Ana Inés Fernández

Removal of ammonium and phosphates from wastewater resulting from the process of cochineal extraction using MgO-containing by-product

The wastewater produced by the cochineal extract process to obtain the carminic acid colouring pigment (carmin red E120) has high concentrations of phosphates and ammonium. It is known that both ions can be precipitated with magnesium in the form of struvite, MgNH(4)PO(4), or ammonium magnesium phosphate (MAP) compounds. In this study, the use of an alternative MgO-containing by-product is investigated. The optimal pH, reaction time and solid/liquid ratio have been studied. It has been found that the low-grade MgO needed is greater than the stoichiometric value for the full removal of ammonium and phosphate as MAP compounds. Although the low-grade MgO (LG-MgO) reacts slower than pure MgO, it has considerable economic advantages. A batch process has been proposed for the removal of ammonium and phosphates from wastewater obtained in cochineal extracts processing, previously to biological treatment to diminish the COD.

Short-term natural weathering of MSWI bottom ash.

The release of heavy metals from MSWI bottom ash has been the key concern in the management of this material. The leaching distribution values obtained from 100 freshly quenched bottom ash samples, according to the German DIN 38414-S4 procedure test, showed the release of lead, zinc and copper to be the main hazards associated with bottom ash utilisation as a secondary building material. Currently, natural weathering of MSWI bottom ash, for an estimated period of 1-3 months, is the most economic treatment available to ensure the eventual utilisation of this material. The leaching of natural weathered bottom ash in the short-term (up to 9 months) was studied. The most significant changes in the bottom ash were found to occur in the first 90 days. At pH values greater than 12, lead, zinc and copper were the main heavy metals to be released from the MSWI freshly quenched bottom ash samples studied. Natural weathering for a period of about 90 days reduced the leaching of heavy metals, stabilising the bottom ash pH to minimise the solubility of metal hydroxides, and enabled the residue to be used as secondary building material. The profile of the pH neutralisation curve is similar to that described by carbonates, which would suggest that the reaction is controlled by CO(2). The formation of insoluble oxides as well as carbonates control the immobilisation of certain heavy metals, e.g. lead and zinc. The leaching of aluminium increases during this short natural weathering stage due to elemental metal oxidation. Aluminium solubility is controlled by the precipitation of gibbsite or other aluminium-sulphate neoformations. The latter may contribute to the immobilisation of heavy metals.

Aggregate material formulated with MSWI bottom ash and APC fly ash for use as secondary building material

The main goal of this paper is to obtain a granular material formulated with Municipal Solid Waste Incineration (MSWI) bottom ash (BA) and air pollution control (APC) fly ash to be used as secondary building material. Previously, an optimum concrete mixture using both MSWI residues as aggregates was formulated. A compromise between the environmental behavior whilst maximizing the reuse of APC fly ash was considered and assessed. Unconfined compressive strength and abrasion resistance values were measured in order to evaluate the mechanical properties. From these results, the granular mixture was not suited for certain applications owing to the high BA/APC fly ash content and low cement percentages used to reduce the costs of the final product. Nevertheless, the leaching test performed showed that the concentrations of all heavy metals were below the limits established by the current Catalan legislation for their reutilization. Therefore, the material studied might be mainly used in embankments, where high mechanical properties are not needed and environmental safety is assured.

A proposal for quantifying the recyclability of materials

Abstract It is becoming of empirical importance that recyclability be defined in such a way that engineers, economists, and policy makers can agree upon and use collectively. This paper defines recyclability as the ability of a material to reacquire the properties that it had in its virgin state, where virgin state refers to the material in its purest form before being processed or shaped for a specific use. Anything less than that can be measured as a degree of its recyclability, defined as recycling index ( R ). It is here proposed that R of a material can be estimated by its devaluation (how much the material devalues during its first use), which is reflected by its loss of monetary value. This way, R can be calculated by a mathematical expression. Because of their thermodynamic and kinetic properties, as well as advances in their recycling technologies, most metals are recyclable. They are therefore used to establish a relationship that determines how truly recyclable materials should behave.

