Non_radioactive_elements_ - 5-8-2024 at 02:25
Hey, I'm performing some experiments on bauxite leaching and I need to determine Al (III) and Fe (III) ions in solution by a titration method to find
out leaching efficiency. Does someone have some suggestion about the method?
I have common reagents for complexometric titrations, such as EDTA, Eriochrome Black T and also thiocyanate. I've seen some articles about using KSCN
as an indicator of Fe (III), but in general the procedures are very complexes and the results are so inaccurate.
RU_KLO - 5-8-2024 at 08:26
hi,
maybe:
1) dissolve the sample in HCl - start with 1 or 2 Mol HCl solution (Fe & Al get into solution as chlorides)
2) add NaOH (1 or 2 Mol), dropwise. At ph 4+ Fe will start precipitating as Fe hydroxide. Aluminum hydroxide precipitated from an aluminum chloride
solution without added anion is most voluminous at pH 5.5 but is precipitated most completely at pH 7.7. (Effect of diverse anions on the pH of
maximum precipitation of “aluminum hydroxide” Stephen P Marion, Arthur W Thomas
https://doi.org/10.1016/0095-8522(46)90044-X).
but as Aluminium is amphoteric, keep adding NaOH till it redissolves (ph14+)
3) filter the Fe hidroxide, calcinate it to transform into Iron Oxide, weigth as oxide and calculate from there.
Fe + 2HCl -> FeCl2 + H2
2Al(s)+6HCl(aq)→2AlCl3(aq)+3H2(g)
FeCl2 + 2NaOH = Fe(OH)2(s) + 2NaCl(aq)
Now regarding if your Fe hidroxide oxidised:
Iron(II)
Fe(OH)2 -heat-> FeO + H2O
Iron (III)
3 Fe(OH)3 → Fe3O4 + H2 + 2 H2O (very simplified, probably a lot of other intermediates exists) - from wikipedia
FeO and Fe2O3 are oxides of iron having different oxidation states of iron atoms. The key difference between FeO and Fe2O3 is that FeO has iron in +2
oxidations state, whereas Fe2O3 has iron in +3 oxidation state. Moreover, FeO is a black powder while Fe2O3 is a red powder.
(maybe you could oxidize Fe(OH)2 to Fe(OH)3 by adding some H2O2 till the slurry is red, heat to remove H2O2 excess.
take into account that Fe catalices H2O2 decomposition. I got better results by adding the H2O2 in the cold solution and then ramping the temperature
slowli till 70C+ where the H2O2 start to decompose more violently. Adding H2O2 to a hot solution of Fe2+, should be added by drops. -Ive already had
to many overflows when working with H2O2.
Probably other oxidizers could be used. hypochlorite for example)
Note: other metal hydroxides that are not amphoteric will be precipitated also.
Edit:
found this
ASTM E738-20
Standard Test Method for Determination of Aluminum in Iron Ores and Related Materials by EDTA Complexometric Titrimetry
hope it helps
Attachment: 0095-85222990044-x aluminium hidroxide precipitation.pdf (711kB)
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[Edited on 5-8-2024 by RU_KLO]
[Edited on 5-8-2024 by RU_KLO]
Attachment: ASTM E738-2011_1875.pdf (42kB)
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bnull - 5-8-2024 at 10:31
You can use ammonium hydroxide instead of NaOH. It doesn't require a careful watch over pH since both iron and aluminum hydroxides are insoluble in
and don't form complexes with it. After filtering and washing the precipitate, you can use NaOH to separate iron from aluminum.
The book Quantitative Chemical Analysis (https://archive.org/details/quantitativechem00hami) by Hamilton & Simpson has many methods to determine the iron content of your sample and
many references for purely chemical methods. Chapters 12 (Permanganate Process) and 13 (Dichromate and Ceric Processes) offer many options.