Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G53/00—Compounds of nickel
  • C01G53/10—Sulfates
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F5/00—Compounds of magnesium
  • C01F5/26—Magnesium halides
  • C01F5/28—Fluorides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G53/00—Compounds of nickel
  • C01G53/08—Halides
  • C01G53/09—Chlorides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B23/00—Obtaining nickel or cobalt
  • C22B23/04—Obtaining nickel or cobalt by wet processes
  • C22B23/0407—Leaching processes
  • C22B23/0415—Leaching processes with acids or salt solutions except ammonium salts solutions
  • C22B23/043—Sulfurated acids or salts thereof
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/006—Wet processes
  • C22B7/007—Wet processes by acid leaching
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
  • B01J23/74—Iron group metals
  • B01J23/755—Nickel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
  • B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
  • B01J27/053—Sulfates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
  • B01J37/031—Precipitation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/06—Washing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/08—Heat treatment
  • B01J37/082—Decomposition and pyrolysis
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to the phytoextraction of heavy metals from the soil. More specifically, it consists of a process for producing a crystallized nickel salt from the ashes of a hyperaccumulator plant of metallic elements including nickel.
• Phytoextraction is an agro-ecological process using plants to extract heavy metals from soils. The process can then make it possible to render two types of services, an environmental service for reducing the impacts of metallic pollution and an industrial service for the production of metals. The latter is called phytomining.
• Phytomining uses heavy metal mining plants as miners to extract metals of commercial value, these metals being initially contained in mineralized soils that can not be exploited by traditional mining processes (Barbaroux, 2009, Hydrometallurgy, 100, p.10-14 Chaney, 2007, J. Environ., Quai., 36, p.1429-1 43).
• the application of the principles of phytoextraction by phytoremediation or phytomining emphasizes the use of plants allowing a sufficient annual accumulation in metals such as Ni, Zn, Cd, Se, Co, As or Ti (Baker, 1989, Biorecovery, 1 , pp. 81-126). Some plants are able to accumulate more than 1,000 mg metal per kilogram of dry matter under natural conditions.
• hyperaccumulators Brooks, 1998, CAB International, Wallinford, England, 380.
• the leaves, flowers and seeds have a ratio of metal concentration to roots greater than one, while that non-hyperaccumulating plants tend to concentrate the metals in their roots (Shallari, 1998, Sci., Total Environment, 209, p.133-142).
• the hyperaccumulating plants that accumulate the metal in their aerial parts are harvested by conventional agronomic methods. More than 400 plant species, represented by about 45 families, have been identified as hyperaccumulators and two-thirds of these hyperaccumulators accumulate nickel (Brooks 1998, Chaney 2007).
• Nickel is present in all compartments of the terrestrial environment in trace amounts, except in serpentine ores and soils, where it is at higher levels.
• Serpentine soils are derived from ultramafic rock alteration and are widely distributed worldwide (Brooks, 1987, Dioscorides Press, Portland, Oregon, US 454, Ghaderian, 2007, Plant Soil, 293, p. 91-97). These soils are characterized by a pH of 6 to 8, by abnormally high levels of metals such as Ni, Cr and Co, as well as high levels of Fe and Mg and a low Ca content. The major elements, K, P and S are present in trace amounts (Shallari, 1998). The concentration of Ni in these soils ranges from 0.5 to 8 g Ni / kg soil (Bani, 2007, Plant Soil, 293, pp. 79-89).
• Nickel is therefore a relatively widespread metal worldwide. However, economically profitable ore mining sites are located in Canada, Russia, Australia, New Caledonia and Brazil. At the industrial level, nickel is mainly produced from ores by pyro- or hydrometallurgical processes. While the metallurgical industry remains by far the largest consumer of nickel (USGC, 2005, US geological survey ores years book, pp.1-25), the chemical industry ranks second.
• Nickel compounds are used for electroplating, battery manufacturing (nickel hydroxide is used as a mass in nickel-cadmium batteries), pigment manufacturing for paints and as a catalyst in many chemical reactions ( Kerfoot, 1995, Handbook of Extractive Metallurgy, Wiley-VCH, Weinheim, Germany, p. 714-786). Since nickel is a transition metal, its compounds are numerous and are not all of interest. Some, however, have a higher economic value than nickel for alloy production, such as the nickel and ammonium double sulphate salt used as an electrolytic salt in the plating industry (Kerfoot, 1995). Precipitation of nickel and ammonium double sulphate salt is possible by adding ammonium sulphate to a mineral solution of concentrated nickel sulphate.
