Caustic solution treatment process
View Patent ↗A method for treating a spent caustic solution having a pH greater than about 10.5 includes the steps of (a) lowering the pH of the caustic solution into the range of between about 10 to 10.5 to produce a pH-modified caustic solution; (b) oxidizing the pH-modified caustic solution until the solution to produce a non-sulfide reactive oxidized solution; and (c) lowering the pH of the oxidized solution to a pH less than 9.
1. A method for treating a spent caustic solution having a pH greater than about 10.5, the method comprising:
(a) lowering the pH of the caustic solution into the range of between about 10 to 10.5 to produce a pH-modified caustic solution;
(b) oxidizing the pH-modified caustic solution to produce a non-sulfide reactive oxidized solution; and
(c) lowering the pH of the oxidized solution to a pH less than 9, wherein steps (a), (b) and (c) are performed at ambient temperature.
2. The method of claim 1 further comprising the step of removing a non-aqueous phase from a solution produced in either pH-lowering step.
3. The method of claim 1 wherein either pH-lowering step comprises the step of exposing the caustic solution or the oxidized solution to an acidic gas selected from the group consisting of CO 2 , SO 2 and HCl.
4. The method of claim 1 wherein the step of lowering the pH of the oxidized solution comprises the step of exposing the oxidized solution to a mineral acid selected from the group consisting of H 2 SO 4 , HCl, H 3 PO 4 , and HNO 3 .
5. The method of claim 1 wherein the step of oxidizing the pH-modified caustic solution comprises the step of exposing the pH-modified caustic solution to an oxidizing agent selected from the group consisting of oxygen, ozone, air, and air enriched with oxygen.
6. The method of claim 1 wherein the oxidation step and the second pH-lowering step are performed simultaneously.
7. The method of claim 1 wherein the second pH-lowering step liberates carbon dioxide, the method further comprising the step of treating additional spent caustic solution with the liberated carbon dioxide.
8. A method for treating a spent caustic solution having a pH greater than about 10.5, the method comprising:
(a) lowering the pH of the caustic solution into the range of between about 10 to 10.5 to produce a pH-modified caustic solution;
(b) oxidizing the pH-modified caustic solution to produce a non-sulfide reactive oxidized solution; and
(c) lowering the pH of the oxidized solution to a pH less than 9,
wherein the second pH-lowering step liberates carbon dioxide, the method further comprising the step of treating additional spent caustic solution with the liberated carbon dioxide.