need help with Al(OH)3 and related inorganic chemistry

[sshep]

I am working on a wastewater treating project that begins with a blowdown from a hydrocarbon process using aluminum chloride (AlCl3) and HCl as a catalysts, which is then washed out in steps with NaOH and water, and then combines with other wastewater streams which can contain ammonia, Fe ions, sulphuric acid, and other ionic stuff. Ultimately we need to steam strip (benzene removal) and nuetralize these waters for discharge. A clumsy process for this treatment already exists, but my greatest worry is about solid precipitates including AL(OH)3 or Al2O3 which may occure in tanks and foul up equipment along the way.

My knowledge of inorganic chemistry is 20 years old, and was insufficient for this job even when fresh. Can anyone direct me to an internet resource or text that could be helpful? I searched around last night and haven't had much luck finding anything useful except for a few Ksp values. I would greatly appreciate a good source of background info that can help me become quickly knowledgable about this branch of chemistry!

thanks and best wishes,
sshep

p.s. I also think that benzene solubility (LLE and VLE) is pH dependent and could use some help with data on that subject as well.

 

[epoisses]

Complicated stuff, sshep. I'm afraid my best advice would be the cliché "re-think the whole process from scratch instead of adding an end-of-pipe treatment", but don't know how willing your management is to invest. Have you considered replacing the NaOH and water washes with alternative ways to recover AlCl3/HCl without producing a wastewater stream? If end-of-pipe is the only option you'd just put a filter in to get the solid precipitates out, but you'd be changing and throwing away filter elements all the time, not very elegant.
I hope somebody else has a more specific answer to your question...

 

[sshep]

Dear epoisses, Thanks for your input. Unfortunately the washing step is integral to the main process and outside the scope of this project. To make a change at that point would be major, although I would be interested in any alternatives you might have for AlCl3/HCl removal.

With respect to treatment of these high pH wastewaters, I am actually trying to sort out a reasonable processing scheme. Today I may know more than yesterday. Al(OH)3 is soluble at high pH as Al(OH)4-, so there are two philosophies with respect to where nuetralization should occure among the 3 processing steps. The three processing steps are: benzene stripping, solids removal, pH adjustment. On one hand there are other solids (such as dirt) which would be nice to remove early, but on the otherhand the facilities for handling benzene contaminated solids do not currently exist.

Any extra advice is appreciated.

best wishes always,
sshep