EP1922425A2

EP1922425A2 - Method of preparing calcium salts

Info

Publication number: EP1922425A2
Application number: EP06794235A
Authority: EP
Inventors: Lyonel Picard; Charles-Elie Lefaucheur
Original assignee: Valdi
Current assignee: VALDI
Priority date: 2005-08-16
Filing date: 2006-07-27
Publication date: 2008-05-21
Also published as: WO2007020338A2; WO2007020338A3; FR2889843B1; FR2889843A1

Abstract

The invention relates to a method of preparing calcium salts from the group containing calcium molybdate, calcium vanadate, calcium tungstate and mixtures of same. The inventive method is characterised in that it comprises the following steps consisting in: a) using spent catalysts comprising a metal or a combination of metals, selected from among molybdenum, vanadium, tungsten and mixtures of same; b) roasting the spent catalysts from step (a) at a temperature varying between 700 and 1100 °C in excess air in order to obtain roasted catalysts and particulate matter; c) leaching the roasted catalysts and/or particulate matter obtained in step (b) using a base solution; d) purifying the aqueous leaching solution obtained in step (c) and comprising elements from the group containing molybdenum, vanadium, tungsten and mixtures of same, by means of treatment at neutral pH at approximately 90 °C; and e) precipitating the calcium salts from the group containing calcium molybdate, calcium vanadate, calcium tungstate and mixtures of same in the purified aqueous leaching solution obtained in step (d), using calcium compounds. The invention also relates to the use of calcium salts selected from among calcium molybdate (CaMoO4), calcium vanadate (CaV2O6), calcium tungsate (CaWO4) and mixtures of same, which are obtained using one such method for producing alloy steels.

Description

Process for the preparation of calcium salts

The present invention relates to a process for the preparation of calcium salts, in particular calcium molybdate (CaMoO ₄ ), calcium tungstate (CaWO ₄ ) and calcium vanadate (CaV ₂ O ₆ ), alone or as a mixture, from used catalysts from, among others, the petroleum industry

(hydrotreatment, hydrodesulphurization and hydrocracking).

In the iron and steel industry, it is sought to manufacture alloy steels, that is to say steels comprising one or more metals which provide the steel with particular desired properties, such as, for example, resistance to temperature, resistance corrosion, or a high mechanical strength, etc. for applications in different industries, such as automotive manufacturing, aeronautics, cutting tools or machining, or transport. Among the metals used in the manufacture of alloy steels, stainless steel, refractory, special or fast, we find molybdenum, tungsten or vanadium. In this case, commonly used as a source of molybdenum, tungsten or vanadium, ferroalloys, such as FeMo, FeV ₁ FeW or oxide briquettes, for example MOO3, V ₂ O ₅ and WO ₃ . The ferroalloys or oxides mentioned above are expensive and constitute an important part of the cost of production of stainless steel or fast steel mentioned above.

On the other hand, the use of ferroalloys or oxide briquettes is not entirely satisfactory because it requires the supply of CaO, usually made by adding quicklime. However, it turns out that the hygroscopic nature of the lime can generate defects, such as pits, blowholes or gas bubbles, which are the cause of scrap metal finished products.

Thus, it would be advantageous to have pure products based on molybdenum, tungsten or vanadium, alone or as a mixture, which can be used in the manufacture of alloy steels, which in particular would be less expensive than the ferroalloys or briquettes of oxides and which would remedy the quality problems of the steels mentioned above.

On the other hand, molybdenum, tungsten and vanadium are themselves expensive metals. These metals are for example used in the composition of catalysts, in particular catalysts used in the petroleum industry, for example for hydrotreatment, hydrodesulfurization and hydrocracking operations.

It is important, for economic and environmental reasons, to recover the precious metals of molybdenum, tungsten and vanadium when these catalysts are used.

