FR2666591A1 - Process and device for selective recovery of silver ions in solution, eluent compositions for recovery and use of the composition - Google Patents

Abstract

- Recovery of industrial products. - Process for the recovery of silver ions, characterised in that it consists: in passing, in at least one passage, the solution containing silver ions over an inorganic ion exchanger compound which has a monovalent acidic function, with a view to selectively trapping the silver ions on the ion exchanger, in recovering the trapped silver ions by passing over the ion exchanged compound an eluent solution with a high affinity for silver ions, with a view to recovering the silver ions in the eluent solution, in subjecting the eluent solution thus recovered to electrolysis, to separate off the silver ions. - Recovery of silver ions.

Description

METHOD AND DEVICE FOR SELECTIVE RECOVERY OF SILVER IONS
SOLUTION, ELUTE RECOVERY COMPOSITION AND USE OF A
Such a composition
The present invention relates to the general technical field of processes, devices and compositions for the recovery of compounds or products intervening at any stage in an industrial process or present, in any form, in expired industrial products or which do not meet requirements and minimum manufacturing tolerances.

 The invention relates, more particularly, to the specific technical field of the recovery of silver ions used or present at various stages in fields, such as electricity, welding, electroplating, catalysts, electronics, industrial effluents. and Industrial washing water for example.

Silver is a metal used very frequently on an industrial level and it is involved, in particular in the manufacture of photographic films and films, in the production of energy storage units, such as batteries and accumulators, where it is associated with zinc, cadmium, mercury. The silver metal is also used in the form of Ag-Au alloy, Ag-Pd,
Ag-Cu, Ag-W for making electrical contacts and it is also found as a component in anti-corrosion surface coatings. Silver is also used in many industrial processes such as, for example, stamping.

 Whatever the manufacturing sector concerned, the recovery of silver metal is of significant economic interest, due to the cost of this metal and the significant tonnages used annually. Furthermore, it must also be considered that the silver ion is highly toxic for all forms of life and, in particular, for microorganisms responsible for cleaning up water courses.

 In view of current legislative developments, the threshold for the concentration of silver in industrial waste should be regulated and set at a relatively low threshold.

 It is therefore of primary importance to take care, both for economic reasons and for reasons of environmental pollution, to recover all or part of the silver ions present in bodies or in solution in the form of industrial waste and residues.

 The recovery of silver at the end of an industrial process, for example in metallurgy, electroplating or electrorefining, can be carried out by solubilization of the silver in an acid medium, for example using nitric acid. and sulfuric acid or, more rarely, phosphoric acid.

 It turns out that the acid solutions obtained contain many other metals, such as copper, cadmium, zinc or lead, for example, and, consequently, the recovery of the silver ion, if it can be obtained, requires a significant financial cost.

 Once the solubilization has been carried out, the selective recovery of the silver is carried out, depending on the case, by electrolysis, by ion exchange resins or, finally, by metal exchanges.

 The use of ion exchange resins, capable of fixing silver from aqueous solutions, is an interesting theoretical solution in terms of its efficiency, but its implementation proves to be extremely delicate, since the product obtained is very stable and that the recovery of silver can only be done quantitatively by destruction of the resin. Such an operation, apart from its complexity, is, of course, of a cost unrelated to the amounts of money recovered and such a technique has moreover, until now, for this reason, been neglected, or even abandoned.

The recovery of the silver ion by the method of
Metallic exchange, by carburizing with more reducing metals, such as copper, iron, zinc or lead, gives results considered satisfactory from a technical point of view. It is difficult to recover the silver present in solutions containing less than 5 ppm with this technique.

Such a technique proves to be insufficient, in particular in the recovery of the silver contained in industrial wastes for which the silver contents are very low and below this limit.

 The object of the invention is therefore to propose a method for recovering silver ions in solution which does not have the drawbacks of the previous methods, which are highly selective with respect to silver ions, whatever the silver content and acidity of the solution containing silver ions, of a simple and fast implementation and a low cost.

 Another object of the invention is to provide a method in which the support for fixing the silver ions can be regenerated indefinitely and which can be used to recover silver ions from solutions with a very low silver content.

 The invention also consists in proposing an eluting solution capable of recovering silver ions from a fixing support in order to regenerate it.

