Controlling Properties of Agglomerates for Chemical Processes

Iron ore pellets are hard spheres made from powdered ore and binders. Pellets are used to make iron, mainly in blast furnaces. Around the time that the pelletizing process was developed, starch was proposed as a binder because it’s viscous, adheres well to iron oxides, does not contaminate pellets and is relatively cheap. In practice, however, starch leads to weak pellets with rough surfaces – these increase the amount of dust generated within process equipment and during pellet shipping and handling. Thus, even though the usual binder (bentonite clay) contaminates pellets, pelletizers prefer it to starch or other organics. This dissertation describes three ways to make good starch-based binders for pellets. Importantly, they solve the usual problems of weak rough pellets and lots of dust. The three approaches are: (1) Addition of clay to starch. This is not a novel idea. In fact, it is the standard method used for their improvement. However, it has not been tested extensively with starch. This approach was expected to be – and indeed was – successful. (2) Addition of a clay-rich layer to green ball surfaces. This approach is a novel idea. The coating\u27s purpose was to mimic the good surface properties of standard bentonite-clay bonded pellets; as a benefit, clay consumption was significantly reduced. This approach was successful. (3) Addition of dispersants to starch. This approach is a novel idea. The intent of the dispersants was to enable pelletization to occur at lower moisture contents, thus leading to denser particle packing and lower porosity. The dispersants resulted in significantly stronger, smoother pellets without contaminating them with silica. Using approaches 1 and 3, starch can be used directly in traditional pelletizing operations, and importantly, in new pelletizing processes for new iron making operations. For approach 2, new application methods must be developed. Future engineering work is suggested as follows: design better dispersants for magnetic magnetite ores; incorporate the dispersing agent and starch into bead form for easy use; design a simple way to add coatings in existing drum-based pelletizing circuits; and optimize the coating composition to decrease both abrasion losses and pellet clustering (for new Direct Reduction pellets)

FACTORS INFLUENCING MATERIAL LOSS DURING IRON ORE PELLET HANDLING

Iron ore concentrate pellets have the potential to fracture and abrade during transportation and handling, which produces unwanted fine particulates and dust. Consequently, pellet producers characterize the abrasion resistance of their pellets, using an Abrasion Index (AI), to indicate whether their products will produce unacceptable levels of fines. However, no one has ever investigated whether the AI correlates to pellet dustiness. During the course of this research, we investigated the relationship between AI and iron ore concentrate pellet dustiness using a wide range of industrial and laboratory pellet samples. The results showed that, in general, AI can be used to indicate high levels of dust. However, for good-quality pellets, there was no correlation between the two. Thus, dust generation from shipping and handling pellets will depend on the quantity of pellets handled and how much they are handled. These results also showed that the type of industrial furnace used to harden iron ore concentrate pellets may affect their fines generation and potential dustiness

Identification of pre-leukaemic haematopoietic stem cells in acute leukaemia.

In acute myeloid leukaemia (AML), the cell of origin, nature and biological consequences of initiating lesions, and order of subsequent mutations remain poorly understood, as AML is typically diagnosed without observation of a pre-leukaemic phase. Here, highly purified haematopoietic stem cells (HSCs), progenitor and mature cell fractions from the blood of AML patients were found to contain recurrent DNMT3A mutations (DNMT3A(mut)) at high allele frequency, but without coincident NPM1 mutations (NPM1c) present in AML blasts. DNMT3A(mut)-bearing HSCs showed a multilineage repopulation advantage over non-mutated HSCs in xenografts, establishing their identity as pre-leukaemic HSCs. Pre-leukaemic HSCs were found in remission samples, indicating that they survive chemotherapy. Therefore DNMT3A(mut) arises early in AML evolution, probably in HSCs, leading to a clonally expanded pool of pre-leukaemic HSCs from which AML evolves. Our findings provide a paradigm for the detection and treatment of pre-leukaemic clones before the acquisition of additional genetic lesions engenders greater therapeutic resistance