The Applicant has discovered a particular process for producing calcium salts, in particular calcium molybdate, calcium tungstate and calcium vanadate, which are particularly pure, alone or as a mixture, from used catalysts comprising molybdenum tungsten and / or vanadium.

In the present application, the term "pure calcium salts", calcium salts substantially free of undesirable pollutants such as arsenic (As) and phosphorus (P), including calcium salts whose respective content of arsenic and phosphorus is strictly less than 200 ppm.

These calcium salts can then be advantageously used in the production of ferroalloys or as an enrichment material in molybdenum, tungsten and / or vanadium in the manufacture of ferrous or non-ferrous alloys, in particular in substitution for ferroalloys FeMo , FeV and FeW or oxide briquettes of MoO ₃ , V ₂ O ₅ and WO ₃ .

An object of the invention is a process for the preparation of calcium salts included in the group consisting of calcium molybdate, calcium vanadate, calcium tungstate and mixtures thereof, characterized in that it comprises the following steps: - a °) there are used catalysts comprising a metal or a combination of metals, selected from molybdenum, vanadium, tungsten and mixtures thereof,

b) the used catalysts combined in a) at a temperature ranging from 700 to 1100 ^° C., in excess of air, are roasted to obtain grilled catalysts and dusts,

(c) leaching of the grilled catalysts and / or dusts obtained in b) with a basic solution is carried out,

- d °) the aqueous leaching solution obtained in c °) and comprising the elements included in the group consisting of molybdenum, tungsten, vanadium and their mixtures, is purified by treatment at neutral pH at about 90 ^° C., in the purified aqueous leaching solution obtained in d °), the calcium salts included in the group consisting of calcium molybdate, calcium vanadate, calcium tungstate and mixtures thereof are precipitated; by calcium compounds. The process according to the invention makes it possible both to recover precious metals in a directly usable form and to produce either pure or combined ferroalloys or enrichment materials made of these metals which are particularly easy to use in the steel industry and in foundry. Furthermore, the calcium salts produced according to the process of the invention can be used in the manufacture of alloy steels without the addition of quicklime: such a use has the advantage of limiting the risks of pitting, blow-molding and gas bubbles. often observed when using quicklime.

In particular, the calcium salts obtained according to the process of the invention are practically free of particularly undesirable pollutants such as arsenic (As) and phosphorus (P).

Finally, the process according to the invention makes it possible to produce calcium salts at a reduced economic cost and to limit damage to the environment by allowing the recycling of valuable raw materials such as molybdenum, tungsten and vanadium contained in end of life products.

By virtue of a specific succession of pyrometallurgical and hydrometallurgical steps chosen, the process according to the invention makes it possible to recycle used catalysts in a simple, fast and inexpensive manner and to produce either ferroalloys or enrichment molybdenum, tungsten and / or vanadium directly usable in the iron and steel industry and in foundries.

In a first step of the process according to the invention, starting materials are combined in the form of used catalysts comprising a metal or a combination of metals, generally supported by the catalyst, chosen from molybdenum, vanadium, tungsten and their mixtures. These catalysts are generally used in the chemical, gas treatment or petroleum industry, in particular in the cracking and refining processes, for example to desulphurize the distillation products. The metal or combination of metals may be selected from Ni-Mo, Co-Mo, Ni-Co-Mo, Ni-Mo-V, Bi-Co-Mo, Ni-W, V- W. The support of these used catalysts is generally chosen from alumina, silica, titanium oxide and mixtures thereof.

Generally, the metal or combination of metals is present in the minor catalyst, preferably at a content ranging from 5 to 30%, more preferably from 15 to 30% by weight, based on the weight of the used catalyst.

Preferably, the support is present in the used catalyst at a content ranging from 65 to 90%, more preferably from 70 to 85%, by weight, relative to the weight of the used catalyst. These catalysts may also include sulfur. The sulfur may be present in the spent catalyst at a level of from 3 to 25%, more preferably from 8 to 12%, by weight, based on the weight of the catalyst.

