非分散式萃取程序分離酸液中貴重金屬之質傳分析

Mass Transfer Analysis on Non-dispersive Extraction Separation of Metal Values from Acidic Solutions

高向前(Hsiang-Chien Kao)

指導教授 ： 莊瑞鑫

共同指導教授 ： 蔡德華

元智大學/工程學院/化學工程與材料科學學系/博士(2005年)

https://doi.org/10.6838/YZU.2005.00001

摘要

本論文模擬廢二次電池之溶蝕酸液，經化學沈澱或電解處理後，研究以溶劑萃取將Co2+/Ni2+及La3+/Nd3+分離與回收。廢二次電池回收分類去除外殼後，經鍛燒、篩選成粉末狀小顆粒後，再以不同的強酸（HCl、H2SO4或HNO3）溶液溶解，調整不同的固液比即可獲得不同的金屬濃度。以市面上用量最多的二次鋰電池為例，其溶蝕廢液成分有Li+、Co2+、Ni2+、Cu2+、Mn2+、La3+、Nd3+、Al3+及Fe3+等金屬離子。此廢液中Cu2+、Al3+、Mn2+及Fe3+，可經由pH調整及化學沉澱或電解前處理，大部份可先後分離出來；主要剩下的Co2+/Ni2+及La3+/Nd3+等金屬離子，由於物理化學性質非常相近，很難應用上述傳統的電解、沈澱等的方法輕易分離回收，而溶劑萃取是濕法冶金程序中回收與純化的一個重要單元，此技術已被廣泛應用。
首先由平衡實驗中找出最佳的分離條件，在鈷、鎳系統中，當採用酸性萃取劑(D2EHPA、PC88A)時，其萃取率都不到20%，而經由皂化後的鈉型萃取劑(Na-D2EHPA、Na-PC88A)，雖然萃取效果有明顯的提昇，但Co2+、Ni2+會同時被萃取至有機相中，無法達到分離之效果。若採用三級胺鹽(TOA)鹼性萃取劑時，其萃取率都低於10%，而經過質子化後之TOA其萃取率有明顯的提昇，但其萃取劑需經由質子化前處理，於工業應用上較不適用。然而採用四級銨鹽Aliquat 336 (NR4Cl)當萃取劑，煤油為稀釋劑，自HCl酸液中可得到較佳萃取的分離效果，而且萃取劑也不需前處理。故於鈷、鎳系統採用四級銨鹽Aliquat 336 (NR4Cl)為萃取劑；分別再以高、低濃度作探討。於低濃度系統(金屬濃度為3.5∼25 mol/m3)單成分萃取平衡實驗中，發現其平衡常數會隨萃取劑濃度有所變化，所以其溶液為非理想狀態；且由於水相中CoCl42－濃度較低及Cl－濃度因變化很小，其非理想情形主要是由有機相所造成的，然而有機相非理想行為可以(gcomplex/gamine2) [amine]-0.84來表示。
而於高濃度鈷(170∼510 mol/m3)系統單成分萃取平衡實驗中，同時考慮水相及有機相均為非理想非理想情況下，其熱力學平衡常數關係式為：

接著利用兩組中空纖維模組同時進行萃取與反萃取，利用熱力學平衡關係及質量守恆原則，配合實驗結果數據提出適當傳送機制，並採用Levenberg-Marquardt修正模式，可得萃取劑與複合物於萃取(km,E)與反萃取(km,S)模組中薄膜中不同質傳係數，分別為km,E = 9.3 x 10-7 m/s，km,S = 2 x 10-8 m/s，利用此模式其計算與實驗標準偏差值都低於5%，可以描述鈷金屬於中空纖維薄膜接觸器之傳送；即可發現於鈷系統中主要控制為反萃取段之薄膜擴散。
其次探討鑭和釹系統，對於單成分系統的，在25 oC下，所得萃取平衡常數分別為Kex,La = 2.30´10-5 與Kex,Nd = 2.39´10-4。再利用直接混合之接觸器探討Me3+/HNO3溶液與PC88A/kerosene之反應動力學，其萃取與反萃取速率可分別表示為
萃取速率 , kf,La = (1.2±0.4)×10-6 m3/2 / (mol1/2 s)
, kf,Nd = (3.3±0.4)×10-7 m3/ (mol s)
反萃取速率 , kb,La=(7.8±0.8)×10-5 mol1/2/ (m3/2 s)
, kb,Nd=(2.7±0.8)×10-4 mol / (m3 s)
而kf為正向反應數率常數；k-b則為逆向反應數率常數。
此外，使用二套中空纖維管膜組，同時進行萃取與反萃取之質傳速率探討；假設系統為穩定狀態，並利用已知的萃取平衡、動力數據及個別質傳係數，導出個別系統之理論質傳速率式，並且分別計算出於萃取與反萃膜組中的進料相擴散，界面反應、薄膜擴散和有機相擴散的各項阻力百分比。對於La、Nd系統，萃取模組之中水相擴散與界面反應阻力可忽略，此模組由有機相與薄膜擴散主控。而在La3+之反萃取模組中，反萃取水相擴散阻力很小，反萃取模組由薄膜擴散、有機相擴散和界面反應控制。對Nd3+之反萃取模組中，有機相擴散很小，質傳阻力則由薄膜擴散與學反應阻力及反萃取水相擴散為控制。

