BACKGROUND

[0001] The present invention relates to a method for processing waste metal chloride solution using batch processing involving different modes of operation of a reactor vessel.

[0002] Furthermore, the present invention relates to a system for processing waste metal chloride solution using batch processing involving different modes of operation of a reactor vessel of the system.

[0003] In a number of industries - such as the iron and steel industry, the zinc plating industry etc. -, pickling treatments with hydrochloric acid are widely used to remove rust and accretion (scales) adhering to the surface of products or processed goods. E.g. metals to be coated require pre-treatment to remove rust or scale, impurities and contaminants. The pickling process generates a considerable quantity of waste liquid (or waste pickling liquor) containing the dissolved metal salts of Iron, Chromium, Copper, Nickel and Zinc as well as residual free acid. Leaching of iron containing ores is often realized by means of hydrochloric acid. Also semiconductor lead frames are often subjected to etching treatments with hydrochloric acid. In these treatments, the hydrochloric acid concentration is usually controlled to remain in the range of 12 - 18% by weight. As the treatment progresses, free hydrochloric acid is converted to iron salts and other metallic salts, thus gradually reducing the washing or etching capacity. Therefore, usually, free hydrochloric acid is added, thus generating large amounts of waste liquid containing iron chloride and optionally free hydrochloric acid. This waste iron chloride solution comprises ferrous chloride, ferric chloride or combinations thereof and optionally reaction products of other treated metals with hydrochloric acid, like chlorides of zinc, nickel, copper, etc., and such liquids have been disposed of as industrial waste. In recent years, the costs of disposal or treatment of such industrial waste have risen sharply, and hydrochloric acid itself is relatively expensive.

Therefore, it is uneconomical to dispose waste iron chloride solution in that manner.

[0004] As this also poses big environmental and pollution problems, methods have been suggested to recover hydrochloric acid, iron oxide, ferric chloride or combinations thereof from waste iron chloride solution. One such recovery method is roasting. However, this method poses environmental problems, such as waste gases (NO _x , HCI, Cl ₂ , dust, etc.) and C0 ₂ emissions, and furthermore, since this method requires very large amounts of fuel, the costs of recovering hydrochloric acid are comparably high. Another method is the liquid phase chlorine oxidation method. However, this method has, inter alia, the drawback that it involves the use of high pressurized chlorine gas, and consequently such facilities need safety measures for high pressure gas and chlorine gas removing equipment, in addition to the recovery being limited to ferric chloride and hydrochloric acid may not be recovered. Another method involves the PORI process (e.g. as described in US 3 682 592 B) or variants thereof, wherein waste iron chloride solution, containing ferrous chloride, is oxidized to convert ferrous chloride to ferric chloride, and the resulting liquid is hydrolyzed to generate iron oxide and to recover hydrochloric acid. Typically, these processes necessarily involve comparatively high investment costs to be conducted economically, thus requiring comparatively large amounts of waste metal chloride solution to be treated (typically of the order of several cubic meters of waste metal chloride solution per hour) such as is the case in metal pickling installations. However, in many industries (such as piece galvanizing lines, small push pull pickling lines, wire pickling lines, pipe pickling lines, long products pickling lines, or the like) smaller volumes of waste metal chloride solution (or waste pickling liquor) are generated that are too small for a pyrohydrolysis regeneration system. For such smaller volumes of waste metal chloride solution (or waste pickling liquor), waste treatment of the waste metal chloride solution (or waste pickling liquor) is typically performed by executing lime treatment of the waste metal chloride solution (or waste pickling liquor), and by using fresh hydrochloric acid (typically also involving transporting the waste metal chloride solution (or waste pickling liquor) away and performing the lime treatment by a waste treatment supplier company.

SUMMARY

[0005] It is therefore an object of the present invention to provide method and a system for processing comparatively small amounts of waste metal chloride solution using batch processing, such that hydrochloric acid may be recovered, and metal oxide (typically iron oxide) be separated easily from the metal chloride (typically iron chloride) solution, such that a treatment of comparatively low volumes of waste metal chloride solution is competitively realizable, the method being effectively feasible using comparatively little energy and in an environmentally friendly manner, as well as providing hydrochloric acid being recovered at the proper concentration to be used, e.g., for washing, leaching and etching again.

