FR2677041A1 - Metal extraction process, device for its use, and its application, especially to the decontamination of effluents - Google Patents

Abstract

Process for extracting metals with the aid of a fungal biomass in which the fungal biomass is continuously placed in contact in a reactor with a liquid containing the said metals and a solid-liquid separation is then performed, a part of the biomass is removed continuously, at least 80 % of the removed part of the biomass being returned to the reactor, and device for use, and application to the decontamination of effluents.

Description

 The present invention relates to a metal extraction process, its implementation device, and its application, in particular to the depollution of effluents.

 Mining operations, metal processing units, metallurgical surface treatment industries produce large amounts of aqueous metalliferous waste. These effluents may contain a wide range of metal ions in varying concentrations, the toxicity of which generally requires treatment prior to their release into the environment.

These solutions are generally too concentrated to allow their rejection, but not rich enough to warrant treatment with conventional recovery channels. A typical example is represented in the mining industry by the treatment of dewatering, or runoff obtained at the output of sterile heaps or sub-marginal ores. Uranium mines commonly generate effluents of this type at metal concentrations of the order of a few ppm to a few tens of ppm. These solutions can be particularly complex, with the presence, for example, of complexing agents, salts, anions or competing cations: iron, ammonium, nitrates in high concentration, up to a few g / l. soot from thermal power plants or heavy fuel oil boilers containing, depending on the origin of the oil, significant concentrations (a few hundred ppm) in vanadium, molybdenum, nickel and raised in iron (several are another example of a complex medium that can be used.

 Conventional recovery treatment techniques involve processes such as: precipitation, flocculation, electrochemical treatment, filtration, micro- or ultrafiltration, or ion exchange resins. While these techniques have proved their worth in the treatment of rich metalliferous effluents, they show their limits when faced with high effluent flows with low concentration.

The adsorption on resins, such as ultrafiltration, are difficult to reconcile with economic objectives, because of the high cost of materials or the implementation of a high flow rate treatment; they can also be accompanied by a release of delicate saline regeneration solutions to be treated. More basic techniques, such as precipitation, have the disadvantage of non-selective recovery of metals (eg mixed hydroxides), as well as a significant increase in the salinity of the discharge. In addition, depending on the metal elements considered, the removal efficiency is too low to reach residual concentrations that comply with the regulatory provisions.

Economic and environmental constraints have led to other technologies that could provide an alternative to these processes. In particular, it has been proposed to take advantage of the ability of certain microorganisms to fix metals. Different mechanisms can come into play: active accumulation by proton pump mechanism, enzymatic and / or cellular synthesis of polysaccharides, phosphates which cause the complexation and precipitation of metals on the cell or in its immediate environment (Norberg and Persson,
Zooqloea will be feeding, Biotechnol. & Bioeng., 1984, XXIII, 129139; Macaskie and Dean, Citrobacter sp., Biotechnol.

Letters, 1985, 7, 7, 55-66). But it can also be a purely passive accumulation: the metals complex and adsorb on the functional groups of the cell walls: proteins, amines, amides, carboxylic functions, phosphates. Among the multitude of biomasses that can be applied (Nakajima and
Sakaguchi, Appl. Microbiol. Biotechnol., 1986, 24, 59-64), the filamentous fungi (Mucor miehei, Penicillium chrysogenum) represent excellent supports both by their fixing performance and by their large size which makes their use easier, in particular during solid / liquid separation step.

The mechanisms involved are purely passive, the main constituents of the cell wall: chitin or chitosan, and the proteins are at the origin of the adsorption, complexation and precipitation which insolubilise, for example, the uranium in and on the outer membrane. The possibility of desorbing the metal after the fixation phase makes it possible to recover the uranium in concentrated solution (eluate titrating a few g of U / l) and to reuse the biomass during several cycles of adsorption / desorption.

Drobot (Engelhard Minerals and Chemicals
Corporation: Br. Fr. 2,475,522 and 2,475,523) proposes to use live or inactivated fungi (Cladosporium, Penicillium, Trichoderma, Aureobasidium and 1, Black
Mycelium ") to separate metals (platinum, rhodium, palladium, ruthenium, gold, silver, iridium, zinc, aluminum, iron, copper, nickel, cobalt manganese, chromium, boron or tin) from their aqueous solutions. industrial culture and batch application The charged biomasses are incinerated for the recovery of metals, or simply disposed of and stored.

