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我国高铝粉煤灰年产量约2500万t，基本处于堆存状态，造成资源巨大浪费及环境严重污染，亟待资源化利用。亚熔盐法高铝粉煤灰提取氧化铝技术可实现氧化铝的高效提取，应用前景广阔。本论文围绕亚熔盐法高铝粉煤灰提铝渣的资源化利用，以硅组分的资源化利用为目标，开展了粉煤灰硅组分形态变化、提铝渣分解转化、水化硅酸钙新材料制备等应用基础研究，取得如下创新性成果： （1）首次系统研究了不同煤在不同压力下燃烧产生粉煤灰的组分变化规律。在相同燃烧条件下，美国PRB次烟煤燃烧产生的亚微米颗粒（0~500 nm）的峰值粒径和峰值数浓度最大，分别为44.5 nm和6.29×107 #/cm3；印度Chandrapur褐煤次之，分别为30.0 nm和4.12×107 #/cm3；中国山西褐煤最小，分别为13.6 nm和1.78×106 #/cm3。增大压力，三种不同煤燃烧产生的亚微米颗粒的峰值粒径逐渐增大，而峰值数浓度逐渐减小。美国PRB粉煤灰矿相主要包含石英、硬石膏、石灰和赤铁矿，其Ca含量较大。印度Chandrapur和中国山西粉煤灰矿相都主要包含石英和莫来石；印度Chandrapur粉煤灰的Si含量最大，而中国山西粉煤灰的Al含量最大。此外，增大压力，较易挥发的物质（Na、Mg、Fe和Ca）富集于亚微米颗粒中，而较难挥发的物质（Si和Al）也会部分转至亚微米颗粒中。（2）阐明了粒度和包覆效应对高铝粉煤灰提铝渣在氢氧化钠稀溶液中分解转化为水化硅酸钙的影响规律和反应机理。通过减小提铝渣粒度，可以显著改善其分解转化率，降低产物的Na2O含量，提铝渣粒度由50-74 μm减小至50 μm以下时，产物Na2O含量可由6.30 wt%降至2.44 wt%。揭示了提铝渣（NaCaHSiO4）分解反应的反应机理符合未反应缩核模型。通过动力学研究发现粒度大的提铝渣分解反应主要为产物层扩散控制，而粒度小的提铝渣分解反应主要为化学反应控制，表明通过减小粒度，可以减弱包覆效应和产物层扩散的影响，从而明显增大提铝渣的分解转化率，并显著减小产物的Na2O含量。（3）提出了高铝粉煤灰提铝渣在碳酸钠浓溶液中分解转化新思路，获得了优化反应条件，并揭示了其分解转化规律。在反应温度为180 ℃，Na2CO3浓度为170 g/L，液固比为10 mL/g，反应时间为2 h的优化条件下，产物的Na2O含量为1.02 wt%，低于NaOH稀溶液分解转化提铝渣的产物Na2O含量（>2 wt%）。反应溶液的液固比为10 mL/g，反应后的溶液具有更高的Na2O浓度（100 g/L），与NaOH稀溶液工艺的Na2O浓度为20 g/L，液固比为20 mL/g相比，Na2CO3浓溶液工艺在Na+循环至亚熔盐法提取氧化铝工艺（Na2O浓度为500 g/L）时，生产每吨氧化铝碱循环部分的水蒸发量由约30 m3降低至约15 m3，碱液蒸发浓度比值从25降低至5，能耗大大降低。（4）建立了水化硅酸钙性能调控新方法。Ca/Si（Ca和Si的摩尔比）由0.8增大至1.4，托贝莫来石的衍射峰强度减弱，产物的Na2O含量由0.80 wt%减小至0.48 wt%，托贝莫来石硅酸盐链的聚合度减小，形成更多碎片状产物，颗粒变松散，孔隙率增大，产物的导热系数减小。Al/Si（Al和Si的摩尔比）由0.05增大至0.20，含铝托贝莫来石的衍射峰强度增强，铝嵌入到托贝莫来石的硅酸盐链结构中使其聚合度增大，更多的Al3+取代Si4+引起更高的电荷逆差导致吸附或者键合更多的Na+来平衡电荷，产物的Na2O含量由0.73 wt%增大至1.82 wt%，产物中纤维数量增多，孔隙率增大，产物的导热系数减小。（5）以粉煤灰提铝渣为原料制备了细长纳米纤维缠绕的变针硅钙石型水化硅酸钙，成型为绝热材料后，其密度小至157.16 kg/m3，孔隙率高达93.56%，而导热系数小至0.0473 W/(m?K)，优于国标GB/T 10699-2015中170号（密度≤170 kg/m3）的导热系数要求（≤0.058 W/(m?K)）。此外，以粉煤灰提铝渣制备了托贝莫来石型水化硅酸钙绝热材料产品，其导热系数为0.0586 W/(m?K)，优于国标GB/T 10699-2015中相应导热系数要求（≤0.065 W/(m?K)）。（6）以纤维状含铝托贝莫来石型水化硅酸钙为主要原料，制备了新型免蒸压纤维增强硅酸钙板产品。纤维增强硅酸钙板的优化制备条件为成型压力45 MPa，纸浆纤维掺量5 wt%和水泥掺量20 wt%。优化条件制备的纤维增强硅酸钙板的抗折强度和导热系数分别为10.55 MPa和0.2424 W/(m?K)，优于国标JC/T 564.1–2008中相应性能要求。明晰了其增韧机理是纤维和基质间存在良好的粘附和渗透，水泥粒子均匀填充于硅酸钙板的孔隙，并且水泥的固化作用增强了纤维和基质间的粘结性，增大了抵抗剪切破坏力和弯曲力的能力。 ;The annual generation of high alumina fly ash (HAFA) in China is approximately 25 million tons, most of them are basically disposed in landfills, causing huge waste of resources and serious environmental pollution. Therefore, it is necessary to develop technologies for resource utilization of HAFA. The extraction of alumina from HAFA by sub-molten salt method can realize the efficient extraction of alumina, which has broad prospects in application. This dissertation focused on the resource utilization of alumina-extracted residue (AER) from HAFA by sub-molten salt method, aiming at the resorce utilization of silicon components. The applied basic researches of the change of silicon components in coal fly ash, the decomposition and transformation of AER, and the preparation of calcium silicate hydrate new materials were carried out. The innovative achievements are as follows:(1) For the first time, the component changing rule of fly ash generated from the combustion of different coals under various pressure conditions were systematically investigated. Under the same combusting conditions, US PRB sub-bituminous generated