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Fernandez A Cirelli - One of the best experts on this subject based on the ideXlab platform.
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cr vi and cr iii removal from aqueous solution by raw and modified lignocellulosic materials a review
Journal of Hazardous Materials, 2010Co-Authors: Patricia Miretzky, Fernandez A CirelliAbstract:In aqueous systems, chromium usually exists in both trivalent and hexavalent oxidation states, being Cr(VI) of particular importance and concern due to its great toxicity. Industrial sources of Cr(VI) are leather tanning, mining of Chrome Ore, production of steel and alloys, etc. The most common conventional method for Cr(VI) removal is reduction to Cr(III) at pH 2.0 and precipitation of Cr (OH)3 with lime at pH 9–10. The disadvantage of precipitation is the disposal of the solid waste. Adsorption of Cr by different low cost materials seems to be a suitable choice for wastewater treatment. Many by-products of agriculture have proved to be suitable low cost adsorbents for Cr(VI) and Cr(III) removal from water. Lignocellulosic residues, which include both wood residues and agricultural residues, have adsorption capacity comparable to other natural sorbents, but they have the advantage of very low or no cost, great availability and simple operational process. This study is a review of the recent literature on the use of natural and modified lignocellulosic residues for Cr adsorption. The Cr maximum adsorption capacity and the adsorption mechanism under different experimental conditions are reported when possibly. © 2010 Elsevier B.V. All rights reserved.
Arup Ghosh - One of the best experts on this subject based on the ideXlab platform.
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effect of mgo and zro2 additions on the properties of magnesite Chrome composite refractory
Ceramics International, 2007Co-Authors: Arup Ghosh, Manas Kamal HaldarAbstract:Abstract Magnesite-Chrome aggregates have been prepared from friable Chrome Ore and magnesia of different reactivity in the presence of an additive, ZrO 2 . Two types of batch compositions using sintered magnesia, caustic magnesia and Chrome Ore have been selected for preparing mag-Chrome composites. The batch consisting of sintered magnesia and friable Chrome Ore (SMC) was vibromilled for 8 h, whereas caustic magnesia compositions were added directly to a vibromilled Chrome Ore (CMC) and mixed in a fluidized bed mixer. Additions of 1–5 wt.% ZrO 2 were made to the batches. Firings were carried out between 1700 and 1750 °C with 2 h soaking. Aggregates were characterized by evaluating densification, hot modulus of rupture and microstructure. The reactivity of magnesia was found to play an important role in the final properties of samples. Introducing less reactive sintered magnesia improved all the properties of the aggregates. ZrO 2 was found to be a good sintering aid in the magnesite-Chrome composites.
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effect of compositional variation on the synthesis of magnesite Chrome composite refractory
Ceramics International, 2004Co-Authors: Manas Kamal Haldar, Himansu Shekhar Tripathi, Arup GhoshAbstract:Magnesite-Chrome composites have been prepared by utilizing sintered magnesite and friable Chrome Ore in presence of titania as additive. Three types of batch compositions containing 5% Cr2O3, 18% Cr2O3 and 30% Cr2O3 have been selected for developing mag-Chrome composites. The aggregates were developed by first vibro milling the raw materials and then additives were incorporated in wt.% along with 5% PVA solution as binder to the different batches. It was then properly mixed by fluidized bed mixer and after sieving in 20-mesh BS sieve briquettes were formed uniaxially at a pressure of 100 MPa. The briquettes were first air dried and subsequently oven dried at 110 +/- 5 degreesC for 24 It. Finally, the green briquettes were fired at 1700 and 1750 degreesC in electrically program controlled muffle furnace. The physical properties as well as thermo-mechanical properties and microstructural studies of the sintered aggregates have been evaluated. The common feature observed in the microstructures is the exsolution of spine] phase in magnesia grains. The hot properties of the composites are superior when the Cr2O3 content is increased to 30%. Additives played a significant role in improving the bulk density and strength. (C) 2003 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Manas Kamal Haldar - One of the best experts on this subject based on the ideXlab platform.
