• 专利附录
  • 专利说明
  • 权利要求
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    • 专利摘要:
    Fig. 1 This invention relates to a method for recycling aqueous sludge from calcium carbonate particles, wherein at least a part of the water present in the sludge is separated, after which the at least partially dewatered sludge is mixed with an amount of quicklime. Such recycled sludge is suitable for use as a soil improver, as an additive for building materials and as an additive for plastics for improving impact resistance. FIG. 1
    公开号:BE1022931B1
    申请号:E2015/5302
    申请日:2015-05-15
    公开日:2016-10-19
    发明作者:Reeth Constant Van
    申请人:Reeth Constant Van；Rimaco；
    IPC主号:
    专利说明:

    Process for recycling calcium carbonate sludge.
    This invention relates to a method for recycling aqueous sludge from calcium carbonate particles, in particular aqueous sludge from the sawing or grinding of calcareous rock, more particularly blue limestone.
    Limestone and dolomite, these are carbonate-based rocks, are widely used as soil improvers for agricultural land because of their slow but continuous action. In order to be absorbed by plants and agricultural crops, it is important that the rock has a sufficiently fine particle size when applied to the soil. In general, the target particle size is obtained by grinding larger particles. However, it is important that the product supplied to agriculture has a constant quality: the presence of too large particles, or a granulate with a very different particle size and / or chemical composition is not desirable. Although the granulate used as a soil improver may contain water, it is not desirable that the water content is too high, since the farmer appreciates a constant, measurable quality. Moreover, transporting an aqueous mass is expensive, and there is also a risk of freezing in the winter. The ground calcium carbonate is dried to solve these problems. An energetically favorable drying process uses quicklime, CaO, which is mixed with the still moist crushed limestone. The mixing gives rise to an exothermic process, which promotes the evaporation of the moisture present.
    Limestone, such as marble, bluestone and bluestone are mined in quarries usually in the form of large blocks or columns, from veins of the rock in question. These blocks are then further sawn into blocks, plates or other shapes with the intended dimensions. The surface can also be polished afterwards. Commonly used sawing devices use water to cool the saw and remove the fine particles of the rock that are formed during sawing, in the form of saw sludge. Sawdust can also be formed when sanding and polishing such rocks.
    Until now, this sludge was mostly dumped.
    It is an object of the present invention to provide a method that permits the useful use of such sludge from calcium carbonate-based rocks. It is a particular object of the present invention to provide a method for recycling sludge from sawing blue limestone. US 1,721,803 describes a method for producing dry crushed limestone that is suitable for use as a fertilizer. The mined limestone is crushed and mixed with an amount of quicklime needed to absorb moisture present in the mined limestone to provide a dry preparation suitable for grinding and transporting. The preparation is then ground to the desired particle size. FR2.620206 describes a method for chemically drying fine calcium carbonate or magnesium carbonate rock. Lime rock or lime magnesium rock is mixed with quicklime in a mixer until a particle size of less than 0.315 micrometres is reached. Part of the water present in the rock is absorbed by reaction with the quicklime. An increased solubility of the carbonate in the soil was observed. The product is considered suitable for use on acidic soils. EP430751 describes how to bring limestone or dolomite, in particular waste from washing of these rocks and dust present on filters from devices used in quarries where the rock is extracted, to a mixer for mixing with quicklime, using an endless screw. The mixture is then passed to a mixer and a mill for the further milling of the product. The amount of quicklime amounts to 30% compared to the rock. Mixing the rock with the quicklime causes an exothermic reaction. The dried material is suitable for use in agriculture, which has a fine particle size, adheres well to the earth and is therefore not easily carried with the wind. WO99 / 55643 describes to convert waste from a cement furnace and other particulate calcium sources containing CaO, Ca (OH) 2 or other hydratable calcium compounds into an agglomerate and used as a soil improver. A method of producing the agglomerate comprises combining particles from a calcium source and a water-soluble binder, to produce agglomerates that are then subjected to a controlled drying process so that the dried agglomerates have a particle size between -7 and +8 mesh Tyler Standard Sieve Series and have a breaking strength of at least 2 pounds (approximately 0.9 kg). The agglomerate is transformed into pellets by mixing with the water-soluble binder and other basic nutrients for agricultural crops.