[0006] The object of the present invention is achieved by a method for processing waste metal chloride solution using batch processing involving different modes of operation of a reactor vessel, the waste metal chloride solution comprising at least one oxidizable component, the method comprising the following steps:

— in a first step, the waste metal chloride solution is fed to the reactor vessel, and - while the reactor vessel being operated in a first mode of operation - an oxidation step is performed within the reactor vessel at an oxidation temperature exceeding 90°C and at an oxidation pressure exceeding 0,3 MPa, wherein at least a part of the waste metal chloride solution is oxidized during the oxidation step, wherein an at least partly oxidized metal chloride solution is obtained from the waste metal chloride solution, wherein the oxidized part of the at least partly oxidized metal chloride solution corresponds to at least a part of the at least one oxidizable component of the waste metal chloride solution prior to the oxidation step,

— in a second step, the at least partly oxidized metal chloride solution is at least partly hydrolyzed during a hydrolyzes step - performed within the reactor vessel while the reactor vessel is operated in a second mode of operation - at a hydrolyzes temperature exceeding 120 °C and at an appropriate hydrolyses pressure, wherein during the hydrolyzes step hydrochloric acid (HCI) and solid ferric oxide Fe ₂ 0 ₃ are obtained.

[0007] By means of using a batch process, involving different modes of operation of a single reactor vessel (or reaction vessel) - thus being able to use the reactor vessel both for the oxidation step and for the hydrolyzes step -, it is advantageously possible according to the present invention that the regeneration of comparatively small amounts of metal chloride solution (or waste pickling liquor) is possible with reduced investment costs (installation costs) involved for realizing the treatment of the waste metal chloride solution (or waste pickling liquor), especially compared to a solution involving an independent reactor vessel for the oxidation step and the hydrolyses step.

[0008] Hence, according to the present invention, a small hydrochloric acid regeneration plant is proposed, using a batch process, in order to regenerate the hydrochloric acid by the decomposition of FeCI ₃ in liquid phase. The proposed method and system has a wide flexibility and is able to also handle small amounts of waste metal chloride solution (or waste pickling liquor) in an economically competitive manner. Thereby, the method and system of the present invention provides the possibility to regenerate hydrochloric acid also to small or medium-sized installations or companies (especially for disposal demands of waste metal chloride solution (or waste pickling liquor) of, say, less than 1000 liters or 1500 liters per hour, especially in the range from 100 liters per hour to 1000 liters per hour (or in the range of 100 liters per hour to 1500 liters per hour) of waste metal chloride solution (or waste pickling liquor)), thereby providing the possibility to be independent from sourcing of hydrochloric acid as well as disposal of waste metal chloride solution (or waste pickling liquor). It is especially advantageous according to the present invention that common acid resistant construction materials and dimensions can be used, thus lowering the investment costs, e.g. DN 50 ceramic valves are standard, DN 400 ceramic valves are not. [0009] The inventive method and system is able to be realized as a standalone unit, able to send data to the process control installations of the process generating the waste metal chloride solution (or waste pickling liquor) to be treated. Additionally, the inventive system is able to be realized as an ISO container solution, i.e. it can be brought to the intended site in a pre-assembled manner, with only connections to be performed in the course of the installation process. Additionally, conducting the process according to the present invention, is able to be fully automated such that only a minimum manpower for operation and maintenance of the process is required, such as - depending on the automation level - between 15% and 50% of an operator is (permanently) required to run the process.

[0010] Additionally, the method and the system according to the present invention not only reduces investment costs for the installation of the system but also reduces the requirements as to space: For example, a system for a feed flow of 500 liters per hour of waste metal chloride solution (or waste pickling liquor) can be installed in two 20' ISO Containers.

[0011] Due to the fact that, according to the present invention, the reactor vessel is not continuously used for the same reaction step (but alternatingly for the oxidation step, as well as for the hydrolyses step), its volume or size needs - while being adapted to the flow volume of waste metal chloride solution to be treated - to be relatively larger (as compared to a reactor vessel, designed to treat the same amount of waste metal chloride solution volume, being used continuously for one and the same reaction step), thus providing the possibility to use the reactor vessel (both for conducting the oxidation step and the hydrolyses step) is an economically competitive manner. Generally the costs for the reactors at required standard sizes are in the same range, and it makes no big difference if it is one size bigger ore smaller. Especially, the present invention provides a solution for the need to have (pickling) acid (especially hydrochloric acid) available for upstream processes, especially pickling processes, and at the same time having a concept for the disposal of waste metal chloride solution (or waste pickling liquor). Especially for medium sized companies, e.g. operating small hydrochloric carbon steel pickling processes, the amount of produced metal chloride solution (or waste pickling liquor) is too small to install a pyro metallurgical regeneration system according to conventional methods as an economically competitive operation of such regeneration systems using conventional methods typically requires volumes of waste metal chloride solution (or waste pickling liquor) per time unit of at least 2 cubic meters per hour. [0012] According to the present invention, the waste metal chloride solution comprises at least one oxidizable component (typically ferrous oxide). During the oxidation step (during which the reactor vessel is operated in the first mode of operation), the at least one oxidizable component is, at least partly, oxidized. Thus, by means of the oxidation step, the waste metal chloride solution is transformed in an at least partly oxidized metal chloride solution. Normally, during the oxidation step, non-soluble components are obtained, notably iron oxide, which are separated, typically during a filtering operation.

