Recirculating valuable substances from exhaust gas cleaning

Abstract

The application relates to a method and a device for recirculating valuable substances in a solid precipitate of an exhaust gas cleaning process for exhaust gas of the metallurgical industry, wherein, after at least a portion of the solid precipitate has been cleaned with dissolving water, extensive separation of water-insoluble material is carried out. The aqueous starting solution obtained during the separation is subjected to a plurality of successive treatment steps until, for a product solution obtained after the treatment steps have been passed through, a limit value specification is achieved. At least a portion of the water-insoluble material obtained during the separation, and / or of a solid material obtained during the treatment steps, and / or of a solid material contained from one or more products of one or more of the treatment steps, is fed to a primary process of the metallurgical industry. The device for recirculating valuable materials comprises appropriate devices such as a feeding device.

Description

Field of industryThe invention relates to a method and to an apparatus forrecirculation of materials of value in solid deposition productsfrom an adsorptive and sodium bicarbonate-based offgas cleaningoperation applied to offgas from a first primary process inmetallurgical industry including deposition of a soliddeposition product.State of the artKnown adsorptive and sodium bicarbonate-based offgas cleaningmethods including deposition of a solid deposition product giverise to large amounts of solid deposition products containingmaterials of value. The deposition products are often disposedof as hazardous waste.Summary of the inventionTechnical problemIt is an object of the present invention to provide a method andan apparatus for recirculation of materials of value in soliddeposition products.Technical solutionThis object is achieved by amethod of recirculating materials of value in solid depositionproduct of an adsorptive and sodium bicarbonate-based offgascleaning operation applied to offgas from a first primaryprocess in the metallurgical industry including deposition of asolid deposition product, wherein combination of at least aportion of the solid deposition product with dissolution waterresults in substantial removal of water-insoluble material,which is characterized in thatit comprisessubjecting the aqueous starting solution obtained in the removalto multiple successive treatment stepsuntil a limit specification is attained for a product solutionobtained after implementation of the treatment steps,wherein one or more limit-relevant parameters are monitored andthe treatment steps are controlled on the basis of the monitoringresults,and wherein at least a portion- of the water-insoluble material obtained in the removal,and / or- of a solid material obtained in the treatment steps,and / or- of a solid material present from one or more products from oneor more of the treatment stepsis fed to the first primary process and / or to another primaryprocess in the metallurgical industry.Advantageous effects of the inventionSodium bicarbonate is NaHCO3 - also called sodium hydrogencarbonate.The method of the invention comprises the method features cited;it may additionally also include other method features.Material of value is understood to mean material present in theoffgas to be cleaned - for example dusts, or a materialcomprising such a material - a material comprising such amaterial may, for example, be material formed from the materialpresent in the offgas to be cleaned via physical reactions - forexample adsorption or absorption - or chemical reactions. Forexample, it may be ore dust discharged in the offgas from asintering plant. Or it may be a material comprising the oredust, for example said ore dust adsorbed on a substance addedto the offgas for offgas cleaning, for instance activatedcarbon.A material of value is a material suitable for feeding into aprimary process or for utilization in a primary process for thepurpose of increasing the yield or forming the product of theprimary process. The aim is to feed materials of value to autilization for the purpose of a more environmentally benign andless resource-intensive mode of operation, for example in theprimary process that produces the offgas subjected to thecleaning operation. The materials of value are, for example,materials added to the primary process for the purpose of productformation therefrom - for example ore dust in the offgas from asintering process; iron ore dust in the case of iron oresintering. Materials of value in the offgas may, for example,leave the primary process without conversion to the desiredproduct - for example ore dust from a sintering process - or bedischarged with the offgas after conversion to the desiredproduct - for example sintered dust from a sintering process.It is resource-conserving and hence environmentally andeconomically viable to feed materials of value in offgases fromprimary processes in a simple manner to utilization in thecircuit of economic value, rather than to treat them as wasteand hence discharge them from the circuit of economic value.Recirculation of materials of value should be considered to befeeding into a primary process within the scope of thisapplication.A primary process is understood to mean a process in which anoffgas to be cleaned is obtained when the product of the primaryprocess is produced; the product of the primary process isunderstood to mean the physical product thereof, not includingheat or electricity as product. The primary process is