High-temperature Phase Transition and the Activity of Tobermorite

The high-temperature phase transition of tobermofite was investigated by TGA/DSC, X-ray diffraction and Infrared spectroscopy （IR）, respectively. The experimental results showed that Si-OH bonds were cleaved at 724℃ and dehydroxylation occured at the same time, implying that the crystal structure of tobermorite was broken. As a result, the dehydroxylatiun tobermorite was metastable state, exhibiting obviously hydrolysis activity. The suspension was alkaline and Ca^2＋ ions content reached a maximum value 4.76% after heat treatment at 724℃. The dehydroxylation tobermorite had potential reactive activity due to the strong hydrolysis activity. The disordered structure recombined to wollastonite, and the crystal structure became ordering and stable at 861℃. Finally, 2M-wollastonite structure can be found in the sample as the temperature reached up to 1 000℃.

Conversion of coal gangue into alumina, tobermorite and TiO_2-rich material

A large amount of coal gangue from coal mining and processing is regarded as waste and usually stockpiled directly. In order to recycle the valuable elements from the coal gangue, an integrated process is proposed. The process consists of three steps: 1concentrating alumina from the coal gangue via activation roasting followed by alkali leaching of Si O2 which produces alumina concentrate for alumina extraction by the Bayer process; 2) synthesizing tobermorite whiskers from the filtrated alkali liquo containing silicate via a hydrothermal method and reusing excess caustic liquor; and 3) enriching titanium component from the Baye process residue by sulfuric acid leaching. Alumina concentrate with 69.5% Al_2O_3 and mass ratio of alumina to silica(A/S) of 5.9pure 1.1 nm tobermorite whisker and TiO_2-rich material containing 33% TiO_2 are produced, respectively, with the optimal parameters Besides, the actual alumina digestion ratio of alumina concentrate reaches 80.4% at 270 oC for 40 min in the Bayer process.

Effect of Al^(3+) on Tobermorite Crystallinity

The difference between the systems of CaO-SiO2,-H2O and CaO-SiO2-Al(OH)3,-H2O, was studied, especially the effect of Al3+on the crystallinity of tobermorite was focussed. As a result, in the system of CaO-SiO2-H2O, tobermorite formed early, however, withreaction time forward, tobermorite was replaced by xonotlite. So far as CaO-SiO2-Al(OH)3,-H2O was concemed, hydrothermal reactionwas cdried out under the same condition as CaO-SiO2-H2O to study the morphological changes of tobermorite crystals. It was found thatAl3+ accelefated the crystal growth of tobermorite to some extent and was in faVor ofplaty crystals. Moreovef, with the Al3+ content in-creasing in the starting material, the morphology of tobermorite did not change magnificently, but platy crystals became more and moreeminent. As soon as the Al2O3 content was over 15.6%, synthetic mineral greatly changed in smicthe and haled into hibschite differentfrom 1 .1 nm tobermorite. Obviously, xonotlite was not apt to form in the presence of Al3+.

Investigation of the Transition Reaction of Tobermorite to Xonotlite under Influence of Additives

The objective of the present work was to investigate the transition reaction of the calcium silicate hydrate tobermorite into xonotlite under influence of additives. Tobermorite is the main binding agent in steam hardened building materials and the appearance of xonotlite indicates the progress of hardening and an overcuring of the material. Hydrothermal experiments under addition of sucrose, calcium formate and calcium chloride dihydrate to the main components quartz and lime were done using temperatures of 220°C and a reaction time of 40.5 h. All experiments were performed with powders as well as with pressed educts. The products of all syntheses were analyzed with XRD, SEM/EDX and FTIR. The references as well as the syntheses with calcium chloride dihydrate led to the formation of 11 &#197 tobermorite and xonotlite. The former showed the best results and even synthesis with pressed educts and calcium chloride dihydrate revealed an accelerating effect of the additive. In contrast syntheses with sucrose had the worst reactivity and led to the formation of calcite beside the CSH-phase scawtite. The additive calcium formate was only slightly oppressing the crystallization of tobermorite and favouring the formation of xonotlite. Syntheses with pressed pellets and sucrose or calcium formate showed generally worse results.

