Abstracts:The effect of surfactants on bubble properties was examined in turbulent conditions. A multi-scale analysis was accomplished with the primary aim to identify the relationship between the size-scale determined surface properties leading to the decrease in bubble size.

Abstracts:Rare earth minerals (REM) may be beneficiated using a variety of separation techniques with froth flotation being the most commonly applied in operating REM separation plants. Many different collectors have been tested with traditional REM such as bastnäsite. The most successful are the hydroxamic acids. The Nechalacho deposit contains many REM for which there is minimal processing information in literature. Thus, experimental investigation into their flotation behaviour is required.

Abstracts:Cu grades at the top of the froth (TOF) were compared to the froth depth (hF ) profiles and froth discharge velocity profiles along rougher flotation circuits. Measurements were performed in two self-aspirated flotation banks, one consisting of nine 130m³ cells (1-2-2-2-2 arrangement), and the other one of six 250m³ cells (1-1-1-1-1-1 arrangement). Two behaviors for the TOF grade were observed: (i) for hF ⩽10cm, a decrease in the TOF grade along the bank was observed because either the decrease in mineral liberation or a potential recovery of slow floating gangue, (ii) for hF ⩾10cm, an increase in the TOF grades with the froth depth was observed, mainly due to an increase in froth selectivity. In addition, an inverse relationship between TOF grades and froth discharge velocities was obtained in most cases. However, in the first rougher cell, both higher froth discharge velocities (7–14cm/s) and higher TOF grades (20–28%Cu) were observed. The froth in the first cell is typically loaded, which favors the froth stability as well as the concentrate discharge velocity.

Abstracts:Batch flotation test data of a mixture of pyrite and calcite were used to compare regression parameters of four kinetic model structures. The work included the use of unoxidized or a mixture of partially oxidized pyrite (by microwave irradiation). The objective of floating oxidized pyrite was to have mineral particles with different floatability, closer to a real situation. The models considered include: single rate constant, distributed rate constants (i.e. rectangular and gamma distributions), and a recently introduced approach based on fractional calculus. Such models were selected due to their good tradeoff between simplicity and accuracy. The regressions were performed (1) taking all the data points and comparing the mean square error (MSE) and adjusted correlation factor $\left(R_{\mathit{Adj}}^2\right)$ as indicators of the goodness of fit; and (2) taking the first data points while neglecting the last ones (from 1 to 3) and observing the variability of the model parameters and the prediction of maximum recovery (R∞ ). For the latter regression scheme, besides MSE and $R_{\mathit{Adj}}^2$, a predictive factor, E, was defined by subtracting the final measured recovery from the calculation obtained by the model. This allowed to measure the ability of each model to extrapolate the omitted points on the recovery vs. time curve.

Abstracts:In a flotation cell, bubble size is a function of both coalescence and breakup phenomena. Two phase tests, conducted in a conventional 5.5L Denver mechanical flotation cell, studied the effect of impeller speed, gas flow rate and frother concentration on bubble size in various electrolyte-frother solutions. The addition of frother to a synthetic sea salt did reduce the measured bubble size (at certain mechanical conditions); whereas the effect of frother addition to NaCl was too small (when compared to measurement errors) to make significant conclusions. This led to more detailed CCC curves (0–50ppm MIBC) for NaCl, NaCl+MgCl2, NaCl+CaSO4, and NaCl+KCl solutions, at constant electrolyte concentrations, to be conducted. They showed an increase in bubble size with the addition of MIBC. This was attributed to the saturation of frother at the air-water interface, reducing local surface tension gradients that help produce smaller bubbles. This occurrence is typically masked in traditional CCC curves due to the dominance of coalescence effects at low frother concentrations.

Abstracts:The beneficiation of rare earth element (REE) minerals may include many different beneficiation unit operations, but the final process choice typically depends on the inherent mineral characteristics. The Nechalacho REE deposit contains multiple low specific gravity, diamagnetic silicate gangue minerals (predominantly feldspars and quartz) and high specific gravity, iron oxide minerals (magnetite and hematite). The valuable REE minerals (REM) in the deposit consist of a variety of relatively high specific gravity, paramagnetic minerals. A process has been proposed to concentrate the value REM through a combination of gravity (rejecting silicate gangue) and magnetic (rejecting iron oxide gangue) separation steps prior to froth flotation.

Abstracts:The application of mineral beneficiation techniques to valuable rare earth element (REE) bearing minerals requires a significant amount of research. A previous paper (Jordens et al., 2016) described a series of physical separation processes employed to pre-concentrate rare earth minerals (REM) and reject iron oxide minerals from the Nechalacho Deposit. In addition to grade and recovery information it is important to understand the performance of these separations from a mineralogical perspective. Information on liberation, mineral associations, magnetic properties and size-by-size recoveries can be used to further improve process designs for this deposit.

Abstracts:As ore grades fall, the amount of tailings production for the same copper production is expected to rise. Flotation recovery of copper sulfide from the El Teniente plant has deteriorated in recent years, in this regard ultrasound treatment of tailings for enhanced copper recovery was evaluated in laboratory experiments. The impact of the ultrasound wave was examined under different conditions, with the conclusion that improved recovery occurs when ultrasound is applied during conditioning and flotation. The results can be explained by the effect of acoustic cavitation that cleans particle surfaces and minimizes slime coatings, facilitating the action of the reagents. In this way, improvement in copper recovery of up to 3.5% were obtained.

Abstracts:Grade Engineering® spans a range of operational techniques that exploits intrinsic grade variability to remove low grade uneconomic material prior to energy intensive and inefficient grinding.

Abstracts:Phosphate rocks are the main phosphorus source, a key nutrient for crop production in the tropics. Besides phosphorus and calcium, phosphate rocks may contain organic matter and heavy metals, such as cadmium and lead, depending on their geological origin. In general, phosphate rocks from sedimentary origin present higher content of heavy metal than igneous phosphate rocks. The world phosphate rock consumption of sedimentary and igneous origin is around 75 and 20%, respectively. The use of cadmium containing phosphate rocks as fertilizers can bring risks to the environment. The objective of this work was to investigate the influence of partial oxidation of organic matter with H2O2 as a pre-treatment to improve cadmium leaching from sedimentary phosphate with high organic matter content. As leaching agents, MgCl2, KCl, Na2-EDTA and citric acid solutions were tested. When cadmium removal was carried out with a 0.1molL⁻¹ Na2-EDTA solution without partial oxidation of organic matter, its content in the sample was reduced from 49.5 to 38.5mgkg⁻¹, after 5h, corresponding to a removal of only 23%. On the other hand, when cadmium leaching was carried out after organic matter oxidation with a 40mgL⁻¹ H2O2 solution, the cadmium content in the sample was reduced from 49.5 to 22.5mgkg⁻¹, corresponding to a removal of 54.5%, turning it more adequate to be used as fertilizer.