Sulfur-based chemical soil-corrective in the form of pellets for agricultural use

A sulfur-based, chemical soil-corrective or conditioner for agricultural use in the form of pellets, said product containing fly sulfur powder, at least 3% by weight of an inert compound selected from the group consisting of clay, bentonite, kaolin and mixtures thereof, and at least 0.5% by weight of a wetting agent; said components are mixed with one another, then subjected to wet extrusion and next to drying, so as to obtain mechanically strong pellets which are porous and suitable to be very easily disgregated when they are in contact with soil moisture.

DESCRIPTION 
This invention relates to a sulfur-based chemical soil-corrective for 
agricultural use, said product being in the form of pellets. More 
particularly this invention relates to a pelletized sulfur-containing 
chemical soil-corrective or soil-conditioner (i.e., a fertilizer whose 
main function is that of correcting the constitutional deficiencies of an 
agricultural soil), whose pellets, though sufficiently strong to resist 
mechanical stresses so as to be handled without undergoing crumbling, are 
rapidly dissolved when in contact with soil moisture so that powder sulfur 
becomes available in a short time. 
As is well known, sulfur is supplied to soil with the main object of 
correcting alkalinity of the same and of intervening in the sodium-calcium 
ionic exchange. In agricultural soils, elements like nitrogen, phosphorus 
or potassium are to be supplied to soil in amounts of the order of tons or 
of quintals per hectare (macroelements) according to the kind of 
cultivation, while other elements like copper, zinc, manganese, iron etc. 
(microelements) are required in amounts just of the order of grams or kg 
per hectare; as a fertilizer, sulfur is considered to be a mesoelement, 
which is to be supplied in some hundred kg per hectare according to the 
kind of cultivation; on the contrary, as a corrective-acidifying agent, 
sulfur is a macroelement, to be administered in amounts of tons per 
hectare according to the alkalinity of the soil or to the presence of 
sodium. 
Once sulfur is present in soil in finely divided form, it is converted into 
sulfate ions by sulfoxidizing microorganisms, like the bacteria of the 
kind Thiobacillus. 
Not much care has been taken in general up to the present time of 
introducing sulfur directly into the soil, as the sulfur requirement was 
already satisfied by sulfate-containing fertilizers, as well as by acid 
rains and by the employment of natural organic manures with high contents 
of such element. 
With the decrease in the employment of such manures and the lowering the 
concentration of sulfuric acid in acid rains, the need for making up for 
lack of sulfur is increased in the recent times. 
It is quite evident that the best form for a rapid availability of the 
sulfur to bacterial attack, owing to its water insolubility, is the powder 
form; more particularly it has been set forth that the average 
granulometry should be lower than 80 mesh. 
However, powdered sulfur cannot be easily distributed over soils because it 
gets easily dispersed into the air and it is irritant, so that it gives 
rise to inconvenience and troubles to workmen, especially as regards the 
eyes. 
In DE-A-2 601 677 and DE-B-1 592 609 there are described sulfur containing 
fertilizers in granular form which are obtained mixing sulfur in finely 
divided form with binders to form an aqueous suspension which, then is 
dried and formed into granules. 
In DE-B-1 024 934, GB-A-499 807, U.S. Pat. No. 1 795 364 e U.S. Pat. No. 4 
062 694 it is described that sulfur in powder is transferred into 
dispersed sulfur compositions in the presence of auxiliary agents, 
including wetting agents. 
In DE-B-1 024 934, U.S. Pat. No. 1 795 364 and U.S. Pat. No. 4 062 694 it 
is further described to make sulfur suspensions in the presence of common 
binders like clay. 
Finally, in U.S. Pat. No. 3 062 637 it is disclosed to add clay in order to 
form clay bonded agricultural granules.

