Immobilization of Hazardous Wastes on One-Part Blast Furnace Slag-Based Geopolymers

: The immobilization of hazardous wastes in ordinary Portland cement (OPC)-based materials has been widely studied and implemented. OPC-based materials have a high carbon footprint associated with their production and geopolymer materials are a sustainable and eco-friendly alternative. Therefore, this work aimed to immobilize two hazardous industrial wastes: copper wastewater sludge and phosphogypsum in one-part geopolymer materials. For that purpose, the precursor was partially substituted by these wastes (5, 10 and 20 wt.%) in the formulations. The geopolymer fresh and hardened state properties were evaluated, and the immobilisation of pollutants was determined through leaching tests. In phosphogypsum pastes (PG5, PG10 and PG20) it was observed that the compressive strength decreased with the increase in its amount, varying between 67 MPa and 19 MPa. In copper sludge pastes, the compressive strength of the specimens (CWS5 and CWS10) reached ~50 MPa. The mortars, MPG10 and MCWSs10, had compressive strengths of 13 MPa and 21 MPa, respectively. Leaching tests showed that pastes and mortars immobilise the hazardous species of the wastes, except for As from copper sludge, whose the best result was found in the compact paste (CWSs10) that leached 2 mg/kg of As. Results suggest that optimized compositions are suitable for the construction sectorThis research was funded by Ministerio de Ciencia e Innovación (MICINN), grant number PID2020-116461RB-C21 and Agencia de Innovación y Desarrollo de Andalucía (IDEA) grant number UHU-1255876. This work was done in the scope of the project CICECO- Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, co-financed by national funds through the FCT/MEC. This research was funded by FCT (Portuguese Foundation for Science and Technology), grant number 2020.01135.CEECIND (R.M.N.) and SFRH/BD/144562/2019 (J.C.

