Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal

Dewatering: Thickening, Filtering, CCD, Water Treatment & Tailings Disposal 2017-04-04T06:57:46+00:00
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Cyanide Detox/destruction with hydrogen peroxide (11 replies and 2 comments)

Bill Fraser
2 years ago
Bill Fraser 2 years ago

Am researching on Cyanide destruction/detox using hydrogen peroxide and/or ferrous sulphate and I am conducting an investigation into the use of hydrogen peroxide and ferrous sulphate for cyanide detoxification. What tests can I conduct to compare the effectiveness of these two methods? Furthermore, how does the presence of Cu2+ ions affect the hydrogen peroxide method of cyanide detoxification?

2 years ago
JohnnyD 2 years ago

Hydrogen peroxide + ferrous sulfate = Fenton reaction. This is one method, not two. Or the third one? Are you sure there is free Cu2+ cation in cyanide media?

Bill Fraser
2 years ago

​I had not yet come across the Fenton method for now I have been mainly focusing on the two methods separately. Thank you for that perspective.

Maya Rothman
2 years ago
Maya Rothman 2 years ago

Ferrous sulphate or ferric sulphate can be used to reduce toxicity in cyanide solutions by reacting with free cyanide to form the strong cyanide complexes ferrocyanide and ferricyanide, which are not readily biologically available. 

Once all the cyanide is complexed the ferricyanide can be precipitated by the addition of Cu to form an insoluble copperferricyanide salt. The final level of cyanide obtainable by this method depends on the other metals in solution which can leave significant levels of WAD cyanide in solution. WAD cyanide is the normal measure used for environmental measurements since this is biologically available.

Hydrogen peroxide is widely used to destroy free and WAD cyanide in solution by oxidation to the much less toxic cyanate (OCN-). Cu2+ is added as a catalyst to increase reaction rates. This can result in very low levels of WAD cyanide.

The peroxide reaction is efficient in solution but very inefficient in slurries due to the peroxide decomposing in the presence of solids.

In both methods I would suggest you should look at the effect of varying the reagent addition rates as a ratio to the cyanide being treated, the time of reaction, and the reaction pH. The effect of various levels of copper sulphate addition in the peroxide tests and the effect of aeration in the ferrous sulphate tests.

You should be measuring the other metal species in solution before and after detox as well as the Free, WAD and total cyanide levels. (You can calculate the total CN reliably from WAD cyanide and Fe assays)

The other main commercial techniques used for destroying cyanide in slurries are SO2/O2 (the INCO process) and Caro's Acid. Hypochlorite can also be used but is generally avoided in mines due to aquatic toxicity.

Bill Fraser
2 years ago

​I am looking into reagent addition, reaction time and pH, and will extend to the variation of Cu2+ concentration in solution.

Bill Fraser
2 years ago
Bill Fraser 2 years ago

At present I have observed a linear relationship between the addition of H2O2 and % CN(FREE) and %CN(WAD) reduction.

Victor Bergman
2 years ago
Victor Bergman 2 years ago

The SO2/AIR process can be applied to the treatment of both cyanide solutions and Pulps. The main advantages of the process are the removal of the total cyanide to levels of about 1 mg/L, in a single-stage continuous reactor and low operating costs. This process will oxidise free cyanide and all cyanide complexed with copper, nickel, zinc, silver, cadmium etc. This process catalysed by soluble copper ions, if required copper sulphate may be added. Stronger cyanide complexes (gold, iron, cobalt) are not oxidised by this process. Gold cyanide should not be a concern for destruction as it is recovered by carbon within the plant.The removal of Iron and cobalt complexes are achieved by precipitation with copper or zinc.SO2/Air process works better in the pH range of 8 to 9 and optimum pH is determined during the test work. H2O2 and Caro’s acid may be used for the detoxification program.

John Koenig
2 years ago
John Koenig 2 years ago

Hydrogen Peroxide:

H2O2 + CN- + Cu+2 Catalyst = OCN- + H2O
Iron-Cyanide Precipitation:
Fe+2 + 6CN- + ¼O2 + H+ = Fe(CN)6-3 + ½H2O
* + 3Fe(CN)6-3 + ¼O2 + H+ = Fe4[Fe(CN)6]3 + ½H2O

The link below should help

Bill Fraser
2 years ago
Bill Fraser 2 years ago

Thanks, I need assistance on the test protocol and with regards to the hydrogen peroxide method.

John Koenig
2 years ago
John Koenig 2 years ago

Let me know if the suggestion below helps:

CN- Destruction from SOLUTIONS: CN- + H2O2 = OCN- + H2O
Total CN- in 1-liter (ppm) 100
Tot CN- (g) 0.1
Cu+2 reqmnt, % of tot CN present 20%
Cu+2 reqmnt (g) 0.02
CuSO4.5H2O reqd (g) 0.08
* 100-wt% H2O2 reqd/1-g CN- oxidized 0.8

@30-wt% H2O2 Conc, required (g) 2.7

* CN- soln in 2-L beaker w/O'head stirrer mechanism.

Solution pH adjusted to 9-9.5 w/H+; Add Cu+2 & peroxide while stirring; take kinetic samples @5-min, 10-min & 30-min; analyze for free CN- by Ion Chromatography (AgNO3 titration may yield meaningless data in the presence of base metal cyanide complexes). If acceptable results, lower peroxide additions. You may also attempt adding peroxide
incrementally over the desired retention period & lower Cu+2 after peroxide volume is fixed.

Bill Fraser
2 years ago
Bill Fraser 2 years ago

This will be helpful. Thanks

David Kano
2 years ago
David Kano 2 years ago

This "batch" method is only really effective at determining what levels of CN discharge can be achieved and will not provide any correlation to plant operating conditions. We offer continuous tests using INCO or Peroxide to model plant performance with directly scaleable results.

John Koenig
2 years ago
John Koenig 2 years ago

I understand. My response was geared towards her query on preliminary bench scale experimentation.

1 year ago
David 1 year ago

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