submicrometer particles (0~500 nm) with the largest peak size and the highest number concentration, which were 44.5 nm and 6.29×107 #/cm3, respectively; India Chandrapur lignite took second place, which were 30.0 nm and 4.12×107 #/cm3, respectively; while China Shanxi lignite generated submicrometer particles with the smallest peak size and the lowest number concentration, which were 13.6 nm and 1.78×106 #/cm3, respectively. With an increase in pressure, for all three coals, the peak particle size of submicrometer particles increased and the total number concentration decreased. Moreover, US PRB coal fly ash mainly contained quartz, anhydrite, lime, and hematite, with a higher Ca content. India Chandrapur and China Shanxi coal fly ash mainly contained quartz and mullite. India Chandrapur coal fly ash specimens had the highest Si content, while China Shanxi coal fly ash specimens contained the largest amount of Al. For all three coal types, by increasing pressure, the more volatile species (Na, Mg, Fe, and Ca) were enriched in the submicrometer particles, and less volatile species (Si and Al) were also partially transferred into submicrometer particles.(2) The effects of particle size and reactant coating on the decomposition and transformation of AER to calcium silicate hydrate in sodium hydroxide diluted solution and the reaction mechanism were studied. By decreasing the particle size, the decomposition and transformation rate of AER could be enhanced obviously and the Na2O content of the products could be decreased effectively. The Na2O content of the product was decreased from 6.30 wt% to 2.44 wt% when the particle size of AER was decreased from 50-74 μm to below 50 μm. The results revealed that the decomposition reaction kinetics of AER (NaCaHSiO4) corresponded with shrinking unreacted core models. According to the kinetic study, the decomposition reaction of AER with larger particle size was mainly under product layer diffusion control, and that of AER with smaller particle size was mainly under chemical reaction control. Therefore, by decreasing the particle size, the effect of reactant coating and product layer diffusion was weakened, thus the decomposition reaction rate of AER could be enhanced obviously and Na2O content of the products could be decreased effectively.(3) A novel method for the decomposition and transformation of AER in concentrated sodium carbonate solution was presented. The optimal conditions were obtained, and the decomposition and transformation rule were revealed. Under optimal conditions of reaction temperature = 180 °C, Na2CO3 concentration = 170 g/L, liquid-to-solid ratio = 10 mL/g, and reaction time = 2 h, a low Na2O content of 1.02 wt% of the products was achieved, which is lower than that (>2 wt%) of products from the decomposition and transformation of AER in diluted NaOH solution. The liquid-to-solid ratio of the reaction solution was 10 mL/g, and the solution after reaction had a higher concentration of Na2O (100 g/L), when Na+ solution was recycled to the alumina extraction process (Na2O = 500 g/L), the evaporated quantity of water for production of alumina per ton was decreased from 30 m3 to 15 m3, approximately, and the concentration ratio for the evoporation of the Na+ solution was decreased from 25 to 5, compared with the NaOH diluted solution process (Na2O = 20 g/L, liquid-to-solid ratio = 20 mL/g), the energy consumption was greatly reduced.