Method and colloidal mixer for colloidal processing of a slurry

Abstract

The invention relates to a method and a colloidal mixer for colloidal processing of a slurry, in particular processing of construction materials, with a colloidal mixer, in which at least one liquid is introduced into a mixing trough, at the lower region of which is arranged an outlet opening with a mixing device having a mixing rotor, which is driven in rotation. According to the invention, the at least one pulverulent solid component is introduced into the mixing trough, the at least one liquid mixed with the at least one pulverulent solid component is induced to flow by the rotatingly driven mixing rotor and is discharged from the mixing trough through the outlet opening, wherein the mixture is led back again for a certain time via a backflow line into an upper region of the mixing trough for further mixing and, after a desired mixing state has been attained, the mixture is discharged as a finished slurry from the outlet opening by means of a discharge line. According to the invention, it is provided that air is incorporated into the at least one liquid and / or the mixture in a targeted manner in a finely dispersed form, wherein a relative density of the liquid, or of the mixture, is reduced.

Description

The invention relates to a method for colloidal processing of a slurry, in particularprocessing of construction materials, with a colloidal mixer, in which at least one liquidis introduced into a mixing trough, at the lower region of which is arranged an outletopening with a mixing device having a mixing rotor, which is driven in rotation, at leastone pulverulent solid component is introduced into the mixing trough, the at least oneliquid is mixed with the at least one pulverulent solid component by means of therotationally driven mixing rotor, is induced to flow and is discharged from the mixingtrough through the outlet opening, wherein the mixture is returned again for a certaintime via a recirculation line to upper region of the mixing trough for further mixing and,after a desired mixing state has been attained, the mixture is discharged as a finishedslurry from the outlet opening by means of a discharge line, according to the preambleof claim 1.The invention further relates to a colloidal mixer for the colloidal processing of a slurry,in particular for the processing of construction materials and in particular for carryingout a method according to the invention, comprising a mixing trough which has anupper feed opening for feeding at least one liquid and at least one pulverulent solidcomponent and a lower outlet opening, a mixing device which has a mixing rotor whichcan be driven in rotation and is arranged in a lower region of the mixing trough, whereinthe at least one liquid and the at least one pulverulent solid component are mixed bythe mixing rotor into a mixture and a flow of the at least one liquid or of the mixture canbe generated towards the outlet opening, a recirculation line which extends from theoutlet opening back again to the upper feed opening of the mixing trough, a dischargeline for discharging a finished slurry from the mixing trough, and a control valve deviceby means of which the recirculation line and the discharge line can be opened orclosed, in particular alternately, according to the preamble of claim 7.A colloidal mixer for the colloidal processing of a slurry, in particular for the processingof construction materials, is for example disclosed in EP 2 363 200 B1.The slurries prepared using these colloidal mixers consist of one or more liquidcomponents, usually water, and one or more mostly mineral solid components, suchas cement, bentonite, stone dust, fly ash, etc.The use of such colloidally decomposed slurries is applied in a wide variety of industrialfields, such as in special civil engineering, mining, building rehabilitation, tunneling,mining, exploration for mineral resources and many more.Initially, continuous colloidal mixers were developed, each of which could process onlyone liquid and one solid component.These slurry mixers are mainly used in diaphragm wall construction, for the productionof supporting liquids (bentonite slurry), but also for cut-off wall slurries in the singlephasediaphragm wall method.In the course of newly developed construction processes, new requirements arose forthe slurry qualities. Slurries composed of several liquid and solid components werealso required.As a result, the solids content in the mixing formulations exceeds the liquid content bya multiple, and slurry densities of 2 kg / dm³ and above are required. The available batchmixing systems are reaching their performance limits. In particular, so-called turbomixers (mixing pumps) or circulation systems with Venturi nozzles are no longercapable of reliably and economically producing these required slurries in the requiredmixing quality.Pulverulent solids have a very large surface area, depending on the fineness ofcrushing, and tend to form lumps (agglomerates) when wetted with liquid.Depending on the loading condition of the mixing vessel and the density of the slurryalready formed in the mixing system, these lumps begin to float on the surface of