Synergistic CO_(2) mineralization using coal fly ash and red mud as a composite system

CO_(2) mineralization plays a critical role in the storage and utilization of CO_(2).Coal fly ash(CFA)and red mud(RM)are widely utilized as CO_(2) mineralizers.However,the inert calcium species in CFA limit its carbonation capacity,meanwhile the substantial Ca^(2+)releasing of RM is hindered by a covering layer of calcium carbonate.In this study,CO_(2) mineralization in a composite system of CFA and RM was investigated to enhance the carbonation capacity.Multiple analyzers were employed to characterize the raw materials and resulting mineralization products.The results demonstrated that a synergistic effect existed in the composite system of CFA and RM,resulting in improving CO_(2) mineralization rate and efficiency.The produced calcium carbonate was ectopically attached the surface of CFA in the composite system,thus slowing down its coverage on the surface of RM.This phenomenon facilitated further releasing Ca^(2+)from the internal RM,thereby enhancing CO_(2) mineralization efficiency.Meanwhile,the inclusion of RM significantly improved the alkalinity of the composite system,which not only promoted the dissolution of Ca^(2+)of the inert CaSO_(4)(H_(2)O)_(2) in CFA,but also accelerated CO_(2) mineralization rate.The investigation would be beneficial to CO_(2) mineralization using industrial solid wastes.

Effect of Oil Shale on Na^+ Solidification of Red Mud-Fly Ash Cementitious Material

Red mud-fly ash based cementitious material mixed with different contents of oil shale calcined at 700 ℃ is investigated in this paper. The effect of active Si and A1 content on the solidification of Na＋ during the hydration process is determined by using X-ray diffraction （XRD）, 27A1 and 29Si magic-angle-spinning nuclear magnetic resonance （MAS-NMR）, infrared （IR）, scanning electronic microscopy （SEM） and X-ray photoelectron spectroscopy （XPS）. It is shown that the content of oil shale has a remarkable effect on the solidified content of Na＋. The hydration process generates a highly reactive intermediate gel phase formed by co-polymerisation of individual alumina and silicate species. This kind of gel is primarily considered as 3D framework of Si04 and A104 tetrahedra interlinked by the shared oxygen atoms randomly. The negative charges and four-coordinated A1 inside the network are mainly charge-balanced by Na＋. The solidifying mechanism of Na＋ is greatly attributed to the forming of this kind of gel.

Investigation of the medium calcium based non-burnt brick made by red mud and fly ash: durability and hydration characteristics

Red mud is a type of highly alkaline waste residue produced in the process of alumina smelting by the Bayer process.Based on the idea of medium calcium content,solid wastes such as red mud and fly ash were used to prepare non-burnt bricks;and the mass ratio of CaO/SiO2 was selected in the range of 0.88–1.42.Mechanical properties and durability were investigated with a compressive strength test.X-ray diffractometry(XRD),scanning electron microscope(SEM),and Fourier transform infrared spectroscopy(FTIR)techniques were used to characterize the hydration characteristic.The environmental performance was analyzed by Inductively Coupled Plasma Mass Spectrometry(ICP).The results indicated that the mechanical properties and the durability were optimal when the mass ratio of CaO/SiO2 was 1.23.The hydration products were mostly C–S–H gel,ettringite,Na4Ca(Si10All6)O32·12H2O and Ca3Al2(SiO4)(OH)8.They were responsible for the strength development,and the CaO/SiO2 mass ratio of 1.23 had the best polymerized structure.The results of an environmental performance test showed that the heavy metals in the raw materials were well-solidified in the brick.Therefore,this paper provides an effective solution for use of solid wastes in building material.

