Mechanism and structure-activity relationship of a new composite binder to improve the quality of green pellets
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摘要: 降低膨潤土用量是提高球團品位、實現節能減排的有效途徑之一。基于新型高效復合粘結劑，通過生球制備、線性擬合分析、生球力學特征分析等手段研究了復合粘結劑對生球質量的影響規律及與重要指標的構效關系，闡明了復合粘結劑提高生球質量的作用機理。結果表明：配比（質量分數）為1.2%膨潤土+0.028%有機粘結劑的復合粘結劑球團，落下強度（0.5 m高度落下次數）達到6.2、平均抗壓強度達到14.5 N、爆裂溫度達到542 ℃，與2.0%膨潤土球團相比，生球質量相近，但膨潤土消耗減少40%；基于構效關系分析，有機粘結劑對生球落下強度、爆裂溫度作用顯著，膨潤土對干球強度影響更大；有機粘結劑通過增強顆粒的親水性、毛細力和黏性力強化了生球落下強度，干燥時在表層形成少量孔隙，有利于球團內水分的排出，提高了生球爆裂溫度，干燥后以固態連接橋的形式強化干球強度，但是孔隙的位點和尺寸可能會降低干球強度，因此，對干球強度起決定性作用的是膨潤土，有機粘結劑對干球強度的影響呈現多面性。Abstract: Reducing bentonite consumption is one of the effective ways to improve the grade of pellets and realize energy saving and emission reduction. Based on the new high-efficiency composite binder, the effect of the composite binder on the quality of green pellets and structure-activity relationship with important indexes were studied by means of green pellet preparation, linear fitting analysis, and green pellet mechanical characteristics analysis. Moreover, the mechanism of the composite binder to improve the quality of the green pellets was expounded. Results show that the composite binder pellet, with a ratio of 1.2% bentonite and 0.028% organic binder, has a drop number (dropped from 0.5 m height) of 6.2, a average crushing strength of 14.5 N, and a shock temperature of 542 ℃. Compared with the pellet with 2.0% bentonite, the mass of the green pellets is similar; however, the bentonite consumption is reduced by 40%. Based on the analysis of the structure-activity relationship, the organic binder has a considerable effect on the drop number and the shock temperature of the green pellets, and the bentonite has a greater effect on the dry-crushing strength. The organic binder strengthens the drop number of the pellets by enhancing the hydrophilicity, capillary force, and viscosity, and it forms small amounts of pores on the surface layer during drying, which is beneficial for discharging water in the pellets and improving the shock temperature of the pellets. After drying, the organic binder strengthens the pellets in the form of a solid connection bridge; however, the site and the size of the pores may reduce the dry-crushing strength. Therefore, bentonite plays a decisive role in the strength of the dry pellets, and the influence of the organic binder on the strength of the dry pellets is multifaceted.
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圖 1 膨潤土用量對生球質量的影響
Figure 1. Influence of bentonite dosage on the quality of green pellets
圖 4 有機粘結劑P比例對復合粘結劑黏度的影響
Figure 4. Influence of organic binder P ratio on the viscosity of composite additive
圖 7 有機粘結劑P的熱重分析和差熱分析
Figure 7. Thermogravimetric analysis and differential thermal analysis of organic binder P
表 1 鐵精礦的主要化學成分及靜態成球指數
Table 1. Main chemical compositions and static pelletization index of iron-containing raw materials
Iron ore Chemical composition（mass fraction）/% LOI Mass fraction of iron ore with ?74 μm/% Mass fraction of iron ore with ?45 μm/% Specific surface area/（cm2·g?1） Static pelletization TFe FeO SiO2 Al2O3 CaO MgO S P A 65.15 24.89 4.95 1.66 0.40 0.54 0.077 0.012 ?0.74 94.0 78.8 1408 Medium B 65.46 25.83 3.76 0.63 1.02 1.62 0.200 0.100 ?1.91 99.5 94.8 1466 Excellent Z 65.75 26.50 6.57 0.84 0.30 0.48 0.054 0.014 ?0.47 93.6 80.3 1568 Good Note: LOI is burning loss. 
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表 2 膨潤土的物化性能
Table 2. Physical and chemical properties of bentonite
Methylene blue adsorbed/
(per 100 g)/gWater absorption
(2 h)/ %Swelling coefficient/
(mL·g?1)Colloid index
(per 15 g)/mL21.69 496 25 580
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表 3 有機粘結劑P灰分化學成分（質量分數）
Table 3. Chemical composition of the organic binder P ash
% Na2O SOx CaO SiO2 Cl MgO Al2O3 K2O 88.4 10.06 0.382 0.366 0.277 0.214 0.168 0.024
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表 4 復合粘結劑用量對生球質量的影響
Table 4. Influence of compound binder dosage on the quality of green pellets
Mass fraction of bentonite/% Mass fraction
of P / %Drop number Average crushing strength
of green pellet / NShock temperature/ ℃ Average crushing strength
of dry pellet / NMoisture content of
green pellet/ %1.1 0.020 3.9 11.0 535 82.3 8.4 0.030 4.7 11.3 550 81.8 8.4 0.040 5.1 11.9 560 90.7 8.8 0.050 5.8 11.6 540 89.5 8.6 1.2 0.020 4.8 14.6 535 59.0 8.1 0.024 5.8 13.8 530 57.1 8.5 0.028 6.2 14.5 542 66.0 8.3 0.032 6.6 13.9 554 73.9 8.6 1.3 0.016 4.1 13.3 540 65.2 8.7 0.020 5.9 12.2 546 72.3 8.6 0.024 6.4 11.7 549 63.3 8.7 0.028 7.0 13.6 555 73.1 8.5 1.4 0.008 4.1 12.1 520 88.4 8.6 0.012 5.2 11.2 535 107.3 8.8 0.016 6.9 12.8 528 98.3 8.7 0.020 7.8 13.8 530 108.1 9.0
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表 5 回歸方程顯著性和擬合度
Table 5. Significance and fitness of regression equation
Factor Significance of variance P Significant correlation R2 Drop number 0.0004 Very significant 0.882 Green crushing strength 0.551 Not relevant 0.433 Shock temperature 0.006 Significant 0.713 Dry crushing strength 0.008 Significant 0.588
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表 6 有機粘結劑P和膨潤土標準化回歸系數
Table 6. Standardized regression coefficient of organic binder P and bentonite
Factor P Bentonite Drop number 0.905 0.734 Shock temperature 0.851 0.206 Dry crushing strength 0.190 0.843
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表 7 膨潤土和有機粘結劑P的黏度
Table 7. Viscosity of bentonite and organic binder P
Binder Viscosity / (mPa·s) Bentonite 3 P 90–120
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