(4) New methods for adjusting and controlling the properties of calcium silicate hydrate were developed. By increasing Ca/Si (molar ratio of Ca and Si) from 0.8 to 1.4, the intensities of the diffraction peaks of tobermorite were decreased, the Na2O content of the product was decreased from 0.80 wt% to 0.48 wt%, the degree of polymerization of the silicate chains of tobermorite was decreased, more fragmentary products were formed, the particles became loose, the porosity was increased, and the thermal conductivity of the product was decreased. By increasing Al/Si (molar ratio of Al and Si) from 0.05 to 0.20, the intensities of the diffraction peaks of aluminum tobermorite were increased, the degree of polymerization of the silicate chains of tobermorite was increased because of the incorporation of aluminum into the silicate structure of tobermorite, the greater charge deficit due to the replacement of Si4+ by Al3+ ions was compensated by increased adsorption or binding of Na+, the Na2O content of the product was increased from 0.73 wt% to 1.82 wt%, more fiber products were formed, the porosity was increased, and the thermal conductivity of the product was decreased.(5) The long nanofiber intertwined foshagite type calcium silicate hydrate was prepared from AER. The thermal insulation was molded, the density was as low as 157.16 kg/m3, the porosity was as high as 93.56 %, and the thermal conductivity was as low as 0.0473 W/(m?K), which was superior to the thermal conductivity requirement (≤ 0.058 W/(m?K)) of 170# thermal insulation (Density ≤ 170 kg/m3) according to GB/T 10699-2015. In addition, the tobermorite type calcium silicate hydrate thermal insulation product was prepared from AER. The thermal conductivity of the product was 0.0586 W/(m?K), which was superior to the thermal conductivity requirement (≤ 0.065 W/(m?K)) of corresponding thermal insulation according to GB/T 10699-2015.(6) A novel non-autoclaved fiber reinforced calcium silicate board product was prepared from fibrous aluminum tobermorite type calcium silicate hydrate. The optimal conditions for preparation of fiber reinforced calcium silicate board were: moulding pressure of 45 MPa, pulp fiber content of 5 wt%, and cement content of 20 wt%. Under optimal conditions, the fiber reinforced calcium silicate board had a high flexural strength of 10.55 MPa and low thermal conductivity of 0.2424 W/(m?K), which were superior to the corresponding properties requirements according to national standard JC/T 564.1–2008. The toughing mechanisms of the fiber reinforced calcium silicate board were that the fibers and the matrix had good adhesion and penetration, the cement particles were uniformly filled in the pores of the calcium silicae board, and the solidification of cement increased cohesiveness between the fibers and the matrix, enhancing the ability of the board to withstand the shear failure and bending force.
|汪泽华. 亚熔盐法粉煤灰提铝渣资源化利用应用基础研究[D]. 中国科学院大学,2019.|
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