US5089275A

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United States Patent 15

Antelman

UNA AAA

US008089275A
(11) Patent Number: 5,089,275

[45] Date of Patent: Feb. 18, 1992

[54] STABILIZED DIVALENT SILVER
BACTERICIDES

{75] Inventor: Marvin S, Antelman, Rehovot, Israel
[73] Assignee: N. Jonas & Co., Inc., Bensalem, Pa.
[21] Appl. No.: 697,781

[22] Filed: May 9, 1991 .
[51] Int. CL» .. CO2F 1/50
[52] US. CL. 424/602; 424/601;

424/618; 514/495; 422/19; 422/28; 210/764;

210/169

[58] Field of Search . 210/764, 169; 422/19,
422/28; 424/618, 602, 601, 604; 514/495;

423/42, 45, 544

[56] References Cited
U.S. PATENT DOCUMENTS

4,055,655 10/1977 Maurer et al.
4,092,245 5/1978 Franks et al.
5,017,295 5/1991 Antelman ....

Primary Examiner—Stanley S. Silverman

Assistant Examiner—Neil M. McCarthy
Attorney, Agent, or Firm—Salter & Michaelson

(57) ABSTRACT

Solid bactericidal compositions are disclosed based on
divalent silver (Ag(II)) as the active sanitized agent.
The compositions are prepared by reacting acid liquid
Ag(II) complexes with anhydrous calcium sulfate so as
to form a solid matrix in which the bactericide is en-
trapped in the resulting hydrated calcium sulfate. Opti-
mum compositions are described consisting of Ag(I)
Phosphate dissolved in phosphoric acid where the ratio
of solid (by weight) to liquid (by volume) is 5:2. The
resulting solid bactericides can be used in water cooling
installations. They are capable of causing 100% kills
within 10 minutes of E. Coli conforms in conformity
with EPA protocols, allowing them to quality as swim-
ming pool and hot tub sanitizers. Since the compositions
are based on calcium sulfate, they are also suitable as
mineralizers, thus providing a dual function.

3 Claims, No Drawings

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5,089,275

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STABILIZED DIVALENT SILVER BACTERICIDES

BACKGROUND OF THE INVENTION

The present invention relates to methods of stabiliz-
ing bactericidally active acid divalent silver (Ag(II))
complexes into solid matrices. Said complexes consti-
tute the subject matter of U.S. Pat. No. 5,017,295 of the
present inventor. In said patent, the inventor described
the preparation of soluble Ag(II) complexes which are
effective bactericides in water utilized for industrial
cooling and for swimming pools. Of the various com-
plexes described, the most viable ones were the Ag(II)
phosphates. These are prepared by dissolving divalent
silver oxide (AgO) in phosphoric acid. It was demon-
strated by the inventor in numerous experiments that
those conditions which favored the formation of diva-
lent silver ions were most effective bactericides, so that
there exists a definite correlation between bactericidal
activity and favorable Ag(II) stability in solution. Two
conditions that favor Ag(II) ion stability are low pH
and the addition of oxidation agents.

These favorable conditions have been described in
the chemical literature. The stabilization under acid
conditions of Ag(II) ions can be expressed by the fol-
lowing equation:

AgO* AG* +2H+ =2Ag?+ +H20.

Said Ag(II) phosphate complexes are stabilized in con-
centrated phosphoric acid solution. The handling of
said solutions poses a safety hazard to the user who is
advised in Material Safety Data Sheets accompanying
the product to use gloves and goggles when handling
the solution. Furthermore, the shipping of such material
fequires hazardous labeling as a corrosive substance.
Accordingly, it was desired to develop a solid form that
could stabilize the Ag(II) acid complexes. After experi-
menting with a series of solid absorbents, it was found
that anhydrous calcium sulfate when mixed in the
proper ratio with various Ag(II) acid complexes would
stabilize and set into hard plaster-like compositions
containing the complexes. These hard compositions
could be ground into solid powders giving rise to a
viable product. Furthermore, the fact that calcium sul-
fate performed in this manner added another feature to
the product, and that was it could be added directly to
swimming pools where calcium chloride is employed as
a mineralizing agent, and thus there would be no neces-
sity to add calcium chloride in addition to this sanitizer
to the pool.

OBJECT OF THE INVENTION

The main object of this invention is to provide solid
stable forms of liquid acid divalent silver bactericides
and especially those of Ag(II) phosphate complexes
dissolved in phosphoric acid for application to waters
used for industrial cooling, swimming pools and hot
tubs, and which will also meet the requirements of the
last two applications which require that the final prod-
uct be capable of 100% kills of select coliform strains
within 10 minutes. Another object of this invention is to
provide for a combined source of bactericide mineraliz-
ing agent which can be applied to swimming pool and
hot tub water where agents such as calcium chloride are
employed.

