Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1997-05-20
1999-01-12
Wyse, Thomas G.
Liquid purification or separation
Processes
Ion exchange or selective sorption
210688, 210912, 502 68, 502 84, 502407, 502411, 502516, C02F 162, B01J 2016
Patent
active
058582428
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an agent for the uptake of heavy metal cations contained in a medium, especially an aqueous effluent.
The invention also relates to an agent for stabilizing the said heavy metal cations.
The incineration of waste material is subject to a quite strict statutory policy.
Legislation in the field of discharges of heavy metals into the environment is, in particular, in full development. The waters from washing (or purification) of the fumes of stations for the incineration of waste material, especially domestic refuse or industrial waste, of industrial effluents of the sulphur-containing effluent type, for example waste sulphuric acids, are media containing heavy metal cations. Similarly, some soils are polluted by the presence of such cations.
Thus, in the field of waters from the washing of the fumes from stations for the incineration of waste material, for example of domestic refuse, a conventional process for the removal of heavy metal cations consists of a basic precipitation carried out using lime, assisted by a finishing treatment using a sulphur-based precipitating agent; the decantation/separation step which follows is generally improved by the incorporation of a flocculant.
However, this process has a certain number of drawbacks.
In particular, a very large volume of sludge is generated by the precipitation using lime; after filtration and compaction in cake form, this sludge must currently be placed in specific dumping grounds.
Furthermore, the use of organic materials, such as the sulphur-based precipitating agent and the flocculant, which are at least partly found in the cake, are harmful to the placing in dumping grounds (degradation with formation of reducing gases over time).
Finally, the sludge composition obtained may be difficult to stabilize (or to immobilize) by the current techniques. The presence of a large amount of calcium in this sludge may greatly inhibit the stabilization (or immobilization) operations such as, for example, the stabilization by vitrification. However, future regulations relating to the storage of final special waste material require the cake to be stabilized (or immobilized), before admission onto the storage site, in order very substantially to reduce the leaching of this type of waste material.
The object of the present invention is especially to provide a means for allowing the efficient uptake (or removal) of heavy metal cations which does not have the aforementioned drawbacks.
To this end, the present invention proposes a novel agent for the uptake (or removal) of heavy metal cations present in a medium, the said agent being an inorganic product comprising at least one compound of the silicate or aluminosilicate type, at least one compound of the carbonate type and, preferably, at least one support, preferably a clay.
The invention also relates to an agent for stabilizing (or immobilizing) the said heavy metal cations comprising the said uptake agent.
The Applicant has found, surprisingly, that the use of an agent for the uptake of heavy metal cations as defined above allowed very efficient removal of the said cations from the media containing them and, advantageously, an improvement of the sludge obtained/supernatant liquid separation and decantation, an improvement of the ability of this sludge to stabilize, that in to say an improvement of the ability of the latter to resist leaching, and a marked decrease in the residual calcium content of the precipitate relative to that which is obtained with the conventional process described above.
Thus, one of the subjects of the invention is an agent for the uptake (or removal) of heavy metal cations contained in a medium, characterized in that the said agent comprises: below as compound A; and B.
The term heavy metal cations refers in particular to the metal cations with a valency greater than or equal to 2, preferably equal to 2, and especially those chosen from antimony, arsenic, bismuth, cadmium, chromium, cobalt, copper, tin, manganese, molybdenum, nickel, gold, lead, thallium, tun
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Chane-Ching Jean-Yves
Mottot Yves
Carleton Katherine L.
Rhone-Poulenc Chimie
Wyse Thomas G.
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