Enhanced flotation of various Au-Cu-Ag ores using zinc/arsenic/pyrite/lead depressants and Eriez column/StackCell high-intensity technologies

The increasing challenges in floating copper (Cu), gold (Au) and silver (Ag) ores are driven by factors such as rapidly growing demand, the complex mineralogy of modern deposits, and declining ore reserves and ore grades. Low-grade porphyry ores require fine or ultrafine grinding to achieve adequate mineral liberation. Extremely fine Cu, Au and Ag mineral particles (smaller than 10 µm) may be physically encapsulated within sulfide minerals like pyrite or arsenopyrite. However, fine and ultrafine particles (smaller than 20 µm) have low collision efficiency with bubbles, resulting in a loss of valuable minerals to the tailings. Porphyry Cu, Au and Ag ores can contain undesirable penalty elements like arsenic (As), zinc (Zn) and lead (Pb), which are difficult to reject. Selective flotation is required using different reagents and pH conditions for each mineral. This paper investigates the improved flotation performance of five low-grade Cu, Au and Ag ores using Eriez column/StackCell high-intensity technologies and various reagents to minimize final concentrate contents of sphalerite (ZnS), arsenopyrite (FeAsS) and galena (PbS) before incurring a penalty. Introduction Eriez column/StackCell high-intensity technologies can improve the flotation of fine and ultrafine particles by generating extremely small bubbles (picobubbles or nanobubbles) that overcome the typical challenges associated with floating tiny materials. The very fine bubbles preferentially nucleate directly onto the surface of hydrophobic (water-repelling) particles. This “bubble frosting” increases the overall hydrophobicity of the particle, making it easier to attach to conventional-sized bubbles. This synergistic effect drastically improves the probability of successful particle-bubble collisions. These benefits include higher recovery rates, better selectivity and lower reagent costs compared to conventional flotation methods. Figure 1 depicts the key features of the Eriez StackCell. The high-turbulence contacting chamber is isolated from a quiescent separation chamber, which allows for independent optimization of the particle collection and froth recovery processes. The StackCell achieves between 75 and 85 percent reduction in flotation residence time requirement by increasing the flotation rate constant of minerals through introduction of air and particles directly into the multistage rotor-stator mechanism within the contacting chamber. This mechanism has an extremely high specific energy input that is converted to turbulent kinetic energy through the rotor blade design and generates between four and five times higher turbulent dissipation rates as compared to conventional flotation machines. As a result, recovery of fine particles and slow floating minerals is increased, and flotation volumetric requirement is reduced. The StackCell has been successfully applied to a wide range of mineral flotation applications, including rougher and cleaner applications (rougher, rougher scavenger, cleaner, cleaner scavenger) for base and precious metals, as well as fine flotation applications for industrial minerals and coal.This paper presents the flotation results of five different ores with various Cu, Au and Ag grades and As, Zn and Pb contents, using various activators, collectors and depressants. Methodology Five Troilus gold ore samples — J-Zone (3 t), SW zone (3 t) with high zinc content, 87-zone (3 t) with high arsenic, zinc and lead contents, and X22-1~2 zone (3 t) with low copper and high arsenic contents — were used to investigate flotation performance with the Eriez flotation column (or StackCell) technologies.Bench-scale mechanical cell flotation tests were conducted to identify the most optimal flotation feed particle size, circuit configuration and reagent scheme. Following identification of the most optimal rougher-scavenger flotation feed grind size, the sample was bulk milled to the appropriate P80 size, followed by rougher-scavenger column flotation in series. Bench-scale flotation kinetics, release and steady-state column flotation testing were utilized to scale up an industrial rougher-scavenger flotation circuit consisting of Eriez StackCells. Succeeding primary column flotation optimization and bulk rougher-scavenger treatment of each zone sample, secondary grinding studies were conducted on the rougher-scavenger concentrate to determine grinding times necessary to achieve P80 grind sizes of 40 and 20 µm. Cleaner flotation testing was then performed using an Eriez automated multistage column (Fig. 2) flotation circuit. Fig. 1 Illustration of the Eriez StackCell. Results Collectors KAX 51 and SPRI 206 were effective to float the five ore samples tested. The addition of 200-400-g/t sodium sulfite (Na2SO3) pyrite depressant in the cleaner stages could effectively depress pyrite, especially for the SW zone ore, with the highest Fe (pyrite) content among the five zone samples investigated; 50 g/t of ZnSO4.H2O depressant selectively depressed zinc sulfide minerals, such as sphalerite; 70 g/t (C3H3NaO2)n depressant reduced concentrate lead content, especially for the X22-2 zone ore, with the highest lead content. Fig. 2 Each zone of the three-stage cleaner column flotation. In the column/StackCell flotation of five ores with various Au, Cu, Ag, Zn, As and Pb contents, the rougher-scavenger-cleaner circuit Cu, Au and Ag flotation recoveries were approximately 90.4 to 95.8 percent at the concentrate copper grade of 13.6 to 17.4 percent and feed copper grade of 0.024 to 0.070 percent; 87.5 to 95.1 percent at the concentrate gold grade of 65.6 to 214.7 g/t and feed gold grade of 0.32 to 0.62 g/t, and 80.7 to 91.8 percent at the concentrate silver grade of 62.6 to 279.7 g/t and the feed silver grade of 0.26 to 1.12 g/t, respectively. The benefits of the Eriez column/StackCell flotation technologies include high flotation selectivity and increased recovery due to unique hydrodynamic designs. Conclusions Enhanced flotation results were achieved for five Troilus ore zones using the Eriez column cell and StackCell (simulated) high-intensity flotation technologies as compared to conventional mechanical flotation. In the treatment of fine material using conventional flotation, recovery losses are attributed to poor bubble/particle collision rates. As a result of the use of cavitation-tube sparged column flotation or high-intensity bubble-particle mixing in an air-supersaturated slurry via StackCell, vastly improved product recoveries were realized, compared to a conventional cell. Additionally, the employment of countercurrent wash water and a deep froth phase yielded optimal concentrate grades. Although the StackCell is designed specifically to expedite flotation rate, its use of wash water and ability to maintain a deep froth bed offer improved product grades, like column flotation cells. Selected references Kohmuench J, Christodoulou L, Fan MM, Mankosa M, Luttrell G (2010) Advancements in coarse and fine particle flotation. In: Proceedings of the 42nd Annual Canadian Mineral Processors Operators Conference, Canadian Mineral Processors, Ontario, pp 55–69 Wyslouzil H, Kohmeunch J, Christodoulou L, Fan MM (2009) Coarse and fine particle flotation, COM 2009, 48th Conference of Metallurgists, Aug. 23-26, Sudbury, Ontario Wasmund EB (2014) Flotation technology for coarse and fine particle recovery. I Congreso Internacional De Flotacion De Minerales. Lima, Peru Aug 2014 Fan MM, Tao D (2008) A study on picobubble enhanced coarse phosphate froth flotation. Sep Sci Technol 43:1–10 Fan MM, Tao D, Honaker R, Luo ZF (2010) Nanobubble generation and its application in froth flotation (part I): nanobubble generation and its effects on properties of microbubble and millimeter scale bubble solutions. Int J of Min Sci and Techn 20(1):1–19

Enhanced flotation of various Au-Cu-Ag ores using zinc/arsenic/pyrite/lead depressants and Eriez column/StackCell high-intensity technologies

Authored by: Maoming Fan, Joe Milbourne, Andrew Hobert, Ryan Letkiewicz, Rahul Singh and Erich Dohm

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To view this article you must be a member of SME/UCA.

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