Application of Chemical Additives in Minerals Beneficiation – Implications on Grinding and Flotation Performance

• The application of chemical additives, known as grinding aids (GAs), dates to 1930 in the cement industry. Unlike the cement industry, where the use of GAs is in the final processing step, it could be one of the first processing steps in ore beneficiation. Further to grinding performance, the successful application of GAs requires understanding the effect on ground products and possible interaction of the GAs in view of downstream processes. Understanding and controlling any GA-separation reagent interactions is critical to ensure that the required downstream process efficiency and integrity of the entire value chain are maintained. In this thesis, the effect of selected chemical additives on dry grinding performance and product properties is investigated. Second, the effect of the additives on surface properties and pulpchemistry, together with the resulting behavior in subsequent froth flotation separation, is investigated.The use of environmentally benign and sustainable alternatives to conventional surfactants is growing within mineral processing. To this end, a polysaccharide-based grinding aid (PGA) (natural polymer) together with a polyacrylic acid-based grinding aid (AAG) (synthetic polymer) were used as grinding aids. The effect of PGA and AAG at varying concentrations was investigated with respect to energy consumption, particle size distribution, BET surface area, roughness, and rheology. The resulting grinding parameters were correlated with the measured rheology indices from the automated FT4 powder rheometer. Moreover, the effect of the GAs on the flotation of quartz from magnetite was investigated using an artificial mixture ore. Zeta potentials, stability measurement, adsorption test, and FTIR analyzes were performed to understand the mechanisms of surface interaction and adsorption.The grinding results indicated that the application of GAs reduced energy consumption by up to 31.1 % and gave a finer-uniform product size, higher specific surface area, and increased surface roughness compared to grinding without. Further studies on powder rheology indicated that the GAs used resulted in improved material flowability compared to grinding without additives. There was a strong correlation (r > 0.93) between the grinding and the flow parameters. Flotation tests on pure samples illustrated that PGA has beneficial effects on magnetite depression (with negligible impact on quartz floatability) through reverse flotation separation. The benefits were further confirmed by the flotation of the artificial mixture in the presence of PGA. The PGA adsorption mechanism was mainly through physical interaction based on UV-Vis spectra, zeta potential tests, Fourier transform infrared spectroscopy (FT-IR), and stability analyses. Additionally, single mineral flotation tests indicated that AAG enhanced quartz collection with minimal effect on magnetite. Mixed mineral flotation revealed that, by using AAG, comparable metallurgical performance could be achieved at a lower collector dosage. The zeta potentials and stability measurements showed that AAG shifts the potential, thus improving the stability and dispersion of the suspension. Adsorption tests revealed that AAG adsorbed on both quartz and magnetite, with the former having a higher capacity. Fourier transform infrared spectroscopy showed that the interaction between AAG and the minerals occurs via a physical interaction.The findings illustrate that GAs improved grinding efficacy at optimum dosage and enhanced product properties. Furthermore, the predominant mechanism of GAs is based on the alteration of rheological properties. Importantly, the feasibility of using GAs to improve grinding performance has been demonstrated with secondary beneficial effects on flotation.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik -- Kemiska processer (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering -- Chemical Process Engineering (hsv//eng)

Nyckelord

Energy

Grinding aid

Flowability

Dry grinding

FT4 Powder Rheometer

Surface properties

Rheology

Flotation

Polymers

Surface chemistry

Green Chemistry

Mineral Processing

Mineral Processing

Mineralteknik

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