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I am a high school student working on a research project that involves producing alginate gel directly from wet seaweed. I am starting the first phase next week, which is using a small batch to practice the full procedure. The guide I am using is somewhat vague, and it mentions having to add calcium chloride to a sodium alginate solution and then mixing "carefully" to ensure a solid precipitate. The exact quote from the paper is "If the calcium solution and filtered extract are mixed carefully, the calcium alginate can be formed as fibres - bad mixing gives a gelatinous solid". (After that, I am supposed to collect the fibers and add acid and then sodium carbonate to get solid sodium alginate.) Any tips on how exactly to go about the mixing?

Here is the link to the full paper if clarification is needed: https://www.fao.org/3/y4765e/y4765e08.htm#bm08.1

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Though I have not tried this myself, it might mean that decanting one solution gently on top of the more dense one (likely the $\ce{CaCl2}$) would form two distinct layers, with the precipitate forming as a sheet where the layers adjoin.

Gently pushing the sheet down at one spot, or lifting the sheet at an edge could extrude the film, creating a long strip, and subsequent stirring would break the sheet into strips or fibers (or fibres, if done across the ocean).

This SWAG is based on the nylon synthesis "rope trick". In that video, note use of a glass stirring-rod to reduce mixing of the second solution as it is poured.

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  • $\begingroup$ Note the description of the procedure by the OP: "mixing "carefully" to ensure a solid precipitate". That seems inconsistent with gentle layering of one solution atop the other. $\endgroup$
    – Buck Thorn
    Oct 20, 2023 at 7:11

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