JP2002529358A - Method for non-exudative fixation of molybdenum compounds in slag - Google Patents

Abstract

SUMMARY OF THE INVENTION The present invention relates, for example, to a process under an oxygen pressure of 10 ^-6 to 10 ^-12 bar, preferably 10 ^-7.5 to 10 ^-9.5 bar, preferably at a temperature above the liquidus temperature of the slag of 50 s. At elevated temperature, the Fe (III) / Fe (II) ratio in the slag is adjusted to a value between 0.25 and 2 under the thermodynamic activity of Fe (II) in the slag above 0.5. A non-exudative fixation of molybdenum compounds in slag by treating a waste stream containing iron and molybdenum under reducing conditions. The resulting slag is then cooled in such a way that a solid solution of MoO _{2 in} the spinel structure is obtained, which spinel structure shows very low leaching values for molybdenum. For this reason, such slag can be used, for example, as a material in the construction industry.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for the non-leaching fixation of molybdenum compounds in slag by melting and subsequently cooling a waste stream containing iron and molybdenum compounds.

[0002] Molybdenum compounds are present in a number of very specific waste streams. Examples thereof are WII (Waste Incineration)
and fly ash from the processing of chemical waste, for example by incineration in a rotary furnace. The source of molybdenum is due in part to the corrosion of the equipment used and is partly in the waste stream processed in said equipment.

[0003] In the building industry, many residues are commonly used before and after pretreatment.
Just like many other elements, molybdenum must comply with leachability requirements if the waste stream being processed is to be used as construction material. In the Netherlands, this requirement is specified in the Bowstoffenbesluit (Building Materials Order).

[0004] From a chemical point of view, molybdenum is one of the elements that form oxyanions, and the compounds containing these ions are usually very soluble in water. This makes it more difficult for molybdenum to comply with leaching requests under the Building Materials Order. This problem is substantially independent of the technical approach taken when processing the waste stream. In both the case of low-temperature fixation (mixing of waste streams with, for example, cement) and the processing in the form of a melt (thermal fixation or pyrometallurgy), the leachability of molybdenum is determined by the building materials order. Are repeatedly found to exceed the standards specified in The standard specified for molybdenum is a maximum emission value of 150 mg / m ² per 100 years.

[0005] Surprisingly, the above problem is a consequence of the reduction conditions under which the oxygen pressure is set to a relatively narrow range so that after crystallization, a slag is obtained which indicates that the leaching of molybdenum is substantially reduced. It has now been found that it can be completely or substantially solved by performing a pyrometallurgical treatment of a molybdenum-containing waste stream below. The waste stream containing molybdenum to be used by the process according to the invention must also contain iron compounds in question in virtually every case in which they occur. However, if such a waste stream does not contain iron compounds, it must be added separately.

[0006] In particular, the present invention provides:-the process temperature exceeds the liquidus temperature of the slag,-the oxygen pressure is adjusted to a value of 10 ^-6 to 10 ^-12 bar,
Are those CO / CO ₂ ratio of 10 can be achieved by setting the fuel to oxygen ratio so as to obtain the gas of the furnace, - thermodynamic activity of Fe (II) in the slag (thermodynamic ac
the slag has a Fe (III) / Fe (II) ratio of 0.25 to 2; and, after removal, a solid solution having a spinel structure is obtained. It relates to the method specified in the preamble, characterized in that the slag is cooled.

[0007] Advantageously, the following conditions are set for the method according to the invention. The operating temperature should preferably be above 50 ° C. of the liquidus temperature of the slag. The oxygen pressure is adjusted to a value between 10 ^-7.5 and 10 ^-9.5 bar. This means
For example, this can be achieved by setting the fuel to oxygen ratio such that a CO / CO ₂ ratio of 0.5 to 5 is obtained in the furnace gas. The slag composition is adjusted such that the thermodynamic activity coefficient of Fe (II) in the slag is ≧ 1. This can be achieved by careful composition determination of the mixture of materials to be melted. The manner in which the activity factor can be calculated is described, for example, in the following references: -Michaels M .; A. J. And Wesker
r) E. 1985, "Thermodynamic modeling of solid-liquid interaction in oxides and silicates": Solid State Ionics 16: 33-38.
And-Michaels M. A. J. And Wesker E. , 1987, "network (network) model for thermodynamics of multicomponent silicate melt, I binary mixture MO-SiO _2." Karufaddo (Calphad), 11 (4) : 3
83-393. The Fe (III) / Fe (II) ratio in the slag is adjusted to be between 0.5 and 1.5, and the residence time in the furnace is used as a parameter for this.

[0008] The resulting slag is then removed and then slowly cooled. therefore,
The cooling must not be sudden (such as "quenching"). Since it prevents crystallization. For example, crystallization can occur by allowing the slag pot where the slag is present to be cooled in air or by imposing a suitable cooling condition on the slag in a cooling oven. Normally, the slag will be removed into a large slag pot having a capacity of approximately one ton and will be cooled in air for approximately 24 hours. Such a cooling procedure gives on average a cooling rate of approximately 60 K / h. Therefore, generally, for the method according to the invention, 10 to 2
A cooling rate of 00 K / h, advantageously 40 to 80 K / h, will be used.
If such conditions are maintained, a spinel belonging to the 2FeO.MoO ₂ —Fe ₃ O ₄ series, to which molybdenum is bonded very hard, with a view to a small degree of leaching, is formed.