 Another object of the invention consists in proposing an eluting recovery solution which is indefinitely regenerable.

 The invention also relates to a device for implementing the recovery method which is particularly simple and safe in design and which makes it possible to rapidly fix the silver ions on the fixing support and recover them.

 Another object of the invention is to propose a recovery device allowing improved recovery of silver ions by electrolysis at the end of the process steps.

The aims assigned to the invention are achieved by a process for recovering silver ions in solution, characterized in that it consists:
- to pass, in at least one pass, the
solution containing silver ions on a compound
inorganic ion exchanger having a
monovalent acid function, in order to trap,
selectively, silver ions on the exchanger
ions,
- to recover trapped silver ions by making
pass, over the ion exchange compound, a
eluting solution hungry for silver ions, in sight
to recover the silver ions in the solution
elective,
- submit your elective solution to electrolysis
thus recovered to separate the silver ions.

 The aims assigned to the invention are also achieved by virtue of an eluting composition for the selective recovery of silver ions in solution, characterized in that it comprises, as active principle, a thiosulfate solution in a proportion of 100 to 500 g / liter of solution and, preferably, around 200 g / liter, either a hydrochloric acid solution at a rate of at least 2 M / liter, or a sulfuric acid solution at a rate of at least 18 M /liter.

The aims assigned to the invention are finally achieved by means of a device for implementing the method according to the invention, characterized in that it comprises
- a reaction chamber, provided with means for
filtering and intended to contain the compound
inorganic ion exchanger,
- a set of separate pipes, connected to
The reaction chamber, comprising at least one
solution supply line to
silver, at least one pipeline
of eluting solution, at least one
channeling a rinse solution and
minus one evacuation pipe connected to
an electrolysis unit,
- a means of pumping and circulating
solutions circulating in the enclosure and
tubing, said means being connected to the tubing
and at the enclosure.

 The invention also relates to the use of antimony compounds as selective trapping products of Ag ions in solution, as well as the use of compositions based on thiosulfate, hydrochloric or sulfuric acid as eluting composition of recovery of Ag ions trapped by an antimony product.

 Various other characteristics will emerge from the description given below with reference to the appended drawings which show, by way of nonlimiting examples, embodiments of the object of the invention.

 Fig. 1 shows a simplified schematic sectional view of a recovery device according to the invention.

Fig 2 shows, in a perspective view, an embodiment of a reaction chamber according to
The invention.

 The fg. 3, 4 and 5 show the different possibilities of supplying the enclosure according to the invention.

The principle on which the silver recovery process is based is based on the significant affinity that the silver cation has for certain inorganic ion exchangers of acidic nature, the crystal structure of which is based on a three-dimensional sequence of M06 octahedra. where the radical M represents one or more strongly electronegative cations. The three-dimensional sequence of octahedra provides cavities which communicate with each other and which allow silver ions to move quickly through them. The inorganic ion-exchange compound has, moreover, one acidic hydrogen per unit of formula which, in solution, is exchanged with monovalent silver ions to effect the fixing, on the exchanger compound, of silver ions. than
The inorganic ion exchanger generally constitutes a solid acid.

In general and in the preferred case, the radical M consists of antimony Sb and the solid ion-exchange compound therefore consists of a mineral ion exchanger based on antimonic acid. Several types and phases of antimonic acid may be suitable for carrying out the absorption of silver ions and, in particular, antimonic acid HSbO3 with pyrochlore structure and antimonic acid HSbO3 with cubic structure I (structural type KSbO3 cubic), the latter having, however, an exchange capacity approximately half as large as that of
Antimonic acid pyrochlore.

Other antimony phases, likely to absorb
Ionic silver, are possible and, in particular, the phase
HSbTeO6 pyrochlore in which half the antimony is replaced by tellurium.

The general principle of the ion exchange between acid hydrogens and silver ions can be summarized as follows
H + n (MO6) + nAg + Ag n (M06) + nH
The radical M therefore represents one or more strongly electronegative cations and thus includes, in particular, at least one Sb antimony atom associated or not with tellurium or potassium.

n varies from 1 to 2.

