Maurício Guimarães Bergerman

REMOVAL OF IRON-BEARING MINERALS FROM GIBBSITIC BAUXITE BY DIRECT FROTH FLOTATION

The refractory bauxite needs to present less than 2.5% of Fe2O3 to be applied in the ceramics industry. The depletion of high Al2O3 grade deposits has stimulated the improvement of bauxite concentration methods in order to remove iron-bearing minerals. The objective of this study was to evaluate the influence of collector dosage, pH and milling time on the gibbsite flotation performance. Firstly, the sample mineralogical composition was determined by means of X-ray diffraction (XRD) and binocular loupe analysis. X-ray fluorescence (XRF) analysis was used to determine the sample chemical composition. Flotation was then accomplished by using hydroxamate as gibbsite collector, sodium silicate as silicate depressant and starch as iron-bearing minerals depressant. The bauxite Fe2O3 content was reduced from 7.66% to 4.81-5.03%. In addition, the flotation performance decreased by diminishing the pH from 9.5 to 8.5 or increasing the pH to 10.5. The milling time influence on the flotation indicates that the presence of slime can significantly affect the gibbsite concentration.

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.

ABRASIVENESS EVALUATION OF PRE-CONCENTRATION OF COPPER SULFIDE ORE PRODUCTS THROUGH LCPC TEST

Ore abrasiveness is usually quantified through the Bond Abrasiveness Index (AI), which is based on the capability of a material wearing out and polishing other materials. This index finds widespread application in the assessment of how much wear a given ore is set to cause in ore processing equipment. Several test methods may be used to determine ore abrasiveness, but the Bond Method is the one most frequently used in the mining industry. Despite being simple, this test has certain limitations as to grain size and required amount of ore sample, which very often makes it difficult or even impossible to apply it in the early stages of a project, geometallurgical and pre-concentration laboratory studies. The LCPC test may offer an alternative, as it requires a smaller amount of fine-grained material. The core objective of this study is to use the LCPC test to evaluate the abrasiveness index of a copper sulfide ore that went through a pre-concentration process. One of the findings is that the pre-concentration process produced a concentrate whose abrasiveness is lower than that of the feed, which helps enhance the pre-concentration gains, in addition to the expected gain by reducing the mass and increasing the grade of ore to be fed into the mill.

STATISTICAL EVALUATION OF SCRUBBING AND SCREENING OPTIMIZATION IN BAUXITE PROCESSING

In the Miraí processing plant (Votorantim Metais), bauxite is processed with an average feed of 1,000 t/h in a circuit with crushing, scrubbing and screening stages. Two plant unit operations needed optimization: (1) The scrubber promoted not only the attrition and disaggregation of bauxite, but was also its griding; (2) The screened fine products had material with significant amounts of available aluminium (AA) and low reactive silica (RS) contents. In this work, modifications were introduced in the scrubber and screening circuit in order to improve the plant performance. A pulp lifter was installed in the scrubber. In addition, the apertures of the primary and secondary screens were changed. Statistical univariate analysis was used to support the process gain due to the introduced modifications. According to the variance analysis (ANOVA), there was no loss of product quality since the resulting AA, RS and iron (Fe) contents agree with the metallurgical specification and the previous results before the optimization work. The mass recovery increased by 3.88%, which means a gain of 43 t/h for the operation.

Performance analysis of the HRCTM HPGR in pilot plant

A pilot scale test program was conducted to evaluate the size reduction performance of HPGR (High Pressure Grinding Rolls) operating in different circuit configurations. For this purpose a series of pilot-HPGR locked cycle tests were performed with medium and high pressures to simulate the HPGR operation in closed circuit with a screen, with partial product recycle, and with edge recycle. Logged instrumentation data such as roller speed, working gap, operating pressure, and power draw were used in combination with material test results such as particle size distributions, flake density, flake thickness, and bulk density of the feed for calculation of HPGR operational parameters. The paper reports the results from the pilot HPGR test work. The analysis reported herein includes an evaluation and comparison of different circuit configurations of the HPGR operation in terms of energy consumption, capacity and product fineness and also discusses the benefits of various circuit arrangements.