There is generation of high supersaturation in my solution consisting of high initial concentrations of PO4 -3, Mg+2 and NH4+. This is resulting in immediate precipitation of struvite . I suppose the high nucleation rate is dominated by growth stage of crystals. I want struvite crystals. Is there any a method to control the high supersaturation generated or avoid high nucleation rates.
Is pH also responsible for high supersaturation condition.
Please help.
Hi
In my guess you can go for surfactants they may control the nucleusion growth.
Best
Hello,
I do agree with Arun above, using a surfactant could be a nice quick way to hinder nucleation allowing crystal growth to dominate, but I have personally had issues in trying to get the right surfactant.
Arun: Would you have more advice in using surfacants, or a link to publication?
I often go for temperature cycling via cooling crystallisation, though I often work with organics it should still work (this could be a case of a hammer only seeing nails).
Put a few ml of your crystal and the mother liquor into a thin vial (an old NMR tube can work well for this). Heat your solution to about 5 - 10 degrees under the boiling point of the solvent keep at this temperature of an hour or two. Check the solution. (If the crystal/solids go into solution note the temperature at which they go into solution and go reduce the temperature to 5 - 10 degrees under this temperature.)
Ideally some of the particles will go into solution with a few crystals left in solution. This most likely going to be you case as you've got a highly saturated solution.
Slowly reduce the temperature to room temperature. Hopefully you'll have desired crystal size. If not, ramp up the temperature again to about 5 - 10 degrees under the boiling point of the solvent, cool the solution by 5 degrees hold the this temperature for about 30minutes or so, then heat the solution by 2 degrees and hold again. Repeat this until room temperature or desired crystal size. This way you should be favouring crystal growth over nucleation while dissolving new smaller particles.
I know it's dull work but I've gotten lovely results from 'difficult' crystals in the past, and all you need is a hot-plate, an NMR or test tube, a beaker of water or oil, a thermometer, and a lot of patients.
All the best of luck,
Pól
Thank you for your answers.
My crystal of struvite lose NH4+ on heating beyond 45 C.
And the solvent boiling point is 100 C. So i cannot heat beyond 45 C. Should I heat it till 45 C?
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