one inthe metallurgical industry; it may, for example, be theoperation of a sintering plant, the operation of a pelletizingplant, the operation of a steelworks converter, for example bythe LD / BOF method, or the operation of an EAF (electric arcfurnace).In a sodium bicarbonate-based offgas cleaning operation appliedto an offgas stream from a primary process, solid material -also called solid deposition product - is separated out of thecleaned offgas. This comprises, for example, dusts from theprimary process - for example ash, iron oxides, unconsumedsodium bicarbonate, sodium carbonate, substances formed throughchemical reaction with components of the offgas stream - forexample sodium sulfate, or other material introduced into theoffgas stream for offgas cleaning - or reaction products thereofwith components of the offgas stream. The latter material is,for example, adsorption material that contributes to cleaningby adsorption - for example activated carbon.At least a portion of the solid deposition product is combinedwith dissolution water; it is also possible to combine theentirety of the solid deposition product with dissolution water.For example, of 100 kg of the solid deposition product, only80 kg, or only 95 kg, or the entire 100 kg is combined withdissolution water. The portion is either of the same compositionas the entire solid deposition product, or it may differ interms of composition; it may, for example, be enriched ordepleted with regard to particular particle sizes or densitiesby comparison with the average composition of the overall soliddeposition product.The combination with dissolution water can be effected batchwiseor continuously.Combination with dissolution water gives rise to a heterogeneoussubstance mixture of liquid and solids composed of waterinsolublematerial that are finely distributed therein - asuspension. Combination with dissolution water results insubstantial removal of the water-insoluble material, and givesan aqueous starting solution. Substantial removal is understoodto mean that at least 70% by mass, preferably at least 90% bymass, of the water-insoluble constituents of the soliddeposition product combined with dissolution water is removed;the aqueous starting solution, after the removal, may alsocontain water-insoluble material to a small degree, for examplein the form of suspended matter. It is advantageous to removeas much water-insoluble material as possible since waterinsolublematerial may contain materials of value and may besuitable for recycling into the primary process, or because itcan impair the effectiveness and / or efficiency of downstreamtreatment steps. Examples of methods that can be used forsubstantial removal include filtration - optionally underpressure, sedimentation, centrifugation; depending on themethod, it is possible to remove water-insoluble constituentswith different degrees of thoroughness using an economicallyacceptable level of resources.The aqueous starting solution obtained in the removal issubjected to multiple successive treatment steps.It is subjected to at least two treatment steps; these may belongto the same mode of treatment or different modes of treatment.It is also possible to conduct multiple treatment steps in onemode of treatment or multiple modes of treatment.In one execution variant, at least one treatment step isconducted batchwise - for example filtration. In this case,buffer capacity should be provided in the upstream anddownstream treatment steps - for example by provision of buffervessels.In a preferred execution variant, all treatment steps follow oneanother in a continuous progression. This enables more compactand economic designs since it is possible to dispense with buffervessels for batchwise operation, and can be controlled moreeasily. It may be necessary to provide redundant systems inorder to be able to conduct process steps continuously in plantcomponents that are not continuously operable - for examplefilter presses. It is preferable that the starting solutionundergoes the treatment steps continuously until the limit isattained.According to the invention, treatment steps is conducted untilthe defined limit for the product solution obtained afterundergoing the treatment steps is attained.According to the invention, there is monitoring - by measurement- of one or more limit-relevant parameters, and the treatmentsteps are controlled on the basis of the monitoring results.Advantageously, in the monitoring by measurement, the scan rateof the measurement is chosen for the one or more limit-relevantparameters such that variances from the limit that are expectedor have occurred and an associated requirement for control canbe recognized in good time. In one variant, for monitoring,measurements are conducted at least at regular time intervals,i.e. continuously. The time intervals in which measurements areneeded to enable adequate control depend on the inertia of therespective treatment steps. The time intervals in whichmeasurement should be effected also depend on the evaluationtime. The time intervals in which measurement is effected alsodepend on the time required for the evaluation. The timeintervals in which measurement is effected may also depend onthe nature of officially defined limits - for example, averagesover time may be required, or spot measurements may be required.Limit-relevant parameters can be obtained by measurement in theproduct solution and / or by measurement in the starting solutionand / or by measurement while undergoing treatment steps, orbefore and / or after a treatment step. If the limit, for example,defines a concentration of fluoride