Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
1998-06-22
2001-04-24
Warden, Jill (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C423S101000, C210S914000
Reexamination Certificate
active
06221128
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to purification and clarification of effluents. More particularly, the present invention pertains to the recovery of mercury from mercury-containing effluent. Even more particularly, the present invention concerns the recovery and removal of elemental mercury from mercury salt-containing effluents.
2. Prior Art
As is known to those skilled in the art to which the present invention pertains, mercury is a highly poisonous element the presence of which in water, either in an elemental or combined state, creates an environmentally hazardous situation. Yet, mercury is a highly valued commercial compound deployed in a multitude of situations, e.g. photography, production of caustic soda, clinical laboratories, etc. Thus, the disposal of spent mercury is an issue which needs to be addressed continuously in a commercial environment since spent mercury is, today, deposited in land fills or otherwise disposed of in potentially hazardous modes.
The present invention, as detailed below, provides a method for recovering elemental mercury from effluents in an efficient manner and which permits substantially total recovery therefrom.
SUMMARY OF THE INVENTION
The process is carried out, preferably, at room temperature under normal ambient conditions. Usually, the aluminum is introduced as sheets or foil which is added to the effluent with stirring at about 10 to about 200 rpm. The aluminum is introduced in molar excess amounts ranging from about 1.5 to about 2.0 molar excess per anion in the mercury-containing salt. Usually, the reaction will be complete in about 12 hours. Subsequent post-treatment of the effluent may be effected to remove trace amounts of mercury remaining in the effluent.
For a more complete understanding of the present invention reference is made to the following detailed description and accompanying examples.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As noted above, in accordance with the present invention cationic mercury is removed from an effluent by a reaction which enables the precipitation of elemental mercury therefrom. The present invention more particularly removes mercury chloride and other mercury salts such as mercury sulfate, mercury acetate, mercury nitrate and the like from such mercury salt-containing effluent by the precipitation of mercury therefrom.
The present invention is achieved by introducing aluminum into mercury salt-containing effluent to cause the precipitation therefrom of elemental mercury. The aluminum reacts with the mercury salt to free the mercury, as described below. The mercury, precipitates out of the water, as elemental mercury and is recovered therefrom.
In practicing the present invention, the aluminum is introduced into the solution in any convenient form and, preferably, as aluminum foil. Aluminum foil is of the type which is well-known and commercially available and may be of any suitable grade and suitable thickness including domestic or consumer grade as well as thin, industrial aluminum foil.
Preferably, and in order to provide sufficient surface area for the reaction between the aluminum and the mercury-containing salt, minute pieces of the foil are introduced into the aqueous effluent. Preferably, the minute pieces have a minimize size of from about 1 to about 2 cm
2
. Of course, it is to be understood that the size of the aluminum foil pieces is not critical hereto only that there be sufficient amounts thereof to provide adequate surface area for the reaction to proceed.
The process is carried out, preferably, at room temperature and pressure, under normal ambient conditions. Typically, the mercury salt-containing effluent -solution has the aluminum foil added thereto with stirring. Typically, stirring will take place at from about 10 rpm to about 200 rpm, and, preferably, from about 25 rpm to about 100 rpm depending on the volume of water to be treated.
Ordinarily, and, again, depending on the quantity of water to be treated the reaction will proceed and be completed in a time period ranging from about one to about 12 hours. The amount of aluminum to be added to the waste water is in excess of stochiometric requirements so that the amount of available aluminum for reaction with the mercury salt is in excess of that which is required under stochiometric conditions. Typically, generally from about 1.5 to about 2.0 molar excess amounts of aluminum is present per anion in the mercury-containing salt.
In carrying out the reaction, the mercury precipitates out from a reaction vessel, as elemental mercury, which after decanting, can be recovered and washed several times. It is contemplated that by practicing the present invention that at least 99.9 percent of mercury present in any effluent as a salt can be recovered, if sufficient aluminum foil is added thereto.
The present invention is contemplated as being useful in connection with any effluent which contains a mercury salt and has particular utility in the removal and recovery of mercury from B-5 fixatives, PVA fixative, Schaudian's fixative, as well as from environmental contaminant containing bodies such as bodies of water and soil or other sources containing mercury chloride in the mercuric form. However, the present invention will also be useful with mercurous forms of the cation, as denoted hereinabove.
Although not wishing to be bound by any theory it appears that when the aluminum is added to the mercury salt containing water there is formed mercury-aluminum amalgam which frees the anionic ion of the mercury salt, and which remains in the water phase.
The mercury-aluminum amalgam, itself, appears to decompose into elemental mercury, aluminum hydroxide and aluminum oxide in the effluent. The aluminum being an electron donor donates its electrons to the mercury ions, as measured by the electromotive forces, to form the elemental mercury. Moreover, the thus formed aluminum ion reacts with the water to form the hydroxide and oxide in solution. Thus, within the effluent, upon introduction of the aluminum, elemental mercury and a mercury-aluminum oxide are being formed. As the reaction proceeds to final, all of the aluminum is consumed.
It appears that there is an equilibrium reaction in the effluent as follows:
where there exists about 0.003%, by weight, of amalgam and about 99.997% of elemental mercury.
Thus, as the reaction proceeds the elemental mercury precipitates out of solution.
It should be noted that the time for the reaction to proceed can be accelerated by carbonyl addition to the effluent such as by aldehyde or ketone addition. Suitable aldehydes include, for example, formaldehyde, acetaldehyde, propionaldehyde, and so forth, as well as mixtures thereof. Suitable keatones include, for example, acetone, methyl ethyl ketone, ethyl ketone, and so forth, as well as mixtures thereof
Generally, from about 0.5 to about 5.0 parts, by volume, per 100 parts, by volume, of water in the effluent, and, preferably, about 1 to about 4 parts, by volume, of carbonyl-containing compound per 100 parts, by volume, of water in the effluent is employed, when used.
Where used, the preferred carbonyl-containing compound is formaldehyde, especially where the effluent is a mercury chloride-containing effluent.
After the reaction with the foil is completed, the effluent is decanted and the elemental mercury is recovered.
Because the reaction does not recover 100 percent of the mercury, where necessary, further treatment of the decanted effluent may be conducted. In such instances, the effluent water is first rendered alkaline by introducing a quantity of alkaline material such as caustic soda, potassium hydroxide, sodium carbonate or the like into the water to raise the pH of the water to a pH ranging from about 11.5 to about 12 or greater to neutralize any acid or free ions, such as metal chloride ions, in the effluent and to promote precipitation the mercury. Thereafter, a quantity of weak organic or mineral acid, such as phosphoric a
McGuthry-Banks Tima
Plunkett & Cooney, P.C.
Warden Jill
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