Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Water – sewage – or other waste water
Reexamination Certificate
1999-01-11
2001-04-03
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Water, sewage, or other waste water
C205S749000, C205S760000, C205S761000
Reexamination Certificate
active
06210558
ABSTRACT:
FIELD OF THE INVENTION
Object of the present invention is the achievement of a steel pickling process and particularly of a stainless steel one, carried out in a bath containing as essential components HF and ferric ions, in which the oxidation of Fe
2+
formed during the pickling process to Fe
3+
necessary in order to maintain the Redox potential of the solution at the predetermined value, is carried out by an electrolytic oxidation method acting directly on the pickling solution exactly as it is, preferably in a continuous way.
The electrolytic oxidation method according to the present invention can be advantageously applied to all the known pickling processes, the electrolytic oxidation of Fe
2+
to Fe
3+
in the pickling solution can replace the traditional oxidation methods of Fe
2+
to Fe
3+
by chemical oxidizers such as for instance H
2
O
2
, peracids, persalts, chlorates, oxygen (air), HNO
3
.
TECHNOLOGICAL BACKGROUND
The electrolytic oxidation of the Fe
2+
ions in an exhausted pickling solution in order to restore the necessary concentration of Fe
3+
ions has been already disclosed by U.S. Pat. No. 3,622,478 for the treatment of a pickling solution based on H
2
SO
4
and Fe
3+
ions introduced in starting solution as Ferric sulphate. The treatment is carried out in an electrolytic cell without separation between the catholyte and the anolyte (cell without separating diaphragm).
In FR 2.341.669 it is disclosed the electrolytic oxidation of Fe
2+
ions in an exhausted pickling solution based on HCl and Fe chlorides, in order to restore the necessary concentration of Fe
3+
ions. The treatment is carried out in a cell provided by separating diaphragm.
The above mentioned process for electrolytic oxidation of Fe
2+
ions are relevant to pickling solutions based on H
2
SO
4
or HCl and not containing HF or F
−
anions.
The presence of HF and F
−
anions in the pickling solution involves the formation of fluorinated complexes of trivalent iron and consequently the properties and behaviour of the solution is not equivalent to those of pickling solutions not containing HF (or F
−
anions).
Consequently the above prior art electrolytic oxidation methods cannot be considered obviously applicable to HF containing pickling solutions.
SUMMARY OF THE INVENTION
According to the present invention the conventional methods of chemical oxidation can be advantageously substituted, in order to restore the preestablished value of the ferric ions concentration defined by the sort of the pickling process and of the material to be treated by a method for the electrolytic oxidation of the pickling solution carried out batch-wise or continuously according to the requirements of the plant.
The solution to be treated can be cooled before entering in the electrolytic cell or can be treated at the same temperature of the pickling process. The electrolytic oxidation according to the present invention is carried out with two electrodes acting respectively as a cathode and as an anode in contact with the pickling solution to be oxidized, to which a continuous tension having a sufficient value for the oxidation of Fe
2+
to Fe
3+
to the anode and for the reduction of H
+
to gaseous H
2
to the cathode is applied.
REFERENCES:
patent: 3844927 (1974-10-01), Smith
patent: 4113588 (1978-09-01), Watanabe et al.
Busnelli Maurizio
Demertzis Ioannis
Giordani Paolo
Pedrazzini Cesare
Hedman & Costigan ,P.C.
Henkel Kommanditgesellschaft auf Aktien
Phasge Arun S,.
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