GB1585198A

GB1585198A - Process for the decomposition of metal silicates

Info

Publication number: GB1585198A
Application number: GB2379577A
Authority: GB
Original assignee: Vereinigte Aluminium Werke AG
Current assignee: Vereinigte Aluminium Werke AG
Priority date: 1976-06-05
Filing date: 1977-06-03
Publication date: 1981-02-25
Also published as: DE2625532B2; IT1083410B; DE2625532C3; FR2353645A1; DE2625532A1; FR2353645B1

Description

(54) PROCESS FOR THE DECOMPOSITION OF METAL SILICATES (71) We, VEREINIGTE ALUMINIUM-WERKE AKTIENGESELLSCHAFT, a body corporate organized under the laws-of the German Federal Republic, of D-5300 Bonn 1, Gerichtsweg 48, Postfach 2468, German Federal Republic, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for treating metal silicate containing slag or ash produced by the burning of coal to decompose metal silicate contained in the slag or ash.

Salts of silicic acid with one or more different cations which either occur in nature or are produced artificially are frequently insoluble or very sparingly soluble in neutral or acid media. Their treatment with basic solutions leads to the formation of, in most cases, water-soluble salts of silicic acid and the base used. In order to dissolve the metal ion(s) in acids, the silicate-containing substance must be ground exceptionally finely and/or heated to a specific temperature in order to achieve the desired dissolving of the cationic metal portion.

According to the present invention there is provided a process for treating metal silicate containing slag or ash produced by the burning of coal, wherein the slag or ash is heated above its melting point and the melt is quenched to form an amorphous product, said amorphous product being obtained in a finely divided state by dispersion during quenching and/or by subsequent mechanical commination, and thereafter decomposing metal silicate in the amorphous product with acid.

It has surprisingly been found that the dissolving speed of monometallic or polymetallic silicates in acids can be considerably increased when the slags or ashes are heated above their melting point and the resulting melts are cooled sufficiently rapidly that the cooled product is amorphous. It is advantageous to accelerate this cooling by forming as fine as possible a dispersion of the silicate melt and thus to obtain a very finely divided material which offers a large a surface as possible to the acid attack, for example by passing the molten slag or ash with steam or air through a nozzle or by quenching the molten slag or ash with a liquid.

The solidified or quenched silicate-containing material is fragile and brittle, so that it can readily be further comminuted; the energy expenditure required for this purpose is substantially less in comparison with non-remelted and unquenched material.

The residue obtained during acid decomposition which consists substantially of silicic acid or acid-insoluble metal silicates proves as a rule to be very surface-active and can, accordingly, be further processed, in manner known per se, e.g. by reaction with bases or metal oxides, particularly alkali metal oxides or alkaline earth metal oxides, in aqueous solution or aqueous dispersion, to give valuable products, so that also the anionic compoment of the decomposed metal silicate can be recovered for processing.

If desired the slag or ash may be heated by direct combustion of the coal from which the slag or ash is formed. In many varieties of coal, alumina and silicic acid are contained as principal ash constituents. In addition, the oxides of iron, titanium, manganese, vanadium, zinc and phosphorus may occur and further elements may be present in trace amounts. If desired a metal silicate may be added to the coal. Both the composition of the coal ash and its behaviour in regard to softening, melting and flow can be influenced by suitable additives, the choice of which can be left to the skilled man. For the determination of the ash-fusion behaviour, attention is drawn to DIN (German Standard Specification) 51 730.

Since in many couritries today the generation of heat from coal, particularly in the case of the use of high-ash coal with low ash-fusion point, is effected by chamber furnaces or cyclone fusion furnaces and the slag, corresponding to the size of the power stations, is obtained in very considerable amounts, the present process is of particular interest for the utilisation of the slag obtained.

In one form of the present process, the slag flowing out of a fusion furnace is cooled rapidly and, simultaneously or subsequently, subjected to acid decomposition.

The metals extracted are, in manner known per se, isolated from the acid decomposition solutions and, where appropriate, further processed.

The invention will now be illustrated by the following Example: A coal ash waste product from a processing plant contained SiO2 CaO Al203 Fe2O3 TiO2 K2O 56.2% 2.3% 26.2% 10.4% 0.9% 4.0% It was heated to about 1 450"C. and quenched with cold water. The resulting brittle granules were amorphous and of a size of about 2 to 5 mm. were subsequently ground to -100 mesh (Tyler standard). 50 kg. of the ground material were boiled under reflux at about 108 C. with azeotropic (22% by weight HC1) hydrochloric acid, the ratio of liquid to solid being 5 : 1.

