Process and process line for recovering metals and fluorides from a pickle liquor

Abstract

The invention relates to a process line and a process for recovering metals and fluorides from a pickling line (1), comprising: a) retrieving a waste solution (WS) from a pickling liquor (PL), b) measuring iron, chromium and fluoride concentration in the retrieved waste solution (WS), c) precipitation of iron and chromium by addition of fluorides, while keeping a major portion of occurring nickel dissolved in the solution, d) separation of iron and chromium, e) precipitation of the nickel in the waste solution (WS) by the addition of basic additives, f) recuperation of the precipitated nickel, g) dissolving the iron fluoride and chromium fluoride from step d) to recuperate fluoride free, metal containing particles while keeping most of the fluorides dissolved, h) recuperation of the precipitated metal containing particles in step g), i) precipitating he CaF2 by addition of CaCl2 or Ca(OH)2, and j) recuperation of the CaF2 and dispensing the remaining liquid solution as wastewater (WW).

Description

[0001] PROCESS AND PROCESS LINE FOR RECOVERING METALS AND FLUORIDES FROM A

[0002] PICKLE LIQUOR

[0003] TECHNICAL FIELD

[0004] The invention relates to a process for recovering fluorides and metals, specifically nickel, from an acid recycling process. The invention also relates to a process line for performing the process.

[0005] Specifically, the invention relates to a process and process line for recovering fluorides and metals from an acid recycling process in which most components of a pickle liquor are recycled such that the need for landfill is minimised.

[0006] BACKGROUND

[0007] In the steel industry pickling is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, and rust or scale from ferrous metals, copper, precious metals and aluminium alloys.

[0008] A solution called pickle liquor, which usually contains acid, is used to remove the surface impurities. It is commonly used to descale or clean steel in various steelmaking processes.

[0009] Spent pickle liquor is considered a hazardous waste by most Environment Protection Authorities (EPA). Pickle liquor from steel processes may be neutralized with lime and disposed of in a landfill since the EPA no longer deems it a hazardous waste after neutralization. The lime neutralization process raises the pH of the spent acid.

[0010] It would be advantageous to achieve a process in which metals, acids and fluorides may be largely recuperated such that the need for landfill is minimised.

[0011] SUMMARY OF THE INVENTION

[0012] It is an object of the invention to provide a process in which a waste solution from an acid recycling process, such as a pickle liquor, will be free from metals, acids and fluorides. A further object is to develop an automated system where the process may be controlled and run with a limited need of operator interference.

[0013] According to a first aspect the invention relates to a process for recovering metals and fluorides from a pickling line, the process comprising the following steps: a) performing an acid recycling process on a pickling liquor from the pickling line to return a major portion of occurring acid in the pickling liquor to the pickling line and to retrieve a waste solution from the pickling liquor, the waste solution containing metals and fluoride, b) measuring iron, chromium and fluoride concentration in the retrieved waste solution, c) selective precipitation of occurring iron, preferably as K2FeF5, and chromium, preferably as CrF3, by addition of a balanced amount of fluorides, preferably KF, to the waste solution based on the measured concentration of iron, chromium and fluoride in the waste solution, while keeping a major portion of occurring nickel dissolved in the solution, d) a first solid / liquid separation step in which the precipitated iron, preferably K2FeF5, and chromium, preferably CrF3, are separated from the nickel containing solution from step c), e) a nickel concentration step in which occurring nickel in the waste solution after the first solid / liquid separation step d) is precipitated by the addition of basic additives to the solution, f) a second solid / liquid separation step in which the precipitated nickel from step e) is filtered and recuperated from the liquid solution, g) a hydrolysis step in which the separated precipitated iron fluoride and chromium fluoride from step d) are at least partially dissolved in a liquid solution to recuperate fluoride free, metal containing particles, such as Fe2O3and Cr(OH)3, while keeping most of the fluorides dissolved, h) a third solid / liquid separation step in which the metal containing particles recuperated in step g), at least one from the group comprising Fe2O3and Cr(OH)3, are filtered and retrieved from the fluoride containing solution, i) a fluoride precipitation step, in which CaCI2or Ca(OH)2is added to the fluoride containing solution to obtain CaF2, and j) a fourth solid / liquid separation step, in which the CaF2from step i) is filtered and recuperated from the liquid solution, wherein the remaining liquid solution contains nitrates and low amounts of fluorides and of heavy metals such that it may be dispensed as wastewater.

