Zinc is a metal of fundamental importance in the economic development of Brazil and other countries. The main application of zinc is in the galvanization process that consists in coating the alloy surface with a thin layer of zinc. Brazil main known reserves of zinc are located in the counties of Vazante and Paracatu in the state of Minas Gerais and both operations belong to Nexa Resources. Nexa is the sixth greatest producer of zinc in the world, with operations concentrated in Brazil and Peru. The main zinc ore of Vazante mine comes from a mineral called willemite (Zn2SiO4). Vazante concentrator consists of unitary operations such as crushing, grinding, classification, flotation, dewatering and auxiliary operations. Previous studies with Vazante ore indicated high variability in industrial flotation performance related to grinding grain sizes. To evaluate the impact of the grinding grain size and the willemite liberation in the flotation process, a study that contemplated sampling, grinding, mineralogical characterization and bench scale flotation was carried out with ore samples of Vazante mine. The studied samples contemplated special and geological characteristics of Vazante mine ore. The mineralogical characterization results showed that it was possible to increase willemite liberation by grinding the samples in five different grain sizes. The willemite liberation spectrum increased in direct proportion to the reduction of the grain size of the samples. In addition to influencing the zinc recovery, the different grain sizes and willemite liberation spectra also had an effect on the zinc concentrate grades, where finer grain size was responsible for reducing this variable. Considering both zinc concentrate grade and zinc recovery, the best results of the willemite flotation process occurred in the grain size of 12% retained in 0.150 mm. By use of the results obtained and the support of the operational teams, it was possible to reduce the grain size of the grinding process of Vazante industrial plant. It used to operate with grain size between 15% to 18% retained in 0.150 mm until the year of 2015 and since 2016, it was reduced to 10% to 12% retained in 0.150 mm, resulting in an increase of approximately 2% in the zinc recovery of the industrial plant.
Nowadays, Nexa Resources (ex-Votorantim Metais) operates two zinc mines in Brazil, represented by the Vazante unit in Vazante-MG and the Morro Agudo unit in Paracatu-MG. The present study was carried out at the Vazante unit, where zinc concentrate is produced from a silicate ore called Willemite (Zn 2 SiO 4) through froth flotation processes. The two main objectives of the study were the determination of the maximum zinc recovery that could be obtained in flotation bench tests with specific controlled conditions and the mineral characterization of the tailings generated, using a SEM/EDS (scanning electron microscope with energy dispersive x-ray spectroscopy) with MLA (mineral liberation analyzer). The flotation results showed a maximum recovery of 91.91 % with 1.68 % of zinc in the tailings after an eleven-minute flotation. Considering the mean results of all the tests, the maximum zinc recovery obtained was 91.07 % with 1.75 % zinc grade in the tailings. Mineral characterization analysis showed that zinc minerals besides Willemite, such as Gahnite and Franklinite are present in the zinc tailings. In addition, the analysis demonstrated that the Willemite present in the tailings is very fine (80 % < 0.015 mm) and well liberated. With no liberation problems, it was concluded that the main reason responsible for preventing zinc recovery to increase even more along the flotation tests was the presence of the extremely fine Willemite minerals. The test results showed that, to increase zinc recovery, two main processes needed to be considered. The grinding process, that will need to be improved and carefully revised to reduce Willemite fine grain size generation; and the flotation process, regarding bubble formation, reagent addition, resident time and a redesign of flotation machines, aiming to increase the recovery of extremely fine Willemite ore particles.
ResumoA usina de beneficiamento da Unidade Vazante da Votorantim Metais concentra zinco a partir de Willemita -Zn 2 SiO 4 por flotação. Através desse processo, é possível obter elevadas recuperações metalúrgicas. Contudo, foi identificado que é possível aumentar ainda mais a recuperação de zinco através de redução de granulometria. Essa redução eleva os custos de energia de um circuito de cominuição, fato que torna fundamental a identificação da relação ideal entre ganho de recuperação e os gastos com maior consumo de energia. Grande parte das frações de Willemita mais grosseiras (acima de 0,15 mm) que passam pelo processo de flotação, vão para o rejeito. Isso ocorre devido a granulometria atual de moagem não atingir a liberação ideal do mineral de interesse, de forma que, grande parte da superfície das partículas ainda apresenta ganga que não é adsorvida pelo coletor especifico da Willemita. Em busca de elevar a recuperação metálica de zinco potencializando o seu aproveitamento, estudos de caracterização mineralógica foram realizados. O trabalho consistiu na utilização de MEV/EDS com MLA (Mineral Liberation Analyzer) e na realização de testes de flotação em escala de bancada e piloto para determinar a granulometria ideal para flotação do mineral Willemita. Através dos resultados obtidos, foi possível concluir que houve ganhos de recuperação de zinco com a redução da granulometria sem comprometer a qualidade do concentrado gerado. Palavras-chave: Willemita; Zinco; Liberação; Flotação. DETERMINATION OF IDEAL GRAIN SIZE FOR ZINC FLOTATION IN VAZANTE UNIT -VOTORANTIM METAIS AbstractThe Votorantim Metais plant located in Vazante-MG-Brazil processes zinc from a silicate mineral called Willemite -Zn 2 SiO 4 through froth flotation. With this process, it is possible to obtain high recoveries of zinc. However, it is likely to increase the recovery through size reduction. Most part of coarser grains of Willemite (> 0.15 mm) are almost entirely lost and sent to tailings. This fact happens because of the current grinding, that do not achieve optimal liberation of the mineral of interest, so that much of the surface of the particles still have gangue which is not adsorbed by the specific collector of Willemite. Seeking to raise the recovery of zinc, consequently raising the production, studies of mineralogical characterization via MLA (Mineral Liberation Analyzer) and laboratorial froth flotation were conducted aiming to determine the optimal particle size for the froth flotation process of Willemite. Through the results, we concluded that there were zinc recovery gains by reducing the particle size without compromising the Zn grade in the concentrate.