Advantageously, the pyrochlore HSbO3 phase is obtained, either by a precipitation and annealing method from a KSb (OH) 6-NaCL mixture or by hydrolysis of SbCL5 or by exchange of
KSb (OH) 6 on an ion exchange resin. These preparation methods lead to the obtaining of an antimonic acid in solid phase, of powdery structure and of average particle size varying from 1 micrometer to 100 micrometers, depending on the method of obtaining.

The silver recovery process according to the invention therefore consists, firstly, in synthesizing an inorganic ion exchange compound consisting of a powder of compound
HMO (with n = 1 or 2) of average particle size varying from 1 micrometer to 100 micrometers and consisting of an antimonic acid HSbO3 with a pyrochlore or cubic I structure.

 The next step consists in passing, in at least one pass, the solution containing the silver ions over the inorganic ion exchange compound thus created, in order to ensure the trapping of the silver ions by the inorganic compound and exchange between the hydrogens. acids and monovalent silver ions.

 Several passes of the solution containing the silver ions can be carried out until the powder is completely saturated. This saturation can be appreciated by highlighting, after passing over the powder, the residual silver in the solution, the concentration of silver ions increasing, in fact, suddenly after passing over the powder When the storage capacity of the powder is exceeded. This demonstration can take place by precipitation with hydrochloric acid and formation of a silver chloride.

 The next step in the process then consists in causing a reverse exchange reaction to recover the silver ions trapped by the cation exchanger, in order to carry out the desorption of the silver ions.

 This selective recovery phase is carried out by passing over the cation exchanger a silver-hungry eluting solution comprising, as active principle, a thiosulfate solution and, for example, sodium thiosulfate at a rate of 100 to 500 g / liter of solution and preferably around 200 g / liter. It is found, in fact, that below 200 g / liter the desorption capacity of the solution decreases, while beyond 200 g / liter the risk of decomposition of the solution can occur.

 It has been found that, in order to obtain as complete and perfect as possible desorption of the silver ions by the eluting solution based on thiosulfate, it was preferable, before the passage of the eluting solution, to rinse the powder to ensure good stability of the eluting solution. The rinsing phase is intended to stabilize the pH of the cation exchanger in a range between 4 and 8, in order to avoid decomposition of the thiosulfate molecules into sulfide and thus make the solution obtained irreversibly unsuitable for electrolysis.

Advantageously, this rinsing phase can be carried out by passing an aqueous solution, until the pH of the washing water obtained stabilizes, for example, in the vicinity of neutrality. Rinsing can be carried out with pure water or with water already containing a weak base (sodium acetate, sodium hydrogencarbonate) to increase the effectiveness of rinsing.
It also turns out to be particularly advantageous to incorporate, in the eluting composition based on thiosulfate, at least one acid and one weak base, at a rate of 50 to 100 g / liter, with a view to buffering the composition to maintain it. at a pH between 5 and 6. In a nonlimiting manner, it is thus possible to add sodium sulfite, sodium acetate and boric acid, for example. These additives have the particularity of not reacting with silver and, also, of not disturbing the electrolysis thereof.

 Obviously, other thiosulfate salts of formula S203 can be used, insofar as they do not disturb the electrolysis, such as ammonium or potassium thiosulfate and, in general, all the alkali or alkaline earth metals.

After the passage of the eluting recovery solution over
The cation exchanger, it also turns out to be necessary to rinse the cation exchanger to reduce the thiosulfate residues. The latter, in fact, would risk decomposing, leading to a certain quantity of sulphide residues which have a tendency to transformation into silver sulphide and colloidal sulfur and cause, in the long run, more or less complete fouling of L cation exchanger and hence of the antimonic acid employed. This second rinsing operation can be carried out using simple washing water.

 This silver ion desorption step can be carried out in a few hours or even be significantly shortened, depending on the geometry of the exchanger used.

 The silver-loaded thiosulfate solution, for example at a rate of 10 to 20 g of Ag / liter, is then electrolyzed using a three-electrode installation, thus allowing precise control of the electrode potentials. . The recovered silver is deposited at the cathode in the form of metal powder, easily detachable, and can be recovered, for example, in a filter. It is also possible to obtain an adherent deposit in the form of solid electrodes depending on the intensity of the current chosen. The eluting thiosulfate solution is regenerated and can therefore be recovered for a new recovery cycle.

