Removal of SO_2 from flue gas using Bayer red mud:Influence factors and mechanism

The absorbent composing of Bayer red mud and water was prepared and applied to removing SO2 from flue gas.Effects of the ratio of liquid to solid(L/S),the absorption temperature,the inlet SO2 concentration,the O2 concentration,SO4^2-and other different components of Bayer red mud on desulfurization were conducted.The mechanism of flue gas desulfurization was also established.The results indicated that L/S was the prominent factor,followed by the inlet SO2 concentration and the temperature was the least among them.The optimum condition was as follows:L/S,the temperature and the SO2 concentration were 20:1,25℃and 1000 mg/m^3,respectively,under the gas flow of 1.5 L/min.The desulfurization efficiency was not significantly influenced when O2 concentration was above 7%.The accumulation of SO4^2-inhibited the desulfurization efficiency.The alkali absorption and metal ions liquid catalytic oxidation were involved in the process,which accounted for 98.61%.

Utilization of Bayer Red Mud Derived from Bauxite for Belite-Ferroaluminate Cement Production

Bayer red mud(BRM)is a kind of industrial solid waste characterized by huge volume and high alkalinity.Its disposal generates serious environmental pollution and occupies a large number of farmland.The utilization and recycling of BRM is currently a crucial issue and needs to be addressed as soon as possible.The chemical composition of BRM is similar to cement clinker.In this study,the feasibility of preparing Belite-ferroaluminate clinker(BFAC)with different BRM was explored.The physical properties,mechanics performance,radioactivity levels and trace harmful metals leaching were measured.XRD,BEI and EDS were used to characterize the mineral formation,and SEM is used to reveal the solidified mechanism of trace harmful metal.The results show that the preparation of BFAC using a certain amount of BRM was feasible.The formed phases in clinkers mainly included C_(4)A_(3)Š,C_(2)S and C_(4)AF.The flexural strength and compressive strength of BFAC at 3 days increased whereas 28 and 90 days decreased with the increase of BRM due to the formation of higher C_(4)AF and lower C_(2)S.The formation of large amounts of Al_(2)O_(3)·3H_(2)O gel and Fe_(2)O_(3)·3H_(2)O gel in hydration products enhanced the adsorption capability to heavy metals and other ions.The trace harmful metal concentration in the leaching solution was much less than the upper limits.The radioactivity level of leaching solution was close to natural radioactive background.BRM is safe as raw material of BFAC.

Influence of Bayer Red Mud on the Operational and Mechanical Characteristics of Composite Cement Mortar

The aim of this study is to enhance the value and utilization of red mud generated in the Bayer process by preparing composite cement mortars.The effects of two different types of Bayer red mud with varying physical and chemical characteristics on the fluidity,mechanical strength,mineral composition,and microstructure of the composite cement mortar were systematically evaluated.The results showed that the optimal addition of red mud A was 10 wt%,while it was 20 wt% for red mud B.The mechanical properties of the composite cement mortar met the standards for P·O42.5 cement.Furthermore,the composite mortar with the addition of red mud B showed higher flexural and compressive strengths compared to the composite mortar with red mud A.This improvement is attributed to the smaller particle size of red mud B,which filled the micro-pores and increased the compactness of the cement stone,as well as its higher content of Na_(2)O,K_(2)O,and other free alkalis,which resulted in more obvious alkali activation,accelerating the hydration of the active minerals in the slurry.

Orthogonal Experiments on Direct Reduction of Carbon-bearing Pellets of Bayer Red Mud

To recycle residual iron efficiently in Bayer red mud, three-factor three-level orthogonal experiments on carbon-bearing pellets of Bayer red mud were conducted on the basis of their characteristics. The influences of CaO dosage, temperature and roast- ing time on total iron content and iron recovery of reduced iron powder were studied. Results showed that these factors slightly influenced iron recovery, but significantly influenced total iron content. The principal factor influencing total iron content was CaO dosage, followed by temperature and roasting time. An increase in CaO dosage could decrease total iron content, whereas an increase in temperature and an extension of roasting time could improve total iron content. The reduced iron powder with total iron content of 88.4 l% and iron recovery rate of 97.97% can be obtained under the optimal conditions of temperature of 1 275 ℃, roasting time of 60 min and CaO dosage of 7.5%. The X-ray diffraction （XRD） and scanning electron microscopy （SEM） analyses of the reduced pellets showed that iron minerals in red mud were almost completely reduced to metallic iron. The principal factor influencing the total iron content of reduced iron powder was the grain size of metallic iron particles. An increase in CaO dosage hindered the growth of metallic iron particles, whereas an increase in temperature and an extension of roasting time could neutralise the effect of CaO dosage. Therefore, CaO dosage should be decreased when iron minerals in red mud can be adequately reduced into metallic iron.