ResumoO objetivo deste trabalho foi estudar a variabilidade do depósito de zinco sulfetado do projeto Ambrósia Sul, da Votorantim Metais localizado em Paracatu -Minas Gerais, frente aos processos de beneficiamento e poder, assim, detalhar o comportamento geometalúrgico dos vários corpos de minério do depósito. Além do estudo da variabilidade dos corpos de minério, o trabalho também inclui testes em escala de bancada durante anos e semestres de operação : 2016, 2017/01, 2017/02, 2018/01, 2018/02, 2019. A metodologia do estudo é resumida nas fases de amostragem de testemunho de sondagem, composição das amostras representativas dos corpos de minério e anos e semestres de operação da mina, testes de moagem, peneiramento, flotação de bancada e caracterização mineralógica da alimentação e produtos dos testes. O teste de bancada desenvolvido neste trabalho, tem como objetivo principal verificar variações significativas entre os corpos mineralizados e/ou semestres de mina de operação, tornando possível identificar potenciais oportunidades de otimização do circuito de tratamento de minérios, maximizando o retorno financeiro de toda a jazida mineral. Palavras-chave: Variabilidade; Geomertalugia; Zinco; Esfalerita. VARIABILITY STUDY OF THE SULPHIDE DEPOSIT OF THE AMBROSIA PROJECT AbstractThe objective of this work was to study the variability of the deposit of sulphide zinc Ambrosia South project, Votorantim Metais located in Paracatu -Minas Gerais, compared to beneficiation processes and can thus detail the geometallurgical behavior of the various bodies of ore deposit. In addition to the study of variability of ore bodies, the work also includes testing at bench scale for years and semesters of operation : 2016, 2017/01, 2017/02, 2018/01, 2018/02, 2019. The methodology of the study is summarized in the stages of drill core sampling, composition of representative samples of the ore bodies and years and semesters of mine operation, grinding tests, screening, bench flotation and mineralogical characterization of food and products testing. The bench test developed in this study has as main objective to verify significant differences between the mineralized bodies and / or semesters operating mine, making it possible to identify potential opportunities for optimization of mineral processing circuit, maximizing the financial return of the entire deposit mineral.
Resumo A Mina de Morro Agudo da Votorantim Metais está localizada na cidade de Paracatu (MG).A mina compreende um depósito de zinco e chumbo e atualmente o método de lavra empregado é o de Câmara e Pilares. O estudo geometalúrgico empregado na unidade tem por objetivo avaliar a performance das câmaras de lavra submetidas a testes de bancada correlacionando características mineralógicas com as etapas de beneficiamento. O minério é constituído predominantemente pelos minerais minério esfalerita (ZnS) e galena (PbS). O trabalho vem sendo desenvolvido com amostras de testemunhos de sondagem e representam as câmaras de lavra dos diversos níveis e regiões da Mina. Além dos testes de bancada que compreendem etapas de moagem, granuloquímica e flotação, as amostras são submetidas às análises químicas e mineralógicas. Foram determinados estatisticamente as classes de teores de alimentação dos testes, com o objetivo de realizar comparações de indivíduos que pertencem à mesma população. As câmaras de lavra são classificadas pelo rendimento geometalúrgico de acordo com a performance da variável recuperação metálica. De acordo com os resultados dos testes em bancada e sua respectiva classificação geometalúrgica, é possível traçar estratégias para que o planejamento de lavras e a usina de beneficiamento possam trabalhar em sinergia, de forma a maximizar o valor econômico de determinada frente de lavra. Palavras-chave: Geometalurgia; Zinco; Chumbo; Variabilidade. GEOMETALLURGICAL CLASSIFICATION OF THE SULPHIDE ORE FROM MORRO AGUDO MINE AbstractMorro Agudo mine located in Paracatu, Northwest Minas Gerais state. The mine comprises a zinc and lead deposit, currently mined in undergroung fashion by rooms and pillars method. The goal of the geometallurgical study, is to evaluate mining rooms performance by means of correlating bench testing to mineralogical chacacteristics with an optimization approach. The sulphide ore consists mainly by mineral ore sphalerite (ZnS) and galena (PbS). Samples are taken from drill cores and represent a universe from different levels and sites of the mine. In addition to the test bench composed grinding steps, chemistry analysis by fraction and flotation, the samples are submitted to chemical and mineralogical characterization. It was possible to stablish statistically population groups according to fedding grade, in order to carry out comparisons of samples belonging to the same population. Mining rooms are classified herby as a function of the variable: metal recovery. From bench testes results, one can drop into conclusions regarding geometallurgical classification in order to optimize mine planning and recovery plant, achieving and integrated perspective of maximum benefit.
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