FR2735120A1 - METHOD FOR IMMOBILIZATION OF RESIDUAL SLUDES CONTAINING METALS - Google Patents

Abstract

The invention relates to a process for immobilizing fluid residues containing metals, wherein the residues are mixed with a cementitious composition, the cement containing at least 5% by weight of high aluminate cement. The cementitious composition preferably comprises a mixture of ordinary Portland cement and high aluminate cement and the properties can be improved by the use of other products, particularly very fine silica and paraffin. The residues thus immobilized have a markedly reduced tendency to flow, even in the presence of highly mobile metals such as zinc.

Description

The present invention relates to the elimination of residual sludge

containing metals.

  Sludges containing metals are byproducts of the metallurgical industries. Their effective and environmentally acceptable disposal is a major problem. The chemical treatment to make the sludge disposable by the normal ways of wastewater disposal is very expensive, because of the large volumes involved and the wide variety of products contained in the sludge, so that a treatment

  chemical that is effective in one case, may not be effective in the other.

  A proposed treatment consisted of mixing these sludges with cement and molding them into blocks which can then be stored or even used. In theory, this idea is interesting because it costs relatively little (Portland cement is cheap) and can be applied to all types of metal-containing residues. In practice, however, it has limitations; in fact, many metals act as retarders of the cement (in some cases, the cement does not harden at all) and the resistance of the blocks is often insufficient. In addition, some metals, particularly zinc, are highly mobile and can

flow from the concrete.

  We have now found that such residues can be successfully immobilized using a particular cementitious composition. The invention thus relates to a method of immobilizing fluid residues containing metals, comprising mixing the residues with a cementitious composition, the cement containing at least 5% by weight of

  high aluminate cement.

  By the term "immobilization" it is meant that the included metals will not or hardly flow, i.e. within acceptable limits. The reference taken for the invention is the strict Swiss or strict Swiss standards (Technische Verordnung uber Abfalle (VAT) of December 1990). According to the required series of tests and as indicated above, the maximum flow

  Tolerable for zinc, which is one of the most mobile metals, is 10 mg / liter.

  This represents the maximum flow allowed for the invention.

  For the practice of the present invention, the cement should contain a minimum of 5% by weight of high aluminate cement (CHTA). In theory, all the cement could be CHTA, but it is very expensive and is not necessary in most cases. In addition, better results can be achieved by mixing the CHTA with much cheaper ordinary Portland cement (CPO). The preferred weight ratio of CHTA to

  CPO is between 5:95 and 90:10, preferably between 10:90 and 60:40.

  According to another embodiment of the invention, it has been found that a number of adjuvants substantially and surprisingly improve the already good performance of the invention. For example, the addition of very fine silica, for example fly ash which is blast furnace residue, reduces the water permeability of the solid material. The silica fume used represents 2 to 40% by weight of the CHTA. A particularly suitable way of adding the fine silica is to incorporate it into the CHTA and then mix the combined adjuvant with the necessary amount of CPO. The invention therefore also relates to an adjuvant which comprises CHTA and fine silica in a ratio

weighted from 95: 5 to 85:15.

  The addition of plasticizers and superplasticizers improves the compressive strength of the cured cementitious compositions. The plasticizers or superplasticizers useful in the present invention can be selected from the wide range of known products and used in the art. Examples include lignin sulfonates, hydroxycarboxylic acids, carbohydrates, condensation products of melamine and formaldehyde, condensation products of P3-naphthalenesulphonate and formaldehyde ("BNS") and styrene copolymers and maleic anhydride. The latter are especially preferred, and those which are particularly preferred are copolymers derived from copolymers of styrene and maleic anhydride in the form of free acids or in the form of salts, chosen from the group having the following types and numbers of monomeric units. :

of CH C + l r-cal

  J I to-> Co '. ## STR2 ## where R is a C 2 -C 6 alkylene group, R 1 is a C 1 -C 6 alkyl group, C 6 -C 6 cycloalkyl or phenyl, x, y and z signify numbers from 0.01 to 100, m means a number from 1 to 100, and n means a number from 10 to 100, with the conditions that i) the ratio of x to (y + z) is from 1:10 to 10: 1 inclusive, ii) the ratio of z: y is from 3: 1 to 100: 1, and iii) m + n = 15-100 and those having the following types and numbers of monomer units: -ICII COc! o A co m co co Ui YIH

J L OH]

  Wherein M is hydrogen or the residue of a polyalkylene glycol or a hydrophobic polysiloxane, R1, m and n are as defined above, x, y and z mean numbers from 1 to 100, with the provisos that i) the ratio of x to (y + z) is from 1:10 to 10: 1 inclusive, ii) the ratio of z: y is from 5: 1 to 100: 1 , and

iii) m + n = 15-100.

