Analysis of the titanium-bearing pellets prepared by a waste titanium-based catalyst and vanadium titanomagnetite
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摘要: 鋼鐵企業煙氣脫硝廢催化劑（危廢）產生量逐年增加，加強對此類廢催化劑的有效處置與利用已成為行業急需解決的關鍵共性難題。本研究首次提出了將廢催化劑添加到球團原料中制備含鈦球團利用的新路徑。將含廢催化劑球團和市場普通含鈦球團的制備過程及冶金性能進行對比研究。結果表明：球團原料中添加質量分數5.0%的廢催化劑可以顯著提高生球綜合性能指標，且明顯優于以釩鈦磁鐵礦制備的普通含鈦球團。球團焙燒后，含廢催化劑球團平均抗壓強度為3083 N，高于普通含鈦球團的2630 N。含廢催化劑球團固結機理表明，廢催化劑中TiO2與鐵氧化物反應形成Fe2TiO5相粘結，部分未反應TiO2會降低球團抗壓強度。兩種含鈦球團冶金性能與普通氧化球團基本相同，說明含廢催化劑球團可以用于高爐護爐冶煉使用。本研究有望為鋼鐵企業煙氣脫硝產生的廢催化劑在企業內部資源化利用提供新思路。Abstract: NH3-selective catalytic reduction of NOx over a V2O5–WO3/TiO2 catalyst is the major control method of NOx and has been successfully promoted and applied in various large steel enterprises in China. The production of waste catalysts (hazardous waste) from flue gas denitrification in iron and steel enterprises increases annually. Harmless landfills and wet purification are widely-employed methods for the treatment of waste catalysts. However, these methods pose environmental problems such as resource wastefulness, excessive amounts of acid/alkali, and considerable secondary pollution. Optimizing the effective use and disposal of such waste catalysts has become a key common problem in the industry. In this work, a novel method for producing titanium-bearing pellets by adding waste catalysts to pellet material was introduced. The feasibility of using waste catalysts to prepare titanium-bearing pellets was comprehensively evaluated by comparing the preparation process and metallurgical properties of the resulting pellets with those of commercially available titanium-containing pellets. The findings of this study reveal that the addition of 5.0% waste catalyst to the raw material can substantially improve the overall comprehensive performance of green pellets. Moreover, the drop number (dropped from 0.5 m height), average compressive strength, and burst temperature of the green pellets increased from 3.8 times, 16.5 N, and 487 ℃ (without waste catalyst addition) to 7.7 times, 21.5 N, and 553 ℃, clearly outperforming the ordinary titanium-bearing pellets prepared using vanadium–titanium magnetite (1.4 times, 15.0 N, and 542 ℃). These results could be attributed to the physical properties of the waste catalyst, which is a porous material with abundant hydrophilic groups on the surface. These hydrophilic groups, comprising hydroxyl groups, lead to the presence of more capillary water on the catalyst particle surfaces. Furthermore, the capillary force played an important role in various interactions in the pelleting process, thus improving the performance of mixtures. After roasting, the average compressive strength of the pellets containing the waste catalyst was 3083 N, higher than the 2630 N for ordinary titanium-bearing pellets. However, the short preheating and roasting time resulted in partially unreacted TiO2 being present in the internal pores of the pellets as rutile-type particles. The consolidation mechanism of pellets containing waste catalysts demonstrated that TiO2 in the waste catalyst reacts with iron oxide to form a Fe2TiO5 bond, while unreacted TiO2 reduces the compressive strength of the pellets. The metallurgical properties of the two titanium-bearing pellets are virtually identical to those of ordinary oxidized pellets, indicating that the pellets containing waste catalysts can be used in blast furnace protection smelting. This study offers a new approach for recycling waste catalysts generated by flue gas denitrification in iron and steel enterprises.