ions, the measurement of thelimit-relevant parameter of fluoride ion concentration can beeffected in the starting solution and in the product solution,or in the starting solution and after undergoing a treatmentstep - followed by other treatment steps - for reduction thereof.According to the invention, at least a portion- of the water-insoluble material obtained in the removal,and / or- of a solid material obtained in the treatment steps,and / or- of a solid material present from one or more products from oneor more of the treatment stepsis fed to the first primary process and / or to another primaryprocess.The water-insoluble material or solid material, with anappropriate moisture content, may also be a sludge.In the feeding operation, entry into the envisaged primaryprocess may also be preceded by processing steps, for examplein order to make the material more easily transportable - forexample compacting to give briquets or pellets, or in order toconcentrate the materials of value. In the feeding operation,entry into the envisaged primary process may also be precededby combination with other material, and then the combined volumemay be fed in.The other primary process is a primary process in themetallurgical industry, comprising, for example, ore processing,metal production, iron production, steel production, for examplethe operation of a sintering plant, the operation of apelletizing plant, the operation of a steelworks converter, forexample by the LD / BOF method, or the operation of an EAF(electric arc furnace).In this way, it is possible to utilize materials of value presentin solid deposition products. This is environmentally friendlyand economically advantageous since it can firstly reduce theraw material input in the primary processes and secondly reducethe resources required for disposal.At least a portion is recycled. For example, all of 100 kg maybe recycled, or at least 95% may be recycled, or a portion of90% or more may be recycled, or only a portion of 80 kg, or itis possible to recycle merely a portion with a grain size abovea particular limit, or it is possible to recycle, for example,only a portion of a particular kind - for example a portion ofthe "activated carbon-based material" kind.If the product obtained in one or more treatment steps is not asolid but a liquid product, this may optionally be treatedsubsequently such that solid material is obtained. This can beaccomplished, for example, by chemical treatment - for exampleprecipitation - or physical treatment - for example adsorptiononto or absorption into solid particles.The treatment steps are preferably chosen from at least onememberof the group of modes of treatment consisting of- chemical treatment,- mechanical treatment,- physical treatment.Chemical treatment is based on chemical reactions with addedreagents to form new substances; for example oxidations orformation of salts. Chemical treatment steps are, for example,adjustment of pH, oxidation with, for example, hydrogen peroxideor a hypochlorite, ion exchange.Physical treatment is based on physical processes, for exampleadsorption or evaporation. Physical treatment steps are, forexample, sedimentation, adsorption by contacting with addedactivated carbon or other adsorbents, for example zeolites,concentration by evaporation or osmosis.Mechanical treatment is likewise based on physical processes,but also additionally includes action or application of force.Mechanical treatment steps are, for example, filtration, forinstance membrane filtration - for example ultrafiltration, sandfiltration, for example under pressure - for example in chamberfilter presses, or under the action of gravity - for examplefiltration without pressure or sedimentation, or centrifugalforce - for example centrifugation.A treatment step may also combine several modes of treatment,for example a heavy metal deposition with sulfides - for exampleorganosulfides - with chemical reaction and with sedimentation,or heavy metal deposition with ion exchange - for example onanionic polymer - with chemical reaction and sedimentation, orother precipitations based on chemical reactions and withaddition of flocculant, or precipitation by means of flocculantwith adsorption and sedimentation.In a preferred embodiment, the product solution is released intothe environment - for example introduced into water bodies, whenits composition has been rendered correspondingly harmless as aresult of the treatment steps.In order to enable unproblematic release into the environment,among other reasons, the starting solution is subjected tomultiple successive treatment steps. The aim is that a limitspecification be attained for the resultant product solutionafter it has undergone the treatment steps. The limitspecification may relate, for example, to the content of anindividual substance present in the starting solution - ormultiple substances present in the starting solution, forexample concentration of heavy metal ions or heavy metalcontainingions, concentration of fluoride or fluoridecontainingions, concentration of phosphates or phosphatecontainingions, concentration of halides or halide-containingions, concentration of dioxins, concentration of aromatics,concentration of PCBs; it may also relate to a quality criterion- or multiple quality criteria - such as COD (chemical oxygendemand) or TOC (total organic carbon) or TN (total nitrogen) orpH.The limit specification is set by the operator of the process,for example based on legal requirements.In a preferred embodiment, the dissolution water, on combinationof the solid deposition product with dissolution water,comprises