Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Reexamination Certificate
2000-06-20
2002-04-23
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
C423S146000, C423SDIG002, C252S175000, C210S716000, C210S722000
Reexamination Certificate
active
06375919
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for the manufacture of a ferric sulfate solution and to a water treatment agent. More particularly, it relates to a method for the manufacture of a ferric sulfate solution which is characterized in dissolving an iron ore containing 30% by weight or more FeOOH as a trivalent iron (Fe
3+
) in sulfuric acid and to the use of a water treatment agent consisting of the basic ferric sulfate solution manufactured by the said method as a coagulant.
PRIOR ART
Especially in recent years, a ferric sulfate solution has occupied the attention as a useful water treatment agent and, particularly, a ferric sulfate solution and a basic ferric sulfate solution have a quick sedimentation speed for the resulting flocs and show good deodorizing ability as compared with a water treatment agent of an aluminum type such as an aluminum sulfate solution and la basic aluminum chloride solution whereby they have been widely used as a water treatment agent for waste water from paper Manufacturing industry, from food industry, from chemical industry. etc. or as a dehydrating aid for sewage sludge. Usually, such a ferric sulfate solution and a basic ferric sulfate solution have been manufactured by dissolving ferrous sulfate in water, adding an appropriate amount of sulfuric acid thereto and being oxidized by air or by an oxidizing agent. In recent years however, ferrous sulfate obtained from washing of steel plate, etc. with acid or discharged and by-produced from titanium industry has been decreasing and the present situation is that a shortage in the material there for is resulted. It is also the present situation that a coagulation performance of the iron-based coagulants manufactured as such is not sufficient.
Under such circumstances, the present inventors have started in studying the manufacture of a ferric sulfate solution and, as a result of various investigations, they have found that iron ore containing
30
% by weight or more FeOOH as a trivalent iron (Fe
3+
) is very easily soluble in sulfuric acid and is able to manufacture a ferric sulfate solution at a low cost and have accomplished the present invention on the basis of such a finding.
Representative examples of iron ore are hematite, limonite and magnetite. Main component of hematite is &agr;-Fe
2
O
3
, that of limonite is &agr;-FeOOH and that of magnetite is Fe
3
O
4
. Until now, various proposals have been made for a method of dissolving iron oxide or ferric hydroxide oxide which is a main component thereof. With regard to &agr;-Fe
2
O
3
, it has been said to be hardly soluble in sulfuric acid in general. With regard to Fe
3
O
4
, there is a disclosure, for example, in the Japanese Examined Patent Hei-02/22012 about a method of manufacturing a polyferric sulfate solution, i.e. a basic ferric sulfate solution, using 3 moles or more but less than 4 moles of sulfuric acid to 1 mole of ferrosoferric oxide (Fe
3
O
4
).
In the Japanese Examined Patent Hei-05/13095, there is a disclosure about a dissolving method for ferrosoferric oxide in which sulfuric acid having a concentration of 35-50% is used and a dissolution is carried out at the temperature of 75° C. or higher. In the Japanese Examined Patent Hei-05/13094, there is a disclosure about a dissolving method where ferrosoferric oxide, etc. and metal iron are dissolved at the temperature of 75° C. or higher using sulfuric acid of 40-45% concentration.
In the Japanese Examined Patent Hei-05/53730, there is a disclosure about a method for the manufacture of an iron sulfate solution in which from 3 moles to less than 10 moles (to 1 mole of ferrosoferric oxide) of sulfuric acid of 30-50% concentration and 0.1-0.5 equivalent (to Fe
2
O
3
in ferrosoferric oxide) of a reducing agent are added to iron oxide mainly consisting of ferrosoferric oxide followed by dissolving at 75° C. or higher.
In the U.S. Pat. No. 4,707,349, there is a disclosure about a method in which iron ore containing an oxide of Fe
2+
and an oxide of Fe
3+
, i.e. a ferrosoferric oxide ore, is dissolved in sulfuric acid.
In an iron sulfate solution manufactured by those methods, not only Fe
3+
but also Fe
2+
are contained in large quantities and, therefore, it is necessary to carry out an oxidation. Therefore, the cost for oxidation is needed and there is a disadvantage that a ferric sulfate solution cannot be manufactured at a low cost.
With regard to FeOOH, there is a disclosure, for example, in the Japanese Laid-Open Patent Hei-07/241404 that, in an iron-based coagulant in which iron oxide is dissolved in sulfuric acid followed, if necessary, by subjecting to .oxidation, ferric hydroxide oxide [FeOOH] produced from a ferric chloride solution is added to a trivalent iron material of the said iron oxide is used.
In this method however, a treatment for the manufacture of the material is necessary and, therefore, it is difficult to manufacture a ferric sulfate Solution at a low cost.
MATTERS TO BE SOLVED BY THE INVENTION
In view of the above, an object of the present invention is to provide a method for the manufacture of a ferric sulfate solution at low cost and in an industrially easy manner by dissolving the iron ore in sulfuric acid directly. Another object of the present invention is to provide an iron-based coagulant having a good coagulating property useful as a water treatment agent or, particularly, a basic ferric sulfate solution useful as a coagulant having a good coagulation performance.
MEANS FOR SOLVING THE MATTER
Thus, the first feature of the present invention relates to a method for the manufacture of a ferric sulfate solution, characterized in that, iron ore containing
30
% by weight or more FeOOH as a trivalent iron (Fe
3+
) is dissolved in sulfuric acid. Further, the second feature of the present invention relates to a method for the manufacture of a ferric sulfate solution according to the first feature wherein the said iron ore is that which is calcined at 200-600° C. Furthermore, the third feature of the present invention relates to an iron-based inorganic coagulant having a good coagulating property as a water treatment agent or, particularly, to a water treatment agent consisting of Et basic ferric sulfate solution.
BEST MODE FOR CARRYING OUT THE INVENTION
The ferric sulfate according to the present invention means that where the molar ratio of SO
4
/Fe is within a range of from 1.25 to 1.5, i.e. a solution of normal salt of ferric sulfate and a solution of basic ferric sulfate.
In the present invention, iron ore is dissolved using sulfuric acid and it is recommended to use the iron ore containing 30% by weight or more FeOOH as a trivalent iron (Fe
3+
) When it is less than 30% by weight, amount of the residue after dissolving is large and the advantage of the present invention cannot be expected. Alternatively, it is desirable that the iron ore is ground using a commonly-used grinding machine such as a jaw crusher, a hammer mill or a ball mill. The smaller the particle size of the iron ore, the better the solubility. Generally, the particle size is preferably 500 &mgr;m or smaller or, more preferably, 300 &mgr;m or smaller.
Quite surprisingly, the present inventors have found that, when iron ore containing FeOOH is calcined, there is a further improvement in its solubility. The calcination temperature is 200-600° C. and, more preferably, 400-500° C. Although the reason why the solubility in sulfuric acid is improved by calcination is not clear, it is likely that FeOOH is dehydrated by calcination resulting in an increase in a specific surface area whereby the solubility is improved. According to the experiment by the present inventors, there is no improvement in the solubility when the temperature is lower than 200° C. Also, there is no improvement in the solubility when it is calcined at higher than 600° C. Although the reason therefor is not clear, it is presumed that FeOOH is changed to a stable &agr;-Fe
2
O
3
whereby the solubility is not improved. With regard to the time f
Kakio Toshihiko
Tsukamoto Tatsuo
Griffin Steven P.
Kolisch Hartwell Dickinson & McCormack & Heuser
Taki Chemical Co. Ltd.
Vanoy Timothy C.
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