[0013] The first mode of operation of the reactor vessel is conducted batch wise for a certain time and the reaction product of the oxidation step is stored in a first storage element. Subsequent to operating the reactor vessel several times (batches) according to the first mode of operation, the reactor vessel is operated in the second mode of operation for some time, during which the hydrolyzes step is performed. During performing the hydrolyzes step, the at least partly oxidized metal chloride solution, stored in the first storage element, is processed in order to recover the hydrochloric acid, especially until the first storage element is emptied or at least emptied to a considerable level of typically more than 50%, preferably more than 70%, and most preferably more than 90% of its volume. Thereafter (i.e.

subsequent to having operated the reactor vessel in the second mode of operation, and having performed the hydrolyses step regarding the at least partly oxidized metal chloride solution stored in the first storage element), the reactor vessel is again operated in the first mode of operation, i.e. for oxidizing several times (fresh) waste metal chloride solution, and the use of the reactor vessel is repeated in view of a batch processing (or semi-continuous process with storage of treated solutions in separate bins or containers between single processing steps) with regard to the waste metal chloride solution.

[0014] In order to operate the reactor vessel in the first mode of operation, waste metal chloride solution is fed (in the first step) to the reactor vessel, and the oxidation step is performed within the reactor vessel at an oxidation temperature exceeding 90°C and at an oxidation pressure exceeding 0,3 MPa. During the oxidation step, at least a part of the waste metal chloride solution is oxidized (thereby, an at least partly oxidized metal chloride solution is obtained from the waste metal chloride solution). The oxidized part of the at least partly oxidized metal chloride solution corresponds to at least a part of the at least one oxidizable component of the waste metal chloride solution prior to the oxidation step. [0015] According to the present invention, it is preferred that - after the reactor vessel being filled with waste metal chloride solution and is operated in the first mode of operation - the oxidation step is initiated by means of feeding pressurized oxygen into the reactor vessel. As the chemical reaction of the oxidation step provides further energy, the content of the reactor vessel is inherently heated, i.e. the temperature increased. However, in order to increase reaction rates (and, hence, shorten processing times), it is possible to additionally add further starting energy. The chemical process within the reactor vessel during the oxidation step is controlled by the supply in oxygen to the reactor vessel; i.e. the oxidation process is terminated in case that additionally suppled oxygen is not absorbed or reacted by the content of the reactor vessel. During the oxidation step, typically non-soluble (solid) iron oxide is produced (Fe ₂ 0 ₃ ). The residual at least partly oxidized metal chloride solution (mostly FeCI ₃ -solution) is pumped to the first storage element.

[0016] According to the present invention, it is preferred that, while the reactor vessel is operated in the first mode of operation, the at least partly oxidized metal chloride solution, obtained during previously conducting the first step, is fed to a first storage element, and additional waste metal chloride solution is fed to the reactor vessel batch wise,

wherein by continuing to operate the reactor vessel in the first mode of operation, the first step is performed (with respect to the additional waste metal chloride solution) and thereby additional at least partly oxidized metal chloride solution obtained from the additional waste metal chloride solution,

wherein subsequent to operating the reactor vessel in the first mode of operation and prior to operating the reactor vessel in the second mode of operation, the at least partly oxidized metal chloride solution - especially additionally, also the additional at least partly oxidized metal chloride solution - is fed, from the first storage element, to the reactor vessel.

[0017] Thereby, it is advantageously possible to realize the batch processing of waste metal chloride solution (or waste pickling liquor) according to the present invention:

— In a first processing step (or in a first point in time), (initial) waste metal chloride solution is fed to the reactor vessel, and the oxidation step is performed (the reactor vessel being operated in the first mode of operation), yielding (initial) at least partly oxidized metal chloride solution, which is fed to the first storage element;

— in a second processing step (or in a second point in time) - especially after emptying the reactor vessel -, additional waste metal chloride solution is fed to the reactor vessel, and the oxidation step is performed (the reactor vessel still being operated in the first mode of operation), yielding additional at least partly oxidized metal chloride solution, which is likewise fed to the first storage element;

— optionally, in one or a plurality of further processing step(s) (or in one or a plurality of further point(s) in time) - and especially after batch wise emptying the reactor vessel after having performed the first step -, further additional waste metal chloride solution is fed to the reactor vessel, and the oxidation step is performed (the reactor vessel being likewise still operated in the first mode of operation), yielding further additional at least partly oxidized metal chloride solution, which is likewise fed to the first storage element;

— in a third processing step (or in a third point in time), subsequent to operating the reactor vessel in the first mode of operation and prior to operating the reactor vessel in the second mode of operation, the at least partly oxidized metal chloride solution (stored in the first storage element) is fed (from the first storage element) to the reactor vessel - typically this feeding operation comprising feeding the reactor vessel with the (initial) at least partly oxidized metal chloride solution, and additionally preferably also with the additional at least partly oxidized metal chloride solution, and/or the further additional at least partly oxidized metal chloride solution, thereby (completely, or almost completely) emptying the first storage element.