 French Patent No. 2,243,264 to "Kernforschungsanlage Julich Gesellschaft mit Beschrankter Haftung" describes the recovery of uranium from seawater by unicellular green algae adapted to high concentrations of uranium (by exposure to X-radiation). These adapted cultures are sown and placed in a filter cage (sieve permeable to seawater) installed in the tidal zone.

 Volesky and Tsezos (US Pat. No. 4,320,093 - 1982) describe the use of a filamentous fungus for the purpose of separating uranium and thorium from mining effluents; comparing the performance of different strains of fungi they select Rhizopus arrhizus. They study its properties and performance, which can reach optimal fixation capacities (depending on pH and metal concentrations) of 180 mgU / g of biomass and 160 mgTh / g.

Brierley JA, CL Brierley CL Decker RF, Goyak
GM (Advanced Mineral Technologies, Inc. Br. US 4,898,827
1990) describe the method of treatment of a bacterium
Bacillus subtilis by means of caustic solutions and their immobilization on support, they describe the application to the treatment of metalliferous solutions (silver, lead, copper, nickel, chromium) and compare the performances with those of other microorganisms.

 Various Patents (Prochazka et al., 1976, Br US 3,993,558, 1978 Br US 4,124,544, Votapek et al., 1978, Br.

 U.S. 4,067,821, Nemec et al. 1977, Br. US 4,021,368) disclose methods for modifying or immobilizing granulation of fungal biomasses for the recovery of heavy metals.

Kasukiyo Onodera et al. (Shin-etsu Chemical Co
Ltd 1990 - Br. GB 2 228 259 A) discloses a process for extracting heavy metals (copper, cadmium, mercury, chromium, arsenic, nickel, gold, silver, iron, cobalt, lead, zinc antimony and tin) in solution by chitosans of fungal origin (Cunninghamella, Rhizopus, Absidia,
Mucor).

Premuzic (United States Department of Energy, 1984 - Br. Fr. 84 13201) describes a method of removing radionuclides from the body by natural chelates extracted from bacteria, from which it selects
Pseudomonas aeruginosa.

 In general, not all metals are removed and usually ion exchange resins are used for finishing. However, resin beds tend to clog. In addition, the resins are regenerated by saline solutions, and it is not known to make salty concentrates of metals thus obtained.

 We are still looking for an industrial process involving the adsorption and desorption of metals to obtain concentrated elements, unsalable and recoverable.

 Therefore, the subject of the present application is a process for extracting metals using a fungal biomass in which the fungal biomass is brought into contact with a liquid containing said metals in a reactor and then carries out a reaction. solid-liquid separation, characterized in that it is carried out continuously and in that a portion of the biomass is continuously removed, at least 80% of the portion of the biomass removed being returned to the reactor.

 The metals that can be extracted in this way can be, for example, vanadium, molybdenum, nickel, uranium, platinum, rhodium, palladium, ruthenium, iridium, gold, silver, cobalt, chromium, arsenic or tin. These will generally be in aqueous solution and may come from mining, metal processing industries, the metallurgical industry, or surface treatment facilities. The extraction is carried out selectively; as a result, the presence of alkali and alkaline earth metals has no influence on the adsorption.

The fungal biomass may consist of common filamentous fungi, especially those used in the food industry, in particular for the synthesis of industrial enzymes. We can mention in particular,
Mucor miehei and Penicillium chrysogenum. Preferably, the fungi constituting the fungal biomasses will belong to the orders of Mucorales and Eurotiales. The mushrooms may optionally be used in a mixture, but will generally belong to the same species.

 The process of the present invention may be carried out in a reactor. By "reactor" is meant in the present invention any device suitable for contacting a solid with a liquid and preferably capable of facilitating, if desired, their separation. There may be mentioned in particular conventional reactors, with or without stirrers, or columns.

