Step optimization of a solid waste-based binder for backfill and a study on hydration and cementation mechanism
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摘要: 充填体强度对安全高效采矿至关重要，而胶凝材料是获得高强度充填体的关键。本文以工业固废为原料，首先借助D-optimal设计方法通过建立强度回归模型和因素影响分析得到矿渣激发剂最佳配比，然后通过矿渣掺量优化试验获得最佳矿渣掺量，进而获得胶凝材料完整配比；并以水泥为参照，借助X射线衍射仪和扫描电镜从水化产物和充填体微观结构揭示充填体强度形成机制。结果表明：（1）激发剂各组分对矿渣敏感顺序为：氢氧化钠﹥熟石灰﹥脱硫石膏﹥硫酸钠，且相互之间存在不同程度的交互作用；（2）在最佳质量配比（矿渣85.00%，熟石灰8.03%，硫酸钠3.96%，脱硫石膏1.85%，氢氧化钠1.16%）下，可获得超过单一水泥3.5倍的早期(1~3 d)强度和2倍的后期(7~28 d)强度；（3）高强度充填体的形成主要与水化产物钙矾石（AFt）和C–S–H有关，钙矾石在早期快速成核与生长，形成有效物理填充作用是形成较高早期强度的主要原因，后期强度则得益于不断累积的C–S–H的包裹黏结作用，使充填体结构进一步致密化。使用该固废基胶凝材料有助于矿山安全采矿；工业固废质量占比86.85%，协同解决了尾砂、矿渣、脱硫石膏等固废；D-optimal设计方法可用于激发剂等多物料混合物的配比设计和因素作用分析。
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关键词:
- 尾砂胶结充填 /
- 胶凝材料 /
- D-optimal混料设计方法 /
- 水化 /
- 抗压强度
Abstract: The key to obtaining high-strength backfill is the cementing material used for backfilling. Therefore, to prepare a new slag-based binder for cemented tailings backfill, hydrated lime, desulfurized gypsum, sodium sulfate, and sodium hydroxide were selected as slag activators. Firstly, the D-optimal mixture design method was used to develop the strength regression model, analyze the influence of hydrated lime, desulfurized gypsum, sodium sulfate, and sodium hydroxide on the strength, and determine the best ratio of slag activator. Secondly, after optimizing the slag content, the optimum proportion of the binder was obtained. Lastly, X-ray diffraction and scanning electron microscopy were used to study the internal mechanism of the hydration products of the slag-based binder, the microstructure of backfill, and strength formation. The results show that the D-optimal mixture design method is a good method of obtaining the formula of the mixture with a less experimental amount. The sensitivity order to slag is sodium hydroxide > hydrated lime > desulfurized gypsum > sodium sulfate, and there are different degrees of interaction, so the weighing accuracy should be considered when batching. At the optimum mass ratio of binder (slag 85.00%, slaked lime 8.03%, sodium sulfate 3.96%, desulfurized gypsum 1.85%, and sodium hydroxide 1.16%), the early strength (1–3 d) is 3.5 times higher than that of cement, and the late strength (7–28 d) is at least two times higher than that of cement. The increased strength of hardened backfill cemented is closely related to ettringite (AFt) and C–S–H, the two primary hydration products of the new slag-based binder. During the early stages of hydration, a large amount of AFt rapidly nucleated on the surface of the slag, the distance between the tailing particles provided plenty of space for ettringite growth, and its long prismatic structure continuously extended into the intergranular pores. The rapid formation of early strength of backfill is primarily because of the physical filling effect of ettringite. In the later stage, the strength of the backfill is primarily attributed to the wrapping and bonding effect of C–S–H, which further optimizes the compact structure of the backfill. The high-strength backfill can be obtained using the new slag-based cementitious material, which is of great significance for safe and efficient mining. The slag-based binder that contains 86.94% (mass fraction) of industrial solid waste helps solve the problem of desulfurized gypsum of coal-fired power plants and mine tailings. Additionally, the D-optimal mixture design proved to be an effective method for designing and optimizing the ratio of multicomponent materials, such as binders and activator components.-
Key words:
- cemented tailings backfill /
- binder /
- D-optimal mixing design method /
- hydration /
- compressive strength
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图 1 尾砂、矿渣、脱硫石膏、熟石灰和OPC的粒径分布
Figure 1. Particle size distribution of tailings, slag, desulfurized gypsum, hydrated lime, and cement
图 2 主要固体粉料的XRD谱图。(a) 尾砂；(b) 矿渣；(c) OPC
Figure 2. XRD patterns of main solid materials: (a) tailings; (b) slag; (c) OPC
