I was planning to extract citric acid from mango juice by first using Aspergillus niger fungus by fermentation to convert the mango juice to citric acid, then extracting by first adding sodium hydroxide until the fermented mango juice is somewhat alkaline.

Then adding the calcium chloride (at 70 °C), thinking the calcium chloride would first react with the hydroxide in the juice, producing calcium hydroxide, which would then react with citric acid to form calcium citrate by the reaction below:

$$\ce{2 C6H8O7 + 3 Ca(OH)2 -> Ca3(C6H5O7)2 ⋅ 4H2O + 2 H2O},\tag{R1}$$

then later adding sulphuric acid, to get citric acid

$$\ce{Ca3(C6H5O7)2 ⋅ 4H2O + 3 H2SO4 -> 2 C6H8O7 + 3 CaSO4 ⋅ 2H2O + 2 H2O},\tag{R2}$$

but I don't get any precipitate (calcium citrate) to continue experiment, just a dark slurry. Please, I need assistance.

  • 1
    $\begingroup$ Food grade citric acid is sold in food stores, where I live, as “sour salt”. It is sprinkled on food to give a tart or sour taste. Maybe buy a bottle (it is inexpensive) and test your protocol on that, just to get a bit of experience and debug the protocol without mango debris obscuring what is happening. $\endgroup$
    – Ed V
    Jul 29, 2021 at 17:13
  • 1
    $\begingroup$ The remaining chloride ions from CaCl2 make the solution neutral, not basic. Start with calcium carbonate (limestone) and wait for a while for it to react, or use CaOH to start. $\endgroup$ Jul 29, 2021 at 18:55


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