GB2170496A

GB2170496A - Vitrification of inorganic materials

Info

Publication number: GB2170496A
Application number: GB08502884A
Authority: GB
Inventors: David Roberts; Henry Stuart Johnson
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-02-05
Filing date: 1985-02-05
Publication date: 1986-08-06
Also published as: GB8502884D0

Abstract

In the conversion of a toxic inorganic material into a glass an aqueous solution or sludge of the inorganic material is agitated with anhydrous sodium carbonate or other anhydrous material in super-stoichiometric amount to form a dry flowable powder that is melted with other glass-making materials.

Description

SPECIFICATION Vitrification of inorganic materials This invention relates to a process for converting aqueous solutions of toxic inorganic materials into nontoxic glass for safe disposal.

The chemical industry produces aqueous sludges of silica and alumina based catalysts containing heavy metals. These toxic sludges present a safe disposal problem. A typical such catalyst sludge contains 50-60% water, the balance being organic residues and spent catalyst. The inorganic materials present can in principle be converted into a glass that is stable against heavy metal leaching, and the -resultant glass can then be disposed of in a safe location that may even be a landfill site. But the conversion of these sludges into glass presents the problems that (a) the sludge needs to be converted into a form in which it is compatible with other glass-making materials, and (b) the comparatively high concentrations of organic material and water present can present problems in the control of the glass chemistry.

We have found that spent catalyst sludges can be converted by the addition of anhydrous sodium carbonate into a dry handleable powder which can be further converted by melting with glass-making materials into a homogeneous glass such as a soda-linre glass. Other anhydrous materials that chemically combine with water and may be used include sodium sulphate, borax, calcium oxide, a sodium silicate such as sodium metasilicate and magnesium sulphate. Materials that physically absorb water may also be used.

Broadly stated the invention provides a method of converting a toxic inorganic material into a glass, comprising agitating an aqueous solution or sludge of the inorganic material with an anhydrous material that physically or chemically absorbs water and is compatible with glass making in a super-stoichiomet ric amount so that the sludge is converted into a dry flowable powder; and melting the powder with glass-making materials to form a glass.

Sodium carbonate is the preferred anhydrous material and the amount to be added will typically be 50 100 parts per 100 parts by weight of the sludge. The sludge and sodium carbonate are simply stirred together at a temperature below 32 degrees C to convert the sodium carbonate into its decahydrate. Addition of sodium carbonate in amounts above the stoichiometric amount results in conversion of the sludge into a dry free-flowing powder.

Glass may be made from the powder in amounts of 10-40% of the total weight of glass-making mate rial, but it may be desirable to agitate the material e.g. by bubbling in order to produce a homogeneous material.

The invention will now be described with reference to the following examples: Example 1 A sludge containing water, organic residues and a catalyst containing heavy metals and silica was treated with sodium carbonate in the amounts and with the results indicated in Table 1 below: TABLE 1 Sodium carbonate drying trials Sludge Sodium Test No. Wt Carbonate Remarks Wt 1 100 40 Formed powder but there is a residual stickiness.

2 100 60 Free-flowing dry powder.

3 100 80 As 2.

The sludge of Test No.3 was used to make 40g pot melts as indicated in Table 2 and with the results there quoted. Although inhomogeneity was observed in many of the melts, this is believed to have been due to the absence of stirring, and it is believed that this inhomogeneity would not be observed using a larger-scale melter with an air bubbling system to stir the glass and oxidise materials present. The analyses of the glasses produced are as shown in Table 3.

TABLE 2 Melting trials

r '0 a) a) 0 a 0 0 a) Co .

