The application of chemical additives, known as grinding aids (GA), dates back to 1930 in the cement industry. As opposed to the cement industry, where the use of GAs is on the final processing step, it could be one of the first process steps in ore beneficiation. A few investigations addressed the GA applications in ore dressing; therefore, further studies are required to better understand the GA effects on the product properties and downstream separation processes. This thesis undertakes a comparative study on the dry grinding of magnetite and the resulting product characteristics with and without GAs. The main aim is to reduce energy consumption and to address some of the challenges associated with dry processing. 

The effects of GAs on the dry batch ball milling of magnetite were examined to analyze the energy consumption (Ec), particle size distribution, flow properties, bulk properties, surface morphology, particle fineness, and surface chemistry of products. Their effects on the ground product were systematically explored by sieve analysis, powder rheology, BET surface measurements, optical microscopy analysis, and zeta potential measurements. Compared with the absence of GAs, the dry grinding efficiency of magnetite increased after using GAs; however, an optimal dosage exists based on the GA type. Among GAs which considered in this investigation (Zalta™ GR20-587 (Commercial GA) and Zalta™ VM1122 (Commercial viscosity aid) as well as sodium hydroxide), Zalta™ VM1122, a polysaccharide-based additive, was the most effective GA where by using this GA; the Ec decreased by 31.1% from 18.0 to 12.4 kWh/t. The PSD became narrower and finer (P80 decreasing from 181 to 142 µm), and the proportion of the particles (38–150 µm) increased from 52.5 to 58.3%. In general, the results reveal that at sufficient GA dosages, they reduce the average particle size, increase the specific surface area, and narrow the particle size distribution. However, an excessive amount of GAs could be detrimental to the grinding performance. 

Further studies on powder rheology indicated that the used GAs resulted in improved material flowability compared to grinding without additives (in the examined dosage range). The rheology measurements by the FT4 Powder Rheometer showed strong linear correlations between basic flow energy, specific energy, and the resulting work index when GAs was considered for grinding. There was a strong correlation between the grinding parameters and flow parameters (r > 0.93). These results confirmed the effect of GA on ground particles' flowability. Zalta™ VM1122 showed the best performance with 38.8% reduction of basic flow energy, 20.4 % reduction of specific energy, 24.6% reduction of aerated basic flow energy, and 38.3% reduction of aerated energy. The present investigation showed that the predominant mechanism of GAs is based on the alteration of rheological properties. Further investigation on the surface properties showed that using GAs could increase the surface roughness, which is beneficial for downstream processes such as froth flotation. Zalta™ VM1122 resulted in increased surface roughness and minimum microstructural defects from the optical microscope images. Furthermore, Zalta™ VM1122 (non-ionic) resulted in similar zeta potentials and pH values for the product compared to experiments without GA. These comparable product properties are advantageous as they minimize any potential negative effects on all possible downstream processes.

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.