Process for producing silico-calcareous mineral fillers by washing earth

Abstract

Process for producing silico-calcareous mineral fillers by washing earth The present invention relates to a process for manufacturing a silico-calcareous mineral filler, said filler comprising the following compounds per 100% by weight: CaCo3: 50%; SiO2: 25%; Al2Si2O5(OH)4 (kaolinite): 10%; KAl2(AlSi3O10)(OH)2 (muscovite): 10%; and MgCO3, Fe3O4, CaSO4.2H2O: 5%.

Description

Title of the invention: Process for producing silico-calcareous mineral fillers by washing earth

[0001] The present invention relates to a silico-calcareous mineral filler which can be used, inter alia, in the plastics and paper industries as a replacement for conventional fillers. It also relates to a process for preparing these mineral fillers.

[0002] The applicant company has developed a process for washing soil described in French patent FR 3102985.

[0003] This process makes it possible to obtain fine sludge (< 63 pm) which can subsequently be used in the manufacture of concrete, as described in French patent FR 3102985.

[0004] Fillers such as calcium carbonate are used in many sectors such as polymers, rubbers or paper to impart mechanical properties to the products into which the fillers are introduced.

[0005] These charges are produced in particular by mining (GCC form - Ground Calcium Carbonate) or in the case of calcium carbonate by chemical precipitation (PCC form - Precipitated Calcium Carbonate). These processes have a significant environmental impact and it is necessary to seek more sustainable practices.

[0006] The applicant company has improved the process of washing earth in order to be able to produce a mineral filler which is suitable for use in the fields of plastics or in the paper industry.

[0007] To this end, the present invention relates to a process for obtaining a mineral filler from earths, characterized in that it comprises the following steps:

[0008] (a) removal of macro-waste, such as pieces of wood, metal, concrete, cables electrical, plastic, from land;

[0009] (b) sludge removal to create a fluid mixture of gravel, sand and fines;

[0010] (c) washing / screening this mixture with high pressure water jets to obtain: • on the one hand, a gravel fraction (G); and • on the other hand, a sandy pulp containing, in water, sand and fines (< 63 pm);

[0011] (d) hydrocycloning of the sandy pulp to obtain, in reverse, a fraction sandy (S) and, in overflow, an aqueous sludge of fines (F) (< 63 pm); or

[0012] (dl)first hydrocycloning of the sandy pulp to obtain: - in the underflow, a watery mud of sand and fines; and - overflow, an aqueous sludge of fines (F);

[0013] (d2) second hydrocycloning of the aqueous sludge of sand and fines resulting from the first hydrocycling to obtain: - on the one hand, a sandy fraction (S); and - on the other hand, an aqueous sludge of fines (F); and

[0014] (e) where appropriate, decantation of the aqueous sludge(s) of fines (F) to reduce water content and / or

[0015] (f) partial dehydration, for example by pressing or centrifuging the aqueous sludge of fines (F);

[0016] (g) sizing / clumping of the filter cakes obtained after step (f) to obtain pieces of size approximately 40 mm;

[0017] (h) pre-drying the pieces obtained in step (g) at a temperature of 750°C in a rotating dryer tube with hot air circulating countercurrently;

[0018] (i) micronization of the dried pieces obtained in step (h) at a temperature of micronization at 450°C by flash drying to obtain a powder with a moisture content of less than 1%;

[0019] (j) classification by a dynamic separator of the pieces dried by flash drying obtained in step (i) to obtain a powder with a diameter D90 < 50 pm.

[0020] A single cycloning (d) can be carried out in the case of a fines content of less than 15% by mass in the raw earth, and two successive cyclonings (d1 and d2) in the case of a fines content in the raw earth of 15 to 40% by mass.

[0021] In step (c), the gravel fraction (G) obtained, for example in a paddle scrubber, can be washed under high-pressure water jets, a small aqueous fraction of fines then being obtained, which can also be used in the manufacture of concrete.

[0022] In step (d1), the aqueous slurry of sand and fines obtained in the underflow can be sent to at least one attrition cell to clean the sand of fine clay particles stuck to it, before sending this slurry to the second hydrocycloning (d2).

