[keyurd1]

I am doing a project on synthesis of generating magnesium sulphate crystals form industrial spent containing sulphuric acid as a major by product {40%) and rest of it is organic component.
I am able to get good amount of white crystals after reaction of the spent with magnesium oxide but after 1-2 days the crystals start turning brownish in colour (sometimes reddish)

Can anyone please help me with this, It urgent and i have tried almost everything but im not able to identify as to why this kind of behaviour is occurring.

[Hunter2]

I think you have to remove of your 60% organic by products. During the crystallization the organic will be trapped into the crystals.

[keyurd1]

I am getting the desired ideal purity of the crystal, i can remove the colour by actvated carbon.
I am interested in this typical behaviour of the crystal.
if the organic product gets trapped in the crystal then it should be coloured right from the time of crystallization.
it takes 2-3 days to catch that colour,
and any possible agent that is present in the organic spent that leads to this kind of behaviour??

[Hunter2]

You didn't tell us what organic chemistry you have. I think its a kind of oxidation of something what change color after few days.

I would suggest to do the carbon treatment before crystallization.

[keyurd1]

Based on your reply I performed some tests on the crystals and got hold of the exact composition of the spent that I was provided

I contacted the company from which I acquired the spent and they provided me with the exact composition

ester amide 1%
cyano pyridone 0.5%
carbamoyl pyridone 0.5%
liquor ammonia 0.5%
sulphuric acid 40-45%
I performed some test on the crystal myself and the following are the results i obtained

1. TLC test reveals that no traces of the original product (pyridone) are left in the crystals.
2. Ammoniacal nitrogen test reveal the presence of 800-1500 ppm amide present in the crystal

So basically the ester amide component in the spent is causing the pain during the crystallization

My research guide wants me to find some suitable and economic ways to decompose the ester amide component in the beginning of the process
and if that doesn't work can you suggest me the names of some de-colouring agent i could use to overcome this problem.

Thank you so much

[Arkcon]

How strong is the spent sulphuric acid?  If it was concentrated (minimal water) and hot, it should oxidize most organic material.  Obviously, it'd be expensive to take spent sulphuric acid, concentrate and purify, and sell as technical grade sulphuric acid, I assume that's why your magnesium sulfate application is viable.  But concentrating it as best you can could possibly destroy enough organic material.

Would you consider recrystallizing your magnesium sulfate?  It would be visually pure, and more marketable.  But then, you'd be leaft with acidic, impurity rich mother liquor, which you'd have to dispose of.

[keyurd1]

Sir,
what you suggested is good the commercial production IN the industry but I am having a specific target pertaining to my project.
The tests i performed on the crystals got approved by the central laboratory and now.
I am supposed to derive ways to decompose of the amide and nitrogen ( traces of which are still present in the crystal)
the spent is concentrated enough to decompose of all the organic products that are initially present.

One of the research fellows in my department suggested me a possible reason for the colouring of the crystal which goes as follows-
"The cyanide component of the spent which is still active in the spent even after concentrating it to a density of 1.25 (45%) reacts with the iron that is present in minute traces in the MgO that is subsequently added. The MgO is added till the pH goes to 7 and the density of the liquid increases to 1.4.
during this process Iron and cyanide react to from FeCN in presence of acidic medium and traces of which gets embedded in the crystals. This component is mainly responsible for the colouring of the crystals"

My focus here is to provide an economic solution to decompose of this cyanide before the addition of MgO starts. If I'm unable to do this then ill have to shift my focus towards the systhesis of a de-colouring agent.

So please help me