Microbial Leaching of Waste Solder for Recovery of Metal

• Main Author: 洪宗良
• Other Authors: 賀陳弘
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/75993664947199293802

碩士 === 國立清華大學 === 動力機械工程學系 === 101 === The increase in use of electrical and electronic equipments (EEE) results in an increase in amount of electronic waste. Solders are used as interconnecting material in electronic packaging. However, metals present in solder can pose negative impacts on both environment and the human body. Pyrometallurgical and hydrometallurgical methods are used for recycling of these waste solders. However, these methods have certain disadvantages, such as consumption of high energy and use of harmful chemicals. There is a need of environmentally benign process to recover metals from waste solders. In the present work bioleaching of lead free and lead containing solders was studied. This was achieved by employing culture supernatants of Acidithiobacillus ferrooxidans (At. ferrooxidans) and Aspergillus niger (A. niger). Two types of lead free solders were used, Sn-Cu and Sn-Cu-Ag. Along with this lead containing (Sn-Pb) solder was also used. It was found that culture supernatant of A. niger removed metals in less time as compared to culture supernatant of At. ferrooxidans. Therefore further bioleaching experiments were carried out with A. niger supernatant to investigate the dissolution behavior of metals under varying process parameters viz. time, temperature, shaking speed, volume of culture supernatant, amount of solder, etc. The results show that for Sn-Cu-Ag solder 99% dissolution was achieved in 60 h, while it required 96 (99%) and 144 (99%) h for Sn-Cu and Sn-Pb solders respectively. For bioleaching experiment 200 rpm shaking speed and 30 oC temperature were found optimum. In another experiment ultrasonic waves are used along with bioleaching process to recover metals from waste PCB. Also experiments were carried out to recover metals from bioleached solution by adding sodium chloride, sodium hydroxide and hydrogen sulfide gas. These results suggest that it is possible to recover metals from waste solders by applying biohydrometallurgical method. The current research is original using Aspergillus niger for solder bioleaching. This method is environmentally friendly. Solder leaching effect of Sn-Cu-Ag reached 97.8% after 36hr and solder leaching effect of Sn-Pb reached 99.4% after 144hr.