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effect of mgo and zro2 additions on the properties of magnesite Chrome composite refractory
Ceramics International, 2007Co-Authors: Arup Ghosh, Manas Kamal HaldarAbstract:Abstract Magnesite-Chrome aggregates have been prepared from friable Chrome Ore and magnesia of different reactivity in the presence of an additive, ZrO 2 . Two types of batch compositions using sintered magnesia, caustic magnesia and Chrome Ore have been selected for preparing mag-Chrome composites. The batch consisting of sintered magnesia and friable Chrome Ore (SMC) was vibromilled for 8 h, whereas caustic magnesia compositions were added directly to a vibromilled Chrome Ore (CMC) and mixed in a fluidized bed mixer. Additions of 1–5 wt.% ZrO 2 were made to the batches. Firings were carried out between 1700 and 1750 °C with 2 h soaking. Aggregates were characterized by evaluating densification, hot modulus of rupture and microstructure. The reactivity of magnesia was found to play an important role in the final properties of samples. Introducing less reactive sintered magnesia improved all the properties of the aggregates. ZrO 2 was found to be a good sintering aid in the magnesite-Chrome composites.
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effect of compositional variation on the synthesis of magnesite Chrome composite refractory
Ceramics International, 2004Co-Authors: Manas Kamal Haldar, Himansu Shekhar Tripathi, Arup GhoshAbstract:Magnesite-Chrome composites have been prepared by utilizing sintered magnesite and friable Chrome Ore in presence of titania as additive. Three types of batch compositions containing 5% Cr2O3, 18% Cr2O3 and 30% Cr2O3 have been selected for developing mag-Chrome composites. The aggregates were developed by first vibro milling the raw materials and then additives were incorporated in wt.% along with 5% PVA solution as binder to the different batches. It was then properly mixed by fluidized bed mixer and after sieving in 20-mesh BS sieve briquettes were formed uniaxially at a pressure of 100 MPa. The briquettes were first air dried and subsequently oven dried at 110 +/- 5 degreesC for 24 It. Finally, the green briquettes were fired at 1700 and 1750 degreesC in electrically program controlled muffle furnace. The physical properties as well as thermo-mechanical properties and microstructural studies of the sintered aggregates have been evaluated. The common feature observed in the microstructures is the exsolution of spine] phase in magnesia grains. The hot properties of the composites are superior when the Cr2O3 content is increased to 30%. Additives played a significant role in improving the bulk density and strength. (C) 2003 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Patricia Miretzky - One of the best experts on this subject based on the ideXlab platform.
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cr vi and cr iii removal from aqueous solution by raw and modified lignocellulosic materials a review
Journal of Hazardous Materials, 2010Co-Authors: Patricia Miretzky, Fernandez A CirelliAbstract:In aqueous systems, chromium usually exists in both trivalent and hexavalent oxidation states, being Cr(VI) of particular importance and concern due to its great toxicity. Industrial sources of Cr(VI) are leather tanning, mining of Chrome Ore, production of steel and alloys, etc. The most common conventional method for Cr(VI) removal is reduction to Cr(III) at pH 2.0 and precipitation of Cr (OH)3 with lime at pH 9–10. The disadvantage of precipitation is the disposal of the solid waste. Adsorption of Cr by different low cost materials seems to be a suitable choice for wastewater treatment. Many by-products of agriculture have proved to be suitable low cost adsorbents for Cr(VI) and Cr(III) removal from water. Lignocellulosic residues, which include both wood residues and agricultural residues, have adsorption capacity comparable to other natural sorbents, but they have the advantage of very low or no cost, great availability and simple operational process. This study is a review of the recent literature on the use of natural and modified lignocellulosic residues for Cr adsorption. The Cr maximum adsorption capacity and the adsorption mechanism under different experimental conditions are reported when possibly. © 2010 Elsevier B.V. All rights reserved.