• the hyperaccumulator Alyssum mural can accumulate up to 20,000 mg Ni / kg DM and a biomass of 10,000 kg / ha can be harvested per year from this plant (Chaney, 2007).
• the serpentine soils contain nickel at levels between 1000 and 7000 mg / kg.
• the ashes of hyperaccumulative plants contain about 15% of nickel whereas the usual rocks from serpentine soils contain only 0.2% of nickel.
• the recovery of nickel from rocks is therefore faced with a problem of poor profitability.
• nickel concentrations in hyperaccumulative plants are well below the minimum concentration required for traditional mining (30,000 mg / kg), they are sufficient to consider the accumulation and extraction of nickel through a pathway. treatment of hyperaccumulating plants (Baker 1989, Broadhust 2004, Plant Soil 265, 225-242, Shallari 1998). The profitability of this recovery route by plants, however, remains a challenge.
• the walled Alyssum (wall-mounted) plant once dried and once harvested, can be pyrometallurgically processed in a foundry (Chaney, 2007) to produce a nickel metal or leach dry mass to produce a concentrated nickel leachate ( Wood, 2006, HortScience, 41, p. 1231-1234). It therefore seems conceivable to produce pure and marketable nickel from the harvest of the mural plant A. on serpentine soils, and then by chemical treatment of this plant.
• nickel phytomining is expected to be a profitable crop production (Chaney, 2007; Li, 2003). It is also possible to use the energy produced during the incineration of the bio-ore to produce electricity (Li, 2003).
• the biomass of A. mural can be treated by incineration to produce ashes.
• the most commonly suggested route for recovering metals from plants produced by phytomining is the incineration of biomass from hyperaccumulator plants and the treatment of ashes in foundries to recover nickel metal (Li, 2003). Chaney et al. (2007) treat the biomass of the mural plant A. in the foundry to recover nickel in metal form.
• the present invention meets at least some of the above requirements by providing a cost effective recovery of the nickel contained in the ashes of hyperaccumulative plants by the production of a chemical compound of nickel.
• Crystallized nickel salts have proven to be an effective selective recovery route from aqueous ionic solutions to solubilize nickel contained in hyperaccumulating plants.
• the crystallized nickel salts preferably include nickel ammonium salt sulfate salt, nickel sulfate salt, and nickel chloride salt.
• a method of extracting nickel from ash of a hyperaccumulator plant of metal elements comprising nickel comprising using an ionic solution to recover nickel in the form of a crystallized nickel salt.
• the process more particularly comprises a step (a) of leaching the ash by the addition of an acid solution, thereby producing a leachate comprising nickel and iron. This results in a step (b) of selective precipitation of leachate iron by addition of a basic solution producing a purified supernatant rich in nickel and an iron-rich precipitate. Then the process comprises a step (c) of crystallization of the crystallized nickel salt.
• step (a) comprises washing the ashes with an aqueous solution prior to step (a) to reduce the ash content in soluble mineral elements and in chlorine.
• Soluble mineral elements include potassium and sodium.
• the method comprises a mechanical separation step, after each steps (a), (b) and (c).
• the mechanical separation may preferably be a filtration separating a filtrate and a residue.
• the acid solution is added to the ashes in step (a) with a molar concentration of 0.25 mol / L to 7 mol / L.
• the leachate has a mass ash concentration of 50 g / L to 300 g / L.
• the mass concentration of ash would be 150 g / L.
• the leaching step (a) is at a temperature between 0 ° C and 100 ° C.
• the basic solution used in step (b) is a solution of quicklime, hydrated lime, hydroxide sodium, potassium hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, sodium carbonate or potassium carbonate.
• the basic solution is added to the leachate with a concentration chosen so that the leachate has a pH between 3.2 and 7, favoring thus the precipitation of iron in order to purify the leachate.
• the solution can be added with a concentration adapted to obtain a pH equal to 5.
• the method comprises evaporation of the water contained in the purified supernatant of step (b) prior to proceeding with step (c).
• the crystallization (c) is cold.
• the process comprises purifying the crystallized nickel salt to reduce the magnesium content.