Thermal Behavior and Determination of the Heated Structure of 11ÅAnomalous Tobermorite by in situ X-ray Diffraction

This article presents the thermal transitions of a tobermorite-bearing sample when heated from 30℃ up to 1200℃,both in vacuum and in static air,including tobermorite transforming to wollastonite,aragonite to calcite and calcite to lime.Characteristics obtained by in situ high temperature X-ray diffraction,field emission scanning electron microscopy and scanning transmission electron microscopy analyses jointly indicate that the investigated tobermorite is anomalous.The variations along the a,b,c axes and the volume changes of tobermorite with increasing temperature are described,and its thermal shrinkage coefficients therefore determined.The comparison between the refined structures at 30℃ and 800℃ demonstrates that the shrinkage degree(Δa/a0)along the a axis is higher than those(Δb/b0,Δc/c0)along the b and c axes.The wollastonite is formed in two ways:Tobermorite converting to wollastonite and lime reacting with quartz to form wollastonite.

Synthesis and Structural Characterization of CSH-Phases in the Range of C/S = 0.41 - 1.66 at Temperatures of the Tobermorite Xonotlite Crossover

Calcium-Silicate-Hydrate-phases (CSH-phases) are important binding agents of building materials. The synthesis of CSH phases and their structural characterization was done to investigate the crystallization in dependence of an increasing CaO/SiO2 ratio (C/S ratios) from 0.41 up to 1.66 at temperatures in the crossover region of tobermorite to xonotlite (180℃ and 230℃). Parallel runs with the same C/S ratio but on the one hand with constant mass of quartz and variation of lime and on the other hand under reverse conditions (constant mass of lime but variable amounts of quartz) were performed at both temperatures. The aim was to clarify the connections of crystallization mechanism and kinetics of phase formation with structure, crystallinity and morphology of the CSH’s in the mentioned C/S ratio for both temperatures in the tobermorite-xonotlite crossover region. The parallel experiments with different mass ratios of the educts are important to study the influence of time evaluation of supersaturation within the solution under the peculiarities of the retrograde solubility of lime but accelerated solubility of quartz. The products were characterized by XRD, SEM/EDX, FTIR and 29Si MAS NMR spectroscopy (using the Q-site nomenclature [1]). The experiments could clarify some important connections of crystallization process and the reaction pathway.

Effect of Al-substitution on phase formation and magnetic properties of barium hexaferrite synthesized with sol-gel auto-combustion method

Al-substituted barium ferrite powders were synthesized using the sol-gel auto-combustion method according to the molecular formula BaAlxFe12-xO19 （x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0）. Compared with non-substituted barium ferrite annealing at 1000 ℃, the vibrating sample magnetometer （VSM） measurement manifested that the optimum magnetic properties formation temperature of Al-substituted barium ferrite was 1 100 ℃. The data from X-ray diffractometer （XRD） showed that with increasing x, the lattice constants （a and c） decreased as well as the unit-cell volume Vcell. Magnetic measurement of non-substituted and Al-substituted powders annealed from 900 ℃ to 1 200 ℃ exhibited that the maximum magnetization M （10 kOe）, the remanent magnetization Mr and the coercivity Hc depended strongly on the chemical composition of powder as well as the annealing temperature. When annealing at 1 100 ℃, BaAl0.5Fe11.5O19 of high coercivity Hc （6584 Oe） was produced. Meanwhile, M （10 kOe） and Mr were 42.83 emu/g and 25.65 emu/g, respectively.

