DE2236223A1 - Porous material contg powdered silver - esp for adsorption of halogens - Google Patents

Abstract

Material esp suitable for adsorption of radioactive iodine is produced by subjecting to shearing action a silicic acid hydrogel (contg. 90-45 wt. %), opt. in mixture with a water-contg alumina gel and/or silicate(s) of a di and/or trivalent metal, whilst admixing a reducible silver cpd. (pref. Ag NO3) and reducing it (pref during the kneading) pref. with hydrazine to metallic Ag; then drying the product at a temp above 80 degrees C; the product can be washed before or after drying to remove excess hydrazine and other impurities. Fine distribution of silver is achieved so that its content can be reduced compared with known similar products.

Description

Carrier loaded with silver metal with pore radius distribution curve and its method of manufacture.

The invention is based on a predominantly silicon dioxide constructed and impregnated with metallic silver material with adsorption properties from liquid or liquid phase. The material produced according to the invention is suitable among other purposes, especially for the removal of halogens, especially of radioactive iodine It is known to incorporate or silver in conventional carriers Soak silica gels with a silver salt solution, which is then poured into a Increase in temperature decomposable boron is transferred and then the metallic Silver is produced through a heating process.

Depending on the concentration of the silver salt used However, this usually creates a compact silo layer within the pores and Voids When comparing, however, it was found that the reactivity increases with decreasing particle size of the silver particles.

It was therefore natural to create a product that can be maintained the adsorption properties of the carrier metallic silver in finest distribution contains.

According to the invention, such a material is obtained by means of that a silica hydrogel alone or in a mixture with hydrous aluminum oxide gel and / or silicates of the bivalent and / or trivalent metals, the water content of the silica hydrogel is between 90 and 45% by weight, the influence of shear forces subjugated, treated with a reducible silver compound and this is preferred during the kneading process by a suitable reducing agent into metallic Silver transfers'd the product at temperatures above 80 ° C and it dries if necessary freed from impurities by washing before or after the drying process.

While numerous variations are possible, the cleanest exists Method therein, as a reducible silver compound, silver nitrate and as a reducing agent Use hydrazine in the commercial form as an approx. 24% aqueous solution.

This takes place within seconds with the escape of nitrogen the clean reduction is already taking place. Annoying impurities are not left behind, the required small excess of hydrazine can either be removed by washing or it is expelled without being washed out when drying at temperatures above 130 ° C. The latter way of working is the most convenient and cleanest.

The type of carrier body can vary depending on its intended use vary by adding appropriate amounts of boric acid after mass reduction and / or borates and / or ammonium carbonate, ammonium hydrogen carbonate or ammonium carbamate or add one of these substances alone.

The dry product is obtained in a form that is easy to shred but if necessary with a binding agent according to DBP ...

(P 1 944 879) in a known manner, e.g. with a granulator, deformed will.

The silver content can be between 0.1 and 50% by weight, preferably between 3 and 9% by weight.

Materials with a relatively low content of silver can be used because of the large surface area of the carrier can also be used for purposes in which the wants to exploit the oligodynamic effect of metallic silver, e.g. in keeping the freshness of cut plants, toothpaste and similar uses.

Examples 1.) 5 kg of silica hydrogel with 25% by weight of SiO2 were used crushed in the Z kneader and then a solution of 265 g of silver nitrate in 800 ml of water are added.

After mixing for 5 minutes, 325 grams of hydrazine were in shape added to the commercial 24% solution. The reduction was in about 40 seconds Then 12 g of ammonium carbonate were added and a further 5 Kneaded minutes. The product was dried in a drying cabinet at 1450C. One washout was not required.

2.) Experiment 1 was repeated analogously, but 4 kg of silica hydrogel were used with 25.5% SiO2 and 1 kg aluminum hydroxide gel (filter cake) with 19% solid matter by weight After the reduction, 15 g of sodium tetaborate were added, which was washed out after the drying process.

3.) Experiment 2 was repeated with the modification that the alumina hydrate was replaced by aluminum metasilicate (filter cake) with 21% by weight of solids. Washing was not required.

4) 5 kg of silica hydrogel with 25.5% by weight of SiO2 were in the Z kneader crushed and mixed with a suspension of 230 g of silver oxide in 500 ml of water. After the kneading process lasted 15 minutes, 130 g of hydrazine, i.e. a Excess, added in the form described above. After a further 10 minutes the material was removed and dried in a drying cabinet at 145 ° C. The finished product contained no more hydrazine. The metal distribution was less fine than in the examples 1 - 3.

Claims (7)

Patent claims: 1. Process for the production of a metallic silver containing Material with a pore radius distribution curve, characterized in that a silica hydrogel alone or in combination with aqueous aluminum oxide gel and / or silicates of the 2 - and / or 3 - valent metals, whereby the water content of the silicic acid hydrogel Between 90 and 45 wt.% Is subjected to the influence of shear forces, with a added reducible silver compound and this preferably during the kneading process converted into metallic silver by a suitable reducing agent, the product dries at temperatures above 80 0C and if necessary by washing impurities freed before or after the drying process. 2. The method according to claim 1, characterized in that as a reducible Silver compound the nitrate is used. 3, method according to claim 1, characterized in that as a reducing agent Hydrazine is used. 4. Process according to claims 1-3, characterized in that the reduction to metallic silver is carried out during the kneading process. 5. Process according to Claims 1 to 4, characterized in that is worked with an excess of hydrazine. 6. The method according to claim 5, characterized in that the drying of the material is made at a temperature above the boiling point of hydrazine hydrate lies. 7. Carrier material loaded with metallic silver and having a surface over 100 m² / g and pore radius distribution curve as well as a ratio of the adsorption from water vapor at 20% relative humidity to that at 40 * relative humidity. of equal to or greater than 1: 1.3 (Method: Wacks, FATS. SOAPS . PAINTING PRODUCTS. THE FOOD INDUSTRY 73, 21-24 (1971).