[0018] In the context of the present invention, the (initial) waste metal chloride solution preferably at least approximately corresponds (chemically) to the additional waste metal chloride solution, and/or to the further additional waste metal chloride solution, the different terms ("initial waste metal chloride solution", "additional waste metal chloride solution", and "further additional waste metal chloride solution") regarding the waste metal chloride solution are primarily used to refer to different points in time that the corresponding volumes are fed to the reactor vessel. The corresponding volumes of waste metal chloride solution are typically (continuously) generated by one and the same upstream process such as a pickling process or the like (or by (at least roughly) one and the same combination of upstream processes such as different pickling processes and/or galvanizing processes, etc.), and, hence, only marginally vary with respect to the respective content of free (hydrochloride) acid, water, and metal chlorides or other constituents. However, according to the present invention, it might also be the case that the corresponding volumes of waste metal chloride solution (i.e. the initial waste metal chloride solution, the additional waste metal chloride solution, etc.) are generated - at different points in time - by different upstream processes (such as different pickling processes, galvanizing processes, etc.), and, hence, comprise more important variations with respect to the respective content of free (hydrochloride) acid, water, and metal chlorides or other residual elements.

[0019] During the oxidation step (i.e. during the reactor vessel being operated in the first mode of operation), the at least partly oxidized metal chloride solution is obtained from the waste metal chloride solution. Likewise (to the waste metal chloride solution mentioned above), also the at least partly oxidized metal chloride solution corresponds (chemically) to the additional at least partly oxidized metal chloride solution, and/or to the further additional at least partly oxidized metal chloride solution, the different terms ("initial at least partly oxidized metal chloride solution", "additional at least partly oxidized metal chloride solution", and "further additional at least partly oxidized metal chloride solution") regarding the at least partly oxidized metal chloride solution are primarily used to refer to different points in time that the corresponding volumes are generated in the reactor vessel and/or fed to the first storage element. [0020] As mentioned above, the waste metal chloride solution comprises at least one oxidizable component (typically ferrous oxide) which is oxidized during the oxidation step, thereby yielding non-soluble components, notably iron oxide, which are separated as part of the oxidation step (i.e. during operating the reactor vessel in the first mode of operation), typically during a filtering operation. This means, that typically a given volume of waste metal chloride solution yields a smaller volume of corresponding at least partly oxidized metal chloride solution. In case that the first storage element has a first storage capacity

corresponding to a predetermined multiple of the capacity of the reactor vessel, it is possible to operate the reactor vessel in the first mode of operation such that (with an empty or almost empty first storage element) at least a volume of the waste metal chloride solution corresponding to the predetermined multiple of the capacity of the reactor vessel can be (successively) fed to the reactor vessel, the oxidation step performed, and the corresponding at least partly oxidized metal chloride solution fed to the first storage element (effectively resulting in (at least virtually) filling and emptying the reactor vessel a number of times corresponding, at least roughly, to the predetermined multiple, prior to requiring to switch the operation of the reactor vessel to the second mode of operation.

[0021] According to the present invention, it is furthermore preferred that

— batch wise, subsequent to conducting the first step with respect to the waste metal chloride solution, and prior to conducting the first step with respect to the additional waste metal chloride solution,

— and, preferably, subsequent to operating the reactor vessel in the first mode of operation and prior to operating the reactor vessel in the second mode of operation,

the reactor vessel is at least partly emptied, preferably at least 50% emptied, more preferably at least 70% empties, most preferably at least 90% emptied.

[0022] By emptying the reactor vessel after having performed the oxidation step with respect to a load (of the reactor vessel) of waste metal chloride solution (i.e. subsequent to conducting the first step with respect to the waste metal chloride solution prior to operating the reactor vessel in the second mode of operation), it is advantageously possible, according to the present invention, that the more or less complete load (of the reactor vessel) of the at least partly oxidized metal chloride solution (as well as the solid (or non-soluble) part being typically removed by filtering) is removed from the reactor vessel such that the reactor vessel is ready to receive - from the first storage element - the at least partly oxidized metal chloride solution in order to perform the hydrolyses step (while the reactor vessel being operated in the second mode of operation),

verstehe ich nicht [0023] According to the present invention, it is preferred that the waste metal chloride solution comprises, as the at least one oxidizable component, ferrous chloride (Iron(ll) chloride), wherein the waste metal chloride solution preferably comprises between 14 weight % to 28 weight %, preferably approximately 22 weight % of ferrous chloride (Iron(ll) chloride). [0024] Thereby, it is advantageously possible according to the present invention that the inventive method and system can be used efficiently in order to treat waste metal chloride solution of a plurality of different industrial processes such as various pickling processes, galvanizing processes or the like.

