Desarrollo de conglomerados con la incorporación de cenizas volantes procedentes de la incineración de residuos sólidos urbanos

Esta tesis presenta los resultados de la investigación realizada sobre la inertización de cenizas volantes procedentes de residuos sólidos urbanos y su posterior encapsulación en distintas matrices de mortero. Durante el proceso de inertización, se ha logrado la inertización de éste residuo tóxico y peligroso (RTP) y también su valorización como subproducto. De esta forma se dispone de nueva “materia prima” a bajo coste y la eliminación de un residuo tóxico y peligroso con la consiguiente conservación de recursos naturales alternativos. La caracterización química de las cenizas analizadas refleja que éstas presentan altas concentraciones de cloruros, Zn y Pb. Durante la investigación se ha desarrollado un proceso de inertización de las cenizas volantes con bicarbonato sódico (NaHCO3) que reduce en un 99% el contenido en cloruros y mantiene el pH en valores óptimos para que la concentración de los metales pesados en el lixiviado sea mínima debido a su estabilización en forma de carbonatos insolubles. Se han elaborado morteros con cuatro tipos distintos de cementos (CEM-I, CEM-II, CAC y CSA) incorporando cenizas volantes inertizadas en una proporción igual a un 10% en peso del árido utilizado. Los morteros ensayados abarcan distintas dosificaciones tanto en la utilización de áridos con distintos diámetros (0/2 y 0/4), como en la relación cemento/árido (1/1 y 1/3). Se han obtenido las propiedades físicas y mecánicas de estos morteros mediante ensayos de Trabajabilidad, Estabilidad Dimensional, Carbonatación, Porosidad y Resistencias Mecánicas. De igual forma, se presentan resultados de ensayos de lixiviación de Zn, Pb, Cu y Cd, sobre probetas monolíticas de los morteros con los mejores comportamientos físico/mecánicos, donde se ha analizado el contenido en iones de dichos metales pesados lixiviados mediante determinación voltamperométrica de redisolución anódica Se concluye que todos los morteros ensayados son técnicamente aceptables, siendo los más favorables los elaborados con Cemento de Sulfoaluminato de Calcio (CSA) y con Cemento de Aluminato de Calcio (CAC). En este último caso, se mejoran las resistencias a compresión de los morteros de referencia en más de un 48%, y las resistencias a flexión en más de un 67%. De igual forma, los ensayos de lixiviado revelan la completa encapsulación de los iones de Zn y la mitigación en el lixiviado de los iones de Pb. Ambos morteros podrían ser perfectamente validos en actuaciones en las que se necesitase un producto de fraguado rápido, altas resistencias iniciales y compensación de las retracciones con una elevada estabilidad dimensional. En base a esto, el material podría ser utilizado como mortero de reparación en viales y pavimentos que requiriesen altas prestaciones, tales como: soleras industriales, pistas de aterrizaje, aparcamientos, etc. O bien, para la confección de elementos prefabricados sin armaduras estructurales, dada su elevada resistencia a flexión. ABSTRACT This dissertation presents the results of a research on inerting fly ash from urban solid waste and its subsequent encapsulation in mortar matrixes. The inerting of this hazardous toxic waste, as well as its valorization as a by-product has been achieved. In this way, a new "raw material" is available through a simple process and the toxic and hazardous waste is eliminated, and consequently, conservation of alternative natural resources is strengthened. Chemical analysis of the ashes analyzed shows high concentrations of soluble chlorides, Zn and Pb. An inerting process of fly ash with sodium bicarbonate (NaHCO3) has been developed which reduces 99% the content of chlorides and maintains pH at optimal values, so that the concentration of heavy metals in the leachate is minimum, due to its stabilization in the form of insoluble carbonates. Mortars with four different types of cements (CEM-I, CEM-II, CAC and CSA) have been developed by the addition of inertized fly ash in the form of carbonates, in the proportion of 10% in weight of the aggregates used. The samples tested include different proportions in the use of aggregates with different sizes (0/2 and 0/4), and in the cement/aggregate ratio (1/1 and 1/3). Physical/mechanical properties of these mortars have been studied through workability, dimensional stability, carbonation, porosity and mechanic strength tests. Leaching tests of Zn, Pb, Cu and Cd ions are also being performed on monolithic samples of the best behavioral mortars. The content in leachated heavy metal ions is being analyzed through stripping voltammetry determination. Conclusions drawn are that the tested CAC and CSA cement mortars present much better behavior than those of CEM-I and CEM-II cement. The results are especially remarkable for the CAC cement mortars, improving reference mortars compression strengths in more than 48%, and also bending strengths in more than 67%. Leaching tests confirm that the encapsulation of Zn and Pb is achieved and leachate of both ions is mitigated within the mortar matrixes. For the above stated reasons, it might be concluded that mortars made with calcium aluminate cements or calcium sulfoaluminate with the incorporation of treated fly ash, may be perfectly valid for uses in which a fast-curing product, with high initial strength and drying shrinkage compensation with a high dimensional stability is required. Based on this, the material could be used as repair mortar for structures, roads and industrial pavements requiring high performance, such as: industrial floorings, landing tracks, parking lots, etc. Alternatively, it could also be used in the manufacture of prefabricated elements without structural reinforcement, given its high bending strength.

