Chemistry: fertilizers – Processes and products – Inorganic material
Reexamination Certificate
2001-07-12
2003-09-02
Sayala, Chhaya D. (Department: 1761)
Chemistry: fertilizers
Processes and products
Inorganic material
C071S031000
Reexamination Certificate
active
06613117
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a silicic fertilizer produced by mainly making the most of a converter slag generated by a molten pig iron preliminary treatment, and a production method of such a silicic fertilizer.
The term “preliminary treatment” or “preliminary process” according to the present invention generally includes desulfurization, desiliconization and dephosphorization treatment of a molten pig iron, and further includes preparatory treatment to adjust the silicon and/or sulfur content contained in a molten pig iron if such contents are high, and further includes a main process of desiliconization and dephosphorization by adding CaO and blowing oxygen into a molten pig iron.
The term “preparatory treatment” according to the present invention includes desulfurization and desiliconization treatment to adjust silicon and sulfur content of a molten pig iron if such contents are high.
The term “main process” according to the present invention includes a desiliconization and dephosphorization process by adding CaO and blowing oxygen into a molten pig iron.
2. Description of the Related Art
Granulated slag, produced by discharging slag from a blast furnace and separating and water-cooling the slag generated in a steel-making process and converter slag generated by a molten pig iron preliminary treatment in a converter, have been effectively utilized in the past to produce fertilizers for grasses such as rice plants, corn and wheat, besides an application as concrete aggregates.
However, the fertilizer utilizing the blast furnace slag is prepared by merely pulverizing the slag to a particle size of not greater than 3 mm, or by adding citric acid-soluble phosphorus oxide (P
2
O
5
) (citric acid solubility), which is not sufficient, to the slag. Therefore, the ratio of soluble silica in silica (SiO
2
) as a constituent material of the slag is small, and the silica does not easily elute into the soil. Incidentally, the term “soluble silica” means the leached silica when a material containing silica is shaken in a 0.5N hydrochloric acid solution at 30° C. for 1 hour, and the term “soluble lime” means the lime (CaO) leached out when a similar test is conducted.
The terms “citric acid-soluble phosphorus oxide”, “citric acid-soluble magnesia” and “citric acid-soluble manganese oxide” all mean phosphorus oxide, magnesia and manganese oxide in materials that elute (dissolve) in 2% citric acid, respectively.
On the other hand, the conventional converter slag is treated at a high temperature of around 1,600° C. after lime, an iron ore and a Mn ore as sub-materials are collectively added besides the supply of oxygen. Because the lime content added is large, the resulting slag is not a slag having low basicity of 3 or below, and the silica content is small, too. Further, the soluble silica content is small in the same way as the blast furnace slag. Since desulfurization is carried out by use of soda ash, the soda content and the sulfur content are large, and the resulting slag is not suitable as a fertilizer for the grasses.
Soluble silica is an important component for the growth of the grasses. If this content is small, the grasses are likely to be blown down by a strong wind, and are not resistant to damage by blight and noxious insects and damage by cold weather. The growth and ripening are thus deteriorated when the soluble silica is not sufficient.
Needless to say, fertilizers having greater contents of effective ingredients are preferred not only for the grasses but also for general plants to those having smaller contents. As the ages of the people engaged in the agricultural production have become higher and higher on the average in recent years, development of a fertilizer that provides the effect equivalent to, or higher than, the conventional fertilizers even with a smaller spray amount, and can improve the efficiency and mitigate the labor has therefore been required.
SUMMARY OF THE INVENTION
Against the background described above, the present invention provides a silicic fertilizer that makes the most of a slag produced in a molten pig iron preliminary process and has a large soluble silica content, and a production method for the silicic fertilizer.
The gist of the present invention for solving the problems described above is listed below.
(1) A silicic fertilizer comprising a slag having basicity (CaO/SiO
2
) of not greater than 3 and containing 15 to 35 mass % (hereinafter expressed merely by “%”) of soluble silica;
(2) A silicic fertilizer comprising a slag containing 15 to 35% of soluble silica, 30 to 45% of soluble lime, not greater than 8% of citric acid-soluble magnesia, 1 to 8% of citric acid-soluble manganese oxide and less than 5% of citric acid-soluble phosphorus oxide;
(3) In the slag of (1) or (2), a silicic fertilizer containing 15 to 35% of soluble silica, 30 to 45% of soluble lime, not greater than 8% of citric acid-soluble magnesia, 1 to 8% of citric acid-soluble manganese oxide and at least 5% of citric acid-soluble phosphorus oxide;
(4) A silicic fertilizer comprising a slag having basicity (CaO/SiO
2
) of not greater than 3 and containing 15 to 35% of soluble silica, 30 to 45% of soluble lime, not greater than 8% of soluble magnesia, 1 to 8% of citric acid-soluble manganese oxide and less than 5% of citric acid-soluble phosphorus oxide;
(5) A silicic fertilizer of (1) or (2) or (4), wherein citric acid-soluble phosphorus oxide is further added to the slag, and the slag contains at least 5% of citric acid-soluble phosphorus oxide.
(6) A silicic fertilizer comprising a slag having basicity (CaO/SiO
2
) of not greater than 3 and containing 15 to 35% of soluble silica, 30 to 45% of soluble lime, not greater than 8% of citric acid-soluble magnesia, 1 to 8% of citric acid-soluble manganese oxide and at least 5% of citric acid-soluble phosphorus oxide;
(7) A method of producing a silicic fertilizer comprising the steps of adding CaO to a molten pig iron, blowing oxygen into the molten pig iron, desiliconizing and dephosphorizing the molten pig iron, and collecting a slag having basicity (CaO/SiO
2
) of not greater than 3 and containing 15 to 35% of soluble silica.
(8) A method of producing a silicic fertilizer comprising the step of conducting either one, or both, of a preparatory treatment step of adding a desulfurizer to a molten pig iron and conducting a desulfurization treatment and a preparatory process step of desiliconization treatment of blowing oxygen into a molten pig iron and adjusting a silicon content; a step of removing the resulting slag formed through the preparatory treatment steps, further adding CaO and blowing oxygen into the molten pig iron to desiliconize and dephosphorize the molten pig iron, and collecting a slag containing 15 to 35% of soluble silica.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The silicic fertilizer according to the present invention makes the most of a slag having a soluble silica content of as high as 15 to 35%. The slag having such a high soluble silica content is presumably formed by the mechanism in which lime and oxygen are added to a molten pig iron originally having low sulfur and silicon contents, or to a molten pig iron the sulfur and silicon contents of which are in advance lowered by desulfurization and desiliconization preparatory treatment, and desiliconization and dephosphorization are then carried out with the result that lime enters the network of silica constituting the slag and weakens the mutual silica bonds. One of the main process steps for obtaining the silicic fertilizer according to the present invention is a step of blowing CaO powder with oxygen to the molten pig iron through a lance, or adding CaO in the lump form to the molten pig iron and blowing oxygen through the lance, and carrying out desiliconization and dephosphorization after the basicity of the slag is thus set to 3 or below, preferably between 1.5 to 2.5. The present invention can thus provide a silicic fertilizer having a high soluble silica content. Incidentally, the molten pig iron
Fukiage Kazunori
Iwasaki Masaki
Matsumoto Hiroshi
Kenyon & Kenyon
Nippon Steel Corporation
Sayala Chhaya D.
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