José M. Chimenos

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.

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.

Electrochemistry of conventional gold cyanidation

Abstract The kinetics of conventional gold cyanidation in air has been studied using open circuit potential measurements, voltammetry and atomic absorption spectrophotometry. The experimental results show that this is a complex process characterized by the interdependency of the different variables (cyanide concentration, pH, temperature and stirring speed). The measurement of the mixed potentials at which the process takes place gives valuable information to ascertain the influence of each variable. A good correlation between mixed potential and dissolution rate, thus having a potential interest for an industrial application, has been found. The study of the current—potential curves for oxygen reduction on gold surface and anodic dissolution of gold in cyanide solutions gives more insight into the control of the process: depending on the experimental conditions, gold dissolution takes place in the active region (oxygen diffusion control) or in the potential region where dissolution of adsorbed species limits the rate of the process. Depending also on the experimental conditions, two or four electrons are transferred per oxygen molecule.

Characterization of fire-refined copper recycled from scrap

Certain properties of fire-refined copper recycled from scrap have been characterized. A method is presented to calculate the half-softening temperature and the annealing temperature that allows 30% elongation to failure, hereinafter referred to as ε30% temperature, on the basis of hardness measurements. The relation between ultimate strain and ultimate elongation has been studied and is described by a mathematicale xpression that seems to be independent of copper composition and annealing temperature. The microstructure of annealed samples reveals that recrystallization begins at half-softening temperature, and is ending at ε30% temperature, although grain growth is not observed. An optimal range of oxygen content has been found that gives the minimum ε30% temperature for each studied composition, and a mathematical expression with which to calculate those minimum temperatures is developed. The influence of cold-working degree on ε30% temperature is also described; these temperatures reach a constant minimum value for each composition at high deformation degrees of cold-working.