The Treatment of Cupric Chloride Solution after the Etching Process by Ion Exchange Membrane Electrodialysis*

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Grace O’Connor’
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1 Desalination, 62 (1987) Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands The Treatment of Cupric Chloride Solution after the Etching Process by Ion Exchange Membrane Electrodialysis* XUE DEMING, SONG DEZHENG and LIU XIAOYING ' The Development Center of Seawater Desalination and Water Treatment Technology, The Second Institute of Oceanography, The State Oceanographic Admmstration, P.O. Box 75, Hangzhou, Zhejiang (China). Tel ; telex NBOHZ CN SUMMARY The cupric chloride solution whih is discharged as wastewater after the etching process was treated by ion exchange membrane electrodialysis. This method not only reuses the water by desalination, which may or may not be connected with ion exchange, it also concentrates the cupric chloride and metal copper can be recovered by electrolysis or some other suitable method, making it a closed system. The results of practical operation show that the electrodialysis method is comparble with precipitation from the point of view of cost and efficiency. We demonstrated that the plant could be operated successfully without damage to the home-made ion exchange membrane and without electrodeposition of the metal copper on the cathode. Furthermore, the energy consumption was less than 3 kwh/t water. The cupric ion concentration of 2,000 mg/l in the wastewater was reduced to less than 1 mg/l at discharge. Keywords: cupric chloride solution, electrodialysis, ion exchange, wastewater, electronics industry, recycling, effluents, metal recovery INTRODUCTION There are now a great many production lines around the world which manufacture printed circuit boards ( PCB ). The process involves the removal by etching of parts of a layer of copper from an insulating substrate in order to provide the desired pattern of conducting links on the surface of the insulating *Presented at the International Symposium on Synthetic Membrane Science and 'Technology. Dalian, China, April 13-18, /87/$ Elsevier Science Publishers H.V.

2 252 substrate. The solution containing the cupric ions which have been rinsed away by water from the boards is discharged as wastewater. This is not only a waste of valuable copper resources, it is also one of the principal sources of environmental pollution. Therefore it is a matter of some urgency to find a better process for treating the etching effluent. Several processes have been reported so far, of which the commonest is the neutralization precipitate process. It consists of adding alkaline agents such as sodium hydroxide, lime, etc. to the wastewater to adjust ph and precipitate the cupric hydroxide and carbonate basic. Although the process works, it has some disadvantages; for example, its high consumption of chemicals, expensive running costs, the need for waste sludge treatment and so on. These drawbacks make it impractical to employ this process in small or medium capacity plants. Another process is the ion exchange method; however, this method is not yet feasible either from a technical or an economic point of view. Because the concentration of cupric ions in the effluent is usually more than 1,000 mg/l, and sometimes as high as 3,000 mg/l, the total ion concentration is about 6,000 mg/l. This means it is necessary to regenerate the ion exchange resin frequently. Fortunately there is another possibility; the effluent can be desalted by ion exchange membrane electrodialysis within the ion concentration range. A desalination system which combines electrodialysis, to remove most of the cupric ions, and ion exchange, to remove the rest, will make it possible to treat solutions with a considerable ion content. It should be noted however that research into this process as reported in various publications, has not yet led to any clear results; this is why the authors of the present paper chose to investigate the subject further. EXPERIMENTAL Apparatus The experimental plant was provided with an electrodialyzer (SHD-Ol), recirculating store tanks, pumps, motors, cation exchange resin (DK 110) column and various instruments such as a Type-721 spectrophotometer, a Type S-3 ph meter, etc. Home-made cationic (3361 ) and anionic (3362) ion exchange membranes and a ruthenium-coated titanium electrode were used in the experimental runs. The effective desalting area per membrane was 640 cm2, the space between membranes 0.85 mm. The membrane stack consisted of 30 cell pairs. Flow sheet The flow sheet of the electrodialysis plant is similar to the one we published previously [ 1 ].

3 253 The raw water was clarified, filtered, had oil removed from it, and was then d into the tanks. The electrode rinse was made of special chemical agents with additive to prevent the deposition of the metals and/or their hydroxide on the cathode. The linear velocity of the solution in the desalting chamber was 6 cm/s. The pressure drop in the concentrating and desalting- and elecde chambers was kept in equilibrium. The temperature of the solution was 30 O C. During operation, the dialysate and the concentrated brine were recirculated parately through their compartments. The voltage was kept at a constant alue for each run. As the desalination progressed, the current density decreased proportion to the ion concentration of the water being dialyzed. However, must always be kept within limiting current density so as to ensure troublefree operation during a run. Solution samples were taken to measure the cupric ion concentration and ph at certain intervals. The cupric ion concentration in both the dialysate and the concentrated brine were measured with the complexometric titration method. After most of the cupric ions had been removed by electrodialysis, the solution was fed into an ion exchange column to remove the rest of them and the filtrate was measured by spectrophotometric method and ph meter. RESULTS AND DISCUSSION Desalting and concentrating the effluent CuC& Cupric chloride solutions with a cupric ion concentration of N, Nand N were desalted in batches at 15.0 and 18.0 V successively. The changes in cupric ion concentration with runing time are shown in Fig. 1. The curpic ion concentration of the dialysate was reduced rapidly at the beginning of the dialyzing process, as can be seen in Fig. 1, and it was reduced to mg/l by the end of the run. Next, and effluent with a cupric ion concentration of N (concentration stream 0.40 N ) and an effluent with a cupric ion concentration of 0.21 N (concentration stream 0.41 N ) were recirculated separately through the stack compartments at 18.0 V. The results of desalting and concentrating these effluents are illustrated in Fig. 2 and Fig. 3 respectively. There was a rapid increase in the cupric ion concentration of the concentrated brine at the beginning of the running period, matching the reduction in cupric ion concentration of the dialysate. The desalination and concentration characteristics of the cupric chloride solution are similar to those of zinc chloride solution; in fact the effluent containing cupric chloride can be both desalted and concentrated better [ 11. It has been reported that the maximum concentration of 4.9 N in cupric chloride solution can be reached by using an extremely high current density [ 21. How-

Wastewater Reuse. Typical treated wastewater is:

Wastewater Reuse. Typical treated wastewater is: Wastewater Reuse Most metal finishing industries have in-house wastewater treatment to economically dispose of the acids, alkali, oils, and dissolved metals in the rinse water and occasional tank solution