Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators, shrinkage compensating agents
  • C04B22/08—Acids or salts thereof
  • C04B22/14—Acids or salts thereof containing sulfur in the anion, e.g. sulfides
  • C04B22/142—Sulfates
  • C04B22/149—Iron-sulfates
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/10—Compositions or ingredients thereof characterised by the absence or the very low content of a specific material
  • C04B2111/1075—Chromium-free or very low chromium-content materials
  • C04B2111/1081—Chromium VI, e.g. for avoiding chromium eczema
• • 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
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Definitions

• European Patent Application No. 81110557.6, publication No. 0 054 3144 discloses a method of producing a dry cement mixture with reduced or substantially eliminated content of water soluble ch romate, said method comprising grinding a starting material including cement binder clin ⁇ ker and having a content of water soluble chromate, and adding a chromate reducing and/or neutralizing agent in a non-dissolved condi ⁇ tion and in an amount of 0.01 -10% by weight of the starting material before, during or after the grinding process in order to eliminate or substantially reduce said water soluble chromate.
• the preferred reducing agent mentioned in the said patent specification is ferrous sulphate (FeSO ⁇ .
• nf- O wherein n is normally 7, preferably provided with an oxidation-preventing coating.
• the product of this type, "MELSTAR M” or “FERROMEL 20TM” specifically disclosed in the patent application is a 96% FeSO 4 .7H «O provided with an oxidation-preventing coating which also gives this particulate material suitable free-flowing properties which allow it to be stored and used in a practical manner in connection with the preparation of the cement product.
• the product may be stored in silos, withdrawn and subjected to pneumatic transport, etc. All of these handling properties depend on the product's capability of being free-flowing and protected against undue oxidation .
• the coating tends to reduce the cor- rosivity otherwise associated with ferrous sulphate heptahydrate.
• OMPI sA- ipo _ The normal commercial or technical grade of ferrous sulphate is a heptahydrate without the above-mentioned coating .
• This heptahydrate contains a small amount of water and thereby has a tendency to be ⁇ come "snowy" (it closely resembles melting snow) and has a tendency to cake or agglomerate when it is handled and stored in silos and feed hoppers .
• These properties render the commercial or technical grade ferrous sulphate heptahydrate unsuitable for storage in silos and for pneumatic transport, etc. : therefore, the commercial or technical grade ferrous sulphate cannot in practice be used as a reducing agent in the above-mentioned chromate reducing process .
• technical or commercial grade ferrous sulphate heptahydrate has increased corrosiveness compared to the coated ferrous sulphate heptahydrate.
• the term "ferrous sulphate heptahydrate” is used to characterize the starting material .
• Some of the treatments dis ⁇ closed in the following may result in removal of part of the crystal water in accordance with what is well known in the art, but it is essential that the product substantially retains the water solubility properties which are characteristic to the heptahydrate, and, for convenience, the product is therefore characterized as heptahydrate or simply hydrate in the present specification and claims.
• the drying is performed in a particular way, that is, at temperatures below 120°C, in particular at temperatures of at the most 80°C, and preferably temperatures of at the most 60°C, such as a temperature in the range of 20-60°C, it has been found possible to avoid oxidation of the ferrous sulphate heptahydrate and hence to obtain a substantial retainment of its chromate-reducing capabilities. Also, the moderate drying has been found to have a beneficial effect on the free flowing properties of the product.
• one aspect of the present invention comprises producing a dry cement mixture, said method comprising grinding a starting material including a cement binder clinker and having a content of water soluble chromate, and adding a chromate reducing and/or neutralizing agent in a non-dissolved condition and in an amount of 0.01 -10% by weight of the starting material before, during or after the grinding process in order to eliminate or substantially reduce said water so- luble chromate, the reducing and/or neutralizing agent being a fer ⁇ rous sulphate hydrate product with a high ratio between ferrous ion and total i ron and a low corrosiveness, the ferrous sulphate hydrate product being prepared from a technical or commercial grade ferrous sulphate heptahydrate product which tends to cake when handle ⁇ , and stored in silos and feed hoppers by rendering loosely bound water of the product unavailable for causing the caking by moderate dr iing .
