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. Methods for oxidizing inorganic substrates in aqueous solutions using an oxidizing agent such as pure oxygen, oxygen-enriched air or ozone are improved by including in the headspace above the aqueous solution a diluent gas and by recycling the oxygen with diluent gas into the reactor.
1. A method for oxidizing a spent caustic solution, the method comprising the steps of:
lowering the pH of the spent caustic solution into the range of between about 10 to 10.5 to produce a pH-modified caustic solution;
mixing the pH-modified caustic solution with an oxidizing gas selected from the group consisting of pure oxygen, oxygen-enriched air and ozone in a reactor at ambient temperature and pressure to produce a non-sulfide reactive oxidized solution and headspace gas;
lowering the pH of the oxidized solution to a pH less than about 9;
diluting the head space gas with a diluent gas; and
recycling the head space gas with the diluent gas into the reactor.
2. The method of claim 1 wherein the head space gas is recycled via an eductor in an untreated wastewater stream.
3. The method of claim 1 wherein the head space gas is recycled via an eductor in a recycled wastewater stream.
4. The method of claim 1 wherein the diluent gas is selected from the group consisting of nitrogen, carbon dioxide and air.