渣工艺,基于化学反应原理,通过熔炼和高温烧结反应,将高铝钒土与其他原料反应生成精炼渣。对比试验结果发现,采用高铝钒土代替萤石和精炼渣,能够解决造渣工艺存在的化渣效果差的问题,改善终渣成分的偏差,降低钢坯的全氧含量,提高钢水的洁净度和流动性。此工艺不仅能够降低造渣生产成本,还有助于降低炉渣对炉衬耐火材料的侵蚀,减少氟化物的挥发,降低环境污染。

Phosphorus Removal of High Phosphorus Iron Ore by Gas-Based Reduction and Melt Separation

A new method （gas-based separation plus melt separation） has been proposed to remove phosphorus of the high phosphorus iron ore which was 1.25 % of phosphorus content and 50. 0% of iron content. HSC chemistry package and the coexistence theory of slag structure were adopted for theoretical analysis. The gas-based reduction was carried out using a fixed bed reactor and the ore sample of 80 g with an average particle size of 2 mm were reduced using CO or H2 at temperature of 1 073 K for 5 hours. 50 g of the reduced sample with 3.0% CaO as additive was then subjected to melt separation in an electric furnace at temperature of 1 873 K under Ar atmosphere. In each run, SEM, EDS, optical microscopic examination and chemical analysis of the reduced ore sample, the metal sample and the slag sample were conducted. Results of all gas-based reduction experiments showed that iron metallization ratios were some 65% and the phosphorus compounds in the ore remained unchanged. It was agreed well with the simula- tions except for the iron metallization rate being less than predicted value; this difference was attributed to kinetics. Results of melt separation experiments showed that P content in metal samples is 0.33% （metal sample from H2 reduction product） and 0.27% （metal sample from CO reduction product）. The phosphorus partition ratios of both cases were less than predicted values. Some P in the metal samples existed as slag inclusion was considered to be the reason for this discrepancy.

Optimization of BF Slag for High Cr_2O_3 Vanadium-titanium Magnetite

In order to clarify the slag system of high Cr2O3 vanadium-titanium magnetite smelting in BF （blast furnace）, the melting properties of slag samples prepared by analytically pure reagents were measured. By means of orthogonal test synthetic weighted score method, the optimal slag for high Cr2O3 vanadium-titanium magnetite was obtained, which contained 10% MgO, 8% TiO2 and 15% Al2O3, with the binary basicity being 1.15. In addition, the effects of basicity, MgO, TiO2 and A12 03 on slag melting properties were investigated by single factor test, and the results showed that, with increasing the basicity or TiO2 content, melting temperature （Tin） increased, whereas initial vis- cosity （r/0） and high temperature viscosity （r/h） decreased. With increasing the MgO content, Tm decreased firstly and then increased. With increasing the Al2 O3 content, Tm increased, and η0 and r/h decreased firstly and then increased.

在高铅渣还原冶炼中替代石灰石熔剂实现石膏污泥的利用与解毒

石膏污泥是有色冶炼行业产生的一种危险固体废弃物,对环境造成了巨大的挑战。为探究用石膏污泥替代石灰石进行冶炼造渣的可行性,通过热力学计算和实验研究了石膏污泥以及冶炼条件对高铅渣还原熔炼的影响。结果表明:石膏污泥中的硫酸钙会消耗还原剂并硫化金属氧化物,需控制其配入量。最有利于有价金属综合回收的条件是:钙硅比0.8、碳粉用量3.5 wt%、硫酸钙与氧化钙摩尔比1:5、还原温度1200℃,还原时间1.5 h。在此条件下铅直收率为94.43%,锌直收率为58.43%。还原渣毒性浸出结果表明,铅、锌、砷、镉重金属离子的浸出毒性均低于国家危险废弃物标准。

Optimization of Calcium Addition to High-strength Low-alloy Steels

Nozzle blockage is a common problem during continuous casting of Al-killed steel, and calcium treatment is widely used to resolve it. In consideration of the production costs, the technology of nonmetallic inclusion control was studied to optimize the Ca consumption. The proposed process of slag washing was employed, and the refining slag composition, deoxidation conditions and alloying systems were optimized. Using these measures, the steel cleanliness before Ca addition was improved significantly, and the corresponding Ca consumption was reduced. More- over, the continuous casting could be conducted smoothly.

高钙高磷钒渣提钒工艺研究进展

为了给解决高钙高磷钒渣难利用问题提供参考,在归纳目前已提出的钠化焙烧—水浸提钒、钙化焙烧—酸浸提钒、钙化焙烧—碳酸钠浸出提钒、含钒溶液溶剂萃取提钒、含钒溶液离子交换提钒等主要的钒渣提钒工艺基础上,着重介绍了其中的钠化焙烧—水浸提钒工艺、钙化焙烧—酸浸提钒工艺、钙化焙烧—碳酸钠浸出提钒工艺以及新提出的钙化焙烧—碳酸铵浸出提钒工艺和钙化焙烧—草酸盐浸出提钒工艺在处理高钙高磷钒渣方面的研究进展,最后针对这些工艺尚存在的缺陷,指出寻找钙化焙烧除磷添加剂、减少碳酸铵浸出时的浸出剂用量、简化草酸盐浸出时的浸出剂种类等应该是高钙高磷钒渣提钒工艺今后的研究方向。

高温烧结磷石膏钙渣制备轻质碳酸钙

以磷石膏钙渣为原料,通过高温煅烧,然后经消化、精制、碳化,制成轻质碳酸钙产品。研究结果表明:高温煅烧的最佳温度为1000℃,最佳煅烧时间为1.0 h;沉淀反应的初始反应温度为60℃,Ca(OH)_2乳液质量浓度为70 g/L,CO_2流量为1.8 L/h。制备的轻质碳酸钙产品各项指标均达到HG/T2226—2000《工业沉淀碳酸钙》标准的要求。其中,沉降体积远优于行业标准,达到了4.0 mL/g。