Tuesday, August 27, 2013

Nitrates from commercial compost 3

I bought more equipment. This is a weakness. I must resist. I have two scales and a nitrate/nitrite test kit. I am continuing the previous experiment while moving on with this one.


  • Leaching may extract more (or less) nitrate over time.
    Check at 1 and 24 hours.
  • According to the literature, the evaporite is going to be a mix of [Na,K,Ca,Mg][CO3,NO2] with either the Ca or the CO3 at zero. Fe and Cl may be present as well.
    We will presume it is the CO3 species that is absent.
  • Potassium carbonate has the highest molecular weight of the various components of potash: 138g/mol.
  • Calcium Nitrate has the highest molecular weight of the various potential components of raw saltpeter: 236g/mol.
  • Suppose we have N grams of a CaCO3 precipitate. To calculate the amount of potash required to provide that much carbonate, divide by the molar mass of CaCO3 (100g) and multiply by the molar mass of potassium carbonate (138g) for a net mass multiplier of 1.38.
    1.38 times the Mass(CaCO3) is the max Mass(potash) to be used.
  • Suppose we have N grams of a Ca(NO3)2.4H2O evaporite. The mass divided by 236g is the number of moles of calcium nitrate. Calcium nitrate mixed 1:1 molar with potash results in 1 mole of calcium carbonate and 2 moles of alkaline nitrate. 138/236 =  0.58, thus:
    0.58 times the Mass(Ca(NO3)2) is the max Mass(potash) to be used.


    Part 1, 1 hour

  1. Place 1kg of compost in a stainless pot
  2. Add 2 liters of distilled water
    Checked: Total mass: 3kg 
  3. Let stand for 1 hour
  4. Filter (seive and paper towels, as above)
  5. Measure 1 liter of fluid
  6. Get mass of solution to estimate dissolved salts, and verify by checking weight of remainder of fluid and soil
    1003g (about 3g, estimate 6g in 1kg of compost)
    Remainder: 1997g
  7. Perform Nitrate test
    Nitrates: < 5mg/L (Well THAT sucks. Maybe it's wrong?)
  8. Return the fluid to the mass

    Part 2, 24 hours

  9. Let stand for 23 hours
  10. Repeat mass measurements

  11. Test for nitrate
  12. Was it worth waiting the 23 hours

    Part 3, Analysis

  13. Extract all the solution
  14. Filter the solution
  15. Evaporate with minimal heat
  16. Weigh evaporite
  17. Calculate the maximum potash required:
    0.58 * mass(evaporite):
  18. Gather the potash
  19. Dissolve the evaporite in a minimum of distilled water
  20. Divide the solution into two halves (S1 and S2)
  21. Divide the potash into two halves (P1 and P2)
  22. Add one tenth of P1 to S1
  23. Observe a precipitate (hopefully)
  24. Add more of P1 to S1 very slowly until no more precipitate is formed
  25. Weigh the dry remainder of P1
  26. Dry and weigh the precipitate from S1
    S1 Precipitate: 
  27. Recalculate the maximum potash required:
    1.38 * mass(precipitate)
  28. If this new "maximum potash" value is lower than the mass of P2, reduce the mass of P2 to the lower maximum.
  29. Add  the (possibly reduced amount of) P2 to S2
    Hopefully this achieves a zero value for both calcium and carbonate, leaving only nitrates in the wake
  30. Dry and weigh the precipitate from S2
    S2 Precipitate
  31. Compare the masses of the precipitates. They should be equal.

The pictures here are very low res because my regular digital camera has been lost, and I am taking stills with a videocamera instead. :P

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