Extraction and characterization of alumina nanopowders from aluminum dross by acid dissolution process

A significant amount of aluminum dross is available as a waste in foundry industries in Bangladesh. In this study, alumina was ex- tracted from aluminum dross collected from two foundry industries situated in Dhamrai and Manikgang, near the capital city, Dhaka. Alu- minum dross samples were found to approximately contain 75wt% A1203 and 12wt% SIO2. An acid dissolution process was used to recover the alumina value from the dross. The effects of various parameters, e.g., temperature, acid concentration, and leaching time, on the extrac- tion of alumina were studied to optimize the dissolution process. First, AI（OH）3 was produced in the form of a gel. Calcination of the AI（OH）3 gel at 1000℃, 1200℃, and 1400℃ for 2 h produced O-AlcOa, （t~＋O）-A1203, and u-alumina powder, respectively. Thermal charac- terization of the AI（OH）3 gel was performed by thermogravimetric/differential thermal analysis （TG/DTA） and differential scanning calo- rimetry （DSC）. The phases and crystallite size of the alumina were determined by X-ray diffraction analysis. The dimensions of the alumina were found to be on the nano level. The chemical compositions of the aluminum dross and alumina were determined by X-ray fluorescence （XRF） spectroscopy. The microstructure and morphology of the alumina were studied with scanning electron microscopy. The purity of the alumina extracted in this study was found to be 99.0%. Thus, it is expected that the obtained alumina powders can be potentially utilized as biomaterials.

Process of aluminum dross recycling and life cycle assessment for Al-Si alloys and brown fused alumina

In 2008,around 596 000 t of aluminum dross was generated from secondary aluminum industry in China;however,it was not sufficiently recycled yet.Approximately 95% of the Al dross was land filled without innocent treatment.The purpose of this work is to investigate Al dross recycling by environmentally efficient and friendly methods.Two methods of Al dross recycling which could utilize Al dross efficiently were presented.High-quality aluminum-silicon alloys and brown fused alumina(BFA) were produced successfully by recycling Al dross.Then,life cycle assessment(LCA) was performed to evaluate environmental impact of two methods of Al dross recycling process.The results show that the two methods are reasonable and the average recovery rate of Al dross is up to 98%.As the LCA results indicate,they have some advantages such as less natural resource consumption and pollutant emissions,which efficiently relieves the burden on the environment in electrolytic aluminum and secondary aluminum industry.

Removal of AlN from secondary aluminum dross by pyrometallurgical treatment

A new process of AlN removal from secondary aluminum dross(SAD)by pyrometallurgical treatment with added cryolite was applied for solving the problem of recycling the secondary aluminum dross.The response surface methodology(RSM)was used to design experiments and optimize parameters.The results show that adding the appropriate amount of cryolite can effectively promote the oxidation of AlN in the SAD,and too much cryolite will reduce the promotion effect.The effects of roasting temperature and cryolite on the denitrification rate are the most significant(p<0.0001)followed by holding time.Predicted values of the denitrification rate are found to be in good agreement with experimental values(R^(2)=0.9894 and R_(adj)^(2)=0.9775),which confirms the validity of the model employed.The optimum conditions of roasting temperature of 750°C,holding time of 194 min,mass fraction of cryolite of 17.7%are obtained according to the quadratic model.Under these conditions,the maximum actual denitrification rate reaches 94.71%and the AlN content in the SAD is only 0.55 wt%.The unfired brick with compressive strength of 18.62 MPa(GB/T 2542−2012)was prepared based on the roasted SAD.

