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phorus stirred in water (see Table 3 and Table 4). The amount of these phosphorus com-
pounds has been calculated as mg/L phosphorus for a straightforward comparison of
values. From these experimental results the following conclusions can be derived:
P-red-AquaChem-06.doc - 14.01.00 Chemical Behaviour of
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Red Phosphorus in Water
BL Flame Retardants
Walz R, Beard A
" The reactions rates of red phosphorus with water are very slow. The overall conversion
rate has been found to be always in linear correlation with the amount of the starting
material as well as the stirring time of red phosphorus in water.
" By taking in account the reasonable stirring time of 24 h only 0.2 % of the starting ma-
terial reacts with water.
" The reaction speed of red phosphorus in water is very slow and probably will never
reach a steady state because the resulting oxo-acids are very well soluble in water.
" We were not able to detect any elemental phosphorus in water
Table 3: Reaction products after stirring 3 000 mg red phosphorus for 24 h in 1 liter of water
concentration fraction
calc. as P [mg/L]
hypophosphite 1.0 18 %
phosphite 2.1 39 %
phosphate 1.4 26 %
unknown compounds 0.9 17 %
total phosphorus compounds 5.4 100 %
= fraction of nominal concentration 0.18 %
(of 3 000 mg/L)
Table 4: Reaction products of 10 000 mg red phosphorus in 1 liter of water after 1 and 4
months
after 1 month after 4 months
concentration fraction concentration fraction
calc. as P [mg/L] calc. as P [mg/L]
hypophosphite 19 19 % 50 19 %
phosphite 38 39 % 105 39 %
phosphate 34 35 % 98 36 %
unknown compounds 7 7 % 17 6 %
total phosphorus compounds 98 100 % 270 100 %
= fraction of nominal concentration 0.98 % 2.7 %
(10 000 mg/L)
P-red-AquaChem-06.doc - 14.01.00 Chemical Behaviour of
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Red Phosphorus in Water
BL Flame Retardants
Walz R, Beard A
4.2.2 No release of white phosphorus from red phosphorus in water
Elemental phosphorus could not be detected in any of the aqueous red phosphorus suspen-
sions of the experiments in Table 3 and Table 4. The detection limit was 1 mg/L. To demon-
strate that the white phosphorus contained in the solid red phosphorus does not dissolve in
water (in contrast to pure white phosphorus which has a solubility of about 3 mg/L), the
following experiments were performed with a type red phosphorus containing the relatively
high concentration of 129 mg/kg white phosphorus:
a) 50 g of red phosphorus were extracted 3 times with 2.5 L of water for one hour. After
extraction the concentration of white phosphorus in the solid red phosphorus had only
slightly decreased to 122 mg/kg. This apparent reduction from the starting concentra-
tion is not significant, because it is within the range of the analytical error which
amounts to ± 5 mg/kg. Furthermore, no elemental phosphorus could be detected in the
water (limit of detection 1 mg/L).
b) 93 g of red phosphorus were extracted with 300 mL of water for three hours. The wa-
ter was subsequently extracted with carbon disulfide (CS2) and analysed for white
phosphorus no phosphorus could be detected at a limit of detection of 0.1 mg/L.
In summary, no elemental white phosphorus could be extracted from red phosphorus with
water. Therefore, for instance an ecotoxicologic assessment of red phosphorus in the
aquatic environment cannot be based on its content of white phosphorus but should be
based on seperate studies with red phosphorus.
If traces of white phosphorus are released from the red phosphorus, they probably quickly
react to phosphorus containing acids the same products that the red phosphorus itself
liberates. The source of these phosphorus containing acids be it white or red phosphorus
cannot be distinguished by chemical analysis, because the products themselves are identi-
cal and red phosphorus as a starting material is present in immense excess.
P-red-AquaChem-06.doc - 14.01.00 Chemical Behaviour of
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Red Phosphorus in Water
BL Flame Retardants
Walz R, Beard A
4.3 Reaction rate of red phosphorus with water
Figure 7 indicates that the concentration of obtained hydrolysis products from red phospho-
rus steadily increases with the amount of dispersed red phosphorus in water. However, the
reaction of red phosphorus with water is extremely slow. The average amount of reaction
products from 100 mg/L after 24 h calculated as phosphorus is about 0.7 %. This fraction
rises very slowly up to a maximum of 3.7 % of the nominal concentration of solid red phos-
phorus in water after 700 hours. In another experiment the soluble reaction compounds in-
creased only up to 2.7 % after 2 880 hours (4 months). These data show that red
phosphorus does not dissolve as such in water which renders the concept of a maximum
solubility unapplicable. Instead, a continuous but slow series of reaction occurs leading to
phosphorus containing acids. The amount of products formed increases with the available
amount of red phosphorus and time.
Fraction of soluble P-compounds versus
amount of red P
2.0
1.5
(least squares 2nd order polynome)
1.0
0.5
0.0
0 50 100 150 200 250
red P, nominal concentration of solid material [mg/L]
Figure 7: Concentration of phosphorus compounds (calculated as total phosphorus) in aqueous
solution versus the amount of added solid red phosphorus
P-red-AquaChem-06.doc - 14.01.00 Chemical Behaviour of
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Red Phosphorus in Water
total P in solution [mg/L ]
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