  These copolymers (referred to as "SMA") are described in US Pat.

  US 5,158,916 and in the French patent application 2,671,090.

  The plasticizers and / or superplasticizers may be added in an amount of 0.05 to 2.5% by weight relative to the total weight of the cement. According to a particularly preferred embodiment of the invention, the plasticizer or the superplasticizer can be incorporated in the CHTA or more preferably in a mixture of CHTA and fine silica as indicated above, which gives an adjuvant especially useful for the immobilization of residues. This can of course be achieved only when the plasticizer or the superplasticizer is dry, that is to say essentially free of water, since the presence of water will have a harmful effect on storage stability. The invention therefore relates to an adjuvant for cementitious residue immobilization compositions comprising a mixture of CHTA and a plasticizer or a dry superplasticizer in a weight ratio of 100: 0.25 to 100: 15. The invention also relates to such an adjuvant which also contains fine silica. These adjuvants are especially good when the superplasticizer is a condensation product

  melamine and formaldehyde or an SMA as defined above.

  According to another preferred embodiment, the addition of paraffin improves the performance. This in particular reduces the flow of metals, even highly mobile metals such as zinc, to a lower level never before achieved. By "paraffin" is meant an upper alkane having a melting point higher than room temperature (see for example "Rompp Chemie Lexikon", 9th edition [Thieme Verlag 1989], Vol. 1, p. 102). The preferred form of paraffin is a paraffin emulsion forming a film, but not a coherent film such as that formed by a paint. The emulsion can be stabilized by any of the appropriate means, but it is preferable to use an anionically emulsified paraffin mixture (melting point: -51 ° C.) with a particle size of less than 21. As examples of such emulsions of paraffins, mention may be made of "Mobilcer" 55 or "Mulrex" 62 from Mobil and "Ubatol" FPG 860 from Cray Valley and "Tecol" BC 60/40 from Trub Emulsion Chemie. Another form of paraffin useful for the implementation of the invention is a solid paraffin in the form of particles of the "microparaffin" type. As an example of this type of paraffin, mention may be made of

  "Luwax" (brand) of BASF.

  Such paraffins do not give as good results as emulsions, but they have a major advantage; being dry, they can be incorporated into any of the three adjuvants described above (CHTA

  + silica, CHTA + plasticizer / superplasticizer, CHTA + silica + plasticizer / super-

  plasticizer), which gives a stable product with good properties.

  The adjuvant comprising the 4 components (CHTA, silica, plasticizer / superplasticizer and paraffin) is a particularly preferred product because of its ease of

  treatment and its good general properties.

  In some situations, it may be necessary to mix the cementitious composition at a site remote from the site of use and to transport it there. There may be a significant lapse of time between mixing and use, which is not recommended with some combinations of CHTA and CPO, known to harden very quickly. This can be overcome by incorporating a retarding admixture into the cementitious composition upon mixing. The latter may be selected from any of the adjuvants known in the art, for example lignin sulphonates, carbohydrates and the like.

  condensation products of melamine and formaldehyde. A description

  Such adjuvants can be found in the documents known in the art, for example in the "Concrete Admixtures Handbook" (Ramachandran edition, Noyes, 1984). However, a particularly preferred class of products which can be suitably used with the products of the invention are the phosphonic acid derivatives which are used to retard the setting of cement and concrete. Preferred phosphonic acid derivatives are those containing carboxy, hydroxy or amino groups. As an example of derivatives containing a carboxy group, there may be mentioned "Bayhibit" AM (brand) from Bayer AG,

Leverkusen, Germany.

  Examples of products containing a hydroxy or amino group include the "Dequest" (Trade Mark) products of Monsanto Co., St. Louis, USA. Examples of "Dequest" products suitable for use in the practice of the invention include the following (more than one product that may be used): - "Dequest" 2000: aminotri (methylenephosphonic acid)

  - "Dequest" 2006: pentasodium salt of aminotriic acid (methylene-

  phosphonic acid) - "Dequest" 2010: 1-hydroxyethylidene-1,1-diphosphonic acid

  - "Dequest" 2016: Tetrasodium salt of 1-hydroxyethylidene acid

  1,1-diphosphonic - "Dequest" 2041: ethylenediaminetetra (methylenephosphonic) acid

  - "Dequest" 2047: calcium and sodium salt of ethylenediamine

  tetra (methylenephosphonic) - "Dequest" 2051: hexamethylenediaminetetra (methylenephosphonic acid)

