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Problem Statement

It is incredibly difficult to find a good source of high purity red iron oxide, Fe2O3, also known as Iron (III) Oxide. I finally discovered that ceramic shops have some pretty good stuff for cheap, but I also wanted to double check and be able to objectively compare between multiple sources.

Visual Inspection

Using a metallurgical darkfield microscope I was able to visually asses the quality as well as particle sizes of the various iron oxide sources. It is clear that some of these sources are just iron rich dirt (iron ore). I was able to overlay a scale bar using mm/pixel data gathered from photographing a rule slide with the exact optical system.

To avoid scrolling, summaries will be posted after the processes are fully described.

Non Acid-Soluble Assay

  • Sulfuric Acid: I attempted to dissolve the iron early on with sulfuric acid, 35%. However, Iron(III) Sulfate is barely soluble, and therefore only the tiniest amounts were created. Given that H2SO4 is very expensive, and an in solution reducing agent would need to be supplied to continue the dissolution process by converting the Iron(III) to Iron(II) which is highly soluble, the process was abandoned. An avenue of interest is that UV light (sunlight) does appear to photo reduce the Iron(III) to Iron(II), though not quickly enough to aid in timely dissolution.
  • HCL proved to be far more promising, as both of the oxidation states are highly soluble. Dissolution is rapidly achieved after just 20 minutes of boiling in a 32% solution. HCL is cheap, about $8 a gallon, and easily distilled out again at 20%, unlike sulfuric acid.

Assay Procedure

  1. Measure 2.000g of Sample
  2. Add 25mL HCl (10M) to Sample in a 250mL flask
  3. Boil for 20 minutes
  4. (Optional) Dry filter paper at 105 degrees C
  5. Add 100mL of warm distilled water to the mixture
  6. Tare the filter paper (!)
  7. Filter the sample through the paper, rinsing the sample flask with additional distilled water as needed to capture all sediment.
  8. Dry at 105 degrees C
  9. Weigh filter immediately before sample and paper reabsorb atmospheric moisture
  10. Subtract filter paper tared weight
  11. (1 - ((Mtotal - Mfilter) / 2.000)) x100% = Percent Soluble Material
  • Note that this is an upper bound to the iron oxide percentage, but could also contain other acid soluble metals and compounds such as nickel, aluminum, copper oxides, etc.

Isolation Procedure

  1. Add 150mL of H2O to 33g of Fe2O3 in a boiling flask
  2. Add 200mL of 10M (32%) HCl
    • The acid is diluted to the azeotropic point (6M) to prevent nasty vapors from escaping the reflux column
  3. Boil for 30 minutes under reflux.
    • Liquid will turn reddish brown.
  4. Filter out clays and insoluble substances once cooled. Liquid will be tea colored.
    • Clays should be light colored and no longer red.
  5. Add 50g of oxalic acid dihydrate OR 410 mL of a 1M solution.
    • No reaction should occur.
  6. Place resulting solution into the sunlight or expose to short wave UV light until it turns from brown orange to yellow green.
  7. Dry in a fume hood.
    • Solution will have a 50% excess of HCl due to Ph solubility of Fe2O3.
      • Distill this excess off to recover and recycle or boil to NEARLY dry
      • Take into account HCl vapors that will form!
    • Do NOT allow to fully dry under heat or exothermic decomposition will occur!!
    • Yellow crust will form.
  8. Add 200mL of H2O to yellow brown crust and bring to a boil then let cool.
    • This is to dissolve water soluble impurities.
  9. Filter off yellow solid and dry.
  10. Add yellow solid iron(II) oxalate to crucible or pan. Break up clumps and "fluff" to allow adequate oxygen supply. Heat to 250 degrees C while stirring to ensure adequate oxygenation during decomposition. Areas of the solid may turn brownish red until decomposition temperature is reached, when a runaway reaction will occur converting the iron(II) oxalate to pyrophoric iron, which will oxidize under stirring to form red Fe2O3.
  11. Grind or mill to fine consistency.