theslurry being in the mixing vessel and are hardly decomposed or not decomposed atall.This leads to slurries of poor quality, where important parameters in view of rheologyare not achieved.The reduction of undesirable condition by installing additional rotating tools in themixing vessel by breaking up these agglomerates is known. The disadvantage,however, is that the mixers are structurally complex and material in the form ofincrustations accumulates on these additional tools, leading to extreme caking,especially with solids containing binders. This results in considerably higher cleaningand maintenance effort.Another well-known method is to increase the circulation flow. This method increasesthe kinetic flow energy. This leads indeed to a partial, but not complete dissolution ofagglomerates. The disadvantage here is also that part of the kinetic energy isintroduced into the slurry in the form of heat, which is undesirable in some cases andcan have negative impacts on hydration, for example, in particular in the case ofcement.The object underlying the invention is to specify a process and a colloidal mixer bymeans of which colloidal processing of a slurry can be carried out in a particularefficient and cost-saving manner.This object is achieved on the one hand by a method having the features of claim 1and on the other hand by a colloidal mixer having the features of claim 7. Preferredembodiments of the invention are indicated in the dependent claims.The method according to the invention is characterized in that air is selectivelyincorporated into the at least one liquid and / or the mixture in finely dispersed form,wherein a relative density of the liquid or the mixture is reduced.A basic idea of the invention is to reduce a relative density of the liquid or the mixtureduring the production of the mixture in a targeted manner by incorporating air in finelydispersedform into the liquid or the mixture. This has the effect that pulverulent solids,which are located on the surface of the liquid or the mixture, sink faster and morereliably and thus no longer float on the surface of the liquid, in particular, if the mixturehas an increased density due to additives. This causes extensive wetting of thepulverulent solid particles and these can be absorbed more quickly in the liquid / mixtureand processed to form the colloidal slurry. Overall, a rapid production of a colloidalslurry with high mixing quality can thus be achieved in a particularly efficient mannerwithout the provision of a large number of additional mixing tools. Due to a fastersinking of the solid components, they enter in the area of the mixing device earlier,which results in faster and better mixing. Conglomerates can be broken up efficiently.The adjustment of the relative density of the mixture by incorporating air depends ineach individual case on the formulation and on the liquid and solid components used.According to a further development of the invention, it is particularly advantageous thatthe relative density of the at least one liquid or of the mixture i s reduced, wherein thevolume of the liquid or of the mixture is increased by 2 percent to 15 percent bysupplying air. The incorporation of air thereby causes a corresponding increase in thevolume of the liquid or the mixture. The relative density is set, in particular in such away, that solid particles on the surface of the liquid or mixture sink into it immediatelyor very quickly and cannot or can hardly be retained by the physical surface tension.In principle, the incorporation of air can take place in various suitable ways. Inparticular, an air supply device can be provided by means of which air can beintroduced into the liquid or mixture in a finely dispersedmanner via one or more supplynozzles.According to a further development of the invention, it is particularly advantageous thatthe recirculation line has a port opening which is directed towards an inner side of themixing trough, wherein the recirculated liquid or mixture impinges on the inner side.During this impingement of the liquid flow, an increase of the surface of the liquid andswirl occurs, wherein embedding of air from the ambient atmosphere is effected.It is particularly advantageous that a backflow from the recirculation line impingesapproximately perpendicularly on the inner side of the mixing trough. Already this flowguidance alone, with an impingement on an inner wall of the mixing trough atapproximately a right angle, makes it possible to achieve a desired incorporation of airand a corresponding reduction in relative density.According to one embodiment variant of the invention, a particularly good integrationof air results from the fact that a backflow from the recirculation line, is essentiallydivided into two partial flows, when it impinges on the inner side of the mixing troughwhich partial flows flow in opposite directions along the inner side of the approximatelydrum-shaped mixing trough. The port opening of the recirculation line and thearrangement with respect to the inner side of the mixing trough can be designed insuch a way that the backflow is divided into approximately two equal partial flows,which then flow in the circumferential direction along the