Kinetic study of carbonation of MgO slurries

Abstract Carbonation of MgO slurries at atmospheric pressure using natural magnesite from Navarra, Spain, was studied. Two processes were observed: the formation of a magnesium bicarbonate solution and the precipitation of magnesium carbonate. Under different conditions, each process was favoured so as to find the optimum conditions to produce the Mg(HCO 3 ) 2 solution that acts as raw material in the production of basic magnesium carbonate. In the absence of precipitation, the kinetic data were examined according to the plot of rate equation 1−(1− X MgO) 1/3 against time. The activation energy of 29.1 kJ/mol suggested a chemical reaction controlling step. A mechanism for carbonation is proposed. The effect of specific surface area on the MgO conversion, as a function of time and temperature of calcination, was also investigated.

A possible recycling method for high grade steels EAFD in polymer composites

This work evaluates the feasibility of incorporating electric arc furnace dust (EAFD), as filler in a polymer matrix, to obtain a moldable heavyweight sheet, useful for acoustic insulation in automotive industry. For this purpose EAFD from a steel factory that manufactures high quality steels, was characterized and different formulations of composites were prepared. Physical and mechanical properties, as well as fire behaviour were tested and compared with a polymer composite compounded with common mineral fillers. Optimum formulation with 25% EAFD fulfils the RoHs Directive used by automotive industry to regulate heavy metals content. Leaching test was also performed on prepared composites to classify the material after use.

Exploring the polyvinyl alcohol method for preparing cuprates and manganites

The polyvinyl alcohol route is investigated in the formation of cuprate and manganite ceramics. By evaporation of the nitrate solution containing the stoichiometric quantities of the cations and the PVA, a spongy mass is produced, which upon a single calcination converts into the desired phases. We chose YBa2Cu3Oy, a high temperature superconductor, and La2/3Ca1/3MnO3, a perovskite manganite showing colossal magnetoresistance as case studies for the preparation of technological interesting ceramic powders. XRD is employed to monitor the phase transformation leading to the single phases. Moreover, carbon content in the final powders is measured to assure complete elimination of carbonaceous species. This preliminar study shows that the PVA solution can be a potentially interesting technique to prepare these advanced ceramic powders as compared to classical ceramic methods. # 2002 Elsevier Science Ltd. All rights reserved.

Materials for Phase Change Material at High Temperature

Abstract To develop a cost effective and efficient latent thermal energy storage system using phase change material (PCM), selecting a suitable material is very critical. It has to satisfy certain criteria in order to fulfill the requirement of repeated heating and cooling cycles. This chapter describes the basic requirements on a material to be considered as a high-temperature PCM. It reviews the available high-temperature inorganic salt PCMs and as a result a database containing the melting point, latent heat of fusion and cost of pure inorganic salts is presented. The PCM composites are also discussed taking into account their preparation methods, effect, mechanism, advantages, and disadvantages. The composite materials include graphite, metal foams, porous metal oxides, and nanomaterials.

Trace metal partitioning in caustic calcined magnesia produced from natural magnesite.

Caustic calcined magnesia from natural magnesite has been widely employed as a source of magnesium. This mineral, depending on the origin, may contain heavy metals and metalloids that can exceed the regulatory limits in some applications. In most cases, heavy metals and metalloids form solid solutions with the mineral phases of the main impurities, or even magnesium oxide itself, replacing other ions in the crystal lattice. Compared with magnesium oxide, most of these impurities such as silica and silicates are much more chemically stable even in concentrated mineral acids under normal temperature and pressure conditions. In this study, the partitioning of the trace metals was monitored using a sequential extraction procedure (SEP), and their potential solubility was determined using the pH-static leaching test. Only a small fraction of magnesium oxide derived from heavily calcined magnesia is soluble in slightly acidic media. The release of the trace metals and metalloids contained in the soluble fractions was less than 40% as determined by total digestion. It can be concluded that SEP is more accurate than total chemical digestion for setting the maximum limits of the undesirable trace metals.

Materials Selection for Thermal Energy Storage Applications—Case Studies

To accomplish their duties, engineers need information, and this must be easily accessible, so they can readily choose among all the possibilities they can find to fit to a specific application. To build a thermal energy storage system, engineers always wonder which the best storage material they can find. The answer always depends on several factors. In the present chapter, the materials selection methodology is introduced to proceed for an optimal material selection for a certain application in thermal energy storage systems. Several case studies using this methodology are explained for different thermal energy storage applications: long term and short term sensible heat thermal energy storage, and phase change materials (PCM) for latent heat thermal energy storage for low temperature applications (buildings sector), and high temperature applications (concentrated solar power plants or CSP).