Chromium removal 4

[lattar]

What are the most common hexavalent chromium removal methods and what kind of analysis methods are available for separating hexavalent and total chromium? I would be very grateful of all information, references and

http://www-sites.

 

[seidelc]

lattar,

This question requires a BIG answer, so I'll just touch base on a couple issues you raise. You can post back and get in touch with me directly if you'd like. My firm has been doing research on Cr6 removal from drinking water for about 3 years now and it is the focus of my PhD research.

Common Cr6 Removal Technologies for Drinking Water Applications - ion exchange, membranes, reduction/precipication/coagulation/filtration, sorptive media

Analysis Methods - I'm assuming you are talking about how to measure Cr6 or CrTotal in samples. CrTotal is most commonly measured on an ICP. Cr6 is most commonly measured on an IC, but can also be measured by colorimetric methods (good for field analysis). Some colleagues of my are publishing a paper on the details of Cr analytics for drinking water applications in Water Research. It should be out soon.

What is your particular application for Cr6 treatment?

Chad

 

[lattar]

seidelc,
Thanks for the relpy.

Something about our situation:
Every once in a while, 1-2 times/month, there is a process fault in our plant. In this interference there happens a water leak. Water has been collected and used in the process a little by little. In the future we would like to let this to go waste water treatment outside our plant. But we have to reduce the chromium(IV) content to 0,1 mg/l. Total chromium is at the moment around 20 mg/l. So i am working (1) to reduce the amount of these process faults but (2) also collecting information about suitable chromium removal methods. The amount of water is 500-1000 m3 per leak and half of it is acidic and half neutral. In one part of our process chromium is in trivalent form and in one part hexavalent form. I have no idea in what is the distribution of these forms in effluent. A guess is 1/3 as hexavalent and 2/3 trivalent form. We have analysed total chromium by ICP.

Which Cr-removal method would propably be most suitable for us? Is there in any refernce book or in some other source good review about chromium removal methods?

 

[aspearin1]

Trivalent and Hexavalent Chromium exist in equilibrium. In the presence of Oxygen, Cr(6) will prevail. It is possible to reduce your Cr(6) to Cr(3) with the addition of Fe(0) (solid iron filings) to your system. You may have to adjust the pH of your water to more acidic, and sparging off oxygen would be helpful. This would leave you with Cr(3) only. If Cr(3) is allowable for discharge, then that should take care of your situation. Cr(3) is actually bioligically quite beneficial, but be reminded that Cr(3) + O2---> Cr(6). For removal, I'd be partial to ion exchange, perhaps even a natural exchange media such as zeolite. It has microporous structure like activated carbon, but also has cation exchange capacity. Good luck.

p.s. for detection, I am most familiar using a UV-vis spectrophotometer. It detects Cr(6) only... Preparation includes the use of a specific dye, sulfuric acid and acetone. You can find the method on a book called Analytical Methods... That's all I can recall.

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[seidelc]

lattar,

The most common industrial Cr treament method (i.e. when influent Cr concentrations are in mg/L concentrations) is reduction/precipitation/fitration. In this process, the Cr6 is reduced to Cr3 typically by some reductant (Fe2 - both ferrous chloride and ferrous sulfate work well, stannous chloride, sodium bisulfate). Then the Cr precipitates as Cr(OH)3 which can be coagulated with ferric and filtered.

An old reference on this topic is:

Besselievre, E. B. (1969) The treatment of industrial wastes, McGraw-Hill, New York.

Aspearin1 is also right about ion exchange. It can definately be a more clean process. Another old, but good reference for this is:

Jakobsen, K. and Laska, R. (1977) Advanced treatment methods for electroplating wasters, Pollution Engineering, 8:42-46

Hope this helps.

 

[Peteypete]

Seidelc is correct in the treatment of Cr6. I can confirm his reported reduction of Cr6 with FeSO4. We did this in acid resin (the acid helps with the reaction). Once Cr+3 is formed, then the acid resin adsorbs it. We also added H2SO4 to the solution of FeSO4 to help with the Cr6 reduction.

Our results showed that Cr6 concentrations of 6 - 20 ppm could be reduced to below 1.0 ppm (for discharge).

 

[seidelc]

Peteypete,

I'm curious about the acid resin you used? Can you provide any more info? I'm dealing with drinking water supplies that are treated to <10 ppb.

Chad

 

[Peteypete]

Chad,
Sorry to get back to you so late - I was on vacation for the summer.

I looked at our data for the reaction and found that we used a strong acid resin from Sybron. I am not sure which one it was as we were able to use old virgin product that was discarded. I am not sure about treated to less than 10 ppb, but it seems interesting.

If I were doing the project, I would inject a dilute aqueous solution of Ferrous Chloride into the feed port of my resin bed. You will need to determine how much iron to add to compensate for DO and still be effective. The resin bed must be able to adsorb all the iron II/III ions. The reduction capacity would be small, but the efficiency may be good. Any iron II breakthrough could be handled by adding air (i.e., oxygen) to the water to form iron III and an additional tailing resin bed.

