以蛋殼-TiO2 改質的永續竹筷生物炭用於酸礦排水中 Pb(II) 與多金屬去除之綜合解決方案

Abstract

酸性礦業排水（AMD）因其高酸度與重金屬濃度而持續受到注目。本研究以循環利用為核心，將廢竹筷再利用，製備為具高附加價值的生物炭，用於處理AMD。本研究透過傳統與微波輔助熱解兩種方式製備 11 種生物炭，並利用 BET、CHN/O、SEM-EDS、FTIR 與 XRD 進行材料孔隙結構及表面性質分析。其中以 450 W 微波熱解製得的生物炭在 Pb(II) 吸附上展現最佳效果，在吸附劑用量為2-g L-1、初始濃度50 mg L-1 的條件下達到可於24小時內達到濃度平衡，其去除率可達99.9%。吸附行為符合 Langmuir 等溫模式（qm 可達 89 mg g-1；R2 = 0.98），動力學則符合準二階反應（R2 = 1.00），顯示化學吸附為主要機制，其表面配位與靜電作用亦有相似結論。 此外，450 W 生物炭進一步以 CaCO3 與 CaCO3/TiO2 進行改質，形成 BC-CaCO3 與 BC-CaCO3/TiO2，並以 Box-Behnken RSM 設計對三種吸附劑進行最佳化。結果顯示投藥量、pH與接觸時間為關鍵因子，其BC、BC-CaCO3及BC-CaCO3/TiO2對Pb(II) 最大去除率分別為：40.65%、86.01%、74.83%，模型擬合相似度高（R2 > 0.98）。MLP 模型亦以良好準確性（R2 可達 0.997）驗證其預測結果。最佳化過程中，各生物炭的吸附均符合 Langmuir 模式，而動力學則呈現差異：BC 符合 Elovich 模式，而改質生物炭符合準二階反應，顯示化學吸附、表面不均質性、陽離子交換、碳酸鹽共沉澱以及 TiO2 強化鍵結等多重機制共同發生。熱力學分析結果證實所有最佳化系統的吸附過程皆具自發性、可行性且為放熱反應。應用於實際AMD時，BC-CaCO3/TiO2 對所有目標金屬均展現良好去除效率，在24小時內達到 97.15–99.99% 的去除率，依據其效益排序分別為為 Fe(III) > Zn(II) > Cu(II) > Mn(II) > Pb(II)，證實其適用於複雜 AMD 水質。 進一步的研究將 BC-CaCO3/TiO2 應用於人工濕地系統，包括控制組（C-CW）、僅含生物炭的人工濕地（BC-CW）以及結合生物炭與植物的人工濕地（BC/T-CW）。其中，BC-CW 改善pH 穩定性並提升 Cu、Pb 與 Zn 的固定能力，而 BC/T-CW 則展現最可靠的整體改良效果，包含維持良好氧化還原條件及更強的 Fe 與 Mn 固定能力。總體基因定序結果顯示，BC/T-CW 可促進具有植物關聯性的微生物群，並富含污染物降解相關的菌群與功能途徑，突顯工程化生物炭與香蒲（Typha latifolia）結合後在 AMD 濕地處理中的疊加效益。 總而言之，本研究證明當廢棄物來源的生物炭經過合理設計與改質，再結合生物系統後，可提供一種務實且具韌性的 AMD 處理方式。透過材料分析、吸附測試、統計最佳化、實際 AMD 驗證及人工濕地應用等整合結果皆顯示，BC-CaCO3/TiO2 無論作為單獨吸附劑或濕地系統中的原料之一時，均展現最穩定且最優越的效能。本研究強調工程材料與人工濕地生態結合，可提供一種具成本效益、循環再利用且效果良好的解決方案，用於處理富含金屬的酸性水體。

Acid mine drainage (AMD) remains a major concern due to its acidity and heavy metal load, and this work explores a circular approach that repurposes waste bamboo chopsticks into high-value biochars for its treatment. Eleven biochars were produced through both conventional and microwave-assisted pyrolysis and characterised using BET, CHN/O, SEM–EDS, FTIR and XRD to understand their structural and surface properties. Among these, the microwave-derived biochar produced at 450 W consistently showed the strongest Pb(II) adsorption, reaching 99.9% removal at a dose of 2 g L-1 and 50 mg L-1 initial concentration, with equilibrium achieved within 24 hours. The adsorption process followed Langmuir behaviour (qm up to 89 mg g⁻¹; R2 = 0.98) and matched pseudo-second-order kinetics (R2 = 1.00), confirming chemisorption as the primary mechanism which is supported by surface complexation and electrostatic interaction. Furthermore, the BC produced at 450 W was further modified with CaCO3 and CaCO3/TiO2 to form BC-CaCO3 and BC-CaCO3/TiO2, and all three adsorbents were optimised using a Box–Behnken RSM design. Dose, pH and contact time emerged as key factors, yielding maximum Pb(II) removals of 40.65% for BC, 86.01% for BC-CaCO3 and 74.83% for BC-CaCO3/TiO2, with strong model fits (R2 > 0.98). MLP modelling confirmed these predictions with high accuracy (R2 up to 0.997). During optimisation, adsorption fitted the Langmuir model across all biochar, while kinetics differed; ranging from Elovich behaviour for BC and pseudo-second-order kinetics for both modified biochar which highlighted a combination of chemisorption, surface heterogeneity, cation exchange, carbonate-assisted precipitation and TiO2-enhanced binding. Thermodynamic results showed that adsorption across all optimised systems was spontaneous, favourable and endothermic. When applied to real AMD, BC-CaCO3/TiO2 demonstrated high removal of all targeted metals, achieving 97.15 - 99.99% extraction within 24 h, with a trend of Fe(III) > Zn(II) > Cu(II) > Mn(II) > Pb(II), confirming its suitability for complex AMD matrices. BC-CaCO3/TiO2, was subsequently applied to further studies which involved constructed wetlands. These wetlands included a control system (C-CW), a biochar-only wetland (BC-CW) and a combined biochar–plant wetland (BC/T-CW). While BC-CW improved pH stability and enhanced Cu, Pb and Zn retention, the BC/T-CW system delivered the most reliable improvements, maintaining favourable redox conditions and stronger Fe and Mn immobilisation. Metagenomic analysis further demonstrated that BC/T-CW supported a specialised, plant-associated microbial community enriched in pollutant-degrading taxa and functional pathways, highlighting the synergistic benefits of combining engineered biochar with Typha latifolia in wetland-based AMD treatment. In essence, this work shows that waste-derived biochar, when purposefully modified and paired with a biological system, can offer a practical and robust way to address AMD. The combination of detailed material characterisation, adsorption testing, statistical optimisation, real AMD trials, and wetland-scale application demonstrated that BC-CaCO3/TiO2 consistently delivered the strongest performance, both as a standalone adsorbent and within a functioning treatment system. The study highlights how combining engineered materials with wetland ecology can provide an affordable, circular and effective approach for mitigating metal-rich acidic waters.