M. Segarra

Characterization of the bottom ash in municipal solid waste incinerator

Abstract The particles with diameter >1 mm present in the bottom ash of Municipal solid waste incinerator (MSWI) were characterized by identifying the main constituent materials. This characterization may be used to evaluate the potential applications of bottom ash and its environmental hazards, and to evaluate the possibilities of recycling its main components. The effectiveness of the voluntary recycling programs of bottom ash can also be assessed. The main components of the bottom ash are glass, magnetic metals, minerals, synthetic ceramics, paramagnetic metals and unburned organic matter. The 4–25 mm size fraction accounts for approximately 50% of the bottom ash weight and comprises mainly glass (>50% of this fraction), synthetic ceramics (>26%) and minerals (>8%), and thus appears to be suitable for reuse as secondary building materials or for glass recycling. Magnetic metals accumulate in the 1–6 mm particle size fraction (6% of this fraction). Heavy metals accumulate in the fraction under 1 mm, unlikely the acid-soluble fraction, which diminishes as particle size diminishes.

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 as a function of particle size

The chemical and material composition of MSWI bottom ash depends on the particle size; this suggests that the mechanisms and kinetics of natural weathering are also a function of particle size. This paper reports the effects of short-term natural weathering on the leaching of heavy metals (mainly Pb, Cu and Zn) from MSWI bottom ash. Initial concentrations of heavy metals were higher for the smallest particle size fractions, but these levels fell dramatically during the first 50 days of weathering before levelling off. The main differences between size fractions were in the pH and the solubility of calcium and aluminium. For the initial stages of weathering and small size fractions, portlandite solubility seemed to control the pH. In contrast, for fractions bigger than 6 mm, the formation of ettringite was the reaction controlling the pH and the solubility of sulphates, aluminium and calcium.

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.

Influence of precursor oxygen stoichiometry on the formation of Hg, Re-1223 superconductors

Thanks to a novel technique (thermobaric analyser or TBA) for measuring the in situ pressure in quartz tubes, we have investigated the precursor quality for the synthesis of the superconductor Hg-1223 which is an essential parameter to control. We have made this study on the samples and we can conclude that this superconductor phase requires a ceramic precursor sintered in a low mixture gas flux. An excessively oxygenated precursor leads to overdoped superconducting phases, presence of other members with lower n, and some unreacted precursor. The precursor oxygenation degree also modifies the kinetics of formation of and the partial melting of the superconductor material may be affected.

Selective leaching of arsenic and antimony contained in the anode slimes from copper refining

Abstract Selenium, tellurium, silver and gold are recovered from the anode slimes of copper electrorefining. Silver-copper selenide-telluride phases must be previously oxidized to obtain selectively leachable compounds. Arsenic and antimony, present in anode slimes as AsSb oxidized compounds, may be selectively and almost completely dissolved in 0.4 M KOH at 80δC. After this extraction, alkaline roasting of anode slimes in the presence of K 2 CO 3 at 600°C solubilizes Se (99%) and less than 2% As and 0.1% of Sb. After Se leaching, Cu and Te can be dissolved in 1.2 M HCl at 25°C as well as in CuSO 4 H 2 SO 4 solution. The residue contains BaSO 4 , PbSO 4 , SiO 2 , Au, Ag and small amounts of Se, Cu and Te and can be smelted in order to obtain a bullion for Ag and Au recovery by the conventional electrorefining process.

Gold cyanidation using hydrogen peroxide

Gold cyanidation, using hydrogen peroxide as an oxidising agent, has been studied by performing kinetic experiments, open circuit potential measurements and voltammetry. Small amounts of hydrogen peroxide make the cyanidation rate lower than that in conventional cyanidation, but higher amounts can make the cyanidation rate double. At low temperatures, the process is controlled by a chemical reaction, whereas at higher temperatures, it is controlled by diffusion with higher rates with respect to conventional gold cyanidation at atmospheric pressure. As the presence of hydrogen peroxide displaces the mixed potential of cyanidation to more anodic potentials, where oxygen activity is nil, cyanidation can be performed under conditions of low oxygen pressure. In these conditions, cyanidation is established at transpassive potential regions of gold anodic dissolution and the cyanidation rate is determined by the cyanide concentration. The cyanidation rate can be tripled by adding small amounts of thallium (I) ions to cyanidation with hydrogen peroxide.

Calculation of Young's Modulus Value by Means of AFM

In the last years, Atomic Force Microscopy (AFM) has become a powerful tool not only to study the surface morphology but also the nanomechanics of all kind of samples. In this paper, the applicability of this technique is reviewed and its basic aspects of operation, advantages and drawbacks of using the AFM probe as a picoindenter (Force Spectroscopy mode, FS-AFM) are discussed. The patents concerning picoindentation measurements are discussed in the text and special attention is paid to measurements performed on hard materials as ceramics, as they have not been as thoroughly reviewed in the literature as in the case of soft matter. The possibilities of AFM in the nanomechanics field include the quantitative determination of the Youngs modulus (E) and the transition force from elastic to plastic deformation regimes, the measurement of adhesion forces and deformation mechanisms while applying vertical forces in the range from tens of pN to μN.

Kinetics of the reaction of gold cyanidation in the presence of a thallium(I) salt

Abstract The heterogeneous kinetics of gold cyanidation in the presence of a thallium(I) salt, which is known to act as accelerator of the reaction, are described in this paper. The rate of gold dissolution in the conventional gold cyanidation decreases dramatically at pH values higher than 11.5. The presence of thallium increases this maximum value of pH to over 13.5. The kinetic orders found for each of the reagents taking part in the reaction are: 0.92 for cyanide; 0.95 for oxygen and 0.1 for thallium(I). These results, as well as the calculated activation energy (9.2 kJ mol −1 ) and the effect of pH and stirring speed on the reaction rate, have disclosed a possible mechanism by which the electrochemical reaction may take place on the gold surface. According to this mechanism, the gold surface may be divided into two areas, one anodic and another cathodic, where the gold oxidation and the thallium(I) reduction take place, respectively. The cathodic area can also be subdivided into anodic and cathodic subareas, where the oxidation of the thallium deposited on the gold surface and the oxygen reduction take place. In contrast to conventional gold cyanidation, when cyanidation takes place in the presence of a thallium(I) salt, the oxygen reduction yields hydroxide ions as a reduction product, and the rate of gold dissolution is four times faster. The equation of the reaction rate that describes the kinetics of the overall process is also presented.