They describe synthesizing solid iodine by oxidizing potassium iodide with ammonium persulfate. Dissolve 50 g KI in 100 ml water and 38 g ammonium persulfate in about 150 ml water. Slowly add the KI solution to the persulfate solution with stirring; iodine forms a red-brown color and initially stays dissolved in KI, then precipitates as more iodide is oxidized. The mixture heats to ~40°C; cool with ice and continue stirring. Crystalline iodine separates and can be seen dancing in the liquid. Stop stirring, allow solids to settle, then filter or decant and rinse with cold water; repeat until the liquid is pale. Vacuum filter and dry thoroughly; damp product is about 40 g, dry weight ≈ 34 g, giving ~90% yield (potentially higher with careful washing/decanting). The method also works with bromides (e.g., sodium bromide) but more slowly, using a small amount of water; it can warm and form a bottom layer of liquid bromine if left too long. Iodine stains are mentioned; have sodium thiosulfate on hand to mop up spills.
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