• the drying is preferably performed at a temperature of at the v
• the loosely bound water of the ferrous sulphate heptahydrate product is rendered unavailable for causing caking of the product by absorption by physical or chemical means.
• absorption by physical or chemical means covers any absorption of the water into a surface of a material or into interstices in the material or into interstices and the surface of a material
• chemical absorption refers to any chemical reaction that will remove the water, typically by combining with the loosely bound water
• the measures for rendering loosely bound water unavailable for causing the caking process comprise one or more treatments selected from moderate drying, powder dilution, physical absorption, and chemical absorption .
• the production of the dry cement mixture, including the grinding of the starting material including a cement binder clinker, and the addition of the chromate reducing and/or neutralizing agent in a non-dissolved condition before, during or after the grinding process may be performed as disclosed in the above-mentioned European Patent Application No. 81110557.6.
• a preferred method of absorbing the loosely bound water is to mix the technical or commercial grade fer ⁇ rous sulphate heptahydrate with a water-absorbing material to provide the resulting ferrous sulphate hydrate with an oxidation-preventing and free flowing properties-imparting coating by powder dilution .
• the water-absorbing material may typically be a powder having a specific
• the 2 surface in excess of about 2000 cm /g and is typically an inorganic material selected from materials occuring as by-products, raw mate- rials or waste products in the cement industry such as clay, fly ash, slag, chalk, gypsum, filter dust, and other products that are readily available in the cement industries (including cement) .
• the material will be a mixture comprising two or more of the above-men ⁇ tioned products .
• the amount of the water-absorbing material may vary within wide limits, such as from 1 to 95%, calculated on the resulting product.
• a particularly useful and cheap water-absorbing material is fly ash from coal-fired power stations.
• Such fly ash having a specific surface
• the fly ash is preferably added in an amount of 20-70%, in particular in an amount of 40-70%, preferably about 50%, calculated on the total mixtu re.
• gypsum Another interesting material with which powder dilution of the ferrous hydrate heptahydrate may advantageously be performed is gypsum, either as such or in its less hydrated forms which are hemihydrate and anhydrite, or as a mixture of two or all of these.
• the gypsum, hemihydrate or anhydrite should preferably have a pH of at the most 7, in particular a pH in the range of 5-7, preferably a pH of about 6, when admixed with the ferrous sulphate heptahydrate.
• the powder dilution is usually performed by mixing in suitable mixing equipment such as a paddle mixer or a kneader or even high shear mixing or crushing equipment, but under conditions where no exces ⁇ sive heating of the material being mixed will take place.
• suitable mixing equipment such as a paddle mixer or a kneader or even high shear mixing or crushing equipment, but under conditions where no exces ⁇ sive heating of the material being mixed will take place.
• the material with which the ferrous sulphate heptahydrate is mixed may initially be in the form of a powder, or in the form of particles of agglomerated powder which, during the mixing, will be disintegrated into particles of powder size, or it may be in the form of granules, which, during the mixing, are reduced to powder size.
• Gypsum, hemihydrate, anhydrite, or mixtures of two or all of these may also advantageously be added in an amount of 20-70%, typically 40-70%, especially an amount of about 50%, calculated on the total mixture, followed by the same moderate drying proceedu re.
• the total amount of the ferrous sulphate hydrate-containing composition of the invention added to the cement is of the order of 0.01 -10% by weight, typically of the order of 1% by weight, and this means that the small amount of additive which is introduced into the cement together with the ferrous sulphate hydrate will not to any substantial extent incur any changes of the properties of the final cement product.
• the powder with which the ferrous sulphate heptahydrate is treated is fly ash or gypsum, it is noteworthy that fly ash and gypsum are recognized desirable additives in cements.
• calcium oxide in a re- latively low amount will be able to absorb the loosely bound water; this is due to chemical reaction with the water with formation of calcium hydroxide. While calcium oxide is, hence, capable of absor ⁇ bing the loosely bound water of the ferrous sulphate heptahydrate, the resulting product, when calcium oxide is used as the sole addi- tive, will normally not be optimal for handling and dosage, and it is often preferred not to use calcium oxide as the sole additive, but to combine it with other materials, such as fly ash, which impart a higher degree of volume or bulk to the product.
