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Chemistry / Re: How can I precipitate silicon from an acidic solution at room temperature?
« on: 22/06/2019 04:19:36 »It's hard to troubleshoot chemistry from afar, so please bear with me as I ask some questions:
How do you prepare the sodium metasilicate solution, and how do you know the concentration of Si in it? (did you make it yourself, or buy it, and then did you titrate it, or use spectroscopy etc.?)
For the dirt extract--do you have a way of confirming that the Si is extracted?
After acidification, is the pH stable, or does it change slowly (sometimes, especially when dealing with solids, endpoints can be very hard to reach--you add acid, and the pH falls quickly, then creeps back up...)?
Are you working from a previously published proceedure to do the extraction? I am somewhat surprised that a 0.2 M solution of NaOH would be sufficient to dissolve silica at a reasonable rate (even at 85°C)?
What temperature is the solution cooled to?
Do you have access to a laser pointer? (This can be used to determine whether a sample is a homogeneous solution or a colloidal suspension--no beam will be visible in the homogeneous solution, but you will be able to clearly see scattered light if there are suspended particles).
Thank you for your response. Yep - I acknowledge that trying to answer a chemistry question is difficult and therefore I appreciate your time. I have provided a response to you questions below:
How do you prepare the sodium metasilicate solution, and how do you know the concentration of Si in it? I purchased a commercially available sodium metasilicate solid (lab grade) with a know Si content of 27 - 29% SiO2.
For the dirt extract--do you have a way of confirming that the Si is extracted? Yes - once I extracted the Si using the NaOH solution I had it analysed at a commercial laboratory. I'm actually using a radiolarite as my source for the Si (84 - 90% SiO2).
After acidification, is the pH stable, or does it change slowly (sometimes, especially when dealing with solids, endpoints can be very hard to reach--you add acid, and the pH falls quickly, then creeps back up...)? Yes - the pH is stable at around 1.3 and has not moved for 3 days.
Are you working from a previously published procedure to do the extraction? I am somewhat surprised that a 0.2 M solution of NaOH would be sufficient to dissolve silica at a reasonable rate (even at 85°C)? The 0.2M was an error and it in fact was 8M NaOH solution with the reaction undertaken at 85 degrees Celsius. I couldn't actually find a published procedure for the dissolution of radiolarite, and I initially tried dissolving it in 2M HCl with no luck. I then saw that I should be using concentrated alkaline solution; hence 8M NaOH was used to dissolve the radiolarite material, resulting in 80 - 95% extraction of the Si. I now want to precipitate the Si out of solution so that I can filter the solid to obtain a relatively pure SiO2 material.