關鍵字

萃取分離 ； 直傳分析 ； 中空纖維薄膜接觸器 ； 貴重金屬回收

並列摘要

In this paper student on several valuable metals (Co2+, Ni2+, La3+, Nd3+) will be recovered and separated from aqueous solutions by solvent extraction technique. The solutions are obtained from acidic leaching wastes of spent secondary batteries but are pretreated by conventional chemical precipitation methods (hydroxide, sulfide,) or electrolysis. Taking the spent lithium battery as an example, the acidic leaching solutions contain Li+, Co2+, Ni2+, Cu2+, Al3+, La3+, Mn2+, Nd3+ and Fe3+. Of these metal ions, Cu2+, Al3+, Mn2+, and Fe3+ can be mostly removed by pretreatment. The remaining Co2+/Ni2+ and La3+/Nd3+ (and possibly the trace amount of Li+) in solutions are difficult to separate because of their similar physicochemical properties. Solvent extraction is an important unit in hydrometallurgical processes, which has been extensively applied for recovery and selective separation of metal ions.
First, the optimal separation conditions were found from batch equilibrium experiment. The extraction efficiency of metals was low when the acidic extractants D2EHPA and PC88A as well as the basic extractants TOA were used, but it increased apparently using the modified acidic extractants Na-D2EHPA and Na-PC88A as well as the protonated TOA. On the other hand, the experimental results indicated that the better extraction efficiency could be obtained from hydrochloric acid solution when Aliquat 336 (R4NCl) dissolved in kerosene was used as extractant.
At relatively low concentrations of CoCl42- (3.5∼25 mol/m3), The equilibrium constants Kex changes with amine concentration. It is assumed that activity coefficient of MCl42- in water containing a large Cl- excess (1000~3000 mol/m3) remains equal (constant ionic medium concept), and that of Cl- is also kept constant. We proposed that the non-ideal behavior of organic phase follows the simplified form (gcomplex/gamine2) [amine]-0.84 for solvent extraction of CoCl42- with Aliquat 336.
In high metal concentration (17∼510 mol/m3) system, the non-ideal phenomena were considered on the aqueous and organic phases. It was shown that the equilibrium constants could be expressed as

Simultaneous extraction and stripping in hollow fibers were studied. On the basis of thermodynamic equilibrium results and the mass-action law, the one considering non-ideality of organic phase, and the one considering non-idealities of both the organic and aqueous phases. The kinetic modeling of hollow fiber extraction and stripping process, the mass transport resistance is dominates by the resistance in the stripping organic membrane, it has been possible to describe successfully the experiment results obtaining the optimum value for extraction and back-extraction membrane mass-transfer coefficient (kmE =9.3x10-7 m/s; kmS =2x10-8 m/s), which allow the design and optimization of the recovery of Co(II) from Chloride Solutions, and it could satisfactorily predict time profiles of Co(II) concentrations with the experimental data (standard deviations of 4.5%).
In lanthanum and neodymium extraction systems, the equilibrium constant of and were 2.30´10-5 and 2.39´10-4, at 25oC.The initial extraction and stripping rates of La and Nd with PC88A(HX) in kerosene were separately measured using a direct mixing cell. At 25oC, the rate equations could be written by
Extraction rate:
, kf,La = (1.2±0.4)×10-6 m3/2/(mol1/2 s)
, kf,Nd = (3.3±0.4)×10-7 m3/(mol s)
Stripping rate:
, kb,La = (7.8±0.8)×10-5 mol1/2/(m3/2 s)
, kb,Nd = (2.7±0.8)×10-4 mol/(m3 s)
Simultaneous extraction and stripping were studied in hollow fibers. Based on the equilibrium and kinetic data, and the individual mass transfer coefficients, the fractional resistance of each step to the overall process can be calculated. For extraction La, Nd system, the resistance of aqueous layer diffusion and interfacial reaction was ignored in the extraction module. The controlling steps were both organic layer diffusion and membrane diffusion. In the stripping module for La, the contribution of stripping phase aqueous layer diffusion could be ignored. This process was dominantly governed by membrane diffusion, and interfacial reaction and organic layer diffusion. In the stripping module for Nd, it was dominantly governed by membrane diffusion interfacial reaction and stripping phase aqueous layer diffusion.

並列關鍵字

Extraction Separation ； Mass Transfer Analysis ； Hollow fiber contactor ； Recovery Valable metals

參考文獻

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