These spent catalysts also generally include hydrocarbons and carbon from the distillation products that these catalysts have been used to desulphurize or gas treatment for example during the cracking of nitrogen oxides to limit emissions of greenhouse gases.

These spent catalysts thus comprise mainly, in whole or in part, oxidized or sulfur compounds of molybdenum (Mo), nickel (Ni), cobalt (Co), tungsten (W), vanadium (V), bismuth (Bi), aluminum (AI), titanium (Ti) and silicon (Si), sulfur (S), carbon (C), hydrocarbons (HC) and residual metals of the arsenic type (As ), phosphorus (P).

In a second step of the process according to the invention, these used catalysts are grid at a temperature ranging from 700 to 1100 ^° C., in excess of air, to obtain grilled catalysts and dust.

Preferably, the used catalysts are selectively grilled and by campaign in a controlled and oxidizing atmosphere. Such a grid makes it possible to extract used catalysts sulfur (S), carbon (C), hydrocarbons (HC) and arsenic (As).

In one embodiment of the process of the invention, used catalysts are burned at a temperature ranging from 800 to 1000 ^° C. The formation of alumina-metal oxide spinels is thus limited, which then allows a better leaching during heating. subsequent step of the process. Moreover, such a temperature makes it possible to sublimate a pollutant such as arsenic (As) that goes through the dust. Such a temperature also makes it possible to pass the sulphides in the form of oxides.

In the roasting step, the metal or combination of metals included in the group consisting of molybdenum, tungsten, vanadium and mixtures thereof, is partially sublimed. For example, molybdenum is sublimated during its oxidation as MoO ₃ . Preferably, this MoO ₃ is recovered at the first stage of a bag filter. The oxidized compounds of the elements Al, As, P, V and W accompany the dust. Thus, these MoO ₃ rich dusts also include A 2 O ₃ , P ₂ O ₅ and I ¹ As ₂ O ₃ .

The deep roasting makes it possible to sublimate up to 70% of the quantity of metal or of the combination of metals included in the group consisting of molybdenum, tungsten, vanadium and their mixtures, initially present in the spent catalyst: the content of metal or combination of metals included in the group consisting of molybdenum, tungsten, vanadium and their mixtures, in used catalysts is greatly reduced.

After roasting, the carbon content (C) in spent catalysts is preferably less than or equal to 5% by weight, relative to the weight of used catalysts.

After roasting, the sulfur content (S) in the used catalysts is preferably less than or equal to 3% by weight, relative to the weight of used catalysts.

After roasting, the content of metal or combination of metals included in the group consisting of molybdenum, tungsten, vanadium and their mixtures, in used catalysts is preferably less than or equal to 6% by weight, relative to the weight of used catalysts.

In one embodiment of the process according to the invention, the gaseous effluents from the roasting can pass through an afterburner chamber after leaving the roasting furnace and can be burned at more than

850 ⁰ C in excess of air. After dedusting, these gaseous effluents are treated with basic salts so as to neutralize and capture in the form of a stable compound SO ₂ sulfur dioxide generated by roasting. The basic salts employed are calcium hydroxide Ca (OH) ₂ or preferentially sodium bicarbonate as for example described in application EP

1,550,495. In a third step of the process according to the invention, namely according to step c °), leaching of the grilled catalysts and / or dusts obtained in b °) is carried out using a basic solution.

The leaching may be carried out with sodium hydroxide NaOH, ammonia NH ₃ or sodium carbonate Na ₂ CO ₃ in aqueous solution.