wastewater from a wet offgas cleaning operation. Thismay be an upstream wet offgas cleaning operation applied to theoffgas, or a wet offgas cleaning operation applied to anotheroffgas from the same primary process, or a wet offgas cleaningoperation applied to an offgas from another primary process.Such a further utilization of wastewater from a wet offgascleaning operation makes the method of the inventionadvantageous in a resource-conserving, environmentally friendlyand economic manner.In a preferred embodiment, at least one treatment step iseffected for reduction of dissolved heavy metal ions ordissolved heavy metal-containing ions. Reduction should beunderstood here to mean reducing the content.In a preferred embodiment, at least one treatment step iseffected for reduction of the COD. Reduction should beunderstood here to mean reducing the level.In a preferred embodiment, at least one treatment step iseffected for reduction of the TOC. Reduction should beunderstood here to mean reducing the level.In a preferred embodiment, at least one treatment step iseffected for establishment of a desired pH.In a preferred embodiment, at least one treatment step iseffected for reduction of dissolved fluoride or dissolvedfluoride-containing ions. Reduction should be understood hereto mean reducing the content.In this treatment step, for example, fluoride is precipitatedby addition of, for example, aluminum chloride - this separatesout a majority of the fluoride present in the starting solution.In a preferred embodiment, at least one treatment step iseffected by means of ion exchange material. The ion exchangematerial is preferably regeneratable. By means of ion exchangematerial, for example, the content of fluoride, nitrate islowered. Use of selective ion exchange material permitscontrolled lowering.In a preferred embodiment, at least one treatment step iseffected for reduction of total nitrogen TN. Reduction shouldbe understood here to mean reducing the level.This can be accomplished, for example, by addition of sodiumhypochlorite and subsequent filtration with an activated carbonfilter.In a preferred embodiment, the product solution is used for adifferent method - i.e. not in the primary process that producesthe offgas to be cleaned - as raw material source, especiallywhen its composition is favorable for the respective method. Forexample, it is possible - for example by means of thermaltreatment by evaporation - to concentrate the product solutionand hence to fractionally crystallize different substances andhence to make them utilizable.For example, it is thus possible to obtain soda or sodiumbicarbonate from the product solution, which can be utilized,for example, for sodium bicarbonate-based offgas cleaning.The present application further provides a signal processingdevice with a machine-readable program code, characterized inthat it includes control commands for performance of a methodof the invention.The present application further provides a machine-readableprogram code for a signal processing device, characterized inthat the program code includes control commands that cause thesignal processing device to perform a method of the invention.The present application further provides a storage medium havinga machine-readable program code of the invention stored thereon.The present application further provides an apparatus forperforming a method of the invention. It is an apparatus forrecirculating materials of value in solid deposition productfrom an adsorptive and sodium bicarbonate-based offgas cleaningoperation applied to offgas from a first primary processincluding deposition of a solid deposition product,comprising- at least one dissolution vessel for combination of soliddeposition product with dissolution water, into which at leastone deposition product addition conduit and at least onedissolution water feed open,- at least one outlet proceeding from the dissolution vessel fordischarge of suspension from the dissolution vessel,- at least one deposition apparatus for removal of waterinsolublematerial from the suspension to produce a startingsolution, wherein the outlet opens into the depositionapparatus,- at least one treatment apparatus for performance of multiplesuccessive treatment steps for production of a product solution,- at least one starting solution conduit proceeding from thedeposition apparatus for introduction of starting solution intothe treatment apparatus,- at least one product solution outlet proceeding from thetreatment apparatus,- at least one monitoring device for detection of at least oneparameter at least in the product solution, connected to atleast one closed-loop control device suitable for closed-loopcontrol of the treatment apparatus on the basis of results fromthe monitoring device,- at least one feed apparatus for feeding solid material to thefirst primary process and / or to another primary process.Optionally present upstream of the dissolution vessel in eachcase are one or more buffer vessels for dissolution water or forsolid deposition product - i.e. virtually in the dissolutionwater feed or in the deposition product addition conduit.Optionally present downstream of the dissolution vessel in eachcase are one or more buffer vessels for suspension - i.e.virtually in the outlet.Optionally present downstream of the deposition apparatus ineach case are one or more buffer vessels - i.e. virtually in thestarting solution conduit.Optionally present downstream of the treatment apparatus in eachcase are one or more buffer vessels - i.e. virtually in theproduct solution outlet.It is also possible for buffer vessels to be provided in