[0014] In this process, a waste solution from an acid recycling process, typically a pickle liquor, will be fully taken care, wherein metals, acids and fluorides are recuperated for reuse and wherein the remaining wastewater solution will be free from metals, acids and fluorides, such that it may be dispensed as wastewater. According to embodiments, the process comprises an electrowinning step k), in which the precipitated nickel from step f) contains nickel hydroxide and is dissolved and used as electrolyte in a process step of electrowinning the nickel.

[0015] According to embodiments the electrowinning step k) is performed at a temperature of 50-65°C, at a pH of 3.5-4.5.

[0016] According to embodiments the cathodes used in the electrowinning step k) are produced from a stainless steel, such as 304 or 316 stainless steel.

[0017] According to embodiments, in the selective precipitation step c), the pH in the waste solution is adjusted to between 3.5 and 5.5, by addition of a balanced amount of KOH or NaOH, preferably KOH.

[0018] According to embodiments the amount fluorides (KF) added to the waste solution (WS) in the selective precipitation step c) results in a concentration in the waste solution of at least 3 times the measured molar content of chromium and 5 times the measured molar content of iron.

[0019] According to embodiments the selective precipitation of occurring iron and chromium in step c) is performed at a temperature of 50-80°C, preferably above 60°C.

[0020] According to embodiments the nickel concentration step e) is performed at a temperature of 40-60°C, and at a pH of 9-12.

[0021] According to embodiments, in the nickel concentration step e), the basic additive is KOH or NaOH and the nickel is precipitated as Ni(OH)2.

[0022] According to embodiments the hydrolysis step g) is performed at a temperature of 40- 65°C and includes adding KOH or NaOH to adjust the pH to 7-10.

[0023] According to embodiments, in the hydrolysis step g), a solid / liquid ratio is kept between 80-350 gram metal containing particles per litre liquid.

[0024] According to embodiments the concentration of fluoride in the fluoride containing solution is measured prior to the fluoride precipitation step i) to add a balanced amount of CaCI2or Ca(OH)2.

[0025] According to embodiments the acid recycling process in step a) comprises a retardation process where a majority of occurring acid in the pickling liquid preferably more than 80%, is separated from the waste solution and is recycled to the pickling line. According to a second aspect the invention relates to a process line arranged to perform the process as defined above on a pickling liquor from a pickling line wherein the process line comprises: an acid filtration unit for filtering acids in the pickling liquor, an acid recycling unit for recycling most of the acids to the pickling line, a metal separation unit for crystallising fluoride iron and fluoride chromium, a first solid / liquid separation unit for separating the precipitated iron fluoride and chromium fluoride, a nickel purification unit in which nickel is precipitated, a second solid / liquid separation unit for separating the precipitated nickel, an electrowinning unit for electrowinning the nickel, a hydrolysis tank in which the separated precipitated iron fluoride and chromium fluoride from the first solid / liquid separation unit are at least partially dissolved in a liquid solution to recuperate fluoride free, metal containing particles, a third solid / liquid separation unit for separating the fluoride free, metal containing particles from the fluoride containing solution, a precipitation unit for precipitation the fluoride in the fluoride containing solution as CaF2, and a fourth solid / liquid separation unit in which the precipitated fluoride is separated from the liquid solution, which thereafter contains low amounts of fluorides and of heavy metals such that it may be dispensed as wastewater.

[0026] Other embodiments and advantages will be apparent from the detailed description and the appended drawings.

[0027] GENERAL PROCESS OVERVIEW

[0028] The proposed metal recycling process is adapted to handle a waste flow from an acid regeneration system of HNO3 / HF pickling lines. Conventionally, such waste flows have been sent to neutralization to end up as landfill.

[0029] The waste flow contains high levels of heavy metals such as Fe, Cr and Ni, fluorides, and nitrates. The object of the proposed metal recycling process is to ultimately recycle all solid products from the system, preferably within the steel production or, if more beneficial, in other industries.

[0030] The solid products from the system will according to a specific embodiment be:

[0031] Solid nickel, for example electroplated on stainless steel cathodes. • Metal oxide / hydroxide sludge, which is free from fluorides, and mainly comprises iron oxide and chromium hydroxide.

[0032] • Calcium fluoride sludge, with a concentration of CaF2over 80 % and low concentrations of all heavy meals, typically below 0.5 % in total.

