Search

The aim of the present work is to characterize the phosphate sludge from the area of Youssoufia (rich in CaO ~ 31%) and to study its thermal behavior alone and when mixed with clay from Safi (Morocco). This may contribute to its valorization as an alternative raw material for ceramic industries. The evolution of phases during the thermal treatment of phosphate sludge, clay and sludge–clay mixtures at different mass ratios (25 wt%, 50 wt%, and 75 wt%) was performed at different levels of temperatures from 600 to 1120 °C. Mineralogical analysis by X-ray diffraction (XRD) showed that the sludge mainly consisted of quartz, calcite, dolomite, and francolite. Dolomite and calcite vanished after sludge heating and two new phases were formed, namely akermanite and monticellite. For clay, it mainly consisted of illite, kaolinite, quartz, calcite, and dolomite. After clay sintering at high temperature, a new phase was formed, i.e. anorthite. The effects of the MO/SiO2 ratio (MO = CaO + MgO) in mixtures (clay + sludge) on the crystallization behavior of diopside and fluorapatite, and the disappearance of the akermanite were investigated. The results showed that the crystallization of diopside–fluorapatite increased when the MO/SiO2 ratio increased. Resumen: El objetivo del presente trabajo es caracterizar un lodo de fosfato del área de Youssoufia (rico en CaO ~ 31%) y estudiar su comportamiento térmico tras su mezcla con una arcilla de Safi (Marruecos). Este estudio puede contribuir a su valorización como materia prima alternativa para la industria cerámica. La evolución de las fases minerales durante el tratamiento térmico de lodos de fosfato, arcilla y mezclas de lodos y arcilla en diferentes proporciones de masa (25, 50 y 75% de peso) se realizó a diferentes temperaturas, desde 600 a 1.120 °C. El análisis por difracción de rayos X (DRX) permitió conocer la composición mineralógica del lodo formado principalmente por cuarzo, calcita, dolomita y francolita. La dolomita y la calcita desaparecieron tras el calentamiento del lodo y se formaron 2 nuevas fases, a saber, akermanita y monticellita. En cuanto a la arcilla, el análisis mineralógico evideció la presencia de illita, caolinita, cuarzo, calcita y dolomita como fases mayoritarias. Tras la descomposicón de la arcilla se formó anortita como fase de alta temperatura. Se investigaron los efectos de la relación MO/SiO2 (MO = CaO + MgO) en mezclas (arcilla + lodo) sobre la cristalización de diópsido y fluorapatita y la desaparición de la akermanita. Los resultados mostraron que la cristalización de diopsido-fluorapatita aumentó cuando creció el cociente MO/SiO2.

In vitro activity is important when considering the choice of a multiphasic bioceramic scaffold as phases can dissolve or transform at different rates. The aim of this study is focused on the synthesis and in vitro analysis of multiphasic ceramics obtained from the melt by directional solidification. Depending on the growth rate of the new composition different bioactive phases coexist in the same sample: akermanite, monticellite, tricalcium phosphate and Nurse's A phase, all of them with potential in the medical area as implant for bone or dental repair. With the knowledge of what and how phases dissolve first, it was possible to design materials to get porous scaffolds or more stable ceramics., The authors would like to acknowledge the use of Servicio General de Apoyo en la Investigación- SAI, Universidad de Zaragoza. BMM wants to acknowledge the financial support awarded by the Spanish Ministry of Science and Innovation through the grant PID2019-103847RJ-I00, as well as the one provided by the Regional government of the ‘Junta de Andalucía’ through the project P18-RTJ-1972.

The Gross Brukkaros massif lies at the southern extremity of the Gibeon kimberlite province in South-West Africa; it is a well-formed volcanic vent with a diameter of approximately 2 km and a height of approximately 650 m above the Great Namaqualand plain. The vent is lined by a 130-m succession of stratified non-pyroclastic microbreccias, blown out by repeated explosions of the central volcano. This activity cuts through the late Pre-cambrian strata of the Nama Supergroup which underlies the microbreccias, and is dominated by vents and radial fissures having kimberlitic, melilititic and carbonatitic affinities. Monticellite peridotite intrusive is also present on the southern slopes of Gross Brukkaros. Pre-explosion fenitizing solutions produced a strong desilication of the argillitic component of the layered microbreccias and have introduced Na, Ca, Mg, Ti, Fe3+, total Fe and C. Post-depositional late-stage fenitizing solutions have also produced a local enrichment in K, P and C. Enrichment in the characteristic elements of the ultramafic suites is shown by data for Cr, Ni, V and Sc. The elements particularly characteristic of residual associations, Li, Nb, Be, Zr, Y and Sr, have also been introduced. From chemical and phase equilibria studies it is concluded that kimberlites, melilite- and monticellite-bearing ultramafic alkaline rocks and carbonatites could have been generated from a common parent. It is postulated that a kimberlitic magma is produced at depths in excess of 100 km. Olivine fractionation, reaction between crystalline phases and magma, and separation of a carbonate phase can account for the observed chemical differences in all these ultramafic alkaline rocks. We think that carbonatites represent, an immiscible phase of the ultramafic alkaline magmas. The petrogenetic model proposed -assumes a multistage rise of kimberlitic magma which was arrested at a deep crystal level where equilibrium conditions included the reaction of olivine and ilmenite to produce melilite and perovskite respectively. This magma then rapidly rose to a hypothetical depth of 2–3 km below surface where an immiscible carbonatitic top developed. The carbonatitic and alkaline ultramafic magmas were in equilibrium, together with their alkali volatile phase which impregnated and fenitised the wall-rocks in joint zones. The volatile pressure built up until it was just greater than the lithostatic pressure and bulging of the roof began. With a breach in the containment of the volatile phase there was violent disruption of the roof. Much of the brecciation and fine disruptive veining is interpreted as episodic failure in containment of fluid pressure. Concomitant with the eruption there was release of high CO2 pressure resulting in a downgrade reaction of the akermanite to monticellite. This monticellite peridotitic magma then intruded the flanks of the volcano. Small-scale structures present in the microbreccias suggest that they were essentially deposited sub-aerially.

Within a swarm of late middle Eocene subsilicic-alkalic diatremes, one diatreme 270 by 370 m and an associated dike contain common xenoliths of granulite and rare xenoliths of spinel peridotite and garnet peridotite. Six garnet lherzolite xenoliths have been found and these show a range of textures. Four are granular, and two are intensely sheared. Phlogopite is absent from the intensely sheared xenoliths and is thought to be primary in part in the granular xenoliths. Estimated temperatures and depths of equilibration of xenolith pyroxenes range from 920°C, 106 km (32 kbar) to 1315°C, 148 km (47 kbar). The xenoliths show increasing amounts of deformation with greater inferred depths of origin. The temperature-depth points suggest a segment of an Eocene geotherm for Montana which is similar in slope to the steep portion of the pyroxene-determined Lesotho geotherm (BOYD and NIXON, this volume) and is considerably steeper than typical calculated shield and continental geotherms at present. The steep trend could be a result of plate-tectonic shearing and magma ascension within an Eocene low-velocity zone. Preservation of intensely sheared textures requires rapid transport of material from about 150 km depth during active deformation of relatively dry rock. The occurrence of monticellite peridotite in this kimberlite diatreme suggests that magmas which crystallized to monticellite peridotite at relatively shallow depth could be one of the primitive types of kimberlite magma.