 The solid / liquid separation may be carried out according to methods well known to those skilled in the art, such as decantation, filtration or centrifugation, continuous or not.

 The characteristics of the present invention reside in the fact that a substantial part, namely at least 80% of the biomass taken, preferably at least 90% and in particular 99% of said biomass, is returned to the reactor. By this is meant that is taken after leaving the reactor a certain amount of the biomass-liquid mixture, at least the prescribed proportion is returned to the reactor. Thus the biomass is put back into contact with the metals that it fixes in greater quantity. The sample is preferably taken after concentration of the biomass; as a result, a lot of biomass and little liquid is removed.

 The biomass removed may not be replaced, but will advantageously be replaced by an equivalent amount of new biomass. By "new biomass" it is meant that the biomass has not yet been brought into contact with the metal laden liquid.

 Similarly, it will advantageously replace the liquid taken at the same time as the biomass, and that removed during the biomass concentration step.

 The process described above can be carried out at pH varied according to the metal ions contained in the liquid. The choice of the most suitable pH is within the skill of those skilled in the art. For example, based on the teaching of Tsezos and Volesky, those skilled in the art will operate for uranium at a pH of about 5. The working pH used is preferably close to the pH of appearance of the hydroxylated forms.

In order to facilitate the concentration of the biomass, it will advantageously operate in the presence of a flocculant, preferably cationic, in particular based on copolymers of acrylamide and quaternized or salified dialkylaminoethyl (meth) acrylate. Flocculants that may be mentioned include, for example, flocculants of the strong cationic type such as those marketed by SN Floerger under the references FO 8350, 8400, 8490 or 8650 and in particular under the reference F0 9400. Usable flocculant products are also marketed by companies such as Allied colloids, American Cyanamid, Röhm,
Nalco or Stockhausen. It can be operated at various concentrations of flocculant, for example from 0.1 to 10 ppm, and preferably to about 1 ppm.

 During the concentration step, one also obtains the treated liquid, freed of the majority of the metals which it contained, and which can thus be rejected directly with the sewer without requiring additional treatment.

 The concentration of the biomass in the reactor may range from 50 g to 2 kg per m 3 of mixture and preferably from 200 g to 800 g per m 3.

 Under preferential conditions of implementation, the process described above is characterized in that the biomass concentrated in metals removed is subjected to desorption.

 This may be carried out especially with the aid of salts such as phosphates, preferably carbonates or hydrogen carbonates, in particular alkali or alkaline earth. Details on the desorption of metals can be found in the aforementioned documents incorporated herein by reference.

 This desorption step may be followed by a solid-liquid separation operation, such as those described above, so as to obtain on the one hand a liquid eluate sufficiently concentrated in metals to be easily recycled according to known methods for recovering the metal, and secondly a metal-free biomass, reusable for the implementation of the method described above.

 Examples of implementation of the method are given below in the experimental part.

 The present application finally relates to a device specially designed for the implementation of the method described above, characterized in that it comprises a reactor provided with an overflow evacuation device connected to a concentration device biomass, a pipeline connecting the biomass concentration device to the inlet of the reactor, a biomass sampling port, a liquid inlet to be treated in the reactor and, if desired, a device new biomass distribution.

 The reactor is preferably placed above the biomass concentration device to use gravity for the circulation of materials. The concentration device is preferably a conical-based decanter.

 The following examples illustrate the present application without limiting it.

EXAMPLE 1
a) The liquid to be treated is mine-minewater from a uranium mine.

It contains about
- 8 ppm of uranium
- 200 to 500 ppm of sulphates
- Salinity in Fe, Al, Mg, Ca, Zn between 5 and 50 ppm
- neutral pH
The liquid to be treated, sucked by a pump 1, arrives continuously via a pipe 2, at a flow rate of 1 m 3 / h, in a buffer tank 3 where the pH is regulated at 5.5, and kept stirred by an agitator 4 The liquid to be treated is withdrawn from the buffer tank by suction using a pump 5 and led into a reactor 6 agitated by stirrer 7, with a flow rate of 1 m 3 / h. The reactor 6, with a volume of 1 m 3, contains 300-400 g / m 3 (expressed as dry weight) of a biomass consisting of Penicillium chrysogenum.