[0033] The obtained nickel can subsequently be recycled directly in the melt shop to adjust the alloy composition.

[0034] The metal oxide / hydroxide sludge can be recycled with further treatment in the melt shop or upstream in a ferrochromium plant or blast furnace.

[0035] The calcium fluoride may, after further treatment, be recycled as hydroflux, which may be used to adjust the viscosity of the slag.

[0036] The process of the system is based on the separation of nickel from other metals and fluorides from the metals. This is achieved with several steps of precipitation and solid / liquid separation. The nickel may ultimately be recycled by electrowinning.

[0037] Nickel separation

[0038] To be able to recycle nickel with electrowinning it is important to control the impurities that may affect the electrowinning process. These impurities include other metals, fluorides and nitrates.

[0039] The step of separating nickel from other metals may be performed by precipitation of metal fluoride salts. At the right conditions iron and chromium forms fluoride containing salts, while the nickel remains in the solution. Consequently, in a first step of the nickel separation > 99% of the iron and > 99% of the chromium are separated as fluoride salts from the nickel solution. This is achieved by balancing both the fluoride to metal ratios and the pH of the solution.

[0040] The pH is increased to lower the solubility of the fluoride salts but needs to be low enough to avoid precipitations of hydroxides, because otherwise nickel may coprecipitate with the iron and the chromium, which of course would negatively affect the recovery of nickel. Further, a hydroxide sludge may be formed, said sludge being hard to dissolve, which may complicate the subsequent separation of metals from the fluorides.

[0041] The chromium fluoride precipitation is highly temperature dependent, wherein an elevated temperature is beneficial for the formation of CrF3crystals. In a first step of the nickel separation, the solution may be treated in a preadjusting step to adjust the metal / fluoride ratio and pH of the solution, which is subsequently fed into a continuous reactor where the metal fluoride salts are formed by final adjustment of fluoride / metal ratio and the pH. The residence time for the crystallizer is chosen to achieve high yields and particles of a uniform size to facilitate the next process step, i.e., a solid / liquid separation. The solid / liquid separation step typically involves large and heavy particles which will set demands on the flowrate, process design and filtration solution.

[0042] Nickel

[0043] In the nickel purification step the dissolved nickel is concentrated and contaminants are removed. The process step is based on the precipitation of nickel hydroxide. At the right conditions nickel hydroxide is formed, wherein fluorides and nitrates remain in the solution. In this step >99% of the nickel may be precipitated and > 99% of the fluorides and nitrates may be excluded from the solid nickel fraction. This is achieved by balancing the pH and the temperature.

[0044] The pH is adjusted to form hydroxides and to precipitate the nickel such that it may be separated from the fluorides and nitrates, which will remain in the solution.

[0045] The precipitation of nickel is temperature dependent, wherein a higher temperature is beneficial for the formation of Ni(OH)2and hence for a good separation of fluorides and nitrates.

[0046] The incoming solution from the nickel separation step is fed into a continuous reactor where the nickel hydroxides are formed by adjusting of the pH. The residence time for the reactor is preferably chosen to get high yields and a uniform particle size to facilitate the subsequent process step, i.e., solid / liquid separation.

[0047] Metal hydrolysis

[0048] The step where the metals and fluorides are separated may be referred to as metal hydrolysis. The separation may, in the right conditions, be achieved by forming hydroxides and oxides while fluorides remain in the solution. In this solid / liquid separation step > 98% of the iron, chromium and other heavy metals may be precipitated and > 98% of the fluorides may be excluded from the solid metal fraction.

[0049] This is achieved by balancing the pH and the temperature. The pH is adjusted to form hydroxides and oxides to precipitate the metals such that they may be separated from the fluorides, which will remain in the solution.

[0050] The precipitation of metal hydroxides is temperature dependent where a higher temperature is beneficial for the formation of precipitates and for a good separation of fluorides.

[0051] The incoming solid fraction from the nickel separation step is fed into a preadjusting tank where the solids are mixed with water to dissolve some of the crystals and to get the right solid liquid ratio. This slurry contains a lot of large and heavy particles which will set demands on the process design. The slurry of water and solids is then fed into a continuous reactor where hydroxides and oxides are formed by adjustment of the pH. The residence time for the crystallizer is chosen to achieve high yields and uniform particle size to facilitate the next process step, which is yet another solid / liquid separation.