inner side of the drum-shaped,preferably cylindrical, mixing trough. Thus, a first partial flow flows clockwise along theinner side of the mixing trough and a second partial flow flows in the opposite directionof rotation along the inner side of the mixing trough.The mixing trough can preferably have a diameter of between 1 meter to 2 meters andbe designed to hold a batch of 1t to 3t of material / medium. Preferably, 300l to 800l ofliquid can be fed at a feed rate of preferably 20 l / s to 100 l / s. The remaining materialcomponent, which depends on the formulation, is formed by the one or more solidcomponents, which are added via conveying devices at a feed rate of preferably 10kg / s to 20 kg / s. Smaller or larger diameters of the mixing trough for deviating batchsizes are also possible in principle.According to a further embodiment of the invention, it is particularly advantageous thatthe two partial flows are generated with a flow velocity such that the partial flows meetunder formation of swirls at a point of the mixing trough which is approximately oppositeto the port opening. The two partial flows flow in opposite directions in each case,around about half the inner circumference of the mixing trough, until the two partialflows meet again and collide. Additional swirl is thus formed in this area, withcorresponding increases in the surface area of the partial flows. This promotes thefurther incorporation of air in finely dispersed form into the respective liquid or mixture.The liquid or mixture can then sink again inside the mixing trough, the bottom area ofwhich is preferably configured conical, and sink to the mixing device with the rotatinglydriven mixing rotor in the area of the outlet opening. The mixing paddles of the mixingrotor are preferably designed and rotationally driven in such a way that cavities areformed in the liquid or mixture in a targeted manner, i. e. short-term cavities withnegative pressure. This further supports finely dispersed incorporation of air and alsowetting of the solid particles.The rotating mixing rotor also operates as a kind of pump, by means of which themixture formed can be discharged from the outlet opening and returned via therecirculation line back again to the upper area of the mixing trough for a further mixingand processing step. As soon as a desired mixing quality has been achieved, which isthe case usually after one to two minutes, the recirculation line can be shut-off and thefinished mixture can be discharged from the mixing trough as a slurry via the outletopening by means of a discharge line. The slurry thus formed can then be transportedon immediately for further processing or for short-term intermediate storage. A furtherbatch of a slurry can then be formed by introducing at least one liquid and at least onepulverulent solid component.The colloidal mixer according to the invention is configured to selectively incorporateair in finely dispersed form into the at least one liquid or the mixture in order to reducea relative density of the liquid or the mixture. The colloidal mixer according to theinvention can, in particular be used for performing the above-described methodaccording to the invention. In doing so, the advantages described above can beachieved.An advantageous further development of the colloidal mixer according to the inventionis that the recirculation line has a port opening which is directed towards an inner sideof the mixing trough. The recirculated medium can thereby impinge on a drum-shapedinner wall of the mixing trough at a flow velocity which can be several meters persecond, preferably 10 m / s to 20 m / s, with this leading to swirl and correspondingincorporation of ambient air.Alternatively or additionally, according to one embodiment of the invention, it may beprovided that an air supply device comprising at least one supply nozzle is arrangedfor injecting air into the liquid or mixture. The at least one supply nozzle can be providedat any suitable location of the colloidal mixer, in particular in a lower region of the mixingtrough. Preferably, a plurality of supply nozzles may be provided, wherein ambient aircan be injected under pressure in a finely dispersed manner into the liquid or mixture,in particular in the region of the mixing rotor.Another preferred embodiment of the invention is that the mixing rotor is arranged in arecess at the bottom of the mixing trough upstream the outlet opening. The mixing rotorwith its radially oriented mixing blades can create a desired swirl as well as cavities inthe liquid or mixture, due to a corresponding design of the edges and surfaces of themixing blades. This achieves a particularly good mixing effect. Openings or aperturescan be formed in the mixing blades of the rotor to even further improve the mixingeffect. At the same time, the mixing rotor can serve as a pump to draw in the liquid ormixture from the upper area of the mixing trough and discharge it at a specified flowrate towards the outlet opening.According to one embodiment variant of the invention, it is particularly advantageousthat the recess having the mixing rotor is arranged centrally or eccentrically at thebottom of the mixing trough relative to the center axis