Desenvolvimento de equipamento produtor de pasta mineral

Abstract

The disposal of tailings in the form of mineral paste, has many advantages in comparison to the dam of tailings, for example; it is needed a very larger area for disposal, presents better water recovery, minor the risk of contamination for the rupture of dam, it reduces the process water contamination; it facilitates the final recovery of theplace. Among others the technology of paste has developed quickly, in the world and more in Brazil. However, it must be standed out that this technology, mainly as for the thickener of paste, is not available, being the information with the manufacturers. This fact shows the necessity of the development of studies, for the best understanding of the involved mechanisms in the thickening of materials with the objective to reach thecharacteristics of mineral paste. The general objectives of this study are characterization of the solid sample proceeding from tailings of manganese of the Companhia Vale do Rio Doce, assessement of cationics, anionics and no ionic floculants, construction andimplementation of a modular equipment in scale of laboratory for production of mineral paste and evaluation of this product by means of reological characterization of the pastes. In the characterization of the solid sample the following physical and chemical properties were determined: density (simple picnometric, gas); size distribution(sieving, centrifugal classification and sympatec analysis); chemical composition (FRX, EDS); mineralogy composition (MEV, DRX and EIV); specific surface area (Blaine and BET). The developed equipment was constructed using acrylic material in modular system that allows the operation in different conditions. It has two modules reaching amaximum height of 1.20m with 10cm of internal diameter. It still makes use of a system for taking samples with holes of 1cm of internal diameter and separated 9cm. The cone of discharge of the paste has an angle of slope of 45° to facilitate the discharge of the mineral paste. Three mechanisms of agitation for processes batch, semicontinuous andcontinuous. It has also a spiral system for feeding and for generation of more compact flocs. The produced mineral pastes were characterized in its reological properties, by means the determination of: viscosity (viscosimetry); consistency (slumps test); fluidity (flume test) and yield stress. From de obtamed results, it can be concluded that: thedensity of the solid material is low (3.142g/cm3); the size distribution represents a fine material (d50=6.23µm); high value specific superficial area (0.893m2/g). In the chemical characterization: the predominant species are Mn, Fe, Si and Al with small amounts of potassium, sodium, magnesium. In the evaluation of floculants, the no ionic SN300 was the best considering the not very high dosages (50g/t), ocours an increase inthe settling velocity of 23.63 times. In the equipment discontinous tests with one module the solid percent in the discharge increases with the volume of pulp for different times of residence, where, the best running time was 10min with a volume of 4000ml reaching 52.9% of solids. The best condition with no addition of floculante in the tests with recirculation of the pulp of 4000ml and residence time equal to 10min was therecirculation from hole 3 to hole 1 with a value of 55.6% of solids. Considering the floculant addition, it was from hole 4 to hole 1 with a value of 53.0% of solids. The best condition with two modules without addition of floculante in the tests of recirculation of the pulp with 7000ml and time of equal residence 10min was the recirculation since outlet 7 for outlet 1 with a value of 56.7% of solids. While that with floculante additionit was since outlet 4 for outlet 1 with a value of 53.7% of solids. For continuous tests with two modules the biggest value of solid percent was obtained with the feed in the hole 6 with 37.4% of solids, not using spiral, the best condition was for a dosage of 50g/t with 52.7% of solids. Using of the floc generator it was reached a value of 55.5% of solids for the same dosage. The profile of concentration with bigger solid percentswithout and with the use of the generator of floculos was for a dosage of 50g/t. In the concentration profile exists a stage of transistion from pulp to paste in the band between 40% and 45%. In the continuous under the best operation condition it was obtained 56.1% of solids. In the flume tests higher values than 8 degrees were reached for the case of the paste prepared with 54.4% of solids, with a paste consistency equivalent to 33.6% of slump. The reological behavior for all the studied pastes presents a double characteristic, thixotropic and reotropic