[0025] According to an alternative embodiment according to the present invention, prior to conducting the first step, the waste metal chloride solution is subjected to a pre- concentration step yielding concentrated waste metal chloride solution, wherein the concentrated waste metal chloride solution comprises, as the at least one oxidizable component, ferrous chloride (Iron(ll) chloride), wherein the concentrated waste metal chloride solution preferably comprises between 22 weight % to 45 weight %, preferably approximately 40 weight % of ferrous chloride (Iron(ll) chloride).

[0026] According to the present invention, it is furthermore preferred that the at least partly oxidized metal chloride solution comprises, as at least part of its oxidized part, ferric chloride (Iron(lll) chloride), wherein the at least partly oxidized metal chloride solution preferably comprises between 12 weight % to 25 weight %, preferably approximately 20 weight %, of ferric chloride (Iron(lll) chloride).

[0027] Thereby, it is advantageously possible according to the present invention that the inventive method and system can be used efficiently in order to recover at least part of the metal (especially iron) (in the form of non-soluble metal oxide (especially iron oxide)) from the total metal content (especially total iron content) that is present in the waste metal chloride solution. The values of the at least partly oxidized metal chloride solution comprising between 12 weight % to 25 weight %, preferably approximately 20 weight %, of ferric chloride (Iron(lll) chloride) are applicable in case that a constant chlorine amount and no special evaporation procedure is applied.

[0028] According to the present invention, it is furthermore also preferred that the waste metal chloride solution comprises, besides the at least one oxidizable component, free hydrochloric acid.

[0029] Thereby, it is advantageously possible according to the present invention that the inventive method and system can be used efficiently in order to recover used hydrochloric acid from waste liquids, especially pickling liquors, of different industrial processes such as various pickling processes, galvanizing processes or the like.

[0030] According to a preferred embodiment of the present invention,

- the oxidation temperature applied during the first step (oxidation step) is equal or superior to 1 10°C and equal or inferior to 250°C, preferably equal or superior to 130°C and equal or inferior to 200°C, more preferably equal or superior to 140°C and equal or inferior to 170°C, most preferably equal or superior to 145°C and equal or inferior to 155°C, and/or

- the hydrolyzes temperature applied during the second step (hydrolyses step) is equal or superior to 130°C and equal or inferior to 300°C, preferably equal or superior to 150°C and equal or inferior to 230°C, more preferably equal or superior to 160°C and equal or inferior to 180°C, most preferably equal or superior to 165°C and equal or inferior to 175°C.

[0031] According to the present invention, it is thereby advantageously possible that the inventive process is conducted in an efficient, especially energy efficient and time efficient, manner. [0032] According to a further preferred embodiment of the present invention,

- the oxidation pressure applied during the first step (oxidation step) is equal or superior to 0,3 MPa and equal or inferior to 1 ,2 MPa, preferably equal or superior to 0,6 MPa and equal or inferior to 1 ,0 MPa, more preferably equal or superior to 0,7 MPa and equal or inferior to 0,9 MPa, most preferably equal or superior to 0,75 MPa and equal or inferior to 0,85 MPa and/or

- the hydrolyses pressure applied during the second step (hydrolyses step) is equal or superior to 0,05 MPa and equal or inferior to 1 ,2 MPa, preferably equal or superior to 0,08 MPa and equal or inferior to 0,8 MPa, more preferably equal or superior to 0,09 MPa and equal or inferior to 0,5 MPa, most preferably equal or superior to 0,95 MPa and equal or inferior to 0,2 MPa.

[0033] It is preferred according to the present invention, that a concentration and heating step occurs during the hydrolyses step, until the boiling point of the solution within the reactor vessel is reached. Afterwards, the solution is progressively boiled down. However, in order to maintain the optimal hydrolyses conditions within the reactor vessel, it is preferred to progressively add at least partly oxidized metal chloride solution from the first storage element. During the conducting the hydrolyses step, hydrochloric acid (or vapor thereof) and iron oxide (Fe ₂ 0 ₃ ) are generated, and thereby the at least partly oxidized metal chloride solution is used until the first storage element is emptied. The content of the reactor vessel at this moment is fed to the first storage element, hence the reactor vessel emptied, in order to be ready for the oxidation step to be performed with a new load of waste metal chloride solution.

[0034] According to the present invention, it is thereby advantageously possible that the inventive process is conducted in an efficient, especially energy efficient and time efficient, manner.