Binding effects in hematite and magnetite concentrates

An industrial taconite facility, \u27Plant F\u27, processed both magnetite and hematite ores during the year. The concentrates were pelletized with a binder, bentonite. Plant personnel believed less bentonite was required to make hematite pellets. Thus, the authors intended to quantify in-plant observations through bench-scale pelletization tests. As-received magnetite and as-received hematite were pelletized and tested for wet-drop number and dry-crush strength. Hematite pellets exceeded industrial minimum wet-drop and dry-crush values of 5 drops and 22 N/pellet without bentonite addition, while magnetite pellets exceeded industrial minimum values at a bentonite dose of 6.6 kg/t (0.66%). It is known that finer particles increase pellet strength, so additional magnetite was ground to a similar particle size distribution as the as-received hematite. The ground magnetite was pelletized and tested for wet-drop number and dry-crush strength. Wet drop and dry crush values increased after grinding the magnetite concentrate. However, they were significantly less than hematite pellets at similar bentonite doses. Consequently, particle size effects were not the dominant cause for higher strengths in the hematite concentrate. © 2011 Elsevier B.V

Iron ore pellet dustiness part II: Effects of firing route and abrasion resistance on fines and dust generation

Copyright © 2015 Taylor & Francis Group, LLC. Iron ore pellets abrade during their production and handling, which lowers product quality and leads to dustiness issues. Pellets were collected from a variety of plants (operating either Straight-Grate (SG) or Grate-Kiln (GK) furnaces) to understand whether furnace type affects fines and dust formation. Results showed that pellets fired in SG furnaces were less abrasion-resistant (3.5 × lower) than pellets fired in GK furnaces. Concurrently, laboratory pellets were prepared using various ores, binders, and firing temperatures. These were tested to understand the relationship between abrasion index and dustiness. AI was observed to range from 1 to 14%. Dustiness, determined via AI and size distributions of abrasion progeny, ranged from 0.2 to 1.6%. For AI greater than 5%, AI can be used to indicate potentially high levels of dust. For AI less than 5%, there was a poor correlation between AI and dustiness. This was explained by the observation that as AI decreased, the abrasion product fineness increased. The results from parts I and II of this investigation suggest that material loss and levels of pellet dustiness may be significantly affected by pellet quality up to a certain point. Poorly fired pellets will be dusty during handling and transportation, while well-fired pellets will generate less - but finer - material as their quality improves. This could lead to little observed changes in dust generation over a wide range of pellet quality. Dust generation at each site would then depend on the quantity of material produced and their extent of handling

Can Modified Starch be Used As A Binder For Iron Ore Pellets?

© 2017 Taylor & Francis. ABSTACT: Organic binders are often desired when making low-silica iron ore pellets. Corn and wheat are grown in large quantities near certain iron ore pelletizing facilities and their starches are easily modified to form cold-water-soluble powders that can be used as binders. We investigated how starch cold-water solubility, starch dose, starch hydration time, green ball moisture content, and firing temperature affected pellet quality. With a fluxed, hematite concentrate, the high-soluble starch led to good wet and dry balls, but weak and friable indurated pellets compared to the standard binder, bentonite clay. As expected, the low-soluble starch did not make as good green balls as the high-soluble starch. Thermogravimetric analyses of unfired pellets and their abrasion products showed that modified starch was inhomogeneously distributed in pellets, with a high concentration near the ball surfaces. The surface concentration increased, and the core concentration decreased, as pellets grew during the pelletizing process. This suggests that starch enrichment near surfaces is a consequence of the agglomeration–compaction process, and may occur with other pelletizing binders. Abrasion mass losses were 81% greater with modified starch than with bentonite at 1100°C, and 31% greater at 1250°C. However, starch contents near the surfaces did not qualitatively correlate to roughness, as the highest starch dose tested gave the smoothest and least dusty pellets

Does the Zeta Potential of an Iron Ore Concentrate Affect the Strength and Dustiness of Unfired and Fired Pellets?