[0023] The present invention also relates to a mineral filler characterized in that it comprises the following compounds per 100% by weight: • CaCO3: 40% to 60%; • SiO2: 20% to 30%; • Al2Si2O5(OH)4 (kaolinite): 5% to 20%; • KAl2(AlSi3Oio)(OH)2 (muscovite): 5% to 20%; and • MgCO3, Fe3O4, CaSO4.2H2O: 0% to 10%.

[0024] In particular, the characterized mineral filler may comprise the following compounds for 100% by weight: • CaCo3: 50%; • SiO2: 25%; • Al2Si2O5(OH)4 (kaolinite): 10%; • KAl2(AlSi3Oio)(OH)2 (muscovite): 10%; And • MgCO3, Fe3O4, CaSO4.2H2O: 5%.

[0025] The mineral filler according to the present invention may have a D90 particle size of 50 μm and a D50 particle size of 15 μm.

[0026] The D50 particle size corresponds to the median grain size, the D90 particle size corresponds to the diameter for which 90% by volume of the particles in the sample have a smaller diameter.

[0027] The filler according to the present invention can be used as a filler in the field of plastics processing by being incorporated into polymers such as PVC or polyolefins such as polypropylene, into rubber or ethylene-propylene-diene monomer (EPDM) elastomers, or in paper manufacturing.

[0028] The following examples illustrate the present invention without, however, limiting its scope. Example 1

[0029] Manufacture of a mineral filler from earths

[0030] The following process was carried out:

[0031] (a) Pre-treatment of land to be treated

[0032] The macro-waste is extracted from the soil to be treated, which contains a percentage of fines of 30%.

[0033] (b) Settling

[0034] The soil obtained in (a) is de-silted. This step allows the gravel to be washed in order to detach the fine mud particles. This step also allows the separation of floating materials, such as plastics, from the macro-waste.

[0035] (c) Underwater screening / sieving

[0036] Thanks to the superposition of three sieves (60 mm, 22 mm and 6 mm), a screening-washing machine ensures the separation of the fragments of material into two parts (6 / 60 mm and 0 / 6 mm).

[0037] The 22mm sieve serves only as an intermediate "protective" sieve, preventing the middle fraction from arriving too quickly and abruptly on the 6mm sieve. The high-pressure water jets placed upstream of the screen exert shear forces on the material and thus promote the separation of the fines. While the vertical movements of the sieves allow the material to be dispersed and the agglomerates to be broken up, the advancement component ensures the progression of the products towards their outlet.

[0038] The gravel (G) (6 / 60mm) is directed towards a paddle de-sludger while a sandy pulp formed of sand (0 / 4mm) and fines (< 63 pm) is sent to a first hydrocyclone.

[0039] Consisting of two shafts resembling worm screws rotating in opposite directions, the paddle scrubber completes the washing of the gravel (G). Passage under high-pressure water jets creates shear forces on the material and thus promotes the separation of the fines and their transfer into the water. The fines are then pumped to the sludge tank. The clean gravel (G) obtained at the outlet is stored in the dedicated area.

[0040] The paddle de-sludger also allows the removal of floating materials (light elements, plastics, porous carbonaceous material, etc.). These floating materials are then stored in the dedicated area.

[0041] (dl) First stage of hydrocycloning

[0042] The sandy pulp obtained at the outlet of the washing screen is sent to a first hydrocyclone. Hydrocyclone separation allows the relatively clean sand fraction to be separated from the fines.

[0043] The operating principle of a hydrocyclone is based on the difference in mass of the particles. It is fed tangentially in its upper part by the mixture of water + sand + fines (<63qm). The centrifugal force created within the cell forms two spiral-shaped movements. While the first movement (descending) precipitates the coarse particles (sand) towards the underflow, the second (ascending) sucks the lighter particles such as fines and a large part of the water towards the overflow of the hydrocyclone.

[0044] At the end of this stage, the sand discharged into the underflow still contains a significant portion of fines (mixture obtained in the underflow: sand 80%, fines 20%). It is therefore sent to attrition cells.

