RT Dissertation/Thesis
T1 Complete transformation of aluminum waste into zeolite and its use in the removal of pollutants from aqueous solution
A1 Sánchez Hernández, Ruth
AB Zero Waste concept aims to minimize the negative effects of the generation andmanagement of waste on human health and the environment, as well as to reduce theuse of natural resources.The novelty of this Thesis comes from the development of a simple procedure tocompletely transform a hazardous aluminum waste into added-value materials of greatindustrial interest, as zeolites, which are used later as adsorbents for the removal ofheavy metals and ammonium from aqueous effluents. There are not previous worksrelated to the use of the hazardous aluminum waste as a raw material for the synthesisof zeolites.In this work the following stages were developed:i) Characterization of different aluminum wastes to get a representative sample.ii) Lab-scale hydrothermal synthesis and characterization of zeolites from aluminumwaste to define the optimal experimental conditions.iii) Scaling up of the process (bench-scale synthesis) to assess its industrialapplication.iv) Development of a more sustainable synthesis process by alkaline effluentsrecycling in order to achieve a zero waste and zero effluents process.v) Using the zeolites as adsorbents for the removal of heavy metals and ammonium todecontaminate water.Aluminum waste, due to its high aluminum content (Al2O3 ~ 66 wt.%), wascharacterized and used as the only aluminum raw material for the lab- and bench-scalesynthesis of zeolites in the Na2O-Al2O3-SiO2-H2O system. The synthesized zeolitesexhibited high cation exchange capacities (CEC) and suitable adsorption properties,resulting in potential adsorbents for the removal of heavy metals and ammonium fromaqueous solutions. The most relevant hazardous features of aluminum waste derivefrom its mineralogical and chemical composition and very fine granulometry (2.5-93μm). It exhibits spontaneous and exothermic reactivity because its high contents ofmetallic aluminum (12.8 wt.%) and aluminum nitride (13.1 wt.%), in contact with water,can generate toxic gases such as ammonia (71 Nm3 per ton of waste) and/orinflammable and explosive gases like hydrogen (162 Nm3 per ton of waste). Besides, itcontains heavy metals, which can be released by leaching under incorrectmanagement and disposal.The development of a simple and one-step hydrothermal synthesis process enabledthe complete transformation of the waste in zeolite. No other solid residues weregenerated in the zeolitization process. The lab-scale synthesis process resulted intothree types of zeolites: NaP1, Sodalite (SOD), and Analcime (ANA), and led to reactionyields of 2.5 kg of zeolite per kg of waste. The preparation of the zeolites has mainlybeen designed by selecting temperature and alkalizing agent (NaOH) concentration.The optimal lab-scale synthesis conditions were:· The NaP1 zeolite was obtained at 120 ºC for 6 h, using 1 M NaOH and liquid/solidratios of 15-25 mL/g, resulting in a Si/Al ratio of 1.85.· The SOD zeolite was prepared at 120 ºC for 6 h, using the highest alkaliconcentration (5 M NaOH) and a liquid/solid ratio of 25 mL/g, leading to a Si/Al ratioof 1.02.· The ANA zeolite was synthesized at the highest temperature (200 ºC) for 6 h, using1 M NaOH and a liquid/solid ratio of 25 mL/g, resulting in a Si/Al ratio of 1.73.The different zeolites (NaP1, SOD, and ANA) were also synthesized via lab-scalesynthesis with mother liquor recycling, involving a decrease of the raw materialsconsumption.The characterization of the obtained NaP1, SOD, and ANA zeolites revealed that theresulting zeolites showed characteristics and properties similar to those of zeolitesprepared from both pure chemical reagents and other waste sources (fly ash, ricehusk, kaolin, etc.). From an industrial point of view, NaP1 is the zeolite with mostinterest in water treatment applications due to its high CEC (2.73 meq NH4+/g).The scaling up of the synthesis of NaP1 with recycling of alkaline effluents (motherliquor and rinse water) was performed for the optimal conditions to assess thefeasibility and reproducibility of the process. It also led to the complete conversion ofthe waste into highly crystalline zeolite, achieving high reaction yields (2.5 ton of zeoliteper ton of waste). The bench-scale zeolitization process involved not only a reductionof the NaOH and water consumptions, but also a significant cost reduction. Theresulting NaP1 zeolites obtained in the scaling up with alkaline effluents recyclingshowed high CEC (2.27-2.37 meq NH4+/g) as well as structural, morphological, textural,and physical-chemical characteristics similar to those synthesized from fresh NaOHsolutions.The removal of Pb2+, Cd2+, and Hg2+ from aqueous solutions was studied, evaluatingthe effects of adsorption parameters on the single- and multi-cation adsorption process.The kinetic of single-cation adsorption process was found to be very rapid, achievinghigh removal efficiencies: 98.9, 93.3, and 99.3 % for Pb2+, Cd2+, and Hg2+, respectively,in the first 15 min for zeolite doses of 0.5-5 g/L. The experimental maximum removalcapacities of the zeolite were: 183.0, 4.37, and 0.23 mg/g for Pb2+, Cd2+, and Hg2+,respectively. The metal cations could be removed by the zeolite through ahomogeneous and physical adsorption process. The zeolite showed the greatestaffinity for Pb2+, due to its smallest size compared with Cd2+ and Hg2+. The multi-cationremoval efficiency of Pb2+ remained practically unchanged in presence of Hg2+ andCd2+, reaching high removal efficiencies (almost 100 %) both at very low contact times(1 min) and at longer times (30 min) for zeolite doses of 2-10 g/L.The elimination of NH4+ from aqueous solutions was also performed using the zeoliteobtained from the waste as adsorbent. The uptake NH4+ showed a fast kinetic, leadingto removal percentages of 88 % in the first 15 min for a zeolite dose of 5 g/L. Theexperimental maximum removal capacity of the zeolite was 37.9 mg/g for NH4+, similarto that found for other sorbent materials.Finally, it can be concluded that the developed zeolitization process would enable toreduce the amount of aluminum waste, which is generally disposed of in securedeposits (involving high treatment cost), preserving natural resources and hencehelping the sustainability of environment.Accordingly, it implies a synergic effect on the environmental protection: firstly, thetransformation of the hazardous aluminum waste into a zeolite can contribute to itsend-of-waste condition, and secondly, the zeolite obtained from aluminum waste canbe considered as a promising adsorbent used for the treatment of aqueous effluentscontaminated by heavy metals (endocrine disruptors) and other inorganic compounds(ammonium).
YR 2018
FD 2018
LK https://hdl.handle.net/10016/27490
UL https://hdl.handle.net/10016/27490
LA eng
NO Mención Internacional en el título de doctor
DS e-Archivo
RD 1 sept. 2024