[0052] Fluoride recvclino

[0053] In the fluoride recycling step fluorides are separated from the wastewater. The separation is dependent on providing conditions in which calcium fluorides are formed. If correctly performed > 99% of the fluoride precipitates from the wastewater.

[0054] This is achieved by inter alia controlling the ratio between the calcium and the fluorides.

[0055] The calcium to fluoride ratio is adjusted to form calcium fluorides and to achieve a very low remaining concentration of fluorides in the wastewater.

[0056] The incoming liquid fraction from the nickel purification and metal hydrolysis steps is fed into a mixing tank. The mixed liquid fraction is then fed into a continuous reactor where calcium fluorides are formed. This can be done by the addition of either Ca(OH)2or Ca(CI)2. The residence time for the crystallizer is chosen to achieve high yields and a uniform particle size to facilitate the next process step, which is a solid / liquid separation.

[0057] There are some differences between utilizing Ca(OH)2or CaCI2. The use of Ca(OH)2will remove the metal residues from previous steps which implies that the CaF2will be less pure when using Ca(OH)2. The use of CaCI2will hence make it possible to provide a purer CaF2. On the other hand, the use of CaCI2will it also give rise to higher levels of chlorides in the wastewater. Electrowinning nickel

[0058] The nickel from the pickling liquid waste will be recycled as solid nickel on cathodes comprised of stainless steel plates, typically of grade 304 or 316 stainless steel.

[0059] The recycling of nickel is achieved by an electrowinning process where plating of the stainless steel plates is achieved with an insoluble anode. DC power is connected to a solution of nickel sulphate and sulfuric acid, wherein occurring nickel cations in the electrolyte solution will be reduced to metal nickel on the cathode, and oxygen and H+ are produced at the anode.

[0060] The nickel is fed into the electrowinning unit as a washed Ni(OH)2 sludge and is dissolved into the electrolyte to be utilized in the electrowinning until. When nickel is added in the form of a hydroxide, both the nickel and the hydroxide will contribute to the process, in view of that the electrowinning needs the addition of hydroxide to keep the pH at a steady level when hydrogen is formed at the anode. The feed of Ni(OH)2can hence stoichiometrically balance the H+ produced during the plating.

[0061] BRIEF DESCRIPTION OF THE DRAWING

[0062] Below, specific embodiments of the invention will be described with reference to the appended drawing, of which:

[0063] Fig. 1 shows a process line according to a specific embodiment of the invention.

[0064] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0065] In Fig. 1 a process line according to a specific embodiment of the invention is shown, with an indication of the different process steps performed along the line.

[0066] The process line comprises: an acid filtration unit 2 for filtering acids in the pickling liquor PL, an acid recycling unit 3 for recycling most of the acids to the pickling line 1 , which is illustrated as a pickling tank, a metal separation unit 4 for crystallising iron fluoride and chromium fluoride, a first solid / liquid separation unit 5 for separating the precipitated iron fluoride and chromium fluoride, a nickel purification unit 6 in which nickel is precipitated, a second solid / liquid separation unit 7 for separating the precipitated nickel, an electrowinning unit 8 for electrowinning the nickel, a hydrolysis tank 9 in which the separated precipitated iron fluoride and chromium fluoride from the first solid / liquid separation unit 5 are at least partially dissolved in a liquid solution to recuperate fluoride free, metal containing particles, a third solid / liquid separation unit 10 for separating the fluoride free, metal containing particles from the fluoride containing solution, a precipitation unit 11 for precipitation the fluoride in the fluoride containing solution as CaF2, and a fourth solid / liquid separation unit 12 in which the precipitated fluoride is separated from the liquid solution, which thereafter contains low amounts of fluorides and of heavy metals such that it may be dispensed as wastewater WW.

[0067] The innovation relates to acid recycling, metal separation with hydrometallurgy, possible electrowinning of metal, and separation of fluorides from metals wherein all solid waste from the process will be recyclable in the steel industry and the wastewater will be free from fluorides and heavy metals thereby eliminating the need of neutralization and landfill.

[0068] The invention relates to a complete process for recovering metals via an acid recycling process following a steel pickling process.