 Figs. 1 and 2 show an exemplary embodiment of a heavy ion recovery device particularly suitable for the recovery of silver ions according to the method of the invention.

 The device for implementing the method comprises a reaction enclosure 1, of any suitable shape and, preferably, comprising a substantially cylindrical main body fixed to a support frame 2 by any suitable means and, for example, by means of arm 3, so that the reaction chamber is disposed substantially vertically, the main axis of the cylindrical body also being substantially vertical. The support frame 2 may consist of a base 4 and one or more panels surrounding, partially or completely, the entire device and comprising, in particular, a rear panel 5 supporting the arms 3 and side panels 6 and a front panel 7. Advantageously, the front panel 7 can be made of plexiglass and extend over the total height of the installation, so as to constitute a panel protecting against acid jets, in the event of a leak in the device. .

The reaction chamber 1 proper can be of various shapes and, in the preferred embodiment shown in FIGS. 1 and 2, the cylindrical main body comprises, at its ends, an upper cap 11 and a lower cap 12, of all appropriate shapes, for example conical or spherical, hermetically mounted on the main body 1 by
The intermediary of sealing means of the Vitton seal type for example. The caps 11 and 12 are preferably made of
Teflon and fitted with glass tubing to resist acid corrosion.

 The interior of Enclosure 1, which may for example consist of a glass reactor, with a useful storage volume varying, depending on its industrial application, from a few kilos of ion exchange powder to several hundred of kilos of powder, is equipped with two filters 13, 14 arranged, respectively, in the lower and upper part of the enclosure and intended to limit, with the walls of said enclosure, the useful storage volume of the exchange powder of ions 15. The mesh of filters 13 and 14 is, of course, adapted to the average particle size of the ion exchange powders used.

 The upper cap it is surmounted by a stop valve 16, itself connected to a purge unit 17.

The upper cap It is also connected, by
The intermediary of an intermediate pipe 18, to a pumping and circulation means 21 responsible for supplying the energy necessary for supplying the reaction vessel 1 with solution. The pumping means 21 comprises, by example, a peristaltic pump 22 with variable speed and reversible and adjustable flow.

 As a variant, it is possible to use a simple tank provided, as a filtering means, with a strainer arranged in relation to the means for supplying the tank.

 The pumping and circulating means 21 is also connected, by a transfer pipe 23, to a first two-way valve 24 connected, by a pipe 25, to a supply source of solution to be treated 26, namely, the solution to be silver. The first two-way valve 24 is, moreover, connected, via a relay line 27, to a second two-way valve 28 connected, individually, by two separate lines 29 and 30, respectively, to a source of supply of eluting solution 31 based on thiosulfate and to a source of rinsing solution 32.

In a preferred embodiment of a device according to the invention, the intermediate pipe 18 comprises an end portion opening out at the bottom of
The reaction vessel 1, so that the solution arriving in
The reaction chamber 1 crosses the latter from bottom to top, thus ensuring mechanical agitation of the ion exchange powder and leading to fluidization, at least partially, of the powder improving the exchange reaction. Such an arrangement can be made by means of a pipe 18a passing through the lower cap 12 and opening out under the filter 13 or by an internal pipe, not shown in the figures, extending the pipe 18 inside the enclosure. to open, also, under the filter 13. Obviously, any other stirring means can be used and, in particular, mechanical stirring means ensuring, for example, a vibration or a stirring of the whole enclosure or, simply, its content.

 The device is completed by an evacuation pipe 33 connected, for example, to the lower cover 12.

 In all cases, the supply lines 25, 29 and 30 are separated, so that the silver solution to be treated can never be mixed with the eluting solution.

 The device for implementing the method is completed by an electrolysis unit 35 connected to the evacuation pipe 33 and constituted, for example, by a circular tank stirred by a magnetic bar. The working electrode (cathode) is composed of a silver metal plate and two graphite plates placed on either side of the cathode act as an anode. The power supply operates as an intensiostat, but a calomel reference electrode is advantageously placed in the vicinity of the cathode plate, in order to protect the electrolyte from excessively high potentials by stopping the generator.