Feasibility of aluminum recovery and MgAl_2O_4 spinel synthesis from secondary aluminum dross

The feasibility of aluminum recovery from secondary aluminum dross by extraction with NaOH solution and the subsequent synthesis of MgAl_2O_4 spinel by sintering the extracted slag were studied. The extraction percentage of soluble aluminum from the dross reached 80% at a temperature of 353 K, liquid-to-solid ratio of 12 mL·g^(-1), stirring speed of 300 r·min^(-1), and an extraction time of 15 min; the hydrolysis percentage of AlN reached 40% with an extraction time of 30 min. The activation energies of the soluble aluminum and AlN extracted from the dross were 7.15 and 8.98 kJ·mol^(-1), respectively, indicating that their kinetics were controlled by outer diffusion without a product layer. The extracted slag was sintered in the temperature range 1373–1773 K; MgAl_2O_4 spinel with a compressive strength as high as 69.4 MPa was produced in the sample sintered at 1673 K for 3 h. This value exceeds the threshold(40 MPa) prescribed by the National Standard for the Magnesia and Magnesia-alumina Refractory Bricks of China(GB/T 2275-2007). These results establish the effectiveness of aluminum recovery from secondary aluminum dross and subsequent MgAl_2O_4 spinel synthesis.

Recycling of Secondary Aluminum Dross to Fabricate Porous <i>γ</i>-Al₂O₃Assisted by Corn Straw as Biotemplate

In the aluminum industry, secondary aluminum dross (SAD) is an inevitable solid residue, which usually contains 30 - 70 wt% Al2O3. In this work, Al(OH)3 was extracted from SAD through acid-leaching and alkali purification process. The as-obtained Al(OH)3 precipitation then was calcinated to synthesize porous γ-Al2O3 assisting by an agricultural waste biomass-corn straw as biotemplate. Effects of H2SO4 concentration, reaction temperature and time on the recovery of SAD were investigated. Furthermore, the dependence of calcination temperature on specific surface area, pore volume and content of porous γ-Al2O3 was analyzed. X-ray diffraction (XRD) and X-ray fluorescence (XRF) were used to inspect the phase compositions and their contents, respectively. Scanning electron microscopy (SEM) was employed to analyze the morphologies of the sintered porous γ-Al2O3. It was found that the highest recycle rate of aluminum from SAD was obtained under optimum conditions of 80&#176;C, acid concentration of 1.6 mol/l, and reaction time of 5 h by acid process. The porous γ-Al2O3 with specific surface area, 261.22 m2/g and average pore diameter, 52.64 nm, was obtained under calcination at 850&#176;C through mixing the as-obtained Al(OH)3 precipitation and corn straw.

Dissolution characteristics of black aluminum dross in Na_(3)AIF_(6)-AIF_(3)-Al_(2)O_(3)molten salt system

The dissolution performance of black aluminum dross(BAD)in cryolite electrolyte is key to its recovery by molten salt electrolysis.The stable operation of the electrolyzer depends mainly on the rapid dissolution of BAD in Na_(3)AlF_(6)-AlF_(3)-Al_(2)O_(3)electrolyte system.In this paper,the dissolution performance and behavior of BAD and its main components in the cryolite system were studied,and the saturation solubility of aluminum nitride in this system was determined.The dissolution performance of BAD in cryolite electrolyte before and after denitration was compared,and the effects of temperature,cryolite ratio,and the doping ratio of BAD and alumina on the dissolution rate were investigated.The obtained results showed that aluminum nitride was the main factor affecting the dissolution performance of BAD in the electrolyte.Aluminum nitride was partly converted toα-Al_(2)O_(3)after addition to the electrolyte,and the convertedα-Al_(2)O_(3)was partially dissolved in the cryolite electrolyte,while the remaining precipitated and accumulated at the bottom with aluminum nitride.Aluminum nitride was almost insoluble in the cryolite electrolyte,with 0.0022%solubility.A higher proportion ofα-Al_(2)O_(3)in BAD was negatively influenced its solubility in the cryolite electrolyte.The dissolution rate of BAD in cryolite electrolytes was effectively improved by mixing BAD withγ-Al_(2)O_(3).