thetreatment apparatus.By means of the buffer vessels, it is possible to mutuallyconnect parts of the method procedure that run at differentspeeds, enabling a continuous method.The treatment apparatus comprises multiple treatment units forperformance of multiple successive treatment steps forperformance of a product solution.It is preferably suitable for performance of multiple successivetreatment steps from at least one member of the group of modesof treatment consisting of- chemical treatment,- mechanical treatment,- physical treatment.For each treatment step, one or more treatment units may beprovided, which may be arranged in sequence or in parallel.For example, it may be envisaged for a treatment step forreduction of the COD to use two treatment units in whichdifferent steps for reduction of the COD are undertakensuccessively. For example, for a treatment step in order toreduce the content of dissolved heavy metal ions or dissolvedheavy metal-containing ions, the use of three treatment unitsmay be envisaged - for example one treatment unit to establisha desired pH, one treatment unit for precipitation, and onetreatment unit to draw off precipitated material. Precipitatedmaterial may, for example - optionally after subsequentdewatering, or in the dried state - be recycled into a primaryprocess or sent to landfill. It may thus be the case that atreatment unit for drawing off precipitated material is part ofa feed apparatus.It would also be possible, for example for the adjustment of pH,to provide two or more treatment units in a parallel arrangementthat are fed by a common conduit for liquid to be treated, andto release the products thereof into a common conduit for thepurpose of feeding to downstream treatment steps or treatmentunits. Corresponding parallel or sequential arrangement is alsopossible for other treatment units or treatment steps.Starting solution enters the first treatment unit viewed in flowdirection from the dissolution vessel to the product solutionoutlet; the liquid product from the preceding treatment unitenters the downstream treatment units in each case. Productsolution emerges from the last treatment unit viewed in flowdirection from the dissolution vessel to the product solutionoutlet.Reagent feeds optionally open into the respective treatmentunits, which serve for controllable feeding of the reagentsrequired for the respective treatment from corresponding reagentstorage vessels.The treatment apparatus preferably comprises at least onetreatment unit for reduction of dissolved heavy metal ions ordissolved heavy metal-containing ions.The treatment apparatus preferably comprises at least onetreatment unit for reduction of the COD.The treatment apparatus preferably comprises at least onetreatment unit for reduction of the TOC.The treatment apparatus preferably comprises at least onetreatment unit for establishment of a desired pH.The treatment apparatus preferably comprises at least onetreatment unit for reduction of dissolved fluoride or dissolvedfluoride-containing ions.The treatment apparatus preferably comprises at least onetreatment unit comprising ion exchange material. The apparatusof the invention preferably also comprises apparatuses forregeneration of the ion exchange material.The treatment apparatus preferably comprises at least onetreatment unit for reduction of total nitrogen - TN.The treatment apparatus preferably comprises at least oneapparatus for removal of solids, for example filter.The monitoring device is suitable for detecting at least oneparameter, at least in the product solution. It is also possibleto detect multiple parameters in the product solution and / or oneor more parameters in one or more of the treatment steps. Thecontrol device is suitable for controlling the treatmentapparatus on the basis of results from the monitoring device;the method of control here may, for example, be control ofindividual treatment units. The control device iscorrespondingly connected to the monitoring device fortransmission of results.It is also possible for there to be multiple monitoring devices,each of which may monitor a single parameter or multipleparameters. It is also possible for there to be multiple controldevices, each of which may control a single parameter or multipleparameters.The monitoring devices and control devices may also beintegrated collectively into one apparatus.The feed apparatus is suitable for supply of solid material tothe first primary process and / or to another primary process. Itis suitable for feeding at least a portion- of the water-insoluble material obtained in the removal,and / or- of a solid material obtained in the treatment steps,and / or- of a solid material present from one or more products from oneor more of the treatment steps,to the first primary process and / or to another primary process.For this purpose, it may comprise, for example, conveyingdevices and / or conduits. Conduits may proceed, for example, fromthe relevant sites of formation of the solid materials or of thewater-insoluble material - in the case of water-insolublematerial obtained in the course of removal, the site of formationis understood to mean the site of removal - and lead toapparatuses for performance of the (first) primary processand / or another primary process. Conveying devices may beprovided, for example, in order to move solid material withinthe conduits. Conveying devices may also comprise conveyorbelts, or comprise movable vessels that receive solid materialat the sites of formation in question for the solid materialsand - optionally after intermediate storage, for example at astorage site or in