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Moist calcium silicate minerals are known to readily react with carbon dioxide (CO2). The Accelerated Carbonation of hazardous wastes is a controlled accelerated version of the naturally occurring process. The solid mixture is carbonated under a gaseous, CO2 rich environment at slightly positive pressures (3 bar), which promotes rapid stiffening of the non-hydrated product into a structural medium within minutes. In addition, an increased binding of toxic metals occurs as the solid carbonates. Today, Accelerated Carbonation is a developing technology, which may have potential for the treatment of wastes and contaminated soils and for the sequestration of CO2, an important greenhouse gas. The consequent significant improvement in the properties of certain treated materials can facilitate reuse in a variety of construction applications. Accelerated Carbonation represents a potential solution to sustainable waste management, the problem of decreasing landfill space in the UK, rising CO2 emission levels and the depletion of natural aggregate resources. This thesis reports on the application of Accelerated Carbonation for the treatment of Municipal Solid Waste Incinerator residues (MSWIr). The treatment imparts chemical and mineralogical changes to the residues, which reduce their environmental impact through encapsulation of hazardous components and cementation by carbonate precipitation. Given the viability of carbonation as a process to treat MSWIr, this investigation focused on optimising the fundamental parameters determining the extent and quality of carbonation of these residues. Major attention was also given to the modelling of the kinetics and mechanism of the carbonation reaction of Air Pollution Control Residues (APCr). The kinetics were studied in a batch carbonation rig designed and built at University College London. In addition, the major physical and chemical changes in APCr and Bottom Ashes (BA) after carbonation were evaluated using various analytical techniques. In addition, a commercial feasibility study has been carried out which confirmed the considerable and immediate potential for the commercialisation of Accelerated Carbonation technology for the treatment of municipal MSWIr. This conclusion was reached by analysing the market and industry for waste management, competing innovations and the capacity of Accelerated Carbonation to enable the recycling and reuse of CO2 and solid wastes. This work provides a fundamental understanding of the Accelerated Carbonation reaction of APCr essential to further ascertain the scale-up parameters required for the design of a large scale continuous process.

Cement -based solidification/stabilisation (s/s) has been applied to the disposal of heavy metal bearing contaminated soil and wastes for approximately 50 years. This work studies the interactions of cement and heavy metals and provides further insight into encapsulation of heavy metals in cement matrices. The pastes and suspensions of calcium oxide, calcium hydroxide, pure cement phases ( 38, C}A, C4AF, Ci 2A7 and CA) and Portland cement with or without heavy metals (Zn2+ , Pb2+, Cu2+ and Cr3+) were examined by a number of analytical techniques. These techniques were X-ray powder diffraction (XRD), solid state magic angle spinning/nuclear magnetic resonance (MAS/NMR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) and thermogravimetry (TG). Thermodynamic modelling using a geochemical code, PHREEQC, and the edited database, was carried out to elucidate the chemical reactions occurring in cement/heavy metal systems. Heavy metals acted as accelerators for hydration of CaO, CaS and Portland cement except that Zn2+ retarded the early-age hydration of Cfi and Portland cement. This work confirmed that the precipitation of portlandite was retarded due to the hydrolysis of heavy metals. Calcium ions resulting from the decomposition of cement phases combined with heavy metals to form calcium-heavy metal double hydroxides, including CaZn2(OH)6.2H2O, Ca2(OH)4Cu(OH)2.mH2O and Ca2Cr(OH)7 .3H2O. The carbonation of CaS and Portland cement resulted in the formation of calcium carbonate and the condensation of silicates from single tetrahedra to branching sites and three-dimensional frameworks (low Ca/Si ratio C-S-H gel). The polymerisation of C-S-H gel, and the polymorphism conversion and decomposition temperature of calcium carbonate were influenced by heavy metals. The incorporation of heavy metal cations in C-S-H gel is similar to that seen in glass. Heavy metals acted as network modifiers or network intermediates. In hydrated Portland cement pastes, aluminium was partitioned in ettringite or calcium carboaluminate. After carbonation, this work revealed that aluminium was in the tetrahedral form, forming mixed AlCVSiC^ branching or three-dimensional networks. This thesis presents the new structural models for C-S-H gel and the chemical mechanisms of 38 reactions with water and carbon dioxide in the presence or absence of heavy metals. In the absence of gypsum, the reaction products detected in the pastes of C3A, C4AF, Ci2A? and CA were gehlenite hydrate, calcium carboaluminate, C4AH X and hydrogarnet. Heavy metals, especially Zn 2+ , inhibited the formation of hydrogarnet and promoted the conversion of C-A-H to calcium carboaluminate and calcium carbonate. In the presence of gypsum, the major hydration product of C^A was ettringite. During carbonation, COs'" substituted for SO 4 2 " and formed calcium carboaluminate, and eventually transformed into calcium carbonate and gibbsite. The conversion of metastable calcium carbonate polymorphs (aragonite and vaterite) to calcite through Ostwald ripening occurred very slowly in the carbonated pastes containing gypsum. The reactivity of C 3 A, C^Ay, CA and C4AF during carbonation was much lower than seen during hydration. Heavy metals influenced the rates and products of hydration or carbonation of CsA, Ci2A7, CA and C4 AF and were completely incorporated in the reaction products of these phases. Thermodynamic modelling confirmed that accelerated carbonation could be beneficially employed to cement-based s/s to improve its effectiveness. Calculations of solubility and equilibrium phase assemblage are consistent with the experimental examination obtained in this work.

