The present invention relates to an ion exchange process and more particularly to a process for the removal of fluoride and phosphorus-type contaminants from acidic process waste waters such as those encountered in conventional wet-process phosphoric acid processing facilities.
In the production of wet-process phosphoric acid, large cooling and gypsum storage ponds are typically employed. More specifically, large amounts of water are circulated and reused in the phosphoric acid processing and a great deal of effort is undertaken in order to utilize this water to the fullest extent possible.
Since the above-described waste water often contains high levels of both fluoride and phosphorus-type contaminants, its disposal has proven to be difficult. Typically, expensive liming processes have been used. Specifically, a two-stage liming system has been employed wherein lime is first added to the pond water to raise the pH to between about 4 and about 5 thereby precipitating the fluoride compounds. The slurry is then clarified and the water treated once again with lime to raise the pH to about 9 for removal of the phosphorus compounds. While somewhat effective, the costs of such a removal system are prohibitive since the fluoride and phosphorus type contamnants, which precipitate upon addition of the lime, are disposed as a sludge which is very diffcult to handle and adds a substantal amount of cost to the purification process. Additionally, the disposal of the fluoride and phosphorus type compounds with the sludge precludes their recovery as potentially valuable commercial products and thus further detracts from the desirability of the two-stage liming. Thus, the conventional two-stage liming processes are not only very difficult to carry out, but also result in the disposal of potentially valuable end products namely, fluoride and phosphorus type compounds.
USPTO Backgrounds
USPTO Backgrounds