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US 4,543,189 AGranted
Removal of complexed zinc-cyanide from wastewater
AssigneeBethlehem Steel Corporation
InventorsMichael A. Rice, Stewart T. Herman
Life of this patent
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Abstract
A method of removing complexed zinc-cyanide from wastewater involving a multiple stage process including, in a first step, control of ferrous ions to a critical minimum concentration of 250 to 400 ppm, together with pH control in the first and also a second step, together with recycling of a portion of sludge precipitated in the process.
Claims6
A method for removing soluble zinc and soluble cyanide from blast furnace blowdown wastewater comprising:
- (a) processing to a first reactor a wastewater containing between 6 and 30 ppm of soluble cyanide and between 15 and 75 ppm soluble zinc, with the cyanide and zinc consisting essentially of a soluble zinc-cyanide complex compound;
- (b) in the first reactor:
- (i) adding soluble ferrous ion from the group consisting of ferrous sulfate, ferrous chlorides, or other soluble ferrous salt to bring the ferrous ion to between at least 250 to 400 ppm;
- (ii) controlling the pH of the wastewater to below 7.0;
- and
- (iii) stirring the wastewater to keep solids in suspension;
- (c) processing the wastewater to a second reactor;
- (d) in the second reactor:
- (i) raising the pH of the wastewater to between 9.5 and 10.0 to form precipitates of prussian blue, zinc hydroxide and ferrous hydroxide;
- and
- (ii) continuously stirring the wastewater to keep the precipitates in suspension;
- and
- (e) processing the wastewater to a settling basin where precipitated zinc hydroxide, prussian blue and ferrous hydroxide settle into a sludge, leaving a liquid having a soluble zinc content of less than 0.45 ppm and a total soluble cyanide content of less than 3 ppm.
10 more elements
Dependencies are inferred from the claim text.