本研究為了降低海水淡化鹵水(以下簡稱海淡鹵水)所造成的環境危害，故以海水淡化過程中產生的副產物-鹵水為標的，進行循環經濟、資源循環與綠色化學的應用。整體研究架構可分為四個部份：海淡鹵水的分析及比較、鹵水應用於二氧化碳捕集與再利用、鹵水中有價資源(硼、銅、銫、銣、鋰)之分離純化與特定元素物質流分析。
第一部份將針對鹵水的基本特性，如元素組成、pH值、ORP值、導電度、等進行分析，並與世界各地的鹵水進行比較。由於此研究與歐盟Sea4value計畫配合，故可透過比較得知臺灣海淡廠的鹵水與世界其他海淡廠的差異，後續再經由比對其他資料，即能獲取可能原因。
分析海淡鹵水後，會利用其含有高濃度鈣、鎂的特性進行碳捕集與再利用。此部份首先利用pH Swing Method將pH值調整至9-14，以依序沉澱氫氧化鎂與氫氧化鈣，接著再將兩者分別透過胺類載體法及Modified Solvay Process捕集二氧化碳，並析出鎂、鈣、鈉化合物。
在第二部份析出鹵水內部分雜質後，將有利於後續稀有資源的分離純化，故本研究於第三部份利用濕法冶金技術，如溶媒萃取法、離子液體萃取法、離子交換法、氫化分解法等，進行硼、銅、銫、銣、鋰的資源循環。為了確認分離純化之資源具有實際應用價值，本研究會進行各式分析，並以所得之銣資源為例，將其合成為銣釩催化劑，運用至硫酸製備中。
獲取海淡鹵水內的資源後，本研究設定從碳捕集與再利用開始至循環有價資源的系統邊界，並透過特定元素物質流分析盤查硼、銅、銫、銣、鋰五種元素於每個步驟中的元素濃度，以得到實驗流程中的應關注熱點。接著再從所有應關注熱點中找尋元素流失最多的程序，以思考在後續研究中如何將其改善。
經由完整資源循環與應用程序後，所獲得的實驗結果為：臺灣澎湖的海淡鹵水具有較高濃度的鈣、鎂離子、較低TDS與較高pH值的特性；透過胺類載體法及Modified Solvay Process，1公升海淡鹵水可捕集7.24g二氧化碳；溶媒萃取與離子液體萃取分別較適合硼及銅的回收；溶媒萃取法、離子液體萃取法及離子交換法三者則皆可運用於銫和銣的循環；透過氫化分解法所獲得的碳酸鋰純度達95.9%；銣釩催化劑可在低溫情況下有效催化二氧化硫轉換為三氧化硫；藉由物質流分析得知共沉澱與共提煉是造成元素流失的兩大因素。
綜觀而言，整體研究希冀解決海淡鹵水所形成之環境問題，並提高其經濟價值，故以碳捕集與再利用及資源循環為研究主軸，以達到循環經濟中“提高資源使用效率的同時，顯著降低環境風險及生態破壞”和SDGs 17中“保育及永續利用海洋與海洋資源，以確保永續發展”的理念。

To reduce the environmental hazards caused by desalination brine, this research aims to utilize the concepts of circular economy, resources circulation, and green chemistry to treat brine from the desalination process. The research can be divided into four parts: analysis and comparison of brine, application of brine for carbon capture and utilization, separation and purification of valuable resources (boron, copper, cesium, rubidium, and lithium) from brine, and substance flow analysis.
In the first part, the basic properties of brine, such as elemental composition, pH value, ORP value, conductivity, and so on, are analyzed and compared with brine from desalination plants worldwide. Since this research cooperates with the Sea4value project of the European Union, the difference in brine between Taiwan and other countries can be realized through comparison. Subsequently, probable causes can be obtained by juxtaposing other information.
Carbon capture and utilization is conducted in the second part by taking advantage of the high concentration of calcium and magnesium in brine. The pH value is initially adjusted to 9-14 by the pH Swing Method, and magnesium hydroxide and calcium hydroxide precipitate sequentially. They are then employed to capture carbon dioxide through the amine carrier method and the Modified Solvay Process, respectively. After carbon capture and utilization, magnesium, calcium, and sodium compounds will precipitate.
Once the impurities in brine precipitate in the second process, it will be beneficial to separate and purify critical resources. Therefore, hydrometallurgy techniques such as solvent extraction, ionic-liquid extraction, ion exchange, and hydrogenation-decomposition methods are applied to recover boron, copper, cesium, rubidium, and lithium resources from brine. To confirm that the separated and purified resources have industrial application value, various analyses will be carried out. Besides, rubidium will be an example to synthesize into a rubidium-vanadium catalyst, which can be used to produce sulfuric acid.
The system boundary is set up from the procedures of carbon capture and utilization to the circulation of valuable resources after obtaining the resources in brine. Substance flow analysis (SFA) is used to investigate the concentrations of boron, copper, cesium, rubidium, and lithium. The concentrations of five elements in each step will be surveyed to find the hotspots in the experimental process. As all the hotspots are explored, programs with the highest loss will be improved in the follow-up research.
The results obtained through a complete process of resources circulation and application are as follows: The desalination brine from Penghu, Taiwan, has the characteristics of higher concentrations of magnesium and calcium, lower TDS, and higher pH value. 1 L of brine can capture 7.24 g of CO2 through the amine carrier method and the Modified Solvay Process. The solvent extraction and ionic liquid extraction systems are the most suitable for the circulation of boron and copper, separately. For cesium and rubidium, solvent extraction, ionic liquid extraction, and ion exchange systems can be applied under different situations. Li2CO3 with 95.9% purity can be acquired through the hydrogenation-decomposition method. The rubidium-vanadium catalyst can convert SO2 to SO3 efficiently at a lower temperature. Through SFA, it can be understood that critical resources are mainly lost due to co precipitation and co-extraction.
To sum up, this research is dedicated to solving the environmental problems caused by desalination brine and enhancing its economic value. Therefore, carbon capture and utilization and resources circulation will be the main parts to achieve the goal of “Improving the efficiency of resource usage while significantly reducing the environmental impact” in the Circular Economy and “Conserve and sustainably use the oceans, seas, and marine resources for sustainable development” in SDGs 17.