A. La Iglesia

Salt crystallization in porous construction materials I Estimation of crystallization pressure

Abstract The crystallization process of soluble salts inside the natural and artificial porous materials partially immersed in different saline solutions has been studied. This procedure is used to simulate the conditions of exposure to salt weathering in which foundations and lower walls of building structures are within the zone of capillary rise of saline ground water. Crystallization pressures that can develop in the samples, which are a function of the pore size and salt-solution interfacial tension, have been calculated and are compared with experimental values of the materials tensile strength, since both these parameters allow the prediction of porous materials behaviour against salt weathering.

Salt crystallization in porous construction materials. II. Mass transport and crystallization processes

In order to study the processes of salt weathering of monumental stones, several samples were partially immersed in sodium, potassium and magnesium sulphate solutions which ascended through their capillary network and, eventually, crystallized. This procedure pretends to simulate the conditions in which foundations and lower walls of building structures are, within the zone of capillary rise of saline groundwater. Mass transport and the rhythmic nature of crystallization fronts inside samples reminds the Liesegang phenomenon, so they have been considered as a form of dissipative structures. The saline deposits developed on the surface of the samples were efflorescences (mirabilite and epsomite), subefflorescences (picromerite, aphthitalite and arcanite) and crusts (aphthitalite and arcanite). The most devastating effects resulted from massive crystallization inside the samples or from surface peeling due to the development of subefflorescences or crusts.

A method of estimating the Gibbs energies of formation of zeolites

Abstract A method for calculation of the standard free energy of formation of zeolites is reported. This method is based on the assumption that the standard free energy of formation of a zeolite (Δ G ° f ) can be written as the sum of the standard free energy of the oxide components (Δ G ° zeol ). Comparison of Δ G ° f experimental values of zeolites with those calculated by our method shows that in each case the deviation is below 0.30%.

HALLOYSITE-KAOLINITE TRANSFORMATION AT ROOM TEMPERATURE

Halloysite (metahalloysite) of various particle sizes has been altered with oxalic and EDTA acids, at room temperature and during different periods of time (5–90 days). The oxalic acid attack at first achieved only a recrystallization of halloysite. The recrystallization is much more significant the smaller the size of the treated halloysite particles. Later the material is destroyed. The EDTA treatment also has provoked during the first days a recrystallization of the halloysitic material which is destroyed again after about 20–25 days. Later kaolinite is formed. The kinetic curve of kaolinite formation is symmetrical with respect to that corresponding to the diminution of amorphous material in the sample. The influence of the halloysite particle size and the complexing effect of the acids in relation to the resulting products are discussed.

Kaolinite synthesis; I, Crystallization conditions at low temperatures and calculation of thermodynamic equilibria; application to laboratory and field observations

The equilibrium diagrams developed for Al-hydroxide and for kaolinite by Garrels and Christ (1965) have been modified by taking into account the existence of gels. From the stability zones obtained, the “appropriate” concentrations can be deduced and utilized for synthesizing these species, provided the requirements to insure good crystal growth are observed. Among procedures to promote these crystallizations, homogeneous precipitation processes (La Iglesia et al., 1974, 1976) appear to be particularly adequate.The theoretical considerations provide an explanation for most of the processes observed until now, both successful and unsuccessful syntheses, and also give an explanation for many field observations. The crystallizations, however, remain poorly reproducible, indicating that many factors are still poorly known. Some points requiring further investigation include (i) better values for ΔGr0, (ii) the influence of organic complexes, (iii) the effect of preexisting crystalline phases, (iv) those involving dehydration processes in these systems.АбстракцияДиаграммы равновесия, построенные Гаррелсом и Кристом /1965/ для гидроокиси А1 и каолинита, были модифицированы с учетом существования гелей. На основе полученных стабильных зон,“надлежащая” концентрация может быть определена и использована для синтезирования этих видов, при условии, что соблюдаются условия, обеспечивающие хороший рост кристаллов. Среди процедур, обеспечивающих такую кристаллизацию, процесс гомогенного осаждения /Ла Игле-сия и др. 1974–1976/ представляется особенно подходящим.Теоретические исследования обеспечивают объяснения большинства процессов, наблюдавшихся до настоящего времени, как успешные так и безуспешные синтезы, а также дают объяснения многим полевым наблюдениям. Кристаллизация, однако, остается плохо воспроизводимой, указывая, что многие факторы еще недостаточно известны. Некоторые вопросы, требующие дальнейших исследований, включают 1) более точные значения для ДС°, 2) влияние органических соединений, 3) воздействие первоначально существовавших кристаллических фаз, 4) вопросы, включающие дегидратационные процессы в этих системах.ZusammenfassungDie Gleichgewichtsdiagramme, welche von Garreis und Christ (1965) für Aluminiumhydroxyd und für Kaolinit entwickelt wurden, wurden umgeändert, indem die Existenz von Gelen in Betracht gezogen wurde. Von den erhaltenen Stabilisierungszonen konnten die geeigneten Konzentrationen abgeleitet und zur Synthese benutzt werden, vorausgesetzt, daß die Bedingungen für die Züchtung von guten Kristallen eingehalten werden. Von denen Methoden, die Kristallisation fördern, erscheint das homogene Ausfällungsverfahren (La Iglesia et al., 1974–1976) besonders angemessen. Die theoretischen Erwägungen geben eine Erklärung für die meisten Verfahren ab, die bis jetzt untersucht wurden und erklären auch viele Beobachtungen im Felde. Die Kristallisationen dagegen bleiben schlecht reproduzierbar, was darauf hindeutet, daß viele Faktoren noch nicht ganz verstanden werden. Einige Punkte, welche weitere Untersuchungen verlangen, sind (i)bessere Werte für ΔGr0,(ii)die Beeinflußung von organischen Komplexen,(iii) der Effekt von präexistierenden kristallinen Phasen,(iv) und die Dehydratationsverfahren in diesen Systemen.RésuméLes diagrammes d’équilibre développés pour l’hydroxide d’Al et pour la kaolinite par Garrels et Christ (1965) ont été modifiés en prenant en considération l’existence de gels. Les concentrations “appropriées” peuvent être déduites des zones de stabilité obtenues et utilisées pour la synthétisation de ces espèces à condition que les exigences pour une bonne croissance de cristaux soient remplies. Parmi les procédés employés pour induire ces cristallisations, ceux de précipitation homogène semblent particulièrement appropriés (La Iglesia et al., 1974–1976).Les considérations théoriques donnent une explication à la plupart des procédés observés jusqu’à présent, à la fois aux synthèses réussies et ratées, et donnent aussi une explication à beaucoup d’observations sur le terrain. Les cristallisations restent cependant mal reproduisibles, indiquant que de nombreux facteurs sont encore mal connus. Certains points demandant une investigation plus profonde sont(i) de meilleures valeurs pour ΔG°,(ii) l’influence des complexes organiques, (iii) l’effet de phases cristal-r lines pré-existentes, (iv) celles impliquant des procédés de déshydratation dans ces systèmes.

