1,720,975 research outputs found
L'affidamento eterofamiliare tra norma e prassi
No full textDa alcuni decenni nell'ambito dei servizi deputati alla tutela dei minori si è registrato un cambiamento nei criteri che guidano l'attuazione degli interventi: si è passati, infatti, da una fase puerocentrica, caratterizzata dal tentativo degli operatori di potenziare le risorse autonome del minore allontanandolo dal proprio nucleo familiare, ad una fase in cui, visti gli insuccessi dell'intervento sul singolo, si è diffusa la tendenza a considerare il bambino entro il suo contesto relazionale, in primo luogo familiare. Al superamento di una modalità d'azione centrata esclusivamente sul minore hanno contribuito i mutamenti culturali e politici, registrati dagli anni Cinquanta in poi negli Stati Uniti e solo più tardi in Italia, che hanno portato alla diffusione del paradigma interazionista per la spiegazione dei fenomeni sociali ed in particolare, per quanto riguarda la psicologia, dell'ottica sistemico-relazionale. Tale prospettiva teorica ritiene che il soggetto sia "ecologicamente connesso" (Vadilonga, 1998) al suo nucleo d'appartenenza e che, pertanto, ogni intervento volto alla tutela del minore in difficoltà per essere efficace debba essere realizzato con l'intero sistema familiar
Analisi qualitativa e quantitativa sull’utilizzo del laser terrestre nella produzione di dati per il catasto strade
No full textNi-bearing smectites in the Wingellina laterite deposit (Western Australia) at nanoscale: TEM-HRTEM evidences of the formation mechanisms
No full textNi-bearing clays represent the main ore minerals in many laterite districts. Although the world-class Wingellina deposit (Western Australia) is an oxide-dominated ore, about 30% of the total Ni resources are hosted in the saprolitic section of the tenure, making the Ni-bearing clays a strategic target to increase the future ore reserves. In this study we present a detailed micro- to nanotextural TEM-HRTEM investigation of Ni-bearing smectites, which at Wingellina represent the main mineralogical species in the phyllosilicates assemblage. Ni-bearing smectites belong mainly to the dioctahedral (i.e. montmorillonite and nontronite) and to the trioctahedral (saponite and ferrosaponite) groups. The nanoscale TEM-HRTEM imaging indicates that Ni-bearing clays occur either as a replacement of the former clay suite (i.e. polygonal serpentine and chlorite) or as porous clay aggregates (i.e. PCA). Most of PCA was found closely associated with nanometric Co-bearing Mn-oxy-hydroxides. This finding not only provides a better understanding of the early stage formation of Mn-oxy-hydroxides in laterite systems, but is also important to better constrain the Co distribution and targeting within unconventional laterite ore facies. The nanoscale HRTEM imaging coupled with SAED allowed detecting minor Ni-bearing chlorite amounts, which were not found through previous XRPD-based techniques. Moreover, the paragenetic association of chlorite with primary serpentine suggests a pre-lateritic formation for chlorite. The detection of Ni-bearing trioctahedral smectite as alteration product of primary chlorite is of relevant importance, as it fills a gap in the knowledge of ore-formation processes occurring in smectite-endowed laterites
Influence of genetic processes on geochemistry of fe-oxy-hydroxides in supergene Zn non-sulfide deposits
Get PDFIn supergene Zn non-sulfide deposits, the Fe-oxy-hydroxides (FeO/OH) are mainly concentrated in the residual zones (gossan) on top of the oxidized ore bodies, although they can also be found throughout the whole weathering profile coexisting with the primary and secondary ore assemblages. Fe-oxy-hydroxides are rarely pure as they form in systems where a wide range of metals, most of them of economic importance (e.g., Zn, Pb, Co, REE, Sc, Ga, Ge, V, etc.), freely circulate and can be “captured” under specific conditions. Although their occurrence can be widespread, and they have a potential to scavenge and accumulate critical metals, FeO/OH are considered gangue phases during the existing processing routes of Zn non-sulfide ores. Moreover, very little is known about the role of the deposit type on the geochemistry of FeO/OH formed in a specific association. Therefore, this paper provides a comprehensive assessment of the trace element footprint of FeO/OH from a number of Zn non-sulfide deposits, in order to define parameters controlling the metals’ enrichment process in the mineral phase. To achieve this, we selected FeO/OH-bearing mineralized samples from four