Research of Microstructure,Phase,and Mechanical Properties of Aluminum-Dross-Based Porous Ceramics

In this study,the effect of sintering temperature and the addition of kaolin,a sintering agent,on the microscopic,phase,and mechanical properties of ceramics were investigated using secondary aluminum dross(SAD)as the main component in the manufacturing of ceramics.The basic phases of the ceramics were Al_(2)O_(3),MgAl_(2)O_(4),NaAl_(11)O_(17),and SiO_(2)without the addition of kaolin.The diffraction peaks of MgAl_(2)O_(4),NaAl_(11)O_(17),and SiO_(2)kept decreasing while those of Al_(2)O_(3)kept increasing with an increase in temperature.In addition,the increase in temperature promoted the growth of the grains.The grains were uniform in size and regular in distribution,with a shrinkage of 2.2%,porosity of 72.5%,bulk density of 1.076 g/cm^(3),and compressive strength of 1.12 MPa.When the sintering temperature was 1450°C,the basic phases of the ceramic after the addition of kaolin were Al_(2)O_(3),MgAl_(2)O_(4),NaAl_(11)O_(17),and SiO_(2).With the increase of kaolin,the diffraction peaks of NaAl_(11)O_(17)and SiO_(2)decreased until they disappeared,while the diffraction peaks of Al_(2)O_(3)increased significantly.When kaolin was added at 30 wt.%,the ceramics obtained had shrinkage of 18%,a porosity of 47.26%,a bulk density of 1.965 g/cm^(3),and compressive strength of 31.9 MPa.Cracks existed inside the ceramics without the addition of kaolin,while the addition of kaolin significantly changed this defect.It is shown that SAD can obtain porous ceramics with good properties at a sintering temperature of 1450°C and a kaolin addition of 30 wt.%.

Multi-stage Electrostatic Separation for Recovering of Aluminum from Fine Granules of Black Dross

Separation of aluminum from fine granules of black dross, which is a waste by-product in secondary aluminum production, was investigated. The separation was performed by a multi-stage electrostatic separation method. There are three stages to complete the separation, including preliminary separation, pulse charging enhancement and secondary concentration. Chemical and mineralogical compositions of collection products were analyzed and determined by X-ray diffraction(XRD) and X-ray Fluorescence(XRF). After multistage electrostatic separation, the Al2O3 content of the collection products increases from 50.74% to 69.77%.The mineralogical phase analysis indicates that the final recovery of metallic aluminum phase increases from 8%to 37%, and the aluminum oxide phase increases from 20% to 26%. The research results show the multi-stage electrostatic separation method is effective for recovering of aluminum from fine granules of black dross, and upgrades the black dross to a recoverable material.

Phase Composition Analysis of TiN-AI_2O_3Synthesized from Aluminum-containing Dross and Rutile by Aluminothermic Reductionnitridation Method

TiN- Al2O3 composite powder was prepared by aluminothermic reduction- nitridation method with starting materials of aluminum-containing dross and rutile,and metallic aluminum in the aluminum-containing dross as reducer. The influences of synthesis temperature（600-1 400 ℃） and aluminum-containing dross addition（20% lower than theoretical value,theoretical value,20% higher than theoretical value,and 50% higher than theoretical value） on phase compositions and microstructure of the composites were investigated,and the reaction mechanism was analyzed. The results show that（1） TiN- Al2O3 composite powder can be synthesized under the experimental conditions; the main phases are TiN,α-Al2O3,a little bytownite,and MgAl2O4;（2）enhancing synthesis temperature or increasing aluminumcontaining dross addition favors the reaction of aluminothermic reduction- nitridation;（3） in the synthesized products,α-Al2O3 is platy or columnar; TiN is sub-micron granular,which reinforces and toughens the composite.

