Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1997-05-05
1999-03-23
Wyse, Thomas G.
Liquid purification or separation
Processes
Ion exchange or selective sorption
210688, 210266, 210268, 210912, B01J 4710, C25D 2122
Patent
active
058854622
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the problem posed by the treatment of aqueous solutions laden with heavy metals, among others of industrial aqueous effluent discharges.
PRIOR ART
It has been pointed out that when superabsorbent acrylic polymers (SAP) for water and aqueous solutions, in particular polyacrylic acids, are placed in contact with a solution containing polyvalent metal ions, they initially swell in considerable proportions and then, having bound the polyvalent ions, they discharge a proportion of their swelling water. This behaviour has been applied to the purification of aqueous effluents before their discharge (see, for example, French Patent Application No. 93 06711). The phenomenon of swelling is a factor in improving the kinetics of the absorption of the ions on the polymer; however, it introduces the disadvantage of a considerable change in the volume of the absorbent bed, and this makes its use impracticable in a stationary bed column.
A consequence linked with these phenomena is the change in density of the particles of superabsorbent in the course of the absorption-swelling-deflation mechanism. The density of each particle drops first of all as a result of its considerable swelling by the aqueous solution. Thus, in the case of a polyacrylic superabsorbent with 25% in acrylic form and 75% in sodium acrylate form, this density changes from approximately 1.6 in the case of the dry particle to a value close to 1 in the case of the swollen particle, the composition of which is then, very approximately: polyacrylate 1 to 5% (by weight), water 90-95%, and then this density rises again as a result of the expulsion of a large proportion of the water and of the trapping of the heavy ions. Depending on the ion trapped, this density then lies between 1.1 and 1.5 g/cm.sup.3. These phenomena used to be treated as a curiosity; in any event, they had never found any application until now.
OUTLINE OF THE INVENTION
The present invention is based on the original idea that, if a particulate superabsorbent is suspended in a vertical vein of a solution of polyvalent ions which is propelled with an upward motion such that the particles in their state of maximum swelling are in a state of stationary dynamic regime, that is to say that they do not settle, nor are they entrained in the liquid vein, then all the particles which will have been laden with heavy ions will take part in settling and will be recoverable at the bottom of the column. The invention thus consists of a process for lowering the content of polyvalent cations in aqueous solutions by adsorption of the said heavy cations onto a superabsorbent polymer, carried out in a column fed at the top with a superabsorbent and at its bottom with the aqueous solution to be extracted, and drained at the top of the purified solution and at the bottom of the enriched superabsorbent, characterized in that the aqueous solution travels in the body of the column with an upward motion the speed of which is lower than the speed of settling of the said superabsorbent when it is laden with polyvalent cation ions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a countercurrent column for the treatment of aqueous solutions laden with heavy metals.
FIG. 2 describes the series of steps involved in the countercurrent rinsing bath of the present invention.
SUMMARY DESCRIPTION OF THE DRAWINGS
The process is implemented in a column the diagram of which is given in FIG. 1. This comprises a cylindrical body 1 mounted on a column bottom 2, supporting a widening 3 which opens onto a circulation circuit 4 looped back to the bottom of the column and driven by a pump 5. The bottom of the column is extended by a cone or else a tube 10 approximately 1.5 litres in volume. The whole dead volume of the plant is first of all filled with solution to be purified via the entry (L1). In a regime state, the system operates as follows. The dry or wet SAP is introduced continuously at the level (S1) via a plunging funnel 6, from a hopper 7. The liquid to be purifie
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Biver Claudine
Cuer Jean-Pierre
Delmas Francois
Garcia Francois
Elf Atochem S.A.
Wyse Thomas G.
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