以酒廠污泥移除水中鉻銅鋅鎳之研究

Abstract

製酒工業的廢棄污泥可有效吸附水中重金屬，但對於污泥性質與吸附機制並不明瞭。本研究之目的包括鑑識酒廠污泥的形態與特微，研究污泥吸附鉻、銅、鋅、鎳和六價鉻的機制，探討溫度、金屬濃度、污泥粒徑對吸附的影響，瞭解實驗金屬對污泥的競爭吸附，以及比較吸附反應在批次法和管柱流法中的差異。宜蘭酒廠污泥pH為 6.2，陽離子交換容量 255 cmolc kg-1，有機質含量約 38％，羧基是吸附重金屬的主要官能基，alkyl-C 和carboxyl-C是含量最多的含碳官能基。無機組成含有鐵、鋁、鈣、鎂、鉀、鈉、錳、矽、氮、磷、硫等成份，存在方式包括無定型氧化物形態、有機錯合形態以及被吸附的離子形態。無機組成溶出試驗、污泥洗鹽法、離子交換法和物理性分離法則被用來研究污泥的無機組成特性、污泥團粒構造以及吸附機制。離子交換應是污泥吸附陽離子重金屬最重要的方式，有機質和無機成份可能以均勻混成的方式構成污泥團粒。物理性分離法對泥污13C NMR和DSC的測定有改善的效果。 鉻的吸附對於 Langmuir 及 Freundlich 等溫吸附模式皆有很高的相關，銅、鎳的吸附較符合 Langmuir 模式，鋅的吸附則較符合 Freundlich 模式。鉻的吸附較符合假一階動力模式，銅、鋅、鎳、六價鉻則和假二階動力模式相關較高。污泥吸附鉻、銅、鋅、鎳、六價鉻的含量及速率隨溫度的上升而增加，卻隨污泥粒徑的增加而減小，金屬濃度較高者雖總吸附量較大，但達吸附平衡的速率卻較低濃度者為小。有機質的溶出，也隨溫度的升高而增加。銅、鋅的活化能分別為 6.961 和 7.820 kJ mole-1。 由花蓮酒廠污泥（pH 4.6）的管柱實驗顯示，鉻管柱到達耗竭點的時間分別為為銅、鋅的 4.0 及8.2 倍，電荷密度明顯影響污泥對金屬的吸附。依 Barry 和Sposito 的延散模式，可得遲滯因子為 鉻（18.3）＞銅（13.0）＞鋅（7.2），延散係數為 鉻（2.36×10-6）＞鋅（6.83×10-7）＞銅（5.89×10-7）m2 s-1。此模式適合描述銅、鋅在污泥管柱內之動態變化，鉻並不適合。Thomas equation 也不適合用來計算鉻管柱的最大吸附量。 競爭吸附系統中，污泥對金屬的吸附能力為 鉻＞銅＞鋅，低溫時鉻的吸附卻略低於銅，溫度上升時鉻的吸附則增加最快。初濃度相同的 鉻/銅、鉻/鋅、銅/鋅、鉻/銅/鋅 混合液，管柱達耗竭點時污泥吸附金屬的含量分別為 6.3：1（鉻：銅）、17.1：1（鉻：鋅）、5.6：1（銅：鋅）、107：18：1（鉻：銅：鋅）。管柱流法無法有效吸附鋅；鉻、銅可取代已吸附的鋅，鉻則無法取代已吸附的銅。Zn2+因軌域填滿及水合離子半徑最大，導致最弱的吸附競爭力。 在六價鉻吸附的反應中，懸浮液之pH由 2.0上升至4.2，減弱了質子化和氧化還原作用，造成六價鉻去除率偏低。同步輻射的研究顯示，六價鉻被有機質還原成三價鉻後才被吸附，未被吸附的Cr3+ 則移轉至液相中。污泥溶出的二價鐵也參與六價鉻的還原，但含量稀少。