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SUMMARY OF THE INVENTION

This invention relates to methods of stabilizing diva-
lent silver liquid acid bactericides utilized in keeping the
water in swimming pools, hot tubs and industrial cool-
ing installations free from bacteria. More particularly,
said methods involve the stabilization and solidification
of said bactericides into a solid end product which will
not lose its efficacy as a bactericide as a result of being
incorporated into this new entity.

Divalent silver bactericides were prepared by dis-
solving varying quantities of AgO in phosphoric acid
which in turn was diluted with water to various concen-
trations. A lesser number of preparations was made
from AgO and nitric acid. These preparations were
incorporated in various amounts into an intimate physi-
cal mixture with anhydrous calcium sulfate. Ultimately,
most of the mixtures set into solids which were easily
ground into fine powers in an agate mortar.

It was finally discovered that the optimum ratio for
evaluating the physical efficacy of these preparations
was at a ratio of solid calcium sulfate (in grams) to liquid
Ag(II) complex (in cubic centimeters) of 5:2. It was also
found that phosphoric acid inhibited the setting time of
the sulfate. For example, Ag(II) phosphate in 87 volume
percent C.P. phosphoric acid (85%) never set even after
a month, and remained a liquid slurry; whereas the same
complex in 24 volume percent acid set within 15 min-
utes. It was also discovered that the addition of electro-
lytes to the slurries would hasten the setting time. Thus,
for example, a 36% phosphoric acid solution containing
Ag(II) ions required one hour to set. However, the
addition of one gram of potassium sulfate to the slurry
achieved solidification within 12 minutes.

Various solid powders formed according to the afore-
mentioned procedures were then checked for their effi-
cacy in killing E. Coli bacteria according to EPA proto-
col AOAC 15th 1990:965:13. The protocol utilizes a
culture containing 100K colonies/cc.

Qualification of a sanitizer for human contact in pools
and tubs requires that the bactericide exhibit 100% kills
within 10 minutes. All the calcium sulfate matrix solids
exhibited. 100% kills within 5 and 10 minutes, and this
was at concentrations of silver as low as 1.4 PPM.

Calculations were carried out to determine optimum
mineralization equivalents of the stabilized calcium
sulfate powders. Commercial mineralization calls for
adding calcium to swimming pools so as to give an
equivalent of 300 PPM of calcium carbonate having a
molecular weight of 100. Calcium chloride is most often
utilized for this purpose. The end product Ag(1I) matri-
ces contain calcium sulfate dihydrate as the final solid
material. The molecular weight of the dihydrate is 172.2
and of the anhydrous sulfate 136.1. Calcium has an
atomic weight of 40.1. The percentage composition of
calcium of these compounds (40.1+ molecular weight
of the particular calcium salt x 100) indicates that 571
PPM of the solid Ag(II) 5:2 matrix material is equiva-
Jent to 300 PPM of calcium carbonate. Solutions were
prepared at this concentration. The solid sank to the
bottom.

Other objects and features of the present invention
will become apparent to those skilled in the art when
the present invention is considered in view of the ac-
companying example. It should, of course, be recog-
nized that the accompanying example illustrates a pre-
ferred embodiment of the present invention and is not

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5,089,275

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intended as a means of defining the limits and scope of
the present invention.

DESCRIPTION OF THE PREFERRED
EMBODIMENT

The following example is given to illustrate a pre-
ferred embodiment of my invention.

A solution of Ag(II) phosphate complex was pre-
pared by dissolving AgO containing one gram of silver
in 50 cc. of 36 volume percent of 85% C.P. phosphoric
acid. Two cubic centimeters of the resulting solution
were intimately mixed with 5 grams of anhydrous cal-
cium sulfate to which was then added one gram of
anhydrous potassium sulfate. The entire mass was then
ground into a fine powder of about 200 mesh in an agate
mortar. This powder was evaluated as a bacteriostat at
a concentration of 250 PPM. When the aforementioned
EPA protocol was employed with E. Coli coliforms,
100% kills were obtained after 5 and 10 minutes. The
final concentration of silver in said solution was 1.4
PPM. The pH of the solution was preadjusted to 7.5,
and 10 PPM of potassium monopersulfate, which is not

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bactericidal at said concentration, was added to pro-
mote equilibria favorable to Ag(II) ions.

As this invention may be embodied in several forms
without departing from the spirit or essential character-
istics thereof, the present embodiment is therefore illus-
trative and not restrictive, since the scope of the inven-
tion is defined by the appended claims rather than by
the description preceding them, and all changes that fall
within the metes and bounds of the claims or that form
their functional as well as conjointly cooperative equiv-
alents, are therefore intended to be embraced by these
claims.

What is claimed is:

1. A solid bactericidal composition for sanitizing the
water of swimming pools, hot tubs and industrial cool-
ing installations which comprises a liquid acid divalent
silver complex that has been reacted with anhydrous
calcium sulfate so as to form a hydrated solid matrix.

2. The composition of claim 1, where the divalent
silver complex is a phosphate and the liquid acid is
phosphoric acid.

3. The composition of claim 1, where the solid matrix

also serves as a calcium mineralizing agent.
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