In order to obviate such drawbacks, some granular products have been 
prepared that can be easily distributed both by hand and by means of 
mechanical devices without dispersions into the air. In such products 
sulfur is mixed with bentonite clay by means of a hot process; the clay 
should make the granule disgregation easier when it is in contact with 
water, because it swells when exposed to moisture. Actually, such granules 
disgregate to a small extent essentially because of the fact that sulfur, 
which is insoluble and compact within the granule, "protects" the clay, so 
that the latter can contact water only after part of the sulfur has been 
removed from the granule due to the direct bacterial attack. It is evident 
that a compact pellet of some millimeters in diameter exposes a very 
limited surface to bacterial attack if compared to the same amount of 
sulfur powder or even sulfur in the form of a porous granule. 
The drawback mentioned above stems mainly from the fact that the disclosed 
granular products are obtained through hot processes, starting from molten 
sulfur. The granule so obtained, even though it contains up to 10% of 
swelling clay, is hard and compact, and solidified sulfur prevents the 
same from being water-degraded. Accordingly, the products in question 
require long times for being assimilated by the soil. 
Therefore, the object of the present invention is to provide a sulfur-based 
soil-corrective which is easy to handle just like the granular products 
already known, but which at the same time can also rapidly disgregate in 
soil water, so that the sulfur can expose a much larger surface to the 
aggressive attack of soil microorganisms. 
In carrying out the above object and other objects of the invention, the 
sulfur-based soil-corrective utilizes micronized sulfur, having a particle 
diameter of less than 100 microns, that is separated from gross sulfur 
with an inert gas and is commercially referred to as a fly sulfur powder. 
This free flowing powder form ventilated sulfur contains up to 5% of inert 
material intended to secure fluidity. 
The fly sulfur powder is mixed with at least 3% by weight of an inert 
product selected from the group consisting of clay, bentonite, kaolin, and 
mixtures thereof and at least 0.5% by weight of a wetting agent. Water is 
added in amounts about equal to the weight of the inert product plus the 
wetting agent to make a paste that is subjected to wet extrusion and dried 
to obtain pellets. 
The advantageous performance of the product according to the present 
invention is due both to the presence of additional ingredients in said 
mix and to the particular wet-process employed for preparing such product 
starting from sulfur powder, which process does not involve the melting 
and the subsequent solidification of the sulfur particles. 
The clay, which can be partially or totally substituted with bentonite 
and/or kaolin, performs the function of a binding agent in the mix and, in 
the finished product, it performs the well known function of swelling once 
it is in contact with water, so as to be of aid in causing the pellet to 
be disgregated. In the mix together with sulfur, the wetting agent and 
water clay also performs the functions of a lubricating agent for 
extrusion, as it makes the mix much more easy to process. 
Moreover, when the pellets so obtained are dried, the mixture as a whole 
does not shrink, but clay by liberating water, contributes to the creation 
of a network of pores throughout the granule, said pores making the 
penetration of water and the consequent disgregation of the granule 
remarkably easier. 
The wetting/dispersing agent clearly performs the function of allowing the 
water-repellent sulfur powder to be wetted and, additionally, it acts as 
an adhesive in the mix once the same has been dried, so preventing it from 
flaking off. 
Accordingly, the present invention specifically provides a sulfur-based 
soil-corrective for agricultural use in the form of pellets, which product 
contains fly sulfur powder, at least 3% by weight of an inert product 
selected from the group consisting of clay, bentonite, kaolin and mixtures 
thereof, and at least 0.5% by weight of a wetting agent, the components 
being mixed with each other and being subjected to wet extrusion and 
subsequent drying to obtain said pellets. 
The wetting agent is preferably selected from among lignin sulfonates or 
residual sugar products like distillation residues or slops; otherwise 
such agent can be any suitable solid or liquid surface active agent, or a 
mixture of two or more of the agents mentioned above. 
A preferred embodiment of the product according to the present invention is 
that containing about 93% by weight of fly sulfur powder, 5% by weight of 
clay and 2% by weight of lignin sulfonate. Preferably, the fly sulfur 
powder is double refined and its fineness on dry basis is 92/95% passing 
through about 325 mesh (45 microns) ASTM. The percentage of moisture 
content in the fly sulfur powder should not exceed about 0.5%. 
Moreover, other inorganic compounds can also be added to the mixture, such 
as for instance gypsum, magnesium sulfate or potassium sulfate. In that 
case, as a portion of sulfur is already present in the form of the sulfate 
ion, it is possible to lower the contents of elemental sulfur. Moreover, 
gypsum has the further advantage of containing the calcium ion for the 
Ca-Na ionic exchange in soil. 
Other fertilizers in the form of powders can also be added to the mixture 
of the present invention, so as to complete the composition of the same. 
More particularly, compounds containing macro and/or meso and/or 
microelements can be added, or other organic manures or amending products 
and/or wastes from agricultural-food industries can be added, such as 
exhausted husks, exhausted grape skins, citrus fruit peels, tomato skins, 
by-products of the distillation industries, and so on. 
The addition of microelements like copper, zinc, manganese, magnesium, 
iron, boron, molybdenum, etc. to the product of the present invention is 
also particularly useful, said product acting as a vehicle for such 
elements, so that their separate distribution in soil in the minimum 
amounts required is avoided. 
The addition of phosphorus-based compounds can also be of particular 
advantage, as the presence of sulfur favors the dissolution of insoluble 
phosphorus, so making easier the absorption of such element by the plants. 
According to a specific procedure for preparing the corrective product of 
the present invention, the components in the form of powders are mixed 
with one another, or better they are crushed and milled together in order 
to favor the homogenization of the mix. Then water is added in amounts 
about equal to the weight of clay plus the wetting agent(s) that are being 
employed, and the mix is fed to a die drawplate by means of rollers or by 
a screw feeder, which also causes further mixing of the paste, thus making 
the same more homogeneous. After extrusion, the product is passed through 
an air stream, so that it dries, thus giving the desired pellets. It has 
been found that with the addition of a greater amount of water, that the 
pellets lose their mechanical properties and cannot sustain the transfer 
toward the drying equipment. If the amount of water is less than 
specified, the extrusion duct is obstructed or the pellets present an 
outer water-proof film. 
Alternatively, hemihydrate calcium sulfate or anhydrous magnesium sulfate 
can be employed in the mix mentioned above as drying agents. The first one 
of said compounds, in addition to act as a fertilizer, also has the 
property of absorbing one part of water per five parts of the material, 
while the second one can absorb one part of water per about one part of 
material. 
As already mentioned above, the pellets are solid and strong, and they do 
not crumble or become crushed during handling, but their microscopic 
structure is highly porous, and as soon as they are in contact with the 
soil moisture they are rapidly disgregated so liberating sulfur powder, so 
that sulfur becomes quickly available for bacterial attack and for its 
transformation into the sulfate ion. 
This invention has been disclosed with specific reference to some preferred 
embodiments thereof, but it is to be understood that modifications and/or 
changes can be introduced by those who are skilled in the art.