| Summary: | 碩士 === 弘光科技大學 === 環境工程研究所 === 102 === In order to avoid the discharged high-tech industry wastewaters have bad influence on human health, the Environmental Protection Agency have included the “Indium (In) and Gallium (Ga)” items in the regulation of wastewater discharge on January 1, 2012. In the “Effluent Standards”, the control limits of In and Mo, are 0.1 and 0.1 mg/L, respectively. In addition, for cutting down the costs, many high-tech companies start to look for methods for recycling the noble metals. Therefore, if the water quality can be handled properly, not only the water can be reused but also the noble metals can be recycled. There are a lot of techniques can be used to separate metals from wastewaters. Ion exchange process is chosen in this study because it has the following properties: easy operation, high recovery, and no pollution.
Indium (In) and Gallium (Ga) are two common ions widely used in the high-tech industry. Ion exchange process is a reversible chemical reaction between ions in the liquid phase and solid phase. When certain ions in the liquid phase are more favorable by the substrate of the resin, ion exchange reaction occurs. To satisfy the law of electroneutrality, when the cation in the liquid phase is adsorbed by the resin, an equivalent ion has to been released from the resin to the liquid.
The main purposes of this study are: (1) to test the removal effect of In and Ga by Amberlite IR-120 resin and to investigate the influence of pH on the removal effect; (2) to explore the regeneration effects of different regenerating reagents under different flow rates. Amberlite IR-120 resin is used in a Hi-Tech Plant for cation exchange process.
From the results of ion exchange experiments, Amberlite IR-120 resin can remove 99.5% and 99.4% of In ion from aqueous solution in acidic (pH=1) and neutral (pH=7) conditions, individually. However, merely 3% of In ion was removed in basic (pH=12) solution. Therefore, Amberlite IR-120 resin was very suitable for the removal of In ion in acidic or neutral conditions. The removal rates of Ga by Amberlite IR-120 resin in the acidic, neutral, and basic conditions were 99.1%, 41.8%, and 28.0%, respectively. It is very clearly that Amberlite IR-120 resin was preferable to adsorption Ga in acidic aqueous solution.
In the study of regeneration of resin, sulfuric acid and nitric acid were serviced as regenerating reagents. The effects of flow rate for sulfuric acid as regenerating reagent were examined at 10, 20, and 30 ml per minute. The results showed that when the flow rate controlled at 10 or 20 min per minute, the regeneration effect was better than it controlled at 30 ml/min. For the run of sulfuric acid at 20 ml/min, the recovery rates of In and Ga ions can reach to 99.5% and 99.1%, individually. Likewise, the nitric acid was test as regenerating reagent. However, the recovery rates of In and Ga were not as good as sulfuric acid did.
In future, the recovered valuable metal ions, In and Ga, from the resins hold the promise to be recycled furthermore.
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