Method for bioleaching a metal present in a material

Abstract

The invention relates to a method for recovering at least one metal present within a material, said material possibly including iron, said method including a step of supplying a ferrous ion, a step of supplying a ferric ion, and a step of bioleaching at least one metal present in the material by the ferric ions, each one of the steps being implemented by a particular bacterial population.

1 . An indirect bioleaching process for extracting at least one metal other than iron present in a material, said process comprising the steps of:
 a) supplying a ferrous ion in a first reaction space,   b) oxidizing the ferrous ion supplied to give a ferric ion in a second reaction space,   c) bioleaching said at least one metal via said ferric ion in a third reaction space, characterized in that the step of supplying a ferrous ion is carried out,
 i) either by bioleaching of an iron present within the material by a first iron-oxidizing bacterial population (B1) which is embedded in a first embedding matrix and immersed in a first reaction medium present within the first reaction space, 
 ii) or by acid leaching of an iron present within the material by adding a strong acid, preferentially sulfuric acid, to the first reaction space, 
 iii) or by adding ferrous ions, 
   
       so as to obtain a ferrous ion concentration of between 2 g/l and 50 g/l in the first reaction medium,
 and in that the steps of oxidizing the ferrous ion and of bioleaching said at least one metal are each carried out in a reaction space comprising a reaction medium and a bacterial population (B2, B3) comprising at least one population of iron-oxidizing acidophilic bacteria, each of the bacterial populations (B2, B3) being embedded in a cell embedding matrix immersed in each of the reaction media of each reaction space, it being possible for the reaction media, the bacterial populations and the materials present in the various reaction spaces to be transferred between these various reaction spaces, 
 and in that an iterative oxidation of a ferrous ion, resulting from the bioleaching of said at least one metal, to give a ferric ion is carried out by the bacterial population (B3) present in the third reaction space, 
 and in that the reaction spaces are different and the bacterial populations (B1, B2, B3) are not identical. 
 
     
     
         2 . The process as claimed in  claim 1 , characterized in that said step of bioleaching said at least one metal is reiterated when the amount of said at least one metal in the material after a bioleaching step is greater than 20% of the initial amount of said at least one metal within the material, and more preferentially greater than 50%. 
     
     
         3 . The process as claimed in  claim 1 , characterized in that the process also comprises at least one of the following steps:
 extraction of at least one substance present in said material and inhibiting a bioleaching bacterial activity and/or an iron-oxidizing bacterial activity, said step being carried out before the step of supplying a ferrous ion,   acidification of the material by supplying an acid solution such that the material is in a solution of which the pH is stabilized between 0.5 and 3.0.   
     
     
         4 . The process as claimed in  claim 1 , characterized in that a step of embedding a bacterial population in a cell embedding matrix is present and in that the embedding step comprises the steps of:
 supplying a liquid embedding medium,   supplying a cell embedding matrix compound in the embedding medium according to a weight-to-volume ratio between the embedding matrix compound and the embedding medium of between 5 g/l and 400 g/l,   supplying an inoculum of the bacterial population in the embedding medium,   forming a cell embedding matrix comprising the bacterial population.   
     
     
         5 . The process as claimed in  claim 4 , characterized in that the cell embedding matrix compound is selected from the group of water-soluble natural or synthetic polymers which can form hydrogels by ionotropic, photochemical or thermal gelling or by crosslinking or polymerization, said group comprising alginate, agar, gerlite (anionic heteropolysaccharide), chitosan, kappa-carrageenan, polyacrylamide, polyacrylamide-hydrazide, co-poly(N-isopropylacrylamide/acrylamide), polyethylene glycol, methacrylates based on monomers of methylacrylamide, hydroxy ethyl methacrylate or methyl methacrylate, epoxy resins, photo-crosslinkable resins, diethylene glycol ester, polyvinylpyrrolidone, silicone, polyvinyl alcohol, polyethylene glycol monomethacrylates or dimethacrylates or diacrylates, polyurethane hydrogel, hydroxyethyl methacrylate, photo-crosslinkable resins or a mixture of several of these compounds. 
     
     
         6 . The process as claimed in  claim 4 , characterized in that a bacterial propagation step is carried out after the step of embedding a bacterial population in a cell embedding matrix, said propagation step comprising the steps of:
 supplying a culture medium which allows the bacterial population to multiply, said culture medium comprising the bacterial population embedded in a cell embedding matrix according to a ratio of volume of embedding matrix and of bacteria embedded therein to the total volume of between 5% and 74%,   adding ferrous ions at an initial concentration of between 2 and 50 g/l,   replacing the culture medium with a fresh culture medium when the oxidation of the ferrous iron to ferric iron is total, and adding ferrous ions so as to obtain the initial concentration of ferrous ions,   stopping the propagation step when the time required to oxidize all of the ferrous iron to ferric iron within the culture medium no longer decreases.   
     
     
         7 . The process as claimed in  claim 1 , characterized in that the first reaction space comprises a first bacterial population (B1) embedded in a first cell embedding matrix, said first bacterial population having, prior to its use in step a) of the process and when iron is present within the material, undergone an acclimatization by culturing said first bacterial population in an acclimatization medium, said acclimatization medium comprising the material, said acclimatization medium being replaced with a fresh acclimatization medium when the redox potential of the acclimatization medium reaches a value greater than 350 mV, preferentially greater than 400 mV, and even more preferentially greater than 450 mV, said fresh acclimatization medium being supplemented at each replacement with an increasing concentration of material, said increasing concentration evolving in steps of 2 g/l to 20 g/l of material, until the concentration of the material in the medium is between 2 g/l and 200 g/l, more preferentially between 50 g/l and 150 g/l, and even more preferentially the concentration is equal to 70 g/l and 80 g/l. 
     
