Textural and mineralogical characters of ore together with technical parameters of enrichment plants strongly affect efficiency of chromite sand concentration with shaking tables. Such parameters were studied at Brieville gravity enrichment plant that works chromite ore from different mines within Andriamena district (Madagascar). Ore is a massive to densely disseminated chromitite hosted within a peridotitic to pyroxenitic country rock. Gangue mineralogy is very rich, comprising ortho and clinopyroxene, tremolitic to edenitic amphibole, phlogopite, chlorite, talc and minor pentlandite, pyrrhotite, ilmenite, rutile and dolomite. Ore is firstly crushed and sieved to a grainsize below 2.5 mm, then it is hydroclassified and sent to shaking tables. As a result of hydroclassification different tables receive sand of decreasing grainsize. Mineralogy, chemistry and granulometry show that hydroclassification operates a preselection of chromite sand and as a consequence tables are fed with sands different not only for grainsize but also for mineralogy and chemistry. Separation of grains in a shaking table occurs due to contrasts in specific weight, grainsize and, to a minor extent, grain shape. Specific weight contrast between grains for a given grainsize distribution of sand depends on density and degree of liberation of phases (Wills and Napier-Munn, 2006). At Brieville degree of liberation of chromite was assessed for each table and for each grainsize. Results show that degree of liberation depends on the relation between Crystal Size Distribution of chromite in the rock and grainsize of sand. For grainsize above 300 m degree of liberation is enough low to considerably reduce enrichment efficiency of tables working such grainsizes. Increase of sorting from feeding sand to concentrate confirms that shaking tables separate grains also according to grainsize and low sorting of feeding sand suggests sieving as a more efficient technique to select sand to be sent to shaking tables rather than hydroclassification. Results of mineralogy distribution suggest that gangue minerals behave in different ways according to their density and habit, showing differential enrichments due to preselection operated by hydroclassification and to selection operated by gravity separation through shaking tables. At Brieville the main parameter affecting efficiency of shaking tables is the degree of liberation of chromite. As a result the table working the coarsest grainsize is able to enrich Cr2O3 content of feeding sand by only 5.14 wt%, against an enrichment of 20.26 wt% for the table working the finest grainsize. This result is disguised by the Cr2O3 pre-enrichment of the coarser sand operated by hydroclassification as the combination of the two processes gives a concentrate sand similar in Cr2O3 content for all the tables. In general results show that a detailed mineralogical and textural study of the ore can provide useful information to get the highest efficiency of the plant through an appropriate choice of crushing degree and shaking table settings and by substitution of hydroclassfiers with sieves.

Textural and mineralogical constraints in chromite sands enrichment by shaking tables at Brieville plant (Madagascar) / G. Grieco, M. Pedrotti, A. Merlini, D. Pileri. - In: ACTA MINERALOGICA-PETROGRAPHICA. - ISSN 0365-8066. - (2010). ((Intervento presentato al 20. convegno General Meeting of the International Mineralogical Association : Bonds and bridges tenutosi a Budapest nel 2010.

Textural and mineralogical constraints in chromite sands enrichment by shaking tables at Brieville plant (Madagascar)

G. Grieco;M. Pedrotti;A. Merlini;
2010

Abstract

Textural and mineralogical characters of ore together with technical parameters of enrichment plants strongly affect efficiency of chromite sand concentration with shaking tables. Such parameters were studied at Brieville gravity enrichment plant that works chromite ore from different mines within Andriamena district (Madagascar). Ore is a massive to densely disseminated chromitite hosted within a peridotitic to pyroxenitic country rock. Gangue mineralogy is very rich, comprising ortho and clinopyroxene, tremolitic to edenitic amphibole, phlogopite, chlorite, talc and minor pentlandite, pyrrhotite, ilmenite, rutile and dolomite. Ore is firstly crushed and sieved to a grainsize below 2.5 mm, then it is hydroclassified and sent to shaking tables. As a result of hydroclassification different tables receive sand of decreasing grainsize. Mineralogy, chemistry and granulometry show that hydroclassification operates a preselection of chromite sand and as a consequence tables are fed with sands different not only for grainsize but also for mineralogy and chemistry. Separation of grains in a shaking table occurs due to contrasts in specific weight, grainsize and, to a minor extent, grain shape. Specific weight contrast between grains for a given grainsize distribution of sand depends on density and degree of liberation of phases (Wills and Napier-Munn, 2006). At Brieville degree of liberation of chromite was assessed for each table and for each grainsize. Results show that degree of liberation depends on the relation between Crystal Size Distribution of chromite in the rock and grainsize of sand. For grainsize above 300 m degree of liberation is enough low to considerably reduce enrichment efficiency of tables working such grainsizes. Increase of sorting from feeding sand to concentrate confirms that shaking tables separate grains also according to grainsize and low sorting of feeding sand suggests sieving as a more efficient technique to select sand to be sent to shaking tables rather than hydroclassification. Results of mineralogy distribution suggest that gangue minerals behave in different ways according to their density and habit, showing differential enrichments due to preselection operated by hydroclassification and to selection operated by gravity separation through shaking tables. At Brieville the main parameter affecting efficiency of shaking tables is the degree of liberation of chromite. As a result the table working the coarsest grainsize is able to enrich Cr2O3 content of feeding sand by only 5.14 wt%, against an enrichment of 20.26 wt% for the table working the finest grainsize. This result is disguised by the Cr2O3 pre-enrichment of the coarser sand operated by hydroclassification as the combination of the two processes gives a concentrate sand similar in Cr2O3 content for all the tables. In general results show that a detailed mineralogical and textural study of the ore can provide useful information to get the highest efficiency of the plant through an appropriate choice of crushing degree and shaking table settings and by substitution of hydroclassfiers with sieves.
Settore GEO/09 - Georisorse Miner.Appl.Mineral.-Petrogr.per l'amb.e i Beni Cul
ACTA MINERALOGICA-PETROGRAPHICA
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/213050
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