• the purification may comprise a step (d) of solubilization of the crystallized salt of nickel in water; a step (e) of adding a sufficient amount of an inorganic compound comprising an anion selected to produce an anion-magnesium precipitate; a step (f) of filtering the anion-magnesium precipitate to separate it from a second purified supernatant; and a step (g) of cold recrystallization of a crystallized salt of purified nickel by addition of the ionic solution in the purified second supernatant.
• the anion would preferably be the fluoride ion.
• the inorganic compound would be more preferably sodium fluoride to produce a magnesium fluoride precipitate in step (e).
• the fluoride ion is added with a molar amount of between 2 and 2.5 mol per mol of magnesium present in the solubilized nickel crystallized salt. in step (d).
• the method comprises mechanical separation, washing and drying of the crystallized salt of purified nickel obtained in step (g).
• Mechanical separation may preferably be filtration.
• Drying of the crystallized salt of purified nickel may preferably be carried out at a temperature between 40 and 150 ° C.
• the nickel is recovered as a nickel ammonium sulphate salt, a nickel sulphate salt or a salt of nickel chloride.
• the ionic solution is an ammonium sulphate solution for recovering nickel in the form of the nickel sulphate salt and the ammonium, the ammonium sulphate solution being added to the supernatant purified during step (c) of crystallization of the nickel sulfate salt of ammonium and ammonium.
• the ionic solution is a sulfuric acid solution for recovering nickel in the form of a nickel sulphate salt. sulfuric acid being used as an acidic solution in the ash leaching step (a).
• the ionic solution is a hydrochloric acid solution for recovering the nickel in the form of a nickel chloride salt. hydrochloric acid being used as an acidic solution in the ash leaching step (a).
• the ionic solution is a solution of sulfuric acid with added brine to recover nickel in the form of a chloride salt.
• nickel, hydrochloric acid being used as an acidic solution in the step (a) of leaching the ashes.
• the brine would be a solution of sodium chloride or potassium chloride.
• the ashes are obtained by incineration of the hyperaccumulator plant of metal elements with the previously dried.
• the hyperaccumulator plant comprises or is a plant of the family Brassicaceae, Cunoniaceae, Flacortiaceae, Violaceae or Euphorbiaceae or a combination thereof.
• the hyperaccumulator plant comprises or is a plant of the mural species A.
• a plant hyperaccumulator of metal elements comprising nickel for the production of a crystallized nickel salt from the ash of the hyperaccumulator plant.
• an ionic solution is used to recover nickel from ashes as the crystallized nickel salt.
• the crystallized nickel salt is the nickel and ammonium double sulfate salt, the nickel sulfate salt or nickel chloride salt.
• the crystallized nickel salt would preferably be the nickel sulfate salt of nickel and ammonium.
• the crystallized nickel salt is nickel ammonium salt sulfate salt, nickel sulfate salt or salt. nickel chloride.
• the crystallized nickel salt would preferably be the nickel ammonium sulphate salt.
• the crystallized nickel salt has a mass concentration of magnesium less than 5 g / kg.
• the mass concentration of magnesium would be less than 0.7 g / kg.
• the crystallized nickel salt has a calcium mass concentration of less than 10 g / kg.
• the mass concentration of calcium would be less than 2.5 g / kg.
• the crystallized nickel salt has a potassium mass concentration of less than 10 g / kg.
• the mass concentration of potassium would be less than 2.5 g / kg.
• the crystallized nickel salt has a nickel mass concentration equal to or greater than 128 g / kg, preferably 130 g / kg.
• FIGS. 1A, 1B, 1C and 1D collectively refer to FIG. 1, which is a diagram of the steps of the nickel extraction and purification process in the form of the nickel and ammonium from A. mural according to an optional aspect of the present invention.
• Figure 2 is a graph showing a mass balance of the incineration of 1.0 kg dry matter of the mural plant A. according to an optional aspect of the present invention.
• Figure 3 is a diffractogram of a sample of nickel and crude ammonium double sulfate salt according to an optional aspect of the present invention.
• Figure 4 is a diffractogram of a purified ammonium and purified ammonium sulfate salt sample according to an optional aspect of the present invention.
• the invention relates to a hydrometallurgical process for treating hyperaccumulator plant ash of metallic elements using a low cost acid as an ash leaching agent.
• the original way of crystallizing a crystallized nickel salt (Ni) is chosen for nickel recovery from ash leachate.
• the process according to the present invention makes it possible to economically and economically produce a crystallized nickel salt such as nickel sulphate salt, nickel chloride salt and nickel and ammonium sulphate salt from ashes. hyperaccumulating plants such as preferably the A. Murale variety.