Leaching with soda involves the following reactions:

MoO ₃ + 2 NaOH → Na ₂ MoO ₄ + H ₂ O

WO ₃ + 2 NaOH → Na ₂ WO ₄ + H ₂ O

V ₂ O ₅ + 2 NaOH → 2 NaVO ₃ + H ₂ O

AI ₂ O ₃ + 2 NaOH → 2 NaAlO ₂ + H ₂ O

Soda ash leaching involves the following reactions:

MoO ₃ + Na ₂ CO ₃ → - Na ₂ MoO ₄ + CO ₂

WO ₃ + Na ₂ CO ₃ → Na ₂ WO ₄ + CO ₂

V ₂ O ₅ + Na ₂ CO ₃ → 2 NaVO ₃ + CO ₂

AI ₂ O ₃ + Na ₂ CO ₃ → 2 Na ₂ O ₂ + CO ₂

During this leaching step, special care must be taken in minimizing the dissolution of the alumina. Indeed, the alumina is necessary later for the purification of the leaching solution and must not be dissolved in large quantities during this leaching step.

Preferably, the used catalysts are leached with sodium hydroxide NaOH or sodium carbonate Na ₂ CO ₃ . Indeed, although ammonia is less aggressive than soda or sodium carbonate towards alumina, it dissolves the elements Co, Ni, Mo and V. However, it is important for the subsequent step of obtaining a leach solution free of Co and Ni.

Preferably, the leaching of used catalysts is carried out with a mixture of sodium hydroxide (NaOH) and sodium carbonate Na 2 CO 3, doped with hydrogen peroxide (H ₂ O ₂ ).

The leaching parameters (pH, redox potential, residence time, flow rates, concentrations, liquid / solid ratio, etc.) are adapted according to the catalyst so as to avoid excessive dissolution of the alumina. Preferably, the sodium hydroxide is present in excess, for example

20%, based on the stoichiometry of the leaching reaction for each oxide MoO ₃ , WO ₃ , V ₂ O ₅ . Such an excess of sodium hydroxide makes it possible to limit the dissolution of alumina.

The leaching step can generally last from 30 to 200 minutes. The leaching is generally carried out at a moderate temperature ranging from 50 to 100 ^° C., preferably ranging from 70 to 90 ^° C., preferably continuously and countercurrently in a series of at least 2 trays, for example 3 12 or more bins per percolation.

It has been observed in one example that in the case of sodium hydroxide, the extraction yield of molybdenum and tungsten, depending on the type of catalyst, is 75 to 85%: that of vanadium is between 65 and 80%.

The leach solution obtained at the end of this step comprises the elements included in the group consisting of molybdenum, tungsten, vanadium and their mixtures as well as impurities such as P, As, Al and optionally Ni and Co. However, preferably, the Ni and Co possibly present in the used starting catalysts are not dissolved and remain on the supports of said catalysts.

In a fourth step of the process according to the invention, namely according to step d °), the aqueous leaching solution obtained in c °) and comprising the elements included in the group consisting of molybdenum, tungsten and vanadium is purified. and their mixtures.

According to the process of the invention, the leaching solution is purified by treatment at neutral pH. This makes it possible to eliminate by precipitation the elements P, As ₁ Al, and the traces of Ni and Co almost completely. The traces of Fe and Si can also be eliminated with very high yields. After this purification, the respective content of each of the elements As, Al, P, Ni, Co, Fe and Si in the leaching solution is preferably less than 2 mg / l.

The mineral acids H ₃ PO ₄ , HNO ₃ , HCl and H ₂ SO ₄ can be used for this precipitation by acid neutralization. Thus, in one embodiment of the process of the invention, during the purification of step d °), the leaching solution is brought to a neutral pH by addition of an acid selected from H ₃ PO ₄ , HNO ₃ , HCl, H ₂ SO ₄ and mixtures thereof. Preferably, the acid is H ₂ SO ₄ .

According to the process of the invention, the treatment at neutral pH or neutralization of the purification step is carried out at about 9O ⁰ C. Such a temperature makes it possible to improve the precipitation of P ₁ As, Fe and Si and simultaneously limits the possible and undesired precipitation of molybdenum and / or vanadium. Thanks to the process of the invention, it is therefore possible to separate unwanted pollutants such as arsenic and phosphorus from the leach solution. The calcium salts obtained at the end of the process are thus practically free of these pollutants.