Ce mémoire porte sur le développement d'un protocole d'extraction sélective de métaux présents dans les accumulateurs Ni-Cd en fin de vie. Classiquement, les procédés hydrométallurgiques appliqués à ce type de solides comportent de nombreuses étapes dont les principales sont la lixiviation et la récupération du métal par électrolyse. Le procédé utilisé permet le couplage des opérations d'Electrolixiviation et d'Electrodéposition (noté E/E) au sein d'une même cellule. La technique est basée sur la lixiviation de la matière active des accumulateurs Ni-Cd par les protons générés à l'anode, les cations lixiviés (Co2+, Ni2+ et Cd2+) migrent vers la cathode où le cadmium est sélectivement réduit. Nous avons étudié les possibilités de récupération des métaux, mais également tenté d'appréhender les phénomènes prenant place dans la cellule lors du couplage E/E. Dans un premier temps, nous avons choisi de démanteler manuellement des accumulateurs en raison de la complexité des broyats industriels. La matière active des accumulateurs Ni-Cd a été caractérisée. Sa composition moyenne est la suivante :Cd(OH)2 : 45,3 %, Cd0 : 0,02 %, Ni(OH)2 : 30,0 %, Ni0 :12,9 %, NiOOH : 0,9%, Co(OH)2 : 2,4 %. Au vu des différentes formes minéralogiques présentes, ce solide peut être considéré comme un déchet modèle pour ce traitement. Avant d'envisager le couplage E/E, la lixiviation chimique de la matière active par H2SO4 a d'abord été étudiée. La modélisation de cette opération a mis en évidence que la cinétique de dissolution de Cd(OH)2 est gouvernée par le transfert de masse des protons, la dissolution de Ni(OH)2 et Co(OH)2 étant quant à elle régie par la réaction chimique de surface. Dans ces conditions de lixiviation douce, le nickel métallique n'est pas oxydé et se retrouve dans le résidu solide avec le carbone. Nous avons pu démontrer ensuite la sélectivité de l'électrodéposition vis-à-vis du Co2+ et du Ni2+ avec un rendement faradique d'environ 99 % à une densité de courant de 350 A.m-2. L'étude cinétique de l'E/E a montré que l'électrolixiviation est l'étape limitante du procédé, phénomène qui a également été modélisé. L'E/E appliquée aux matériaux d'électrodes permet en 5 h 30 de lixivier 97 % du cadmium initialement présent. Le solide résiduel est composé à 82 % de nickel, principalement sous la forme métallique, 4 % de cadmium, 0,5 % de cobalt et 3 % de carbone. Le dépôt de cadmium est obtenu avec une pureté supérieure à 97 % et un rendement faradique de déposition supérieur à 74 % à une densité de courant de 350 A.m-2. La faisabilité du couplage E/E appliqué au traitement d'accumulateurs Ni-Cd en fin de vie a été démontrée malgré la complexité de la matrice. Les premiers essais d'application de ce traitement à des échantillons industriels (Cd(OH)2 : 36,1 %, Ni(OH)2 : 24,1 %, Ni0 : 16,6 %, NiOOH : 5,5 %, Co(OH)2 : 2,4 % et Fe :1% en masse) confirment les résultats obtenus avec les matériaux d'électrodes provenant du démantèlement manuel / This thesis focuses on the development of a protocol for selective extraction of metals from spent Ni-Cd batteries. Conventionally, hydrometallurgical processes applied to this type of solids involve several steps, the main ones being the leaching and the metal recovery by electrolysis. The method used consists in coupling Electroleaching to Electrodeposition operation (denoted E/E) within the same cell. The technique is based on the leaching of the active material of Ni-Cd batteries by protons generated at the anode: the cations (Co2+, Ni2+ and Cd2+) released by leaching migrate to the cathode where the cadmium is selectively reduced. We studied the possibility of metals recovery, but also tried to understand the phenomena occurring in the cell during the E/E experiments. Initially, it was preferred to manually dismantle batteries due to the complexity of industrial waste crushed. The active matter of Ni-Cd has been characterized. Its average composition is as follows: Cd(OH)2: 45.3%, Cd0: 0.02%, Ni(OH)2: 30.0%, Ni0: 12.9%, NiOOH: 0.9%, Co(OH)2: 2.4%. In view of these different mineralogical forms, this solid can be considered a model for the waste treatment. Before considering the E/E treatment, chemical leaching of the active matter by H2SO4 was first studied. Modelling of the tests carried out showed that the kinetics of Cd(OH)2 dissolution is governed by mass transfer of protons and the dissolution of Ni(OH)2 and Co(OH)2 by the surface chemical reaction. Under these conditions of soft leaching, metal nickel is not oxidized and is found in the solid residue, with carbon. We had to demonstrate the cadmium electrowinning selectivity, for separation from Co2+ and Ni2+ species, with a current efficiency up to 99% at a current density of 350 A.m-2. The kinetic study of the E/E showed that electroleaching is mainly governed by H+ generation at the anode. Besides, the overall process is largerly controlled by cations transport from the anode to the cathode side: this transport phenomenon had also been modeled. The E/E applied to the electrode materials for 5 h 30 allows the leaching of 97% of the cadmium initially present. The residual solid is composed by 82% of nickel, mainly in the metallic form, 4% of cadmium, 0.5% of cobalt and 3% carbon. The deposition of cadmium is obtained with a purity greater than 97% and a current efficiency greater than 74% at a current density of 350 A.m-2. The feasibility of the E/E coupling applied to the spent Ni-Cd batteries treatment has been demonstrated despite the complexity of the matrix. The first tests to apply this treatment to industrial samples (Cd(OH)2: 36.1% Ni(OH)2: 24.1% Ni0: 16.6% NiOOH: 5.5% Co(OH)2: 2.4% and Fe: 1% by weight) confirm the results obtained with the electrode material from the manual dismantling