Red mud and fly ash-based ceramic foams using starch and manganese dioxide as foaming agent

Ceramic foams were prepared using red mud and fly ash as raw materials with sodium borate as sintering aid agent,starchand MnO2as foaming agent,respectively.The influence of the amount of starch or MnO2on the crystalline phase,pore morphologyand physical–chemical porosities was studied.The results showed that the main crystal phases of samples with starch addition andMnO2addition were sodalite phase Na6(AlSiO4)6and Na8(SiAlO4)6MnO4,respectively.The SEM images showed that the variation ofporous structure was mainly dominated by the addition of foaming agent.With the increase of foaming agent,the samples exhibitedbetter comprehensive properties:bulk density of0.59?0.96g/cm3,porosity of41.82%?63.51%,water absorption of3.16%?9.17%,compressive strength of4.22?8.38MPa,flexural strength of2.44?5.82MPa,acid resistance of95.59%?99.60%,alkali resistance of99.82%?99.99%.Based on these properties,the ceramic foams can be used in building field.

Enhanced strength in novel nanocomposites prepared by reinforcing graphene in red soil and fly ash bricks

Low-dimensional nanomaterials such as graphene can be used as a reinforcing agent in building materials to enhance the strength and durability. Common building materials burnt red soil bricks and fly ash bricks were reinforced with various amounts of graphene, and the effect of graphene on the strength of these newly developed nanocomposites was studied. The fly ash brick nanocomposite samples were cured as per their standard curing time, and the burnt red soil brick nanocomposite samples were merely dried in the sun instead of being subjected to the traditional heat treatment for days to achieve sufficient strength. The water absorption ability of the fly ash bricks was also discussed. The compressive strength of all of the graphene-reinforced nanocomposite samples was tested, along with that of some standard (without graphene) composite samples with the same dimensions, to evaluate the effects of the addition of various amounts of graphene on the compressive strength of the bricks.

Sliding Wear Performance Evaluation of Red Mud (RM), RM + Fly Ash (FA) and RM + FA + Al Coatings on Mild Steel

The research paper focuses on evaluating the dry sliding wear behaviour of plasma sprayed coatings like red mud (RM), RM + 5% Fly Ash (FA) and RM + 5% FA + 5% Al on mild steel cylindrical shape substrate. Spraying was done at 10 kW operating power level. A conventional pin on disc wear tester is adopted for wear analysis. The wear test was performed at track diameter of 50 mm and sliding speed of 60 rpm (0.157 m/s) with normal load of 10 N. The duration of sliding varies from 54 minutes for pure red mud coating to a maximum value of 102 minutes for RM + 5% FA + 5% Al composite coating. A significant decrease in wear rate (in terms of mass loss) is observed by reinforcement of fly ash and aluminium to red mud, which might be due to improved interfacial properties.

Wettability, Thermal and Sliding Behavior of Thermally Sprayed Fly Ash Premixed Red Mud Coatings on Mild Steel

The present experimental work reveals the surface characteristics like wettability, thermal and sliding wear behaviour of plasma-sprayed red mud (RM) coatings premixed with fly ash (FA). Varying weight % of FA (10, 20, 30 and 40)—RM composite powder is used as precursor for coating. Atmospheric plasma-sprayed coatings are developed at different operating power like 5 kW, 10 kW, 15 kW and 20 kW separately on mild steel substrate. Tribological behaviour viz. sliding wear properties are studied at distinct operating load (10N, 15N, 20N, 25N), speed (40 rpm, 50 rpm, 60 rpm, 70 rpm) and track diameter of 100 mm using a pin on disc tribometer for duration of 30 minutes with 3 minute gap period for each experiment. The DSC and TGA experiments of the coatings are performed to understand the high temperature application areas. The contact angle result signifies the wettability of the prepared coatings is principally a function of composition. The reaction of surface roughness and spraying power is in-significant on water contact angle (WCA). In conclusion, the sliding wear experiments are optimized by Taguchi method to ascertain the influencing parameter on wear.

