Chromate removal by long life IX resins without continuous pH adjustment
The mechanism of removal in long life resins used for chromate removal is ion exchange, followed by reduction of hexavalent chromium to trivalent chromium, followed by precipitation into the IX resin polymer. The second step is rate limiting and pH dependent and is the reason why lowering pH before treatment has until now been necessary.
However, there is a simple way to use these long life resins that does not require continuous pH adjustment. By taking a portion of the treatment vessels off line and soaking them in a low pH solution, the rate constant for the reduction step is increased sufficiently to catch up, making the ion exchange step the limiting factor. This step is much longer. Rejuvenated vessels can then be put back on line and operated at the natural pH of the feedwater.