| 1. |
- He, Mingzhao, et al.
(författare)
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Influence of slurry rheology on stirred media milling of limestone
- 2006
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Ingår i: Advances in Comminution. - Littleton, Colo : Society for Mining, Metalurgy and Exploration. - 0873352467 ; , s. 243-260
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper reviews the influences of solids concentrations and dispersants with a range of molecular weights on the flowability of limestone slurries as well as the effects on wet ultrafine grinding in order to reduce energy cost and increase the fineness of a product. Sodium pofyacrylate with a molecular weight of 5,500 (i.e., Dispersant S40) appears most effective for the grinding due to the effective reduction of apparent viscosities and the maintenance of steady flowability. Optimal solids concentration exists at a certain beads load for the effective wet ultrafine grinding of limestone, and a rheological explanation is presented.
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| 2. |
- He, Mingzhao, et al.
(författare)
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Influence of slurry rheology on stirred media milling of quartzite
- 2007
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Ingår i: International Journal of Mineral Processing. - : Elsevier BV. - 0301-7516 .- 1879-3525. ; 84:1-4, s. 240-251
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Tidskriftsartikel (refereegranskat)abstract
- The role of slurry rheology in stirred media milling of quartzite has been investigated by varying important grinding parameters such as media bead density and size, addition of chemicals, solids concentration, stirrer rotational speed as well as the combined effect of these factors. Media bead density has an evident but complex effect on stirred milling performance, depending on stirrer rotational speed and solids concentration. The effect of media bead size on the ultra-fine grinding of quartzite is relevant to the feed size. Optimal ratio of media bead size to the median size of a feed is between 150 and 200. The combined effect of grinding bead size and stirrer speed or solids concentration is insignificant. The addition of Dispersant S40 or a lower solids concentration results in better grinding performance (i.e., a higher energy efficiency and a smaller median size) due to the maintenance of lower viscosities at shear rates investigated during grinding. Stirrer rotational speed interacts with solids concentration. For a given solids concentration, an optimal stirrer speed exists. The observed phenomena can be explained by the interaction of slurry rheology and the stress intensity of individual grinding bead. In addition, an empirical particle size-energy model provides a good fit (R2 > 0.904) to the grinding results under the experimental conditions investigated. Furthermore, the wear of grinding media beads is involved. ZrO2 beads have a lowest wear rate whereas the wear of SiO2 beads is most serious. The wear rate of Al2O3 beads is related to bead size.
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| 3. |
- He, Mingzhao, et al.
(författare)
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Parameter effects on wet ultrafine grinding of limestone through slurry rheology in a stirred media mill
- 2006
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 161:1, s. 10-21
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Tidskriftsartikel (refereegranskat)abstract
- Wet ultra-fine grinding of a limestone powder ( less than or equal 100 μm) has been investigated in a stirred media mill with respect to the effect of slurry rheology. The grinding results obtained by various parameters (i.e., molecular weight of a dispersant, solids concentration, additive dosage, addition method and beads load) are evaluated in terms of energy efficiency and the fineness of a product. A polymeric dispersant called Dispersant S40 with a molecular weight of 5500 gives the best grinding results. For a certain level of beads load, an optimal solids concentration exists. In the case of the additive dosage of Dispersant S40 at 0.1 wt.% or more, a smaller additive amount of Dispersant S40 gives a higher energy efficiency and a smaller median size at a lower level of specific energy input. However, the excessive amount of the dispersant could cause a cushion layer formed on milling beads and thus lowers stress intensities from the collisions of milling beads, leading to an inefficient milling operation. This can be avoided by either the multi-point addition of the dispersant or a higher beads load ( greater than or equal 83 vol.%). In addition, it was found that the higher the beads load, the better the cumulative energy efficiency, and the smaller the product size at the same specific energy consumption. For a given solids concentration, the relationships between the specific surface area and the particle size of an FP product and the additive amount of Dispersant S40 are explored, respectively. Furthermore, an empirical particle size-energy model provides a good fit (R2 > 0.991) to the grinding results under the experimental conditions investigated.
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| 4. |
- He, Mingzhao, et al.
(författare)
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Parameter studies on the rheology of limestone slurries
- 2006
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Ingår i: International Journal of Mineral Processing. - : Elsevier BV. - 0301-7516 .- 1879-3525. ; 78:2, s. 63-77
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Tidskriftsartikel (refereegranskat)abstract
- The influences of solids concentration, molecular weight of dispersant, particle size and distribution, and temperature on the rheological behaviour of limestone slurries have been investigated. The results reveal that when the solids concentration of a limestone slurry (< 100 μm) is increased from 60 wt.% (35.71 vol.%) to 78.5 wt.% (57.49 vol.%), the rheological behaviour of the slurry is transformed from a weakly dilatant characteristic to a pseudoplastic one with a yield stress, which is in combination with a thixotropic property at a higher solids concentration (i.e., ≥ 75 wt.% or 52.63 vol.%). At a certain shear rate, the apparent viscosity and the relative viscosity of the slurry increase exponentially with solids concentration. The extrapolated Bingham yield stress increases rather sharply in a power-law form with increasing solids concentration when the solids concentration of the slurry is larger than 70 wt.% (i.e., 46.36 vol.%)...