  - "Dequest" 2054: Potassium salt of hexamethylenediaminetetraacetic acid

  (methylenephosphonic) - "Dequest" 2060: Diethylenetriaminepenta (methylenephosphonic acid)

  - "Dequest" 2066: sodium salt of diethylenetriaminepenta acid (methylene

  phosphonic). According to a preferred embodiment, these products are used in combination with hydroxycarboxylic acids, citric acid being particularly preferred. Without in any way limiting the invention, it is believed that these products serve to slow or even completely stop the hydration reactions that occur when water is added to a hydraulic binder such as cement. In addition to these phosphonic acid derivatives, it is also possible to use an activating agent to restart the hydration reaction. Such a system is described, for example, in US Pat. No. 4,964,917. Examples of products that may be used include admixtures according to ASTM C 494 of Class C, preferably those free of chloride, such as nitrate. and calcium formate, thiocyanates, triethanolamine and

  acetylene diurea (tetrahydroimidazo [4,5-d] imidazole-2,5- (1H, 3H) dione).

  The process and adjuvants of the present invention are useful for the treatment of metal-containing fluid residues. The term "fluid" means that the residues are naturally fluid (which is usually the case) or that they can be fluidized, for example by the addition of a suitable liquid such as water or an organic solvent. Ideally, the residues should have a water content of about 40-60% by weight; in most cases, this requires

  elimination of water which is easily carried out according to the usual methods

  the. The process of the present invention simply involves mixing the residues with the cementitious composition and curing it. The quantities of products required to immobilize given residues will depend on a number of factors, such as the nature of the residues and their solids content, and it is therefore impossible to indicate the precise quantities that will be effective in each case. However, it will be easy for the specialist to determine the appropriate quantities by a simple test. The usual amounts required are as follows: CHTA: CPO 5-80% by weight based on the total weight of the composition * (weight ratio 5: 95-90: 10) Silica fume 2-20% by weight of CPO + CHTA Superplasticizer ** 0.1-5.0% by weight of CPO + CHTA Paraffin emulsion 0.5-5.0% by weight of CPO + CHTA Residues 20-90% by weight in relation to total * Water required to complete the cement-based mixture with minimum workability is not included in this composition, since the components generally contain enough water, which makes it unnecessary to add additional water. Otherwise, the specialist can easily add the

  (low) amount of water needed.

  ** The amount of superplasticizer listed here refers to commercial products that are aqueous solutions. The quantities of active agents indicated above

should be respected.

  The residues and the cementitious composition can be mixed in any mixing apparatus (eg a concrete mixer). They can then be put into the appropriate form, for example cast as slabs or molded into blocks. In all cases, the residues went from the Swiss "Sonderabfall" [special residues] (residues requiring special treatment and storage precautions) to the "Reststoff" category (residues requiring less precautions). ), and in many cases the residues may be classified as "Inertstoff" [inert material] (residues not requiring precautions) In some cases, the blocks or slabs must not be essentially rubble but

  are pretty inert to use.

  The following examples illustrate the present invention without any

limit the scope.

Examples 1-10:

  From the components indicated in Table 1 below, a number of cement batches, numbered from 1 to 10, are prepared. To each of these was added a sludge containing zinc (from the

  galvanization and having 131,800 mg Zn per kg of residues (measured by spectroscopy).

  atomic absorption copy). The cement is molded in block form and strength tests are carried out according to the German standard DIN 18555. The flow test is carried out by adding 1000 ml of deionized water to 100 g of crushed solid cement (of one maximum particle size of 5mm) and then CO2 is injected into the system. The CO2 injection is carried out for 24 hours in order to saturate the water. It is then filtered through a 0.45 Pin filter and

  the filtrate is analyzed by atomic absorption spectroscopy.

  The results of the test are shown in Table 1.

TABLE 1

  Mixed No. 1 2 3 4 5 6 7 8 9 10 Type of mixture CHTA parts 475 475 475 475 475 475 475 285 665 500 Silica fume in 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 3 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 gou-2n 500 500 500 500 500 500 500 700 300 500 Water 350 325 300 275 325 325 325 300 385 300 Fresh Blend

  Air content [% 1.10 0.6 0.5 0.4 1.3 2.9 4.0 0.8 0.6 ---

  Unit weight [Kg / m3] 1617 1657 1683 1696 1634 1608 1592 1548 1730 Resistance to bending

  At 7 days [MPa] 0.36 0.30 0.57 0.62 0.45 0.32 0, 37 0 16. ..