supergene Zn non-sulfide ores in diverse settings, namely Hakkari (Turkey), Jabali (Yemen), Cristal (Peru) and Kabwe (Zambia). The petrography of FeO/OH was investigated by means of scanning electron microscope energy dispersive analysis (SEM-EDS), while the trace element composition was assessed using laser ablation-ICP-MS (LA-ICP-MS). Statistical analyses performed on LA-ICP-MS data defined several interelement associations, which can be ascribed to the different nature of the studied deposits, the dominant ore-formation process and subsequent evolution of the deposits and the environmental conditions under which FeO/OH phases were formed. Based on our results, the main new inferences are: (A) Zinc, Si, Pb, Ga and Ge enrichment in FeO/OH is favored in ores where the direct replacement of sulfides is the dominant process and/or where the pyrite is abundant (e.g., Cristal and Hakkari). (B) When the dissolution of the host-rock is a key process during the supergene ore formation (i.e., Jabali), the buffering toward basic pH of the solutions favors the uptake in FeO/OH of elements leached from the host carbonate rock (i.e., Mn), whilst restricting the uptake of elements derived from the dissolution of sulfides (i.e., Zn, Pb, Ga and Ge), as well as silica. (C) The input of exotic phases can produce significant enrichment in “unconventional” metals in FeO/OH (i.e., Cr and Co at Kabwe; Y at Cristal) depending on whether the optimal pH-Eh conditions are attained. (D) In the Kabwe deposit, FeO/OH records heterogeneous geochemical conditions within the system: where locally basic conditions prevailed during the alteration process, the V and U concentration in FeO/OH is favored; yet conversely, more acidic weathering produced Zn-and Si-bearing FeO/OH
Trace element geochemistry of iron-(oxy)-hydroxides in Ni(Co)-laterites: Review, new data and implications for ore forming processes
Get PDFIron-(oxy)-hydroxide (FeO/OH) phases are abundant in all supergene ore deposits. The most common FeO/OH phase in supergene environments is goethite, although hematite, lepidocrocite, ferrihydrite, and maghemite can also occur. Natural FeO/OHs are rarely chemically pure, as a range of metal cations can be readily incorporated into their mineral structure. Although an extensive body of literature exists on the scavenging action of synthetic FeO/OHs, there is a general lack of studies of natural systems and, more specifically, of studies dealing with the geochemistry of trace elements in FeO/OHs associated with supergene ores. Furthermore, although it is known that FeO/OHs in supergene ore systems typically contain elevated levels of useful metals like REE, Sc, V, Co, Mn, Cr, and Ni, in most cases, these phases are considered as gangue and hence, the metals are not recovered. Only in the case of Ni(Co)-laterite deposits the FeO/OHs are often exploited for Ni and Co, and sometimes for Sc. Most previous works on Ni(Co)-laterite deposits have focused on the lateritization process of the parent rocks and the mineralogy of the resulting Ni(Co)-bearing minerals. Only rarely have published studies focused on REE, V, Sc, and PGE deportment within FeO/OHs. In this study, we describe new mineralogical and chemical data (XRPD, SEM-EDS, EPMA, ICP-AES, LA-ICP-MS, and TEM-HRTEM) obtained from a range of natural FeO/OH samples collected from four important Ni(Co)-laterite deposits, namely Wingellina (Western Australia), Piauí (Brazil), Karaçam and Çaldağ (Turkey). In the course of this study, we investigated the geochemistry of goethite and hematite within the oxidation zone of the respective laterite profiles, evaluating the deportment of minor metals such as Ti, Sc, Cr, Ni, Co, V, Zn, and Mn. Although derived from different parent rocks located in different geographic areas, the FeO/OH samples collected share a number of common features. In particular, there are commonalities in ore textures, mineralogy, and metal deportment. Based on multivariate statistical analysis, the chemistry of the studied FeO/OHs define three major elemental associations: i) Mn–Al–Ti–Sc–V as evident in goethite samples from Wingellina; ii) Mg–Ni–Si–Zn as exemplified by samples from Karaçam and Piauí, and iii) Cr–V as illustrated by the Çaldağ samples. These contrasting geochemical footprints can be explained in terms of first- and second-order controls with the chemical composition of the parent rock representing the first-order, and favorable pH conditions for the fixation of trace elements within FeO/OHs representing the second-order control. Seasonality and maturation may be additional factors influencing FeO/OHs mineralogy, as periods of arid climate may have favored the dehydration of some FeO/OHs to form more stable species (such as goethite to hematite) over time. In summary, our observations have helped to better understand the ore deposition model relating to surficial weathering systems and have also established the parameters that control the distribution of economically relevant by-product metals in FeO/OHs in diverse conditions during the formation of Ni(Co)-laterites
