Arthur Pinto Chaves

Mechanisms of bioleaching of a refractory mineral of gold with Thiobacillus ferrooxidans

A quick, simple and reproducible method for the indirect determination of the population of the absorbed and suspended bacterias in the cultivation media is the Bradfords method. It has been used to evaluate the fraction of bacteria adhered to the mineral during the bioleaching process and the suspended fraction. It was observed that a significant fraction of the bacteria is adhered to the mineral surface. This proportion varies with the environmental conditions, mainly pH, the presence of ferric ions and the way to supply the mineral sulphide. It has also been observed that the fraction adhered to the solid shows a progressive loss of its oxidative activity. The results can help demonstrate that the sulphides leaching is due to the combination of the direct bacterial action on the sulphide mineral surface with the indirect leaching by the ferric ion produced by the bacteria into the solution.

Process design for gold ores: A diagnostic approach☆

Abstract Much careful work and thought are needed from the time an ore is discovered until a marketable product is produced. Most often, incomplete or imprecise information on the deposit must be used to decide to continue or not with the development and implementation of a project. This paper presents a diagnostic methodology to deal with gold projects at the preliminary stages. We have developed “IntelliGold”—an expert system for gold process design. A knowledge base on gold mineralogy and processing is used to provide the user with feasibility information on a given gold ore. Decision-makers can have a preliminary, yet reliable view of the mineral processing project, based on lab results supported by mineralogical characteristics, operational issues and economic analysis.

Concentration of bauxite fines via froth flotation

A Companhia Brasileira de Aluminio (CBA) tem usinas de beneficiamento de bauxita em Pocos de Caldas e Itamarati de Minas e uma nova unidade de producao em Mirai (junho de 2008), todas localizadas no Estado de Minas Gerais. As usinas de beneficiamento tem as operacoes unitarias de britagem, desagregacao em escrubers e peneiramento. O oversize das peneiras e o concentrado ou bauxita lavada. Em Itamarati de Minas, os finos sao deslamados e concentrados por diferenca de peso especifico em espirais de Reichert, complementadas por separacao magnetica de alta intensidade. Os rejeitos ainda contem bauxita, que pode ser separada por flotacao reversa da silica e depressao da bauxita. Usam-se amido como depressor e amina como coletor. O pH precisa estar em torno de 10,0. Os minerais portadores de ferro e de titânio acompanham a bauxita, o que exige uma operacao adicional de separacao magnetica para atingir o teor desejado de alumina aproveitavel. Esse trabalho descreve o desenvolvimento de processo para o minerio de Itamarati de Minas, em escala de bancada, realizado nos laboratorios da Escola Politecnica da USP.

MINERALOGICAL CHARACTERIZATION OF Ni-BEARING SMECTITES FROM NIQUELÂNDIA, BRAZIL

Nickel-lateritic ore is the most common source of nickel in Brazil. The Niquelândia deposit, located in State of Goias, is one of the most famous deposits due to the large amounts of nickel associated with both oxidized and mainly silicated ores. The terms oxidized and silicated ores are used to specify two different ores formed exclusively by oxides and silicate (clay) minerals, respectively. The aim of the present study was to characterize thoroughly the silicated ore to identify the Ni-bearing clay minerals and their crystal chemistry in support of developing a better mineral-processing method or optimizing the current one to improve Ni recoveries. X-ray diffraction, chemical analyses, scanning electron microscopy, and Fourier transform infrared (FTIR) spectroscopy demonstrated that nickel is associated with Ni-rich stevensite and to a lesser extent with Fe-rich montmorillonite. The crystal chemistry performed by FTIR spectroscopy revealed that Ni is present in the octahedral positions, substituting for Mg or Fe, which results in significant chemical and layer-charge heterogeneity in the samples. This heterogeneity seems to be responsible for reduction in Ni recoveries during the hydrometallurgical process.

An Innovative Approach to Mine Blast Fragmentation Management Using Complexity Analysis: Three Case Studies

This paper introduces an innovative solution for devising a robust blasting plan that will present consistently good fragmentation performance under highly uncertain environments. The analysis will be carried out using complexity analysis tools, a model-free approach to complex systems which is particularly well suited to the problem of finding non-deterministic dependencies between multiple variables. The study is backed-up by data from over 2,000 blast records from Brazilian mines and identifies what are the critical aspects of the system and how to manage the blasting plan to reduce their impact on its performance.

Concentration of bauxite fines via gravity concentration

Companhia Brasileira de Aluminio (CBA) has a preparation plant at Itamarati de Minas, MG. This plant washes two different kinds of bauxite ore, one originating from the laterization of gnaisses and another from amphybolites. Both ores have the same behavior in the coarser size fractions but behave differently under 0.355 mm (42# Tyler). In these small sizes, gneissic ores are rich in quartz and amphybolitic ores are rich in iron and titanium bearing ores. The unit operations are: scrubbing of the feed in drum scrubbers, desliming in cyclones, and screening of the scrubbed bauxite in high frequency screens (0.355 mm) - the +0.355 mm product is a final concentrate. The -0.355 mm fraction is desliming in two stage cyclones and goes to a fines gravity concentration circuit of Reichert spirals complemented by magnetic separation of the light product from the spirals. The research work, including mineralogy, process development, batch tests and pilot plant tests, is described and compared to the actual results in the industrial circuit.

Reciclagem de fios e cabos elétricos - cabo paralelo

O descarte de produtos eletro-eletronicos vem crescendo anualmente. Por esse motivo, necessita-se de reciclagem para que se evite o desperdicio de recursos naturais nao-renovaveis. O objetivo desse trabalho e estudar a reciclagem dos cabos tipo cordao paralelo atraves de operacoes unitarias de tratamento de minerios. As seguintes operacoes unitarias foram testadas: moagem, separacao granulometrica, separacao em meio denso, separacao eletrostatica, atricao, bateamento e elutriacao. Ao final desses processos, observou-se que as operacoes utilizadas obtiveram concentrados de cobre com baixo grau de contaminacao. Observou-se que todas as tecnicas precisam de uma outra tecnica para complementa-las. Concluiu-se, ainda, que a moagem em moinho de facas com grelha de 3mm e necessaria para se conseguir a total liberacao dos materiais.

Flotação do carvão contido em um rejeito carbonoso

The processes involved in coal preparation produce harmful effects for the environment, mainly by the quantity and nature of wastes that are generated. These tailings generally called “pyritic”, even though not presenting a high pyrite content, are an acid material harmful to the environment. These tailings are usually disposed of in tailings dams. The tailings, studied in this work come from a process involving dense-medium cyclones and spirals. They have an ash content of 56% and a calorific value of 5,800 BTU / Lb, the sulfur content is 1.2%. In terms of size, the material is considered as ultrafine, as 63% of it is less than 0,014 mm. The coal matter content of these tailings is easily recovered by froth flotation, as evidenced in this work. Its possible to recover 74% of the coal matter and to obtain a product with 7.3% ash and calorific value of 14,225 BTU / lb in dry basis.