thereof. A central arrangementof the recess with the mixing rotor to a central axis of the mixing trough results insymmetrical flow conditions inside the colloidal mixer. An eccentric arrangement of themixing rotor to the center axis of the mixing trough can result in an additional swirleffect.According to a preferred embodiment of the invention, particularly good mixing isachieved in that a rotor axis of the mixing rotor and a center axis of the drum-shapedmixing trough are located in a center plane of the mixing trough, and in that a backflowfrom the port opening of the recirculation line impinges on the inner side of the mixingtrough approximately parallel to the center plane.The recently developed colloidal or slurry mixer can have a dispersion zone, the actualcolloidal mixing device, in which the disintegration of the components takes place, anda convection zone, which holds the actual batch volume, the so-called mixing vessel.These two zones can be designed with different cylindrical diameters and arepreferably connected to one another via an asymmetrical cone.The dispersion zone can have a tangential outlet which, on the one hand, can beconnected by means of a Y-piece to a return or circulation line tothe convection zoneand on the other hand to a drain line. Both branchings at the Y-piece can preferablybe closed and controlled by means of a pneumatic pinch valve depending on theoperating state.Located inside the mixing device is a rotating rotor with special mixing paddles, alsocalled mixing blades. This rotor, preferably driven by a three-phase current motor withtoothed belt drive, describes a circular movement at a defined circumferential speed.This leads to motion and force transmission and thus to acceleration of the liquid orliquefied components (such as water, pulverulent solid) located in the mixer.By way of example, the following operating states can be set:Operating state: MixingThe rotor rotates and the components are accelerated. The circulation line is openwhile the pinch valve of the discharge or drain line is closed. A defined circulation ofthe liquid medium located in the system takes place.Operating state: DrainingThe rotor turns and the components are accelerated. The pinch valve on therecirculation or circulation line is closed and the circulation is stopped. The pinch valveon the drain line is opened. The liquid medium located in the system is pressed intothe drain line and discharged from the mixing system.On the colloidal mixer there is preferably a lid construction with various inlet openingsfor liquids, solids, additives and, among other things, for the circulation line. A so-calleddeflecting tube can be attached to the port opening for the circulation line.In the mixing operating state, the mixing medium circulates between the mixer and themixing vessel, preferably in a defined volume flow of up to 200 m³ / h. The deflectingtube, which is installed in a defined position and inclination, allows the volume flow tobe divided into two approximately equal partial flows. This is achieved by deflecting thevolume flow to the cylindrical wall of the mixing vessel. The two partial flows move inopposite directions along the cylindrical wall of the mixing vessel and meet oppositethe deflecting tube.The meeting of the two partial flows now causes the backflow to continue centrally inthe mixing vessel above the inlet of the mixer and the aspiration of the mixing mediumfrom the mixer is promoted.At the beginning of each mixing batch, water is first preferably metered into the mixingsystem as a liquid component. During water metering, the mixing system can alreadybe in the operating state "mixing". This means that the circulation described aboveoccurs from the beginning on from a certain filling level. Since the resulting volume flowcollides with the liquid level from above, a lot of air is now entrained in the liquid (water)and fed to the mixer by means of the created flow.Due to the high flows, the air cannot escape and now passes through the mixer(dispersion zone) together with the metered water.Since the mixer generates cavitation due to its technical design, which cavitation wasdetermined by means of a high-speed camera, the air in the water is dispersedparticularly finely. This effect supports that the relative density of the dosed water isartificially lowered. This takes place during the entire mixing and metering process forall mixing components.Evidence of this effect can be considered the fact that the water in the mixing systembecomes milky cloudy. If the mixing system is switched off, the water immediately orvery quickly deaerates, countless tiny air bubbles rise and the water becomes clearagain in a very short time.If pulverulent mineral solids are now added as a further metering step, the solid cansink more quickly in the water and is thus more easily suctioned by the mixer(dispersion zone).The cavitation acting in the colloidal mixer now ensures that each individual solidparticle is wetted with water and can thus be disintegrated almost optimally. A majorpositive effect with regard to the metering of mineral solids can be seen, too. Cavitationis caused by the negative pressure generated behind the mixing blades, in which