G. Grieco - One of the best experts on this subject based on the ideXlab platform.
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Chromite Grain Diameter (CGD) from the Ore-hosting dunite of the Xerolivado-Skoumtsa Chrome mine (Vourinos,Western Macedonia, Greece): implications for Chrome Ore exploration
2018Co-Authors: E. Tzamos, Ewing A. Rassios, G. Grieco, M. Bussolesi, K. Stamoulis, Athanasios GodelitsasAbstract:The largest Chrome-Ore bearing dunite of the Vourinos Complex occurs within the Xerolivado-Skoumtsa Mine District. The host dunite body has a surface exposure of 3 km2 and extends at least 400m into the subsurface. The dunite body is hosted by harzburgite tectonite interfolded with the dunite body during ductile phases of deformation. The Xerolivado-Skoumtsa mine is one of the world\u2019s largest ophiolite-hosted Chrome deposits with a potential of 6 million tons of Ore assaying at 22 wt.% Cr2O3. Even so, Chrome Ore bodies compose less than 1% of the volume of the dunite body. Exploration consisted chiefly of expensive drilling programs. A well-documented suite of Chrome Ores from the south sector of the mine were collected during the final years of its operation (1987-1988). Samples include twenty-seven (27) samples of serpentinite altered from primary olivine that originally coexisted with the chromite. Two types of serpentinised dunite were distinguished: Type A samples are from serpentinised dunite 1m from the Ore bodies, and Type B samples are silicates infolded with the Ores during original high-temperature mantle deformation. Thin-polished sections were studied via optical microscopes (transmitted and reflected light). All chromite grains (2,776 total measurements) were photographed and measured in eight directions at angular resolution of 22.5o, starting from the maximum diameter. The average and median chromite grain diameter (CGD) was calculated for each sample. These geometric analyses indicate that CGD decreases depending on the position (Type A or Type B) of the samples: the average and the median of the CGD were smaller in the serpentinites next to the chromite Ore bodies (Type A) than those within consecutive chromite Ore bodies (Type B). A decrease of the average and median CGD was found in (today\u2019s) vertical Ore dimension: samples from mine level 717m have larger average and median CGD than samples from over-lying mine level 738m and from the underlying mine level 692m. This concurs with the position of the thickest size of the Ore bodies, decreasing towards the overlying levels and underlying levels. The grain size of chromite in these dunites is due to a combination processes of original Cr-spinel crystallization and grain break-up and deformation concurrent to original dunite thinning around the Ore layers. With the lack of preserved olivine morphology, these structures are the only \u201cfingerprints\u201d of the type of deformation undergone on grain scale. These results could provide a \u201cpetrographic tool\u201d useful for the exploration of schlieren-type Chrome Ores: host dunite (serpentinite) samples present lower average and median CGD when they are found closer to the Ore bodies. Future research on this subject should focus on the verification of the results in other similar Ore-hosting dunites and mineralogical and/or metallogenetic interpretation of the numeric results
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Processes of primary and re-equilibration mineralization affecting chromitite Ore geochemistry within the Vourinos ultramafic sequence, Vourinos ophiolite (West Macedonia, Greece)
'Elsevier BV', 2018Co-Authors: G. Grieco, E. Tzamos, M. Bussolesi, A. Rassios, A. KapsiotisAbstract:The Vourinos ophiolite is a complete ophiolite sequence covering an area of 3c450 km2, that hosts the largest chromite mining district in Europe. Chrome Ore deposits range in size from several millions of tonnes of Xerolivado-Skoumtsa mine to some thousand tonnes of the smallest exploited Ores. Widespread mining activity closed in the 1990s, leaving behind good exposures of chromitite bodies within the closed mines. Samples from 10 of these mines, 4 located in the Northern part of the massif and 6 located in its Southern part, were collected in order to study the spatial variability of chromite and olivine mineral chemistry in these Ores at different scales, and to infer the roles of primary magmatic and secondary post-magmatic re-equilibration processes. Chromites from chromitites show higher XCr (0.75\u20130.87) than scattered spinels in peridotites and serpentinites (0.45\u20130.70) and largely variable XMg (0.40\u20130.78). Chromite compositions of North and South Vourinos Ores largely overlap, while they show differences at the scale of single