    However, these known methods always contain a step in which particle reduction or grinding must be carried out in order to arrive at a product with the desired particle size.
    It is an object of this invention to provide a method for recycling sludge from sawing calcium carbonate-based rocks, in particular blue limestone, without the need for subjecting the sludge to particle reduction.
    To this end, the method of this invention is characterized in that at least a part of the water present in the sludge is separated, after which the at least partially dewatered sludge is mixed with an amount of quicklime for drying the sludge.
    The prior separation of at least a part of the water present in the sludge, followed by the further drying of the at least partially dewatered sludge with quicklime as a drying agent for the sludge, offers the advantage that the particle size of the calcium carbonate sludge particles during drying inside the limitation can be kept and does not increase too much, so that the dried calcium carbonate sludge is suitable for direct use as a soil improver, without it being necessary to subject the dried sludge to an additional grinding step in order to obtain particles of the desired size.
    Without wishing to be bound by this theory, the inventor assumes that this is at least in part due to the particle size of the calcium carbonate present in the sludge, which is sufficiently small.
    The calcium carbonate particles obtained in this way have the advantage that they have a very irregular shape, with numerous protrusions and angles, as shown in the photos in Figures 1 and 2. The irregular shape reduces the mobility of the particles. Once applied to the soil, there is a minimal risk of rolling away, and an increased chance of being absorbed into the soil. The irregular shape results in a better dispersibility of the particles in other substances, for example liquids, viscous materials or molten plastics, making the particles particularly suitable for use as a functional filler for plastics, for example in injection molding for the manufacture of panels, crates and other objects made of plastic.
    The calcium carbonate obtained in this way also has the advantage that it has a high purity. The calcium carbonate concentration in the dried sludge will usually be higher than 70 wt. %, preferably higher than 75 wt. %, more preferably higher than 80 wt. %. In addition to calcium carbonate, the sludge may contain other inorganic compounds such as calcium magnesium carbonate, calcium hydroxide, alpha alumina, silicon dioxide. The concentration of these materials can vary within wide limits, depending on the composition of the rock from which the sludge is extracted, and the geographic location of the rock. In particular, the concentration of impurities such as heavy metals, mono- and polycyclic aromatic hydrocarbons, and other organic substances is very low. More specifically, the content of As, Cd, Cr, Cu, Hg, Pb, Ni, Zn is very low. The concentration of As is usually lower than 40 ppm, preferably lower than 20 ppm; the amount of Cd is usually less than 1 ppm, preferably less than 0.5 ppm; the amount of Cr is usually less than 10 ppm, preferably less than 5 ppm; the amount of Cu is usually less than 50 ppm, preferably less than 25 ppm, the amount of Hg is usually less than 0.2 ppm, more preferably less than 0.1 ppm, the amount of lead is usually less than 20 ppm, preferably less than 10 ppm ppm, the amount of Nik is usually less than 15 ppm, preferably less than 8.5 ppm and the amount of Zn is usually less than 50 ppm, preferably less than 25 ppm. The calcium carbonate can also contain P and / or N, these are desirable components for a soil conditioner. The phosphorus concentration will usually be at least 1 g per kg, preferably at least 1.5 g per kg. The amount of N will preferably be at least 0.5 g / kg, more preferably at least 0.75 g / kg, more preferably at least 0.9 g / kg.
