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
  • C04B11/00—Calcium sulfate cements
• • 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 or shrinkage compensating agents
  • C04B22/0006—Waste inorganic materials
• • 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 or 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
  • C04B7/00—Hydraulic cements
  • C04B7/22—Iron ore cements ; Iron rich cements, e.g. Ferrari cements, Kühl cements
• • 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

Definitions

• Portland cement always contains a certain amount of readily soluble hexavalent chromium in the form of chromates, usu- ally 10-20 ppm Cr , stemming from” the raw material and in smaller amounts from the fuel, the kiln lining and the various machines.
• This chromium produces eczema in brick ⁇ layers and concrete workers among others.
• a known and tested additive for reducing the content of easily soluble hexavalent chromium in the concrete, and thus reducing the risk of chromium contact eczema, is divalent iron in the form of ferrous sulfate.
• Ferrous sulfate is present in large amounts in the form of so-called green salt, a waste product from certain chemical and hydrometallurgical process industries.
• green salt a waste product from certain chemical and hydrometallurgical process industries.
• 3-4 tons of green salt are obtained for example for each ton of titanium dioxide.
• a small amount of this can be used for water purification, but the major portion is deposited as waste or is pumped into the sea.
• Green salt is such ferrous sulfate which leaves a precipita ⁇ tion process after a varying degree of mechanical dehydra- ti ⁇ n by filtering and possibly centrifuging.
• the major component of the green salt is ferrous sulfate with 7 hygro ⁇ scopic water, FeS0 4 «7H 2 0, with varying amounts of impurities and a moisture content of 2-25 % by weight depending on the dehydration method. Centrifuged green salt has the consis- tency of wet snow.
• Green salt has been approved as a concrete additive and is sold in 25 kg plastic bags for manual addition in conjunc ⁇ tion with the mixing of concrete.
• green salt can have a negative effect on the grinding pro ⁇ cess itself by hardened deposits in the mill with tendencies for blockage especially at the mill inlet.
• an excessively high water content of the ferrous sulfate can cause the chromate-reducing effect to be lossed when the green salt with an excess of water is subjected in the cement mill to an alkaline environment and high temper ⁇ ature.
• the handling problem can be avoided by dumping the salt directly into a tank for dissolving and then add the ferrous sulfate solution to the process.
• a corresponding technique has also been tried in the cement industry by spraying a saturated aqueous solution of the green salt into the cement mill, but this produced insufficient chromate reduction in the concrete.
• Another method which has been tested is to pump into the mill a slurry consisting of undissolved ferrous sulfate and saturated ferrous sulfate solution, but this process did not produce sufficient chromate reduction either.
• the present invention intends to produce cement with an additive of green salt in a mechanized and automated process with already existing equipment, by a method which does not produce the negative effects on the cement mill operation and which produces sufficient chro ate reduction to eliminate the risk of eczema.
• Cement refers here to all hydraulic binders and mortar products containing Portland cement clinker as the major component, 1-10 % by weight gypsum, CaS0 4 «2H-0 as a regulator of setting time and varying amounts of additives such as limestone, ash, slag and silicon powder, e.g. an amorphous, finely dispersed kieselguhr from the manufacture of silicon, ferrosilicon and ferrochromium.
• Green salt refers to a wet to moist salt containing 15-20 % iron in the form of FeS0 4 «7H 0 and 2-25 % by weight of non- chemically bonded water.
• the invention is based on replacing the ordinary gypsum • component in the cement milling with a mixture of gypsum and green salt, called ferrogypsum in the following, which is responsible in the process both for controlling the setting time and chromate reduction.
• the gypsum can be natural gypsum or so-called chemical gypsum, a by-product of certain chemical processes. especially the production of phosphoric acid.
• the granules of chemical gypsum are normally fine and can be easily mixed with green salt into a homogeneous mixture which will not separate during handling up to the cement mill.
• natural gypsum one should select a quality witha low proportion of heavy particles over about 20 mm, so that the separation of gypsum and green salt will be minimized.
• the composition of the ferrogypsum must be such that the amount of sulfate which regulates the setting time and the amount of divalent iron for reducing chromates have a certain relative proportion in view of the desired sulfate content in the finished cement, the original content of easily soluble chromate and the desired chromate reduction.