铅锌尾矿/电石渣基加气混凝土的组成及结构

为了综合利用固体废弃物,以铅锌尾矿和电石渣为原料制备加气混凝土(AAC)。综合应用宏观与微观的分析方法,研究了铅锌尾矿的细度和掺量对加气混凝土性能的影响,以及不同养护阶段加气混凝土的物相组成、微观结构和蒸压反应机理。结果表明:随着铅锌尾矿细度减小,料浆的流动性提高,水化反应速度加快。但细度过小,易导致料浆过稠,影响加气混凝土良好气孔结构形成和性能;铅锌尾矿掺量过大,体系内未反应的铅锌尾矿残余颗粒堆积增多,颗粒间缝隙减小,影响了水化产物的生长和结晶,导致加气混凝土制品性能下降;当铅锌尾矿比表面积为420 m^(2)/kg、掺量为63%(质量分数)时,加气混凝土的绝干密度和抗压强度分别为590 kg/m^(3)、4.98 MPa,达到了《蒸压加气混凝土砌块》(GB/T 11968-2020)规定的A3.5、B06级加气混凝土合格品的要求。静停养护前加气混凝土坯体内水化产物为C-S-H凝胶和钙矾石(AFt),经静停和蒸压养护后AFt分解,主要水化产物为C-S-H凝胶和托贝莫来石。

焚烧飞灰水热合成托贝莫来石过程中重金属的固化特性

城市生活垃圾焚烧飞灰的环境安全利用处置已成为当前环境管理部门和行业部门亟待解决的问题。为降低焚烧飞灰中重金属对环境的潜在风险,以水洗飞灰为原料水热合成托贝莫来石,探讨Ca与(Si+Al)的摩尔比[以Ca/(Si+Al)表示]对水热产物的晶相组成、微观形貌和表面官能团的影响,研究水热过程中重金属(Hg、Ni、Pb、Zn和Cr)的浸出浓度、浸出率、液相迁移率、形态分布和环境风险的变化。结果表明:Ca/(Si+Al)对水热产物的类型具有重要影响,Ca/(Si+Al)的增加有利于抑制沸石类结构的生成,促进托贝莫来石的形成。随着托贝莫来石的形成,水热产物中5种重金属的毒性浸出浓度和浸出率逐渐降低,相较于水洗飞灰,在最佳比例为1.10的条件下水热产物中重金属的浸出浓度分别下降99.5%、99.0%、99.4%、88.9%和63.7%,浸出率低至0.25%、0.08%、0.01%、0.01%和2.73%,同时重金属向液相的迁移率仅为1.41%、4.28%、0.29%、0.05%和0%,表明大部分重金属均稳定地存在于固相产物中,而不是迁移至水热液中。这归因于托贝莫来石的形成增加了5种重金属残渣态的占比,降低了重金属的迁移性。风险评价指数(risk assesssment code,RAC)结果显示,最佳比例条件下水热产物中5种重金属的RAC均低于10%,达到环境低风险水平。综上,水热合成托贝莫来石是一种稳定焚烧飞灰中重金属很有前景的方法,为富含重金属的危险废物的安全处置和回收利用提供了一种可行的替代方案。

粉煤灰基托贝莫来石的合成及应用进展

托贝莫来石是一类重要的硅酸盐矿物,因具有优良的离子交换性能被广泛用于去除水中的重金属离子。但由于天然托贝莫来石矿物含量少、纯度低,因此往往采用水热法合成它。每年产生的粉煤灰含有大量活性玻璃相和丰富的Ca、Si、Al元素,可以作为合成托贝莫来石的主要原材料。因此,总结了粉煤灰的分类、理化性质以及托贝莫来石合成机制、影响因素、合成工艺和环保应用。以粉煤灰为原料可以合成结晶良好的针状托贝莫来石,它具有良好的吸附性能,可广泛用于处理废水中的重金属离子,其吸附效果理想且成本较低,可以实现以废治废。

不同生物质炉渣对蒸压加气混凝土浆料性能与力学性能的影响

在电厂利用生物质发电过程中,不同焚烧工艺产生的焚烧炉渣的成分和性质不同,这为其资源化利用带来了较大的难题。本研究以生物质炉渣、水泥、石灰为主要原料制备蒸压加气混凝土(AAC),对比研究两种主流燃烧工艺产生的炉渣对AAC制品浆料性能和力学性能的影响,并通过XRD和SEM对其水化产物及微观形貌进行过测试分析。结果表明:随着机械炉排炉渣(MGI)掺量的增加,AAC浆料的初始流动度明显下降,流动度损失增大,发气体积下降;AAC试块的比强度先增大后减小,当MGI质量分数为28%时,为兼顾AAC强度和密度的最佳掺量,抗压强度和密度分别为3.6 MPa、593.22 kg/m^(3)。循环流化床炉渣(CFBC)中大量的硬石膏和游离氧化钙会影响浆料的凝结硬化,随着CFBC掺量的增加,AAC浆料初始流动度逐渐增大,发气体积上升,AAC试块的比强度持续减小。此外,AAC中的水化产物——托贝莫来石的形态和堆积密度对制品的力学性能有着显著影响。