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| 5. |
- He, Mingzhao, et al.
(författare)
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Rheological behaviors in wet ultrafine grinding of limestone
- 2007
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Ingår i: Minerals & metallurgical processing. - 0747-9182. ; 24:1, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the effects of solids concentration and the addition of Dispersant S40 on the flowability of original and ground limestone slurries. A rotational viscometer with a concentric cylinder geometry and a controlled-stress rheometer with a cone-and-plate geometry were used to characterize the rheological behaviors of limestone slurries. The rheological behavior of original limestone slurries ( < 100 gm) is transformed through different types of flows with increasing solids concentration. The use of Dispersant S40 can improve the slurry flowability by decreasing viscosity and eliminating Casson yield stress. It is therefore used as a grinding aid for the wet ultrafine grinding of limestone. The rheological behaviors of ground limestone slurries vary with grinding from a starting dilatant flow-ability to a resulting pseudoplastic one with an evident Casson yield stress in combination with a thixotropic character. The appearance of pseudoplastic flowability combining thixotropy is related to the fineness of a ground product and its specific surface area, which are both correlated to solids concentration and the additive amount of Dispersant S40. In addition, the accurate rheological characterization of time-dependent fluids is dependent on the instruments used and operation conditions.
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| 6. |
- He, Mingzhao, et al.
(författare)
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Rheological behaviours in stirred media milling of limestone
- 2006
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Ingår i: Proceedings of the XXIII International Mineral Processing Congress. - Istanbul : IMPC. ; , s. 75-80
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Konferensbidrag (refereegranskat)abstract
- This paper has investigated the effect of solids concentration and the addition of a dispersant called Dispersant S40 on the flowability of unground and ground limestone slurries. The rheological behaviour of the unground slurries (<100 μm) is transformed through different types of flows with increasing solids concentration. The use of Dispersant S40 can improve the slurry flowability by decreasing viscosity and eliminating Bingham yield stress. The rheological behaviours of ground limestone slurries vary with grinding from a starting dilatant flowability to a resulting pseudoplastic one with an evident Bingham yield stress combining a thixotropic character, whose appearance is correlated to the fineness of a ground product, solids concentration, and the additive amount of Dispersant S40. In addition, the accurate rheological characterization of time-dependent fluids is dependent upon the used instruments and operation conditions.
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| 7. |
- He, Mingzhao, et al.
(författare)
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Slurry rheology in wet ultrafine grinding of industrial minerals
- 2004
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 147:1-3, s. 94-112
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Tidskriftsartikel (refereegranskat)abstract
- Wet ultrafine grinding has been increasingly used for production of ultrafine powders in various industries. It has been known that slurry rheology significantly influences the grindability of industrial minerals in wet ultrafine grinding. This review represents some previous work with respect to slurry rheology in ultrafine grinding. In this review, some methods for the characterization of the slurry rheology and some empirical equations modelling rheological behaviours of slurries were presented. The semiempirical model incorporating slurry rheology, solids concentration, particle size and slurry temperature was described. In addition, on-line measurement for the slurry rheology control was also discussed. In the case of ultrafine grinding, various parameters (such as solid concentration, particle size and distribution, particle shape, temperature, rotation and pH, use of dispersants), which affect the slurry rheology, have been described. It was revealed that the optimization of the rheological behaviours of slurry in ultrafine grinding could increase throughput, energy efficiency and product fineness as well. It is suggested to further study the mechanisms of slurry rheology in the presence of chemical dispersants in wet ultrafine grinding. It is desired to develop a model, which can represent a relation among slurry rheology, comminution parameters, amount of dispersant, energy efficiency and particle size characterization.
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| 8. |
- He, Mingzhao, et al.
(författare)
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Ultrasonication-assisted synthesis of calcium carbonate nanoparticles
- 2005
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Ingår i: Chemical Engineering Communications. - : Informa UK Limited. - 0098-6445 .- 1563-5201. ; 192:11, s. 1468-1481
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a batch carbonation method with ultrasonication to synthesize monodispersed nanoparticles of calcium carbonate (CaCO3). The synthesis processes with and without ultrasonication were compared. The results showed that the application of ultrasonication into the synthesis caused a supersaturation of Ca2+ ions in the synthesis, leading to a rapid nucleation of calcium carbonate and improved the solute transfer as well as. It was also found that the effect of ultrasonication on the grain size of the nanoparticles synthesized was related to other synthesis conditions, such as initial temperature for carbonation, mass fraction of Ca(OH)2 suspension, and CO2 flow rate. The initial temperature applied for the carbonation was increased by at least 5°C when ultrasonication was applied. The nanoparticles formed in the presence of ultrasonication became smaller with a narrower particle size distribution at 6–12 wt.% of Ca(OH)2 suspension or at 1.28 l/h of CO2 consumed by per gram of Ca(OH)2 or more.
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