Aplicação da tecnologia eletroquímica para a remoção e monitoramento de metais pesados em efluentes aquosos

Heavy metals are present in industrial waste. These metals can generate a large environmental impact contaminating water, soil and plants. The chemical action of heavy metals has attracted environmental interest. In this context, this study aimed to test t he performance of electrochemical technologies for removing and quantifying heavy metals. First ly , the electroanalytical technique of stripping voltammetry with glassy carbon electrode (GC) was standardized in order to use this method for the quantificatio n of metals during their removal by electrocoagulation process (EC). A nalytical curves were evaluated to obtain reliability of the determin ation and quantification of Cd 2+ and Pb 2+ separately or in a mixture. Meanwhile , EC process was developed using an el ectrochemical cell in a continuous flow (EFC) for removing Pb 2+ and Cd 2+ . The se experiments were performed using Al parallel plates with 10 cm of diameter (  63.5 cm 2 ) . The optimization of conditions for removing Pb 2+ and Cd 2+ , dissolved in 2 L of solution at 151 L h - 1 , were studied by applying different values of current for 30 min. Cd 2+ and Pb 2+ concentrations were monitored during electrolysis using stripping voltammetry. The results showed that the removal of Pb 2 + was effective when the EC pro cess is used, obtaining removals of 98% in 30 min. This behavior is dependent on the applied current, which implies an increase in power consumption. From the results also verified that the stripping voltammetry technique is quite reliable deter mining Pb 2+ concentration , when compared with the measurements obtained by atomic absorption method (AA). In view of this, t he second objective of this study was to evaluate the removal of Cd 2+ and Pb 2+ (mixture solution) by EC . Removal efficiency increasing current was confirmed when 93% and 100% of Cd 2+ and Pb 2+ was removed after 30 min . The increase in the current promotes the oxidation of sacrificial electrodes, and consequently increased amount of coagulant, which influences the removal of heavy metals in solution. Adsortive voltammetry is a fast, reliable, economical and simple way to determine Cd 2+ and Pb 2+ during their removal. I t is more economical than those normally used, which require the use of toxic and expensive reagents. Our results demonstrated the potential use of electroanalytical techniques to monitor the course of environmental interventions. Thus, the application of the two techniques associated can be a reliable way to monitor environmental impacts due to the pollution of aquatic ecosystems by heavy metals.

Aplicação e otimização de métodos eletroquímicos combinados para remoção e determinação de cromo hexavalente em efluentes simulados