Kaolinite crystallization at room temperature by homogeneous precipitation; III, Hydrolysis of feldspars

The kaolinite crystallization by homogeneous precipitation with previous hydrolysis of the feldspars added has been followed by pH and potassium concentration measurements. The synthesized products were studied by X-ray powder diffraction and electron microscopy and consist of kaolinite and mica, accompanied occasionally by traces of smectite. The relative quantities of the synthesized minerals depend fundamentally on the supply rate of the alkaline ions.

Estimation of thermodynamic properties of mineral carbonates at high and low temperatures from the sum of polyhedral contributions

Abstract Using the basic polyhedral units model of Hazen and employing the iteration technique of Gauss-Seidel, the contribution of twenty basic units to the free energy, enthalpy and entropy at 298 K and 1 bar of pressure, has been calculated for mineral carbonates. The contribution of these basic units to the free energy and heat capacity at higher temperatures has also been calculated. This calculated parameters allow the estimation of thermodynamic properties of carbonates by summing the contributions of the distinct polyhedral units, with more accuracy than the methods published up until now.

Crystallinity variations in kaolinite induced by grinding and pressure treatments

Kaolinite samples treated with uniaxial pressures higher than 0.1 GPa or grinding times greater than 0.3 h show changes in their crystallinity. These changes are easily detected by the X-ray diffraction (XRD) technique and can be quantified from Hinckley (HI), Lietard (R2) and also reference intensity ratio (RIR) index studies. The sensitivity of these indices to the Crystallinity changes is; HI>RIR>R2. In the range of pressures and grinding times considered, these values can be diminished by 50%. The variations in these indices with either the pressure or grinding time follow logarithmic laws whose correlation coefficients are closed to unity. Infrared (IR) spectroscopy and thermal analysis studies show low sensitivity to the changes introduced by grinding or pressure. Nevertheless, thermal gravimetric curves confirm the decrease in the dehydroxylation starting point of about 100°C for the pressed and ground samples. Transmission electron microscopy (TEM) reveals important changes in kaolinite particle morphologies after pressure and grinding treatments. The samples compressed at 0.1, 0.32, 0.85, 1.0 and 2.0 GPa show a large number of defects (fractures, bending, deformations and rolling of layers, glide and rotation of the shell). The ground samples show grain boundaries, dislocations, twins and rounded voids. These defects are responsible for the decrease in crystallinity of the kaolinite samples shown in the XRD and IR studies.

Viability of the use of pickling baths from aluminium surface treatment for synthesizing low Si/AI zeolites

Abstract Currently, the European extruded aluminium profile industry generates 3.000.000 litres per year of waste liquors from the pickling and etching baths. There are two trends for their treatment: the precipitation of aluminium and its disposal in controlled landfills or their incorporation in the water treatment system of the plants. The former way wastes the possible recovery and the latter one increases the amount of produced muds which are one of the most important problems that this industry must face up. We propose the synthesis of low Si/Al ratio zeolites as recovery treatment. Real industrial pickling baths with their changing characteristics were used and zeolites fulfilling the specifications for their use in the formulation of detergents were obtained without the necessity of acting on the operation conditions of the plant that is the main factor when a recovery process is implemented in a working plant.

Optimization of 4A zeolite synthesis as recovery of wastes from aluminum finishing.

A model representing the synthesis process of 4A zeolite from wastes of aluminum finishing plants was obtained and validated through statistical tests. From this model, the optimum values for the molar ratios SiO2/Al2O3, Na2O/SiO2 and H2O/Na2O, which define the type and quality of the synthesized zeolite, were estimated for the use of these wastes as raw material. The obtained zeolites could be used as water softeners in the formulation of detergents. The resulting liquors could be reused in the cleaning of the extrusion matrices used for aluminum profiles or recycled for new zeolites synthesis.