© 2017 Taylor & Francis. We show how pelletizing additives affect the zeta potential, sedimentation and agglomeration behavior of a hematitic iron ore concentrate. When the additives stabilized the particle–water system—indicated by higher zeta potential, higher total suspended solids content and denser settled sludge—pellet strength increased and dustiness decreased. Conversely, when the additives destabilized the particle-water system—indicated by lower zeta potential, lower total suspended solids content and rarer settled sludge—pellets became weaker and dustier. Specifically, our results show that problems related to starch binders can be resolved using carefully selected dispersants, and starch-dispersant mixtures are better pellet binders than starch alone. In general, our results suggest that sedimentation and zeta potential tests may be effective techniques for understanding pellet–water–binder systems; organic dispersants are good alternatives to bentonite for making low-silica binders; and understanding surface properties and water chemistry of the balling feed is necessary to understand its agglomeration behavior. We believe that understanding the interactions between the balling feed minerals, pore water, and binder will become more important as balling feeds become finer and process waters more complex

A new on-line method for predicting iron ore pellet quality

© 2015 Taylor & Francis Group, LLC. The Abrasion Index (AI) describes fines generation from iron ore pellets, and is one of the most common indicators of pellet quality. In a typical pellet plant, dust is generated during the process and then captured. Can the dust be measured and used to predict AI? In this paper, the feasibility of using airborne dust measurements as an indicator of AI is investigated through laboratory tests and using data from a pellet plant. Bentonite clay, polyacrylamide and pregelled cornstarch contents, and induration temperature were adjusted to control the abrasion resistance of laboratory iron ore pellets. AI were observed to range from approximately 1% to 12%. Size distributions of the abrasion progeny were measured and used to estimate quantities of PM \u3c inf\u3e 10 (particulate matter with aerodynamic diameter less than 10 μm) produced during abrasion. A very good correlation between AI and PM \u3c inf\u3e 10 (R \u3c sup\u3e 2 = 0.90) was observed using the laboratory pellets. Similarly, a correlation was observed between AI and PM measured in the screening chimney at a straight-grate pelletization plant in Brazil, with an R \u3c sup\u3e 2 value of 0.65. Thus, the laboratory and industry data suggest that measuring dust generation from fired pellets may be an effective on-line measurement of pellet quality. The data also showed that particulate emissions from pelletization plants may be directly affected by AI

Cold bonding of iron ore concentrate pellets

© 2015 Taylor & Francis Group, LLC. Iron ore concentrate pellets are traditionally hardened at high temperatures in horizontal grates and grate-kiln furnaces. However, heat induration requires tremendous quantities of energy to produce high-quality pellets, and is consequently expensive. Cold bonding is a low-temperature alternative to heat induration. Pellets can be cold bonded using lime, cement, sponge iron powder, and organic materials such as starch and flour. Cold bonding consumes less energy than heat induration, and has found favor for bonding self-reducing pellets and for refractory ores that are difficult to heat-treat. Herein, we review the principal cold bonding methods and their fundamentals

Iron ore pellet dustiness part I: Factors affecting dust generation

© 2015 Taylor and Francis Group, LLC. Iron ore pellets abrade during handling and produce dust. This study was conducted to determine what factors affect pellet dustiness, and whether dustiness can be related to the abrasion index. Factors studied included bed depth within a straight grate furnace; pellet chemistry; firing temperature; coke breeze addition; and tumble index. Abrasion indices for all pellet samples ranged from 1.9-5.0% (20 samples) and from 7.1-27.5% (5 samples). Pellets were dropped in an enclosed tower, which enabled the collection of airborne particles generated during pellet breakdown. The quantity of airborne particles generated by each pellet type was 10-100 mg/kg-drop, or 50-500 mg/kg over five drops through the tower. Pellet dustiness was predominantly affected by pellet chemistry and by pellet firing temperature. Results showed a nearly 21% increase in dustiness for every percent decrease in firing temperature-this was based on a typical firing temperature of 1280°C. Pellet dustiness was regressed to the pellet abrasion index (for AI \u3c 5%), which yielded a correlation coefficient of 0.22. These results show that, although AI is one of the best indicators of fired pellet quality and can indicate high levels of dust, it could not explain the dustiness of good quality pellets.The second paper (Iron Ore Pellet Dustiness Part II) explains the relationship between AI and dust for good-quality pellets; and compares fines generation between pellets fired in Straight-Grate (Traveling Grate) and Grate-Kiln furnaces