Abatement of NOx emissions in nitric acid plants during transient regimes

Tese de Doutoramento em Engenharia da Refinação, Petroquímica e Química, apresentada ao Departamento de Engenharia Química da Faculdade de Ciências e Tecnologia da Universidade de CoimbraNOx emissions in nitric acid plants during transient operation periods, specifically, the start-up and shutdown, remains a technologically challenging problem. Despite the presence of downstream NOx abatement reactors aiming to reduce their concentrations to nearly zero, these systems cannot be used during start-up and shutdown since explosive byproducts can be formed. Although the transient emissions do not violate current environmental regulations, they have a perceptual visual impact and may lead to complains from the surrounding populations. Furthermore, stricter regulations are expected in the near future impacting the transient periods and requiring additional operational measures. The present work focus on the NOx absorption process and the main goal is extracting knowledge that can help to reduce the emissions of nitric acid plants during transient regimes. We started by analysing the nitric acid production and alternative NOx abatement processes such as selective catalytic reduction (SCR), electrochemical process, ozone oxidation, absorption with NaOH and with H2O2. The technologies were compared taking into account the cost, complexity, safety, efficiency and potential integration with the nitric acid plant. This study has led to the conclusion that the absorption with hydrogen peroxide seems to be the most promising solution to be installed in the nitric acid plant referred above. The development of a rigorous model capable of reproducing both the steady state and the dynamic behaviour of these units can help industrial players in the optimization and control. Therefore, in this work we propose a new rigorous rate-based model of the NOx absorption column. For this purpose, the operation of the nitric acid plant under analysis was characterized in order to extract knowledge regarding plant's operation, finding consistent set-points which can, subsequently, be used as parameters and initial conditions for the mathematical model developed as well as gathering industrial data that can be used for the model validation. A complete characterization of the absorption column inlet gas stream is currently unknown which has led us to solve a data reconciliation problem to find a consistent composition which takes into account component molar balances at steady state as well as equilibria relationships and measured data. The proposed reactive absorption model was firstly simulated at steady state and fulfils some gaps found in the literature such as, rigorous simulation at nitric acid azeotropic concentration, 68%wt. and high operation pressures, nearly 1000kPa. The developed model is based on the two film theory and takes into account: the gas and liquid kinetic reactions, the heterogeneous equilibrium, the interfacial equilibria, the mass transfer with and without reaction and the tray hydraulics. Despite the extension of the model to new operational concentrations and pressures, the nitrous acid decomposition and the heterogeneous equilibrium were modelled differently from related previous works. Our steady state NOx absorption model was solved as a constrained nonlinear algebraic equation system (formed by approximately 25000 equations) and was implemented in GAMS in order to take advantage of the robust nonlinear optimization solvers available. A combination of numerical techniques was used to consistently initialize the model so that convergence is attained. The model’s prediction was compared with licensor and industrial plant data, regarding the composition of the liquid stream in nitric and nitrous acids combined along the column. A reasonably good agreement is obtained in both cases. Post processing included several sensitivity analyses to infer the behaviour of the NOx absorption column. Finally, the model was extended to predict the transient state of the NOx absorption column. Our new rigorous dynamic mathematical model was implemented in Mathematica requiring several initialization strategies as well as the partition of the simulation total time domain into nth continuous subintervals to avoid discontinuities. The model was validated at steady and transient state considering a situation where a disturbance in the total inlet pressure of plant's nitric acid column occurs. Moreover, the model response to a very rapid ramp disturbance in the total pressure was also analysed. Furthermore, a nitric acid plant start-up was simulated modelling the most important operational procedures. Process responses to modifications in the lateral stream nitric acid concentration and flow rate were analysed as well as in the secondary air flow rate procedure. Finally, based on the gathered knowledge, a critical analysis was done to further reduce the NOx emissions during column's start-up and some guidelines where proposed to Bondalti Chemicals: 1. use all trays available in the column as a way to increase the absorption capacity; 2. lower the lateral feed tray; 3. decrease the lateral feed stream nitric acid concentration; 4. set an optimal procedure for the water flow rate; 5. analyse the reduction of the column's temperature; 6. analyse the impact of using hydrogen peroxide in the absorption column during plant's start-up.As emissões de NOx em fábricas de ácido nítrico durante a operação em regime transiente (nomeadamente nos procedimentos de arranque e paragem) são actualmente um problema. Apesar da existência de um sistema de abatimento dos NOx que reduz as suas concentrações aproximadamente para zero durante o estado estacionário, no arranque e na paragem o sistema não pode ser utilizado devido à formação de nitrito e nitrato de amónia – produtos explosivos. Apesar das emissões não violarem as atuais regulamentações ambientais, têm um impacto visual negativo e podem levar à apresentação de queixas ou petições por parte das populações residentes nas localidades vizinhas. Num futuro próximo são expectáveis legislações mais rigorosas que irão afetar os regimes transientes, requerendo, por isso, medidas adicionais. Este trabalho é focado no estudo do processo de absorção dos óxidos de nitrogénio para reduzir as emissões das fábricas de ácido nítrico durante os regimes de operação transiente. Começámos por analisar o processo de produção do ácido nítrico e os processos de abatimentos dos NOx disponíveis, nomeadamente a redução catalítica selectiva (SCR), processos electroquímicos, oxidação com ozono, absorção com NaOH e com H2O2. As tecnologias foram comparadas tendo em conta o seu custo, complexidadade, segurança, eficiência e potencial de integração com a fábrica alvo deste estudo. Concluiu-se que a absorção com peróxido de hidrogénio aponta ser a tecnologia com maior potencial para ser instalada na unidade fabril. A existência de um modelo matemático detalhado capaz de reproduzir os estados estacionário e transiente pode ajudar a otimizar e controlar a coluna de absorção. Por este motivo, neste trabalho desenvolvemos um novo e rigoroso modelo da coluna de absorção dos NOx. Para tal, a unidade fabril sob o qual este estudo incidiu foi caraterizada de modo a obter conhecimento das operações da fábrica, encontrar dados de referência consistentes e recolher dados industriais fundamentais para a validação do modelo. Estes dados foram subsequentemente usados como parâmetros e/ou condições iniciais para o modelo matemático desenvolvido. Na ausência de uma caracterização completa do gás de entrada da coluna de absorção, resolvemos um problema de reconciliação de dados para encontrar uma composição consistente que tem em conta os balanços molares em estado estacionário, bem como as relações de equilíbrio e dados medidos. O modelo de absorção reativa proposto foi inicialmente simulado em estado estacionário e permite preencher algumas lacunas encontradas na literatura. O estado da arte actual não contempla a simulação rigorosa em concentrações azeotrópicas de ácido nítrico, 68 %wt. e a altas pressões de operação, 1000 kPa. O modelo desenvolvido é baseado na teoria dos dois filmes e tem em conta as reações cinéticas no gás e no líquido, o equilíbrio heterogénio, o equilíbrio interfacial, a transferência de massa com e sem reação e a hidráulica do prato. Além da extensão do modelo para novas concentrações e pressões operacionais, também a decomposição do ácido nitroso e o equilíbrio heterogéneo foram modelados de forma diferente, comparando com trabalhos anteriores disponíveis na literatura. O modelo resultante de absorção dos NOx tem a forma de um sistema de equações algébricas não-lineares, composto por aproximadamente 25.000 equações. Este foi implementado em GAMS para tirar partido dos solvers de otimização não-lineare disponíveis. Foi uitilizada uma combinação de técnicas numéricas para inicializar consistentemente o modelo de forma a obter convergência. Os resultados do modelo foram comparados com dados de referência e com dados industriais tendo em conta a composição de ácidos nítrico e nitroso na fase líquida, verificando-se uma boa concordância entre ambos os casos. De forma a estudar o comportamento da coluna de absorção dos NOx várias análises de sensibilidade foram realizadas. Por fim, o modelo foi estendido para prever o estado transiente da coluna de absorção. O novo e rigoroso modelo dinâmico desenvolvido foi implementado em Mathematica® recorrendo a várias estratégias de inicialização bem como à partição do tempo total de simulação em n subintervalos contínuos para evitar descontinuidades. O modelo escrito nesta nova framework foi validado em estado estacionário e transiente promovendo perturbações na pressão total de entrada da coluna. Foi também analisada a resposta do modelo face a perturbações em rampa muito rápida. Foi ainda simulado um arranque da coluna da fábrica considerando os procedimentos operacionais mais importantes. As respostas do processo à mudança na concentração de ácido nítrico da corrente lateral e do caudal foram analisadas, bem como alterações no procedimento do caudal de ar secundário. O trabalho é concluído com uma análise crítica para reduzir as emissões de NOx durante o arranque da fábrica de ácido nítrico e algumas diretrizes foram propostas à Bondalti Chemicals, nomeadamente: 1. usar todos os pratos disponiveis da coluna por forma a aumentar a capacidade de absorção; 2. baixar o prato de alimentação lateral; 3. reduzir a concentração de ácido nítrico na corrente de alimentação; 4. definir um procedimento optimo para o caudal de alimentação de água; 5. analisar a redução da temperatura da coluna de absorção; 6. analisar o impacto de utilizar o peróxido de hidrogénio na coluna de absorção durante o arranque da fábrica.Bondalti Chemicals (previously known as Companhia de União Fabril -- Químicos Industriais