• the sulfate content and the chromate content in the cement vary from case to case, but have been shown to be virtually constant over time for a particular production unit. It is therefore possible to maintain the composition of the ferro ⁇ gypsum once it has been determined.
• a suitable addition of ferrous sulfate is 3-12 kg FeSO. «7H 2 0 per ton of finished cement, depending on the original con ⁇ tent of Cr in the cement clinker and the desired chromate reduction.
• the addi ⁇ tion of gypsum is reduced by 0.6 parts gypsum for each part ferrous sulfate heptahydrate added.
• the proportion of green salt in the ferrogypsum can also be reduced if the original content of Cr in the cement is lower than 10 ppm or if the chromate reduction is not to be carried as far.
• the mixing in of green salt in the ferrogypsum can be calculated from the size of the gypsum addition if it is initially greater or less than 50 kg per ton of cement.
• the proportion of green salt in the ferrogypsum can then vary from case to case between 2 and 90 % by weight, preferably between 5 and 25 % by weight.
• the ferrogypsum has good storage stability and the cement grinding process is rela- tively insensitive to fluctuations in the composition of the ferrogypsum, due to inhomogeneity. This allows the ferrogypsum to be prepared with simple equipment and at the.most advantageous location for transport, for example at the factory or delivery location for gypsum or green salt, at the reloading terminal or at the cement factory.
• the preparation of the ferrogypsum can be done by laying out a specific quantity of gypsum on a flat supporting surface in a layer about one meter thick. On top of this there is then laid a layer of a certain amount of green salt corresponding to the desired mixing proportions.
• the materials can be laid out with a bucket loader and the mixture can be homogenized by redigging with the loader, whereafter the mixture is loaded into a bin for transport to the next station, which can be a ship or a transport vehicle, intermediate storage plant or dosing bin for feeding into a cement mill.
• the ferrogypsum thus produced can then be used as a re ⁇ placement for gypsum in the making of cement after recal ⁇ culating the dosing as specified above.
• the chromium contents refer to analyses done after two minutes of shaking of equal amounts of cement and water.
• the ferrogypsum had better handling pro ⁇ perties than both green salt and gypsum individually due to less dust and easy passage through loading bins and shuts.
• the invention provides a method for using green salt as a chromate reducing raw material because - the ferrogypsum has significantly better handling charac ⁇ teristics than green salt, and at least equally good handling characteristics as gypsum;
• the ferrogypsum does not negatively affect the operation of the cement mill with baked-on deposits and the like, as is the case when using green salt and gypsum individu ⁇ ally;
• the divalent iron in the ferrogypsum is only oxidated to an insignificant degree to trivalent iron during the milling process, which can be done by direct addition of wet green salt and gypsum individually.
• the invention permits the replacement of two additives by a single additive which provides appreciable advantages as regards transport and economy. No extra investments are required for the addition of ferrous sulfate in each produc ⁇ tion line, as is the case with separate addition of ferrous sulfate and gypsum. Rather, existing equipment is used.
• OMPI done in fewer and larger boats, and the existing receiving and storage system for gypsum at the cement plant can be used.
• the present invention thus provides a simple method for producing a cement with significantly reduced risk of chromium eczema, without changing existing production lines, by using an inexpensive waste product, and the finished cement has equally good properties as cement without the addition, and at the same time without risk of causing chromium eczema.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Environmental & Geological Engineering (AREA)
• Curing Cements, Concrete, And Artificial Stone (AREA)

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Publications (1)

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Family Applications (1)

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Cited By (12)

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Citations (4)

• 1984
  • 1984-01-17 EP EP84900553A patent/EP0133434A1/en not_active Withdrawn
  • 1984-01-17 GR GR73541A patent/GR79711B/el unknown
  • 1984-01-17 AU AU24342/84A patent/AU2434284A/en not_active Abandoned
  • 1984-01-17 WO PCT/SE1984/000011 patent/WO1984002900A1/en unknown
  • 1984-01-20 KR KR1019840000257A patent/KR840007392A/ko not_active Withdrawn
  • 1984-01-20 IT IT19258/84A patent/IT1173095B/it active
  • 1984-01-20 DD DD84259515A patent/DD217503A5/de unknown
  • 1984-01-20 PL PL24583584A patent/PL245835A1/xx unknown
  • 1984-01-20 YU YU00096/84A patent/YU9684A/xx unknown
  • 1984-09-20 RO RO115758A patent/RO90804B/ro unknown

Patent Citations (4)

Non-Patent Citations (2)

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