ION the Prize

One of the many benefits of continuous electrodeionisation (CEDI) is the fact that the chemical waste created in conventional ion exchange pre-treatment is eliminated. The new breed of CEDI system offers a clean, environmentally superior alternative to chemically regenerated, mixed bed ion exchange plant, while matching it in performance.

Although clearly advantageous, neither the green aspect of the new technology nor its low operating cost have been key factors in meeting the needs of semiconductor production. The stringent demands on water purity already made by the microelectronics industry in general have intensified with the increasing complexity of microprocessor chips. Before CEDI was introduced to the industry, it relied heavily on mixed bed systems for ion removal.

However, in semiconductor fabrication processes, the use of conventional mixed bed deionisation for producing ultrapure water has its drawbacks, due to fluctuations in produced water quality. This is caused by exhaustion and regeneration of ion exchange beds. As CEDI, by definition, is free from regeneration, it is free from this fluctuation, and it is becoming increasingly competitive with conventional mixed bed DI, especially due to improved module performance, increasing module reliability and lowering the overall cost of ownership of CEDI systems.

Product water specifications for CEDI technologies are typically in the range of 10-16 megohm-cm with removal of weakly dissociated species such as silica and boron in the 90- 98 per cent range. This is sufficient for many industrial uses, including water production in the pharmaceutical and power generation markets. However, this quality is not sufficient for use in the microelectronics industry which requires greater than 18 megohm-cm, with most species nondetectable. In this case, and in many applications where there is a stringent silica requirement, CEDI is followed by ion exchange polishing.