Development of Coloured Stoneware Bodies through the Incorporation of Industrial Cr/Ni Electroplating Sludge

Electroplating sludge (ES) is currently disposed in landfills and, because of its heavy metal content, poses serious threats to the environment and human health. However, ES might have potential use as colouring agent due to its high concentration of chromium and nickel. Thus, the present work aims at studying the effect of ES incorporation into stoneware bodies. The influence on the final characteristics of fired samples, ES amount and pre-treatment were analysed. It was found that stoneware pastes having uniform brownish hues can be obtained with only 3 wt.% of sieved (<212 μm) ES. The obtained specimens have, once fired, the desired technical and aesthetical characteristics. Further, leaching tests confirmed the immobilisation of hazardous ES species in the ceramic matrix. Hence, it can be concluded that this waste can be used as colouring agent of stoneware pastes substituting commercial pigments and contributing to more sustainable consumption and production in the ceramic sector

Valorization of Fly Ashes and Sands Wastes from Biomass Boilers in One-Part Geopolymers

Fly ash (FA) and exhausted bed sands (sands wastes) that are generated in biomass burners for energy production are two of the wastes generated in the pulp and paper industry. The worldwide production of FA biomass is estimated at 10 million tons/year and is expected to increase. In this context, the present work aims to develop one-part alkali-activated materials with biomass FA (0–100 wt.% of the binder) and sands wastes (100 wt.% of the aggregate). FA from two different boilers, CA and CT, was characterized and the mortar’s properties, in the fresh and hardened conditions, were evaluated. Overall, the incorporation of FA decreases the compressive strength of the specimens. However, values higher than 30 MPa are reached with 50 wt.% of FA incorporation. For CA and CT, the compressive strength of mortars with 28 days of curing was 59.2 MPa (0 wt.%), 56.9 and 57.0 MPa (25 wt.%), 34.9 and 46.8 MPa (50 wt.%), 20.5 and 13.5 MPa (75 wt.%), and 9.2 and 0.2 MPa (100 wt.%), respectively. The other evaluated characteristics (density, water absorption, leached components and freeze–thaw resistance) showed no significant differences, except for the specimen with 100 wt.% of CA. Therefore, this work proved that one-part geopolymeric materials with up to 90 wt.% of pulp and paper industrial residues (FA and sand) can be produced, thus reducing the carbon footprint associated with the construction sector

Waste-Based One-Part Alkali Activated Materials

Ordinary Portland Cement is the most widely used binder in the construction sector; however, a very high carbon footprint is associated with its production process. Consequently, more sustainable alternative construction materials are being investigated, namely, one-part alkali activated materials (AAMs). In this work, waste-based one-part AAMs binders were developed using only a blast furnace slag, as the solid precursor, and sodium metasilicate, as the solid activator. For the first time, mortars in which the commercial sand was replaced by two exhausted sands from biomass boilers (CA and CT) were developed. Firstly, the characterization of the slag and sands (aggregates) was performed. After, the AAMs fresh and hardened state properties were evaluated, being the characterization complemented by FTIR and microstructural analysis. The binder and the mortars prepared with commercial sand presented high compressive strength values after 28 days of curing-56 MPa and 79 MPa, respectively. The mortars developed with exhausted sands exhibit outstanding compressive strength values, 86 and 70 MPa for CT and CA, respectively, and the other material’s properties were not affected. Consequently, this work proved that high compressive strength waste-based one-part AAMs mortars can be produced and that it is feasible to use another waste as aggregate in the mortar’s formulations: the exhausted sands from biomass boilers