 After having placed inside the reaction enclosure 1, between the two filters 13 and 14, an inorganic ion-exchange compound, in the form, for example, of antimonic acid with pyrochlore structure, we send to L using the peristaltic pump 22, the acid solution charged with the silver to be recovered which is withdrawn from the source 26. The valve 24 is in the position shown in fig 3, which excludes any mixing with the other two feed sources. The solution to be de-silvered passes through the powder of the reaction chamber from bottom to top, lifting the powder and thus allowing the chamber to operate in a fluidized bed. The contact time, between the silver solution and the ion exchange powder, in this case the antimonic acid, is chosen according to the agitation of the powder, since it is observed that, the more the the greater the agitation, the faster the absorption reaction. The absorption reaction is carried out moreover, generally, over a period of less than 10 minutes and it has been found that there was no maximum contact time, the antimonic acid proving to remain stable in the presence of corrosive silver solutions to be treated, whatever the contact time.

 The passage of the silver solution over the ion exchange powder can be done in one or more passes and the average nominal flow rate used can be close to 1 liter / min.

The supply of solution to be de-silvered is then stopped when the ion-exchange powder has reached its maximum storage capacity, which is revealed by analysis of the solution leaving the reaction chamber 1 via line 33 with a solution based on hydrochloric acid. There is then carried out a reverse exchange reaction for the selective recovery of the trapped silver ions, taking care first of all to rinse the ion exchange powder by passing rinsing water from source 32. For this rinsing phase, the two-way valves 24 and 28 occupy
The positions shown in fig. 4. The rinsing phases are continued until the pH of the washing water stabilizes around neutral.

 The recovery of the silver ions can then begin, by sending the eluting solution based on thiosulfate coming from the source 31, via the line 29. The two-way valves 24 and 28 then occupy the positions shown in FIG. 5. The passage of the thiosulfate solution over the ion exchange powder leads to a displacement of the silver ions and to their solubilization in the thiosulfate solution. It turns out that the contact time, necessary between the ion exchange powder and the eluting solution, must be extended over a period of at least one hour, concomitantly with a phase of agitation of the ion exchange powder. .

 The reaction chamber 1 is then emptied through line 33 and the eluting solution, charged with silver ions, is directed to an electrolysis unit in which the metal silver is recovered at the cathode in the form of metal powders.

Simultaneously, the eluting solution is thus regenerated and can be reused in subsequent desorption cycles.

 The ion-exchange compound thus regenerated is freed, by rinsing with water, of all traces of eluting solution and can thus be used for a new absorption cycle.

EXAMPLE 1: Recovery of silver ions from a solution
highly acidic industrial effluents
An important source of silver losses in the electroplating workshops (electroplating from silver cyanide salts) comes from pickling solutions which make it possible to remove the silver plating on parts having defects and cathode hooks which support the parts to be treated during the ElectroLyse. These very acidic solutions, of the sulfonitric type (H2SO4: 60%) are saturated at 10-30 g of silver per liter.

 A volume of 2.5 l of sulfonitric solution, containing 11 g of silver per liter, is filtered through the reaction chamber forming a filter cartridge containing 200 g of powder of antimonic acid HSbO3 pyrochlore.

 After a passage lasting two hours, the silver remaining in the solution is dosed using a 0.1 M hydrochloric acid solution by precipitation of AgCl.

- The solution initially contains 27.5 g of dissolved silver.

- The solution after treatment still contains 2.5 g.

- The cartridge therefore absorbed 25 g of silver and the yield of
The absorption is 90%.

 After absorption, the cartridge is carefully rinsed with water until a neutral pH.

 A volume of three liters of eluting solution based on sodium thiosulfate was used to desorb the silver from the cartridge.

Composition for one liter of aqueous solution - Sodium thiosulfate ............................. 200 g - Sodium bisulfite .... ........................... 50 g - Sodium acetate = 50 g
The flow rate in the cartridge is adjusted to 0.5 l / hour.

After the first liter of solution has passed through the cartridge, the silver is dosed with a solution of sodium sulfide by precipitation of Ag2S.

- 1st liter ........................................ 10.5 g Ag - 2nd liter ........................................ 8 g Ag - 3rd liter ........................................ 5 g Ag - Yield of desorption ........................ 94%
EXAMPLE 2 Selective recovery of silver ions from
weakly acidic industrial effluents rich in
copper and other metals (tar and precious metals).

