Abstract
Abstract 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 (Zn2SiO4) 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.
Highlights
Nowadays, Nexa Resources operates two zinc mines in Brazil, represented by the Vazante unit in Vazante - MG and the Morro Agudo unit in Paracatu - MG
From the eleventh minute to the twelfth, there is no increase in zinc recovery for any of the samples tested, showing that the maximum zinc recovery is reached in the eleventh minute of the flotation procedure
Through flotation to exhaust testing of the ore that feed the Vazante Plant, it was discovered that the maximum zinc recovery that can be achieved in experimental conditions was 91.07% with 1.68 % of zinc grade in the tailings after an elevenminute flotation
Summary
Nexa Resources (exVotorantim Metais) operates two zinc mines in Brazil, represented by the Vazante unit in Vazante - MG and the Morro Agudo unit in Paracatu - MG. Its main zinc ore is Willemite (Zn2SiO4), and its concentration process consists of mining, ore transportation, crushing, grinding, classification by size, direct flotation, filtration and shipping. The zinc concentrate produced in Vazante is sent to the Três Marias plant (smelter), where it goes through hydro-metallurgical and electrolysis processing, turning into metallic zinc to produce alloys that are used in several other applications. The present study aims to determine the maximum recovery of zinc that can be obtained under controlled conditions of bench flotation tests, and to perform a mineralogical characterization of the tailings generated, mainly to identify which are the factors that prevent zinc recovery from being higher
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