  At 28 days IMPa] 0.13 0.67 0.55 0.77 0.42 053 0.69 0.29 ....

  to compressio A 7 days [MPa] 3,50 3,97 5,27 5,84 5,51 3,62 3,30 0,72

  At 28 days [MPa] 3,14 5,17 7,09 8,75 5/84 5t22 4, 76 1.25. ....

E_a i dC ounlel-

  in [mg / l] 0.36 0.31 0.34 0 # 28 0.20 0.20 0.19 0.46 0.12 2 1

  the "Rheobuild" 3520 of the company MBT (Switzerland) S.A.

  aJ "Masterkure" 122 of MBT (Switzerland) S.A.

  These results show that - the zinc content of the flow solution decreases when the cement content increases (tempered 1, 8, 9), - the compressive strength is higher when the amount of superplasticizer increases (tempered 1 -4), - the zinc content of the flow solution is reduced by the presence of the paraffin emulsion (tempered 2 and 5), - the replacement of 10% of the cement by silica fume causes a

  reduced zinc flow (tempered 1 and 10).

  Examples 11-14: These examples use mixtures of CHTA and CPO. The mixtures are subjected to the same tests as those of Examples 1-10 and the

  The results are shown in Table 2.

Table 2

  Mixed No. 11 12 13 14 Mixture Type CPO [g] 300 225 0 CHTA [g] 0 75 300 Superplasticizer [g] 7.5 7.5 7.5

Ashes of thread

  tration2 [g] 100 800 600 600 Water [g] 500 550 550 Resistance to compression A 7 days [MPa] 0 2,6 3,3

Flow test

  Zinc [mg / 1] 301.7 21.2 4.9 3, 6 (1) superplasticizer of Examples 1-10 (2) waste incinerator residues It is found that the CHTA / CPO mixture causes a flow of zinc and gives very good results of resistance to 7 days, good enough to classify the residues in the best category. In addition, they are almost as good as those of the CHTA used alone and are obtained at a

cost greatly reduced.

Claims (10)

  A method for immobilizing fluid residues containing metals, wherein the residues are mixed with a cementitious composition, wherein the cement contains at least 5% by weight of cementitious high aluminate content.   2. A method according to claim 1, characterized in that   cement is a cement with a high content of aluminate.   3. A process according to claim 1, characterized in that the cement is a mixture of cement with a high content of aluminate and cement   Ordinary Portland in a weighted ratio of 5:95 to 90:10.   4. A process according to any one of claims 1 to   3, characterized in that the cementitious composition also contains very fine silica representing from 2 to 40% by weight relative to the total weight of the   high aluminate cement.   5. A method according to any one of claims 1 to   4, characterized in that the cementitious composition also contains   paraffin, in the form of solid particles or in the form of an aqueous emulsion.   6. A method according to any one of claims 1 to   characterized in that the cementitious composition also contains a   plasticizer and / or a superplasticizer.   7. A process according to claim 6, characterized in that the superplasticizer is chosen from copolymers derived from copolymers of styrene and maleic anhydride in the form of free acids or in the form of salts, chosen from the group having the following types: and the following number of monomer units: ## STR2 ## R represents a C 2 -C 6 alkylene group, R 1 means (C 1 -C 2 alkyl) -, (C 6 -C 9 cycloalkyl) - or phenyl, x, y and z mean numbers from 0.01 to 100, m means a number from 1 to 100, and n means a number from 10 to 100, with the conditions that i) the ratio of x to (y + z) is from 1:10 to 10: 1 inclusive, ii) the ratio of z: y is from 3: 1 to 100 : 1, and iii) m + n = 15-100 and those having the following types and numbers of monomeric units: CH-CHT H -H H   ## STR5 ## wherein R (O); R1 where M is hydrogen or the residue of a polyalkylene glycol or a hydrophobic polysiloxane, R1, m and n are as defined above, x, y and z are numbers from 1 to 100, with the conditions that i) the ratio of x to (y + z) is from 1:10 to 10: 1 inclusive, ii) the ratio of z: y is from 5: 1 to 100: 1, and iii) m + n = 15-100.   8. A process according to any one of claims 1 to 7,   characterized in that the cementitious composition also contains a retardant adjuvant.   9. A process according to claim 8, characterized in that the retarding adjuvant is a phosphonic acid derivative containing a carboxy group, hydroxy or amino.   10. A cementitious solid composition suitable for use in the immobilization of fluid residues containing metals, characterized in that it comprises a mixture of cement with a high aluminate content, very fine silica, a plasticizer / superplasticizer and a paraffin under form of solid particles.