Using Sorghum Stalk as a Partial Replacement of Lime in the Stabilization of Red Clay Soil for Road Sub-Grade Construction

This research aimed at testing the viability of using Sorghum Stalk Ash (SSA) as a partial replacement of lime in the stabilization of red clay soils for road subgrade construction. Red clay soils have been identified as highly expansive soils, which are affected by both climatic conditions and loading patterns. The consideration of both traffic loading patterns and climatic effects on these soils has been taken into account. A penetration test of 2.5 mm has been used on both pure red soils and stabilized soils at 10% and 15% partial replacement of lime with SSA and showed an improvement in the CBR of stabilized red clay soils up to 11.6%. Again, the PI of stabilized soils at 15% partial replacement of lime reduced up to 11.2%. The results obtained on both CBR and PI of these red clay soils are within the recommended values for the effective subgrade required for laying both permanent and flexible pavements. As a result, a recommendation of making use of SSA to lower the quantities of lime and its costs used in the stabilization of highly expansive soils have been tested through this research. However, further research on a more percentage partial replacement of lime to improve the PI of these soils to below 10% while keeping the CBR levels within the road construction regulations is welcomed.

粉煤灰改良红层泥岩填料静三轴试验研究

红层泥岩的吸水软化和体积膨胀特性易造成路基翻浆冒泥现象及路基不均匀沉降等病害,在作为公路路基填料时应对其进行改良。本文选用粉煤灰作为改良剂,通过室内X射线衍射试验、化学成分测试和易溶盐等试验,分析红层泥岩和粉煤灰的成分组成及离子含量;通过无侧限抗压强度试验、室内变水头渗透试验和固结等试验分析了试样改良前后物理力学特性;通过常规三轴UU试验,研究了不同粉煤灰掺量对改良试样剪切应力-应变及抗剪强度的影响;分析了粉煤灰掺量为10%时,养护龄期对改良试验抗剪强度参数的影响。结果表明:该地区红层泥岩属低液限黏土,其易溶盐溶液中的SO42-离子含量最高,pH值呈碱性;三轴剪切试验中,改良和未改良试样均呈塑性破坏,试样粉煤灰掺量和龄期均对试样抗剪强度提高具有促进作用,且黏聚力增长幅度远大于内摩擦角;粉煤灰掺量为10%龄期28 d时,试样黏聚力较未改良未养护试样和10%掺量未养护试样分别提升37.9%和6.9%,内摩擦角分别增大了1.2°和0.7°。试样的静力学试验均验证了粉煤灰改良的可靠性。

电解锰渣-赤泥-粉煤灰路面砖的力学性能及浸出毒性研究

针对大宗工业固废回收利用难的问题,实现多种固废减量化、无害化、资源化的目标,通过利用取自中国西南地区企业的石膏类、碱性及硅铝质三类典型大宗固废中的电解锰渣、赤泥、粉煤灰协同处理的无害化渣制备环保型透水混凝土路面砖(permeable concrete paving bricks,PCB),研究了水洗、掺渣量对所制备PCB的力学性能与浸出毒性的影响,并通过X射线衍射(XRD)和扫描电子显微镜(SEM)对最佳性能PCB的物相组成与微观形貌结构进行分析.结果表明:①随着无害化渣与水洗无害化渣掺入量的提升,路面砖的劈裂抗拉强度、线性破坏荷载发生明显变化,总体呈下降趋势.当无害化渣掺入量为6%、水洗无害化渣掺入量为14%时,经28 d养护,所制备砖体的劈裂抗拉强度分别为4.09和3.46 MPa,达到了《透水路面砖和透水路面板》(GB/T 25993-2010)中规定的f_(ts)4.0与f_(ts)3.0等级.②路面砖的重金属与NH_(4)^(+)-N的浸出毒性均低于《水泥窑协同处置固体废物技术规范》(GB 30760-2014)的要求.路面砖的主要物相中方解石、石英与钙矾石是主要支撑性物质.研究显示,电解锰渣、赤泥、粉煤灰协同处理的无害化渣可替代部分原材料制备透水混凝土路面砖,满足力学性能与浸出毒性相关标准,能有效促进固体废弃物的减量化与资源化,建议进一步开展砖体在实际应用场景中的环境风险试验,以期为电解锰渣、赤泥、粉煤灰的综合利用技术发展提供更明确的支撑.