图 5 熟石灰、硫酸钠、脱硫石膏和氢氧化钠对充填体强度的影响
Figure 5. Influence of hydrated lime, sodium sulfate, desulfurized gypsum, and sodium hydroxide on the strength of cemented backfill
图 7 矿渣掺量对尾砂充填体强度的影响
Figure 7. Effect of slag dosage on strength of cemented tailings backfill
图 8 使用OPC和新型胶凝材料制备充填体的强度对比
Figure 8. Strength comparison between backfill prepared with OPC and new binder
图 9 矿渣基碱激发胶凝材料（a）和OPC制备（b）净浆样品水化3 d和14 d的XRD谱图（H—氢氧化钙；E—钙矾石(AFt)；R—水化硅酸钙(C–S–H)；Z—针硅钙石；C—碳酸钙；Q—石英；G—GaSO4·2H2O；A—铝酸三钙; F—铁铝酸四钙；D—硅酸二钙；B—半水硫酸钙；T—硅酸三钙）
Figure 9. XRD patterns of paste sample prepared using a new alkali-activated slag-based binder (a) and cement (b) after hydration for 3 and 14 d (H—Calcium hydroxide; E—Ettringite (AFt); R—Calcium silicate hydrate (C–S–H); Z—Hillebrandite; C—Calcium carbonate; Q—Quartz; G—Gypsum; A—Calcium aluminate; F—Tetracalcium aluminoferrite; D—Dicalcium silicate; B—Hemihydrate gypsum; T—Tricalcium silicate)
图 10 新型胶凝材料和OPC制备充填体内部微观形貌对比。(a)新型胶凝材料样品，养护3 d；(b)新型胶凝材料样品，养护14 d；(c) OPC样品，养护3 d；(d) OPC样品，养护14 d
Figure 10. Comparison of the internal morphology of backfill prepared using the new binder and cement: (a) new binder sample, cured for 3 d; (b) new binder sample, cured for 14 d; (c) cement sample, cured for 3 d; (d) cement sample, cured for 14 d
表 1 固体材料化学组成（质量分数）
Table 1. Chemical compositions of solid materials by mass
% Solid material CaO SiO2 Al2O3 MgO SO3 Na2O TiO2 Fe2O3 K2O MnO P2O5 Tailings 2.72 70.70 15.00 1.10 0.27 3.52 0.15 1.28 4.93 0.04 0.06 Slag 39.80 27.30 14.50 11.40 2.50 — 1.07 0.24 0.27 0.33 0.02 Desulfurized gypsum 41.98 2.86 1.34 2.48 51.03 — — 0.41 0.14 — 0.02 OPC 50.34 24.21 8.94 6.64 4.01 0.86 0.38 2.34 1.21 0.21 0.06 
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表 2 D-optimal设计方案及强度结果
Table 2. Scheme and strength results of D-optimal mixture design
Order Mass fraction / % Mean strength-7 d/MPa Slag A: Hydrated lime B: Sodium sulfate C: Desulfurized gypsum D: Sodium hydroxide 1 60 19.47 14.51 5.00 1.02 1.87 2 60 15.00 19.00 1.00 5.00 1.91 3 60 20.19 12.13 3.16 4.52 2.28 4 60 26.34 5.00 5.00 3.66 2.40 5 60 25.72 10.67 1.00 2.61 2.18 6 60 15.84 14.16 5.00 5.00 2.34 7 60 13.83 20.00 3.34 2.83 2.30 8 60 33.00 5.00 1.00 1.00 1.96 9 60 12.16 17.84 5.00 5.00 2.05 10 60 13.83 20.00 3.34 2.83 2.24 11 60 21.80 16.20 1.00 1.00 2.17 12 60 20.19 12.13 3.16 4.52 2.24 13 60 26.34 5.00 5.00 3.66 2.44 14 60 18.05 19.95 1.00 1.00 2.30 15 60 20.19 12.13 3.16 4.52 2.24 16 60 23.21 10.81 4.98 1.00 2.32 17 60 25.72 10.67 1.00 2.61 2.06 18 60 29.17 7.10 2.73 1.00 2.00 19 60 23.01 8.19 3.80 5.00 2.14 20 60 29.00 5.00 1.00 5.00 1.90
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表 3 方差分析结果
Table 3. Results of variance analysis
Source Sum of squares Degree of freedom Mean square F-value P-value Remark Model 0.5539 13 0.0426 17.41 0.0011 Significant Linear mixture 0.1058 3 0.0353 14.41 0.0038 — AB 0.0006 1 0.0006 0.2461 0.6375 — AC 0.0018 1 0.0018 0.7254 0.4271 — AD 0.0625 1 0.0625 25.52 0.0023 — BC 0.0237 1 0.0237 9.70 0.0207 — BD 0.0501 1 0.0501 20.45 0.0040 — CD 0.0084 1 0.0084 3.42 0.1138 — ABC 0.0528 1 0.0528 21.56 0.0035 — ABD 0.0252 1 0.0252 10.28 0.0185 — ACD 0.0001 1 0.0001 0.0529 0.8257 — BCD 0.0048 1 0.0048 1.98 0.2094 — Residual 0.0147 6 0.0024 — — — Lack of fit 0.0038 1 0.0038 1.76 0.2423 Not significant Corrected total 0.5686 19 — — — —
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表 4 优化组合及其期望值
Table 4. Optimized combination and its expected value
Order Optimized combination/% Predicted value/MPa Expected value/MPa A B C D 1 21.42 10.57 4.92 3.09 3.02 0.865 2 19.77 13.00 4.28 2.96 2.93 0.796 3 24.69 9.00 3.50 2.81 2.86 0.743
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表 5 验证试验及其结果
Table 5. Optimized combination and its expected value
Order Optimized combination/% Predicted value/MPa Actual value/MPa Deviation/% A B C D 1 21.42 10.57 4.92 3.09 3.02 2.72 9.93 2 19.77 13.00 4.28 3.09 2.93 2.55 13.00 3 24.69 9.00 3.50 3.09 2.86 2.49 12.87
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