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Activated carbon used to remove Chromium 6

Do you have any information or data relating to the use of activated carbon to remove chromium 6 from wastewater other than Lewis Environmental's ENVIRO-CLEAN PROCESS? If so, could you provide me with the source of the data and/or the company using this technology?

Wayne S [last name deleted for privacy by Editor]
- Bridgeville, Pennsylvania, USA
2001

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I once worked for a company that had a recycle water system. It was a carbon, cation, anion sequence. When we ran chromate passivating rinses we could see the orange color enter the carbon (clear plastic hose) but it never showed in the effluent.

I was told by an engineer experienced in IX that carbon will adsorb hex chrome quite readily, but it will sometimes also let it go in high concentration slugs without warning, so the process is unreliable.

The other issue is disposal. How do you regenerate or dispose of the carbon if it is loaded with hex chrome.

Bill Vins
microwave & cable assemblies - Mesa (what a place-a), Arizona
2001

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Activated carbon adsorption for hex chrome, such as in the technology you mentioned, will indeed leak excessively when high concentrations may be present. However, I believe the mechanism is not a reverse of the absorption, but a simple physical limitation of the ability of carbon to effectively absorb the mass vs the transfer coefficient - in other words, the flow is too high! The carbon can be 'regenerated' by using sulfuric acid, however the integrity of the carbon is adversely effected, as you may have experienced. From what I remember, it can go through perhaps 4-5 stripping cycles before it is essentially useless, less if lower grades are used (such as coal based in lieu of carbonized coconut shell).

If you could define your goals, perhaps some other technology would be better suited to meet your application. If its simply returning to bath from rinses or purifying baths, there are at least 2 alternate technologies come to mind that can do that efficiently. If its simply removal of the chrome from rinses and treating (without trying to electrowin chrome as a powder), the range of options actually opens up without the need to make hazardous sludge - i.e a recycle by-product for resale.

Tom Baker
wastewater treatment specialist - Warminster, Pennsylvania
2001

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Activated carbon will act to remove hexavalent chromium from water, but it has a finite and limited capacity. In the 1960's and 70's the EPA sponsored several studies on the use of activated carbon to remove it. Typically, it was removed from the carbon by either sodium hydroxide or hydrochloric acid. The reports from these studies are probably still available from the NTIS.

My experience is that ion exchange resins have higher capacity and, at least when dealing with dilute concentrations, a longer useful life for this application.

All IX media have some difficulties in achieving low ppb concentrations. This was studied by Sengupta at the University of Texas and his published papers are probably the best reference if you are looking for low, low concentrations. There are also several case studies in recent literature regarding groundwater clean-up, and removal of hexavalent chromium to < 0.05 mg/l.

Lyle Kirman
consultant - Cleveland Heights, Ohio
2001

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Dear Wayne:

My limited experience of Chromium removal is groundwater applications at nuclear and former nuclear sites where Sodium Bichromate has been used as reactor coolant. Ion Chromatography (IC) may be used to measure chromium concentration down to 100 ppb. Whether from dissolved chromic acid (in H2O), pure chromium metal reacting with hydroxide, chromium hydroxide dissolving in very alkaline water (high pH), dissociation of chromium (VI) oxide + excess water or dissolved sodium bichromate - chromium is typically present in contaminated groundwater as -ve charged oxy-anions which are readily removed by a strong base Styrene DVB Type 1 Synthetic Anion Exchange resin. 6+ve valence (hexavalent) chromium reacts with water to form chromium trioxide and hydronium ions. So these are pH controlled reactions which result in either chromium oxy-anions (acidic conditions) or elemental hexavalent chromium cations (basic conditions).