粉煤灰和烧结法赤泥制备地聚合物及其性能

这是一篇陶瓷及复合材料领域的论文。为实现粉煤灰和烧结法赤泥的综合利用,本研究以粉煤灰为主要原料,烧结法赤泥作为辅料,氢氧化钠为碱激发剂协同制备地聚合物。结果表明,地聚合物较佳制备条件为:粉煤灰采取分级(细粒提取)的预处理方式,分级粒径为37μm,细颗粒粉煤灰与烧结法赤泥质量比为7∶3 (g∶g),氢氧化钠的用量为前驱粉体的15%,此时地聚合物室温养护28 d的抗压强度可达35.52 MPa,满足中国《通用硅酸盐水泥》32.5R矿渣硅酸盐水泥的强度标准。通过XRF、XRD、ICP-OES和SEM-EDS对不同预处理方式下的原料及其所制备的地聚合物进行分析测试表明:相比于机械研磨,分级预处理更能有效改善粉煤灰的反应性,使更多活性硅铝组分参与地聚合反应;烧结法赤泥的加入可以促进富钙铝硅酸盐凝胶的形成,使地聚合物的微观结构致密化。本研究为粉煤灰和烧结法赤泥的综合利用提供了新的思路。

赤泥、粉煤灰、磷石膏协同高温烧结回收铁铝试验研究

赤泥(RM)、粉煤灰(FA)、磷石膏(PG)这3种固废具有产生量大、利用率低的特点,长期堆存会对水资源、土壤、空气等产生严重影响。本文提出用磷石膏代替碱石灰CaO,采用高温烧结-碱浸提铝-磁选提铁工艺协同处理3种固废回收铝、铁,并考察烧结工序工艺条件对铝、铁回收率的影响,得到以下主要结论。在烧结温度1100℃、保温时间30 min、钙比2.0条件下,铁回收率达到79.2%、铁品位达到74.5%、铝溶出率达到75.9%;升高烧结温度有利于铁、铝回收,但温度高于1100℃时熟料会出现粘黏阻碍铝的溶出;保温时间对铝铁回收影响较小;CaO与Na_(2)CO_(3)有助于激活粉煤灰中莫来石的活性,提高铝回收率;磷石膏添加过量时高温下会生成Fe_(3)Ti_(3)O_(10)、Ca_(3)Fe_(15)O_(25),导致铁品位和铁回收率降低。采用本试验工艺,每消纳10 g赤泥、6.5 g粉煤灰、15 g磷石膏,可回收75.9%的铝和3 g铁精矿,而且生产中可实现碱循环,同时生成的副产品2CaO·SiO_(2)可用来制备硫铝酸盐水泥,整个工艺流程实现了3种固废绿色协同消纳,有效实现了资源的综合利用。

利用生物浸出技术从固废中回收稀有金属的研究进展

稀有金属支撑着各国经济的发展和高精尖技术的进步,我国稀有金属储量大、原矿品位高,但分布稀散、人均可利用量少且提取率较低。富矿资源的消耗并不能完全满足工业生产需求,因此从低品位矿石中提取或从废矿、废弃物中回收稀有金属已成为目前研究的热点。固废的堆积严重影响地下水和表层土壤的酸碱平衡、造成严重的重金属污染、破坏生态系统原有的稳态结构。研究表明固废中富集了大量稀有金属元素,利用生物浸出技术从固废中浸提稀有金属可以极大提高固废附加值。本文介绍了多种常见固废的产量和理化性质、生物浸出机理、分类和工艺,并总结了常见固废生物浸出技术的研究进展。结果发现,目前的固废生物浸出技术仍存在智能化水平低、短期收益低、周期长、工艺链路复杂等诸多问题,有新型浸矿菌种的选育、微生物对固废的适应性、针对单一元素特异性浸提的难点和突破点,并提出了向新质生产力靠拢、发展智能化生物浸出技术、优化工艺结构的一系列建议。固废的综合利用仍处于不断发展的阶段,研究开发资源节约型、环境友好型的生物浸出技术对稀有金属资源的高效利用有重要意义。