• the high added value of the nickel sulphate salt of nickel and ammonium makes it a salt preferably targeted by the present invention.
• the process steps, as described and claimed, are however adaptable (type of ionic solution used, concentrations of the various compounds, etc.) to the production of other nickel salts such as nickel sulphate or nickel chloride.
• the present invention relates to the use of hyperaccumulator plants of metal elements comprising nickel to produce a crystallized nickel salt, obtainable by the process described and claimed.
• the present invention also relates to a purified composition of a crystallized nickel salt derived from ash of plants hyperaccumulating metal elements comprising nickel, this composition can be obtained by the method described and claimed.
• Figure 1 details the various possible steps of a process for producing the nickel sulfate salt of ammonium and ammonium according to an optional aspect of the process.
• the hyperaccumulator plant is the mural A. plant (AP) which was previously dried and then incinerated in an oven at 550 ° C.
• the nickel-containing ash (AA1) was recovered and washed twice with deionized water.
• the washed ash (AA3) was then leached in a 1 M sulfuric acid solution at 85 ° C. for 4 hours.
• the supernatant leachate was recovered by filtration, the residue was washed, and then treated as waste (SW1).
• the acid solution used to leach the ashes may be a sulfuric acid solution as illustrated in FIG. 1, but it may also be chosen from nitric, hydrochloric, acetic, sulfurous acid solutions, a mixture of thereof, a derivative thereof or from the corresponding spent acid solutions.
• This crude leachate (L1) was then brought to pH 5 by addition of 5M NaOH and then evaporated in a beaker by heating at 100 ° C using a hot plate.
• the treated leachate was recovered, the residue washed, then treated as waste (SW2).
• a specific mass of ammonium sulfate was dissolved in the treated leachate (L2), the temperature of which was then raised to 0 ° C for 6 hours.
• the supernatant (PE3) was then separated from the salt which crystallized (NS1) by filtration.
• the salt was then washed and dried at 25 ° C (NS2).
• the salts are then solubilized in deionized water (L3).
• a specific amount of solid sodium fluoride was then added and dissolved in this solubilization solution.
• the supernatant was filtered off from the residue of MgF 2 (SW3) that formed during this step.
• a specific amount of ammonium sulfate was added and dissolved in the purified solubilization solution (L4).
• the temperature of this solution was then raised to 0 ° C for 6 h.
• the supernatant (PE5) was then filtered off from the crystallized salts. These salts were washed, dried and stored at 25 ° C (NS3).
• the supernatant (PE5) which still contains nickel, will be recycled to the process later.
• the single salt of nickel sulphate is obtained very similarly to the nickel sulphate salt of nickel and ammonium by direct crystallization of the leachate of ash treated with sulfuric acid (L2, FIG. 1), without the addition of sulphate of sulphate. 'ammonium.
• the crystallized salt of nickel sulphate can then be separated from a remaining supernatant.
• the crystallized salt of nickel sulphate can then be re solubilized in the presence of sodium fluoride in order to purify it of its magnesium content by forming a residue of magnesium fluoride.
• the process steps remain the same as those illustrated in FIG.
• the successive cold crystallizations in order to obtain the nickel sulphate salt with increasing purity, are carried out without the addition of sodium sulfate. 'ammonium.
• the washed ashes (AA3, Figure 1) are leached with a solution of hydrochloric acid (HCI) in place of sulfuric acid (H 2 SO 4 ).
• HCI hydrochloric acid
• sulfuric acid H 2 SO 4
• the production of crystallized salt of nickel chloride could alternatively be done by adding an ionic solution comprising sulfuric acid and an excess of brine, during step (a) in order to obtain livixiat ( L1, Figure 1).
• This alternative avoids the use of hydrochloric acid, the cost is much higher than sulfuric acid.
• the brine would preferably be potassium chloride or sodium chloride. Chloride ions are thus introduced in excess into the leachate, thus preferably forming a nickel chloride salt during the crystallization step.
• the crystallization step is preferably a cold crystallization but could also be a crystallization by evaporation of water, or any other crystallization technique known to a person skilled in the art.
• nickel sulphate salt of nickel and ammonium is here described in more detail in the light of the following example.
• a mural samples were collected at Pojske in the Pogradec region of Bulgaria (latitude: 40 ° 59'55.28 "N and longitude: 20 ° 38'0.92" E).