二次铝灰产品化方案及评价

综述了近年来以二次铝灰为原料制备氧化铝、净水剂、耐火材料、冰晶石、分子筛和陶瓷材料的现状,同时分析其产品及技术特点,对二次铝灰产品化利用给出评价和建议。

Characterization of Solid Wastes from Aluminum Tertiary Sector: The Current State of Spanish Industry

Aluminum recycling is an important activity that allows returning this metal to the market saving energy and resources. This activity generates slag and dross, both hazardous materials, which are recovered by other industries (tertiary sector). In that process, new wastes are produced, but most of them are disposed in security storage facilities because of their hazardousness and scarce marketable value. In Spain, the statistical data analysis on waste reveals that this sector is increasing every year. This study aims to characterize the wastes generated by the tertiary aluminum industries in Spain. Samples were collected in different aluminum recycling industries and characterized by chemical analyses, X-ray fluorescence, X-ray diffraction and particle size determination. Wastes rich in aluminum oxide and alkaline elements also comprise metallic aluminum and aluminum nitride. Such components are the main responsible for the waste hazardousness since they generate toxic gases in the presence of water. Besides, their fine granulometry (x50 < 30 μm) also contributes highly to the hazardousness.

二次铝灰无害化处理和资源化利用研究进展

二次铝灰是铝熔渣经提取金属铝后得到的固体废弃物,含有氮化铝以及盐类精炼剂,二次铝灰具有污染和资源的双重属性,长期堆存会对环境构成威胁,而夹杂其中的铝化合物可用于二次回收利用,缓解环境危机。目前,二次铝灰的回收利用方法主要包括湿法冶金和火法冶金,湿法冶金主要是将二次铝灰进行溶解,提取里面的铝元素制备氧化铝、聚合氯化铝等;火法冶金主要是在高温条件下煅烧,制备微晶玻璃、耐火材料等。本文总结了二次铝灰的危害,概述了二次铝灰的无害化处理和资源化利用的现状,以期提高二次铝灰的资源化利用效率,降低二次铝灰对环境的污染。

铝灰水解制氢过程动力学研究

研究设计了一套铝灰水解制氢装置,考察了反应温度、液固体积质量比、搅拌速度及铝灰粒径对铝灰水解制氢过程的影响,并探讨了铝灰水解制氢过程的动力学。结果表明:铝灰水解制氢的最佳工艺条件为反应温度85℃,液固体积质量比10 mL/1 g,搅拌速度130 r/min,铝灰粒径>80目;最佳条件下所得水解渣的主要物相为MgAl_(2)O_(4)、Al(OH)_(3)及Al_(2)O_(3);铝灰水解制氢过程受化学反应控制,化学表观活化能为67.01 kJ/mol,浸出过程符合Avrami-Erofeyev模型。该法可为铝灰水解制氢工艺过程的设计提供一定技术参考。

我国铝工业固危废资源化利用现状及发展趋势

系统梳理了我国铝工业大宗固危废赤泥、铝灰、电解槽大修渣、阳极炭渣的产排情况及对环境的危害,总结了当前各种固危废资源化利用的技术研发和工业化应用的现状,剖析了当前固危废资源化利用中存在的主要问题,指出了我国铝工业固危废安全治理及资源化利用技术的研究及发展趋势。

钙固化碱焙烧−水浸法从二次铝渣中分离氟和铝

设计一种钙固化碱焙烧−水浸出联合工艺处置二次铝渣,研究CaO用量、NaOH用量、焙烧温度和时间对铝溶出和氟固化行为的影响。在最佳实验条件(焙烧温度1000℃、Al与NaOH摩尔比1꞉0.6、F与CaO摩尔比1꞉2.5、焙烧时间2.0 h)下,氟和铝被分离,其中氟固化率为99.98%,铝溶出率为52.97%。水浸液经蒸发结晶,可得到符合中国工业标准的NaAlO_(2)产品;水浸渣可作为速凝水泥原料。总体而言,此研究为处置二次铝渣提供了一个有效、环保的解决方案。

混掺垃圾飞灰和二次铝灰活性粉末混凝土性能研究

将二次铝灰(SAD)与焚烧垃圾飞灰(WFA)混掺制备成活性粉末混凝土(RPC),研究二次铝灰在两种混合料中的掺量对RPC流变性能参数(扩展度和塑性黏度)、抗折强度、抗压强度以及干燥收缩率的影响,并测定RPC在水中的重金属元素(Cr和Zn)渗出量;观察RPC的微观形貌,揭示RPC性能的机理。结果表明:当二次铝灰的掺量为60%时,RPC的扩展度、抗折强度与抗压强度以及干燥收缩率达到最高,此时RPC的塑性黏度值最小;RPC中Cr与Zn的渗出量与其渗出时间成正相关,与RPC中二次铝灰的掺量成反相关;当二次铝灰掺入60%时,RPC的微观结构最密实。