[0045] The aqueous sludge of fines obtained in overflow is sent to the sludge recovery basin.

[0046] (d2) Second hydrocycloning

[0047] Attrition cells improve the final quality of the sand by removing a large quantity of fines. Each cell has a rotating shaft equipped with two specifically shaped blades to vigorously mix the sand suspension. As they pass successively through the cells, the sand particles are subjected to significant frictional forces against each other. These forces have the effect of detaching the remaining fine clay particles.

[0048] The suspension obtained at the outlet of the last cell feeds a second hydrocyclone which, like the first, makes it possible to separate the sand fraction (S) from the aqueous sludge of fines.

[0049] The clean sand (S) obtained at the outlet of the second hydrocyclone then passes over a vibrating table to dewater it. At the end of this treatment, it comes out clean with a residual fines concentration of 3-4% and a water content of 8-10%. It is then moved and stored in a dedicated area.

[0050] The water loaded with fines is collected throughout the process (at the paddle desludger level, the two hydrocycloning stages) and is sent to the sludge recovery tank. The humidity rate of the sludge in the tank is 90 to 95%.

[0051] (e) Decanting the aqueous sludge of fines

[0052] The water from the sludge recovery tank is then pumped to a settling silo. In order to accelerate the settling process within the silo, a flocculant can be added. This flocculant is injected into the solution via a process called in-line homogenization, i.e. the flocculant is injected at several points in the pipe that brings the solution to the top of the settling silo. The settling time of the fines in the silo is approximately 120s. This extremely rapid speed explains the continuous filling of the basin with clear water at the outlet of the silo.

[0053] In the settling silo, the fines are recovered in the overflow to a sludge basin feeding the filter presses while the clean water is discharged in the overflow into the clear water basin before being reinjected after filtration into the process. The humidity level of the sludge collected in the sludge basin is around 60%.

[0054] (f) Filtration of sludge on filter presses

[0055] The sludge stored in the sludge basin is then conveyed to filter presses in order to reduce the humidity level from 60% to 30%.

[0056] A filter press consists of several chambers arranged next to each other. The fines are injected at the inlet with a pressure of 12 bars (pressure which will be kept constant during filtration). The fines are injected into each chamber by central injection. Small holes in the walls of each chamber allow the water to drain.

[0057] The water discharged by the filtration leaves the filter and flows along a recovery gutter. At the outlet of this gutter, a probe measures the flow rate of water discharged in real time. When this flow rate has become sufficiently low, the filtration is finished. The probe sends the information to the PLC which controls the removal of the plates. The humidity rate of the filter cakes at the outlet of the process amounts to 30%.

[0058] The cycle time of the filter presses can vary, depending on the nature of the fines, between 45 minutes and 4 hours.

[0059] The filter cakes are stored in the dedicated tent hangar to allow natural drying of the material.

[0060] (g) Calibration / lumping

[0061] The materials stored in the tent hangar will be taken by a loader and emptied into a feed hopper which will allow the rate of the overall process to be regulated. The hopper is equipped with a system for breaking up / calibrating the material to a size of approximately 40mm.

[0062] (h) Pre-drying

[0063] The crumbled pieces obtained in step (g) are introduced into a rotary dryer tube with hot air at a temperature of 750°C circulating countercurrently to the crumbled pieces. This pre-drying makes it possible to remove approximately 90% of the residual moisture.

[0064] The pre-dried pieces exit the rotary dryer tube with a residual moisture content of approximately 3% H2O.

[0065] (i) Micronization

[0066] The pre-dried pieces then undergo intensive micronization by flash drying in a high temperature environment (approximately 450°C) which completes the drying while breaking up the mineral aggregates. The powder obtained has a humidity of less than 1%.

[0067] (j) Classification

[0068] The micronized powder is sent to a dynamic separator to obtain the charge at the desired particle size with a D90 of less than 50 pm, i.e. 90% of the powder has a diameter of less than 50 pm.

[0069] The classification refusal is returned to the input of the micronizer of step (i).