• the soils of this region are ultramafic with Ni levels of the order of 3.0 g Ni / kg soil.
• the Ni content of the top layer of Pojke soil (0 to 25 cm deep) was measured at 3.44 mg Ni / kg.
• the Plants were harvested by hand, dried in the sun, and stored at room temperature (20 ⁇ 2 ° C) pending experimentation.
• the sampling campaign was conducted in July 2009, during the flowering period, at the Pojske site in the Pogradec region of Bulgaria.
• the leaves were no longer attached to the stems and the flowers were widely present. There were also seeds from this period.
• a high Ni content in the upper parts of the plant was revealed during the previous sampling. This time it was shown that the stems, which represent 65.4% of the total biomass, were also rich in Ni.
• the stems had a Ni content of 6,100 mg Ni / kg DM which represented 51.8% of the total Ni.
• the entire aerial parts of the plant were therefore used as bio-ore.
• the roots have not been used because they remain difficult to harvest and weakly concentrated in Ni.
• the plants were crushed finely using a Kika-Werke mill, model M20.S3.
• the particle size was determined using successive sieves and it was shown that 39% of the particles had a size between 250 and 425 ⁇ . Metal concentrations in the wall A. dry mass were determined.
• the incineration tests of A. mural were performed by depositing 25 g of finely crushed A. wall plant in a 150 mL porcelain crucible. The crucible was then introduced into an oven (1400 Furnace, Barnstead Thermolyne, Duduque, Lana, USA) whose temperature was raised to 550 ° C for 2 hours. During the incineration, the plants were regularly mixed using a stainless steel rod to avoid the formation of coal. After 2 h, the end of the burning of the plants was noted, the crucible was removed from the oven and the ashes were recovered, weighed and stored in dry at 25 ° C. A total mass of 1000 g of finely ground plant A. was thus treated in this way. The concentration of metals in the ash has been determined. 1 .3. A wall ash wash
• Ca was found either in Ca 3 (PO 4 ) 2 or in carbonate form.
• the high solubility of K 2 CO 3 of the order of 1 12 g / 100 mL water (20 ° C), made it possible to eliminate a large part of the K contained in the ash by a simple washing with water.
• the contents of major and minor elements of the wash water were measured. This wash water was then treated as waste (PE1). In order to optimize the removal of K from ash, the washing was carried out twice (PE2). The metal concentration in the mass of the washed ash (AA3) was determined. The mass balances for Ca, K, Mg and Ni of these ash washing steps were performed.
• Nickel solubilization tests from the washed ash were carried out in order to optimize the leaching parameters, the molarity of the acid solution, the percentage of mass, the period and the leaching temperature. All the tests were carried out by adding a specific mass of ash in a 100 ml beaker containing 50 ml of a H 2 SO 4 solution of specific molarity. The beaker was then placed in a bain-marie system so that the reaction proceeded at a temperature of 100 ° C. A first series of leaching was carried out using an acid solution at 0.25, 0.5 and 1.0 M in the presence of 10 g / l of ash. Samples (1 mL) were collected after 120 and 240 min, filtered and analyzed.
• a second step two series of leaching were carried out with solid concentrations of 100 and 150 g / l of ash.
• the leaching period was set at 240 min.
• a The first leaching run was carried out using an acid solution at 0.5, 1, 0 and 1 .125 M in the presence of 100 g / l of ash.
• the second leaching run was carried out using a 0.5, 1 .0 and 1 .125 M acid solution in the presence of 150 g / l of ash.
• the Ni contents of the leachates obtained were measured and the extraction yields were determined.
• the neutralization of the leachate was carried out by introducing 60 ml into a 100 ml beaker with magnetic stirring.
• the leachate was neutralized to pH 5 by the dropwise addition of a 5M NaOH solution.
• the neutralization step was followed by evaporation.
• the 100 mL beaker was placed on a hot plate equipped with a magnetic stirring system.
• the temperature control was ensured by the use of a heating plate equipped with a thermostat.
• the volume of the solution is controlled by the use of a graduated beaker.
• the leachate temperature was raised to 100 ° C. Evaporation continued until the leachate volume was reduced by a factor of 3.
• the supernatant was then separated from the residue by filtration using a vacuum pump placed on a filtration system. magnetic. Filtration was followed by washing the residue (4 mL) produced by this step of neutralization and evaporation of the leachate. The The leachate thus treated and the washing solution were then mixed.
