Method for treating a nitric aqueous liquid effluent by calcination and vitrification
A method for treating a nitric aqueous liquid effluent containing nitrates of metals or metalloids, comprising a step for calcination of the effluent in order to convert the nitrates of metals or metalloids into oxides of said metals or metalloids, at least one compound selected from the nitrates of metals or metalloids and the other compounds of the effluent leading upon calcination to a tacky oxide, and a dilution adjuvant comprising at least one nitrate of metal or metalloid leading upon calcination to a non-tacky oxide being added to the effluent prior to the calcination step in order to give a mixture of effluent and of dilution adjuvant.
1. A method for treating a nitric aqueous liquid effluent containing nitrates of metals or metalloids, comprising the steps of:
adding a dilution adjuvant to the effluent; and
a step for calcination of the effluent in order to convert the nitrates of metals or metalloids into oxides of said metals or metalloids, at least one compound selected from the nitrates of metals or metalloids and the other compounds of the effluent leading upon calcination to a tacky oxide,
wherein the dilution adjuvant comprises at least one nitrate of metal or metalloid leading upon calcination to a non-tacky oxide, the dilution adjuvant being added to the effluent prior to the calcination step in order to give a mixture of effluent and dilution adjuvant, in which the mixture meets the two following inequations (1) (2):
mass
of
sodium
nitrate
of
the
mixture
expressed
in
terms
of
oxide
Na
2
O
mass
of
all
the
compounds
of
the
mixture
expressed
in
terms
of
oxides
≤
0.3
(
1
)
mass
of
all
the
compounds
of
the
mixture
leading
upon
their
calcination
to
tacky
oxides
,
expressed
in
terms
of
oxides
mass
of
all
the
compounds
of
the
mixture
expressed
in
terms
of
oxides
≤
0.35
.
(
2
)
2. The method according to claim 1 , wherein the dilution adjuvant comprises aluminium nitrate and optionally at least one other nitrate selected from iron nitrate and rare earth nitrates.
3. The method according to claim 2 , wherein the dilution adjuvant comprises aluminium nitrate and optionally at least one other nitrate selected from iron nitrate, lanthanum nitrate, cerium nitrate, praseodymium nitrate and neodymium nitrate.
4. The method according to claim 1 , wherein said at least one compound leading upon calcination to one or more tacky oxide(s), is (are) selected from sodium nitrate, phosphomolybdic acid, boron nitrate and mixtures thereof.
5. The method according to claim 1 , wherein the content of nitrate(s) and of other compound(s) leading upon calcination to a tacky oxide, expressed as oxide, based on the total mass of the salts contained in the effluent, expressed as oxide, is greater than 35% by mass.
6. The method according to claim 5 , wherein the effluent has a sodium nitrate content expressed as sodium oxide Na 2 O, based on the total mass of the salts contained in the effluent, expressed as oxide, greater than 30% by mass.
7. The method according to claim 1 , wherein the calcination step is carried out at a temperature leading to a calcinate temperature at the outlet of an oven of about 400° C.
8. The method according to claim 1 , wherein the calcination is carried out in a heated rotating tube.
9. The method according to claim 1 , wherein after the calcination step, a vitrification step is carried out wherein the calcinate from the calcination step is melted with a glass frit whereby a confinement, containment glass is obtained.
10. The method according to claim 1 , wherein the dilution adjuvant consists essentially of at least one nitrate of metal or metalloid leading upon calcination to a non-tacky oxide.