Methods for removing fine particles from wastewater streams

Abstract

Method for removing fine particles from wastewater streams during the treatment of mineral substances using centrifugal separators, comprising the following steps: - Collection of the wastewater to be treated (AW), containing fine particles of essentially ≤ 250 µm particle size, in a first pump sump tank (B01); - Conveying the contents from the first container (B01) to a first centrifugal separator (F01) for classification with a separation cut (d 50 ) of essentially 8 - 10 µm grain size; - Directing the underflow product from the first centrifugal separator (F01) into a second pump sump tank (B02); - Guiding the overflow product from the first centrifugal separator (F01) to a thickener or into a settling pond (AT); - Conveying the contents from the second container (B02) to a second centrifugal separator (F02) for thickening, whereby the underflow product is transferred to a linear vibrating conveyor (F03) for further thickening by means of residual dewatering; - Returning the overflow product from the second centrifugal separator (F02) to the first container (B01); and - Initiating the linear oscillator pass into the second container (B02).

Description

[0001] The invention relates to a method for removing fine particles from wastewater streams during the processing of mineral substances using centrifugal separators according to claim 1.

[0002] US Patent 7,514,011 B2 discloses a system for separating solids from a liquid stream. The system comprises a first separation device fixed to a container. The container includes a settling chamber and a baffle plate module, the settling chamber receiving the liquid from the first separation device. The separation device includes a linear vibrator. A further separation device interacts with a combination of a cyclone separator and another linear vibrator.

[0003] The portable device for separating and recovering fine particles according to US 2017 / 151573 A1 includes an inlet cyclone separator mounted on a portable frame. The device also includes a screening unit that removes larger particles from the underflow stream of the cyclone.

[0004] US Patent 2019 / 351429 A1 discloses a device for washing and sorting sand or sand-containing materials, comprising a first vibrating screen with a lid designed to receive feed material. Oversized material flows over the deck of the first vibrating screen to be collected. Undersized material and water are collected in a pump sump and then enter a hydrocyclone. Another vibrating screen is connected to the underflow of the hydrocyclone, with the overflow entering a settling tank. A water reservoir receives the water overflowing from the settling tank, while sludge residue is collected and removed from the bottom of the tank. The vibrating screens are designed to wash and clean the sand material.

[0005] Further procedures are known from publications US 2010 / 0 059 453 A1 and US 5 080 721 A.

[0006] It is therefore known from the prior art to clean and fractionate materials containing sand. Wastewater is typically fed into a thickener or directed into a settling pond. Particularly when flocculants cannot be used for various reasons, especially environmental ones, there is a risk that settling ponds will silt up very quickly.

[0007] For this reason, as much as possible of fine sand, silt and clay particles should be removed from a wastewater stream, for example from a mineral processing plant.

[0008] Therefore, it is also known that a cyclone stage with a separation cut is present in the wastewater stream. 50 based on particles with a density of 2650 kg / m³ 3 A particle size of approximately 40 µm is required. Cyclones with a diameter between 150 mm and 300 mm are used here.

[0009] The separation cut d 50The cut-off size is defined as the particle size that can enter both the underflow and overflow of a separator with a 50% probability. Particles finer than the specified cut-off size primarily enter the overflow. Particles coarser than the specified cut-off size predominantly enter the underflow.

[0010] However, according to the current state of the art, the problem of fine particles remains, i.e., particles with grain sizes ≥ 8 to approximately 10 µm. So far, it has not been possible to satisfactorily extract and thicken or dewater such fine particles from a wastewater stream or suspension using conventional methods.

[0011] Therefore, the object of the invention is to provide a further developed method for removing fine particles from wastewater streams during the processing of mineral substances using centrifugal separators, which meets the technical requirements and can be implemented with manageable technical and technological effort.

[0012] The problem of the invention is solved by a method as defined in claim 1, wherein the dependent claims represent at least expedient embodiments and further developments.

[0013] The inventive method for removing fine particles from wastewater streams during the processing of mineral substances initially uses centrifugal separators known per se in combination with a linear vibrator.

[0014] The process begins with the collection or feeding of the wastewater to be treated, containing fine particles with a grain size of essentially < 250 µm, into a first pump sump tank.

[0015] The contents from the first container are then fed into a first centrifugal separator for classification using a separation cut d. 50 promoted with a grain size of essentially 8 - 10 µm.

[0016] The underflow product from the first centrifugal separator is transferred to a second pump sump tank.

[0017] The overflow product from the first centrifugal separator is transferred to a thickener, which is known per se, or is placed in a settling pond.

[0018] The contents from the second container are conveyed to a second centrifugal separator for thickening, with the underflow product passing onto a linear vibrating conveyor for further thickening by means of residual dewatering.

[0019] The overflow product from the second centrifugal separator is returned to the first container.

[0020] Furthermore, the linear vibrator is introduced into the second container.

[0021] In a further development of the invention, a partial flow of the overflow from the second centrifugal separator is directed into the second container to control the pump sump.

[0022] Also optional and for further development purposes, a partial flow of the overflow from the first centrifugal separator can be directed into the first tank to control the pump sump.