• the principle of selective recovery of Ni from the treated leachate of ash from the mural A. plant was based on the crystallization of the double sulphate salt of Ni and ammonium from the wall ash ash leachate.
• the physical characteristic exploited during this crystallization was the low solubility of the double salt of Ni at 0 ° C. which is 1 .6 g / 100 ml.
• the formation of the double sulphate salt of Ni and ammonium from Ni sulphate and ammonium sulphate is presented in Equation 1.
• Equation 1 NiSO 4 + (NH 4 ) 2 SO 4 + 6H 2 O ⁇ Ni (NH 4 ) 2 (SO 4 ) 2 .6H 2 O
• the treated leachate (L2) was introduced into a 100 mL beaker.
• An amount of (NH 4 ) 2 SO 4 equal to the stoichiometric amount of Ni contained in the leachate with an excess of 20% was added to the 100 mL beaker.
• Dissolution of the ammonium sulfate was ensured by the use of a hot plate provided with a magnetic stirring system.
• the leachate temperature was then raised to 60 ° C.
• the beaker was brought to room temperature (25 ° C). It was placed in a polystyrene box containing ice for a period of 6 hours.
• the leachate temperature was monitored and measured at 2 ° C.
• the leachate was removed from the ice.
• the supernatant was then separated from the crystallized salts (NS1) by filtration using a vacuum pump placed on a magnetic filtration system. Filtration was followed by washing the residue (2 mL) with deionized water at a temperature of 0 ° C. Filtration waters (PE4) were added to the supernatant (PE3) and the resulting solution (PE4) was analyzed.
• the Ni salts were dried at 25 ° C and then stored dry at room temperature. The metal concentration of these Ni salts was measured. The mass balance for Ca, K, Mg and Ni of this crystallization step of the crude Ni salts was carried out.
• a step of purifying and removing magnesium from the Ni salts produced was carried out. This step was based on the very low solubility of magnesium fluoride which is 0.076 g / 100 mL. The solubility of NiF 2 is much higher, ie 40 g / l.
• the double sulphate salts of Ni and ammonium (NS2) which have been produced are introduced into a 100 ml beaker and solubilized in a volume of 40 ml of demineralized water.
• This solution (L3) was analyzed.
• This solubilization solution of the Ni (L3) salts was then neutralized to pH 7 by the dropwise addition of a 5M NaOH solution.
• a default amount of NaF equal to 95% of the stoichiometric amount in Mg contained in the solubilization solution was added to the 100 mL beaker.
• the dissolution of NaF is described by Equation 2:
• the supernatant was then separated from the MgF 2 residue (SW3) by filtration using a vacuum pump placed on a magnetic filtration system.
• the leachate thus treated (L4) was introduced into a 100 ml beaker.
• Samples (1 mL) were taken from the leachate thus treated (L4) and the metal concentration was measured.
• the metal concentrations in this purified solution of solubilization of salts were measured.
• the filtration residue obtained was recovered, dried at 100 ° C. and then stored at room temperature. The metal contents and major elements of this MgF 2 residue were determined.
• the mass balance for Ca, K, Mg and Ni of this purification step of this solution (L4) was carried out.
• the beaker containing the purified Mg solubilization solution (L4) by addition of NaF was placed in a polystyrene box containing ice for a period of 6 h.
• the leachate temperature that was regularly monitored was measured at 2 ° C.
• the temperature control was ensured by the use of a thermometer.
• the leachate was removed from the ice.
• the supernatant was then separated from the product salts (NS3) by filtration using a vacuum pump placed on a magnetic filtration system. Filtration was followed by washing the Ni salts with deionized water (2 mL) at a temperature of 0 ° C.
• the wash water (PE6) was mixed in the solution of the supernatant (PE5) whose contents of metals and major elements were then determined by ICP-AES analysis.
• the Ni salts (NS5) were then dried at room temperature and then stored in a dry state at a temperature of 25 ° C.
• the metal concentrations in these salts (NS5) were measured by ICP-AES analysis.
• XRD analysis of the salts produced by this purification phase was carried out. The aim of this analysis was to identify the crystalline species present in these salts in order to identify the salts produced as double sulphates of Ni and ammonium. 1 .9. TCLP test for metals
• the danger as a toxic waste of the filtration residue resulting from the purification phase of the solubilization solution of the crude salts was evaluated by the TCLP test.