    The concentration of monocyclic aromatic hydrocarbons such as, for example, benzene, ethylbenzene, styrene, toluene, xylene is usually lower than 0.1 ppm, preferably lower than 0.05 ppm for each of the aforementioned compounds. The concentration of polycyclic aromatic hydrocarbons such as, for example, benzo (a) anthracene, benzo (a) pyrene, chresene, phenanthrene, flurorantene, naphthalene, etc. is generally lower than 0.05 ppm, preferably lower than 0.01 ppm for each of the individual fabrics. Also materials such as hexachlorobenzene, 1,2-dichloroethane, dichloromethane, trichlorethylene, tertrachlorethylene, tetrachloromethane, vinyl chloride will usually not be present in a concentration higher than 0.05 ppm, preferably not higher than 0.01 ppm for each individual component. Also the concentration of other organic substances such as 1,1,1 trichloroethane, 1,1,2 trichloroethane is usually lower than 0.05 ppm, preferably lower than 0.02 ppm, ethane, hexane, hetptane, octane are usually present in a concentration lower than 0.5 ppm; mineral oil, C10-C12 hydrocarbons, C12-C20 hydrocarbons, C20-C30 hydrocarbons, C30-C40 hydrocarbons are usually present in a concentration below 20 ppm.
    The average particle size of calcium carbonate particles present in sludge from cutting calcium carbonate based rock is usually between 0.06 and 2.0 mm, preferably between 0.040 mm and 1.5 mm, more preferably between 0.5 and 500 microns. The majority of the particles have a particle size between 5 and 250 microns. The inventors have found that drying such particles by adding quicklime produces particles with an average size suitable for direct use as a soil improver, without the necessity of subjecting the dried particles to an additional reduction step. This is an important advantage.
    The average particle size of calcium carbonate particles present in sludge from sawing calcium carbonate based rock is usually less than 0.25 mm, preferably less than 0.225 mm, more preferably less than 0.20 nmm, most preferably less then 0.175 mm.
    In particular, at least 90% of the calcium carbonate particles present in the sludge have an average particle size of less than 0.100 mm, preferably less than 0.075 mm, more preferably less than 0.065 mm.
    The aqueous sludge from the sawing can contain widely varying amounts of water. To prevent too much quicklime or too much
    CaO must be used to achieve a sufficient drying, the aqueous sludge is preferably at least partially dewatered before adding quicklime. The sludge is preferably dewatered prior to contact with quicklime to a water content of a maximum of 50 wt. %, more preferably a maximum of 40 wt. %, most preferably maximum wt. %.
    For dewatering the aqueous sludge prior to contacting with the quicklime, a wide range of techniques known to those skilled in the art can be used. Known techniques are filtering the sludge, whereby the sludge remains on the filter and the water is collected as a filtrate, centrifuging, and settling. The sludge is preferably allowed to settle, the sludge depositing at the bottom and the water being separated as the above layer. The settling of the sludge can be carried out in one, two or more steps, with water always being removed in the meantime. The sludge is preferably inverted between two successive settling steps to promote water separation.
    The amount of quicklime added to the at least partially dewatered sludge to achieve further drying of the sludge can vary within wide limits and is usually chosen by those skilled in the art taking into account the amount of water present in the sludge. However, the amount of added quicklime usually varies from 1.0-3.0 g of quicklime per g of water present in the at least partially dewatered sludge, preferably 1.5-2.5 g of quicklime per g of water. The exothermic reaction of the quicklime with the water makes it possible that drying of the sludge is caused by two simultaneously occurring phenomena, in particular on the one hand the exothermic reaction of the quicklime with the water, and on the other hand evaporating the water by heating the sludge due to exothermia. This makes it possible to minimize the amount of quicklime needed. The dried sludge usually has a water content that does not exceed 30 wt. % with respect to the total weight of the sludge, preferably the water content is not higher than 25.0 wt. %, more preferably not higher than 20.0 wt. %.
    In a preferred embodiment, the heat generated in the exothermic reaction of the quicklime with the at least partially dried sludge is collected in a heat exchanger. This heat can be used in a subsequent stage for drying water-containing sludge.
    The method of this invention is suitable for recycling sludge waste from a wide range of calcium carbonate-containing rocks, for example limestone, marble, dolomite, dolomite limestone, gypsum, calcite, freestone, and mixtures of sludge from two or more aforementioned rocks . Preferably, however, use is made of sludge from sawing or grinding blue hard stone, because of the high purity of this stone. Bluestone or bluestone or coal limestone consists almost entirely of limestone, the amount of metals or other substances such as phosphorus than calcium carbonate present in the stone is minimal. Bluestone is characterized by the presence of very many remains of crinoids, animals with a lime skeleton. The stone is a concatenation of crinoids in a cement of microcrystalline calcite.
