利用廢棄污泥製備環保吸附材並應用於重金屬吸附之研究

摘要本研究以“以廢制廢”的概念進行研究，將利用特定樣本醫院污泥實驗製備成新型生質碳吸附材料，試驗捕捉水中有害之砷離子與鉻離子。其實驗方法首先，採用微波碳化技術對污泥進行碳化，然後用ZnCl2在高溫下進行化學活化，以提高污泥的孔隙率和表面積。然後添加氯化鐵進行二次活化成新型金屬摻雜生質碳(Fe-SBC)材料對水中無機砷與鉻進行吸附性能評估。並採用各項實驗儀器檢測新生質碳材料特性如氮氣等溫吸/脫附法(BET)測定其比表面積、孔徑分佈和孔徑體積。又通過掃描電子顯微鏡(SEM)和能譜分析(EDS)測定了生質碳的形態與化學成分。再用X-射線繞射分析儀(XRD)測定了生質碳的晶相。及用熱重分析儀(TGA)研究分析生質碳的重量損失。經實驗儀器檢測特性分析結果顯示，50%ZnCl2-SBC的比表面積為525 m2 g−1，平均孔體積為0.35 cm3 g−1，孔徑為8.71 nm。SEM-EDS結果表明，新生質碳材料具有均勻的孔徑以及成分與活性碳非常相似，成分包括：C、O、K、Ca、Si和P。XRD分析結果表明，Fe-SBC在2θ= 36°和57°時可以觀察到FeOOH的Fe-O典型峰。運用傅立葉轉換紅外線光譜儀(Fourier-transform infrared spectroscopy；簡稱FT-IR)分析結果發現，生質碳在3400 cm-1處，對應O-H鍵和N-H鍵的彎曲振動，為胺基的特徵峰，在不同比例之ZnCl2的SBC也可發現，而且有明顯增強之特性相符趨勢。新型金屬摻雜生質碳(Fe-SBC)對As(III)的最高去除效率為91％在pH 3條件下，吸附容量為2.9 mg g-1。Fe-SBC對As(V)的最高去除效率為97％，吸附容量為3.72 mg g-1。在陰離子與As(V)和As(III)競爭吸附影響的順序排列如PO43- > CO32- > SO42- > NO3- > Cl-。另外此新型金屬摻雜生質碳(Fe-SBC)對樣對於較低之pH值環境條件下，Cr(VI)吸附效率亦可達到近90%。且依實驗結果隨著Fe-SBC投加量的增加，其吸附效率越來越好，Cr(VI)吸附效率可達99%以上。Cr(VI)吸附能力可達到67.7 mg g-1。另外在等溫吸附模擬結果可看出在砷吸附實驗中，用Langmuir模式(R2As(III) = 0.992; R2As(V) = 0.995)比Freundlich模式(R2As(III) = 0.894; R2As(V) = 0.891)適合；而在鉻吸附實驗中，亦是用Langmuir模式(R2Ct(VI) = 0.995)比Freundlich模式(R2Cr(VI) = 0.889)適合。動力學模擬結果顯示擬二階具有良好結果，As(III)線性圖的迴歸係數高於0.99；As(V)線性圖的迴歸係數高於0.98；Cr(VI)線性圖的迴歸係數高於0.99，證明本實驗新材料之可信賴度。而吸附過程可觀察到之實驗數據是由顆粒內擴散控制，並呈現吸附過程由兩個因素控制。第一條線性關係屬於材料之表面吸附；第二條線性關係是指污染物緩慢的向材料內部擴散。由本研究所繪製的吸附反應機理可分為三個途徑，第一條途徑污染物被吸附是由羥基氧化鐵官能團在SBC材料表面的附著並被氧取代。第二種途徑是砷離子與鉻離子被吸附在材料表面，是因為SBC材料表面帶正電與負離子砷分子與鉻分子之間產生靜電作用。第三個途徑是砷離子與鉻離子通過物理吸附並附著在SBC材料上，然後逐漸擴散到材料孔洞中，這可能是(包括Freundlich模式和Langmuir模式)吸附作用所產生的結果。本研究已利用特定樣本醫院生活污水處理廠產生之廢污泥材料，實驗將其碳化為新型生質碳吸附材料，試驗捕捉水中有害之砷離子與鉻離子有所成效。且因污泥取得成本極低，因此若有機會進一步工廠實地做小型研究測試，驗證可行之後對於處理有害廢水處理領域中將具有非常可觀的前景。關鍵字：生質碳、表面活化、污泥、砷與鉻、吸附

