Composition to Absorb Mercury

The invention relates to a composition able to absorb mercury vapour and to suppress formation of the vapour and to a method of absorbing and suppressing mercury vapour using the composition.

Liquid mercury is used in industry, hospitals, laboratories and dental offices. Mercury is a substance of considerable toxicity and emission of mercury vapour may occur from accidental spilling or volatilization. During the process of amalgamation or other operations with mercury-rich substances, mercury liquid or mercury-rich materials will release mercury vapour at room temperature and high concentrations can occur. Inhalation of low levels of mercury vapour over years can produce symptoms of brain and neural disorders. The adverse affects of mercury are demonstrated by the extreme symptoms of brain disorder and body malfunction in people eating fish caught in waters polluted by mercury. The worst instances appear to have been in Japan but there have also been reports of cases in Northern Ontario and Quebec. Recent reports also show that dentists over age 50 have neurological symptoms, and female dentists and dental assistants may have obstetric problems due to their exposure to mercury and its vapours. The perinatal and neonatal effects of the mother's exposure to mercury vapour are a major concern.

At present two of the most important means of cleaning up mercury spills include powdered sulphur and iodine impregnated on charcoal. However both of these materials have the disadvantages that they require considerable time (days rather than hours) to react with the mercury. It is also necessary to maintain contact of the powder and the mercury indefinitely and, of course, there is the general messiness of both sulphur and charcoal, which are either fine powders or can easily form fine powders. Since charcoal is also black a mercury spill on colored carpets in dental offices for example, cannot easily be cleaned up by spreading charcoal and maintaining a charcoal layer in contact with the spilled mercury.

In the prior art copper iodide has been described as a mercury contamination indicator in U.S. Pat. No. 4,226,600 to Seidenberger. Zhang in the journal Huanjing Kexue of the People's Republic of China, Volume 1, issue 1, pages 29-34 (1980), describes a method for recovering mercury dissolved in dilute salt solutions using silver thiosulphate-treated activated carbon. But the use of silver in a mercury removal device is prohibitively expensive.

Irkhin et al. in Russian Pat. No. 688,440 describe the use of alkaline sodium thiosulphate for the removal of dissolved mercury from the effluent of plants manufacturing organic chemicals. Romanian Pat. No. 63,241 to Zeana et al. describes the use of sodium thiosulphate in calcium chloride-containing Solvay process wastes.

U.S. Pat. No. 4,094,777 to Sugier describes a process for removing mercury from a gas or liquid by absorption on a solid mass that contains copper sulphides. Kurikami, in U.S. Pat. No. 3,875,287, describes a method of removing mercury from highly concentrated sulphuric acid by adding iodides to precipitate the mercury as mercuric iodide.

Canadian Pat. No. 1,203,525 describes a composition to absorb mercury vapour and to suppress mercury vapour. The composition comprises a polyhydric alcohol as a carrier liquid, copper ions and thiosulphate ions. However thiosulphate containing compositions have three major drawbacks:

1. Slow release of sulphur dioxide during prolonged storage.

2. Wasted reagents as the composition is a suspension, not a solution.

3. Colour change to black in some cases during prolonged storage.

The present invention provides compositions that do not suffer from the disadvantages of thiosulphate-containing formulations.

Accordingly the present invention provides a composition to absorb mercury vapour and to suppress mercury vapour, the composition comprising (a) an iodide; and (b) a polyhydric alcohol.

The iodide may be selected from ammonium iodide, an alkaline metal iodide, ethylenediamine dihydroiodide and cuprous iodide.

The polyhydric alcohol may, for example, be selected from propylene glycol, glycerol and dipropylene glycol. Generally speaking the polyhydric alcohol would be selected for its low toxicity and ability to dissolve iodine.

In a preferred embodiment the composition includes a Lewis acid. Preferred Lewis acids are those selected from ammonium chloride, ferric chloride, aluminum chloride, stannous chloride, zinc bromide and ferric sulphate.

The iodide may be formed in situ by reacting hydrogen iodide with a basic compound containing the desired cation eg. cuprous carbonate to form cuprous iodide.

In a further aspect the present invention provides a method of absorbing mercury comprising applying to the source of the mercury a composition comprising (a) an iodide; and (b) a polyhydric alcohol.

The invention is further illustrated in the following Examples which show the performance of various combinations of ingredients to effect the cleanup and vapour suppression of mercury.

1. 2 mL of each test liquid was used to coat the bottom inside surface of a 50 mL Erlenmeyer flask.

2. Approximately 0.2 g (1 drop) liquid mercury was dropped into the test liquid. The test liquid meniscus was just sufficient to coat the mercury droplet.

3. The mercury vapour level 1-2 cm above the test liquid surface was measured using a Perkin Elmer Coleman Mercury Analyzer System (i.e. cold vapour atomic absorption).

4. Mercury vapour levels above the test liquid were measured at various time intervals and were expressed in micrograms mercury per cubic meter of air within the flask.