    The dried calcium carbonate obtained by the method of this invention can be used as such as soil improver, in agriculture, for example fruit or vegetable growing, in growing crops, etc. However, within the scope of this invention it is also possible to use additional nutrients such as, for example, Add N, P, K sources. Examples of such fertilizers are ammonium nitrate, ammonium sulfate, alkali metal nitrate, urea, ammonium phosphate, phosphates, aluminum phosphate, potassium salts, for example chlorides, sulfates and nitrates.
    The dried calcium carbonate obtained by the method of this invention is particularly suitable for use on acidic soils or in combination with acidic fertilizers or soil improvers, since it develops a basic pH in the presence of water and thus a neutralization of an overly acidic soil or an all acidic fertilizer to the desired level.
    The dried calcium carbonate obtained by the process of this invention is further particularly suitable for use as a filler with plastics, for example as a filler with plastics for injection molding of molds such as plastic panels, crates, etc., which must have a high impact resistance. The dried calcium carbonate obtained by the process of this invention is furthermore particularly suitable for use as an additive for silica residual streams, or as a filler in building materials.
    Figure 1 shows the dried sludge of this invention in a photo taken with an electron microscope, magnification 500 μιη.
    Figure 2 shows the dried sludge of this invention in a photo taken with an electron microscope, magnification 100 µm.
    FIG. 3 shows the particle size distribution of a typical sample of dried sludge measured by electron microscopy.
    权利要求:
    Claims (11)
    [1]
    CONCLUSIONS
    A method for recycling aqueous sludge from calcium carbonate particles, characterized in that at least a part of the water present in the sludge is separated, after which the at least partially dewatered sludge is mixed with an amount of quicklime.
    [2]
    A method according to claim 1, wherein the calcium carbonate particles present in the sludge have a particle size between 0.06 and 2.0 mm, preferably between 0.040 mm and 1.5 mm.
    [3]
    A method according to claim 1 or 2, wherein the calcium carbonate particles present in the sludge have an average particle size of less than 0.25 mm, preferably less than 0.225 mm, more preferably less than 0.20 mm, with most preferably smaller than 0.175 mm.
    [4]
    A method according to any one of the preceding claims, wherein at least 90% of the calcium carbonate particles present in the sludge has an average particle size that is smaller than 0.100 mm, preferably smaller than 0.075 mm, more preferably smaller than 0.065 mm.
    [5]
    A method according to any one of the preceding claims, wherein the sludge is at least partially dewatered by sedimentation of the water prior to the addition of quicklime, followed by separation of the supernatant water and the underlying moist sludge.
    [6]
    A method according to any one of the preceding claims, wherein the at least partially dewatered sludge is at most 50 wt. % water contains, preferably a maximum of 40 wt. %, more preferably a maximum of 30 wt. %.
    [7]
    A method according to any one of the preceding claims, wherein the amount of added quicklime varies from 1.0-3.0 g of quicklime per g of water present in the sludge, preferably 1.5-2.5 g of quicklime per g of water.
    [8]
    A method according to any one of the preceding claims, wherein the dried sludge is at most 30.0 wt. % water contains, preferably a maximum of 25.0 wt. %, more preferably a maximum of 20.0 wt. %.
    [9]
    A method according to any one of the preceding claims, wherein the aqueous sludge comes from bluestone.
    [10]
    A method according to any one of the preceding claims, wherein the amount of calcium carbonate present in the sludge is at least 75 wt. %, preferably at least 80.0 wt. %, more preferably at least 85.0 wt. %.
    [11]
    A method wherein the recycled sludge according to any of claims 1 to 10 is used as a soil improver in agriculture, as a filler in building materials, as an additive in the processing of plastics.
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