[0035] The present invention also relates to a system for processing waste metal chloride solution using batch processing involving different modes of operation of a reactor vessel of the system, the waste metal chloride solution comprising at least one oxidizable component, the system comprising at least the reactor vessel, wherein the system is configured such that the reactor vessel is operable in a first mode of operation and in a second mode of operation and such that:

— the waste metal chloride solution is fed batch wise to the reactor vessel, and - while the reactor vessel being operated in the first mode of operation - an oxidation step is performed within the reactor vessel at an oxidation temperature exceeding 90°C and at an oxidation pressure exceeding 0,3 MPa, wherein at least a part of the waste metal chloride solution is oxidized during the oxidation step, wherein an at least partly oxidized metal chloride solution is obtained from the waste metal chloride solution, wherein the oxidized part of the at least partly oxidized metal chloride solution corresponds to at least a part of the at least one oxidizable component of the waste metal chloride solution prior to the oxidation step, — the at least partly oxidized metal chloride solution is at least partly hydrolyzed during a hydrolyzes step - performed within the reactor vessel while the reactor vessel is operated in a second mode of operation - at a hydrolyzes temperature exceeding 120 °C and at an appropriate hydrolyses pressure, wherein during the hydrolyzes step hydrochloric acid (HCI) and solid ferric oxide Fe ₂ 0 ₃ are obtained. [0036] According to the present invention, it is thereby advantageously possible to provide a system (or a treatment station) that requires comparatively low installation costs as well as reduced maintenance costs. According to the present invention, it is advantageously possible to combine the advantages of spray pickling and dip pickling and to minimize the risk of over-pickling. It is furthermore advantageous that the spent acid of such a system is of a quality such that it can be treated in regeneration plants without additional investment considering in particular the FeCI ₃ concentration in such spent acid.

Verstehe ich nicht.

[0037] According to a preferred embodiment of the present invention - especially regarding the inventive system -, the system additionally comprises a first storage element, wherein the system is configured such that, while the reactor vessel is - especially repeatedly - operated in the first mode of operation, the at least partly oxidized metal chloride solution (30), obtained during previously conducting the first step, is fed to a first storage element (210), and additional waste metal chloride solution is fed to the reactor vessel batch wise,

wherein by continuing to operate the reactor vessel in the first mode of operation, additional at least partly oxidized metal chloride solution is obtained from the additional waste metal chloride solution,

wherein the system is configured such that subsequent to operating the reactor vessel in the first mode of operation and prior to operating the reactor vessel in the second mode of operation, the at least partly oxidized metal chloride solution - especially additionally, also the additional at least partly oxidized metal chloride solution - is fed, from the first storage element, to the reactor vessel.

[0038] According to a preferred embodiment of the present invention - especially regarding the inventive system -, the system additionally comprises a second storage element, wherein the system is configured such that - during the hydrolyzes step - additional waste metal chloride solution (from upstream process) is fed to and stored in the second storage element.

[0039] By means of providing a second storage element for storing additional waste metal chloride solution, it is advantageously possible that - despite the inventive method operating (or the inventive system being operated) according to a batch processing - waste metal chloride solution can be generated continuously and is stored in the second storage element.

[0040] According to a preferred embodiment of the present invention - especially regarding the inventive system -, the first storage element has a first storage capacity, and the reactor vessel has a second storage capacity, wherein the ratio of the first and second storage capacity is greater than 2:1 , preferably greater than 3:1 , more preferably greater than 5:1 , and most preferably greater than 10:1.

[0041] According to the present invention, it is thereby advantageously possible to avoid that changes in the mode of operation of the reactor vessel need to occur too often: In case that the first storage capacity corresponds to roughly 5 times the second storage capacity, it is possible to operate the reactor vessel at least for five batches of its effective volume (regarding the first mode of operation, i.e. the oxidation step) until the first storage element is completely filled. Hence, the more the first storage capacity is increased (relative to the effective volume of the reactor vessel regarding the first mode of operation), the less frequent a change in the mode of operation of the reactor vessel needs to be applied. This also means that, according to the present invention, the effective volume of the reactor vessel, and hence its size (but also the size of tubing equipment or the like), is able to be scaled according to the needs of the upstream processes.

[0042] According to still a further preferred embodiment of the present invention - especially regarding the inventive system -, the system is configured to treat a quantity of waste metal chloride solution corresponding to equal to or superior to 10 l/hour and equal to or inferior to 5000 l/hour, preferably corresponding to equal to or superior to 30 l/hour and equal to or inferior to 3000 l/hour, more preferably corresponding to equal to or superior to 60 l/hour and equal to or inferior to 2000 l/hour, most preferably corresponding to equal to or superior to 100 l/hour and equal to or inferior to 1500 l/hour.

