Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/006—Wet processes
  • C22B7/007—Wet processes by acid leaching
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B17/00—Sulfur; Compounds thereof
  • C01B17/69—Sulfur trioxide; Sulfuric acid
  • C01B17/90—Separation; Purification
  • C01B17/901—Recovery from spent acids containing metallic ions, e.g. hydrolysis acids, pickling acids
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B7/00—Halogens; Halogen acids
  • C01B7/19—Fluorine; Hydrogen fluoride
  • C01B7/191—Hydrogen fluoride
  • C01B7/195—Separation; Purification
  • C01B7/196—Separation; Purification by distillation
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G37/00—Compounds of chromium
  • C01G37/02—Oxides or hydrates thereof
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G37/00—Compounds of chromium
  • C01G37/08—Chromium sulfates
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G49/00—Compounds of iron
  • C01G49/02—Oxides; Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G49/00—Compounds of iron
  • C01G49/14—Sulfates
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G53/00—Compounds of nickel
  • C01G53/04—Oxides; Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G53/00—Compounds of nickel
  • C01G53/10—Sulfates
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B23/00—Obtaining nickel or cobalt
  • C22B23/04—Obtaining nickel or cobalt by wet processes
  • C22B23/0453—Treatment or purification of solutions, e.g. obtained by leaching
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B23/00—Obtaining nickel or cobalt
  • C22B23/04—Obtaining nickel or cobalt by wet processes
  • C22B23/0453—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B23/0461—Treatment or purification of solutions, e.g. obtained by leaching by chemical methods
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
  • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
  • C22B3/08—Sulfuric acid, other sulfurated acids or salts thereof
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical processes
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B34/00—Obtaining refractory metals
  • C22B34/30—Obtaining chromium, molybdenum or tungsten
  • C22B34/32—Obtaining chromium
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/36—Regeneration of waste pickling liquors
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/80—Compositional purity
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to the recovery of metals and acids coming from exhausted pickling solutions and/or neutralization sludge of stainless steel in their total separation into secondary raw materials that can be reused, such as refractory oxides, iron sulphates and hydroxides, chromium hydroxide or metallic chromium or chromates, metallic nickel and hydrofluoric, nitric and/or sulphuric acids.
• secondary raw materials such as refractory oxides, iron sulphates and hydroxides, chromium hydroxide or metallic chromium or chromates, metallic nickel and hydrofluoric, nitric and/or sulphuric acids.
• the discharged bath portion is generally neutralized with kmewash for obtaining a sludge comprising metals, mainly iron, chromium and nickel in the form of hydroxides and anions, fluorides and sulphates in the form of calcium salts.
• a sludge comprising metals, mainly iron, chromium and nickel in the form of hydroxides and anions, fluorides and sulphates in the form of calcium salts.
• the object of the present invention is a process of treating and recovering almost all the components of pickling waste, allowing to split it into fully recyclable secondary raw materials, avoiding to forward it to the dump site.
• the present invention relates also to the treatment of sludge produced by neutralization of waste, even when already stored in a dump site, where it is necessary to provide for a previous redissolution in an acidic medium as disclosed hereinafter.
• the first stage of the process firstly provides for the separation of the insoluble oxides included in waste, through a decantation, washing and compaction unit. These oxides may be reused in the smelting furnace. By the same unit it is also possible to recover the oxides lost in the quenching section and in the rinsing steps after pickling.
• the pickling solution after oxide separation, is forwarded to a distillation unit where it is brought to boiling after addition of a suitable quantity of 98% sulphuric acid.
• volatile acids such as nitric or hydrofluoric acid
• hydrofluoric acid is obtained industrially by attack of sulphuric acid on fluorite.
• Nitric acid too at a higher concentration than the azeotropic one, is produced by distillation in presence of sulphuric acid.
• sulphuric acid moves nitric and hydrofluoric acids from their salts and complexes, reforming the free acids allowing their almost complete distillation.
• the distilled nitric and hydrofluoric acids are condensed and forwarded to the work tanks or storage.
• the clear solution essentially comprising high concentration sulphuric acid, part of chromium and nickel sulphates and traces of iron sulphates is added with 98% sulphuric acid until the acid concentration required by the process is restored, and then is forwarded to the evaporator in place of fresh sulphuric acid to treat another pickling solution.
• the precipitated salts are rinsed with an aqueous solution of sulphuric acid of suitable concentration. This treatment causes the redissolution of the precipitated nickel and chromium salts while iron sulphate remains undissolved and may be recovered.
• the acidic solution containing chromium and nickel and iron traces is forwarded to a first neutralization stage, after oxidation of divalent to trivalent iron, if required.
• the clear solution and the sludge rinsing waters are additionally neutralized up to pH 8-9, i.e. to complete nickel precipitation.
• the precipitated hydroxide is then dewatered by microfiltration, filter pressing or other suitable means.
• neutralization is conducted eidier with sodium hydroxide or hmewash.
• Nickel hydroxide may be further treated until metal in its elementary form is obtained.