This example concerns Effluent solutions from
The refining of Silver from very impure silver metallic anodes. The electrorefining process uses these anodes which are dissolved by electrolysis in a bath of dilute nitric acid.

The silver is deposited at the cathode, the other metals remain in the electrolyte.

The losses of silver for this electrolysis are on several levels 1 - Used electrolytes contain on average several
hundreds of grams of silver per liter. These are baths
very rich in copper. This may, therefore, be
deposit on the cathode with Silver. These solutions are
titrated to 20-35 g Ag / l.

2 - During the anodic attack by electrolysis, grains
metallic decant at the bottom of the tank. These grains are composed
of precious metals which are not dissolved by electrolysis at
because of their high ionization potential and grains
money which, no longer in touch with the potential
anodic, remain insoluble. This set of solid residues,
called anodic sludge, is attacked with nitric acid to
solubilize the money. These solutions are titrated to 200-250 g
money per liter.

 A volume of 300 ml of a nitric solution loaded with 230 g of Ag / l is treated with 500 g of HSbO3, xH2O pyrochlore powder. The duration of the absorption corresponds to four passages of the same solution of 5 min each through the cartridge.

- The solution contains, initially, 69 g of Ag.

- The solution after treatment contains <0.1 g of Ag (dosage with
0.1 M HCl solution).

- The cartridge therefore absorbed 69 g of Ag and the yield of
The absorption is 100%.

 A volume of three liters of eluting solution is used to desorb the silver from the ion exchange cartridge.

Composition for one liter of solution - Sodium thiosulfate ............................. 300 g - Sodium acetate ..... ............................ 100 g - Sodium sulphite ................ ................. 50 g - Boric acid ............................ ......... 50 g
The exchanger cartridge operates in a closed circuit for two hours. The solution takes on an orange color due to the presence of silver thiosulfate complexes.

First desorption
The eluting solution contains 38 g of Ag at the end of desorption (assay with Na2S by precipitation of Ag2S). The solution at the end of the electrolysis contains <0.1 g of Ag (electrolysis operating in 0.5 A intensiostat, duration of 24 h).

Second desorption
The eluting solution contains, at the end of desorption, 27 g of Ag. The solution at the end of the electrolysis contains <0.1 g of Ag (Electrolysis operating in 0.5 A intensiostat, duration of 12 h).

- Desorption efficiency ........................... 94%
EXAMPLE 3:
The starting solution contains five times more cupric ions than silver ions - AgNO3 (2.10 mole) ........................... .... 3.4 g - Cu (NO3) 2, 2H2O (10 1 mole) dissolved in 100 cm3
distilled water ................................... 24.2 g
This solution is stirred for 15 min with 39.5 g of
HSbO3, xH2O pyrochlore (0.2 M).

 The powder is extracted from the solution by decantation, 3 rinsed and introduced into 50 cmJ of 37% HCL to desorb the silver in the form of AgCL. The duration of the agitation is only 5 minutes.

The AGACE pyrochlore and precipitate unit is extracted from the solution by decantation, rinsed to a neutral pH, then introduced into a thiosulfate solution containing - Sodium thiosulfate ................ ............. 200 g - Sodium acetate ............................... .. 50 g 3 - Sodium bisulphite in 500 cm of distilled water - 20 g
After stirring the suspension obtained for 15 min, a sample of 10 cm 3 of the solution was taken, which was introduced into a test tube containing ammonia. There was no appearance of the blue ammonia complex characteristic of copper.

 The solution was electrolysed and the mass of metallic silver recovered at the cathode is 1.6 g of Ag. This example highlights the good selectivity of Silver absorption from the pyrochlore HSbO3 phase, even in a medium rich in copper and, above all, it shows that hydrochloric acid is an effective eluting solution.

EXAMPLE 4: 3
A 50 cm solution of distilled water containing 100 ppm of silver is prepared and stirred for 15 min with 0.2 g (10 2 mole) of HSbO3 pyrochlore. Then the solution is filtered and analyzed by spectroscopy.

 A concentration less than 50 ppb is measured. The concentration of silver, after treatment with pyrochlore, is therefore 2,000 times lower.

EXAMPLE 5:
3
A very acidic 50 cm sulfonitric solution from an industrial process and containing 10 g of Ag / l is filtered through 0.2 g of HSbO3 pyrochlore.