The method of the present invention will be described in more detail based on the following examples.

Example A waste stream was melted in a melting facility under reducing conditions. The furnace of the melting plant consisted of a cylindrical water-cooled chamber, in which part of the molten slag solidified as a thin layer on the walls, the slag inside falling down and being collected in the slag bath.
The slag bath was periodically emptied several times and the removed slag was cooled in a slag pot in air. The cooling took approximately 24 hours. The furnace was further equipped with an oxy-fuel burner in which the oil was burned with technical grade oxygen.
The feed was fed to the furnace through a flame. The off-gas was after combustion, then the acid component was removed in a wet gas scrubber, after which the flying material was separated.

[0011] Four different waste streams were treated to create different mixtures. Regarding the most important elements, the composition of the waste stream is given in Table 1 below (except Mo and Pb in% (m / m), given in ppm).

[Table 1]

Two mixtures having the mixing ratios specified in Table 2 (in%) were made from the respective starting materials.

[Table 2]

In addition, 21 kg of magnesium hydroxide and 15 kg of coke per 100 kg of feed mixture were also added to the two mixtures. Magnesium hydroxide serves to obtain the correct slag composition with the relevant desired crystallization behavior.

The calculated liquidus temperature, which is the temperature at which the entire mixture is liquid, was 1250 ° C. for both mixtures. The calculated activity coefficients of FeO were 1.2 and 1.4 for a given slag composition, respectively.

[0015] Mixture 1 melted under significantly higher oxygen pressure than Mixture 2, with oxygen pressures of 10 ^-5 and 10 ^-9 bar, respectively. The temperature in the furnace is at least 1350
° C. Both slags were well crystallized and had a black color.

[0016] The composition of the slag and the composition of the related flying materials only for the relevant elements are given in Table 3 below.

[Table 3]

The volatilization of elemental zinc and lead can be calculated from the results given in Table 3.
For mixture 1, their values are 71% and 59%. For the test on mixture 2, their values are 93% and 81%. The greater volatility in the case of the test on mixture 2 is consistent with the stronger reducing conditions imposed.

The following crystalline phases can be observed in the slag crystallized by X-ray diffraction. In mixture 1: diopside (diopside), forsterite (magnesium olivine) / firelite (iron olivine); they belong to the pyroxene and olivine families, respectively. In mixture 2: diopside, forsterite / firelite and magnetite (magnetite); the latter belongs to the spinel.

The exudation of molybdenum from slag was quantified according to NEN 7343 specified in the Building Materials Order. Generally, the material has been ground and screened for this leaching test. The 4 mm screening fraction is introduced into a column through which nitric acid at pH 4 passes. Seven samples are taken after a number of (specified) volumes have passed. The composition of the exuded liquid is then measured, and the quantified concentration is converted to obtain the release, which is then compared to a standard. Further details regarding the leaching test are given in NEN 7343.

The ratio of the amount of molybdenum exuded from the slag to the amount of the approved standard is 7.6 for mixture 1 and 0.64 for mixture 2. Thus, it is clear that the slag that crystallizes with spinel magnetite (FeO.Fe ₂ O ₃ ), in which a solid solution of MoO ₂ is present, shows molybdenum leaching clearly smaller than the standard.
As a result, as far as molybdenum exudation is concerned, such slag can be used freely in the construction industry.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID , IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW (71 ) Applicant Industristraat 8, 3281 LB Numandsdorp, The Netherlands F term (reference) 4D004 AA37 AB03 BA02 CA29 CA32 DA02 DA03 DA06 DA07 DA10 DA20 4G012 JB00 JB03 JC04 JC00 JF03 J

Claims (6)

[Claims] A method for non-leaching fixation of a molybdenum compound in a slag by melting and subsequently cooling a waste stream containing iron and molybdenum compound, wherein the treatment temperature is the liquid phase of the slag Above the linear temperature, the oxygen pressure is adjusted to a value between 10 ^-6 and 10 ^-12 bar, the thermodynamic activity of Fe (II) in the slag is ≧ 0.5, III) / Fe (II) ratio of 0.25 to 2, wherein after removal, the obtained slag is cooled to obtain a solid solution having a spinel structure. 2. The method according to claim 1, wherein the treatment temperature for the waste stream is at least 50 ° C. above the liquidus temperature of the slag. 3. The method according to claim 1, wherein the oxygen pressure is adjusted to a value between 10 ^−7.5 and 10 ^9.5 bar. 4. The method according to claim 1, wherein the thermodynamic activity of Fe (II) in the slag is ≧ 1. 5. The method according to claim 1, wherein the ratio of Fe (III) / Fe (II) in the slag is 0.5 to 1.5. 6. The method according to claim 1, wherein the obtained slag is converted into a solid solution having a 2FeO.MoO ₂ —Fe ₃ O ₄ spinel structure by cooling.