~ Co a) Co 0 Remarks U cutj m z s = = - - = Viscous glass much undesolved material 2 - 50.7 - 67.5 17.7 0.74 - - - 3 - 50.7 - 67.5 17.7 0.925 - - - ) Mainly glass but significant streakiness - no significant difference o, 50.7 : 67.5 17.7 1.11 E = with changes in nitrate 5 - 50.7 - 67.5 17.7 3.5 - - - > i 67.5 17.7 - 2.7 3 ZZ < Q < < < m 7 - 50.7 - 67.5 17.7 - 8.1 - - - Noticeably better but still streaking y3eq 9 epos , , , , , , . , N N N t0 00 10 - 28.0 - 37.3 9.8 - - - - 25 Good glass but streaky, as 7 11 - 26.1 - 34.8 9.1 - - - - 25 As7 12 - 26.1 - 34.8 9.1 - 1.4 - - 25 As7 8-1 3sal alln3 o (a) The composition of this was 100 g sludge, 40 g sodium carbonate.

t N gON9N , . X | AUOJSRU117 N b b b b b b ueS u) uz uz u: u: uz S X oo ao oo cn P e 1 o gOveN > (e) epoS X N N N N oN /a6pnls o co CD CD c0 , S IS) ID S U) U) U) . N N N CD .~ a) aDpnlS g s E N t t S O N co N Cn t o alqel TABLE 3 Glass composition Oxides % WIW Melt Number Sio2 Na2O CaO Sub203 Uo2 MoO At203 1 28.0 54.5 - 15.4 1.7 0.5 2 76.8 9.4 11.1 2.4 0.26 0.08 3 76.7 9.5 11.1 2.4 0.26 0.08 4 76.7 9.5 11.1 2.4 0.26 0.08 5 76.0 10.4 11.0 2.3 0.25 0.08 6 76.0 10.3 11.0 2.3 0.25 0.08 7 74.0 12.7 10.7 2.3 0.25 0.08 8 73.0 13.8 10.5 2.3 0.25 0.08 9 73.2 13.7 10.5 1.15 0.13 0.04 0.5 10 75.7 10.5 11.0 1.7 0.18 0.06 0.2 11 75.6 10.6 11.0 1.7 0.18 0.06 0.2 12 75.4 11.4 10.9 1.6 0.17 0.06 0.2 13 75.5 11.6 11.1 1.07 0.15 0.03 0.6 14 74.5 13.1 11.2 0.32 0.04 0.01 0.87 Example 2 A spent catalyst sludge or so-called "pond sludge" having the composition given in Table 4 was conditioned by adding anhydrous sodium carbonate to the sludge, whilst stirring, at a temperature below 32"C. The formation of sodium carbonate decahydrate absorbed all the water - and by increasing the amount of carbonate, sufficient of the organic liquids as well. The resultant dry powder was used a sodium source to produce a conventional soda-lime glass. The test was intended to demonstrate that the sludge could be totally absorbed into a finished glass and that the high level of organic materials did not interfere with glass making. After early attempts where some of the metals were not absorbed, a mix and melting schedule were found which gave a homogeneous black glass.

TABLE 4 Pond sludge composition Uranium % wiz 0.59 Molybdenum % wiz 0.18 Antimony %w/w 5.1 Free Cyanide ppm 0.2 Total Cyanide % wiz 0.038 AMM N2 %w/w 0.97 Ash %w/w 17.0 Water % w/w 63.0 Orgs + AMM Sulphate % 20.0

Claims

1. A method of converting a toxic inorganic material into a glass, comprising: agitating an aqueous solution or sludge of the inorganic material with an anhydrous material that physically or chemically absorbs water and is compatible with glass making in a super-stoichiometric amount so that the sludge is converted into a dry flowable powder; and melting the powder with glass-making materials to form a glass.

2. A process according to claim 1, wherein the anhydrous material is sodium sulphate, borax, calcium oxide, sodium silicate or magnesium sulphate or a xeolite.

3. A process according to claim 1, wherein the anhydrous material is sodium carbonate.

4. A process according to claim 3, wherein the anhydrous sodium carbonate is added in an amount of 50-100 parts by weight per 100 parts by weight of solution or sludge.

5. A process according to claim 3 or 4, wherein the solution or sludge is maintained at a temperature below 32 degrees C during conversion to the dry powder.

6. A process according to any preceding claim wherein the dry powder is added in an amount of 1040% by weight based on the total weight of the glass-making materials.

7. A process according to any preceding claim, wherein the glass-making materials include sand and limestone.

8. A process according to any preceding claim, wherein the catalyst is-a heavy metal supported on silica or alumina and is present in the sludge together with organic materials.