碱激发矿渣-钢渣复合胶凝体系的性能研究

以氢氧化钠和水玻璃为激发剂制备矿渣-钢渣复合胶凝材料,研究矿渣掺量、碱当量和水玻璃模数对复合胶凝材料抗压强度的影响,并采用XRD、SEM对硬化试样的显微形貌和水化产物组成进行了分析。结果表明:随矿渣掺量减少,抗压强度降低。随碱当量的增加,抗压强度先提高后降低,碱当量为11%时强度达到最高。随水玻璃模数的增大,抗压强度先提高后降低,当水玻璃模数为1.2时强度达到最高。水化产物主要为CaCO3、C-S-H凝胶、C-A-S-H凝胶、托贝莫来石及RO惰性相。

大掺量磷石膏对蒸压加气混凝土性能的影响研究

为提高磷石膏的利用率,文章探究了磷石膏作为蒸压加气混凝土原料的可行性。研究了不同掺量磷石膏对蒸压加气混凝土的发泡性能、抗压强度、孔结构和水化产物的影响。结果表明,磷石膏的加入细化了样品的孔隙结构,显著提升了样品的抗压强度。并且托勃莫来石的形态随磷石膏增加而发生了显著变化,其显微形貌由窄的草状结构转变为树叶状结构。当磷石膏的掺量为54%时,成功制备出28 d抗压强度和干密度分别为4.9 MPa和622 kg/m^(3)的样品,其干密度和强度达到国家标准(GB/T11968—2020)B06、A 3.5级别干密度和抗压强度性能要求。

硅酸钙结合蛭石轻质材料制备及孔隙结构研究

为了探寻电力防火领域对轻质新型防火材料的需求,采用氢氧化钙和粉石英为钙、硅原料,膨胀蛭石为骨料,配合增强纤维,经静态水热蒸压反应,制备了体积密度介于538~859 kg/m3的硅酸钙结合蛭石轻质材料。探讨了蛭石加入量20%~40%、成型压力1.0~4.0 MPa对材料体积密度与强度的影响。结果表明,托贝莫来石和硬硅钙石组成的结合相中微细孔隙结构与蛭石片层间的孔隙使得材料孔隙率高达60%以上。同时,结合相与蛭石的穿插结合结构使材料具有较高强度。蛭石加入量30%、压力2.0 MPa下成型的样品,抗拉拔强度接近40 MPa,热面温度1000℃时其导热系数只有0.209 W/(m·K)。这种材料在高温下的低收缩和低导热系数特性使得其在电力防火领域具有潜在用途。

煤矸石与铁尾矿制备加气混凝土的试验研究

为综合利用固体废弃物煤矿石与铁尾矿,以煤矸石和铁尾矿为主要原料制备加气混凝土,用X射线衍射(XRD)、场发射扫描电镜(FE-SEM)和X-射线能谱(EDX)分析制品的水化产物和微观形貌,研究了煤矸石的最佳热活化温度以及各原料组分对加气混凝土物理力学性能的影响。结果表明,煤矸石最佳煅烧温度为600℃,制备出绝干密度为608 kg/m3、抗压强度为3.64 MPa的制品,符号《蒸压加气混凝土砌块》(GB 11968—2006)规定的A3.5,B06级加气混凝土合格品的要求;蒸压前水化产物中出现钙矾石,蒸压后制品中主要的水化产物为托贝莫来石、C-S-H凝胶和葡萄状水钙铝榴石。