[0069] Pickle liquor PL, containing acid and various metals such as nickel, iron and chromium is received at a pickling tank that forms part of a pickle line 1 where the pickle liquor PL is used to remove surface impurities on steel products. Pickle liquor is commonly used to descale or clean steel in various steelmaking processes. The metal mixture contained in the pickle liquor will depend on previous process steps and on the alloy being pickled. A mixture of HNO3 / HF is usually used on austenitic steel containing high levels of nickel, such that the pickle liquor PL will normally contain nickel, HNO3 and HF.

[0070] In a pre-step of the inventive process up to 90% of the HNO3 and up to 90% of the HF is recycled in an acid recycling step a) and returned to the pickling line 1 . The process is based on acid retardation. The acid retardation process requires clean acid. Therefore, the first step is an acid filtration step at an acid filtration unit 2, where particles are removed to get a particle free acid. The retardation process is based on that metal cations can be separated from free acids by an absorption process. This is achieved in an acid recycling unit 3 comprising a bed with a special resin, referred to as a retardation resin or an ion exchange resin. The spent pickling acid is fed to the bed and the acids will be separated from the metal ions with retardation. The resin absorption is higher for the acids. The movement of the acid will be retarded relative to the movement of metal ions. Regeneration of the bed is done with water to clean out the pickling solution. This yields a waste solution WS with a low acid content and a high metal content and a separated acid product A with a high acid content and low metal content.

[0071] The waste solution WS which is the by-product from the acid recycling step contains approximately 10% of the HNO3 and HF and 75% of the dissolved metals.

[0072] This diluted waste solution WS resulting from the acid recycling step gives benefits in the following process since less acid needs to be treated by the process, but most of the dissolved metals are still in the solution.

[0073] The waste solution WS from the acid recycling step, which contain metals and fluoride, is procured to a metal separation unit 4.

[0074] In the metal separation unit 4 the metals are separated with hydrometallurgy. In view of that nickel is a high value metal, the object of this step is to separate nickel from other metals, primarily iron and chromium. The separation is done by selective precipitation of iron and chromium fluoride crystals. This is achieved by controlling the ratio between dissolved iron and chromium and fluoride and by also controlling the pH.

[0075] The ratio should preferably be higher than 3 times the molar concentration of chromium and 5 times the molar concentration of iron up to and excess of 30%. The aim for pH is about 3.5 to 5,5. This prevents the formation of hydroxides and the coprecipitation of nickel, the process keeps the nickel in solution (over 90%) and removes > 99% of iron and chromium as iron fluoride (KsFeFs) and chromium fluoride (CrFs).

[0076] To achieve the above, the concentration of iron, chromium and fluoride in the waste solution WS is measured in a preceding step b).

[0077] In a step c), selective precipitation of occurring iron and chromium is achieved by the addition of a balanced amount of fluorides to the waste solution WS based on the measured iron, chromium and fluoride concentration in the waste solution WS. Step c) is performed at a temperature of about 50-70°C, preferably about 60-65°C.

[0078] Step d) is a first solid / liquid separation step, wherein the precipitated iron and chromium are separated from the nickel containing solution from step c) as precipitated iron and chromium fluoride. Namely, if electrowinning is to be performed, it is important to separate the nickel from chromium, fluorides, nitrates and other contaminants since the electroplating is sensitive to such contaminants. The first solid / liquid separation step is performed in a filtration unit 5, which may comprise candle filters, a belt vacuum filter or other types of filtration units suitable for the particle size of the solids.

[0079] Preceding the electrowinning, a nickel concentration step e) is performed in a nickel purification unit 6, wherein occurring nickel is precipitated by the addition of basic additives such as hydroxide to the solution.

[0080] Subsequently, a second solid / liquid separation step f), in which the precipitated nickel from step e) is filtered and recuperated from the liquid solution, is performed in a second solid / liquid separation unit 7.

[0081] Further, before electrowinning is to be performed it is desirable to wash the precipitated nickel to obtain a solid product that is pure enough for recycling so as to be suited for electrowinning. This may basically be achieved by washing the precipitated nickel with water to remove fluorides and nitrates.

[0082] Subsequently, the precipitated and filtered nickel hydroxide from step e) and f) may be recovered. Typically, it may be dissolved and used as electrolyte in an electrowinning step k) for electrowinning of the nickel.

[0083] The electrowinning step k) is performed in an electrowinning unit 8, preferably at a temperature of 50-65°C, a pH of 3.5-4.5, and preferably at a nickel concentration of at least 30 g / l.

[0084] The cathodes may be produced from a stainless steel, such as 304 or 316 stainless steel such that it may be recycled in the steel mill.