So theoretically, chromium oxy-anions and hexavalent chromium may be precipitated out of solution as chromium trioxide by experimenting with pH control which is probably the preferred removal method at plating operations prior to thorough wastewater treatment. As you know chromium (VI) oxide powder is a highly toxic cancer suspect agent - so you still have the problem of disposal assuming you could precipitate it out effectively. Since this seems to be difficult and costly to determine (the form of chromium present in contaminated groundwater) - the most sensible approach seems to me to be dual ion exchange columns in series - one with strong acid cation exchange resin followed by strong basic anion exchange resin. That way you get out all the chromium whether it is +ve cation or -ve oxy-anion form. Carbon polishing step or perhaps pre-filtration could protect the resin bed from organic fouling. Organically modified clays also show promise of protecting ion exchange resin beds as a pre-treatment although they require higher operating pressures.

In any case, you are left with resin, clay and/or carbon loaded up with chromium in some form which poses yet another disposal problem. There are companies able to handle this type of hazardous waste. That is my suggestion - buy ion exchange resin columns and carbon polishing filters from me - then hire a licensed haz waste disposal outfit to take care of the spent resins and carbon. Resins used in this application may be regenerated in situ for years with good performance and remaining exchange capacity - provided the regenerant is properly removed and disposed of.

Laurence D [last name deleted for privacy by Editor]
- Red Bluff, California, USA
2001

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Success has been achieved for removal of Chromium VI from groundwaters with the use of filter columns (placed in series) through cation exchange containing natural (non-synthetic) clay materials mined and blended. The chromium VI adsorbed by the CA materials can be removed by a relatively inexpensive regeneration process.

The naturally occurring clays are also relatively inexpensive when compared to costs of resins and/or synthetic clays or aluminosilicates.

Bob. A [last name deleted for privacy by Editor]
- Brookhaven, Mississippi US
2003

I think the removal of hexavalent chromium by activated carbon is not cost-effective because of the lower removal capacity and higher regenerating costs.

Hu j [last name deleted for privacy by Editor]
- Hong Kong
2003

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There are lot of ways of removal of hexavalent chromium including (adsorption by activated gypsum , activated charcoal ) then di-phenyl carbazide reaction ( reaction of hexavalent chromium waste water with hydrogen peroxide in acidic solution ) & reaction with zirconium hydroxide ceramic & reaction with ferrous sapponite clay . while fuel cell membrane and porous ceramic cell membrane is also available .

Babar S [last name deleted for privacy by Editor]
- Lahore, Punjab, Pakistan
2006

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Gentlemen:
It seems a convenient out-of-sight-out-of-mind item to hire HazMat people to carry the carcinogenic hexavalent chromium away to dispose of it.... hopefully in a legal, non-polluting and safe manner.

Is it simply stored in 55 gallon (208 liter) metal drums in a cave somewhere?

I would like to know if there the possibility of actually returning the clay, resin or carbon harvested chromium 6 back into the pretreatment process?

This would cut off the temporary disposal option and would make a nice closed loop "cradle to cradle" operation.

Jonathan Miller
architect-specifier - Vergennes, Vermont, USA
2007

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The thread is wandering a bit, Jonathan, so it's hard to answer your query; sorry. If the resin is being used to remove hex chrome from an aquifer, as some are referring to, it may have got there as the result of a cooling tower treatment decades ago, and returning it "back into the pretreatment process" won't have an understandable meaning.

But if the chrome is being used in a plating process, usually it is simply returned to make good evaporation losses, and any chrome that escapes is more incidental (a mix of chrome and dirt of various sorts on filter cartridges, a mix of greases and chrome from wipe downs of tank rims and blowdowns of dry packing, etc.). It's been many years since I've seen a chrome tank where a good degree of recovery wasn't already being practiced at the source.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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August 26, 2008

Respected sir,

I'm working on chromium removal removal by electrocoagulation.now I will do the work on chromium removal from synthetic water but I have no any idea so please give me an idea and which types experimental set up perform for Cr removal from synthetic water. and give me a suggestion on which content include into my thesis on chromium removal by electrocoagulation.
please sir give me any suggestion in like a index form.

your faithfully,

Patel Nirav
student - Ahmedabad, Gujarat, India