     
         8 . The process as claimed in  claim 7 , characterized in that the second reaction space comprises a second bacterial population (B2) embedded in a second cell embedding matrix, said second bacterial population having, prior to its use in step b) of the process and when an iron is present within the material, undergone an acclimatization by culturing said second bacterial population embedded in a cell embedding matrix in a second acclimatization medium, said second acclimatization medium consisting of the various successive acclimatization media resulting from the step of acclimatization of the first bacterial system from which the material was removed, the concentration of ferrous iron being maintained at a concentration of between 2 g/l and 50 g/l in said acclimatization medium, said acclimatization medium being optionally supplemented by the addition of ferrous iron. 
     
     
         9 . The process as claimed in  claim 8 , characterized in that the third reaction space comprises a third bacterial population (B3) embedded in a third cell embedding matrix, said third bacterial population having, prior to its use in step c) of the process, undergone an acclimatization by culturing said third bacterial population embedded in a third cell embedding matrix in a third acclimatization medium, said third acclimatization medium consisting of the various successive media resulting from the step of acclimatization of the second bacterial system and supplemented with a concentration increasing in steps of 2 g/l to 20 g/l of treated material, said treated material consisting of the first material after acclimatization of the first bacterial population when the material contains iron, or the material resulting from the step of extracting substances inhibiting a bioleaching bacterial activity and/or an iron-oxidizing activity, when the material does not contain iron, or the acidified material when the material contains neither an iron nor a substance inhibiting a bioleaching bacterial activity and/or an iron-oxidizing activity, up to a concentration equivalent to 20 g/l to 200 g/l, preferentially from 50 g/l to 150 g/l, and even more preferentially from 70 g/l to 80 g/l of material in the reaction medium. 
     
     
         10 . The process as claimed in any one of  claims 7  to  9 , characterized in that a ratio of a volume of the bacterial population embedded in a cell embedding matrix to a total volume within an acclimatization space is between 5% and 74%. 
     
     
         11 . The process as claimed in  claim 1 , characterized in that step a) of supplying ferrous ions is carried out with a ratio of the volume of the first bacterial population (B1) embedded in a first cell embedding matrix to the volume of the first reaction space of between 5% and 74%, when an iron is present in the material, in that the pH of said first reaction medium is between 0.5 and 3.0, and in that the concentration of material within the first reaction space is, when said material contains an iron, between 20 g/l and 200 g/l, preferentially between 50 g/l and 150 g/l, and even more preferentially between 70 g/l and 80 g/l of material in the reaction medium. 
     
     
         12 . The process as claimed in  claim 1 , characterized in that step b) of oxidizing the ferrous ions to ferric ions is carried out with a ratio of the volume of the second bacterial population (B2) embedded in a second cell embedding matrix to the volume of the second reaction space of between 5% and 74%, said second reaction medium consisting of the first reaction medium after step a) of supplying a ferrous ion, and in that the concentration of ferrous ions is adjusted to between 2 g/l and 50 g/l, and in that the pH of the reaction medium is less than 3.0. 
     
     
         13 . The process as claimed in  claim 1 , characterized in that step c) of bioleaching said at least one metal is carried out with a ratio of the volume of the third bacterial population (B3) embedded in a third cell embedding matrix to the volume of the third reaction space of between 5% and 74%, said third reaction medium consisting of the second reaction medium after step b) of oxidizing the ferrous iron to ferric iron, a pH of the reaction medium being between 0.5 and 3.0, and in that the concentration of material is between 20 and 200 g/l, preferentially between 50 and 150 g/l, and even more preferentially between 70 g/l and 80 g/l of material in the reaction medium, said material consisting of the material after leaching of the iron by the first bacterial population (B1) when the material contains iron, and/or the material resulting from the step of acidification and/or extraction of substances inhibiting a bioleaching bacterial activity and/or an iron-oxidizing activity. 
     
     
         14 . The process as claimed in  claim 1 , characterized in that the bacterial populations (B1, B2, B3) comprise acidophilic bacteria in pure cultures or in mixed cultures having at least one characteristic among each of the following groups selected from the groups comprising heterotrophic, mixotrophic, autotrophic, chemoautotrophic or chemolithoautotrophic bacteria which oxidize iron and/or sulfur and/or reduced forms of sulfur, psychrophilic, mesophilic, moderately thermophilic, hyperthermophilic and acidophilic bacteria, said bacteria having a growth and activity pH of between 0.5 and 3.0, and more preferentially the group comprising the bacteria  Acidiferrobacter thiooxydans, Acidithiobacillus ferrooxidans, Leptospirillum ferroxidans, Leptospirillum ferriphilum, Acidimicrobium ferrooxidans Sulfobacillus thermosulfidooxidans, Acidithiobacillus caldus, Acidianus brierley, Sulfobacillus acidophilus, Actinobacterium  sp.,  Acidocaldus organivorans  and  Alicyclobacillus ferroplasma.    
     
     
         15 . The process as claimed in  claim 1 , characterized in that the material is selected from the group of industrial waste, by-products or residues comprising non-ferrous metals and/or noble metals, said material being composed of at least one metal optionally in combination with iron, said metal being selected from the group comprising copper, zinc, nickel, tin, aluminum, gold, silver, platinum, rhodium, ruthenium, iridium, osmium, palladium, titanium, cobalt, vanadium, molybdenum, tungsten, beryllium, bismuth, cerium, cadmium, niobium, technetium, indium, gallium, germanium, lithium, selenium, tantalum, tellurium, arsenic, antimony, bismuth, lead, and mercury, or a combination of these metals. 
     
     
         16 . The process as claimed in  claim 1 , characterized in that the material is in the form of powder and has a particle size of less than 1 mm, preferentially less than 0.5 mm.