Ni-Co enrichment and High-Tech metals geochemistry in the Wingellina Ni-Co oxide-type laterite deposit (Western Australia)
No full textThe aim of this study is to evaluate the Ni-Co enrichment and the high-tech metals (REE and Sc) geochemistry in the Wingellina Ni-Co oxide-type laterite deposit (Western Australia). The study has been carried out on two mineralized cores (WPDD0012 and WPDD0019 drillcores) originating from two areas of the deposit. The geochemical assessments have been integrated with the analysis of laterite facies and sample mineralogy. In both the studied laterite profiles Ni enrichment was mostly controlled by the paragenetic evolution of the laterite itself, whereas Co enrichment was related to the formation of Mn-oxy-hydroxide-rich horizons in the limonitic ore-body. Significant REEs concentrations (up to 890 ppm) have been observed within the limonite zones. The correlation between REEs and the major oxides shows a decoupling between Ce and the other REEs, likely reflecting either a variable enrichment process among the different REEs, or a heterogeneous mineralogy of the REEs-bearing phases. Differently from other Ni-Co laterite deposits, Sc is only in limited part correlated with Fe2O3, having been most commonly detected in Ni- and SiO2-rich zones of the saprolitic parts of the profiles. All the geochemical features, the facies characteristics and the Ni-Co, REEs and Sc grades observed in the two studied profiles seems to be the results of the interactions between two main controlling factors: distinct parent rock lithology and diverse degree of serpentinization
Vanadium ore resources of the African continent: State of the Art
Get PDFAs part of the critical metals group, vanadium is an essential commodity for the low- and zero-CO2 energy generation, storage and transport. This contribution aims to carry out a review of the known vanadium ore sources and mineralizations located in Africa, which are highly diversified in their geological and mineralogical characteristics, and can be classified in: 1. Vanadiferous (titano)magnetite deposits; 2. Sandstone-hosted (U)-vanadium deposits; 3. Calcrete-hosted (U)-vanadium deposits; 4. Vanadate deposits; 5. Graphite-associated vanadium deposits; 6. Vanadium occurrences associated with laterite, bauxite, and phosphate ores. The economically most significant vanadium sources in Africa are associated with titanomagnetite layers in mafic–ultramafic layered magmatic intrusions (e.g., the Bushveld Complex in South Africa and the Great Dyke in Zimbabwe). Vanadium has been historically mined also in vanadate deposits deriving from the supergene alteration of Pb-Zn-Cu sulfide ores in Namibia and Zambia. Several areas in these countries, where potentially re-processable old tailings and slags have been accumulated, still have economic potential. Vanadium mineralizations are associated with graphite bodies in the Mozambique Metamorphic Belt. Vanadium is also enriched in uranium ores occurring in the Upper Paleozoic-Mesozoic Karoo continental sediments: typical examples are found in Botswana, South Africa, and Zimbabwe. Significant uranium-vanadium concentrations (where carnotite prevails) occur in relatively recent (Tertiary-Quaternary) calcrete duricrusts in paleo-fluviatile beds, which are widespread throughout the African continent. These derive from the weathering of U-(V)-fertile source rocks, which under favorable paleoclimatic conditions resulted in the vanadium precipitation in the critical zone. Variable vanadium amounts have been also recorded in iron ore deposits, phosphorites, and laterites, even though the phosphate deposits seem to have the most favorable characteristics for potentially economic vanadium concentrations. On the whole, South Africa holds the most significant vanadium ore resources globally. However, also many other African countries, where this metal could be profitably extracted as a by-product from other economic ores, will probably be at the forefront of vanadium production in the near future
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
