Laurindo de Salles Leal Filho

Distribuição de tempos de residência da polpa em células mecânicas de flotação

The Residence-Time Distribution (RTD) technique is a tool widely used in the mineral industry for assessing the mixture quality found in flotation cells. It involves introducing a tracer pulse at the feed of the cell and controlling the tracer concentration at its discharge. This technique provides the RTD function and the mean residence time (t m ) and variance (σ 2 ). This work presents and discusses the application of the RTD technique on mechanical flotation cells of the Rio Paracatu Mineracao, Paracatu-MG. The results provided technical guidance towards which cells operate in better or worse mixing conditions.

Dimensionamento de espessadores: validação experimental de três técnicas convencionais

This work reviews the fundamentals of three important techniques currently used to dimension thickeners: Flux of Solids, Talmadge-Fitch, and Roberts. They were applied to validate the calculation of diameter (D) and sedimentation area (A) of a real thickener, which clarifies brine in a plant located at Cubatao-SP. The calculation of thickener dimension (A and D) was based on the sedimentation behavior of salt particles in brine on a laboratory scale. The values of D and A (D=13,9-14,1m; A=151,7-156,1m²), which were calculated by the three techniques, were compared with the diameter of the real equipment (D=20,0m). On the other hand, corrected values of D and A (D=18,1-18,3m; A=257,0-263,0m²) were obtained by using a scale factor (f=1,3). These results are 10% lower than the real equipment.

True flotation versus entrainment in reverse cationic flotation for the concentration of iron ore at industrial scale

ABSTRACT The loss of iron-bearing minerals to the tailings, especially in the finest fractions (−44 μm), is a problem that must be endured due to the depletion of deposits containing high-Fe hematite. The two main mechanisms for iron mineral loss in the froth in reverse cationic flotation are hydrodynamic dragging and true flotation. This last one being attributed to failures in the conditioning processes regarding the depression of iron mineral by starch. In this work, two industrial mechanical flotation circuits located in Minas Gerais—Brazil, namely Conceição Itabiritos II and Pico, operating with mineralogically distinct iron minerals, had their tailings analyzed in order to attribute reasons for the iron-bearing minerals losses. Liberation studies excluded losses due to the presence of composite particles where hematite was combined to silica or goethite. The method known as two-liquid flotation was applied to the several particle fractions present in the tailings to evaluate the particles surfaces hydrophobicity/hydrophilicity. The results indicated that for Conceição Itabiritos II, the loss of iron minerals was due to a combination of true flotation and hydrodynamic dragging. True flotation probably took place because of depression failure. For Pico, the results revealed that most of the iron-bearing particles were lost due to hydrodynamic dragging. The shape factor and terminal velocity, both obtained via permeametry, confirmed the two-liquid flotation results. Two-liquid flotation was shown to be a fast and simple method to qualitatively assess the hydrophobicity of particles in froth flotation, thus allowing quick improvements in the process.

Parâmetros de dispersão de ar em células mecânicas de flotação em usinas brasileiras

The aim of this paper is to present and discuss the air dispersion parameters determined for industrial Brazilian flotation circuits. The rougher and scavenger circuits of RPM, Taquari-Vassouras, Copebras and Fosfertil-Catalao (today Vale Fertilizantes) were investigated. For RPM and Taquari-Vassouras, the superficial gas velocity (Jg), gas hold-up (e g ), bubble size diameter (d 32 ) and superficial area bubble flux (S b ) were measured, whereas only the J g and e g were measured in the other circuits. The results pointed out that, except for RPM, all the circuits presented very low values for the air dispersion parameters. Taquari-Vassouras presented the lowest values for average J g and gas hold-up: 0.05 cm/s and 5%, respectively. The highest J g value was presented for the rougher circuit of Copebras, 1.17cm/s, while RPM presented the highest values for e g and bubble size, respectively 31% and 2.61mm. In the circuits where the calculation of the S b parameter was possible, the results obtained lay in a range lower than those reported in literature.

Importância da hidrodinâmica na cinética de flotação de partículas grossas

The processes that govern the rate of particle recovery in a fl otation cell include the following sub-processes: collision, attachment, and stability of the aggregate formed by particles and bubbles. Collision is controlled by bulk hydrodynamics inside the fl otation cell, while attachment is largely dominated by variables that belong to the domain of surface chemistry (contact angle, induction time). As for the stability of the particle/bubble aggregate, its effi ciency depends on both hydrodynamics plus surface chemistry variables of the system.

Caracterização hidrodinâmica de células mecânicas de flotação: capacidade de bombeamento de célula denver de laboratório

The ability of impellers to produce bulk fluid flow may be expressed by the impeller flow rate (Qb) or the pumping number (NQ). Both parameters are very useful to characterize the hydrodynamics of mechanical flotation cells. In this work, an apparatus composed of a micromolen attached to an optic sensor was used to determine the impellers water flow velocity (vb), Qb and NQ of a Denver laboratory flotation cell from the Laboratory of Mineral Processing, University of Sao Paulo. Under usual working conditions (1,100-1,300 rpm), in the presence and absence of air, the equipment operates at vb=20-30 cm/s, Qb=298-454 cm³/s e NQ~0,05. The value of NQ related to a laboratory cell was similar to an industrial one (NQ~0.05). Since Denver cells are sub-aerated, the presence of air in the system decreased the magnitude of vb and Qb when the impeller operated under higher rotational speed.

Influência do estado de agregação da polpa na flotação de quartzo, apatita e calcita

Many academic studies were carried out in the United States during the 1930s and 1940s, motivated by the correlation between the pulp aggregation state and the recovery at the flotation process, observed in industrial circuits. The aim of this work is to contribute to a better understanding of the phenomenon within the Brazilian reality. Microflotation and dispersion tests were carried out with quartz, apatite and calcite particles. The results strengthen the assertion by Taggart and co-workers that the aggregation occurs in the pulp as an effect of the reagents action and not as the primary cause of good flotability.