[0085] Namely, in this way, the nickel will not need to be removed from the cathodes, which is conventionally the most common way of performing electrowinning. Instead, the stainless steel cathode may be recycled together with the nickel plated thereon.

[0086] An object of steps e) and f) is to obtain a solid, fluoride free, nickel containing product that can be recycled in the steel industry, preferably by forming particles of an even distribution at the precipitation so that a following solid / liquid separation step j) is repeatable and can be applied with an industrial solution. With a correct setup it is possible to obtain a solid product that is free from fluorides and may have an even particle distribution of about 7-14 pm. Another object is to obtain the highest possible fluorides concentration in the liquid fraction. In parallel to the Nickel process steps e), f) and k), a fluoride / metal separation is performed on the separated precipitated iron fluoride and chromium fluoride retrieved from step d).

[0087] Namely, to obtain a solid product that is recyclable and doesn’t need to be sent to landfill the metals need to be separated from the fluoride.

[0088] The solid phase from the first solid / liquid separation step d), which typically contains iron, chromium and fluorides, is treated with basic components to obtain metal oxides and metal hydroxides as a solid product and to get the fluorides as a dissolved salt in the liquid phase.

[0089] A hydrolysis step g) is performed on the solid phase from the first solid / liquid separation step d), preferably by the addition of KOH or NaOH to a pH 7-10, preferably 8-10, and preferably at a temperature of about 40-65 C.

[0090] Specifically, in the hydrolysis step g), in the separated precipitated iron fluoride and chromium fluoride from step d) are partially dissolved in a liquid solution, preferably water. Typically, the precipitated iron fluoride and chromium fluoride are only partially dissolved to obtain a slurry of a specific solid-liquid ratio. Tests have indicated that an optimum solid / liquid ratio is 300 g wet solids per Liter water, with an advantageous ratio ranging from 80-500 g wet solids per Liter water, preferably 80-350 g.

[0091] Hydroxides, such as KOH or NaOH are added to the slurry to recuperate fluoride free metal salts such as Fe2O3and Cr(OH)3and keep the fluorides dissolved in the solution.

[0092] In a subsequent third solid / liquid separation step h), metal salts, of which at least one pertains to the group comprising Fe2O3and Cr(OH)3, are filtered from the fluoride containing solution.

[0093] Subsequently, in step i), which is a fluoride precipitation step, CaCI2or Ca(OH)2is added to the fluoride containing solution to obtain CaF2, and in the following step j) which is a fourth solid / liquid separation step j), the CaF2from step i) is filtered and recuperated from the liquid solution, wherein the liquid solution contains low amounts of fluorides and heavy metals such that it may be dispensed as wastewater WW.

[0094] The fourth solid liquid / separation step j), where the CaF2solids are removed from the wastewater WW, can be done with candle filters, belt vacuum filter or other available filtration units suitable for the relevant particle size of the solids. The solids may also need to be washed to obtain a solid product that is pure enough to be treated for recycling.

[0095] Above, the invention has been described with reference to specific embodiments. The invention is however not limited to these embodiments. It is obvious to a person skilled in the art that other embodiments are possible within the scope of the following claims.

Claims

CLAIMS1 . A process for recovering metals and fluorides from a pickling line (1 ), the process comprising the following steps: a) performing an acid recycling process on a pickling liquor (PL) from the pickling line (1 ) to return a major portion of occurring acid in the pickling liquor (PL) to the pickling line (1) and to retrieve a waste solution (WS) from the pickling liquor (PL), the waste solution (WS) containing metals and fluoride, b) measuring iron, chromium and fluoride concentration in the retrieved waste solution (WS), c) selective precipitation of occurring iron, preferably as K2FeF5, and chromium, preferably as CrF3, by addition of a balanced amount of fluorides, preferably KF, to the waste solution (WS) based on the measured concentration of iron, chromium and fluoride in the waste solution (WS), while keeping a major portion of occurring nickel dissolved in the solution, d) a first solid / liquid separation step in which the precipitated iron, preferably K2FeF5, and chromium, preferably CrF3, are separated from the nickel containing solution from step c), e) a nickel concentration step in which occurring nickel in the waste solution (WS) after the first solid / liquid separation step d) is precipitated by the addition of basic additives to the solution, f) a second solid / liquid separation step in which the precipitated nickel from step e) is filtered and recuperated from the liquid solution, g) a hydrolysis step in which the separated precipitated iron fluoride and chromium fluoride from step d) are at least partially dissolved in a liquid solution to recuperate fluoride free, metal containing particles, such as Fe2O3and Cr(OH)3, while keeping most of the fluorides dissolved, h) a third solid / liquid separation step in which the metal containing particles recuperated in step g), at least one from the group comprising Fe2O3and Cr(OH)3, are filtered and retrieved from the fluoride containing solution, i) a fluoride precipitation step, in which CaCI2or Ca(OH)2is added to the fluoride containing solution to obtain CaF2, and j) a fourth solid / liquid separation step, in which the CaF2from step i) is filtered and recuperated from the liquid solution, wherein the remaining liquid solution has a fluoride concentration under 50 mg / l and all heavy meals under 1 mg / l such that it may be dispensed as wastewater.