• the TCLP test developed by the USEPA assesses the hazardous or non-hazardous nature of solid waste for landfill (EPA Method 131 1) (US EPA, 1992, EPA, method 131 1, United States Environment Protection Agency, Washington , DC, United States, p.35). This test was carried out on the magnesium fluoride precipitate obtained during the purification phase of the double salts of Ni. The concentrations of toxic metals and total fluorides measured in the extraction liquid of the TCLP test were then compared with the maximum concentrations authorized in Quebec.
• the metal distribution within the tissues of the mural A. plant is given in Table 1.
• the results show a high Ni concentration of 9.7 g / kg of dry matter (DM). This result is consistent with the literature where Ni levels between 8.4 and 9.1 g Ni / kg DM in the mural A. plant were observed (Bani 2007, Shallari 1998).
• the high and harvestable parts (neglecting stems and roots) of A. mural have high levels of Ni.
• the stems have Ni contents, of the order of 6 g / kg DM, which is lower than the Ni contents observed in the upper parts. But the stems represent a high percentage of the total biomass of the plant, of the order of 65%.
• the whole plant A. wall, rods and high parts was used as a raw material to test the solubilization and recovery of Ni.
• the results in Table 1 show high concentrations of Mg (4 g / kg DM), Ca (8.4 g / kg DM) and K (7.6 g / kg DM). These results are typical for plants growing on serpentine-based soils.
• the high Mg content is characteristic of hyperaccumulating plants such as A. mural that are adapted to the serpentine-based soils unique to the Pogradec region of Bulgaria.
• Table 1 Detailed composition of dry matter, ashes and ash washed from the plant A. mural
• Figure 2 shows a mass balance performed on the metals and major elements contained in the dry matter of the mural A. plant and those contained in the ash. This review shows that the major primary elements K and P and secondary Mg tend to remain in the ashes, recovery rates are close to 100%.
• the recovery rate of Ni after incineration of the mural A. plant is 98.9 ⁇ 0.1%.
• the results for As, Cd, Co, Cr, Cu, Mn, Pb, Se and Zn show the high volatility of As, Cd and Se during incineration with recovery rates close to 2.7%, 0% and 3.5. %.
• the volatility of these metals shows that care must be taken to treat the flue gases.
• the results show that Ca, Co, Cr and Zn remain in the ashes during incineration with recovery rates of 1 18%, 96.6%, 1 19% and 92.8%.
• the washing of the ashes of A. two-stage mural causes a 23.6% decrease in the mass of ash.
• the analysis of the metals and major elements of the two wash waters PE1 and PE2 shows that these solutions are highly concentrated in K with contents of 9090 mg / L for PE1 and 346 mg / L for PE2.
• Other metals and major elements such as Ni or Mg are present in these wash waters only in trace amounts.
• Table 3 shows the effect of the H 2 SO 4 concentration on the solubilization of Ni from the wall ash.
• the results show that for a total solids concentration of 10 g / L, the recovery rates of Ni for H 2 SO 4 acid concentrations of 0.25, 0.5 and 1 M were respectively measured at 91.2, 94.7 and 96.6. % after a reaction time of 120 min and 98.9, 100 and 100% for a reaction time of 240 min.
• the reaction time seems to be an important parameter for the dissolution of the Ni.
• a duration of 2 h results in a variable and increasing recovery rate as a function of the acid concentration.
• a duration of 4 h allows a low variability of the solubilization of Ni depending on the acid concentration whose recovery rate remains close to 100%.
• a duration of 4 ha was therefore chosen for the following experiments.
• the solid concentration of 10 g / L does not seem suitable for industrial recovery of the ash of mural A. Higher solids concentrations were therefore tested.
• Table 3 Yield of Ni Extraction from Wall Ash As a Function of Acid Concentration, Reaction Time and Solid Concentration
• Solid concentrations of 100 g / L and 150 g / L were tested for the solubilization of Ni from the ash of A. mural.
• An assay of the total basicity of the ashes of the mural A. plant was carried out (results not shown) and made it possible to better estimate the amount of H 2 SO 4 acid to be used for dissolving the Ni contained in these ashes. .
• Table 3 shows the effect of the H 2 SO 4 concentration on the solubilization of Ni from mural ash with an ST concentration of 100 g / L.
• the recovery rates of Ni for H 2 SO 4 concentrations of 0.5, 1 .0, 1 .125 and 1 .5 M were measured at 0, 93.2, 96.2 and 100%, respectively, after a reaction period of 4 h.