• ferrous sulphate heptahydrate may be effectively modified into a free-flowing powder with retention of its reducing capabilities by means of addition of an absorbing or reactive substance and/or by drying, it is within the capacity of the skilled art worker to combine the measures to obtain an optimum combination of free flowing pro ⁇ perties, high reduction capability, and low corrosiveness .
• preferred measures at present seem to be a combination as mentioned above of addition of about an equal amount
• the granulate product resulting from this process can be charac- terized as a substantially free-flowing powder comprising ferrous sulphate hydrate in admixture with fly ash or gypsum, the ferrous sulphate hydrate of the mixtures being readily soluble in water and having a high ratio of ferrous ions, such as more than 80% and pre ⁇ ferably more than 90%, to total iron content in the ferrous sulphate heptahydrate.
• the ferrous sulphate hydrate in the compo ⁇ sition according to the invention will have a considerably increased pH as compared to the untreated ferrous sulphate heptahydrate, the pH increase typically being 1 pH unit or higher, with resulting re ⁇ duction of the corrosiveness of the product.
• the composition of the present invention is employed in the same manner as described for the ferrous sulphate heptahydrate product used in the above-mentioned patent application , but normally in larger amounts corresponding to the lower content of ferrous ions due to content of the absorbing or reacting powders in the product.
• a suitable plant for preparing a ferrous sulphate heptahydrate com ⁇ position of the present invention is a paddle mixer with a dedusting unit in which the ferrous sulphate heptahydrate of technical grade can be mixed with the material, typically fly ash, in connection with a drying drum to which the mixture is passed after thorough mixing . If necessary, the dried product can be subjected to disintegration, and thereafter, the resulting free-flowing, stable ferrous sulphate hepta- hydrate composition of reduced corrosivity can be stored and handled in the same manner as the coated ferrous sulphate heptahydrate product described in the above-mentioned patent application .
• the mixing ratio may, if desired, be adapted so that the resulting mixture is directly suitable for addition to the cement as the total gypsum addition to the cement in question .
• the mixing ratio between ferrous sulphate heptahydrate and the gypsum, hemihydrate, anhydrite, or mixture of two or all of these may be between 1 :2 and 1 : 50, in particular be ⁇ tween 1 :5 and 1 : 20, such as about 1 : 10.
• an absorbing material in particular fly ash
• fly ash may be used to solve the problems of agglomeration and acidity associated with technical or commercial grade ferrous sulphate heptahydrate used as a reducing agent for addition to cement before, during or after the milling thereof in order to eliminate water soluble chromate in the cement during the use of the cement
• other reducing agents which are used for the same purpose in a similar manner and which show similar handling problems with respect to caking or agglomeration and/or acidity can be brought into a readily dispersable form showing similar advantages as described herein by admixture with an absorb ⁇ ing powder, in particular an absorbing powder comprising fly ash, in the manner described herein, suitably combined with drying as de ⁇ scribed herein and such improvement of such other reducing agents is within the scope of the present invention .
• the reserve potential chromate reducing capability of the cement can then be calculated from the following formula
• the resulting product was subjected to moderate drying at 40°C to a weight loss of 1 .3%. Thereafter, the product was a dry, free-flowing powder having a particle size of about 0.5 mm.
• the ferrous sulphate heptahydrate was mixed with 3% by weight, calculated on the ferrous sulphate, of powdery calcium oxide. After the mixing, the mixture was subjected to mo ⁇ derate drying at 40°C. Again, the result was a free-flowing dry powder. The particle size was about 0.5 mm. On these powders, the reduction capability, measured as the content
• the product was dispensed by means of a feed hopper and a weighfeeder. From the weighfeeder, the product was conveyed by pneumatic transport over a distance of about 150 m to the inlet into the cement mill . The dosing was performed for about 1 hour 20 minutes, and the total consumption of the product was about 800 kg.
• samples of the ferrous sulphate/fly ash pro ⁇ duct were withdrawn, and every tenth minute, samples of the cement after the primary cement mill (without addition of the ferrous sul ⁇ phate/fly ash product) and after the secondary mill (with addition of the ferrous sulphate/fly ash product) were withdrawn .
