CARACTERIZAÇÃO TECNOLÓGICA DE UM SINTER FEED HEMATÍTICO CONTENDO DIFERENTES PROPORÇÕES E TIPOS DE SÍLICA NAS FRAÇÕES ADERENTES, INTERMEDIÁRIAS E NUCLEANTES
Victor Pereira Padula
DATA DE PUBLICAÇÃO
There are important Vale iron ore reserves located in the state of Minas Gerais. The hematite/itabirite relationship in the ROMs has been decreasing compared to the last decade. The beneficiation plants have been concentrating its efforts on reducing the silica content in the sinter feed in order to reach the quality levels demanded for the sintering process. Although the process routes are being adequated, this is occurring without the profound knowledge required with regard to the quality impact of the sinter feed silica within the sintering process parameters and the physical and metallurgical quality of the sinter product. The objective of this study is to characterize a hematite sinter feed containing different silica proportions and types in the following grain size distribution: aderent, intermediate and nucleant. The sinter feed base had received silica from different sources. The three silica sources used were: compact itabirite from Itabira, jig tailing from Água Limpa and finally the quartzite produced in the state of Espírito Santo. For the sinter feed base and silica source characterizations the following chemical, grain size distribution, mineralogical and microstructural analyses were performed. The methods involved were: an X-ray florescence, a humidity technique, an electronic and optic microscope and X-ray diffraction. Nine combined mixtures with different proportions of silica sources were added in different grain size distributions and tested in the sintering plant (pot grate) representing on average 26% of the total mixture or 35% of the iron ore combination (sinter feed base + added silica sources). The produced sinter was submitted to chemical, physical, metallurgical and mineralogical analyses and the obtained results were treated using the statistical DOE and ANOVA method but at times just the overall view tendencies. The sinter feed base chemical results presented a global silica content of 2.51%. The variation of the silica content among the three added sources was from 17.03% for compact itabirite to 96.13% for quartzite in all granulometric fractions. The jig tailing presented the highest level of alumina content, above 2%, regardless of the grain size distribution. The silica iron ore mixture (sinter feed base + added silica sources) was on average 3.76%. The nucleant fraction of the compact itabirite is non liberated (SM) for intermediate and aderent fractions they are both liberated monocrystaliine. The jig tailing was classified in all grain size fractions as liberated monocrystaliine. Finally, the quartzite was classified as liberated policrystaliine. The nine silica sinter product variations were between 4.15% and 4.45% and the binary basicity between 1.72 and 1.77. The average size varied from 25.99mm to 22.99mm, the mineralogical composition (area percentage) was: hematite 40%, magnetite 32%, ferrite 20%, silicates 6%, residual calcareous 1.5% and residual quartz 0.5%. Maintaining the same grain size distribution, the compact itabirite has the highest silicate percentage, whereas, the jig tailing has the lowest. The different silica characteristics and/or its added distribution proportions influenced the physical and metallurgical results of the sinter product. The best tumbler index results were obtained by the usage of aderent fraction, whereas in the shatter test, the result tendencies were reduction, except for the liberated policrystaliine silica (SLP). The compact itabirite tumbler index results contributed minimally. Moreover, its aderent fraction showed the lowest level for this test and second lowest result in the shatter test. At the bottom level of the scale was the compact itabirite in the aderent fraction. Regardless of the fraction, the jig tailing demonstrated the best tumbler resistance level. Due to the aderent silica proportion increase, the RDI tests presented its lowest results (meaning the best). For practically all the fractions, the jig tailing reached the highest RDI level (meaning the worst). The best and most stable reducibility results were obtained with the usage of quartzite. There is an inversion tendency between jig tailing (aderent fraction 72.3%) and compact itabirite (nucleant fraction 71.9%). The different silica characteristics and/or its added distribution proportions influenced the fuel consumption and productivity results of the sintering process. In the nucleant fraction, there exists a strong tendency for obtaining the best productivity levels in the sintering process. In addition, the compact itabirite contributed to the highest productivity levels. The nucleant fraction resulted in lower fuel consumption. With the jig tailing usage, there exists a tendency of a lower fuel consumption with the exception of aderent fraction.
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