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圖 1 廢催化劑宏觀結構及微觀形貌圖. (a)廢催化劑預處理過程；(b) 廢催化劑XRD圖譜；(c) 廢催化劑微觀形貌
Figure 1. Macrostructure and micromorphology of the waste catalyst: (a) pretreatment process of the waste catalyst; (b) XRD pattern of the waste catalyst; (c) micromorphology of the waste catalyst
圖 2 不同生球團的落下強度和平均抗壓強度對比
Figure 2. Drop number and average compressive strength of different green pellets
Pellet-1— ordinary oxidized pellets; Pellet-2— pellets containing waste catalysts;Pellet-3— ordinary titanium-bearing pellets
圖 3 不同生球團爆裂溫度和干球平均抗壓強度對比
Figure 3. Burst temperature of green pellets and average compressive strength of dry pellets
圖 8 不同焙燒球團礦相結構. (a)普通氧化球團; (b)普通含鈦球團; (c)含廢催化劑球團; (d)圖(c)中局部顆粒放大圖
Figure 8. Microstructure of different roasted pellets: (a) oxide pellet; (b) titanium pellet; (c) waste catalyst pellet; (d) enlargement of a local area in photograph (c)
圖 9 含廢催化劑球團主要物相SEM圖. (a)廢催化劑顆粒；(b)照片(a)中局部放大圖
Figure 9. SEM image of the pellet containing waste catalyst: (a) waste catalyst particle; (b) enlargement of a local area in photograph (a)
表 1 含鐵原料主要化學成分（質量分數）
Table 1. Main chemical compositions of iron-containing raw materials
% Raw material TFe FeO SiO2 CaO MgO Al2O3 TiO2 V2O5 K2O Na2O MCa 65.75 26.50 6.57 0.30 0.48 0.84 — — — — VTMb 53.62 30.91 3.73 0.98 2.96 3.35 12.17 0.53 — — Bentonite 2.21 69.43 2.50 2.21 17.40 — — 2.48 2.77 MC a: Magnetite concentrate; VTM b: Vanadium titanomagnetite. 
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表 2 含鐵原料粒度組成（質量分數）
Table 2. Particle size composition of iron-containing raw materials
% Raw material Size composition +0.074 mm +0.045–0.074 mm ?0.074 mm ?0.045 mm MC 6.4 13.3 93.6 80.3 VTM 32.8 29.1 67.2 38.1
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表 3 廢催化劑及堵塞物飛灰主要化學成分（質量分數）
Table 3. Main chemical composition of the waste catalyst and fly ash
% TiO2 WO3 SiO2 CaO Al2O3 V2O5 Fe2O3 P2O5 Na2O K2O Sx 87.27 4.66 3.64 1.32 0.87 0.52 0.07 0.15 0.12 0.09 0.43
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表 4 不同球團礦RSI指數和密度
Table 4. RSI index and density of different pellets
Scheme Pre-reduction volume/cm3 Reduced volume/cm3 RSI/% Pre-reduction mass/g Pellet density/(g·cm?3) Pellet-1 22.1 24.2 9.6 87.24 3.95 Pellet-2 23.5 25.6 9.1 85.75 3.65 Pellet-3 22.8 24.6 8.1 87.10 3.82
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表 5 不同球團礦RI和RDI性能
Table 5. RI and RDI performance of different pellets
Scheme Mass fraction of TFe/% Mass fraction of FeO/% RI/% RDI+6.3/% RDI+3.15/% RDI?0.5/% Pellet-1 64.38 0.75 61.7 92.2 96.3 1.5 Pellet-2 61.07 1.79 63.3 96.6 97.8 1.2 Pellet-3 60.03 1.08 56.4 98.7 98.7 1.7
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表 6 不同球團礦熔滴性能
Table 6. Meltdown properties of different roasted pellets
Scheme Ta/℃ Ts/℃ ΔTsa/℃ Tm/℃ Td/℃ ΔTdm/℃ Pellet-1 1157 1198 41 1205 1331 126 Pellet-2 1163 1209 47 1211 1341 130 Pellet-3 1188 1228 40 1238 1339 101
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表 7 含廢催化劑球團主要物相EDS結果
Table 7. EDS results of the pellets containing waste catalyst
Scheme Mass fraction/% O Ti Fe V W Si Point 1 35.99 41.27 3.94 0.08 5.71 — Point 2 36.70 2.97 60.32 — — — Point 3 31.57 0.59 67.84 — — — Point 4 44.40 30.66 20.07 0.40 2.98 1.49
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