deposits, with a remarkable higher XMg at Xerolivado-Skoumtsa. High variability internal to each deposit is due to different re-equilibration conditions at variable olivine/spinel volume ratios. Olivine and chromite XMg values are positively correlated to chromite modal content, while XCr of chromite is not significantly affected by re-equilibration. Calculated re-equilibration temperatures are higher for the larger Xerolivado-Skoumtsa deposit (777\u2013837 \ub0C) than for the other smaller ones (715\u2013746 \ub0C). The inferred magmatic temperature is 1243 \ub0C for Xerolivado-Skoumtsa and 982 \ub0C for the other chromite deposits. Calculated melt compositions are very consistent for the 10 studied mines that all show a boninitic affinity. The whole set of data shows that Vourinos chromitites were formed in an island arc environment from a heterogeneous mantle source that underwent different degrees of melting. Subsolidus re-equilibration occurred during cooling at temperatures as low as 700 \ub0C, partially obliterating primary magmatic features
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Metallogeny of the Chrome Ores of the Xerolivado-Skoumtsa Mine, Vourinos Ophiolite, Greece : implications on the genesis of IPGE-bearing high-Cr chromitites within a heterogeneously depleted mantle section
'Elsevier BV', 2017Co-Authors: E. Tzamos, Ewing A. Rassios, G. Grieco, A. Filippidis, A. Koroneos, P.n. Gamaletsos, A. Kapsiotis, N. Kantiranis, A. Papadopoulos, Athanasios GodelitsasAbstract:Chrome Ore deposits comprise less than 1% of the volume of a pervasively serpentinized dunite body ( 3c3.5km3) that constitutes the Xerolivado-Skoumtsa Mine of the Vourinos Ophiolite in northwestern Greece. Ores have been examined to aid determination of their geological mode of occurrence, their mineralogy and mineral chemistry (Cr-spinel and olivine), and platinum-group element (PGE) geochemistry. The Ore bodies are highly deformed and of the schlieren type, where Cr-spinel-rich and serpentine (after olivine)-rich layers (1-20cm thick) alternate. The Cr-spinel displays a limited range in Cr# [100 7Cr/(Cr+Al)] atomic ratio (77-85) and TiO2 content (0.05-0.22wt%). The Mg# [100 7Mg/(Mg+Fe2+)] of Cr-spinel shows a wider variation (52-74) indicating that subsolidus (Mg Sp -Fe2+Ol ) re-equilibration occurred. Remnant fresh olivine in the serpentine-rich layers is typical forsterite [Fo#: 100 7Mg/(Mg+Fe2+)=93-95]. The Cr-rich chromitite Ores have total PGE and Au abundances that range between 74.3 and 205ppb: they show a general enrichment in Ir and Ru over PPGE (Rh, Pt and Pd) resulting mostly in a negatively-sloping C1 chondrite-normalized PGE profile with a quite strong Ru peak. Field observations indicate that the schlieren banding of the deformed Ore bodies is a tectonometamorphic feature acquired within ductile deformation of the ophiolitic slab. Geochemical calculations demonstrate that the parental melts of the Xerolivado-Skoumtsa high-Cr chromitites were boninitic. Their high Ru content and variation in Cr# Sp values indicate a polygenetic origin from geochemically similar, but spatially distinct melt inputs. These melts originated within a hydrated mantle wedge beneath a fOrearc basin within an evolving lithospheric slab. We emphasize that the PGE budget of the Xerolivado-Skoumtsa chromitites was not inherited from interactions of the migrating melts with their parental harzburgites, but it is an intrinsic feature of the deep-seated and heterogeneously depleted mantle source of these magmas
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Major and minor element geochemistry of chromite from the Xerolivado-Skoumtsa mine, Southern Vourinos : Implications for Chrome Ore exploration
'Elsevier BV', 2016Co-Authors: E. Tzamos, G. Grieco, K. Stamoulis, A. Filippidis, A. Rassios, K. Michailidis, A. Koroneos, M. Pedrotti, P.n. GamaletsosAbstract:The concentration of major (Cr, Al, Mg, Fe) and minor (Ti, V, Mn, Ni, Zn) elements was studied in chromitite Ores and accessory Chrome spinels within serpentinite host rocks from the Xerolivado-Skoumtsa mine (Southern Vourinos, Western Macedonia, Greece) by means of electron microprobe techniques. Chrome Ores in the mine occur in seven extensive Ore bodies. Chromite was analyzed with respect to its position within or between Ore bodies, including the following classifications: chromitite (schlieren Ore) band, accessory chromite in intercalated serpentine within the Ore bodies, disseminated chromite in non-Ore bearing host rocks, and chromite within serpentinites intermediately adjacent to Ore bodies. Chrome spinel originally forms at temperatures of around 1300 \ub0C, but their hosts undergo ductile deformation to temperatures down to around 700 \ub0C, thus facilitating solid