vessels, containers or in silos - lead todevices for performance of the first primary process and / oranother primary process.The feed apparatus may comprise, for example, apparatuses forstorage of solid material.The feed apparatus may comprise, for example, apparatuses forstorage of products from treatment steps.The feed apparatus may comprise, for example, apparatuses forobtaining solid material from products from treatment steps.Storage may be provided, for example, when the feeding of solidmaterial to the first primary process and / or to another primaryprocess is not to be continuous but batchwise, and, therefore,buffering of the amounts obtained is necessary.The feed apparatus may comprise, for example, apparatuses forprocessing, for example for concentration of materials of value.The feeding can be effected via direct connections of thetreatment apparatus and / or the deposition apparatus to theprimary process or - for example in the presence of storageapparatuses for buffering of the amounts obtained, or in thepresence of processing apparatuses that serve for furtherprocessing, for example concentration, of material to berecycled - via indirect connections of the treatment apparatusand / or the deposition apparatus to the primary process.Such an apparatus can be used to perform a method of theinvention.Brief description of the drawingsThe invention is elucidated by schematic illustrative diagramsof embodiments.Figure 1 shows, using a schematic of one embodiment, the generalscheme for the sequence of a method of the invention in anapparatus of the invention.Figure 2 shows a treatment apparatus as may be executed infigure 1 in more detail.Figure 3 shows a schematic of an apparatus for performance of amethod of the invention in connection with a first primaryprocess.Description of embodimentsExamplesFigure 1 shows, with reference to one embodiment, in schematicform, the sequence of a method of the invention in an apparatusof the invention.Solid deposition product 1 from an adsorptive and sodiumbicarbonate-based offgas cleaning operation in a primary processis directed via a deposition product addition conduit 2 into adissolution vessel 3, where it is combined with dissolutionwater from a dissolution water feed 4. The suspension formed inthe dissolution vessel 3 is fed via the outlet 5 from adeposition apparatus 6, shown here schematically as a filter. Abuffer vessel 20 for suspension which is optionally present inthe outlet 5 is shown outlined with dotted lines. By means ofdeposition apparatus 6, water-insoluble material is largelyremoved; in the case shown with a filter, at least 90% by massof the water-insoluble material is removed. The aqueous startingsolution obtained in the removal is introduced into a treatmentapparatus 8 via the starting solution conduit 7a. It would bepossible for buffer vessels to be disposed in the startingsolution conduit 7a between the filter and treatment apparatus,which is not shown specially for better clarity.What is shown is a material outlet 7b proceeding from thedeposition apparatus 6 - i.e. the site of formation of the waterinsolublematerial for the purposes of the present application.It is part of a feed apparatus. For better clarity, it is notshown specially where the feed leads. The feed apparatus mayrecirculate the water-insoluble material, for example into theprimary process from which the offgas to be cleaned originates;this is shown schematically in figure 3.The treatment apparatus 8 serves to perform multiple successivetreatment stepsfrom at least one memberof the group of modes of treatment consisting of- chemical treatment,- mechanical treatment,- physical treatment.The treatment steps produce a product solution 9 which isdischarged from the treatment apparatus 8 via the productsolution outlet 10a.The material outlet 10b symbolizes one or more conduits thatproceed from the sites of formation of solid materials in thecourse of the treatment steps. It is / they are parts of a feedapparatus. For better clarity, it is not shown specially wherethe feeds lead; the feed apparatus may recirculate the solidmaterial, for example into the primary process from which theoffgas to be cleaned originates; this is shown schematically infigure 3.The properties of the product solution 9 are to attain a definedlimit - for example with multiple parameters to be achieved. Amonitoring device 11 monitors the parameters in the productsolution 9 that are of relevance for the defined limit, shownschematically by a straight monitoring conduit. The treatmentsteps conducted in the treatment apparatus 8 are controlled onthe basis of the results of the monitoring by a control device12, shown schematically by a wavy connection to the treatmentapparatus that proceeds from the control device 12. Transmissionof monitoring results to the control device 12 is illustratedschematically by a connection between control device 12 andmonitoring device 11.The product solution may be released into the environment, forexample, shown schematically by arrow A, and / or used as rawmaterial source, shown schematically by arrow B.Figure 2 shows a schematic of a variant of the sequence in atreatment apparatus 8.The treatment apparatus 8 comprises multiple treatment units forperformance of multiple successive treatment steps forproduction of the product solution 9. For the treatment step U,reduction of the COD, two treatment units 13 and 14 in sequentialarrangement are present. For better clarity, the diagram doesnot show the feeding of the iron(II) sulfate FeSO4, sulfuricacid H2SO4 and hydrogen peroxide H2O2 reagents from correspondingreagent storage