Appeal No. 95-5092
Application 08/032,581
1. A process of reducing hexavalent chromium to trivalent chromium and
precipitating the trivalent chromium from a waste water stream to form a
sludge for disposal, said process comprising the steps of:
(a) adding soluble sulfide ion to said stream in a ratio of sulfide ion to
hexavalent chromium of from about 0.7 to 2.5;
(b) adding soluble ferrous ion to said stream in a ratio of ferrous ion
to hexavalent chromium of from about 0.5 to 5.0.;
(c) thereafter adjusting pH of said stream to about 7.2 to 8.4;
(d) adding a flocculating polymer to said stream to promote
formation of a floc comprising precipitated trivalent chromium;
(e) forming a sludge bed comprising said precipitated trivalent
chromium; and
(f) thereafter filtering the floc from said stream using said sludge bed
containing said precipitated trivalent chromium.
The examiner relies upon the following references as evidence of obviousness:
Senda et al. 4,362,629 Dec. 07, 1982
Aldrich 4,705,639 Nov. 10, 1987
Schlauch et al. (Schlauch) , "Treatment of Metal Finishing Wastes by Sulfide
Precipitation," Report No. EPA-600/2-77-049 (Feb. 1977).
Appellants' claimed invention is directed to a method of treating waste water to
reduce the hexavalent chromium therein to trivalent chromium. The method involves
adding soluble sulfide ion and soluble ferrous ion in the recited amounts to the waste water
stream and thereafter adjusting the pH of the stream to about 7.2 to 8.4.
2
Page: Previous 1 2 3 4 5 6 Next
Last modified: November 3, 2007