Electron probe microanalysis for revealing occurrence mode of scandium in Bayer red mud

Red mud is a bauxite residue generated during the process of alumina production. In this research, the occur- rence mode of scandium in the Bayer red mud was investi- gated mainly by electron probe microanalysis （EPMA）. The Bayer red mud used in this work is composed of 21.47 wt% hematite, 12.13 wt% goethite, 8.86 wt% gibbsite, 5.02 wt% perovskite, 9.70 wt% quartz, 3.23 wt% anhydrite, 29.92 wt% Na_2Al_2Si_5O_14 and 9.67 wt% Al_3Fe_5O_12. Besides, the scandium content in the Bayer red mud is 84.32 × 10-6, indicating that this Bayer red mud is an important scandium resource deserving exploitation. The EPMA results show that the scandium within the Bayer red mud is mainly occurring in the iron minerals of hematite and goethite with the isomorphism form, but its distribution is not homogeneous in these iron minerals with the Sc_2O_3 content between 330 × 10-6 and 2040 × 10-6. This study provides a theoretical base for the further experimental work on the scandium extraction from this Bayer red mud.

Influence of laterite nickel ore on extracting iron from Bayer red mud by carbothermal smelting reduction

In view of the difficulty of extracting iron from Bayer red mud,a new idea of adding laterite nickel ore into red mud was proposed to prepare a high value-added product.Toward this,the influences of laterite nickel ore on thermodynamic reaction,slagging and smelting reduction of extracting iron from red mud were studied.The results indicated that the product of extracting iron from red mud(R100)was changed with the addition of laterite nickel ore(R70L30).The slag of R100 was strongly basic,while the R70L30 was weakly acidic with composition closer to the ideal blast furnace slag.The metal recovery of R100 was 75.16%and that of R70L30 was 94.05%.At the same temperature,the slag viscosity of R70L30 was significantly lower than that of R100,which proved that laterite nickel ore can adjust the basicity,reduce melting point of slag and improve metal recovery.Because Fe,Ni and Cr in red mud and laterite nickel ore can be reduced sufficiently,a low Ni–Cr alloy cast iron can be directly prepared.

拜耳法赤泥特性对水泥砂浆工作性能和力学性能的影响研究

为提高拜耳法赤泥的利用率和附加值,对比研究了不同物化特性的赤泥A和赤泥B对拜耳法赤泥-水泥复合砂浆流动度、力学强度及微结构的影响规律。研究结果表明:赤泥A的最佳掺量为10%,赤泥B的最佳掺量为20%,此时配制的拜耳法赤泥-水泥复合砂浆的力学性能可到达P·O 42.5级水泥标准要求。另外,与赤泥A相比,赤泥B的掺入可赋予复合砂浆具有更高的力学性能,这主要是因为一方面赤泥B的颗粒尺寸较为细小,有助于填充砂浆微孔,提高水泥石密实性,另一方面赤泥B含有更多的Na_(2)O、K_(2)O等游离碱,碱激发作用更为明显,可加快浆体中活性矿物的水化所导致的。

赤泥基路用材料中主要金属的浸出行为及其路用固化效果

赤泥高碱高氟和多金属含量等污染特性会影响其资源化利用。针对赤泥路用存在潜在环境风险的主要金属,重点研究赤泥基路用材料制备过程对主要金属污染物的浸出环境行为与固化效果的影响。结果表明,不同赤泥基路用材料金属总量大小与浸出含量水平受铝土矿产地、氧化铝生产工艺以及制备过程添加的材料等的影响,赤泥基路用材料的制备过程对Al、As、V、Se、Mo有显著固化效果,使其浸出含量分别降低了10.97%~75.77%、97.84%~99.90%、98.16%~100.00%、90.62%~99.34%、61.60%~87.66%,但对Na、Fe、K、Ba、Cr的固化效果不明显反而会使其浸出含量增加,应注重材料制备过程的质量控制。在实际道路应用过程中长期风险评估应重点关注但不限于赤泥基路用材料中Na、总Cr、Cr^(6+)、V、Se、Mo的迁移转化等环境行为。