vessels via reagent feeds. Starting solutionenters the first treatment unit 13 viewed in flow direction fromthe dissolution vessel 3 toward the product solution outlet 10.The liquid product from the upstream treatment unit 13 entersthe downstream treatment unit 14.The treatment step U is followed by the treatment step V in thetreatment unit 15, shown here as optional fluoride precipitationwith a dotted outline. For better clarity, the diagram does notshow the feeding of the aluminum chloride AlCl3 reagent fromcorresponding reagent storage vessels via reagent feeds.The treatment step V is followed by the treatment step W forreduction in the content of dissolved heavy metal ions ordissolved heavy metal-containing ions. For this purpose, as aminor treatment step in treatment unit 16, the pH is adjustedby adding sodium hydroxide solution NaOH, and precipitation isinduced by addition of organic sulfides, which is continued intreatment unit 17 by addition of anionic polymer. In treatmentunit 18a, for example in treatment unit 16 and / or 17, suspendedsolid material formed by precipitation and precipitated materialare very substantially removed. For better clarity, the diagramdoes not show the feeding of the reagents from correspondingreagent storage vessels via reagent feeds.Solid material is sent to a destination via the material outlet18b which proceeds from the treatment unit 18a and is part of afeed apparatus. For better clarity, it is not shown speciallywhere the feed leads. The feed apparatus may recirculate thewater-insoluble material, for example into the primary processfrom which the offgas to be cleaned originates; this is shownschematically in figure 3, since the material outlet 18b maycorrespond to the material outlet 10b.The liquid product from the treatment unit 18a enters treatmentunit 19 in which treatment step X, reduction of total nitrogen- TN, is conducted. For better clarity, the diagram does notshow the feeding of the sodium hypochlorite reagent, NaOCl, fromcorresponding reagent storage vessels via reagent feeds.Filtration is effected in the subsequent treatment step Y,wherein an activated carbon filter is also used.In the subsequent treatment step Z, by means of ion exchange,the fluoride content in the filtrate from the treatment step Yis reduced.This affords the product solution 9.Treatment steps X and Z are optional and therefore have a dottedoutline.Figure 3 shows a schematic of a first primary process 21, forexample a sintering process, the offgas from which is subjectedto an adsorptive and sodium bicarbonate-based offgas cleaningoperation in offgas conduit 22. Discharge of cleaned offgas issymbolized by a wavy arrow that branches off from conduit 22.Solid deposition product from this offgas cleaning operation istreated as shown in figure 1; this is symbolized in figure 3 inthat the offgas conduit 22 opens into rectangle 23; rectangle23 symbolizes the content of figure 1. A feed apparatus 24 issymbolized by the material outlets 7b and 10b; these correspondto the conduits addressed in figure 1. The storage apparatus 25and processing apparatus 26 that are optionally present in theseconduits of the feed apparatus are shown by dotted lines.The description of advantageous configurations of the inventionthat has been given so far contains numerous features that arereproduced in the individual subsidiary claims, in some caseswith several combined. However, these features may appropriatelyalso be considered individually and be combined to give viablefurther combinations. In particular, these features are eachcombinable individually and in any suitable combination in amethod of the invention.Even though the description and the claims use some termsrespectively in the singular or in connection with a number, thescope of the invention for these terms shall not be limited tothe singular or the respective number. Moreover, the word "a"shall be considered not to mean the number one but to mean theindefinite article.The properties, features and advantages of the invention asdescribed, and the manner in which they are achieved, becomemore clearly and distinctly comprehensible in connection withthe description of the working example(s) of the invention,which are elucidated in detail in connection with the drawings.The working example(s) serve(s) to elucidate the invention anddo not limit the invention to combinations of features specifiedtherein, not even in relation to functional features. Moreover,suitable features of each working example may also explicitlybe considered in isolation, removed from a working example,introduced into another working example for supplementationthereof, and combined with any of the claims.Even though the invention has been illustrated and described indetail by virtue of the preferred working example(s), theinvention is not limited by the example(s) disclosed, and othervariations may be inferred therefrom without leaving the scopeof protection of the invention according to the claims.List of reference numerals1 Solid deposition product2 Deposition product addition conduit3 Dissolution vessel4 Dissolution water feed5 Outlet6 Deposition apparatus7a Starting solution conduit7b Material outlet8 Treatment apparatus9 Product solution10a Product solution outlet10b Material outlet11 Monitoring device12 Control device13 Treatment unit14 Treatment unit15 Treatment unit16 Treatment unit17 Treatment unit18a Treatment unit18b Material outlet19 Treatment unit20 Buffer vessel21 Primary process22 Offgas conduit23 Rectangle24 Feed apparatusU Treatment stepV Treatment stepW Treatment stepX Treatment stepY Treatment stepZ Treatment step