• the addition per hour of the product was 583 kg to a cement/fly ash product comprising about 84 tons per hour of cement and about 4 tons per hour of added fly ash . This corresponds to a dosage of the ferrous sulphate/fly ash product of about 0.7%.
• Table IV indicates the samples withdrawn during the experiment and the content of water soluble chromate in the cement samples, mea ⁇ sured after 1 day, after 8 days and after 14 days, respectively.
• the reference sample (after the primary mill) contains an average of 6.2 mg Cr /kg cement, and that addition of about 0.7% of the ferrous sulphate/fly ash product, corresponding to about 0.35% FeSO 4 .7H 2 O, a complete reduction of the content of water soluble chromate compounds in the cement after the secondary cement mill is obtained .
• the mixture of ferrous sulphate heptahydrate and fly ash was fed to the drying drum by means of a weighfeeder.
• a pro ⁇ duction rate of about 7 tons/hour was found to give an optimum pro ⁇ duct quality as regards free flowing properties and retained chromate reduction capability measured in per cent of the chromate reduction capability of the ferrous sulphate heptahydrate contained in the feed.
• a total amount of about 95 tons of ferrous sulphate/fly ash mixture was produced and loaded into road bulk tankers for transport to the cement mill plant.
• An average sample from the 95 tons test batch had a retained chromate reduction capability of 95%, and the pH of a 1% slurry was 4.2.
• the gypsum used for the test production was synthetically produced industrial gypsum form Boliden Kemi, Sweden, of the type normally used in the manufacturing process for all cement made in Denmark.
• Technical data for the gypsum are set out in Table V below:
• pH of 25% slurry 6.0.
• the air flow through the drying drum was kept at about 13,000
• the outlet air temperature was kept be ⁇ tween 65°C and 70°C throughout the test period.
• the optimum production rate was found to be about 8 tons/hour.
• a total amount of about 25 tons of ferrous sulphate/gypsum mixture was produced and loaded into a road bulk tanker for transport to the cement mill plant.
• An average sample from the 25 tons test batch had a retained chromate reduction capability of 98%, and the pH of 1% slurry made with the product was 4.5.
• the said production control samples were also tested for content of g . Cr after 8 and 14 days, and all such tests showed that the content g + of Cr was below 0. 1 mg/kg cement.
• the 22 tons test batch was received and handled by the installations normally used for taking gypsum to the cement mill feed silos .
• This installation comprises a feed hopper with extraction belt and a system of rubber belt conveyors for transport and distribution to the gypsum feed silos for the cement mills .
• the test batch was loaded into the gypsum feed silo for the same two serially connected cement mills as used for the experiments described in Examples 3, 4 and 5, and over a period of 5 hours, all of the 22 tons were fed to the inlet of the first stage mill as combined addition of gypsum and chromate reduction additive.
• ferrous sulphate/gypsum mixture had the same handling properties as gypsum without addition of ferrous sul ⁇ phate heptahydrate. No difficulties were encountered with extraction and transport during the experiment.

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• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Inorganic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Ceramic Products (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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• 1983
  • 1983-11-09 WO PCT/DK1983/000106 patent/WO1984001942A1/en not_active Application Discontinuation
  • 1983-11-09 JP JP58503664A patent/JPS59501825A/ja active Pending
  • 1983-11-09 AU AU22601/83A patent/AU2260183A/en not_active Abandoned
  • 1983-11-09 EP EP83903537A patent/EP0125267A1/de not_active Withdrawn
  • 1983-11-16 ES ES527312A patent/ES8504646A1/es not_active Expired
  • 1983-11-17 DD DD83256816A patent/DD212727A5/de unknown
  • 1983-11-17 PL PL24460983A patent/PL244609A1/xx unknown
• 1984
  • 1984-07-02 ES ES533929A patent/ES8507422A1/es not_active Expired
  • 1984-07-16 NO NO842906A patent/NO842906L/no unknown
  • 1984-07-17 FI FI842873A patent/FI842873A0/fi not_active Application Discontinuation

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