Industrial processes for Ferrous Chloride oxidation to Ferric Chloride 1

[WG Chem]

Dear colleagues,

Short and straight to the point question: in your expertize or knowledge, what are the best consolidated industrial processes to oxidize Ferrous Chloride in HCl solution to Ferric Chloride at an average productivity range of 500-1000 kg/h?

Long version: I'll have a chemical process that will use about 20 tons/day of Ferric Chloride 36-40% solution (Fe3+) as oxidant. This process generates a huge amount of Ferrous Chloride (Fe2+) wastewater whose initial treatment proposal is a simple precipitation with lime, coagulation/flocculation, filtering and drying of sludge and evaporation of clarified liquid. This is a not very cheap process due to high amount of ferrous sludge generation, but is economically acceptable due to high aggregated value of product itself, simplicity to assemble and put in operation in a short project schedule and necessity to reduce strategical dependency of external destination of wastes.

Short term concern adressed, but still is a huge waste of money in the long run, so i'm researching for alternatives to re-oxidize some of the Ferrous Chloride back to Ferric Chloride. The wastewater stream has very low amount of organics (COD of less than 20.000 ppm, and the oxidation reaction of the product is fast and selective enough to work with recycled Ferric Chloride with impurities from the most commom recovery routes that i researched. The problem is that the technical literature is vast on this subject and i would like to focus the energy researching and testing with the already known and consolidated routes.

Thank you all in advance
Best Regards

 

[georgeverghese]

There is a patent pending on the internet which relies on the reaction of HCl with FeCl2 in the presence of O2 (or perhaps air should be good enough) to get FeCl3. Not sure what the role of O2 is in this reaction, but I would suggest a dilute solution of H2O2 instead of air if this will speed up the reaction. What do yo make of this process ?

 

[WG Chem]

Hi George,
This oxidation is part of a fungicide synthesis route.
I'm inclined to think that Peroxide oxidation of Fe2+ is probable one of the best routes. It's well know mechanism with high yield (source on PubChem:"Reaction between Ferrous Iron and Peroxides. I. Reaction with Hydrogen Peroxide in the Absence of Oxygen"). It also has lower plant complexity in comparison to alternatives like with chlorine gas or hypochlorite. One of the main concern would be the peroxide costs and the presence of organic matter, since it's the wastewater from an organic/water phase separation.
There is a patent that put together your two suggestions: oxigen rich air oxidation helped by peroxide for speed up mas completion of Fe2+ oxidation.

 

[moltenmetal]

20 tonnes per day of FeCl2 will require an enormous amount of peroxide. Unless this is a short term operation, you'll want to use air or oxygen which will both be MUCH cheaper. Iron (II) oxidizes readily back to iron (III) as long as the pH is low enough to keep the resulting iron (III) in solution- below about pH 3. Tonnes per day of peroxide solution are going to cost enough that payback on a little more process complexity running a gas-liquid contactor rather than just bunging peroxide in through a static mixer will be of benefit.

If that is 20 ppm of organics, this is no problem. If it is 20,000 ppm of organics (2%), you'll be in trouble irrespective how you try to do this, with air or oxygen or peroxide.

Peroxide added to iron (II) below pH 3 will generate hydroxyl radicals and results in powerful oxidation (Fenton's reaction). You will generate oxidized organic species, some of which may chelate iron.

 

[georgeverghese]

The reaction with H202 may be better done with the organics removed to the extent possible, since these organics would compete with Fe2+ for O2, though at a much slower rate.