Hexavalent chromium is a heavy metal present in various industrial effluents, and depending on its concentration may cause irreparable damage to the environment and to humans. Facing this surrounding context, this study aimed on the application of electrochemical methods to determine and remove the hexavalent chromium (Cr6+) in simulated wastewater. To determine was applied to cathodic stripping voltammetry (CSV) using ultra trace graphite electrodes ultra trace (work), Ag/AgCl (reference) and platinum (counter electrode), the samples were complexed with 1,5- diphenylcarbazide and then subjected to analysis. The removal of Cr6+ was applied electrocoagulation process (EC) using Fe and Al electrodes. The variables that constituted the factorial design 24, applied to optimizing the EC process, were: current density (5 and 10 mA.cm-2), temperature (25 and 60 ºC), concentration (50 and 100 ppm) and agitation rate (400 and 600 RPM). Through the preliminary test it was possible the adequacy of applying the CSV for determining of Cr6+, removed during the EC process. The Fe and Al electrodes as anodes sacrifice showed satisfactory results in the EC process, however Fe favored complete removal in 30 min, whereas with Al occurred at 240 min. In the application of factorial design 24 and analysis of Response Surface Methodology was possible to optimize the EC process for removal of Cr6+ in H2SO4 solution (0.5 mol.L-1), in which the temperature, with positive effect, was the variable that presented higher statistical significance compared with other variables and interactions, while in optimizing the EC process for removal of Cr6+ in NaCl solution (0.1 mol.L-1) the current density, with positive effect, and concentration, with a negative effect were the variables that had greater statistical significance with greater statistical significance compared with other variables and interactions. The utilization of electrolytes supports NaCl and Na2SO4 showed no significant differences, however NaCl resulted in rapid improvement in Cr6+ removal kinetics and increasing the NaCl concentration provided an increase in conductivity of the solution, resulting in lower energy consumption. The wear of the electrodes evaluated in all the process of EC showed that the Al in H2SO4 solution (0.5 mol.L-1), undergoes during the process of anodization CE, then the experimental mass loss is less than the theoretical mass loss, however, the Fe in the same medium showed a loss of mass greater experimental estimated theoretically. This fact is due to a spontaneous reaction of Fe with H2SO4, and when the reaction medium was the NaCl and Na2SO4 loss experimental mass approached the theoretical mass loss. Furthermore, it was observed the energy consumption of all processes involved in this study had a low operating cost, thus enabling the application of the EC process for treating industrial effluents. The results were satisfactory, it was achieved complete removal of Cr6+ in all processes used in this study.

Determinação voltamétrica de zinco empregando eletrodos quimicamente modificados com bismuto

This dissertation presents the development of voltammetric methods to zinc determination in multivitamin commercial samples, talc, and art materials for painting (soft pastel) combining an alkaline extraction with 1.0 mol L-1 NaOH aqueous solution and bismuth modified electrodes. Two electrodes were used to zinc quantification in the samples, bismuth film electrode (BiFE) plated in situ onto glassy carbon and carbon paste electrode chemically modified with strongly acidic ion exchange resin Amberlite® IR 120 and bismuth nanostructures (EPCAmbBi). It was verified that the best concentration of Bi3+ for Bi film deposition onto glassy carbon was 4.0 μmol L-1 using an 0.1 mol L-1 acetate buffer aqueous solution (pH = 4.5) as supporting electrolyte. The best condition to formation of Bi nanostructures in the EPC modified with 10 % Amberlite® IR 120 was the use of 30 s to pre-concentration (open circuit) in 0.5 mmol L-1 Bi3+ aqueous solution (pH 5.5) prepared with supporting electrolyte solution. The obtained analytical curve for Zn2+ using BiFE presented linear range from 0.5 to 5.0 μmol L-1, the limit of detection (LD) was 41 nmol L-1. For EPCAmbBi only one linear range was observed for the analytical curve varying the Zn2+ concentration from 0.05 to 8.2 μmol L-1, LD obtained in this curve it was equal to 10 nmol L-1. The EPCAmbBi presented the most intense and sharp anodic stripping peaks for Zn2+ presenting, therefore, a better voltammetric profile, with sensitivity higher than obtained with the BiFE. Moreover, the EPCAmbBi presented a LD lower than that obtained with the BiFE. Alkaline extraction was an efficient sample pretreatment to extract Zn2+ from solid samples, besides that, this procedure was less susceptible to interferences from Cu2+, since it remains at extracting vessel as insoluble Cu(OH)2. The combination of alkaline extraction with the EPCAmbBi is a simple, fast, efficient and low cost for the zinc determination in pharmaceutical formulations and art materials for painting (soft pastel) samples, which can be employed as a low-cost alternative method to the atomic absorption spectroscopy.

Effects of Natural Organic Matter on the Dissolution Kinetics and Bioavailability of Metal Oxide Nanoparticles

The rapid development of nanotechnology and wider applications of engineered nanomaterials (ENMs) in the last few decades have generated concerns regarding their environmental and health risks. After release into the environment, ENMs undergo aggregation, transformation, and, for metal-based nanomaterials, dissolution processes, which together determine their fate, bioavailability and toxicity to living organisms in the ecosystems. The rates of these processes are dependent on nanomaterial characteristics as well as complex environmental factors, including natural organic matter (NOM). As a ubiquitous component of aquatic systems, NOM plays a key role in the aggregation, dissolution and transformation of metal-based nanomaterials and colloids in aquatic environments.