[0023] This reliably prevents the pump belonging to the centrifugal separator in question from running dry.

[0024] The linear vibrator used has slotted screens and electric motor drives for generating unbalance vibrations, wherein, according to the invention, the unbalance frequency can be optionally set or regulated in order to optimize the residence time of the particles on the linear vibrator so that there is a sufficient possibility of water release.

[0025] The product obtained from the linear vibrator is therefore a fine sand fraction with a grain size ≥ 8 µm, which can be further dewatered if necessary.

[0026] The invention will be described below with reference to the Fig. 1, which represents a plant diagram, will be explained in more detail.

[0027] The wastewater stream containing fine particles, for example from a mineral processing plant, enters a first container B01. In this respect, the wastewater contains particles with a grain size of ≤ 250 µm.

[0028] The wastewater enters a first centrifugal separator F01 via a pump P01, which is connected to the pump sump of the tank B01.

[0029] The overflow from the first centrifugal separator F01, which contains a proportion of particles, flows to a settling pond or thickener.

[0030] A partial flow can be used for pump sump regulation.

[0031] The corresponding control unit with float and valve is labelled RE1 in the diagram.

[0032] The underflow from the first centrifugal separator F01 enters a second container B02 with a corresponding pump sump and connected pump P02.

[0033] The second centrifugal separator F02 is fed by means of the pump P02.

[0034] The second centrifugal separator F02 is used to further thicken the fed material.

[0035] The lower flow from the second centrifugal separator F02 is fed onto the linear vibrator F03.

[0036] The linear vibrator F03 can be equipped with a frequency converter control to optimize the vibration behavior of the slotted screen implemented here.

[0037] The overflow from the second centrifugal separator stage F02, which still contains fine particles below the cut d 50 The contents would be returned to the first container P01, similar to the principle of a countercurrent wash.

[0038] A partial flow of the overflow is in turn used to regulate the level of the upstream pump sump in the tank B02 by means of the control unit RE2.

[0039] The entire sieve material from the linear vibrator F03 is returned to the second container B02 in order to be able to pass through the stage with the second centrifugal separator F02 again.

[0040] The starting material for the processing is a fine sand fraction with a grain size > 8 µm and can be transported away, for example, by means of a conveyor belt or, if necessary, further dewatered either statically or mechanically. Units such as belt filters or flat filters are suitable for dewatering.

[0041] According to the exemplary embodiment, due to the very high proportion of fine particles in the wastewater stream, the separation point is therefore significantly lower than in the prior art. In this respect, the wastewater stream is first classified using 50 mm centrifugal separators in order to achieve a separation point d 50The goal is to achieve a particle size of approximately 8-10 µm. The underflow, i.e., the fine sand fraction, is then thickened using a further centrifugal separator stage, before finally being dewatered using a linear vibrating screen. Surprisingly, it has been shown that dewatering such a fine fraction is indeed possible with a linear vibrating screen or a suitable sieve arrangement.

[0042] The mass available at the bottom of the second centrifugal separator F02 is thickened to such an extent that a sufficient residence time on the linear vibrator is ensured, especially when the control of the unbalance vibration generation is adapted to the properties of the material to be dried.

[0043] The method according to the invention can therefore usefully complement known systems for treating wastewater containing particles and help prevent the silting up of settling ponds that would otherwise occur.

Claims

[1] Method for removing fine particles from wastewater streams during the treatment of mineral substances using centrifugal separators, comprising the following steps: - Collection of the wastewater to be treated (AW), containing fine particles of essentially ≤ 250 µm particle size, in a first pump sump tank (B01); - Conveying the contents from the first container (B01) to a first centrifugal separator (F01) for classification with a separation cut (d 50 ) of essentially 8 - 10 µm grain size; - Directing the underflow product from the first centrifugal separator (F01) into a second pump sump tank (B02); - Guiding the overflow product from the first centrifugal separator (F01) to a thickener or into a settling pond (AT); - Conveying the contents from the second container (B02) to a second centrifugal separator (F02) for thickening, whereby the underflow product is transferred to a linear vibrating conveyor (F03) for further thickening by means of residual dewatering; - Returning the overflow product from the second centrifugal separator (F02) to the first container (B01); and - Initiating the linear oscillator pass into the second container (B02). [2] Method according to claim 1, characterized by , that a partial flow of the overflow from the second centrifugal separator (F02) is directed into the second container (B02) for the control of the pump sump by means of a control unit (RE2). [3] Method according to claim 1 and / or 2, characterized by , that a partial flow of the overflow from the first centrifugal separator (F01) is directed into the first container (B01) for the control of the pump sump by means of a control unit (RE1). [4] Method according to any of the preceding claims, characterized by , that the linear oscillator (F03) has slotted screens and electromechanical drives for generating unbalance vibrations, whereby the unbalance frequency is controlled. [5] Method according to any of the preceding claims, characterized by , that the product obtained at the linear vibrator (F03) is a fine sand fraction (FS) with a grain size > 8 µm, which is subjected to further dewatering if required.

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