[0043] According to the present invention, it is thereby advantageously possible to provide hydrochloric acid regeneration also for processes generating comparably small volumes per time unit.

[0044] These and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 schematically illustrates a system according to the present invention for processing waste metal chloride solution using batch processing involving different modes of operation of a reactor vessel of the system, wherein the system comprises the reactor vessel, a first storage element as well as a second storage element.

DETAILED DESCRIPTION

[0046] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. [0047] Where an indefinite or definite article is used when referring to a singular noun, e.g. "a", "an", "the", this includes a plural of that noun unless something else is specifically stated.

[0048] Furthermore, the terms first, second, third and the like in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described of illustrated herein. [0049] Figure 1 schematically illustrates a system 100 according to the present invention for processing waste metal chloride solution using batch processing involving different modes of operation of a reactor vessel 200 of the system 100, wherein the system 100 comprises the reactor vessel 200, a first storage element 210 as well as a second storage element 220. In the exemplary embodiment according to Figure 1 , the system 100 comprises - besides the reactor vessel 200, the first storage element 210, and the second storage element 220 - a first ball valve 121 (preferably an automatic ball valve), a second ball valve 122 (preferably an automatic ball valve), a feeding pump 123, a filter element 124, a circulation pump 125, a filter pump 126, a cooling element 127 (or cooler), a pressure valve 128, a condenser 129, and a regenerated acid storage tank 130 (third storage element 130) having an outlet 131 connected to the upstream process requiring fresh (or regenerated acid). The reactor vessel 200 comprises an oxygen inlet 132, and the filter (or filter element 124 comprises an oxide outlet 133. In the exemplary embodiment according to Figure 1 , the system 100 also comprises a heating module that is able to provide additional heating for the contents of the reactor vessel 200. The heating module comprises an additional pump 134 and a heating element 135: The content of the reactor vessel 200 is pumped, at least partly, by the additional pump 134 to the heating element 135, is heated in the heating element 135, and is afterwards re-introduced in the reactor vessel 200 (arrow designated by encircled reference sign 7). However, the heating module does not necessarily be provided or installed as part of the system 100. By additionally heating the content of the reactor vessel 200 by means of the heating element, it is advantageously possible to shorten the time required for completely conducting the reaction within the reactor vessel 200, especially the reaction of the first (oxidation) step - especially with respect to the initial phase of the oxidation step, i.e. according to an alternative embodiment according to the present invention, the oxidation step is performed with the heating module switched on during an initial phase of the oxidation step (covering, e.g. 10% to 70% of the total time required for performing the oxidation step), and during the residual time of the oxidation step (after the initial phase), the heating module is switched off (as the reaction itself is producing sufficient heat).

[0050] The first storage element 210 is a FeCI ₃ storage tank, used to store the at least partly oxidized metal chloride solution 30. The second storage element 220 is a waste acid storage tank, i.e. a buffer tank to store waste metal chloride solution 10 during time intervals of the reactor vessel 200 being used in the second mode of operation.

[0051] The inventive process is carried out as follows: Waste metal chloride solution 10 (as produced by an upstream process, not shown in Figure 1 ) is fed to or buffered in the second storage element 220 (arrow designated by encircled reference sign 1 ). In a first point in time, it is assumed that the reactor vessel 200 is operated in the first mode of operation (being more or less empty). The (initial or initial portion of) waste metal chloride solution 10 is fed (trough the feeding pump 123) from the second storage element 220 to the reactor vessel 200 (arrow designated by encircled reference sign 2). In the reactor vessel 200 oxygen is added to the waste metal chloride solution 10 (through oxygen inlet 132) in order to perform the oxidation step with regard to the (initial) waste metal chloride solution 10. This results in at least a part of the waste metal chloride solution 10 being oxidized, thus obtaining an (initial) at least partly oxidized metal chloride solution 30 from the (initial) waste metal chloride solution 10, the oxidized part of the at least partly oxidized metal chloride solution 30 corresponding to at least a part of the at least one oxidizable component of the waste metal chloride solution 10 prior to the oxidation step. After the oxidation step, non-soluble parts (generated in the liquid within the reactor vessel 200) are filtered by filter element 124 (involving the filter pump 126 and the cooling element 127), removed from the filter element 124 by means of the oxide outlet 133, and the resulting at least partly oxidized metal chloride solution 30 is fed to the first storage element 210 (arrow designated by encircled reference sign 3), thereby emptying the reactor vessel 200. The first or initial batch of waste metal chloride solution has thus been processed regarding the oxidation step. Typically the process is continued by feeding an additional waste metal chloride solution 10' from the second storage element 220 to the reactor vessel 200 (arrow designated by encircled reference sign 2), and performing the oxidation step in an analogous manner, thereby obtaining additional at least partly oxidized metal chloride solution 30' (as well as non-soluble parts being removed by means of the oxide outlet 133), the additional at least partly oxidized metal chloride solution 30' being likewise fed to the first storage element 210 (arrow designated by encircled reference sign 1 ). After emptying the reactor vessel 200, the process might be further continued by feeding (once or more often) further additional waste metal chloride solution, and obtaining further additional at least partly oxidized metal chloride solution until the first storage element 210 is filled with at least partly oxidized metal chloride solution 30. Thereafter, the reactor vessel 200 is operated in the second mode of operation, performing the hydrolyses step: the at least partly oxidized metal chloride solution 30 (either fed from the first storage element 210 (arrow designated by encircled reference sign 4) or the residual at least partly oxidized metal chloride solution of the last batch of performing the first step (arrow designated by encircled reference sign 5)) is at least partly hydrolyzed during the hydrolyses step. The reactor vessel 200 is operated in the second mode of operation, at a hydrolyzes temperature exceeding 120 °C and at an appropriate hydrolyses pressure.