theliquid evaporates, thus creating vapor bubbles. When these bubbles enter a zone oflower pressure, the vapor condenses again and the volume decreases significantly.This creates a brief, extreme pressure difference with respect to the surroundings, sothat agglomerates of solid particles, in particular are, as it were, suctioned into theresulting cavity and decomposed. This enables and / or improves the wetting of theindividual solid particles with liquid and ensures a particularly homogeneous mixture.All mineral solids tend to form agglomerates (lumps) in the dry state due to storage ormechanical impacts. Furthermore, mineral solids usually have a bulk density of approx.1kg / dm³. Due to this technical fact, solid agglomerates would float on the water surfaceand could only be poorly influenced or mechanically decomposed into their individualparticles by means of flow. By reducing the density of the water according to theinvention, the floating of these solid agglomerates is completely prevented or at leastconsiderably reduced.The solid and agglomerates contained therein are thus fed to the dispersion zone in atargeted manner, where they are disintegrated in a very efficient manner.Due to the high circulation rate in the mixing system, this also ensures that the entirebatch content, consisting of water and solid, passes through the dispersion zonemultiple times, and thus a very good homogenization takes place.According to the invention, an advantageous embodiment of the colloidal mixer is thatthe mixing rotor has mixing blades which are provided with a hole pattern. The mixingblade is preferably formed from a base plate, wherein a plurality of through holes areformed in the base plate by the hole pattern, preferably by means of machining, (laser)cutting or punching. Preferably, the holes of the hole pattern may have a circularcontour in whole or in part. The holes may have a diameter of between 5 mm and 50mm and, in particular, may be arranged in a grid with uniform grid spacing. Other holesizes and in particular other hole contours, such as angular or polygonal, are possible.The hole pattern in the mixing blades results in a significant increase in the effectiveflow edges on the mixing blade. This increases the effect of swirl and, in particular alsothe formation of relatively small cavities in a large number. Preferably, the hole patternwith the through holes can form a total opening area which accounts for between 25%to 35%, particularly preferably between 26% to 28%, of the total area of the mixingblade. The ratio of the effects of flow edge length to flow resistance is most favorablein this case. In particular, the holes are located in the lower approximately 65%,preferably 62% to 66%, of the blade height. The dimensions of the mixing blades arebased on the dimensions of the recess or receptacle in the mixer, with marginal edgesof the mixing blades extending as close as possible to the wall. The mixing blade canpreferably be approximately rectangular in design and, in particular, have a width of 50mm to 400 mm and a height of 150 mm to 700 mm. Other dimensions are possibledepending on the shape of the mixer.Another positive effect resides in that the change in flow resistance reduces the energyrequired for rotationally driving the mixing rotor at a predetermined rotational speed.Thus, an improvement of the mixing and homogenization effect of the colloidal mixercan be achieved with a reduced energy requirement. The mixing rotor can preferablybe driven at a rotational speed between 100 rpm to 800 rpm. Deviations are possiblewith regard to the formulation of the mixture.The mixer and / or the mixing blades can preferably be formed from a resistant stainlesssteel, in particular a Hardox material.The invention is described in greater detail below with reference to a preferredexemplary embodiment, which is shown schematically in the accompanying drawings.The drawings show in:Fig. 1 a side view of a colloidal mixer according to the invention;Fig. 2 a cross-sectional view through a colloidal mixer according to the inventionaccording to Fig. 1;Fig. 3 a top view of the colloidal mixer of Fig. 1, but without lid;Fig. 4 an enlarged illustration of a mixing blade in a side view with a hole pattern;Fig. 5 a frontal view of the sheet metal-type mixing blade of Fig. 4;Fig. 6 an enlarged illustration of detail A of Fig. 4; andFig. 7 an enlarged illustration of detail B of Fig. 4.Figures 1 to 3 show an exemplary embodiment of a colloidal mixer 10 according to theinvention with a drum-shaped mixing trough 12, which is arranged on a frame 11. Thedrum-shaped mixing trough 12 has a cylindrical inner surface 13 or inner wall in itsupper portion, and is closed at its upper surface by a lid 14. A lower portion of themixing trough 12 is formed by a conically configured bottom 16, which merges via anopening into a downwardly directed receptacle or recess 20 with a mixing device 30.The opening having the recess 20 is arranged eccentrically to a center axis of thecylindrical upper section of the mixing trough 12, as can be seen clearly in Fig. 3.The mixing device 30 in the recess 20 on the underside of the mixing trough 12 has arotationally driven mixing rotor 32 with a