關鍵字

生質碳；表面活化；污泥；砷與鉻；吸附

並列摘要

ABSTRACT The utilization of domestic sludge, hospital sludge and aquatic product sludge form waste water treatment plants as biochar adsorbent was investigated. The sludge was carbonized using microwave carbonization and then chemically activated at high temperatures by using ZnCl2 to enhance porosity and surface area. A newly designed metal doped sludge biochar (such as Fe-SBC) presents effective inorganic arsenic adsorption in water. The specific surface area, pore size distribution and pore volume were determined by performing nitrogen adsorption-desorption measurements (BET). The morphology of the biochar carbon was measured through a scanning electron microscope (SEM) with energy-dispersive X-ray (EDS) analysis. The crystal phase of the biochar carbon was determined by an X-ray diffraction (XRD). The thermal properties of carbonized and biochar carbon were studied by a thermo gravimetric analysis (TGA) instrument. Results show that the surface area, average pore volume and pore size of 50%ZnCl2-SBC are 525 m2 g−1, 0.35 cm3 g−1and 8.71 nm, respectively. SEM results reveal that biochar carbon has uniform pore size. XRD results show Fe-O typical peak of FeOOH were observed for Fe-SBC at 2θ = 36° and 57°. The maximum removal efficiency of As(III) by Fe-SBC was 91% and the adsorption capacity was 2.9 mg g-1 at pH 3. The maximum removal efficiency of As(V) by Fe-SBC was 97%, and the adsorption capacity was 3.72 mg g-1. The order of competitive adsorption effect between anions and arsenic was PO43- > CO32- > SO42- > NO3- > Cl-. The adsorption efficiency of Cr(VI) reached nearly 90% at low pH. With the increase of the dosage of Fe-SBC, the adsorption efficiency becomes better and better, and the adsorption efficiency can reach more than 99%.The adsorption capacity can reach 67.7 mg g-1. The adsorption data could be described well by the Langmuir model (R2As(III) = 0.998; R2As(V) = 0.995) rather than by the Freundlich model (R2As(III) = 0.982; R2As(V) = 0.987); Langmuir model (R2Ct(VI) = 0.995) rather than by the Freundlich model (R2Cr(VI) = 0.889). These data indicate that the adsorption process was fitted to a monolayer adsorption on a homogeneous surface. The values of the rate constant (k2) were found to increase from2.9x10-3 to 4.1x10-3 with As(III), and 3.1 x10-4 to 10.3 x10-3 with As(V). The data shows good compliance with the pseudo second order equation and the regression coefficients for the linear plots were higher than 0.97. The reaction mechanism is divided into three pathways. The first pathway is the attachment of arsenic ions and chromium ions onto the biochar via physical adsorption, which may be attributed to van der Waals forces. The second pathway is the adsorption of arsenic species and chromium species, which depends largely on the surface chemistry of the adsorbent and on the chemistry of the aqueous phase. Furthermore, the activated carbon possesses both acidic and basic groups so that its surface charge density can be positive at low pH. The third pathway is the attachment of metal functional groups onto the surface of adsorbents and their replacement with oxygen groups, which is a modification method for producing strong adsorbents toward heavy metals. In this study, the waste sludge material produced by the domestic sewage treatment plant has been used to carbonize it into a new type of biomass carbon adsorption material, and the experiment has been effective in capturing the harmful arsenic and chromium ions in the water. And because the cost of obtaining sludge is extremely low, if there is an opportunity for further small-scale research and testing in the factory, it will have a very promising prospect for the treatment of hazardous wastewater after the verification is feasible. Keyword: Biochar Carbon, Surface activation, Sludge, Arsenic and Chromium, Adsorption