Thereby, hydrochloric acid (HCI) is generated (and fed through pressure valve 128 and condenser 129 (arrow designated by encircled reference sign 6) to the regenerated acid storage tank 130 (third storage element 130); from there, the regenerated acid is recycled through outlet 131 towards the upstream process generating the waste metal chloride solution 10) and solid ferric oxide Fe ₂ 0 ₃ areobtained (and removed through outlet 133). This operation is continued until the first storage element 210 is emptied. During operating the reactor vessel 200 in the second mode of operation, further waste metal chloride solution 10 has typically been generated and stored or buffered in the second storage element 220, thus the operation can be repeated again.

[0052] The description of the inventive process and the inventive system in the previous paragraph referred to waste metal chloride solution 10 having a relatively low concentration of typically between 14 weight % and 28 weight % of the at least one oxidizable component. According to an alternative embodiment of the present invention, instead of treating the waste metal chloride solution 10 by means of the inventive method and within the inventive system, a concentrated waste metal chloride solution 20 (having a higher concentration of an at least one oxidizable component) is treated in the reactor vessel 200 according to the same method. Typically, the upstream processes (generating the waste metal chloride solution 10) do not provide a concentrated waste metal chloride solution 20 (having such higher concentration of the at least one oxidizable component), hence, the waste metal chloride solution 10 being generated by the upstream processes is subjected to a pre-concentration step yielding the concentrated waste metal chloride solution 20. However, this pre- concentration step is not shown in Figure 1 . Typically, the concentrated waste metal chloride solution 20 comprises, as the at least one oxidizable component, ferrous chloride (Iron(ll) chloride), in a concentration of preferably between 22 weight % to 45 weight %.

[0053] From the above description, it follows that according to the present invention, the regeneration of the hydrochloric acid is executed in a batch wise manner in two steps, comprising the oxidation step and the hydrolyses step. In the oxidation step, the waste metal chloride solution (or waste pickling liquor) is oxidized by oxygen (0 ₂ ) and converted to FeCI ₃ (i.e. the at least partly oxidized metal chloride solution 30). This process step is repeated and the at least partly oxidized metal chloride solution 30 (FeCI ₃ ) is stored in a buffer tank (first storage element 210). Afterwards, the operation mode is switched and the FeCI ₃ is decomposed by heating the solution up to a certain temperature (hydrolyses temperature). By that decomposition process, hydrochloric acid (HCI) and iron oxide are produced. The regenerated HCI is condensed and can be used again, the iron oxide is separated as byproduct. According to the present invention, the same vessel, i.e. the reactor vessel 200, is used for the oxidation step and for the hydrolyses step. This approach advantageously reduces space requirements, CAPEX (capital expenditure), and allows to serve a market segment which has currently no access to total waste metal chloride solution (or waste pickling liquor) regeneration systems.

REFERENCE SIGNS

1 waste metal chloride solution feed to second storage element

2 waste metal chloride solution feed to reactor vessel

3 at least partly oxidized metal chloride solution feed to first storage element

4 at least partly oxidized metal chloride solution feed to reactor vessel

5 at least partly oxidized metal chloride solution feed to reactor vessel

6 outlet of regenerated hydrochloric acid

10 waste metal chloride solution

20 concentrated waste metal chloride solution

30 at least partly oxidized metal chloride solution

100 system

121 first ball valve

122 second ball valve

123 feeding pump

124 filter element

125 circulation pump

126 filter pump

127 cooling element

128 pressure valve

129 condenser

130 regenerated acid storage tank / third storage element

131 outlet connected to the upstream process requiring fresh / regenerated acid

132 oxygen inlet

133 oxide outlet

200 reactor vessel

210 first storage element

220 second storage element