| 1. |
- Chipakwe, Vitalis, et al.
(författare)
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A comparative study on the effect of chemical additives on dry grinding of magnetite ore
- 2020
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Ingår i: South African Journal of Chemical Engineering. - : Elsevier. - 1026-9185. ; 34, s. 135-141
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Tidskriftsartikel (refereegranskat)abstract
- Dry grinding as an alternative to wet grinding is one of Sweden's strategic research areas to promote dry beneficiation. However, dry grinding has remained unpopular due to its higher specific energy consumption (Ec), wider particle size distribution (PSD), difficult material handling, and purported effects on downstream processes. In this work, the effects of the new additives (Zalta™ GR20–587, Zalta™ VM1122, and Sodium hydroxide) employed as grinding aids (GA) on dry grinding and product characteristics of a magnetite ore were studied in light of possible downstream effects. The grinding efficiency of Magnetite increased after using GAs in comparison without the GAs; however, an optimal dosage exists for each of the chemical additives investigated. Comparing to grinding without GA, Zalta™ VM1122, a viscosity modifier was selected as 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 (the P80 decreasing from 181 to 142 µm), and the proportion of the particles (38–150 µm) increased from 52.5 to 58.3%. Zalta™ VM1122 resulted in increased surface roughness and minimum microstructural defects. Further, it was found that Zalta™ VM1122 resulted in similar zeta potentials and pH values for the product compared to grinding without GA. These comparable product properties are advantageous as they minimize any potential negative effects on all possible downstream processes such as flotation.
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| 2. |
- Chipakwe, Vitalis, et al.
(författare)
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A critical review on the mechanisms of chemical additives used in grinding and their effects on the downstream processes
- 2020
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854 .- 2214-0697. ; 9:4, s. 8148-8162
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Forskningsöversikt (refereegranskat)abstract
- Grinding aids (GAs) have been an important advent in the comminution circuits. Over the last few decades, in order to address the high energy consumption and scarcity of potable water for mineral processing, chemical additives have become a promising alternative. Using GAs can have some advantages such as enhancing grinding efficiency, reducing water usage, improving material flowability, and narrowing the particle size distribution of the grinding products. A study on the effect of GAs on size reduction units is crucial for the beneficiation value chain of minerals and the impact on downstream processes. However, our understanding of the effects of these materials on the particle size reduction is quite limited. This article analyses the literature, which used GAs and provides a comprehensive review of their applications in the ore beneficiation processes. The outcomes of this investigation indicated that the current understanding on the mechanism of GA effects focuses only on their impacts on the product fineness and size distribution, and neglecting the aspect of energy expended and physicochemical environment. The application of GAs is mainly for rationalisation of energy where the type of reagent, pH, and ionic strength of the grinding environment is important. Gaps in knowledge of GAs are discussed in the context of addressing their use in the mineral industry, considering the mechanism of their effect, effect on grinding efficiency, and effect on the downstream processes. Addressing these gaps will pave the way for the application of GAs in improving size reduction efficiencies, which ultimately reduces environmental impacts.
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| 3. |
- Chipakwe, Vitalis
(författare)
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Application of Chemical Additives in Minerals Beneficiation – Implications on Grinding and Flotation Performance
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- Chipakwe, Vitalis, et al.
(författare)
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Beneficial effects of a polysaccharide-based grinding aid on magnetite flotation: a green approach
- 2022
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Grinding is the most energy-intensive step in mineral beneficiation processes. The use of grinding aids (GAs) could be an innovative solution to reduce the high energy consumption associated with size reduction. Surprisingly, little is known about the effects of GAs on downstream mineral beneficiation processes, such as flotation separation. The use of ecofriendly GAs such as polysaccharide-based materials would help multiply the reduction of environmental issues in mineral processing plants. As a practical approach, this work explored the effects of a novel polysaccharide-based grinding aid (PGA) on magnetite's grinding and its reverse flotation. Batch grinding tests indicated that PGA improved grinding performance by reducing energy consumption, narrowing particle size distribution of products, and increasing their surface area compared to grinding without PGA. Flotation tests on pure samples illustrated that PGA has beneficial effects on magnetite depression (with negligible effect on quartz floatability) through reverse flotation separation. Flotation of the artificial mixture ground sample in the presence of PGA confirmed the benefits, giving a maximum Fe recovery and grade of 84.4 and 62.5%, respectively. In the absence of starch (depressant), PGA resulted in a separation efficiency of 56.1% compared to 43.7% without PGA. The PGA adsorption mechanism was mainly via physical interaction based on UV–vis spectra, zeta potential tests, Fourier transform infrared spectroscopy (FT-IR), and stability analyses. In general, the feasibility of using PGA, a natural green polymer, was beneficial for both grinding and reverse flotation separation performance.