铝灰综合利用技术及应用研究

文章简要介绍了铝灰的来源和分类,概述了一次铝灰提铝的不同方法和应用,综述了二次铝灰湿法处理、火法处理、湿法火法联合处理及其他技术的研究和应用现状。针对铝灰综合利用目前存在的问题,提出了分质梯级利用技术,详细介绍了其工艺流程及优势,展望了铝灰综合利用的未来发展趋势。

二次铝灰脱氮制备铝酸钙的实验研究

铝及铝材熔铸过程产生的铝灰中含有大量氧化铝,是重要的二次含铝资源。作为铝工业的危险固体废弃物,铝灰可以转化为价值较高的铝酸钙、氢氧化铝等产品。本文以二次铝灰为原料、碳酸钙为药剂制备铝酸钙,探讨了钙铝比、保温时间及焙烧温度对铝酸钙制备工艺的影响,结果表明:在钙铝比1.1~1.2,保温时间1.25~1.5 h,焙烧温度1150~1200℃的条件下,产物中C_(12)A_7的质量分数较高。各因素影响的次序是:钙铝比的影响显著,保温时间次之,焙烧温度最弱。在钙铝比1.2、保温时间1.5 h、焙烧温度1150℃的条件下制备了铝酸钙,产品中C_(12)A_7的质量分数为75.1%,含少量镁铝尖晶石和硅酸盐。初步探讨了二次铝灰中氧化铝和碳酸钙的固-固反应机理。

预处理二次铝灰制备炼钢用铝酸钙

二次铝灰是铝工业产生的危险废物,同时也是一种富铝资源。以二次铝灰湿法预处理高铝料和石灰石为原料,通过混合、球磨、成型、烧结工艺制备炼钢用铝酸钙。优选了铝酸钙的最佳制备工艺条件为:高铝料与石灰石质量比0.50、烧结温度1350℃、成型压力10 MPa,制备的铝酸钙样品Al_(2)O_(3)和CaO含量符合《炼钢用预熔型铝酸钙》(YB/T 4265—2011)CA-40牌号成分要求,主要物相为12CaO·7Al_(2)O_(3),同时具有低硅、低镁、低氧化铁、低磷、低硫、低氟和低碳的性能,熔点为1378℃,符合炼钢用预熔型铝酸钙产品质量标准要求。

利用低压电瓷废料和二次铝灰制备莫来石陶瓷基多孔骨料

为找到一种有效且低成本的多孔骨料制备新工艺,同时缓解工业固废对社会、环境和经济产生的压力,以低压电瓷废料和二次铝灰为主要原料,活性炭粉为造孔剂,采用低温烧结法制备了莫来石陶瓷基多孔骨料,研究了二次铝灰加入量(加入质量分数为5%~40%)对试样性能的影响。结果表明:1)随着二次铝灰加入量的增加,试样的容重逐渐降低,而显气孔率逐渐增加,最终两者均趋于稳定,线收缩率先略微增加后降低,室温压缩强度逐渐降低。2)二次铝灰的加入一方面促进了莫来石晶核的形成,并降低了铝硅液相的黏度,从而使内部气体更容易通过液相扩散到材料表面,形成较大的孔隙;另一方面莫来石晶体线生长速率增加伴随的体积膨胀进一步抑制了液相的烧结收缩。室温压缩强度下降与液相黏度降低有关,冷却到室温后骨料表面形成一层铝硅玻璃相涂层,微孔数目降低,大孔隙数目增加,导致孔隙周围应力集中增加。3)当二次铝灰加入量为25%(w)时,试样的综合性能最优。