[0070] The mineral load is then stored in atmospheric storage silos controlled to avoid moisture regain in the dried material.

[0071] Throughout the process, the drying fumes are treated by passing through high-temperature bag filters, with recirculation loops to preheat the gases, and therefore reduce consumption. The treated gases are released into the atmosphere via a chimney.

[0072] The mineral filler obtained has the following composition, in percentage by mass:

[0073] Calcium carbonate (CaCO3): 50%

[0074] Silica (SiO2): 25%

[0075] Kaolinite (Al2Si2O5(OH)4): 10%

[0076] Muscovite KAl2(AlSi3O10)(OH)2: 10%

[0077] Magnesium carbonate (MgCO3), Iron (II, III) oxide (Fe3O4), Gypsum (CaSO4, 2H2O): 5% Example 2

[0078] Incorporation of the filler according to the invention into PVC formulas Formulation

[0079] Two formulations having the following compositions were prepared: According to the invention Reference Component Quantity (% by mass) Quantity (% by mass) PVC (vinyl chloride homopolymer of KWert 70 marketed by Arkema under the name Lacovyl® S7015 47.3 47.3 Plasticizer DOPT (bis(2-ethylhexyl) terephthalate) 42.6 42.6 Protective agent TQP601 0.7 0.7 Filler according to the invention 9.5 - Treated calcium carbonate marketed by Omya under the name Omya® EXH1 - 9.5 Obtaining plates

[0080] All the ingredients of the formulation were mixed in a container in order to obtain a homogeneous paste.

[0081] A cylinder mixer (No. 5000) is used with cylinder temperatures of 165°C and rotation speeds of 20 revolutions per minute and 18 revolutions per minute for the front cylinder and the rear cylinder respectively.

[0082] The dough is gradually placed on the cylinders and comes out of the cylinders in the form of pancakes.

[0083] Plates are then obtained by compression in a frame mold. Results

[0084] The results of the formulation according to the invention and of the comparative formulation are indicated in the following table. According to the invention Comparison Shore A hardness (according to ISO 48-4 standard) 69.4 67.5 Electrical resistivity (according to NF EN 62631-3-1: 2016 standard) (Qm) 1.71*10" 4.31*1O10

[0085] The formulation according to the present invention exhibits better hardness and much better electrical resistivity compared to the comparative formulation. Example 3

[0086] Incorporation of the filler according to the invention into an elastomer Formulation

[0087] Two formulations having the following compositions were prepared: According to the invention Comparative Ingredients Quantity (pce) Quantity (pce) ethylene-propylene-diene monomer (EP DM) marketed by the company Arlanxe o under the name Keltan® 8550 100 100 Carbon black N550 50 50 Mineral oil marketed by the company Total under the name Tordis® 6 200 15 15 Mixture of paraffins and micro-waxes marketed by the company Rhein Chemie Rheinau GmbH under the name Antilu x® 500 1 1 Stearic acid 1 1 ZnO 3 3 Sulfur 1.5 1.5 Hardening accelerator marketed by the company Rhein Chemie Rheinau G mbH under the name Rhenogran® C BS80 2.5 2.5 Dibenzothiazyl disulfide (MBTS) 1 1 Disulfide bis(dimethylthiocarbamoyl) (TBzTD 70) 1 1 Charge according to the invention 75 - Calcium carbonate marketed by the company Imerys under the name Micronic O - 75 Obtaining

[0088] The mixtures were prepared in a 3.2 L Banbury internal mixer with a control temperature of 60°C and an initial rotor speed of 60 rpm with a mixture mass of 2834 g. The compounds are introduced then a piston stroke is made after 1'30”, a piston stroke is made after 3'00” and the speed increases to 50 rpm. A piston stroke is made after 4'00” and the mixture falls after 5'00”.

[0089] Then the mixtures are accelerated on an AGILA open mixer (0 300x700) with a control temperature of 60°C, a rubber guide spacing of 40 cm, a front cylinder speed of 16 revolutions per minute and a rear cylinder speed of 13 revolutions per minute.