Good Luck....

Peter

You can contact me at pmorton@ecsrefining.com

 

[gooseinco]

Dear Lattar,

Have you solved your chromium problem yet? I'm new to Eng-Tips (just today). An inexpensive solution might be a reducing bioreactor powered by bacteria and a slowly-decaying organic source like wood chips and sawdust. Small amounts of animal manure usually provide the bacterial strains necessary to kick-start the cell. The reducing conditions force the Cr6 to Cr3 and bacterial reduction of sulfate (producing bicarbonate) raises the pH (if it's low) to precip the Cr hydroxide. The wood chips and sawdust also function as a filtering media. As you can imagine, this process can be very cost-efficient since waste materials are put to beneficial use.

We've been using this technique for treating acid mine drainage from coal and metal mines for over a decade and usually find that trace amounts of chromium are removed quite effectively, along with nearly every other heavy metal. We've been designing systems with longevities on the order decades, so change out of the organic media is not a frequent issue. The biggest one built to date (running continuously 24-7 since 1996) is a 1,200 gpm system at a lead mine in Missouri. It won several ACEC awards.

We typically design systems on a bench or pilot scale and then scale up after we've done our "homework".

Jim

 

[stamopoulos]

dear group,
we are thinking as a municipal company of constructing a brackish water ro plant with >10000m3/day permeate, but we found in the feed water that Ba=2ppm and Cu=2.22 ppm. Shall we need any kind of pre or post treatment?
Also is it true that i can found an approximate value of the salinity of the feed water using only the conductivity and if yes can anybody tell me if the conductivity is 5,98mS/cm how much would be the salinity?
Really appreciate for your attention
George, Civil Engineer

 

[jmj5152]

Concentration with ion exchange resins, and regenerant being treated by precipitation would be an optimum solution. In your situation, it cannot be assumed as suggested above that the trivalent will be cationic in valence. Trivalent Chrome oxide can also exist as an anion, depending on pH of the solution.
Assuming you have 20 ppm in 1000M3 of water, that would take a large precipitation system. However, if 1/3 is trivalent, as per your estimate, and, we assume it is cationic, you would exhaust approximately 12 CF of strong acid cation resin, generating approximately 2.0 M3 of waste with trivalent chrome. The hexavalent will be a chromate oxyanion and can be picked up by a type I or type II strong base anion. If the pH is acidic, a weak base anion in the free base form, will also remove the chromate (as chromic acid). Assuming 2/3 of the volume is hexavalent, you will exhaust approximately 10 CF of this resin, generating another 2M3 of waste. This 4M3 waste can then easily be batch treated in a 1500 gallon tank. First step is to acidify, then add reducing agent, then adjust pH up. Procedure is well documented in EPA literature.
Hope this helps.

 

[Waterdogs]

Dear everybody.
I am new to this forum, but have found this thread while looking for chromium removal. I will have my dissertation on water treatment in 11 days from now, and is asked to give a presentation on chromium removal and chromium effect on biological waste water treatment processes - in which I have not much idea...
I have seen all the nice "chemical" answeers here, thank you, but I wonder if one may use reverse osmosis for the job, or any other more simpler processes. Does anubody have some answer, and preferably a reference?
Thanks!!!

 

[Waterdogs]

To Chad (Ceidelc)
Data from your work (PH.D) on chromium removal would be great. Is it ready? Can you give us any references on it or on sub-work?

 

[aspearin1]

Waterdogs,
Yes, RO will work. Activated Carbon, Zeolites and Ion exchange resins will also reduce or remove Chromium.

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[steppen]

Hi,

I am working on a project in North Hollywood. We have a Hexavalent Chromium concentration of 1000 to 2000 ug/L and achieve groundwater extraction rates of 150 gpm. What would you recommend for treatment? My boss is thinking of ex-situ electrochemical treatment or reverse osmosis. I have never heard of using reverse osmosis for Cr removal.

Thoughts?

Thanks,
Steve

 

[steppen]

Hi Water dogs

I am working on a CrVI removal project and want to recommend IE for simplicity and cost to our client, but I hear or read tidbits of information regarding chemical treatment being less expensive. Anybody have experience with this?

Thanks,
Steve

 

[kenvlach]

steppen,

1.) Start a new thread in the
Soil/Groundwater environmental engineering Forum
forum193

2.) Give an informative title, like “Cr⁺⁶ Removal from Groundwater.”

3.) Provide more information, i.e., water analysis. Lots of other anions besides CrO₄^-2?

4.) Also, the level you need to reach & whether conversion to Cr⁺³ would suffice.

5.) Does your boss want to use electrocoagulation or what? His reasoning?

6.) Finally, reply to this thread with a link to the new one.

 

[grhardy3]

We have used a ph neutralizer followed by a vacuum evaporator to remove hex chrome, and all other metals, from our electroplating shop waste water. Our incoming levels are about 100 ppm; effluent < 1ppm.

 

[Akie]

i would like to know what is the most effiecient industrial way of Cr-removal nowadays.