不同活化方式对拜耳法赤泥中铝、硅浸出性能的影响

本文针对拜耳法赤泥在碱激发条件下所含铝、硅相溶出率低,无法满足制备地聚物所需[AlO_(4)]和[SiO_(4)]单体的问题,提出分别采用微波活化、焙烧活化和机械活化的方式对赤泥进行活化处理。主要研究了不同活化方式对赤泥中Al_(2)O_(3)、SiO_(2)浸出率的影响,并探讨了三种活化方式中赤泥的物相转变及活化机理。结果表明,微波活化温度为800℃时,赤泥中SiO_(2)和Al_(2)O_(3)的浸出率最高,分别为0.54%和25.1%;焙烧活化在400和1200℃时SiO_(2)和Al_(2)O_(3)浸出率最高,分别为0.42%和23.3%;而机械活化对赤泥中Al_(2)O_(3)和SiO_(2)的活性提升效果不显著,Al_(2)O_(3)和SiO_(2)的最高浸出率仅为2.32%和0.63%。赤泥活化过程XRD表明,微波和焙烧活化条件下,400~800℃时,主要发生赤泥中的铁水化石榴石、钙霞石分解,微波和焙烧活化分别形成了钙铝黄长石和硅酸钠钙相;800~1200℃时,钙铝黄长石分解,形成硅酸二钙和钙铁辉石相,而硅酸钙相稳定存在于赤泥中,微波和焙烧活化时,赤泥中分别形成了立方结构和斜方结构的硅铝酸钠相。

贵州某赤泥工艺矿物学特性研究

为深入探究贵州某赤泥中铝铁钛矿物组成、嵌布特征及元素赋存形式,明确适宜的回收方法,对其开展了工艺矿物学研究。分别采用化学多元素分析、激光粒度仪分析和SEM-EDS-BPMA矿物自动定量分析系统对赤泥的化学组成、粒度特性、元素分布和矿物嵌布特征进行了详细分析。研究结果表明,赤泥样品中富含铁、铝和钛等可具回收价值的金属成分;赤泥粒度极细,-25μm的产率高达77.60%。矿物组成复杂,主要矿物包括赤铁矿、铝硅酸铁、铁铝硅酸钙和钙铁氧化物。赤铁矿富连生体较多,嵌布粒度较粗;然而,硬水铝石和金红石等矿物含量较低,嵌布粒度细小,分布稀散,分离提取难度较大。本研究进一步明确了铝、铁、钛在赤泥中的赋存形式,为拜耳法赤泥制定高效利用方案提供了重要矿物学依据。

赤泥基全固废矿井充填材料的制备与性能研究

为实现拜耳法赤泥的资源化利用,采用拜耳法赤泥、电石渣、矿粉和煤矸石等制备了赤泥基全固废矿井充填材料.研究了不同赤泥、电石渣掺量对充填材料力学性能与工作性能的影响,并采用X射线衍射仪(XRD)、扫描电子显微镜及能谱仪(SEM-EDS)、电感耦合等离子体发射光谱仪(ICP-OES)等微观测试手段,分析了赤泥基全固废矿井充填料浆的水化产物、微观结构演变以及重金属浸出毒性.结果表明:矿井充填材料中,当赤泥占胶凝材料的50%,充填浓度为75%时,充填料浆的流动度可达230 mm,充填料浆硬化体7、28 d的抗压强度分别达到2.29、2.88 MPa,满足大多数矿井充填材料工作性能与力学性能的要求.使用赤泥制备矿井充填材料后,As、Cd、Cr、Pb等重金属离子的浸出浓度显著下降,远低于GB/T 14848—2017《地下水环境质量标准》要求的浸出毒性限制.

