Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1998-06-22
2001-04-10
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C205S291000, C210S668000, C210S669000, C210S677000, C210S688000, C210S904000, C210S912000
Reexamination Certificate
active
06214233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to method and apparatus for removing cyanide based contaminants and recovering heavy metal such as copper, silver, nickel, iron, cobalt and the like from waste water streams, and more particularly to a process for removing cyanide base contaminants and heavy metal components from an effluent stream by adsorption of the heavy metal on a medium and thereafter stripping the adsorbed metal from the medium for recovering by electrolytic deposition.
2. Description of the Prior Art
The treatment of heavy metal and cyanide bearing effluent streams to prevent the discharge of pollutants in waterways has become the subject of federal legislation. The Environmental Protection Agency (EPA) has been charged with enforcing effluent limitations in publishing guidelines for the discharge of electroplating wastes into waterways. The need for such legislation has resulted from the use of copper, silver and the like in metal treating operations, such as plating, anodizing, conversion coatings, corrosion inhibition, pickling, and ore processing. These limitations also extend to the discharge of other plating solutions containing cyanide, copper, silver, nickel, iron, cobalt, and other multi-valent metals.
It is known to remove cyanide bearing compounds and heavy metal contaminants from waste water streams by performing a pH adjustment on the waste water stream in the range of 9-10. An oxidizing agent such as hypochlorite and sodium hydroxide is fed into the waste water stream to oxidize the cyanide bearing compounds. This reaction oxidizes the cyanides to cyanates (CNO) with complete oxidation obtained when the cyanates are further oxidized to carbon dioxide (CO
2
) and nitrogen gas (N
2
). Since this reaction is pH dependent, oxygen is also required in the reaction. Chemical precipitation is performed on the oxidized mixture to remove the heavy metals resulting in a heavy metal sludge material which requires disposal. Also, the remaining effluent is not suitable for recycling.
Another process for removing cyanide bearing compounds from waste water includes catalytic oxidation as disclosed in U.S. Pat. No. 5,635,078. The waste water is passed through a bed of an adsorbent catalyst, such as activated carbon, and a small amount of heavy metal is added to the stream. In the presence of cyanide and oxygen, the metal present in the stream reacts to give up electrons to drive the oxidation process. The metals are then adsorbed onto the activated carbon bed. The cyanide is oxidized by the reaction to nondetection levels, effectively removing the cyanide from the waste water.
While various methods are known to treat cyanide and heavy metal bearing effluents for the oxidation of the cyanide and the removal of metal contaminants, the known devices not only require substantial capital investment for equipment costs but create a secondary problem in the disposal of the recovered pollutant, particularly for disposal of the sludge which is extracted from the recovery process. The sludge must be handled in a manner that meets the requirements of disposal of solid wastes. Metallic sludges when mixed with garbage and organic wastes are likely to go back into solution as organic acids. When the pollutant is recovered as a metallic salt strict procedures must be followed to process them as a sanitary waste. Therefore there is need for method and apparatus in the treatment of cyanide and heavy metal bearing effluents that eliminates the problems associated with toxic metal sludges and produces an effluent stream which is environmentally safe.
There is a further need for a cyanide catalytic oxidation process which permits recovery of heavy metals present in the effluent stream, extends the operative life of the bed of adsorption material and produces an effluent which is suitable for recycling to the process area.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a method for oxidizing cyanide and recovering heavy metal from waste water that includes the steps of oxygenating a waste water stream containing cyanide and heavy metal with air. The pH of the waste water stream is adjusted to a range between about 8.5 to 10. The surface of a bed of adsorption material is pretreated by a chemical solution having a pH in the range between about 8.5 to 11. The oxygenated waste water is passed through a bed of pretreated adsorption material to oxidize the cyanide bearing compounds in the waste water and adsorb the heavy metal in the waste water onto the surface of the adsorption material. The waste water free of heavy metal and cyanide is directed as an effluent stream away from the bed of adsorption material for discharge. The pH of the effluent stream exiting the bed of adsorption material is monitored to evaluate the capacity of the bed to adsorb the heavy metal while the bed remains on line. A decrease in pH of the effluent stream is detected to a preselected control point. A caustic solution of a preselected pH is supplied to reactivate the bed of adsorption material while on line when the pH of the effluent stream reaches the control point to restore the adsorptive capacity of the bed. The caustic solution is maintained in contact with the bed of exhausted adsorption material for a preselected period of time until the pH of the surface of the bed of adsorption material is restored to a preselected pH level. An acid stripping solution is passed through the bed of the adsorption material to strip the heavy metal from the surface of the adsorption material. The stripping solution containing the heavy metal is passed to an electrolytic recovery unit. The heavy metal from the stripping solution is electrolytically deposited onto a cathode terminal in the electrolytic unit. The heavy metal deposited onto the cathode terminal is recovered. The retained stripping solution is reused in subsequent cycles of stripping heavy metal from the surface of the adsorption material.
Further in accordance with the present invention there is provided a method for oxidizing cyanide while simultaneously recovering copper from waste water that includes the steps of oxygenating a waste water stream containing cyanide and copper with air. The pH level of the waste water stream is adjusted to a range between about 8.5 to 10. A bed of activated carbon is pretreated by circulating in a closed loop a solution containing 1% to 20% by volume sodium hydroxide through the bed of activated carbon for a preselected period of time until the pH of the surface of the bed reaches a level of 8.5 to 11. The waste water stream containing cyanide and copper is directed through the bed of activated carbon. The copper is adsorbed onto the surface of the activated carbon bed while oxidizing the cyanide. The pH of the waste water stream exiting the bed of activated carbon is monitored to evaluate the capacity of the bed to adsorb the copper while the bed remains on line. A decrease in the pH of the waste water stream is detected to a preselected control point. A caustic solution of a preselected pH is supplied to reactivate the activated carbon bed while in operation when the pH of the waste water stream reaches a control point to restore the adsorptive capacity of the bed. The caustic solution is maintained in contact with the activated carbon bed for a preselected period of time until the pH of the surface of the carbon bed is restored to a preselected pH level. A flow of waste water is interrupted once the adsorptive capacity of the adsorption material in the carbon bed is exhausted. A stripping solution containing 10% to 20% by volume sulfuric acid is passed through the exhausted activated carbon bed to strip the copper from the bed. The pH of the stripping solution is maintained at a level between about 1.5 to 2.5 by feeding fresh acid into the stripping solution to continue stripping copper from the bed. The stripping solution containing copper is directed to an electrolytic recovery unit. Copper from the stripping solution is electrolytically deposited
Cintins Ivars
Price & Adams
LandOfFree
Process for simultaneous oxidation of cyanide and recovery... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for simultaneous oxidation of cyanide and recovery..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for simultaneous oxidation of cyanide and recovery... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2494454