LU84729A1 - PROCESS FOR IMPROVING SOIL STRUCTURE - Google Patents

Description

K? DESCRIPTIVE MEMORY filed in support of a

PATENT INVENTION APPLICATION

formed by the so-called Company: LABOFINA S.A.

for "Process for improving soil structure".

(Inventors: Messrs M. De Boodt and W. Minjauw).

The present invention relates to a process for conditioning soil and more particularly relates to a process for improving the structure of sandy soils.

The structure of a soil is an important property. In a soil with a suitable structure, the fine particles are agglomerated into stable aggregates, which allow the air to easily reach their interstices and which retain humidity or irrigation water. In addition, such a soil is much less prone to erosion by wind or by water (rain or irrigation water). Basic research on soil physics has clearly shown that a soil is stable and supports the unfavorable conditions to which it can be subjected when it is made up of stable, porous aggregates, forming an aerated structure.

* One method of improving the structure or structural stability of soils is to impregnate them with long-chain organic polymers, in particular water-soluble acrylamide polymers. One method consists in treating the soil particles with an aqueous polyacrylamide solution and with a dialdehyde, in particular glyoxal, which acts as a crosslinking agent for the polyacrylamide. This process is described in the Belgian patent n ° 757,161 of the Applicant. The term "polyacrylamide" includes not only homopolymers of acrylamide, but also water-soluble copolymers based on acrylamide in admixture with "less amount of comonomer. Generally, the polyacrylamide has a molecular weight of between about 50,000 and 1,500,000. The amount of polyacrylamide (calculated on a dry basis), necessary for the formation of stable aggregates, depends on the type of soil to be treated; this amount varies between about 0.05 and 0.5% of the weight of particles. When a sandy soil is treated with an aqueous solution of polyacrylamide and glyoxal or other aldehyde, an insoluble gel forms around and between the particles which are thus agglomerated into stable aggregates.

The present invention relates to an improvement of this soil stabilization technique.

To this end, the process of treating the sandy soil particles with an aqueous solution of polyacrylamide and dialdehyde is improved when the particles are also treated with an aqueous solution of iron compound.

* "The process of the present invention therefore consists of treating sandy soils with an aqueous solution of polyacrylamide and dialdehyde in combination with an aqueous solution of iron compound in an amount corresponding to 0.05 - 1% of iron ions based on the weight of dry soil particles.

The process of the invention is advantageously used for the treatment of particles of sandy soil whose pH does not exceed approximately 5. Soils consisting mainly of particles of white sand or loamy sand have a pH of the order of 4 to 4 , 5 and they are particularly improved with regard to aggregation and stability. The favorable effects of the process of the invention are less pronounced when treating calcareous or sodic soils.

. As iron compounds, water-soluble compounds, such as chloride, nitrate, sulfate, acetate and the like, are used. When it is spread on the ground, a ferrous compound is oxidized by atmospheric oxygen to the corresponding ferric compound. In the process of the invention, both ferrous and ferric compounds can be used. According to an advantageous embodiment of the process of the invention, ferrous sulphate is used, since it is a by-product of many industries and it is therefore readily available at low cost.

The minimum quantity of aqueous iron compound solution which makes it possible to improve the treatment with an aqueous solution of polyacrylamide and glyoxal corresponds to approximately 0.05% of iron ions, calculated on the weight of dry particles to be treated. You can use quantities of the order of 1% and even more. However, aqueous solutions of iron compound are used corresponding to the use of 0.05 to 0.75, in particular approximately 0.10 to 0.50% of iron ions, calculated on the dry weight of particles of ground.

By using the process of the present invention, the amount of polyacrylamide required to impart structural stability to sandy soil is significantly less, compared to a process without the use of iron compound. By using an aqueous solution of iron compound in combination with an aqueous solution of polyacrylamide and dialdehyde, the rate of agglomeration of soil particles is increased, as well as the stability of the aggregates formed. In general, the method of the present invention is applied using the aqueous polyacrylamide solution in an amount of the order of 0.05 to 0.3% of the weight of dry particles of the soil to be treated. Under these conditions, stable, aerated aggregates are obtained, retaining moisture, irrigation water or aqueous solutions of nutrient compositions for vegetation. Larger quantities of polyacrylamide would lead, when used in conjunction with iron compounds, to the formation of impermeable compact masses (coagulum).