Wine processing waste sludge (WPWS) has been shown to be an effective sorbent for sorption of some heavy metals, but the properties of WPWS and sorption mechanism of heavy metal by WPWS were remained obscured. This study aimed to (i) examine the characteristics of WPWS; (ii) explore the sorption mechanism of WPWS for heavy metals; (iii) determine the effects of temperature, initial concentration of metals and different particle sizes on the adsorption reaction; and (iv) conduct the competitive adsorption by batch and fixed-bed columns methods using Cr, Cu, Zn and Ni as sorbates. The sludges contain high contents of organic matter (38%) and cation-exchange capacity (CEC, 255 cmolc kg-1). From IR analysis revealed that prominent functional groups is carboxyl which interact with metals. The alkyl-C and carboxyl-C were major organic functional groups in WPWS which was quantified by 13C NMR analysis. The composition of inorganic element in WPWS contain Fe, Al, Ca, Mg, K, Na, Mn, Si, N, P and S, which may be complexed by organic matter or exist in amorphous oxides form. Methods of dissolution of inorganic compositions, WPWS rinsing, ion exchange and physical separation were employed to study the properties and aggregates of WPWS and sorption mechanism. Ion exchange is the most important way for WPWS to adsorb toxic metals. The aggregate of WPWS consist of well mixture of organic and inorganic components. Method of physical separation of WPWS can improve the determinations of 13C NMR and Differential scanning calorimetry. The WPWS sorption isotherms of Cr(III) are well described by both Langmuir and Freundlich isotherm, whereas Cu and Ni are well described by only Langmuir isotherms and Zn were Freundlich isotherms. A pseudo-second-order sorption kinetic model describes successfully the kinetics of sorption of Cu, Zn, Ni and Cr(VI) onto WPWS at different operation parameters (i.e., pH, initial Ni concentration, and particle size), but pseudo-first-order shows good compliance with Cr(III) sorption. The sorption of Cr, Cu, Zn and Ni increase with increasing temperature, but it decreases with increasing in metal concentration and particle size. The dissolution of organic matter also increases with increasing temperature. The activated energies of Cu and Zn sorbed by WPWS are 6.961 and 7.820 kJ mole-1, respectively. The column studies showed that the times approach exhausted point for Cu and Zn were 4.0 and 8.2 times greater than that of Cr, respectively. The charge density of metal can affect the sorption time and sorption amount. The retardation factor for Cr, Cu and Zn column are shown the following order: Cr (18.3) > Cu (13.0 )> Zn (7.2), and the order of dispersive coefficient is: Cr (2.36×10-6) > Zn (6.83×10-7) > Cu (7.25.89×10-7) m2 s-1, which is calculated from a one dimensional convection–dispersion model recommended by Barry and Sposito. The dynamic transports of Cu and Zn can be described well by this model, bur for Cr. Thomas equation is not adopted for Cr to determine the maximum sorption capacity The sorption of metals by WPWS show the trend in competitive system: Cr > Cu >Zn. The sorption of Cr is less than that of Cu at low temperature, but the increase in sorption of Cr is more than that of Cu and Zn. The ratios of sorption amount were 6.3:1 (Cr:Cu), 17.1:1 (Cr:Zn), 5.6:1 (Cu:Zn) and 107:18:1 (Cr:Cu:Zn) for Cr/Cu, Cr/Zn, Cu/Zn and Cr/Cu/Zn mixtures with same initial concentration at exhausted point, respectively. Zn can not be sorbed effectively by column method. The adsorbed Zn can be replaced by both of Cr and Cu, but Cr can not replace the adsorbed Cu. The least competitive sorption for Zn(II) can be attributed to its largest hydrated radius and full-filled electric orbital. All kinetic experiments of Cr(VI) sorption were conducted at an initial pH of 2.0, and the final pH of the suspensions were approximately 4.2. Thus, both protonation and the oxidation-reduction reaction weakened, and this led to low Cr removal. Some of the Cr(VI) ions are reduced to Cr(III) ions and then adsorbed on WPWS, as indicated by monitoring using the X-ray absorption near-edge spectroscopic (XANES) technique. The other Cr(III) remained in the liquid phase. The Cr(VI) can also be reduced by little ferrous ions dissolved from WPWS.