Printed Circuit Board (PCB) industry is one of the two major Integrated Circuit (IC) part manufacturing industries in Taiwan, but it derives many environmental problems because large amount of chemicals and special materials are used in its process, especially copper sludge generated from wastewater treatment. Although the heavy metal sludge can be treated by solidification, heavy metals contained in the sludge may still be leached out due to longtime exposure to acid rain. Therefore, there are urgent needs of research and development of technologies regarding how to reduce both quantity and volume of the hazardous heavy metal sludge and how to recycle the valuable heavy metals.
Acid leaching method, chemical exchange method and ferrite process are applied to study how to recycle and stabilize copper sludge of PCB industry. The ultimate goal is to achieve cleaning production and sustainable development by transforming the hazardous waste into valuable byproducts, reducing the amount of the waste and lowering the treatment costs.
Experimental results show that a method is successfully developed to recycle copper from the sludge generated by PCB industry by using the combination of acid leaching, chemical exchange and ferrite process. Via this method, not only is pure copper powder recycled, but highly valuable nano-scaled catalyst-CuFe2O4 is also produced. Hence, the problem that copper sludge has nowhere to go is solved, as well as the high cost of catalyst in catalytic incineration is reduced to nearly zero. The achievements of this study are summarized as follow:
(1) Characteristic analysis of industrial sludge
Water content and pH of the sludge is 60% and 7.05, respectively. The drop in quantity of ignition is 23%. The screening test results show that particle size of the sludge varies from 0.4 £gm to 200 £gm, with D50 of 25.0 £gm. Cu, Pb, Cd, Zn, Ni and Cr are found in the sludge, and the biggest part of heavy metals is Cu, with a concentration of 158,000 mg/kg (dry basis), whereas the other heavy metals are all below 105 mg/kg (dry basis).
(2) Study of recycling of pure copper powder
The optimal operational condition of acid leaching method is that concentration of sulfuric acid is 2.0 N, temperature is 50¢J and treatment time is 60 minutes. Under this operational condition, more than 99% of heavy metals can be extracted to liquid phase and the sediment of treated sludge meet Toxicity Characteristic Leaching Procedure (TCLP) standards and therefore is considered as general industrial waste. The optimal operational condition of chemical exchange method is that molar ratio of Fe/Cu is 5.0, pH is 2.0 and treatment temperature is 50¢J. Under this operational condition, more than 95.0% of Cu can be recovered. The optimal operational condition of ferrite process is that Fe/Cu=10.0, pH=9.0, treatment temperature=80¢J, aeration rate=3 L/min/per liter waste liquid and reaction time = 30 min. Under this operational condition, TCLP concentrations of all heavy metals of both supernatant and sludge are well below regulatory standards, which proves that ferrite process is very effective.
(3) Resourcing of spinel sludge
In the potential of catalytic incineration of volatile organic compounds test, the sludge generated from ferrite process is used to catalyze the isopropyl alcohol (IPA). The catalyst is replaced by the same volume of glass wool on a reactive bed as a blank. Experimental result shows that the conversion of IPA is only 10% at 200¢J and 75% at 500¢J in the absence of catalyst under the conditions that IPA inlet concentration=1,700 ppm, space velocity=24,000 hr-1, O2 concentration=21%, and relative humidity=19%, which indicates that the destruction of IPA is associated with the consumption of much energy when no catalyst was used. But when ferrite catalyst is applied, IPA is decomposed completely at 200¢J, showing that the sludge has great potential of catalyst.
(4) Synthesizing five VOCs catalyzing ferrite catalysts via ferrite process
As to the synthesis of five ferrite catalysts in the laboratory, IPA conversion rate is higher than 58% at 200¢J. The sequence of IPA conversion from good to bad is Cu-ferrite catalyst > Mn-ferrite catalyst > Ni-ferrite catalyst > Zn-ferrite catalyst > Cr-ferrite catalyst, where Cu/Fe is most efficiency, with IPA conversion rate of 75% at 150¢J and 100% at 200¢J.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0905107-160948 |
| Date | 05 September 2007 |
| Creators | Tu, Yao-jen |
| Contributors | none, none, none, none, none, Jie-Chung Lou |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0905107-160948 |
| Rights | withheld, Copyright information available at source archive |
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