The amount of dialdehyde added to the aqueous polyacrylamide solution is such that there is no more than one aldehyde group per amide group in the polymer. In the specific case of glyoxal, this • dialdehyde can be used in an amount of between approximately 0.05 and 10% of the weight of dry polymer, in particular between 0.1 to 2%.

The process of the invention can be carried out by applying - to the soil an aqueous solution containing the iron compound, the polyacrylamide and the dialdehyde. In certain cases, one can work in two stages: an application of an aqueous solution of iron compound, then an application of an aqueous solution of polyacrylamide and dialdehyde.

»- 4 - ^ The following examples are given by way of illustration and are not intended to be limiting.

In these examples: - the index of instability of an aggregate is given by the difference in millimeters between the average diameter of aggregates before and after their screening under water; - the stability index is the reverse of the previous one; - the stability quotient is given by the formula

Stability quotient =% aggregation x stability index; - PAM = aqueous polyacrylamide solution (molecular weight 200,000) containing 0.1% glyoxal, calculated on the weight of dry polymer.

Example 1.

Several trials were carried out by applying varying amounts of PAM to white sand. In some cases, the sand had been previously treated with an aqueous solution of ferrous sulfate.

In Table 1, the respective amounts of PAM are given. (calculated on a dry basis) and ferrous sulfate (expressed as ferrous ions), based on the weight of dry sand particles, as well as the stability quotient obtained during each test.

TABLE 1.

j Fe + (ions) Polyacrylamide Stability quotient:; - 0.05 8; I 0.1 0.05 23:: 0.3 0.05 44; i 0.5 0.05 46.5: - ο, ιο 15; I 0.05 0.10 25:: ο, ι ο, ιο 4i; 0.3 0.10 62:: 0.5 0.10 81; : 0.20 48:: 0.1 0.20 53; ! 0.3 0.20 63:: 0.5 0.20 92 a - 5 -

These results show that the stability quotient is improved when the sand is treated with an iron compound and PAM in comparison with a treatment with PAM alone.

The stability quotient obtained during treatment with 0.1% PAM and 0.3% Fe ions is better than that obtained by treating with 0.2% PAM alone.

Example 2.

Different portions of silty sand were treated either with an aqueous solution of ferrous sulfate, or with PAM, or again with an aqueous solution of ferrous sulfate and PAM.

The results are shown in Table 2.

TABLE 2,: Treatment Percenta- I.I (a) Q.S (b) Aggregates (c) ge of ogre- ^ 0.3 0.3-2.0 2.0-8.0 ‘: gation:; Control 17.8 0.787 22.6 86.8 11.7 1.5:; 0.3% Fe2 + 19.6 0.733 26 72.3 23.1 4.1; : 0.1% MAP 21.6 0.279 77.4 63.9 21 15.1:: 0J% MAP 22.2 0.276 80.4 52.8 30J 17.1: 0.2% MAP 24.5 0.252 97 , 2 58.7 22.7 20.6:: 0.2% PAM 28.6 0.286 100 46.2 29'7 24.1 (a) II = Instability index (b) QS = Stability quotient (c) Water stable aggregates (%) having the dimensions (in mm) indicated above.

These results show that the application of ferrous sulphate, alone, * improves the formation of aggregates, water-stable, by 0.3-2.0 mm, at the expense * of aggregates smaller than 0.3 mm . This improvement is equivalent to that obtained with the application of PAM alone. The joint use of ferrous sulfate and PAM leads to an increased improvement in the percentage and the stability of these aggregates.

Claims (5)

1. A method for improving the structure of sandy soils, characterized in that these soils are treated with an aqueous solution of polyacrylamide and dialdehyde in combination with an aqueous solution of iron compound in an amount corresponding to 0.05-1 % of iron ions, based on the weight of dry soil particles. 2. Method according to claim 1, characterized in that the iron compound is a ferrous or ferric compound soluble in water. 3) 'Method according to claim 2, characterized in that the iron compound is ferrous sulfate 4. Method according to any one of claims 1 to 3, characterized in that the iron compound is used in an amount between 0.05 and 0.75%, especially between 0.1 and 0.3%, based on the dry weight of soil particles. 5. Method according to any one of claims 1 to 4, characterized in that an aqueous solution of polyacrylamide and dialdehyde containing from 0.05 to 0.3% of polyacrylamide is used, based on the dry weight of:, soil particles, and 0.05-10% dialdehyde, based on the dry weight of polyacrylamide. Brussels, By proxy from the so-called LABOFINA Company.