It has been observed that the initial Al content of the leaching solution has a significant effect on the purification and the precipitation yield of As, Mo, V, P, Ni and Co. In fact, the following behavior is observed (cf. table 1):

Precipitation yield (% w)

Table 1: Precipitation yield of elements Ni, Co ₁ As, P, Mo and V according to the Al content of the leaching solution

The sedimentation of the precipitates formed is favored by the addition of flocculants in the presence of bubbling air. Once the purification has been carried out, a fifth step of the process according to the invention is carried out, namely according to step e °), a precipitation of the calcium salts included in the group consisting of calcium molybdate and calcium vanadate. calcium tungstate and mixtures thereof with calcium compounds.

In one embodiment of the invention, the purified leach solution is precipitated by addition of calcium chloride (CaCl ₂ ) or lime milk to obtain calcium salts of the metals of the group consisting of molybdenum, vanadium, tungsten and their mixtures. In one embodiment of the invention, nonselective precipitation of vanadium and molybdenum is achieved; the purified leaching solution is then, for example, acidified to a pH ranging from 4 to 5 by addition of hydrochloric acid HCl or nitric acid HNO ₃ . CaCl ₂ is then added to precipitate the molybdenum contained in solution. The reactions involved are the following:

Na ₂ MoO ₄ + 2 HCl → 2 NaCl + MoO ₃ -H ₂ O and NaVO ₃ + HCl → NaCl + HVO ₃

Na ₂ MoO ₄ + 2 HNO ₃ → NaNO ₃ + MoO ₃ -H ₂ O and NaVO ₃ + HNO ₃ → NaNO ₃ + HVO ₃

Na ₂ MoO ₄ + CaCl ₂ -> 2NaCl + CaMoO ₄ and 2NaVO ₃ + CaCl ₂ -> 2NaCl + CaV ₂ O ₆

In another embodiment of the process according to the invention, a selective precipitation of vanadium and molybdenum is carried out; the leaching solution is then, for example, first neutralized to a pH of between 7 and 8 by addition of ammonium chloride NH ₄ Cl. Vanadium is precipitated in the form of sodium metavanadate NH ₄ VO ₃ according to the reaction:

NaVO ₃ + NH ₄ CI → NH ₄ VO ₃ + NaCl A solid / liquid separation, using a filter press for example, makes it possible to expell the solution of sodium metavanadate crystals which are dried before conditioning.

The sodium molybdate present in the solution thus clarified is then precipitated by addition of calcium chloride CaCb according to the reaction:

Na ₂ MoO ₄ + CaCl ₂ → 2 NaCl + CaMoO ₄

In another embodiment of the process according to the invention, milk of lime can also be used.

Finally, a solid / liquid separation, using a filter press for example, makes it possible to expell the solution of the calcium molybdate crystals with or without the calcium vanadates and calcium tungstates in a mixture. These crystals can be dried or calcined before conditioning. In one embodiment of the process according to the invention, so as to produce a calcium molybdate free of sulfur and phosphorus, harmful impurities in metallurgical applications, the precipitation of molybdenum can be pushed up to 80% of molybdenum precipitated relative to to the total amount of molybdenum present in the leach solution. The solution is filtered and precipitated again with production of a calcium molybdate, with or without the calcium vanadates and calcium tungstates in mixture, and containing sulfur in particular.

The calcium molybdate (CaMoO ₄ ) obtained can either be sold as is or put back in the lead of the leaching process. In one embodiment of the process of the invention, the salts obtained in the fifth stage, namely calcium molybdate (CaMoO ₄ ), calcium tungstate (CaWO ₄ ), are optionally dried and / or calcined. calcium vanadate (CaV ₂ Oe) and / or mixtures thereof.