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| 5. |
- Chipakwe, Vitalis
(författare)
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Comparative Study of Chemical Additives Effects on Dry Grinding Performance
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Chipakwe, Vitalis, et al.
(författare)
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Effects of Chemical Additives on Rheological Properties of Dry Ground Ore - a Comparative Study
- 2022
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Ingår i: Mineral Processing and Extractive Metallurgy Review. - : Taylor & Francis. - 0882-7508 .- 1547-7401. ; 43:3, s. 380-389
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Tidskriftsartikel (refereegranskat)abstract
- It is well documented that chemical additives (grinding aid “GA”) during grinding can increase mill throughput, reduce water and energy consumption, narrow the particle size distribution of products, and improve material flowability. These advantages have been linked to their effects on the rheology, although there is a gap in understanding GA effectiveness mechanism on the flow properties. The present study aims to fill this gap using different GAs (Zalta™ GR20-587, Zalta™ VM1122, and sodium hydroxide) through batch grinding experiments of magnetite ore and addressing the mechanisms of their effects on the rheology by an FT4 Powder Rheometer as a unique system. Experimental results showed that GA improved grinding efficiency (energy consumption and product fineness), which were well-correlated with basic flow energy, specific energy, aerated basic flow energy, and aerated energy. Moreover, the rheometry measurement showed strong linear correlations between basic flow energy, specific energy, and the resulting work index when GAs was considered for grinding, which confirmed the effect of GA on ground particles’ flowability. Zalta™ VM1122, a polysaccharide-based grinding aid, 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. It also showed the strongest correlation between the grinding parameters and flow parameters (r > 0.93). The present investigation shows a strong indication that the predominant mechanism of GAs is based on the alteration of rheological properties and identify Zalta™ VM1122 as the best GA.
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| 7. |
- Chipakwe, Vitalis, et al.
(författare)
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Exploring the effect of a polyacrylic acid-based grinding aid on magnetite-quartz flotation separation
- 2023
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Ingår i: Separation and Purification Technology. - : Elsevier. - 1383-5866 .- 1873-3794. ; 305
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Tidskriftsartikel (refereegranskat)abstract
- It is well documented that the use of grinding aids (GAs) can reduce milling energy consumption. However, the impact of GAs on downstream processes must be addressed in view of complex processes such as froth flotation separation. This study investigates the effects of polyacrylic-based grinding aids (Zalta™ GR20-587: AAG) on the grinding performance and quartz flotation from magnetite. Various AAG dosages and conditions were examined. The grinding results showed lower energy consumption and a finer, more uniform product size with roughened surfaces for AAG compared to grinding without the grinding aid. Flotation tests of single pure minerals showed that AAG enhanced quartz collection with minimal effect on magnetite. Mixed mineral flotation showed that by using AAG, Fe recovery of 92.1 % and 64.5 % Fe grade could be achieved with a lower collector dosage of 100 g/t compared to 200 g/t in the absence of AAG. Zeta potentials and stability measurements showed that AAG shifts the potential, thus improving the stability and dispersion of the suspension. Adsorption tests illustrated that AAG adsorbed on both quartz and magnetite, the former having a higher capacity. FTIR indicated the physisorption interaction between AAG and the minerals. Therefore, the presence of AAG not only improved grinding efficiency but could potentially decrease the amount of collector required to achieve comparable metallurgical performance.
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