 After analysis, a silver content of 19 ppm is found.

After treatment, the silver concentration is therefore 500 times lower.

EXAMPLE 6
3
Absorption in 50 cm solutions of very dilute distilled water of silver in the presence of 0.2 g of absorbent
TITLE OF SOLUTIONS
BEFORE ABSORPTION AFTER ABSORPTION. first solution ... 100 ppm ...................... 0.08 ppm second solution ... 10 ppm .......... .......... 0.05 ppm. third solution. - 1 ppm .................... <0.03 ppm
The process according to the invention thus allows the recovery of silver ions from neutral or strongly acidic solutions, even when very low concentrations of silver ions are present in industrial or residual effluents or solutions. It turns out that antimony powders used are unassailable by acidic or strongly acidic solutions and that the absorption kinetics of silver, by the ion exchange powders according to the invention, are extremely rapid. Furthermore, the eluting solution based on thiosulfate is entirely regenerable, since it suffices to recover it after the electrolysis phase, which leads to a particularly economical process.

EXAMPLE 7 Use of the antimony compound HSbTeO6 pyrochLore.

 The starting solution contains five times more silver ions than sites available in L'absorbent.

- AgNO3 (5.10- 3 mole) .............................. 0.54 g of Ag
dissolved in 50 cm - HSbTeO6 pyrochlore (10 mole) ................... 0.364 g
This solution is stirred for 15 minutes.

 The powder is extracted from the solution by decantation.

This solution is subsequently dosed with its remaining silver by weighing the precipitate of AgCL after having introduced 10 ml of a dilute solution of 0.1 M hydrochloric acid.

It remains in the solution ........................ 0.488 g of Ag It has been absorbed ............ ..................... 0.052 g Ag
The absorption capacity of the HSbTeO6 pyrochlore powder is 140 g of Ag / kg of absorbent.

EXAMPLE 8 Use of the cubic HSbO3 antimony compound I.

 The starting solution contains five times more silver ions than sites available in the absorbent.

- AgNO3 (5.10 mole) .............................. 0.54 g of Ag dissolved in 50 cm of water distilled - cubic HSbO3 I (10- 3 mol) ....................... 0.187 g
This solution is stirred for 15 min.

 The powder is extracted from the solution by decantation.

This solution is subsequently dosed with its remaining silver by weighing the precipitate of AgCL after having introduced 10 ml of a dilute solution of 0.1 M hydrochloric acid.

It remains in the solution ........................ 0.484 g of AG IL has been absorbed ............ ..................... 0.056 g Ag
The absorption capacity of the cubic HSbO3 powder I is 300 g of Ag / kg of absorbent.

EXAMPLE 9 Use of the antimony compound HSbO pyrochlore.

3
The starting solution contains 10 -3 moles of the pyrochlore phase HSbO3 (0.198 g) and 2.10 -3 moles of AgNO3 (0.34 g) dissolved in 50 cm of distilled water are added thereto.

 This solution is stirred for approximately 15 minutes to effect the absorption or trapping of the silver by the antimony compound. The filling rate (percentage of acid sites replaced by silver ions) is 75 ta.

 The powder is then extracted from the solution, then brought into contact with 50 cm3 of a solution of H2SO4 at 18 moles / liter. The desorption of money is almost total, since we see that the filling rate is less than 5%.

 The invention is not limited to the examples described and shown, since various modifications can be made thereto without departing from its scope, as defined by the claims.

Claims (20)

