[changhk]

Hello everyone

recently we are facing a trace heavy metal problem in our project.

We are using an aqueous oxidizing agent which contains a tiny amount of heavy metal ion. In our application, we aim at basically ELIMINATING TOTALLY ALL heavy metal ion in the liquid oxidizer.

example of heavy metal ions are As, Ba, Cd, Cr, Pb, Se...etc

Is there any practical well known approach to achieve this goal(to be as clean and pure as possible)?

Thank you for your advise.
Chang

[Borek]

Purifying reagents is an art in itself. Depending on the situation it is sometimes easier to change the supplier or to produce the agent by yourself using some non-standard approach, than to purify.

Not that I am able of supplying better, more detailed information. Eons ago members of the group I was working in were involved in trace analysis, and purity of reagents was a paramount - I remember some general discussions from the time, but not many details.

[Arkcon]

Like Borek: said, there isn't much to say, but I'd like to ask -- what have you tried?  And for that matter, what purity do you have, and how do you know how much impurity there is, and how do you know how pure you need?

Example:  your oxidation reagent, in working solution is 10 ppm lead.  You analyze this by ICP, or wet chemistry analysis?  Which?  Your specification, as given by the USP?  some other regulation?  your application fails at what ppm? is what -- 5 ppm, 7 ppm, 3 ppm?  Did you try to recrystallize your solid reagent?  And what did you get?  Did you try again, discarding more mother liquor?  And did that help.

Sometimes, a total chemistry noob will ask us, "I need absolutely pure water for my brilliant idea"  and we have to ask them to try to understand the very basics of analytical chemistry.  How pure is it now, how do you know how pure it is, how pure do you need it to be?

[changhk]

Currently we use ICP to measure the heavy metal content.

The "target" specification is what another company can achieve. They can basically achieve in a manner that some of the heavy metal are below detection limit.

In general, they are 40x to 100x lower than what we have. We did not paid much attention before on heavy metal ion. Currently we are trying to increase the pH by adding more OH. Will see if we could precipitate out the heavy metal.

currently we are searching if there could be "filter" or suitable "cation exchange resin" which could suit the purpose.

[Arkcon]

Good.  A cation exchange resin would be a good way to finish polishing the product after trying to precip at higher pH.  Don't neglect the possibility that your competitor may simply be using faulty analysis.  Buy some of their stuff, and run it on your ICP with your procedures and method.  See if its really as good as they say.

[eazye1334]

Yeah, ion exchange will definitely work well as a finishing step, but can get very expensive if the solution is heavily contaminated. We use it on our plating wastewater but only in emergencies.

[Enthalpy]

You didn't tell what aqueous oxidizing agent... If it's >70% hydrogen peroxide, any contact with a resin will make boom.