| Summary: | 碩士 === 元智大學 === 化學工程學系 === 92 === Abstract
Printed circuit board (PCB) and semiconductor are two high-tech products that play crucial role in the economic development of this country. In spite of their growing importance, manufacturing of these products leads inherently to production of waste solution and sludge that contain high concentration heavy metals. Proper disposal of these solution and sludge are necessary in order to minimize their negative environmental impact. This research represents an attempt to deal with waste solution and sludge that contain high concentration copper. Electrolysis and ion exchange processes were adopted for this purpose.
In the electrolytic process, both simulated and real waste copper solutions were employed. This process was intended to recover copper from the waste solution by greatly reducing the copper concentration from over 20% to hundreds of ppm. The primary operating variables considered in the test runs included current, initial pH and copper concentration. The effects of these variables on the copper recovery were thoroughly examined. The test results indicated that under the condition of pH<1, a current of 8 A and 24 h of electrolysis, a 99.9% copper recovery could be achieved in this process using the simulated waste solution. For the real plant copper solution obtained from the PCB etching process, the pH effect was found to be relatively small and hence current became the prime control variable. The copper recovery under optimal current condition was found to be quite good, exceeding 99.5%.
For treatment of waste sludge from a PCB plant, the sludge was first broken up into small pieces which in turn were mixed with acid extractant (sulfuric acid). A solution containing 20% sulfuric acid was found to provide the best copper extraction. The sulfuric solution containing over 10% copper was then subject to electrolysis. Again the copper recovery was found to be excellent, being greater than 99.5%.
The residual solution after electrolysis contained a copper concentration under 500 mg/l which was not acceptable for direct discharge. To further reduce the copper concentration, ion exchange was adopted. Both batch equilibrium and column ion exchange experimental tests were performed. The batch equilibrium data were modeled by Langmuir and Freundlich isotherms for optimal model discretion. In the column tests, the main control variables included solution feed rate and inlet copper concentration. The experimental data were employed to verify the ion exchange column model. Both simplified and general logistic models were found to describe the present ion exchange reasonably well. The verified column model could significantly facilitate predictions of the breakthrough time and capacity. The exhuasted ion exchange resins after breakthrough need to be regenerated for reuse for cost reason. Preliminary batch regeneration of exhausted ion exchange resins was performed. Test results indicated that after three ion-exchange/regeneration cycles, an ion exchange capacity of 94.3% was still retained.
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