The goal of this dissertation work is to investigate how NOM fractions with different chemical and molecular properties affect the dissolution kinetics of metal oxide ENMs, such as zinc oxide (ZnO) and copper oxide (CuO) nanoparticles (NPs), and consequently their bioavailability to aquatic vertebrate, with Gulf killifish (Fundulus grandis) embryos as model organisms.

ZnO NPs are known to dissolve at relatively fast rates, and the rate of dissolution is influenced by water chemistry, including the presence of Zn-chelating ligands. A challenge, however, remains in quantifying the dissolution of ZnO NPs, particularly for time scales that are short enough to determine rates. This dissertation assessed the application of anodic stripping voltammetry (ASV) with a hanging mercury drop electrode to directly measure the concentration of dissolved Zn in ZnO NP suspensions, without separation of the ZnO NPs from the aqueous phase. Dissolved zinc concentration measured by ASV ([Zn]ASV) was compared with that measured by inductively coupled plasma mass spectrometry (ICP-MS) after ultracentrifugation ([Zn]ICP-MS), for four types of ZnO NPs with different coatings and primary particle diameters. For small ZnO NPs (4-5 nm), [Zn]ASV was 20% higher than [Zn]ICP-MS, suggesting that these small NPs contributed to the voltammetric measurement. For larger ZnO NPs (approximately 20 nm), [Zn]ASV was (79±19)% of [Zn]ICP-MS, despite the high concentrations of ZnO NPs in suspension, suggesting that ASV can be used to accurately measure the dissolution kinetics of ZnO NPs of this primary particle size.

Using the ASV technique to directly measure dissolved zinc concentration, we examined the effects of 16 different NOM isolates on the dissolution kinetics of ZnO NPs in buffered potassium chloride solution. The observed dissolution rate constants (kobs) and dissolved zinc concentrations at equilibrium increased linearly with NOM concentration (from 0 to 40 mg-C L-1) for Suwannee River humic acid (SRHA), Suwannee River fulvic acid and Pony Lake fulvic acid. When dissolution rates were compared for the 16 NOM isolates, kobs was positively correlated with certain properties of NOM, including specific ultraviolet absorbance (SUVA), aromatic and carbonyl carbon contents, and molecular weight. Dissolution rate constants were negatively correlated to hydrogen/carbon ratio and aliphatic carbon content. The observed correlations indicate that aromatic carbon content is a key factor in determining the rate of NOM-promoted dissolution of ZnO NPs. NOM isolates with higher SUVA were also more effective at enhancing the colloidal stability of the NPs; however, the NOM-promoted dissolution was likely due to enhanced interactions between surface metal ions and NOM rather than smaller aggregate size.

Based on the above results, we designed experiments to quantitatively link the dissolution kinetics and bioavailability of CuO NPs to Gulf killifish embryos under the influence of NOM. The CuO NPs dissolved to varying degrees and at different rates in diluted 5‰ artificial seawater buffered to different pH (6.3-7.5), with or without selected NOM isolates at various concentrations (0.1-10 mg-C L-1). NOM isolates with higher SUVA and aromatic carbon content (such as SRHA) were more effective at promoting the dissolution of CuO NPs, as with ZnO NPs, especially at higher NOM concentrations. On the other hand, the presence of NOM decreased the bioavailability of dissolved Cu ions, with the uptake rate constant negatively correlated to dissolved organic carbon concentration ([DOC]) multiplied by SUVA, a combined parameter indicative of aromatic carbon concentration in the media. When the embryos were exposed to CuO NP suspension, changes in their Cu content were due to the uptake of both dissolved Cu ions and nanoparticulate CuO. The uptake rate constant of nanoparticulate CuO was also negatively correlated to [DOC]×SUVA, in a fashion roughly proportional to changes in dissolved Cu uptake rate constant. Thus, the ratio of uptake rate constants from dissolved Cu and nanoparticulate CuO (ranging from 12 to 22, on average 17±4) were insensitive to NOM type or concentration. Instead, the relative contributions of these two Cu forms were largely determined by the percentage of CuO NP that was dissolved.

Overall, this dissertation elucidated the important role that dissolved NOM plays in affecting the environmental fate and bioavailability of soluble metal-based nanomaterials. This dissertation work identified aromatic carbon content and its indicator SUVA as key NOM properties that influence the dissolution, aggregation and biouptake kinetics of metal oxide NPs and highlighted dissolution rate as a useful functional assay for assessing the relative contributions of dissolved and nanoparticulate forms to metal bioavailability. Findings of this dissertation work will be helpful for predicting the environmental risks of engineered nanomaterials.