以具分散反萃取相支撐式液膜回收鈷離子

Abstract

金屬鈷具有優異的物理和化學性質被廣泛應用於電池、合金等領域中，且近年來隨著電動車產業的發展，鋰離子電池的關鍵材料鈷成為全球矚目之過渡金屬，然而全球超過一半之鈷礦位在剛果民主共和國，此地區戰亂頻繁，造成鈷的供應不穩定，使其價格逐年攀升，因此，若能回收工業廢水中之鈷離子並重複使用，將能減省製程上的成本。 本研究使用具分散反萃取相支撐式液膜技術回收並濃縮鈷離子，首先探討純鈷系統下，具分散反萃取相支撐式液膜操作參數如進料氫離子濃度、萃取劑濃度對鈷離子透過係數之影響。第二部分探討含螯合劑乙二胺之系統，研究結果顯示鈷離子之透過係數會分成兩段，以使用萃取劑D2EHPA為例，於過程中控制進料溶液pH值為4的條件下，透過係數分別為1.0×10-4 (m/min)及5.3×10-6 (m/min)。進一步使用UV-Vis光譜探討進料溶液中鈷-乙二胺螯合物之性質，得知第二段透過係數較慢的原因為溶液中存在穩定之鈷(III)-乙二胺螯合物所致。為了提升第二段較慢的透過係數，在進入具分散反萃取相支撐式液膜前，本研究將進料溶液分別使用還原法和H2O2/UV光法進行前處理。還原法為添加還原劑連二亞硫酸鈉將鈷(III)-乙二胺螯合物還原成鈷(II)-乙二胺螯合物，接著使用具分散反萃取相支撐式液膜回收鈷離子，可提升透過係數為1.5×10-4 (m/min)。 H2O2/UV光法主要利用雙氧水分解產生之自由基將乙二胺降解來破壞螯合，經由具分散反萃取相支撐式液膜操作也可提升透過係數為1.8×10-4 (m/min)。 本研究也對實務上之廢水進行測試，先進行UV-Vis光譜分析得知水樣中含有鈷(III)-乙二胺螯合物，直接進行具分散反萃取相支撐式液膜操作會有兩段透過係數，分別為6.0×10-5 (m/min)及4.4×10-6 (m/min)，因此嘗試進行還原法及H2O2/UV光法前處理，此兩方式皆可提升透過係數且只有一段(分別為2.6×10-4 m/min、4.5×10-4 m/min)，研究結果顯示具分散反萃取相支撐式液膜技術結合前處理方法具有應用在工業上之潛力。

Cobalt has excellent physical and chemical properties, making it widely used in battery and alloy fields, etc. Moreover, the electric vehicle industry is rising and cobalt is one of the key materials used in the rechargeable battery, so people expect the demand for cobalt will be very large in the next few years. However, more than one-half of cobalt ores are located in Congo, where we can not get a stable amount of cobalt due to this war-ridden country. This leads to the increasing price of cobalt. Therefore, if we can recover cobalt ions from the wastewater, that will be helpful to reduce the cost in the process. Herein, we present a technique called supported liquid membrane with strip dispersion (SLMSD) to recover cobalt ions. At first, we investigated the effects of pH value in feed and extractant concentration in organic on the permeability of pure cobalt ions. In the second part, we studied the cobalt solution containing ethylenediamine chelating agent, and the results showed that cobalt ions had two permeability segments. Take the extractant of D2EHPA (pH control at 4 in feed) as an example, two values, 1.0×10-4 (m/min) and 5.3×10-6 (m/min) were obtained. The UV-Vis spectra verified that the slower permeability was due to the existence of stable Co(III)-ethylenediamine complex. In order to increase the slower permeability, we proposed two pretreatment approaches before starting SLMSD. One is the reduction approach, and the other one is the H2O2/UV approach. For reduction approach, we used sodium dithionite as a reductant to reduce Co(III)-ethylenediamine to Co(II)-ethylenediamine. After the pretreatment, the permeability increased to 1.5×10-4 (m/min) by SLMSD operation. On the other hand, adopting the H2O2/UV approach could degrade ethylenediamine molecules, making the permeability also increase to 1.8×10-4 (m/min). In addition to lab research, we also dealt with cobalt-containing wastewater from industry to recover cobalt ions. By UV-Vis spectra, we knew there was Co(III)-ethylenediamine complex existing in the wastewater. Without any pretreatment, the permeability of cobalt ions was divided into 6.0×10-5 (m/min) and 4.4×10-6 (m/min). Using either reduction or H2O2/UV pretreatment approach, we could get higher permeability, which was 2.6×10-4 (m/min) and 4.5×10-4 (m/min), respectively. Therefore, SLMSD technique combining with pretreatment approaches has the potential to be used in the industry.