• Table 3 also shows the effect of H 2 SO 4 concentration on Ni solubilization from mural ash with an ST concentration of 150 g / L.
• Ni recovery rates for H 2 SO 4 concentrations of 1 .7, 1 .8, 1 .9 and 2.0 M were measured at 75, 93.3, 96.2 and 100%, respectively, after 240 min.
• These experiments were conducted in order to solubilize a minimum of 95% of the Ni contained in the dry mass of A. mural with a minimum amount of sulfuric acid.
• the cost of using sulfuric acid is not prohibitive (with an average price of $ 100 / tonne H 2 S0 4 ). But it is important to limit the quantity used because the process currently used for the recovery requires the neutralization of the leachate of A. mural ash and therefore the use of concentrated NaOH whose price is much higher than that of the acid. sulfuric acid (with an average cost of $ 500 / tonne of 100% NaOH in Quebec).
• the high Ni content in the treated leachate (L2) will be optimal for the crystallization phase of the double sulphate salt of Ni and ammonium (Mullin, 1967, J. Chem., And Eng., Data, 12, 4, p. 516-517, Tavare et al., 1985).
• Table 4 Detailed composition of the ash leachate of the mural A. plant, ash leachate treated by neutralization at pH 5 and dehydration of the crystallization water
• a high concentration of K was also measured with a value of 3228 mg K / L, as well as high levels of secondary major elements, Mg and Ca respectively of 13 680 mg Mg / L and 1086 mg Ca / L.
• Other metals such as Co, Mn or Zn are found in lower concentrations in the range of 14.6 mg Co / L, 45.2 mg Mn / L and 10.1 mg Zn / L.
• Other metals such as As, Cd or Cu are present but remain in concentration ranges close to 1 mg / L.
• the analysis of the metals and major elements of the Fe residue (SW2) shows high Fe contents of the order of 97 g / kg and Ni of the order of 108 g / kg (Table 6). The high Fe content is explained by the precipitation of Fe in the form of Fe hydroxide during the neutralization of the leachate at pH 5 according to the reaction described by Equation 4.
• Equation 4 Fe 3+ + 3 OH " ⁇ Fe (OH) 3 (s)
• Ni sulphate has a high solubility, 630 g / L at 80 ° C (Linke, 1965) and would not precipitate according to the reaction described by Equation 5. Equation 5 Ni 2+ + S0 4 2 " ⁇ NiS0 4 (s) Table 6 Detailed composition of the iron residue, the crude Ni and ammonium sulphate salt and the MgF 2 residue
• SW2 Elements Iron Residue (SW2) Raw Salt (NS2) Residue of mgF2 (SW3)
• the removal of the Mg contained in the double sulphate salts of Ni and ammonium was achieved by a purification step. This step involves the solubilization of the salts produced in an aqueous solution of demineralised water.
• the concentrations of metals and major elements contained in the purification solution (L4) are presented in Table 8. These results showed that the purification solution (L4) had a high content of Ni with a measured concentration of 9 1 16 mg Ni / L. In contrast, the concentration measured in Mg in the purification solution was only 38.9 mg Mg / L.
• Ni can not be explained by the precipitation in the form of soluble Ni hydroxide at neutral pH.
• a precipitation in the form of soluble NiF 2 at neutral pH at 90 ° C is also not possible.
• the formation of NiF 2 is described by Equation 6.
• the amount of F " necessary to precipitate the Ni present in the solubilization solution of the crude salts (L3) as NiF 2 should be 40 times greater than the amount actually introduced in the protocol. adsorption of Ni during the precipitation of MgF 2 at pH 7 may be the explanation for the presence of Ni in this residue.This co-precipitation may be due to the too sudden introduction of the specific amount of NaF in solid form in solution L 3. The introduction of the same quantity of NaF in liquid form drop by drop would undoubtedly allow a better specificity of the precipitation of MgF 2 without trapping Ni.
• Crystallization from the solubilization solution allowed the increase of the Ni content in the purified salt. It was caused by recrystallization of this double salt at 0 ° C where 97% of Ni, 1 1 .4% of K and only 1 .4% of Mg were included in the crystal structure of the double salt.
• Table 8 gives the contents of metals and major elements of the crystallization solution (PE5, with reference to FIG. 1). These results show significant K and Ni contents with measured values of 1,126 mg / L and 1,498 mg / L. The Ni of this water of crystallization can be recycled in the production process of Ni from the mural plant A.

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