The process according to the invention makes it possible to recover precious metals in a directly usable form to produce pure or combined ferroalloys or to produce enrichment materials made of these precious metals that are particularly simple to use in the iron and steel industry and in foundries. Moreover, the calcium salts produced according to the process of the invention are particularly pure and can be used in the manufacture of alloy steels without the addition of quicklime: such a use has the advantage of reduce the risk of punctures, blisters and gas bubbles that are usually observed when using quicklime.

The process according to the invention makes it possible in particular to obtain calcium salts which are practically free of undesirable pollutants such as arsenic and phosphorus.

The present invention further relates to the use of calcium salts selected from calcium molybdate (CaMoO ₄ ), calcium vanadate (CaV ₂ O ₆ ), calcium tungstate (CaWO ₄ ) and mixtures thereof, obtained according to the above method for making alloy steels.

The present invention will now be illustrated by the following examples:

EXAMPLE 1

In a first step, used catalysts are available from the hydrotreating of petroleum fractions, having the following composition:

Table 2: Chemical composition of used hydrotreating catalyst of petroleum cuts (renormalization of the contents after removal of carbon and sulfur) Toasting:

In a second step, these catalysts are roasted in excess of air at a temperature ranging from 700 to 800 ^° C. Used burnt catalysts and dust rich in oxides of molybdenum, tungsten and / or vanadium are recovered.

Leaching;

In a third step, the used grilled catalysts obtained in the preceding step are leached with sodium hydroxide.

200 g of grilled catalysts obtained in the preceding step are leached with 300 ml of sodium hydroxide concentrated at 60 g / l for 3 hours at 90 ^° C. Table 3 shows the results obtained.

Table 3: Results of leaching hydrotreating catalyst with sodium hydroxide

The leaching yields of Mo, V and Al are respectively 86%, 65% and 3%.

Purification by precipitation in a neutral medium:

In a fourth step, the leaching solution obtained in the preceding step is purified by treating this solution at neutral pH.

The precipitation is carried out at 90 ^° C. A volume of 14 ml of concentrated sulfuric acid H ₂ SO ₄ at 100 g / l is added to 100 ml of leaching solution of pH 11.8. After adding H ₂ SO-I, the pH is raised from 11.8 to 7. The volume of the purified solution is 114 ml and the pH is 6.6. A precipitate is collected: its mass is 2 g.

Table 4 shows the results obtained during the purification.

Table 4: Results of the purification of the hydrotreating catalyst leaching solution with sodium hydroxide

The precipitation yields of Mo, V, Al and As are respectively 8%, 28%,> 98% and 97%. Thus, the separation of arsenic, and thus its elimination, is particularly powerful.

Precipitation of V and Mo: case of selective precipitation

In a fifth step, a selective precipitation of vanadium and molybdenum is carried out.

The selective precipitation of Mo and V contained in the purified leaching solution is carried out on 100 ml of purified solution at 90 ^° C. with the addition of 38 ml of aqueous solution of ammonium chloride NH ₄ CI concentrated to 100 g / l.

The precipitation yields of molybdenum and vanadium are respectively 1, 5% and greater than 95%. The solution is filtered and clarified. Then, the solution thus clarified and freed from vanadium is mixed with 14 ml of aqueous solution of CaCl ₂ concentrated to 100 g / l.

The precipitation yield of the molybdenum is greater than 95%. The solution is filtered and clarified.

The moisture content of the filtered calcium molybdate in filter press is 40 to 45%. The Mo content of calcium molybdate, on a dry basis, is between 35 and 45%. Calcium molybdate is powdery after drying. A calcination step between 500 and 700 ⁰ C or granulation makes it possible to obtain respectively sintered blocks (diameter less than 100 mm) or granules (diameter less than 50 mm).

The calcination makes it possible to bring the molybdenum content, on a dry basis, between 40 and 46% Mo.

The typical chemical composition of calcium molybdate at the filter press outlet, on a dry basis, is presented in Table 5.