state re-equilibration. Results showed that Mg in chromite was found to be substituted during re-equilibration mainly by Fe and, to a minor extent, by Mn and Zn. Cr is mainly substituted by Al and, to a minor extent, V. Compositions were found to vary in accessory chromite crystals as a function of their distance from chromitite bands. Specifically, the average concentrations of Cr and Mg are higher in spinels within chromitite Ores than for the disseminated spinels in serpentine gangue layers within chromitites. Chrome spinels in schlieren Ore layers have higher Mg and Cr concentrations compared to the disseminated chromites in the serpentinites immediately adjacent to the chromite Ore bodies and also slightly higher concentrations of Mg and Cr than the disseminated chromites in the host serpentinites. Fe2+, Mn, Zn, Al and V cations show exactly the opposite trend. We attribute these variations in the spinel chemistry to subsolidus reactions between chromite, silicate mineral phases and fluids. Geochemical maps presenting the spatial variation of these elements in disseminated Cr spinels of the Xerolivado mine can serve to delineate the precise position of the Chrome Ore bodies
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Geochemical trends within Madagascar chromite Ores
Department of Mineralogy Geochemistry and Petrology University of Szeged (Hungary), 2010Co-Authors: A. Merlini, G. GriecoAbstract:The most important chromitite deposits of Africa are mainly located in South Africa, in the well known Bushveld complex, nevertheless Madagascar hosts some important chromitite deposits making Madagascar the world's 10th largest chromite producer. Kraomita Malagasy, the state-owned mining company, produces a chromite concentrate grading between 48 and 50 wt% Cr2O3 with 0.002 to 0.003 wt% P2O5 and lumpy Chrome Ore grading from 42 to 44 wt% Cr2O3. The main chromitite deposits of Madagascar are located in Andriamena, Befandriana and Tamatave regions and are related to archean basic-ultrabasic intrusions set in the central zone of the island. The mineralized regions present different geochemical and textural features that have influenced the explotaition and the general developing of chromite mining industry of Madagascar. Since strong quality parameters are required for the commercialization of both concentrate and lumpy products, a detailed chemical and textural analysis of such mineralization has been focused on understanding quality profile of these Ores in ordrer to maximize future exploitation that strongly depends on chrmical and textural features of the Ore itself. The Andriamena complex, located at the southern end of the Tsaratanana Mineral Field, has been the leading Chrome producing region of Madagascar for the last decades. In Andriamena complex most of the chromite production comes from three mines: Ankazotaolana mine is characterized by a series of ultramafic lenses hosted by a gneissic rock of archean age. Chromitite shows values of C2O3 wt% between 35 and 40 with a Cr/Fe ratio up to 2.7; Bemanevika mine, characterized by a series of parallel lenses at different depth, has an average C2O3 content of 40 wt% and a Cr/Fe ratio of 2.3. Recent estimates predict 2.6 Mt of reserves for this area; the small deposit of Telomita has been recently reopened to increase the production. Telomita is charachterized by a C2O3 content similar to that of Ankazotaolana and a Cr/Fe ratio of 2.2. Befandriana district represents another strategic zone where chromitite lenses, ranging from few meters up to 10 meters in thickness, are highly massive, with C2O3 close to 53 wt% and Cr/Fe ratio close to 2.6. Tamatave district was the first to be exploited in the \u201960 of last century and is characterized by highly deformed and metamorphosed chromitite lenses located in two main sites: Ambodiriana and Ranomena. Generally Tamatave chromitites show a low C2O3 content, close to 30 wt% and a Cr/Fe ratio lower than 1.5. Some important differences among studied Ores have been highlightet by textural and chemical analyses. Andriamena chromitites show an average good quality, but with differences between mines. Befandriana Ores show the best quality due to their massive texture together with high Cr2O3 content of chromite. Chromitite from Tamatave results to be absolutely unsuitable due to the low C2O3 content of chromite. On the other hand a surplus value of Tamatave chromitite is the presence of Platinum Group Minerals (PGM) mainly of laurite or complex solutions observed both included in chromite grains as well in the matrix. In general main chromite Ores of Madagascar show a trend of decreasing Cr2O3 content from north to south, related to differences in Ore genesis, that strongly affects Ore quality for exploitation