Claims

1. A method of recirculating materials of value in solid deposition product of an adsorptive and sodium bicarbonate-based offgas cleaning operation applied to offgas from a first primary process in the metallurgical industry including deposition of a solid deposition product, wherein combination of at least a portion of the solid deposition product with dissolution water results in substantial removal of water-insoluble material, wherein the first primary process is the operation of a sintering plant or the operation of a pelletizing plant, and the materials of value are ore dust and / or material comprising ore dust, which is characterized in that it comprises subjecting the aqueous starting solution obtained in the removal to multiple successive treatment steps until a limit specification is attained for a product solution obtained after implementation of the treatment steps, wherein one or more limit-relevant parameters are monitored and the treatment steps are controlled on the basis of the monitoring results, and wherein at least a portion - of the water-insoluble material obtained in the removal, and / or - of a solid material obtained in the treatment steps, and / or - of a solid material present from one or more products from one or more of the treatment steps is fed to the first primary process.

2. The method as claimed in claim 1, characterized in that the feeding includes processing steps.

3. The method as claimed in either of claims 1 and 2, characterized in that the treatment steps are chosen from at least one member of the group of modes of treatment consisting of - chemical treatment, - mechanical treatment, - physical treatment.

4. The method as claimed in any of claims 1 to 3, characterized in that the product solution is released into the environment.

5. The method as claimed in any of claims 1 to 4, characterized in that the dissolution water comprises wastewater from a wet offgas cleaning operation.

6. The method as claimed in any of claims 1 to 5, characterized in that at least one treatment step is effected for reduction of dissolved heavy metal ions or dissolved heavy metalcontaining ions.

7. The method as claimed in any of claims 1 to 8, characterized in that the product solution is used as raw material source for a different process.

8. An apparatus for recirculating materials of value in solid deposition product from an adsorptive and sodium bicarbonatebased offgas cleaning operation applied to offgas from a first primary process including deposition of a solid deposition product, wherein the first primary process is the operation of a sintering plant or the operation of a pelletizing plant, and the materials of value are ore dust and / or material comprising ore dust, comprising - at least one dissolution vessel for combination of solid deposition product with dissolution water, into which at least one deposition product addition conduit and at least one dissolution water feed open, - at least one outlet proceeding from the dissolution vessel for discharge of suspension from the dissolution vessel, - at least one deposition apparatus for removal of waterinsoluble material from the suspension to produce a starting solution, wherein the outlet opens into the deposition apparatus, - at least one treatment apparatus for performance of multiple successive treatment steps for production of a product solution, - at least one starting solution conduit proceeding from the deposition apparatus for introduction of starting solution into the treatment apparatus, - at least one product solution outlet proceeding from the treatment apparatus, - at least one monitoring device for detection of at least one parameter at least in the product solution, connected to at least one closed-loop control device suitable for closed-loop control of the treatment apparatus on the basis of results from the monitoring device, - at least one feed apparatus for feeding solid material to the first primary process.

9. The apparatus as claimed in claim 8, characterized in that the treatment apparatus comprises at least one treatment unit for reduction of dissolved heavy metal ions or dissolved heavy metal-containing ions.

10. The apparatus as claimed in claim 8 or claim 9, characterized in that the treatment apparatus comprises at least one apparatus for removal of solids.

11. The apparatus as claimed in any of claims 8 to 10, characterized in that the feed apparatus comprises apparatuses for storage of solid material.

12. The apparatus as claimed in any of claims 8 to 11, characterized in that the feed apparatus comprises apparatuses for obtaining solid material from products from treatment steps.

13. The apparatus as claimed in any of claims 8 to 12, characterized in that the feed apparatus comprises apparatuses for processing.