Table 5: Chemical composition of calcium molybdate produced from hydrotreatment catalysts

As is clear from Table 5, the calcium molybdate obtained by the process according to the invention is practically free of undesirable pollutants such as arsenic and phosphorus, the latter being present at levels strictly below 200 ppm. EXAMPLE 2

Table 6: Chemical Composition of Used Hydrotreating Catalyst of Petroleum Cuts (renormalization of the contents after removal of carbon and sulfur)

Toasting:

In a second step, these catalysts are roasted in excess of air at a temperature ranging from 700 to 1000 ^° C. Used burnt catalysts and dust rich in molybdenum oxides are recovered.

Leaching;

200 g of grilled catalysts obtained in the preceding step are leached with 500 ml of concentrated sodium hydroxide solution at 70 g / l for 3 hours at 90 ^° C. in order to respect a mass ratio NaOH in Kg / Mo in Kg = 2. 7 presents the results obtained.

Table 7: Results of leaching hydrotreating catalyst with sodium hydroxide

The leaching yields of Mo and Al are respectively 80% and 9.9%.

Purification by precipitation in a neutral medium;

The precipitation is carried out at 90 ^° C. for 1 hour with stirring.

A volume of 17 ml of sulfuric acid H ₂ SO ₄ at 98% purity is added to 450 ml of leaching solution of pH 13-14, in order to bring the pH to 7. The volume of the purified solution is 467 ml and the pH of 7. A precipitate is collected: its mass is 32.3 g. This precipitate mainly comprises arsenic (As), aluminum (Al) and a small proportion of molybdenum (Mo).

Table 8 shows the results obtained during the purification.

Table 8: Results of the purification of the leaching solution of hydroprocessing catalyst with sodium hydroxide The loss of molybdenum due to the precipitation of part of the molybdenum during the purification represents 5 to 15% of the molybdenum present in the leaching solution before purification.

The precipitation yields of Al and As during the purification range from 40 to 60% and from 60 to 85%, respectively.

Thus, the separation of arsenic, and thus its elimination, is particularly powerful.

Precipitation of Mo: case of a non-selective precipitation

To the purified solution obtained in the previous step is added acid (HCl at 37% purity or HNO ₃ at 69% purity) in order to bring the pH of the purified solution to between 4 and 5.

CaCl _{2 is} then added, respecting a mass ratio of 1 between the amount of CaCl ₂ and that of the theoretical Mo. After stirring, a precipitate is obtained.

The molybdenum precipitation yield is greater than 60%.

A washing with clear water of the formed precipitate can be carried out to eliminate the residual salts such as Cl, Na, ...

The moisture content of the filter-filtered calcium molybdate is 30 to 50%. The Mo content of calcium molybdate, on a dry basis, is between 20 and 30%. Calcium molybdate is powdery after drying. A calcination step between 500 and 700 ⁰ C or granulation makes it possible to obtain respectively sintered blocks (diameter less than 100 mm) or granules (diameter less than 50 mm).

The calcination makes it possible to bring the molybdenum content, on a dry basis, between 25 and 45% Mo, according to the residual impurities.

The typical chemical composition of calcium molybdate at the filter press outlet, on a dry basis, is presented in Table 9.

Table 9: Chemical composition of calcium molybdate produced from hydrotreatment catalysts

As is clear from Table 9, the calcium molybdate obtained by the process according to the invention is practically free of undesirable pollutants such as arsenic and phosphorus, the latter being present at levels strictly below 200 ppm.

EXAMPLE 3 Production of ferroalloys from calcium molybdate, calcium vanadate, calcium tungstate, pure or mixed:

The pure or mixed molybdates, tungstates, calcium vanadates produced from used catalysts for the refining of petroleum fractions can be used in the production of ferroalloys of the FeMo, FeV, FeW, FeMoV, FeVW or FeMoW type, for example, or in the form of enrichment. ferrous or non-ferrous alloys.