rotor hub 33 and radially oriented mixingblades 34 attached thereto. Altogether, the mixing rotor 32 with the mixing blades 34is configured such that at least one liquid component introduced into the mixing trough12 is mixed with at least one pulverulent solid component supplied into the mixingtrough 12 by means of the rotating mixing rotor 32. In this case, a circumferential speedof the mixing rotor 32 is set in such a way and the shape of the mixing blades 34 isdesigned in such a way that cavities are formed in a targeted manner in the at leastone liquid or the mixture forming, which further support a mixing effect and a finedistribution of air.The at least one liquid or the forming mixture is discharged by means of the rotationallydriven mixing rotor 32 to a lateral outlet opening 22 with a Y-pipe section 24, at the twooutlet connections of which a backflow line 40 on the one hand and a discharge line50 on the other hand are arranged. An actuator 38 can be used to control whether themixture formed is returned to the mixing trough 12 via the backflow line 40 forcontinuation of the mixing process or is discharged from the colloidal mixer 10 via thedischarge line 50.For forming the actuator 38, a first pinch valve 42 is arranged on the backflow line 40and a second pinch valve 52 is arranged on the discharge line 50, which can be closedor opened in particular by supplying a pressure medium, in particular compressed air.When the first pinch valve 42 is open and the second pinch valve 52 is closed, liquidor mixture is returned again from the Y-pipe section 24 to an upper portion of the mixingtrough 12 via the backflow line 40 through a feed opening 15 in the lid 14, as illustratedclearly in Figures 2 and 3.In this case, the free end of the backflow line 40 has a deflecting tube or port opening44, which is directed towards the inner side 13 of the mixing trough 12. As a result ofthe of the liquid or mixture exiting the port opening 44 and impinging on the inner side13 of the mixing trough 12, ambient air is finely dispersed incorporated in the liquid ormixture. This is supported by the fact that the backflow is divided into two partial flowsby the orientation of the port opening 44, which flow along the inner side 13 of themixing trough 12 in opposite directions in the circumferential direction. At a flow velocityof several meters per second, the partial flows can thus meet again in an opposite areaon the inner side 13 of the mixing trough 12, wherein further air is incorporated into theliquid or mixture by additional swirl.The incorporation and fine distribution of the air is further increased by the rotatingmotion of the mixing rotor 32 with the mixing blades 34, as already described above.The mixing process can preferably last between 100 seconds to 200 seconds.Once a desired consistency or homogeneity of the mixture has been achieved, the firstpinch valve 42 on the backflow line 40 can be closed and the second pinch valve 52on the discharge line 50 can be opened. In this manner, the ready formed mixture orslurry is discharged from the colloidal mixer 10 through the discharge line 50 and outof the outlet opening 22 by the pumping action of the mixing device 30.After emptying the mixing trough 12, another mixing process for a new batch can bestarted.Figures 4 to 7 show a possible embodiment for a mixing blade 34, which can be usedon a mixing rotor 32 of a mixing device 30 of the colloidal mixer 10 described above.For fastening the mixing blade 34 to a rotor hub 33 of the mixing rotor 32, fasteningelements 37 are shown schematically on one fastening side. These elements serve fordetachable fastening of the mixing blade 34 to the rotor hub 33. Fig. 6 shows detail Awith the fastening element 37 of Fig. 4 in greater detail.The mixing blade 34 is formed from a base metal sheet 35 with a thickness d, as canclearly be discerned in Fig. 5. The thickness d can range from 3 mm to 20 mm. A holepattern 36 having a plurality of through holes is formed in the actual mixing region ofthe mixing blade 34. The side surfaces of the mixing blade 34 can be surface treated.A diameter of the through holes can range between 5 mm and 50 mm. The materialwebs located between the through holes may have a size of a few mm. Overall, thehole pattern 36 with the through holes may form a total opening area which accountsfor between 40% to 80% of the total face of the mixing blade 34.Figure 7 shows a partial area of the hole pattern 36 in greater detail, wherein the holepattern 36 is formed from a plurality of through holes arranged in rows next to oneanother in a grid. Grid or material webs with corresponding flow edges remain betweenthe through holes, which ensure for good swirl and a particularly finely distributedformation of cavities over the surface of the mixing blade 34. In principle, a web widthbetween the holes can be between 10% and 40%, preferably between 16% and 33%,of the hole diameter. Here, a sheet thickness may be between 20% to 75%, preferablybetween 33% to about 66%, of the hole diameter. Preferably, the hole diameter isbetween 10 mm to 20 mm, more preferably about 12 mm.Referring to Fig. 7, a lower corner portion of the mixing blade 34 may be chamfered orangled.