碱性工业固废堆存对周边环境的危害分析及应对措施

碱性大宗工业固废产量巨大且利用率低,导致堆存量大,高达数十亿吨。本文综述了钢铁渣、电石渣、粉煤灰、赤泥几种大宗碱性工业固废的产生以及堆存后对周边生态环境污染和危害,并对碱性大宗工业固废堆存场地的环境风险管控和未来处置利用方向提出了建议,提出碱性工业固废资源化利用及其矿化固碳技术将是未来的产业化发展方向,以期为碱性工业固废处置及综合利用提供参考,减少不规范堆存对周边生态环境的污染。

CFB灰渣对水泥稳定红砂岩集料的增强改性作用

针对红砂岩均质性差,红砂岩集料性能和水泥稳定红砂岩集料路用性能不明确的问题,以水泥稳定石灰岩集料为对照,分别研究了红砂岩粗、细集料取代率。研究了循环流化床(CFB)炉渣、CFB飞灰掺量对水泥稳定红砂岩集料7 d无侧限抗压强度、长期强度、抗干缩性能和抗冻性能的影响规律。采用SEM揭示了CFB灰渣对水泥稳定红砂岩集料的改性作用机理。结果表明:红砂岩集料的组成成分和物理性能与粒径大小存在明显相关性,集料粒径越小,集料中的黏土矿物含量越高,压碎值越低,塑性指数越高,表明可以通过破碎筛分将不同类型红砂岩分离,提高红砂岩集料均质性。水泥稳定红砂岩集料的强度、抗裂性能、抗冻性受红砂岩粗集料替代率影响小,受红砂岩细集料替代率影响大。采用CFB炉渣和CFB飞灰作复合细集料可显著提高水泥稳定红砂岩集料的路用性能。与同水泥掺量水泥稳定石灰石集料相比,经改性后的水泥稳定红砂岩集料7 d无侧限抗压强度高0.8 MPa,干缩应变低49.5%,抗冻性持平。从SEM的试验结果中可以观察到针棒状钙矾石和絮状C—S—H凝胶,这表明CFB灰渣的水化产物起到了胶结增强作用,针棒状钙矾石形成产生的膨胀与CFB炉渣的多孔“内养生”作用可协同降低干缩、防止冻融破坏。

改性粉煤灰制备及对刚果红吸附性能的综合实验设计

设计了改性粉煤灰用于吸附废水中刚果红的本科教学实验。以氢氧化剂为活化剂,通过焙烧-水热法对粉煤灰进行改性。采用红外光谱对改性前后的煤粉灰结构进行了表征,并研究了改性后的粉煤灰对废水中刚果红的吸附性能。不仅解决了固废问题,又能缓解水环境污染问题。通过本实验可以提高学生的实验操作和科研思维能力,培养学生的综合实践能力、绿色环保意识和节能减排发展观,为学生进一步开展科学研究奠定坚实的基础。

赤泥基固定飞灰制备地聚合物的研究

为了有效处理城市垃圾,一般需要对城市垃圾进行焚烧,但在焚烧过程中会产生大量危险固废物飞灰。赤泥中的氧化铝、二氧化硅和氧化钠可以与飞灰中的活性氧化铝、二氧化硅发生地聚反应,生成的地聚合物能够有效固定飞灰中的镉(Cd)、铅(Pb)等重金属,防止其浸出。采用X-射线衍射(XRD)、热重差热分析(TG-DTA)和扫描电镜(SEM)测试手段,对实验相关样品的化学成分、形貌特征进行表征分析。结果表明:在800℃和5%(质量浓度)氢氧化钠(NaOH)的条件下,赤泥的活化效果最佳;赤泥活化后,将赤泥与飞灰(质量比为1∶1,水灰比为0.5)进行均匀混合,赤泥与飞灰的混合物置于养护箱中养护14天(d),即可获得地聚合物样品;XRD表明,聚合物样品中有新矿物[Ca_(6)Al_(2)(SO_(4))(OH)_(12)·6H_(2)O]的衍射峰出现,证明赤泥和飞灰之间发生了地聚合反应;抗压强度测试表明,最佳地聚合物样品的抗压强度为1.63兆帕(MPa);赤泥固化飞灰后的地聚合物渗滤液中的重金属含量达到垃圾焚烧飞灰卫生填埋标准(GB 16889-2008),说明利用赤泥基能够有效固定飞灰中的重金属,证明“以废治废”的技术是可行的。

