math - 4-9-2012 at 20:45
Hello,
I'd like to know which safe methods I could use for disposal (make it harmless to the environment) of an aqueous solution of sodium aluminate, NaAlO2.
Thank you 
woelen - 4-9-2012 at 22:21
As long as you are not producing industrial scale waste amounts, sodium aluminate is harmless for the environment. No need to neutralize it. Just
flush it down the dfrain with a lot of water.
The reason I say this is that some fertilizers for plants like Hortensia contain aluminium salts and these are put in the garden in kg amounts. If
that is no problem at all, then a small quantity of aluminate should do no harm at all.
math - 4-9-2012 at 22:24
Quantity would be less than 0.6kg. Since you say Al salts are used as fertilizer, could it be flushed in soil directly?
woelen - 4-9-2012 at 23:26
No, I would not add it to soil. Al-salts, used in fertilizer are based on alum or aluminium sulfate and these are nearly neutral or very slightly
acidic. Your solution is strongly alkaline and that would be quite harmful in soil.
With 'harmless for the environment' I mean that in a normal sewer system the compound does no harm. Acids and bases, which are otherwise nontoxic
(e.g. sulfuric acid and sodium hydroxide) can go in a sewer system. In fact, frequently such acids or bases indeed go into a sewer system as drain
cleaner. In the sewer waste, these are quickly neutralized and diluted. This is true as well for your aluminate solution. Direct addition to soil is
another thing. Even normal fertilizer can spoil soil if too much is added.
AJKOER - 5-9-2012 at 08:54
Or, one could carefully add an aqueous solution of Oxalic acid, H2C2O4, and everything becomes an insoluble salt. Cool!
2 NaAl(OH)4 + H2C2O4 => Na2C2O4 (s) + 2 Al(OH)3 (s) + 2 H2O
I am not sure as to whether the Aluminum hydroxide produced would be in the form of a gel or an amorphous white powder. Sodium oxalate is a slightly
soluble white toxic salt (so do not wash the salt down the drain). Upon strong heating of Na2C2O4 (commences 290 C, complete at 750) one has thermal
decomposition forming CO and Na2CO3. Sodium carbonate itself begins to decompose at 810 C (see http://www.ncbi.nlm.nih.gov/pubmed/18962335 ).
[Edited on 5-9-2012 by AJKOER]
unionised - 5-9-2012 at 10:00
That's a great idea if
1
You happen to have lots of spare oxalic acid and
2
you want to produce lots of rather toxic (and fairly soluble - a few % or so) sodium oxalate
If you blow enough air through the solution most of the aluminate will be converted to aluminium hydroxide and sodium carbonate.
(blowing CO2 through it would be better- do you make home brew?)
Filter of the solid + pour the liquid down the drain.
Wash the solid by decantation then chuck it on some waste ground somewhere.
But really, flush the lot down the drain with a lot of water.
AJKOER - 16-9-2012 at 08:47
Here is a possibly better suggestion than using Oxalic acid. Add Ammonium chloride to your NaAl(OH)4. I would speculate the reaction to proceed as
follows :
Na[Al(OH)4] + NH4Cl ----> NaCl + Al(OH)3 + NH3 + H2O
The ammonia may actually not escape from solution but, instead, could dissolved in the Aluminum hydroxide gel.
Also, here is the reaction with CO2 (assuming your hot air holds up):
CO2 + NaAl (OH) 4 -> Al (OH) 3 + NaHCO3
This questionable source also cites both of these reactions: http://diendan.hocmai.vn/archive/index.php/t-127879.html
Vargouille - 16-9-2012 at 09:53
Or just pour it down the toilet (provided you don't have a septic tank). At least one crystal drain opener consists of NaOH, Al, and a few other
things. In water, that would react to form sodium aluminate. No problem.