2. The process according to claim 1 , further comprising an electrowinning step k), in which the precipitated nickel from step f) contains nickel hydroxide and is dissolved and used as electrolyte in a process step of electrowinning the nickel.

3. The process according to claim 2, wherein the electrowinning step k) is performed at a temperature of 50-65°C, at a pH of 3.5-4.5.

4. The process according to claim 2 or 3, wherein the cathodes used in the electrowinning step k) are produced from a stainless steel, such as 304 or 316 stainless steel.

5. The process according to any one of the preceding claims, wherein in the selective precipitation step c), the pH in the waste solution is adjusted to between 3.5 and 5.5, by addition of a balanced amount of KOH or NaOH, preferably KOH.

6. The process according to any one of the preceding claims, wherein the amount of fluorides added to the waste solution (WS) in the selective precipitation step c) results in a total fluoride concentration of at least 3 times the measured molar content of chromium and 5 times the measured molar content of iron.

7. The process according to any one of the preceding claims, wherein the selective precipitation of occurring iron and chromium in step c) is performed at a temperature of 50-80°C, preferably above 60°C.

8. The process according to any one of the preceding claims, wherein the nickel concentration step e) is performed at a temperature of 40-60°C, and at a pH of 9-12.

9. The process according to any one of the preceding claims, wherein in the nickel concentration step e), the basic additive is KOH or NaOH and the nickel is precipitated as Ni(OH)2.

10. The process according to anyone of the preceding claims, wherein the hydrolysis step g) is performed at a temperature of 40-65°C and includes adding KOH or NaOH to adjust the pH to 7-10.11 . The process according to anyone of the preceding claims, wherein, in the hydrolysis step g), a solid / liquid ratio is kept between 80-350 gram metal containing particles per litre liquid.

12. The process according to any one of the preceding claims, wherein a concentration of fluoride in the fluoride containing solution is measured prior to the fluoride precipitation step i) to add a balanced amount of CaCI2or Ca(OH)2.

13. The process according to any one of the preceding claims, wherein the acid recycling process in step a) comprises a retardation process where a majority of occurring acid in the pickling liquid (PL) preferably more than 80%, is separated from the waste solution (WS) and is recycled to the pickling line (1 ).

14. A process line arranged to perform the process according to anyone of the preceding claims on a pickling liquor (PL) from a pickling line (1 ) characterised in that the process line comprises: an acid filtration unit (2) for filtering acids in the pickling liquor (PL), an acid recycling unit (3) for recycling most of the acids to the pickling line (1 ), a metal separation unit (4) for crystallising fluoride iron and fluoride chromium, a first solid / liquid separation unit (5) for separating the precipitated iron fluoride and chromium fluoride, a nickel purification unit (6) in which nickel is precipitated, a second solid / liquid separation unit (7) for separating the precipitated nickel, an electrowinning unit (8) for electrowinning the nickel, a hydrolysis tank (9) in which the separated precipitated iron fluoride and chromium fluoride from the first solid / liquid separation unit (5) are at least partially dissolved in a liquid solution to recuperate fluoride free, metal containing particles, a third solid / liquid separation unit (10) for separating the fluoride free, metal containing particles from the fluoride containing solution, a precipitation unit (11 ) for precipitation the fluoride in the fluoride containing solution as CaF2, and a fourth solid / liquid separation unit (12) in which the precipitated fluoride is separated from the liquid solution, which thereafter contains low amounts of fluorides and of heavy metals such that it may be dispensed as wastewater (WW).

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