CLAIMS:  1 - Method for recovering silver ions in solution, characterized in that it consists of:  - to pass, in at least one pass, the  solution containing silver ions on a compound  inorganic ion exchanger having a  monovalent acid function, in order to trap  selectively Silver ions on the exchanger  ions,  - to recover trapped silver ions by making  pass, over the ion exchange compound, a  eluting solution hungry for silver ions, in sight  to recover the silver ions in the solution  elective,  - subjecting the eluting solution to electrolysis  thus recovered, to separate the silver ions.  2 - Process according to claim 1, characterized in that it consists in using, as an inorganic ion exchange compound, a solid compound, preferably powdery, having a crystal structure with three-dimensional octahedral structure, of formula H2Sb2O6 or HSbTeO6 pyrochlore.  3 - Process according to claim 2, characterized in that the compound is antimonic acid with pyrochlore or cubic structure I.  4 - Process according to claim 2, characterized in that the antimony can be replaced, for half, by tellurium to form a new acid HSbTeO6 pyrochlore.  5 - Method according to one of claims 1 to 4, characterized in that it consists in using an inorganic ion exchange compound, in powder form, with an average particle size varying from 1 pm to 100 pm.  6 - Method according to one of claims 2 to 5, characterized in that it consists in passing the solution containing the silver ions over the solid ion-exchange compound by subjecting the latter to stirring consisting, preferably, in fluidization to form a fluidized bed.  7 - Method according to one of claims 1 to 6, characterized in that it consists, after trapping the silver ions by the ion exchange compound, to provide a decantation phase, then a phase of rinsing the compound, in order to reduce the acidity of the compound.  8 - Process according to claim 7, characterized in that the rinsing phase consists in rinsing the compound using a pure aqueous solution or with the addition of a weak base, until the pH of the water of washing is between 4 and 8 and, preferably, close to neutral.  9 - Method according to one of claims 1 to 8, characterized in that the contact time of the eluting solution and the ion-exchange compound is at least 1 hour and is carried out concomitantly with stirring of said compound.  10 - Method according to one of claims 1 to 9, characterized in that the active principle of the eluting solution is based on buffered thiosulfate, hydrochloric acid or sulfuric acid.  it - Method according to one of claims 1 to 10, characterized in that, after the passage of the eluting solution, the regenerated ion-exchange compound is washed by rinsing, in particular, then subjected to the passage of at least one other solution containing silver ions according to the steps previously defined.  12 - Eluting composition for the recovery of silver ions trapped in an inorganic ion exchanger, characterized in that it comprises, as active principle, a solution based on thiosulfate at a rate of 100 to 500 g / liter of solution and preferably around 200 g / liter, either a solution of HCL at a rate of at least 2 M / liter, or a solution of H2SO4 at a rate of at least 18 M / liter.  13 - Composition according to Claim 12, characterized in that the thiosulfate-based solution is chosen from Sodium thiosulfate, ammonium thiosulfate and potassium thiosulfate.  14 - Composition according to claim 13, characterized in that The thiosulfate-based solution further comprises additional compounds including at least one acid and a weak base to buffer the composition and maintain the pH between 5 and 6.  15 - Composition according to claim 14, characterized in that the additional compounds are chosen from sodium sulfite, sodium acetate and boric acid and provided in an amount of 50 to 100 g / liter.  16 - Device for implementing the method according to one of claims 1 to 11, characterized in that it comprises  - a reaction chamber (1) provided with means for  filtering (13, 14) and intended to contain the  inorganic ion exchange compound (15),  - a set of separate pipes connected to  the reaction chamber (1), comprising at least  a solution supply line (25)  to de-silver (26), at least one pipe  supply (29) in eluting solution (31), at  minus a line (30) of a solution of  rinse (32) and at least one pipe  outlet (33) connected to a unit  electrolysis (35),  - a means of pumping and circulating  (21, 22) of the solutions circulating in the enclosure  (1) and The pipelines, said means being  connected to the pipes and the enclosure (1).  17 - Device according to claim 16, characterized in that the pumping and circulation means (21, 22) is connected to the reaction chamber (1) by a pipe (18, 18a) opening into the lower part of the enclosure (1), so as to circulate in the enclosure the solutions from bottom to top and to produce agitation of the ion-exchange compound.  18 - Device according to claim 17, characterized in that the supply pipes (25, 29, 30) comprise control valves (24, 28) with two parallel paths.  19 - Device according to one of claims 16 to 18, characterized in that the electrolysis unit (35) comprises an electrolysis tank connected to the evacuation pipe (323), said tank comprising a silver cathode metal, at least one graphite plate placed on either side of the cathode, as anodes, and a calomel reference electrode placed in the vicinity of the cathode.  20 - Use of an antimonic acid powder (HSbO3) with a pyrochlore or cubic structure (I) for the selective trapping of silver ions in solution.  21 - Use of an eluting composition according to one of claims 12 to 15 for the recovery of silver trapped in an inorganic ion exchanger.