水热法分解钾长石制备雪硅钙石的实验研究

采用CaO作为助剂,在低温、中压的水热条件下分解钾长石,继而合成一种水合硅酸钙--雪硅钙石,同时得到KOH稀溶液,可用于制备高纯碳酸钾.影响晶化反应的主要因素有n(Ca)/n(Al+Si)、晶化温度、晶化时间、水固比(质量比)、搅拌速度等.讨论了各因素对钾长石分解及雪硅钙石形成的影响,通过X射线粉末衍射、热重-差热分析、扫描电镜等手段对合成产物进行结构性能表征.实验结果表明,以CaO为助剂分解钾长石,同时合成雪硅钙石的工艺方法可行,资源利用率接近100%.实验得到的优化工艺条件为:晶化温度为220～250 ℃,n(Ca)/n(Al+Si)在0.8～1.0之间,晶化时间5～8 h,水固比为20～25,搅拌速度400 r/min.在此条件下,钾长石中K2O的溶出率达80%以上,同时得到结晶良好的针状雪硅钙石晶体.

山西灵丘低硅铁尾矿制备加气混凝土的试验研究

以低硅铁尾矿作为主要原料,铝粉作为发气剂,成功制备出了符合GB/T 11968—2006的A3.5,B06级加气混凝土制品。考虑最大限度使用铁尾矿的情况下,铁尾矿、硅砂、石灰、水泥和脱硫石膏的最优化配合比(质量比)为40∶20∶25∶10∶5,铝粉加入量为0.057%,水料比为0.57,静停养护温度为70℃,加气混凝土制品的抗压强度达到4.11 MPa,此时体积密度为590 kg/m3,比强度为6.97 MPa。由X射线衍射测试分析可知,成品中主要的矿物成分为托贝莫来石,此外还有硬石膏和残留的石英等。扫描电镜和能谱分析结果显示,成品中形成了CSH和托贝莫来石相互交织的网状结构,有效的提高了加气混凝土的强度。

用首钢大石河铁尾矿制备蒸压加气混凝土

利用首钢大石河铁尾矿进行制备蒸压加气混凝土的试验研究,为该铁尾矿的资源化利用提供技术依据。结果表明,在铁尾矿磨矿细度为-0.08 mm占97.2%,4种原料铁尾矿、石灰、水泥、石膏的配比为60∶25∶10∶5,铝粉膏加入量为原料总量的0.06%,液固比为0.6,稳泡剂用量为总水量的8%,料浆浇注温度为50℃,静停养护温度和时间分别为60℃和4 h,蒸养压力、温度、时间分别为1.25 MPa、180℃、8 h的条件下,可制得强度等级为A3.5、密度等级为B06的蒸压加气混凝土。X射线衍射分析结果显示,制品中的主要物相是0.9、1.1、1.4 nm托贝莫来石及铁尾矿中的残留矿物。

以合成雪硅钙石为晶种回收废水中的磷

以合成雪硅钙石为晶种,探索了用结晶法以磷酸钙形式回收废水中磷的适宜条件。结果表明,在实验水质条件下,模拟废水pH=8、n(Ca)/n(P)=2、晶种用量大于1.6g/L、振荡24h后溶液中残留磷可达到国家污水综合排放标准一级(0.5mg/L)以下;在优化条件下证实了合成雪硅钙石的供碱能力,循环利用18次,回收磷的效果仍然很好。运用XRD、FTIR、SEM和EDS等测试手段对在实验条件下重复使用18次的雪硅钙石进行了表征,证明回收的磷主要以结晶度不高的羟基磷灰石形态存在。

低品位硅藻土的水热固化过程及其力学性能研究

以低品位硅藻土、氢氧化钙和水为主要原料,系统考察了焙烧活化制度、原料配比、水热反应条件、成型压力等工艺条件,对硅藻土水热固化体力学强度和微观结构的影响规律,并对其作用机制进行细致讨论。实验通过硅藻土的焙烧活化以及反应配比和水热反应参数的优化,控制形成结晶性水化硅酸钙即托勃莫来石相,所获样品具有轻质高强性能特征。研究结果可用于低品位硅藻土的强化固化,并将其转化为具有较高经济价值的建材制品,满足当前市场对高防火性无机建筑保温材料的迫切需求。