[0090] Test tubes were prepared from the mixed compositions. Results

[0091] The results of the formulation according to the invention and of the comparative formulation are indicated in the following table. According to the invention Comparison Shore A hardness (according to ISO 48-4 standard) 74.7 71.5 DIDC hardness (according to ISO 48-2 standard) 76.5 75.8 Uniaxial tension (according to ISO 37 standard) Elongation at break (%) 297 331 DELFT tearing (according to ISO 34-2 standard) Fmaximum (N) Ftearing (N) 35.4 19.7 26.4 19.7 Compression set (according to ISO 815-1 standard) DRC (%) 28.2 31.9

[0092] The mechanical properties of the elastomer with the filler according to the present invention are better than that with calcium carbonate as filler, with in particular better properties of hardness, uniaxial tension, tear resistance and better elastic return after compression. Example 4

[0093] Incorporation of the filler according to the invention into paper Preparation

[0094] Sheets of paper were prepared using a dynamic sheeter with 15% by mass of filler according to the invention in order to obtain sheets with a grammage of 70g / m2. Results

[0095] The sheets with the filler according to the invention were compared with sheets prepared with 15% by mass of calcium carbonate. According to the invention Comparative Burst index (kPa.m2 / g) 170 172 Bendtsen roughness (mL / min) 920 850 Bendtsen permeability (cm3 / m2.Pa.s) 1100 750 Whiteness R475 (%) 50 87 Opacity (%) 98 86

[0096] The papers according to the present invention have good mechanical properties, as well as better roughness and air permeability properties. If the fillers according to the invention have an impact on the whiteness of the paper obtained, they do, however, make it possible to obtain a paper with very good opacity.

Claims

Claims

1. - Process for obtaining a mineral charge from earths, characterized by the fact that it includes the following steps: (a) removal of macro-waste, such as pieces of wood, metal, concrete, electrical cables, plastic material, from land; (b) sludge removal to create a fluid mixture of gravel, sand and fines; (c) washing / screening this mixture by high pressure water jets to obtain: • on the one hand, a gravel fraction (G); and • on the other hand, a sandy pulp containing, in water, sand and fines; (d) hydrocycloning of the sandy pulp to obtain, in the underflow, a sandy fraction (S) and, in the overflow, an aqueous sludge of fines (Mad (dl)first hydrocycloning of the sandy pulp to obtain: - in the underflow, a watery mud of sand and fines; and - overflow, an aqueous sludge of fines (F); (d2) second hydrocycloning of the aqueous slurry of sand and fines resulting from the first hydrocycloning to obtain: - on the one hand, a sandy fraction (S); and - on the other hand, an aqueous sludge of fines (F); and (e) where appropriate, decantation of the aqueous sludge(s) of fines (F) to reduce its water content and / or (f) partial dehydration, for example by pressing or centrifuging, of the aqueous sludge(s) of fines (F); (g) sizing / clumping of the filter cakes obtained after the step (f) to obtain pieces of size approximately 40 mm; (h) pre-drying the pieces obtained in step (g) at a temperature of 750°C in a rotary dryer tube with hot air circulating counter-currently; (i) micronizing the dried pieces obtained in step (h) at a micronization temperature of 450°C by flash drying to obtain a powder having a moisture content of less than 1%; (j) classification by a dynamic separator of the flash-dried pieces obtained in step (i) to obtain a powder with a diameter D90 <50 pm.

2. - Method according to claim 1, characterized in that a single cycloning (d) is carried out in the case of a fines content of less than 15% by mass in the raw earth, and two successive cyclonings (d1 and d2) in the case of a fines content in the raw earth of 15 to 40% by mass.

3. - Method according to one of claims 1 and 2, characterized in that in step (c), the gravel fraction (G) obtained for example in a paddle scrubber is washed under high-pressure water jets, a small aqueous fraction of fines then being obtained, which can also be used in the manufacture of concrete.

4. - Method according to one of claims 1 to 3, characterized in that in step (dl), the aqueous slurry of sand and fines obtained in the underflow is sent to at least one attrition cell to clean the sand of fine clay particles stuck to it, before sending this slurry to the second hydrocycloning (d2).