固废基ZSM-5合成及其改性研究进展

工业生产过程中产生大量粉煤灰、赤泥和煤气化渣,其堆积不仅侵占土地,还会严重破坏生态环境,危及人类健康。这3种固废均含有硅铝元素,且含量较高,硅铝比(氧化硅和氧化铝物质的量比)波动幅度较大。ZSM-5(Zeolite Socony Mobil 5)是一类硅铝比范围较宽的沸石分子筛,具有独特的孔道结构和良好的稳定性,在吸附和催化方面应用广泛。利用富含硅铝的固废制备ZSM-5是其高值化和资源化利用的重要途径之一。系统总结了富含硅铝的固废的活化除杂预处理通用方法,并且基于粉煤灰、赤泥和煤气化渣的理化性质特点,综述了固废基ZSM-5的合成及金属改性、磷改性、水热改性和酸碱改性4种方法的研究进展。分析固废作为硅铝源对ZSM-5合成、结构和性能的影响,指出固废在活化除杂过程中硅铝比的调控、杂质元素的去除转化、及主要元素的迁移转化规律是研究重点;讨论不同改性方法对ZSM-5结构和性能的影响机制,提出固废基ZSM-5中硅铝在骨架和非骨架中的分布、铁钙等杂元素的含量和存在形态、孔结构对改性效果起到非常重要的作用。通过对典型富含硅铝元素的固废基ZSM-5合成及其改性过程中存在问题和研究现状的分析和讨论,提出了粉煤灰、赤泥和煤气化渣多源固废复配,在无机模板剂或无模板剂条件下水热晶化制备ZSM-5,对固废基ZSM-5高效精准改性是未来发展方向。

赤泥-粉煤灰协同稳定沥青路面回收料力学强度性能研究

采用工业副产品赤泥和粉煤灰协同稳定沥青路面回收料(RAP),并评估混合料作为路面基层材料的可行性。测试了6种不同配合比混合料在7 d、14 d和28 d龄期下的无侧限抗压强度(UCS),并用毒性浸出试验测定了重金属含量。研究发现,赤泥-粉煤灰稳定RAP的UCS与赤泥的含量和龄期有关;较低的赤泥替代率可产生较高的UCS,RAP对混合料体系强度的贡献率大于复合胶凝材料,当RAP掺量为80%和赤泥掺量为4%时,体系7 d UCS达到最大值3.41 MPa,满足现行规范中二级和二级公路以下重交通荷载等级下最低抗压强度要求。毒性浸出试验结果表明,RAP混合料中危害元素均在环保标准要求范围内。

基于正交试验的改良红黏土力学特性研究

为改善红黏土的力学特性及水稳性能,文章混合偏高岭土、粉煤灰和高炉矿渣作为固化剂,改良红黏土。基于正交试验,对不同含量的偏高岭土、粉煤灰和高炉矿渣改良红黏土进行无侧限抗压强度试验,确定偏高岭土、粉煤灰和高炉矿渣最优组合配比。随后开展偏高岭土、粉煤灰和高炉矿渣最优组合配比下不同含量的改良红黏土无侧限抗压试验。结果表明,偏高岭土、粉煤灰和高炉矿渣对改良红黏土无侧限抗压强度影响程度依次为粉煤灰>偏高岭土>高炉矿渣,最佳配比为偏高岭土15%、粉煤灰8%和高炉矿渣6%。改良红黏土的无侧限抗压强度随固化剂含量的增长呈现明显的峰值变化,并在14%含量时达到最大,且随着养护时间的增长,其强度逐渐增加。