The vanadate, tungstate and calcium molybdate are advantageously charged as a material for the substitution of MoO ₃ , WO _{3 or} WO ₂ O ₅ technical oxides or ferroalloys FeMo, FeV and FeW associated therewith. Ferroalliaqes:

For example, to produce one ton of FeMo containing 70% Mo, 1488 kg of CaMoO _{4 are used} with a yield of 98%. This equates to 1071 kg of MoO ₃ technical oxide and 417 kg CaO equivalent to 435 kg of charging lime.

Enrichment:

For example, to produce one tonne of tool steel typically containing 5% Mo, 6% W and 1.5% V, 106 kg CaMoO ₄ , 96 kg CaWO ₄ and 36 kg CaV ₂ O _{6 are used} .

Claims

A process for the preparation of calcium salts included in the group consisting of calcium molybdate (CaMoO ₄ ), calcium vanadate (CaV ₂ O ₆ ), calcium tungstate (CaWO ₄ ) and mixtures thereof, characterized in that that it includes the following steps:

- a °) there are used catalysts comprising a metal or a combination of metals, selected from molybdenum, vanadium, tungsten and mixtures thereof - b) the used catalysts are reunited in a) at a temperature of from 700 to 1100 ^° C., in excess of air, to obtain grilled catalysts and dust,

(c) leaching of the grilled catalysts and / or dusts obtained in (b) with a basic solution is carried out; (d) the aqueous leaching solution obtained in (c) is purified and comprising the elements included in the group consisting of molybdenum, tungsten, vanadium and their mixtures, by treatment at neutral pH at about 90 ⁰ C,

in the purified aqueous leaching solution obtained in d °), the calcium salts included in the group consisting of calcium molybdate, calcium vanadate, calcium tungstate and mixtures thereof are precipitated; by calcium compounds.

2. Method according to claim 1, characterized in that, in step b °), the used catalysts are grid at a temperature ranging from 800 to 1000 ° C.

3. Method according to claim 1 or 2, characterized in that, in step c), the used catalysts are leached with a mixture of sodium hydroxide (NaOH) and sodium carbonate Na ₂ CO ₃ , doped with hydrogen peroxide (H ₂ O ₂ ).

4. Method according to the preceding claim, characterized in that the sodium hydroxide is present in excess of 20% relative to the stoichiometry of the leaching reaction for each oxide MoO ₃ , WO ₃ , V ₂ Os.

5. A method according to any one of the preceding claims, characterized in that, in step c), the leaching is carried out at a moderate temperature ranging from 50 to 100 ⁰ C ₁ preferably ranging from 70 to 90 ° C .

6. Method according to any one of the preceding claims, characterized in that, during the purification of step d °), the leaching solution is brought to neutral pH by adding an acid selected from H ₃ PO ₄ , HNO ₃ , HCl, H ₂ SO ₄ and mixtures thereof.

7. Process according to the preceding claim, characterized in that the acid is H ₂ SO ₄ .

8. Method according to any one of the preceding claims, characterized in that, in step e °), the purified leaching solution is precipitated by adding calcium chloride (CaCl ₂ ) or milk of lime to obtain calcium salts of the metals of the group consisting of molybdenum, vanadium, tungsten and mixtures thereof.

9. Process according to any one of the preceding claims, characterized in that, in step e °), non-selective precipitation of vanadium and molybdenum is carried out.

10. Process according to any one of claims 1 to 8, characterized in that, in step e °), a selective precipitation of vanadium and molybdenum is carried out.

11. Process according to any one of the preceding claims, characterized in that a drying and / or calcination of the salts obtained in step e °) is carried out.

12. Use of calcium salts selected from calcium molybdate (CaMoO ₄ ), calcium vanadate (CaV ₂ O ₆ ), calcium tungstate (CaWO ₄ ) and mixtures thereof, obtained according to the process according to one of the following: any of claims 1 to 11 for making alloy steels.