Marc Degrez

Self-colour anodizing of titanium

Abstract Relations between the colours and the electrochemical parameters (current density, quantity of electricity and temperature of the electrolyte) during the anodization of titanium sheets were studied in a 1 M H 2 SO 4 solution. Mathematical theories were developed for the kinetics of growth of the anodic film and for the colours of this film. These theories show that the relation between the growth and the colour of the film is complicated. Nevertheless, it was possible to find experimental conditions that led to uniform and well-defined colours.

Applications of electrodialysis for acid pickling wastewater treatment

Abstract In acid pickling before electroplating, the effective acid concentration deteriorates while the dissolved metal concentration increases continuously. By introducing electrodialysis (ED) between this operation and the following rinsing baths, these disadvantages are largely rectified. Recovered acid is continuously returned to the pickling bath and the amount of waste is drastically reduced. Depleted solution is reused in rinsing baths. Moreover, ED can avoid metallic impurity build-up in the acid pickling bath. First manipulations conducted on our laboratory equipment failed. So, ion-exchange membranes (IEMs) were characterized by conductivity measurements and polarization curves. Afterwards, a new selection of IEMs was performed. Faradic yields were calculated for various commercial anion- and cation-exchange membranes (AEMs and CEMs) in a Hittorf cell and ED conditions were refined. The relation between the hydrodynamics of ED and the limiting current density was checked by new measurements based on a tracer method successfully applied to electrochemical cells by our laboratory.

Belgian MSWI fly ashes and APC residues: A characterisation study

Municipal Solid Waste Incineration (MSWI) produces different sorts of residues, bottom ash, fly ashes and Air Pollution Control (APC) residues. Generally, fly ashes and APC residues are mixed at the MSWI plant and manage as a sole residue. In this study, fly ashes and APC residues have been sampled separately at different Belgian MSWI plant and analysed by X-ray fluorescence in order to highlight the composition differences that may appear between the solids. Ca and Cl are found to be the major elements in most of the samples. Lithophilic elements, such as Al and Si, are richer in furnace and boiler ashes, as can be expected. Leaching tests also show differences between the residues; leachates from furnace and boiler ashes are alkaline while those from bag filter residues present a pH value of 6, which impacts the leaching of heavy metals (Pb and Zn). The results suggest that it could be advantageous to manage fly ashes and APC residues separately by adjusting the treatment to their specificities.

MSWI boiler fly ashes: Magnetic separation for material recovery

Nowadays, ferrous materials are usually recovered from Municipal Solid Waste Incineration (MSWI) bottom ash by magnetic separation. To our knowledge, such a physical technique has not been applied so far to other MSWI residues. This study focuses thus on the applicability of magnetic separation on boiler fly ashes (BFA). Different types of magnet are used to extract the magnetic particles. We investigate the magnetic particle composition, as well as their leaching behaviour (EN 12457-1 leaching test). The magnetic particles present higher Cr, Fe, Mn and Ni concentration than the non-magnetic (NM) fraction. Magnetic separation does not improve the leachability of the NM fraction. To approximate industrial conditions, magnetic separation is also applied to BFA mixed with water by using a pilot. BFA magnetic separation is economically evaluated. This study globally shows that it is possible to extract some magnetic particles from MSWI boiler fly ashes. However, the magnetic particles only represent from 23 to 120 g/kg of the BFA and, though they are enriched in Fe, are composed of similar elements to the raw ashes. The industrial application of magnetic separation would only be profitable if large amounts of ashes were treated (more than 15 kt/y), and the process should be ideally completed by other recovery methods or advanced treatments.

Evaluation of mass transport in copper and zinc electrodeposition using tracer methods

Control of the electrocrystallization process is essential in the deposition of metals from aqueous electrolytes. A knowledge of the influence of mass transfer on the metal ion reduction is a critical element in any number of electrolytic processes, particularly where relatively high current densities are desired. The use of more positive ion tracer techniques as a means of experimentally determining some of the mass transport properties of interest are described. Examples for copper, zinc and zinc alloys electrolysis are included.

Combining sieving and washing, a way to treat MSWI boiler fly ash

Municipal Solid Waste Incineration (MSWI) fly ashes contain some compounds that could be extracted and valorised. A process based on wet sieving and washing steps has been developed aiming to reach this objective. Such unique combination in MSWI fly ash treatment led to a non-hazardous fraction from incineration fly ashes. More specifically, MSWI Boiler Fly Ash (BFA) was separately sampled and treated. The BFA finer particles (13wt%) were found to be more contaminated in Pb and Zn than the coarser fractions. After three washing steps, the coarser fractions presented leaching concentrations acceptable to landfill for non-hazardous materials so that an eventual subsequent valorisation may be foreseen. At the contrary, too much Pb leached from the finest particles and this fraction should be further treated. Wet sieving and washing permit thus to reduce the leachability of MSWI BFA and to concentrate the Pb and Zn contamination in a small (in particle size and volume) fraction. Such combination would therefore constitute a straightforward and efficient basis to valorise coarse particles from MSWI fly ashes.

Recycling by electrodialysis: from lab to industrial applications☆

The purpose of this paper is to describe an experimental method developed to study the use of electrodialysis (ED) as a recycling process introduced within some operations in the surface treatment industry. The case study is acid picking before electroplating. The first step is the study and selection of ion-exchange membrane couples. The second step is the development of tools to promote the use of ED applied to industry. Tracer methods and surface treatment models are described.

Simulation of hydrodynamics and inhibitor consumption in hydrometallurgical plants

Mathematical models are presented for the consumption of the inhibitors of electrocrystallization in hydrometallurgical plants involved with the copper electrorefining and zinc electrowinning. Continuously-stirred tank reactors (CSTR) and plug flow reactors (PFR) in which first order chemical and electrochemical reactions take place are used in these models. The time dependent behaviours of the industrial plants are predicted. Tests with metallic tracers show the validity of the models. Possible uses in electrocrystallization studies are described.

Carbonation of municipal solid waste incineration electrostatic precipitator fly ashes in solution

Carbonation was applied to a Pb- and Zn-contaminated fraction of municipal solid waste incineration electrofilter fly ashes in order to reduce heavy metal leaching. Carbonation tests were performed in solution, by Na2CO3 addition or CO2 bubbling, and were compared with washing (with water only). The injection of CO2 during the washing did not modify the mineralogy, but the addition of Na2CO3 induced the reaction with anhydrite, forming calcite. Microprobe analyses showed that Pb and Zn contamination was rather diffuse and that the various treatments had no effect on Pb and Zn speciation in the residues. The leaching tests indicated that carbonation using Na2CO3 was successful because it gave a residue that could be considered as non-hazardous material. With CO2 bubbling, Pb and Zn leaching was strongly decreased compared with material washed with water alone, but the amount of chromium extracted became higher than the non-hazardous waste limits for landfilling.

Thermal Fatigue of Anticorrosive Coatings and Multilayer Coatings: A Performance Index Approach

A strategy is proposed to cope with combined thermal fatigue and hot corrosion resistance affecting industrial coatings. It allows comparing different materials, coatings and geometries with respect to thermal cracking and then properly selecting protective coatings. It uses a thermo-mechanical model combining the heat transfer conditions, thermal and mechanical properties of the materials and the system geometry. The model is applied to two cases: (i) borided steel, with experimental support; (ii) multilayer coating made of a thermal barrier layer, aimed at reducing thermal gradients in the system, and a corrosion layer.