以流體化床反應器處理含銅廢水之研究

Studies of Copper Removal from Wastewater in the Fluidized-Bed Reactor

李嘉宜(Chia-I Lee)

指導教授 ： 楊萬發

國立臺灣大學/工學院/環境工程學研究所/博士(2005年)

https://doi.org/10.6342/NTU.2005.00254

摘要

本文應用流體化床反應槽為本體，分別應用流體化床結晶及吸附二種技術處理含銅廢水，以解決傳統含重金屬廢水處理所衍生之大量污泥之問題。
在應用流體化床結晶技術處理含銅廢水部分，分別針對最小流體化速度、銅離子與結晶試劑介穩區及最佳銅離子去除條件，加以研究。應用流體化床結晶技術處理含銅廢水需將操作條件控制於低過飽和度，以使得銅離子以核沉澱方式包覆於流體化床內之擔體表面。本實驗中相關之影響因子包括:pH值、結晶試劑與銅離子之莫耳比、水力負荷及結晶試劑種類等。實驗結果指出: 由介穩區之界定結果顯示當結晶試劑與銅離子之莫耳比([CT]/[Cu])=2時，相對之銅離子濃度限制為40 mg/L，然而在實際之流體化床反應槽操作下，因其流體化之擔體進行高速運動，形同一種快速攪拌行為，因此對於進流銅離子濃度限制較高為20 mg/L。當進流銅離子濃度為10 mg/L時，出流水銅離子去除率可達96%；最佳之結晶試劑為Na2CO3；最佳之結晶試劑與銅離子之莫耳比([CT]/[Cu])為2；水力負荷方面則不宜超過30 m/H。此外，避免於流體化床反應槽內發生沉澱反應(homogeneous nucleation)亦為一項非常重要之操作因子。一旦於流體化床反應槽內發生沉澱反應將導致出流水銅離子濃度增加，而將進流廢水與結晶試劑於流體化床擔體內進行混合，將可有效的降低於反應槽底部所發生之沉澱現象。針對結晶物分別利用掃瞄式電子顯微鏡(Scanning Electron Microscope, SEM)針對樣品表面進行觀察及照相，本實驗所使用之機種配有能量散射光譜儀(Energy Dispersive X-ray Spectrum, EDS)，可同時針對樣品進行定性分析。而利用元素分析儀之分析結果推估結晶物中CuCO3及Cu(OH)2所佔之比例分別為46%及54%。
在應用流體化床吸附技術處理含銅廢水部分，本實驗係利用將錳砂填充於反應槽內做為吸附劑，利用將填充之錳砂以流體化方式，以有效去除廢水中之銅離子。本實驗中分別針對錳砂之吸附特性、錳砂對銅離子之吸附平衡及流體化床內錳砂對於銅離子之去除成效加以探討。
在錳砂表面性質及其吸附特性方面，利用掃瞄式電子顯微鏡針對樣品表面進行觀察及照相，並利用能量散射光譜儀進行錳砂之組成分分析，錳砂中重金屬錳含量利用消化方式測量結果約為8.03 mg-Mn/g-錳砂。實驗結果指出:利用流體化床反應槽內填充錳砂去除廢水中之銅離子，銅離子之去除受pH值高度影響，當pH值增加時，銅離子去除率亦隨之提升，而當錳砂吸附銅離子結束後，溶液中之pH值呈現下降情形。當錳砂添加量大於10 g/L時，應用流體化床反應槽去除銅離子之效果與傳統應用振盪器去除銅離子之效果幾乎相等，而當錳砂添加量達40 g/L時，應用流體化床反應槽吸附銅離子之效果則大於使用振盪器吸附銅離子之效果。此結果顯示於反應槽中添加錳砂做為吸附劑並將其流體化後，吸附劑表面之吸附位址(sites)可有效被利用。在等溫吸附實驗方面，利用錳砂吸附廢水中銅離子之實驗結果符合Langmuir等溫吸附方程式。此外，實驗結果亦顯示:當於溶液中進行曝氣時，有助於銅離子於錳砂表面之吸附。

關鍵字

流體化床反應槽 ； 過飽和 ； 沉澱 ； 均相成核 ； 錳砂 ； 吸附

並列摘要

In this study, a fluidized-bed reactor (FBR) was employed to treat copper-containing wastewater by mean of copper precipitation on the surface of sand grains and adsorpted by manganese-coated sand (MCS).
In the study of copper crystallization on the sand surface, the conditions for optimum copper removal efficiency were also investigated. This technology was controlled so as to keep supersaturation low to induce the nucleated precipitation of copper coating on the sand surface in an FBR. The effects of relevant parameters, such as the pH value, the molar ratio of [CT] to [Cu], hydraulic loading and the types of chemical reagents used, were examined. The experimental results indicated that 96% copper removal efficiency could be achieved when the influent copper concentration was 10 mg/L. The optimum chemical reagent was Na2CO3; the molar ratio of [CT]/[Cu] was 2, and the optimal hydraulic loading was not be more than 30 m/h. In addition, preventing homogeneous nucleation in the FBR was an important operation parameter. Homogeneous nucleation and molecular growth would lead to undesirable microparticle formation in the effluent. A good mixture of carbonate and copper in the presence of sand grains could reduce the level of homogeneous nucleation in the bottom of the reactor. Energy Dispersive Analysis (EDS) of X-rays provided insight into the copper coating on the sand surface, and element analysis indicated the weight percentages of CuCO3 and Cu(OH)2 in precipitate are 46% and 54%.
Besides, by using of MCS to treat copper containing wastewater, it was performed in a fluidized-bed reactor (FBR) filled with MCS to treat copper-contaminated wastewater. The adsorption characteristics of MCS, the adsorption equilibrium of MCS, and the copper removal capacity by MCS in FBR were investigated. In terms of the adsorption characteristics of MCS, the surface of MCS was evaluated using a scanning electron microscope (SEM). Energy Dispersive Analysis (EDS) of X-rays indicated the composition of MCS, and the quantity of manganese on MCS was determined by means of acid digestion analysis. The experimental results indicated that copper was removed by both sorption (ion exchange and adsorption) and coprecipitation on the surface of MCS in FBR. Copper removal efficiency was highly dependent on the pH and increased with increasing pH from pH 2 to 8. After the copper adsorption by MCS, the pH in solution was decreased. When the MCS concentration was greater than 10 g/L, the copper adsorptivities obtained by FBR were almost the same as that from the shaker and when the MCS concentration reached 40 g/L, the copper adsorptivity in FBR was greater than that from the shaker. The adsorption sites of MCS could be used efficiently by the FBR. A Langmuir adsorption isotherm equation fit the measured adsorption data from the batch equilibrium adsorption test better than the Freundlich adsorption isotherm equation did. In addition, the adsorption rate increased when the influent wastewater was aerated.

並列關鍵字

Fluidized-bed reactor ； copper removal ； supersaturation ； precipitation ； homogeneous nucleation ； manganese-coated sand ； adsorption

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