The results achieved are set out in Table 1. Efficiency of Mercury Absorbing Mixtures Mercury Absorber % Composition by Weight Mercury Solution Mercury Vapour Levels in .mu.g/m.sup.3 Above Absorber Sodium Iodide or Mercury Absorber at Various Times # Water Thiosulphate Polyol Salt** Lewis Acid Other Components Suspension 0 min 15 min 30 min 1 hr 1 day 1 51.26 1.84 PG-40 KI-1.91 0 CuSO.sub.4 5H.sub.2 O--2.57.CaCl.sub. 2 --2.42 Suspension 33 23 128 NM 8 2 0 0 PG-99.9 CI-0.10 0 0 Suspension 58 297 88 NM 371 3 0 0 PG-95.0 0 NH.sub.4 Cl-5.00 0 Solution 30 41 67 NM 2,300. 4 0 0 PG-98.5 ED-1.50 0 0 Solution 26 0 1 1 NM 5 0 0 PG-99.58 ED-0.16 0 CuSO.sub.4 .5H.sub. 2 O--.26 Suspension 8 0 0 0 0 6 0 0 PG-93.18 ED-1.82 NH.sub.4 Cl-5.00 0 Solution 27 14 19 15 0 7 0 0 PG-95.00 AI-5.00 0 0 Solution 26 25 14 13 11 8 0 0 PG-93.39 ED-1.50 NH.sub.4 Cl-5.00 CuSO.sub.4 .5H.sub. 2 O--0.01 Solution 24 0 0 NM 0 CI-0.10 9 0 0 PG-93.18 ED-1.82 FeCl.sub.3 -5.00 0 Solution 9 0 0 0 0 10 0 0 PG-93.18 ED-1.82 SnCl.sub.2 -5.00 0 Solution 19 4 0 0 0 11 0 0 PG-93.18 ED-1.82 AlCl.sub.3 -5.00 0 Solution 26 0 0 0 0 12 0 0 PG-93.08 ED-1.82 ZnBr.sub.2 -5.00 0 Suspension 16 0 0 0 0 CI-0.1 13 0 0 PG-96.0 ED-2.00 FeCl.sub.3 -2.00 0 Solution 3 0 0 0 0 14 0 0 DPG-97.7 AI-2.00 FeCl.sub.3 -0.10 0 Solution 24 0 0 0 0 15 0 0 DPG-97.9 KI-2.00 AlCl.sub.3 -0.10 0 Solution 23 0 0 0 0 16 0 0 DPG-97.9 AI-2.00 AlCl.sub.3 -0.10 0 Solution 25 0 0 0 0 17 98.5 0 0 KI-1.50 0 0 Solution 71 2000 0 0 71 18 49.25 0 PG-49.25 KI-1.50 0 0 Solution 22 0 0 0 7 19 98.5 0 0 ED-1.50 0 0 Solution 19 900 26 71 1500 20 49.25 0 PG-49.25 ED-1.50 0 0 Solution 25 0 0 18 0 21 0 0 DPG-97.9 ED-2.00 Fe.sub.2 (SO.sub.4).sub.3 -0.01 0 Suspension 27 4 3 1 0 22 0 0 G-97.9 AI-2.00 AlCl.sub.3 -0.10 0 Solution 132 17 4 3 0 23 5.00 0 DPG-92.9 AI-2.00 AlCl.sub.3 -0.10 0 Solution 23 0 0 0 0 *PG propylene glycerol, G--glycol, DPG dipropylene glycol **KI potassium iodide, AI ammonium iodide, CI copper iodide, ED ethylenediamine dihydriodide (AJAY Chemicals Inc, Powder Springs, Florida ***NM not measured

Results show that mercury absorbing solutions containing an iodide salt, Lewis acid and a polyol are superior to solutions lacking any of these components even though some two component formulations, for example ammonium iodide and polyethylene glycol and ethylenediamine dihydroiodide with polypropylene glycol, will produce satisfactory results. These two last formulations are, it should be emphasized, superior to prior art formulations containing thiosulphate ion viewed from the point of view of speed of action with mercury, ease of formulation and lack of sulphur dioxide formation.

It is believed that the compositions according to the present invention become active on exposure to air and light by forming free iodine, which reacts rapidly with mercury. Polyols have low vapour pressures, coat mercury well and are excellent solvents for the active reagents, including the iodine produced in situ.

The Lewis acid is believed to stimulate the dissociation of the iodide to free iodine.

As indicated above, large numbers of polyols are appropriate but, in general, the compounds that will be chosen are those having least toxicity. The information concerning the solubility of the iodides in the polyhydric alcohol and of iodine in polyhydric alcohols can be found in Solubilities of Inorganic and Metal Organic Compound by Seidell, revised by Linke, 4th edition, volume 1, 1958 published by the American Chemical Society, pages 1267 and 1268.