• the hydroxide is taken to a dissolution equipment kept at pH controlled by sulphuric acid. Dissolution pH is kept at about 3.5-4.5, so that nickel hydroxide goes in solution as sulphate, while the possible traces of iron and chromium hydroxides due to incomplete precipitation during the first neutralization, as well as calcium sulphate present when limewash is used in the second neutralization, remain undissolved.
• the sludge coming from microfiltration or filter pressing after neutralization with sodium hydroxide, essentially consists of nickel hydroxide that is totally dissolved in sulphuric acid leaving only a litde residue.
• sludge from filter press after neutralization with limewash, leaves a heavy residue of calcium sulphate.
• this precipitate is heavy and compact, so that it may be separated from the clear solution of nickel sulphate in a quick and complete manner by simple settling.
• As the sludge coming from filter press contain less water than sludge from microfiltration, after dissolution they produce solutions which have more nickel, thus easier to be treated by electrodeposition.
• the nickel sulphate solution is then fed to the cathode area of an electrodialysis cell, where nickel in metal form is deposited on the cathode.
• the working conditions are such that the deposit is dendritic and can be easily removed by stripping plates passing near the cathode at fixed times.
• the metal stripped from the electrode in the form of pellets is collected in a suitable container at the cell bottom. After filtering and rinsing steps, these nickel pellets may be recovered directly in the steelworks.
• this acid When this acid reaches a fixed concentration, it is discharged to be recovered in the above described stage of hydroxide dissolution.
• Use of a membrane cell was preferred in place of an undivided cell, as it allows to avoid the anodic oxidation of the chromium ion, traces of which are possibly present in the solution of nickel sulphate, into chromate and to keep low the acid concentration at the cathode, so as to have always a very high faradic yield.
• the addition of some components like chelating and buffer agents in the sulphate solution allows to optimize the faradic yield.
• a further integration of the disclosed process concerns the separation of chromium from iron in the first produced hydroxide sludge, this separation being possible because of the amphoteric behaviour of chromium, having a trend to return in solution at strongly alkaline pHs, as shown in the Pourbaix diagram illustrated in the figure of the annexed drawing.
• the sludge precipitated at a pH between 3.5 and 4.5 after settling, rinsing and removal of the clear solution, is further alkalized with sodium hydroxide up to pH 10, thus redissolving chromium hydroxide. After removal of the clear solution, the undissolved iron hydroxide is rinsed and again filter pressed.
• the alkaline solution of trivalent chromium, combined with the sludge rinsing water, may be again neutralized up to pH 7.5-8 where trivalent chromium is again fully precipitated in the form of hydroxide or the solution may again undergo electrochemical reduction to obtain chromium in metal state or even undergo oxidation to obtain a chromate solution. If one decides to use this technique for sludge produced by neutralization of pickling baths already stored in authorized dump sites, it is necessary to add to the process a preliminary passage of dissolving sludge in an acid.
• the sulphuric solution containing the metal salts initially present in the sludge follows step by step the process above described for the exhausted pickling baths.
• the insoluble fraction before going to the settling, rinsing and compacting stage as hereinbefore described must be treated with hydrochloric acid so as to dissolve calcium sulphate contained in the fraction.
• the obtained acidic solution of calcium salts after neutralization and drying steps may be used as road antifreeze.
• a pickling bath solution of the following composition is used: Iron (III) 22 g/1
• Nitrates 55 g/1 To 1 1 of this solution an equal volume of 98% sulphuric acid is added. Distillation is conducted at atmospheric pressure for 5 hr, up to constant volume. Boiling temperature attains 12O 0 C. At the end of distillation the concentrated solution is placed in a IMOF cone to determine the existing liquid fraction. Details are as follows:
• the clear fraction has the following composition indicated as percentage on the total of each component initially present:
• Example 1 The experiment illustrated in Example 1 was repeated as described. However the solid fraction was not redissolved in water but underwent consecutive extractions with a solution of 1 % sulphuric acid. This treatment causes the total redissolution of nickel and chromium salts, leaving undissolved the iron salts. The obtained sulphuric solution contains as percentage:
• the salty fraction of the concentrate of a distillation test after dissolution in a solution of 1% sulphuric acid, has the following composition: Iron (III) 0.05 g/1
• the first neutralization phase at pH between 3.5 and 4.5 was conducted either with IN sodium hydroxide or 10% limewash. The obtained results are shown in the following tables.
• the sludge was dissolved in nitromuriatic acid and the sample was analyzed obtaining the following results.
• the sludge was dissolved in nitromuriatic acid and the sample was analyzed obtaining the following results
• the obtained solution has the following composition Nickel (II) 12 g/1
• EXAMPLE 6 A steelworks sludge coming from a storage dump site and having a dry contents of

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Inorganic Chemistry (AREA)
• Metallurgy (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• General Life Sciences & Earth Sciences (AREA)
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• Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Treatment Of Sludge (AREA)

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• 2008
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