低温拜耳法赤泥高温溶出行为

赤泥是氧化铝生产过程中排放的强碱性固体废物,尤其对于三水铝石矿低温拜耳法产生的赤泥,其中含有大量的Al_(2)O_(3)未被溶出,造成资源的极大浪费。以低温拜耳法赤泥为原料,通过高温溶出回收其中的Al_(2)O_(3),系统研究了石灰添加量、循环母液苛碱浓度、溶出温度、固含、溶出时间对Al_(2)O_(3)溶出性能的影响规律,获得了溶出过程中物相转变机理和溶出动力学。结果表明:低温拜耳法赤泥高温溶出过程中,Al_(2)O_(3)溶出率随苛碱浓度、溶出温度、时间的增加而增加,随着石灰添加量和固含的增加而降低。推荐Al_(2)O_(3)的溶出条件为:固含500 g/L、苛碱浓度210 g/L、溶出温度270℃、溶出时间60 min、溶出过程不添加石灰,在此条件下Al_(2)O_(3)溶出率为50.36%,溶出液硅量指数为260。Al_(2)O_(3)溶出过程受内扩散控制,表观活化能为33.46 kJ mol,动力学方程为1-2α3-(1-α)^(2/3)=0.00101×^(e-3346 RT)×t;在高温溶出过程中,一水软铝石发生溶解,同时铝针铁矿转化为赤铁矿,导致氧化铝溶出率提高。

拜耳法赤泥中钪、钇浸出行为及动力学研究

采用两步酸浸法浸出赤泥中的钪和钇,用磷酸对赤泥进行一段酸浸,实现脱碱和脱硅并富集稀土金属钪、钇;用硫酸对磷酸浸出渣进行二段酸浸,考察了硫酸浓度、液固比、反应温度、反应时间对钪、钇浸出过程的影响,并进行了浸出动力学分析。结果表明,赤泥经磷酸浸出后,脱碱和脱硅效果较好,K、Na、Si浸出率分别为75.62%、87.82%、80.25%;在硫酸浓度2.5 mol/L、液固比7∶1、反应温度70℃、反应时间45 min条件下进行二段硫酸浸出,Sc、Y平均浸出率分别为74.49%、80.02%。Sc和Y的硫酸浸出过程均符合多相液固区域反应模型,受扩散控制,表观反应活化能分别为18.50 kJ/mol和16.74 kJ/mol。

高温活化及养护方式对赤泥-矿粉复合材料性能的影响

以活化后的拜耳法赤泥和矿粉为原料,按照70∶30的配比制备胶砂试件,研究了赤泥的活化方式及养护方式对赤泥-矿粉复合材料力学性能、水化产物及微观结构的影响。结果表明,在相同的养护制度下,800℃高温煅烧后的赤泥制成的试件强度比105℃直接干燥后的赤泥制成的试件强度高约20%,其密实度更高。在相同活化方式下,60℃热固化24 h后在20℃环境下覆膜养护的试件3 d抗压强度最高,但是会产生较为明显的裂缝,随着养护时间的延长,强度降低;标准养护制度下试件28 d抗压强度最高。

拜耳法赤泥替代烧结法氧化铝生产中高铁矿石实践

拜耳法溶出赤泥中的铁矿物(铝针铁矿和赤铁矿)含量达到60%以上,可替代高铁矿石作为辅料调配烧结法熟料,提高氧化铝净溶出率。本文先从理论出发,并进行了实验室实验,分析采用赤泥配矿后烧结用矿品位的变化、熟料化学成分、熟料溶出指标以及熟料溶出沉降性能,并与高铁矿石配矿模式下的指标进行对比。实验结果表明,使用低温拜耳法赤泥调配烧结法熟料,熟料的氧化铝含量及铝硅比A/S有所下降,但氧化铝及氧化钠的标准溶出率基本相当,熟料溶出后粗液的吸光度有所降低,熟料溶出产生的赤泥的沉降压缩性能相当。因此,使用低温拜耳法赤泥调配烧结法熟料在工艺上可行。采用赤泥配矿后,生产实际现场通过调整熟料碱比和钙比、修正[F/A]控制范围、调整生料浆固定碳含量等措施,达到了烧结法氧化铝生产运行指标的优化提高,既降低了烧结法系统的用矿成本,又实现了赤泥的再利用,对国内低品位铝土矿烧结法氧化铝生产在提高氧化铝净溶出率方面具有一定的借鉴意义。

