Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1997-09-03
1999-10-19
Ryan, Patrick
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
75710, 75392, 148513, 210702, 210663, C01G 900
Patent
active
059682299
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for the purification of metal containing solutions, in particular pickling solutions containing iron and zinc.
The object of the present invention is to obtain a process to recover metal compounds from spent solutions containing metal salts, and then in particular zinc and iron salts from spent pickling baths.
BACKGROUND OF THE INVENTION
In connection with surface treatment of metallic objects these are pickled in acidic baths, whereby in particular hydrochloric acid is generally used, in order to provide the metal object with a clean surface to which the surface treatment adheres. Hereby metal and metal oxides are dissolved from the metallic objects, which metal will be found in the pickling solutions in the form of ions, which can be recovered in the form of salts of different kinds. Most of all pickling solutions containing iron, aluminium, and zinc are present, which pickling solutions are a great problem as they can not be deposited in any arbitrary way as the metals present can create an environmental problem. Furthermore, the metals present are a resource if they should be able to be recovered.
EP-A1-0 141 313 discloses a process for recovering iron and zinc from spent pickling solutions, whereby the pickling solution is first treated with an absorption agent to eliminate any organic material present, whereupon the iron present in three valence form is first reduced using metallic iron and zinc, to two valence form, the zinc present is extracted using a complex forming solvent, whereupon zinc and iron are recovered in a traditional way. The addition of zinc is carried out in a step following the addition of metallic iron in order to precipitate heavy metals present by means of a cementation. In connection with the cementation zinc will dissolve and can then be recovered as zinc chloride. When the zinc chloride has been eliminated by means of extraction iron can be recovered as a solution of iron(III) chloride after oxidation of the two valence iron. The process is hereby based on a cementation of the heavy metals present and a solvent extraction of the zinc present by means of trioctyl amine in a mixture with kerosine/isodecanol. The use of the organic solvent is a complication as these have to be recovered, partly for cost reasons, partly for environmental reasons.
There is thus a desire for a more simplified and cost efficient process for recovering the metals present, and in particular to eliminate the need for organic solvents.
DESCRIPTION OF THE PRESENT INVENTION
It has now surprisingly been found possible to meet these requirements by means of the present invention which is characterized in that the ingoing solution containing metals is neutralized using magnetite and/or metallic iron, that the ingoing iron (III) is reduced to iron(II) by means of an addition of metallic iron, that ingoing heavy metals are precipitated by the addition of a precipitating amount of a sulphide, whereby the metal sulphides precipitated are recovered by means of filtration, that the solution is, optionally, subjected to ion exchange operation to transfer ingoing zinc into non-complex bound form, whereupon zinc is recovered as zinc carbonate, that iron(II) in the remaining solution is oxidized to iron(III), whereupon the solution is used as such or is further treated for increasing the metal content for the purpose intended.
Further characteristics are evident from the accompanying claims.
By means of the present invention it is obtained that many types of spent metal containing solutions can be recovered such as pickling baths containing hydrochloric acid, and sulphuric acid, other liquid effluent streams, solid disposals (materials dissolved in acid (scrap, oxides, hydroxides, etc.), as well as purification of iron(II) sulphate which is a large source of iron, and which is obtained as a residual product from other processes, such as the production of titanium; free acid in the ingoing baths can easily be neutralized using different sources of iron,
REFERENCES:
patent: 3617562 (1971-11-01), Cywin et al.
patent: 3800024 (1974-03-01), Forsell et al.
patent: 3801481 (1974-04-01), Eddleman
patent: 3931007 (1976-01-01), Sugano et al.
Elve M. Alexandra
Kemira Kemi AB
Ryan Patrick
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