SK277929B6 - Method of disposal of heavy metals in soil - Google Patents

Abstract

Heavy metals, mainly cadmium contained in soil is disposabled by alkaline silicates, which are at sweetening of soil added into milled limestone. By addition of silicate potassium is soil most enriched with potassium.

Description

Technical field

The invention relates to a process for the disposal of heavy metals in soil.

the penetration of heavy metals into the food chain can be prevented.

BACKGROUND OF THE INVENTION

Heavy metals in the soil, where they have been clogged with fertilizer or dropped from the atmosphere, are easily adsorbed by ion exchange or complex bonds. For example, when preparing drinking water, 1 kg of calcium carbonate captures hundreds of milligrams of dangerous heavy metals. Soil itself has a certain sorption capacity to bind heavy metals, but yields decrease as they accumulate. By increasing the acidity of the soil, heavy metals are easily released and then penetrate the food chain. Therefore, the soil is also alkalinized with finely ground limestone or a mixture of quicklime powdered lime. Powdered limestone according to various locations contains up to 80 to 98.5% pure calcium carbonate. For dolomitic limestone, the calcium content is lower, but magnesium is also present in the soil.

A disadvantage of this conventional liming process is that heavy metals, especially cadmium, are only trapped by the limestone sorption processes. By dropping the pH, heavy metals are easily released again in the soil.

Furthermore, it is known to add calcium silicate to the soil in rice cultivation according to Japanese patent no. 01,132,318 / 89,132,318 /. A disadvantage of the process of this patent is the high dose of calcium silicate, 200 kg per 10 acres, which is 2000 kg per hectare. However, this quantity is also linked to a phosphorus fertilizer containing 500 kg of phosphorus per ha.

SUMMARY OF THE INVENTION

The above-mentioned disadvantages are eliminated by the method of neutralizing heavy metals in the soil by ground limestone, which according to the invention is carried out by admixing the limestone into the soil in a mixture with at least one water-soluble alkali silicate in a weight ratio of 100: 1 to 100: 5. 50 to 200 g of calcium oxide per kg. The composition is produced by admixing the silicate to the limestone during grinding, preferably further with the addition of calcium oxide.

As the alkaline silicate according to the invention, it is very advantageous to use potassium silicate, which in practice releases the necessary potassium into the soil. This results in a mixture containing calcium silicate in a surprisingly active form which destroys better heavy metals.

This also results in a lower degree of dosing of the active compounds in liming the soil. For example, at a soil acidity of pH 5.1-5.5, a conventional dose of ground limestone of 2.1 tons per hectare is used, but with only 20 kg of alkali silicate, which is sufficient to bind the metals.

The significance of the use of the water-soluble alkali silicate in the composition according to the invention is that the silicate anions which form insoluble heavy metal silicates are in water-soluble ionic form. As a result, they show a high reactivity to heavy metals. Preferably, the reactions of heavy metal cations of greater atomic mass then take place. Ongoing reactions accelerate sufficient soil moisture. thus

DETAILED DESCRIPTION OF THE INVENTION

1. Crushed limestone is sprinkled with water-soluble potassium silicate in the following ratio before grinding: 1000 wt. parts by weight of limestone, 10 wt. parts of potassium silicate (potassium water glass) with a density of 1300 - 1400 kg.m- ³ and grinding in a spherical or similar kind of mill. After reaching the required fineness it is used for fertilization.

2. The crushed limestone is sprinkled with water-soluble sodium silicate in the same ratio and grinding as described in Example 1 before grinding.

3. Spray the crushed limestone before grinding with a 1: 1 mixture of alkaline potassium silicate and sodium, following the procedure of Example 1.

4. Powdered alkaline potassium or sodium silicate is added to the finely ground limestone in a ratio of: 1000 wt. parts by weight of finely ground limestone, 6 wt. parts of powdered potassium or sodium silicate, or mixtures thereof.

5. To the mixture of ground limestone with alkaline water-soluble silicate is added quicklime powder in a total ratio of: 1000 wt. parts by weight of finely ground limestone with potassium or sodium silicate according to Examples 1 and 2, 200 wt. parts of quicklime powder.

All mixtures of limestone with potassium or sodium silicate according to Examples 1-5, optionally with quicklime powder, are ready for use without further treatment. The amount of alkali silicate added to the ground limestone is controlled by the degree of heavy metal soil contamination. The ground alkaline silicate mixture of limestone shows a synergistic effect.

Claims (4)

A process for the disposal of heavy metals in soil by ground limestone, characterized in that limestone is admixed with at least one water-soluble alkali silicate in a weight ratio of from 100: 1 to 100: 5. The process of claim 1, wherein the mixture further comprises calcium oxide in an amount of from 50 g to 200 g per kg. 3. A method for producing a heavy metal neutralizing agent in a soil, comprising mixing at least one water-soluble silicate in a weight ratio of from 100: 1 to 100: 5 when grinding the limestone. Method according to claim 3, characterized in that the mixture is still added from 50 g to 200 g of calcium oxide per kg of mixture.