 The excess mixture is discharged from the reactor via an overflow line 8, and added with flocculant at the rate of 1 ppm, taken by a pump 9 from a flocculant tank 10, and falls by gravity. in a decanter, itself stirred slowly (about 6 revolutions / h). The flocculant used is that marketed by SN Floerger under the reference F0 9400.

 At the bottom of the decanter, the concentrated biomass is removed and returned, largely (80%) by a pump 11 in the reactor. A new biomass is added using a metering hopper 13 in order to compensate for the biomass taken but not returned.

At the top of the decanter, 14 is obtained a clear liquid, free of its metals. His analysis concluded that
- the concentration of uranium is less than 0.8 ppm,
there is no adsorption of the alkalis and alkaline earths,
the fixation of the transition elements is negligible: their concentration in solution remains constant,
- the pH of the liquid is neutral.

 b) Desorption of the biomass taken.

The rest is then desorbed as follows
The biomass recovered is filtered with a filter press and then resuspended and stirred in a bath of sodium bicarbonate (concentration between 0.1 and 1 M), with Solid (mg) / liquid (ml) ratios of about 100. After two hours of contact a new solid / liquid separation step makes it possible to recover an eluate rich in uranium (between 10 and 20 g / l). The biomass is washed in water (solid / liquid ratio close to 100 mg / ml), then reused for new adsorption-desorption cycles. The eluate is then recovered by conventional solvent extraction techniques (quaternary amines, for example AliquatR 336, AdogenR 464) and precipitation. The washings are optionally recycled at the head of the process by contact with the biomass if their concentration of metal ions justifies it.

EXAMPLE 2 Valorization of a Vanadiferous Effluent
The soot leaching of heavy fuel thermal power plants generates acidic effluents rich in vanadium (400 mgV / l, pH 2.5), containing significant concentrations of iron (1-1.2 gFe / l), nickel (170 mgNi / l), and in molybdenum (50-100 mgMo / l). The contacting of these leachates in batch with the biomasses according to Example 1 allows in a very short time (1 h 30) to obtain a selective extraction of vanadium. The concentration of vanadium in the effluent is less than 10 ppm, while the concentration of iron, nickel and molybdenum is almost unaffected. The X-ray fluorescence analyzes of the adsorbent samples before and after fixation confirm this. The vanadium binding capacity varies with the L / S ratio (liquid volume (ml) / volume of solid (g)), but it tends to 80 mgVa / g of biomass in the range 0 <L / S <60. The desorption of vanadium with acidic solutions makes it possible to recover the metal, to improve the selective extraction of vanadium and to recycle the biomass.

Claims (10)

 A method of extracting metals using a fungal biomass in which the fungal biomass is contacted in a reactor with a liquid containing said metals, and then performs a solid-liquid separation, characterized in that the operation is continuous and in that a portion of the biomass is continuously removed, at least 80% of the portion of the biomass removed being returned to the reactor.  2. Method according to claim 1, characterized in that at least 90% of the portion of the biomass removed is returned to the reactor.  3. Method according to claim 1 or 2, characterized in that the portion of the biomass removed is replaced by new biomass.  4. Method according to any one of claims 1 to 3, characterized in that the biomass comprises elements belonging to the orders of Mucorales or Eurotiales.  5. Method according to any one of claims 1 to 4, characterized in that the biomass removed is subjected to desorption.  6. Process according to claim 5, characterized in that the desorption is carried out using carbonates or hydrogenocarbonates.  7. Method according to any one of claims 5 or 6, characterized in that the mixture after desorption is subjected to a solid-liquid separation.  8. Method according to claim 6 or 7, characterized in that the liquid part is subjected to a metal recovery treatment.  9. Device for the implementation of the product according to any one of claims 1 to 8, characterized in that it comprises a reactor provided with an overflow discharge dis positive connected to a concentration device of biomass, a pipe connecting the biomass concentration device to the inlet of the reactor, a biomass sampling port, a liquid inlet to be treated in the reactor and, if desired, a device for distribution of new biomass.  10. Application of the process according to any one of claims 1 to 8 to the depollution of effluents.