拜耳赤泥吸收低浓度二氧化硫的研究

考察了赤泥液固质量比、反应温度、搅拌转速对二氧化硫吸收率和赤泥脱碱率的影响.同时,考察了二氧化硫吸收率与时间的关系.实验结果表明:从二氧化硫吸收率和赤泥脱碱率两方面考虑,拜耳赤泥吸收低浓度SO2的适宜条件为:液固质量比5∶1,搅拌转速150r/min,反应温度25℃;此时,SO2吸收率为93.14%,尾气中SO2的浓度达到国家排放标准,二氧化硫吸收率随时间的增长而降低;赤泥的脱碱率为70.45%,此时脱碱赤泥的碱度达到水泥的碱度要求,可作为原料生产水泥.

NaOH亚熔盐法处理拜尔法赤泥的铝硅行为

针对拜尔法赤泥铝/硅比偏高的问题,对NaOH亚熔盐法处理拜耳法赤泥过程中的Al,Si行为进行了研究.考察了溶出温度、碱/泥比、添加CaO等主要因素对终赤泥化学成分和物相结构的影响.结果表明,溶出温度高、碱/泥比大有利于Al2O3的回收,相应的终赤泥的铝/硅比较低.在碱/泥比6、溶出温度230℃、时间2h的条件下,氧化铝回收率可达79.22%,终赤泥的铝/硅比可降到0.39,终赤泥中的硅主要以NaCaHSiO4和Ca3(Fe0.87Al0.13)2(SiO4)1.65(OH)5.4形式存在.在处理CaO/SiO2>1.2的拜尔法赤泥时继续添加CaO并不能继续提高Al2O3的回收率.

利用赤泥制备高强陶粒的试验研究

利用拜耳法赤泥、页岩和粉煤灰等原料制备了高强陶粒。赤泥掺入量为50%时,陶粒堆积密度840 kg/m3,筒压强度达到7.5 MPa,强度标号45 MPa1,h吸水率7.6%,表观密度1 000 kg/m3,孔隙率16.0%,放射性能够满足作为轻集料的活度要求。利用XRD、SEM等分析手段,对赤泥陶粒烧结机理进行了探讨。

低浓度拜耳赤泥充填材料制备及水化机理

针对矿山充填中拜耳法赤泥利用率较低或低浓度赤泥充填材料存在强度低、泌水量高、易收缩等问题,研究粉煤灰添加比例、脱硫石膏、石灰及激发剂对赤泥充填材料早期强度及体积稳定性的影响,采用扫描电子显微镜-能谱仪(SEMEDS)和X射线衍射(XRD)分析手段探讨赤泥基充填材料的水化机理.结果表明,脱硫石膏促进钙矾石的生成,石灰促进粉煤灰火山灰效应,激发剂可以加快赤泥-粉煤灰水化反应进程,三者协同作用提高赤泥充填体强度.充填材料28 d抗压强度3.35 MPa,且初始及60 min流动度在200 mm以上.微观实验表明,硬化体水化产物为钙矾石、硬柱石、硅铝酸盐凝胶类矿物,水化产物通过填充孔隙,提高浆体强度.赤泥基充填材料固体废弃物利用率达到92%,无泌水,无沉缩,具有较高的经济价值和环保价值.

拜耳法赤泥脱硫特性研究

通过自制鼓泡反应器和XRD等手段研究赤泥处理低浓度SO2的脱硫效果及其脱硫机理。试验结果表明,当赤泥浆液固液比为1∶20,赤泥浆液在排放标准内能容硫362.7 mg/g,且赤泥浆液能够在酸性条件下净化SO_2,其浆液p H值能降至1.58左右。浆液脱硫过程中固相物质发挥了更大脱硫作用,并提出赤泥分阶段脱硫机理:碱性物质脱硫阶段和铁离子催化氧化脱硫阶段。试验还证明了在赤泥浆液pH≤4时,浆液中铁离子的溶出促进SO_2的吸收,且这种促进作用为催化氧化作用。SO_2与赤泥反应的最终产物主要为硫酸钙和斜钠明矾。