Claims

1. Method for the colloidal processing of a slurry, in particular processing of construction materials, using a colloidal mixer (10), in particular according to any one of claims 7 to 12, in which - at least one liquid is introduced into a mixing trough (12), at the lower region of which is arranged an outlet opening (22) with a mixing device (30) having a mixing rotor (32) which is driven in rotation, - at least one pulverulent solid component is introduced into the mixing trough (12), - the at least one liquid is mixed with the at least one pulverulent solid component by means of the rotationally driven mixing rotor (32), is induced to flow, and is discharged from the mixing trough (12) through the outlet opening (22), - wherein the mixture is returned again for a certain time via a flowback line (40) to an upper region of the mixing trough (12) for further mixing, and - after reaching a desired mixing state, the mixture is discharged as a finished slurry from the outlet opening (22) by means of a discharge line (50), characterized in that air is incorporated into the at least one liquid and / or the mixture in finely dispersed form in a targeted manner, wherein a relative density of the liquid, or of the mixture, is reduced.

2. Method according to claim 1, characterized in that the relative density of the at least one liquid or the mixture is reduced, wherein the volume of the liquid or of the mixture is increased by 2 percent to 15 percent by supplying air.

3. Method according to any one of claims 1 or 2, characterized in that the backflow line (40) comprises a port opening (44) which is directed towards an inner side (13) of the mixing trough (12), wherein the led back liquid or mixture impinges on the inner side (13).

4. Method according to claim 3, characterized in that a backflow from the backflow line (40) impinges approximately perpendicularly on the inner side (13) of the mixing trough (12).

5. Method according to claim 3 or 4, characterized in that a backflow from the backflow line (40) is essentially divided into two partial flows when it impinges on the inner side (13) of the mixing trough (12), which partial flows flow in opposite directions along the inner side (13) of the approximately drum-shaped mixing trough (12).

6. Method according to claim 5, characterized in that the two partial flows are generated with a flow velocity such that the partial flows meet, along with a formation of swirls, at a point of the mixing trough (12) which is approximately opposite to the port opening (44).

7. Colloidal mixer for the colloidal processing of a slurry, in particular for the processing of construction materials and in particular for performing a method according to any one of claims 1 to 6, comprising - a mixing trough (12) which comprises an upper feed opening (15) for feeding at least one liquid and at least one pulverulent solid component and a lower outlet opening (22), - a mixing device (30) which comprises a mixing rotor (32) which can be driven in rotation and is arranged in a lower region of the mixing trough (12), wherein the at least one liquid and the at least one pulverulent solid component are mixed by the mixing rotor (32) into a mixture and a flow of the at least one liquid or of the mixture can be generated towards the outlet opening (22), - a backflow line (40) which extends from the outlet opening (22) back again to the upper feed opening (15) of the mixing trough (12), - a discharge line (40) for discharging a finished slurry from the mixing trough (12), and - a control valve device (38) by means of which the backflow line (40) and the discharge line (50) can be opened or closed, in particular alternately, characterized in that the colloidal mixer (10) is configured to incorporate air in finely dispersed form into the at least one liquid, or the mixture, in a targeted manner in order to reduce a relative density of the liquid, or of the mixture.

8. Colloidal mixer according to claim 7, characterized in that the backflow line (40) comprises a port opening (44) which is directed towards an inner side (13) of the mixing trough (12).

9. Colloidal mixer according to claim 7 or 8, characterized in that an air supply device comprising at least one supply nozzle is arranged for injecting air into the liquid or mixture.

10. Colloidal mixer according to any one of claims 7 to 9, characterized in that the mixing rotor (32) is arranged in a recess (20) at the bottom (16) of the mixing trough (12) upstream the outlet opening (22).

11. Colloidal mixer according to claim 10, characterized in that the recess (20) with the mixing rotor (32) is arranged centrally or eccentrically on the bottom (16) of the mixing trough (12) relative to the center axis thereof.

12. Colloidal mixer according to any one of claims 7 to 9, characterized in that a rotor axis of the mixing rotor (32) and a center axis of the drum-shaped mixing trough (12) are located in a center plane of the mixing trough (12) and, in that a backflow from the port opening (44) of the backflow line (40) impinges on the inner side (13) of the mixing trough (12) approximately parallel to the center plane.

13. Colloidal mixer according to any one of claims 7 to 12, characterized in that the mixing rotor (32) comprises mixing blades (34) which are provided with a hole pattern (36).