Process for treating caustic cyanide metal wastes

Claim 2

In a process for treating by wet oxidation a caustic cyanide and metal wastewater showing a potential to form scale upon heating, wherein said raw wastewater is introduced by a first inlet conduit into a pressurized wet oxidation reactor without preheating, and wherein a preheated mixture of oxygen containing gas and dilution water is introduced by a second inlet conduit into said reactor, and wherein said wastewater, dilution water and oxygen containing gas are maintained within said reactor at an elevated temperature and pressure for sufficient time to destroy cyanide and produce an oxidized waste effluent and an oxygen depleted offgas which are removed from said reactor, wherein the improvement comprises the steps; (a) discharging said oxidized effluent and offgas from said reactor through a first effluent conduit while at the same time introducing a dilute mineral acid solution into said reactor through a second effluent conduit to prevent scale and solids buildup therein; and (b) alternating the flow of oxidized effluent and offgas and dilute mineral acid whereby oxidized effluent and offgas discharge from the reactor through said second effluent conduit and dilute mineral acid solution enters the reactor through said first effluent conduit to remove scale and solids therefrom.

Claim 3

A process according to claim 1 further comprising the steps; (c) cooling said oxidized effluent and offgases by cooling means; and (d) separating said cooled oxidized effluent from said offgases by separating means to produce a separated liquid phase and a separated gas phase.

Claim 4

A process according to claim 2 wherein said cooling means of step (c) is a cold water heat exchanger.

Claim 5

A process according to claim 2 wherein said cooling means of step (c) is a heat exchanger which preheats said mixture of dilution water and oxygen containing gas introduced into said reactor.

Claim 6

A process according to claim 1 wherein said dilution water and oxygen containing gas are preheated by an external heat source.

Claim 7

A process according to claim 1 wherein said dilute mineral acid of steps (a) and (b) is nitric acid.

Claim 8

A process according to claim 6 wherein said dilute nitric acid is at a concentration of 5% to 20%.

Claim 9

A process according to claim 1 wherein said elevated temperature is between about 200° C. (392° F.) and 370° C. (698° F.) and said elevated pressure is between about 300 psig (2,068 KPa) and 3500 psig (24,129 KPa).

Claim 10

A process according to claim 1 wherein said elevated temperature is between about 200° C. (392° F.) and 300° C. (572° F.) and said elevated pressure is between about 300 psig (2,068 KPa) and 2000 psig (13,788 KPa).

Claim 11

A process according to claim 1 wherein said wet oxidation reactor is a vertical bubble column.

Claim 12

A process according to claim 1 wherein said oxygen containing gas is air.

Claim 13

A process according to claim 1 wherein said alternating step (b) is performed after two hours to four hours of system operation.

Claim 14

In a process for treating by wet oxidation a caustic cyanide and metal wastewater showing a potential to form scale upon heating, wherein said raw wastewater is introduced by a first inlet conduit into a pressurized wet oxidation reactor without preheating, and wherein a preheated mixture of oxygen containing gas and dilution water is introduced by a second inlet conduit into said reactor, and wherein said wastewater, dilution water and oxygemn containing gas are maintained within said reactor at an elevated temperature and pressure for sufficient time to destroy cyanide and produce an oxidized waste effluent and an oxygen depleted offgas which are removed from said reactor, wherein the improvement comprises the steps; (a) discharging said oxidized effluent and offgas from said reactor through a first effluent conduit while at the same time introducing a dilute mineral acid solution into said reactor through a second effluent conduit to prevent scale and solids buildup therein; (b) alternating the flow of oxidized effluent and offgas and dilute mineral acid whereby oxidized effluent and offgas discharge from the reactor through said second effluent conduit and dilute mineral acid solution enters the reactor through said first effluent conduit to remove scale and solids therefrom; (c) cooling said oxidized effluent and offgases by cooling means; and (d) separating said cooled oxidized effluent from said offgases by separating means to produce a separated liquid phase and a separated gas phase.

Claim 15

In a process for treating by wet oxidation a caustic cyanide and metal wastewater showing a potential to form scale upon heating, wherein said raw wastewater is introduced by a first inlet conduit into a pressurized wet oxidation reactor without preheating, and wherein a preheated mixture of oxygen containing gas and dilution water is introduced by a second inlet conduit into said reactor, and wherein said wastewater, dilution water and oxygemn containing gas are maintained within said reactor at an elevated temperature and pressure for sufficient time to destroy cyanide and produce an oxidized waste effluent and an oxygen depleted offgas which are removed from said reactor, wherein the improvement comprises the steps; (a) discharging said oxidized effluent and offgas from said reactor through a first effluent conduit while at the same time introducing a dilute mineral acid solution into said reactor through a second effluent conduit to prevent scale and solids buildup therein; (b) alternating the flow of oxidized effluent and offgas and dilute mineral acid whereby oxidized effluent and offgas discharge from the reactor through said second effluent conduit and dilute mineral acid solution enters the reactor through said first effluent conduit to remove scale and solids therefrom; (c) cooling said oxidized effluent and offgases by cooling means; and (d) separating said cooled oxidized effluent from said offgases by separating means to produce a separated liquid phase and a separated gas phase.