After 4 hours' reaction time, the readily filterable solid residue was separated off, washed and dried until weight constancy.

The weight of the residue was 30.15 kg. and the residue had the following composition Fe203 TiO2 CaO Al203 K2O 0.58% 0.70% 0.15% 1.4% 0.15% The remainder was SiO2.

Accordingly, there have dissolved Fe2O3 TiO2 CaO Al203 K2O 96.6% 53.3% - 96.8% 97.6% From an equally finely ground, but unquenched, comparative sample, there were dissolved under the conditions Fe203 TiO2 CaO Al203 K2O 32.10% 10.2% - 31.30% 44.4% WHAT WE CLAIM IS: 1. A process for treating metal silicate containing slag or ash produced by the burning of coal, wherein the slag or ash is heated above its melting point and the melt is quenched to form an amorphous product, said amorphous product being obtained in a finely divided state by dispersion during quenching and/or by subsequently mechanical commination, and thereafter decomposing metal silicate in the amorphous product with acid.

2. A process as claimed in Claim 1, wherein the melt is cooled by quenching it in liquid.

3. A process as claimed in Claim 2, wherein the melt is quenched in an aqueous liquid.

4. A process as claimed in Claim 2 or 3, wherein the melt is quenched in an acid.

5. A process as claimed in Claim 2, 3 or 4, wherein the melt is sprayed through a nozzle with steam and/or air.

6. A process as claimed in any one of the preceding claims, wherein the slag or ash is heated by direct combustion of admixed fuel.

7. A process as claimed in any one of Claims 1 to 5, wherein the slag or ash is heated by direct combustion of the coal from which the said slag or ash is formed.

8. A process as claimed in Claim 7, wherein the coal has a low ash-fusion point.

9. A process as claimed in Claim 7 or 8, wherein substances are added to the coal which lower the ash-fusion point thereof.

10. A process as claimed in anyone of Claims 7, 8 or 9 wherein a metal silicate is added to the coal.

11. A process as claimed in anyone of Claims 7 to 10 wherein slag granulate from coal

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Since in many couritries today the generation of heat from coal, particularly in the case of the use of high-ash coal with low ash-fusion point, is effected by chamber furnaces or cyclone fusion furnaces and the slag, corresponding to the size of the power stations, is obtained in very considerable amounts, the present process is of particular interest for the utilisation of the slag obtained. In one form of the present process, the slag flowing out of a fusion furnace is cooled rapidly and, simultaneously or subsequently, subjected to acid decomposition. The metals extracted are, in manner known per se, isolated from the acid decomposition solutions and, where appropriate, further processed. The invention will now be illustrated by the following Example: A coal ash waste product from a processing plant contained SiO2 CaO Al203 Fe2O3 TiO2 K2O 56.2% 2.3% 26.2% 10.4% 0.9% 4.0% It was heated to about 1 450"C. and quenched with cold water. The resulting brittle granules were amorphous and of a size of about 2 to 5 mm. were subsequently ground to -100 mesh (Tyler standard). 50 kg. of the ground material were boiled under reflux at about 108 C. with azeotropic (22% by weight HC1) hydrochloric acid, the ratio of liquid to solid being 5 : 1. After 4 hours' reaction time, the readily filterable solid residue was separated off, washed and dried until weight constancy. The weight of the residue was 30.15 kg. and the residue had the following composition Fe203 TiO2 CaO Al203 K2O 0.58% 0.70% 0.15% 1.4% 0.15% The remainder was SiO2. Accordingly, there have dissolved Fe2O3 TiO2 CaO Al203 K2O 96.6% 53.3% - 96.8% 97.6% From an equally finely ground, but unquenched, comparative sample, there were dissolved under the conditions Fe203 TiO2 CaO Al203 K2O 32.10% 10.2% - 31.30% 44.4% WHAT WE CLAIM IS:

1. A process for treating metal silicate containing slag or ash produced by the burning of coal, wherein the slag or ash is heated above its melting point and the melt is quenched to form an amorphous product, said amorphous product being obtained in a finely divided state by dispersion during quenching and/or by subsequently mechanical commination, and thereafter decomposing metal silicate in the amorphous product with acid.

fusion furnaces is used.

12. A process for the decomposition of a metal silicate with acid in accordance with Claim 1 substantially as hereinbefore described in the foregoing Example.