CS255678B1 - Method for decomposing phosphate glasses - Google Patents

Abstract

The method of decomposition of phosphate glasses containing silver ions, suitable for recovering silver from waste of these glasses, generated during their processing and usually contaminated with oily and resinous substances, is relatively simple and inexpensive, while the isolation of silver from the decomposition products is easy to perform, namely by treating the glass with a substance containing halide ions X" soluble in water, or with boric phosphate BPO^ and further with phosphoric acid H3PO4 or sulfuric acid H2SO4 and water H2O in the molar, or ionic ratio (X + BPO4) : Ag+ = 5 + 4.8, (H2SO4 + H3PO4) : PO3" = 3 + 2.5, (H2SO4 + + H3PO4) : H2O = 2 + 1.95, where Ag+ and PO3” indicate the content of silver and phosphate ions in decomposed glass.

Description

(54) Method of decomposition of phosphate glasses

The method of decomposition of phosphate glasses containing silver ions, suitable for recovering silver from waste of these glasses, generated during their processing and usually contaminated with oily and resinous substances, is relatively simple and inexpensive, while the isolation of silver from the decomposition products is easily carried out, namely by treating the glass with a substance containing halide ions X soluble in water, or with boric phosphate BPO^ and further with phosphoric acid H ₃ PO ₄ or sulfuric acid H ₂ SO ₄ ^and water H2O in the molar, or ionic ratio (X + BPO4) : Ag ⁺ = 5 + 4.8, (H2SO ₄ + H ₃ PO ₄ ) : PO ₃ = 3 + 2.5, (H ₂ SO ₄ + + H ₃ PO ₄ ) : H ₂ O = 2 + 1.95, where Ag ⁺ and

PO ₃ ” indicates the content of silver and phosphate ions in the decomposed glass.

The invention relates to a method for the decomposition of phosphate glasses containing silver, suitable for the recovery of silver from glass waste.

Phosphate or metaphosphate glasses containing silver ions Ag ⁺ have significant applications in ionizing radiation dosimetry. However, their chemical stability is somewhat lower than that of conventional silicate glasses.

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However, when the above mentioned glasses or their waste are deliberately decomposed for the purpose of obtaining silver, the decomposition products dissolved in the reagent used and adhering to the glass surface can significantly slow down the decomposition reactions. Etching in concentrated sulfuric or phosphoric acid alone, which is suitable for cleaning the surface of larger pieces of glass under certain circumstances, is usually unsuitable for fine waste because it is often accompanied by its sticking together.

Etching in aqueous and especially molten alkali hydroxides again results in the formation of fine silver which adheres to the surface of the decomposed glass and to the impurities which usually accompany it. Also the consumption of alkali hydroxide necessary for the complete decomposition of the glass is high because at an increased ratio of phosphate ions to hydroxyl ions in the solution the decomposition of the glass stops.

The above-mentioned shortcomings and difficulties are eliminated by the method of decomposition of phosphate glasses containing silver ions according to the invention, the essence of which lies in the fact that the glass is treated with a substance containing halide ions X* soluble in water, or with boric phosphate BPO^, and further with phosphoric or sulfuric acid H^SO^ and water in the molar, respectively ionic ratio (X~ + BPO ₄ ) : Ag ⁺ =5+4.8 (H ₂ SO ₄ + H ₃ PO ₄ ) : P0 ₃ =3+2.5 (H ₂ SO ₄ + H ₃ PO ₄ ) : H ₂ 0 = 2 + 1.95, where Ag and P0 ₃ denote the content of silver and phosphate ions in the decomposed glass.

The given ratios apply to phosphate glasses with the usual silver phosphate content.

AgPO,, i.e. in the molar range of 2 to 10 i. Above this range, the addition of BPO would need to ^be related to the content of _{P0 3} ^ions in the glass.

Boron phosphate and/or silver chloride formed at the relatively low water content mentioned by dissolving the glass in phosphoric or sulfuric acid coat the particles of the not yet decomposed glass and thus prevent them from sticking together. Therefore, decomposition can also take place at room temperature.

If the glass contains borate ions, borate phosphate is formed by the decomposition of the glass, and therefore the addition of this substance or halide ions can be quite low to prevent the glass particles from sticking together at the beginning of the decomposition. The time and temperature of the decomposition depend on the size of the glass particles and the concentration of phosphoric acid.

The method according to the invention can be used to decompose phosphate glass residues containing silver very simply and cheaply, while the isolation of silver from the decomposition products is also easy to perform.

Example 1

Waste containing 90% glass with a molar composition of 47% aluminum phosphate Al(PO ₃ > ₃ , % KPO ₃ , 25% silver phosphate AgPO 4S with a grain size below 0.3 mm, and also 10% mineral oil and substances of a resinous nature, was decomposed using the same mass amount of 85% phosphoric acid. If the resulting mixture was not stirred intensively, the glass separated at the bottom of the decomposed container, where its particles stuck together into a solid, practically indecomposable layer. The same result was also achieved when using waste that had been previously extracted with gasoline.

On the other hand, if sodium chloride was added according to the invention together with phosphoric acid in an amount corresponding to 3% by weight of the amount of waste used, the glass did not separate from the reaction mixture even after 48 hours. The reaction mixture was then diluted with 5 parts by volume of water and after the silver chloride AgCl and other insoluble residues had settled, the clear solution was decanted. The deposit was washed on a filter with a 10% ammonia solution and pure silver chloride was precipitated from the resulting silver amocomplex, also containing chloride ions, after the addition of nitric acid HN0 _3. Its yield corresponded to 97% of the silver contained in the initial glass waste. A similar result was achieved when sodium chloride was replaced by a double weight addition of boron triphosphate BPO^.

Example 2

176 g of ground glass waste with a molar composition of 28% lithium phosphate LiPO ₃ , 50% aluminum phosphate A1(PO ₃ ) ₃ , 4.4% silver phosphate AgPOj and 17.6% boron oxide Β ₃ Ο ₃ was decomposed using four times the mass amount of 60% sulfuric acid E^SO^. After mixing the acid and glass waste, unwanted sticking of waste particles regularly occurred, which in practice limited the processing of larger batches of waste, because it was not possible to mix them quickly throughout the entire volume.

The sticking was more pronounced at higher acid concentrations, at lower concentrations the decomposition lasted a disproportionately long time. In the case where, according to the invention, the waste was thoroughly mixed with 3 g of boron triphosphate BPO^ before mixing with sulfuric acid, the sticking did not occur and after 24 h of heating to 45 °C the decomposition of the glass was completed. After dilution with water to four times the volume, the clear solution was poured off and by precipitation with sodium iodide NaJ, silver iodide AgJ was obtained. The yield of silver iodide was 98% of the theoretical amount.

Claims (1)

SUBJECT OF THE INVENTION Method for decomposing silver ions containing silver ions, characterized in that the glass is treated with a water-soluble substance containing halide ions X and / or boron phosphate BPO 2 and further with phosphoric acid H 3 PO 4 or sulfuric H 2 SO 4 and water in molar and ionic ratios ( X ^- + BPO ₄ ): Ag ⁺ = 5 '+ 4.8, (H ₂ SO ₄ + H ₃ PO ₄ ): Ρθ | ~ = 3 + 2.5 a (H ₂ SO ₄ + H ₃ PO ₄ ) : H ₂ O = 2 + 1.95, where Ag ⁺ denotes the content of silver ions and PO ₃ denotes the content of phosphate ions in the decomposed glass.