Water purifier abstract
A water purifier consisting essentially of manganese dioxide particles
having a 20 to 48 mesh size and macroscopic pores which are so large
in size as to permit passage of water therethrough. The particles
may have active sites of needle-like or columnar crystals of manganese
dioxide on the surfaces thereof. A method for making such water
purifier is also described.
Water purifier claims
What is claimed is:
1. A water purifier for use in the purification of water comprising
means for passing water through a column which consists essentially
of discrete particles of manganese dioxide, having macroscopic pores
through which water is able to pass, wherein said manganese dioxide
is (a) of beta form; (b) gamma and beta-mixed form and wherein said
particles have needle-like or columnar crystals on the surfaces.
2. The water purifier according to claim 1 wherein said manganese
dioxide is of the beta form and exhibits a sharp x-ray diffraction
pattern at 2.theta.=36.degree. using iron bulbs.
3. The water purifier according to claim 1 wherein said manganese
dioxide is of the beta and gamma mixed form and exhibits a x-ray
diffraction pattern at 2.theta.=28.degree. or 36.degree. using iron
4. The water purifier according to claim 1 wherein said discrete
particles of manganese dioxide is of size between 20 and 48 mesh.
5. The method of purifying raw water from impurities of manganese,
iron and coloring matters which consists of passing the raw water
through a water purifier which consists essentially of discrete
particles of manganese dioxide having macroscopic pores through
which water is able to pass, wherein said manganese dioxide is (a)
of beta form; (b) gamma and beta-mixed form and wherein said particles
have needle-like or columnar crystals on the surfaces.
Water purifier description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to water treatments and more particularly
to water purifiers which are useful in purifying raw water from
lakes or rivers in order to remove manganese and iron components
and colored matters therefrom. It also relates to a method for making
such water purifiers.
2. Description of the Prior Art
Recent trends toward pollution of lakes and rivers are beyond the
bounds of imagination, leading to an increase in amount of raw water
which is rather unsuitable for use as city water. This in turn requires
complicated treating apparatus with an attendant rise of treatment
Several methods of removing manganese and iron components and coloring
matters such as humus from raw water are known including an oxidation
method using ozone or oxidizing agents, an adsorption method using
active carbon, a contact filtration method using manganese-deposited
zeolites, a coagulating sedimentation method using coagulants, and
combinations of these methods.
The oxidation method using ozone or an oxidizing agent such as
potassium permanganate is disadvantageous because of the high treating
cost. Especially, use of ozone requires an additional equipment
for preventing air pollution. The adsorption method using active
carbon is not effective because active carbon has little adsorptivity
of manganese and iron components and is low in removability of coloring
The contact filtration method makes use of manganese zeolite which
has manganese dioxide deposited on the surface. This type of zeolite
is prepared by immersing zeolite in a solution containing divalent
manganese ions and adding an oxidizing agent such as, for example,
potassium permanganate to have manganese dioxide deposited on the
surface of zeolite. In this method, however, a large amount of an
expensive chemical such as potassium permanganate is used, leading
to a high treatment cost. If raw water being treated has a high
content of manganese, it cannot be removed efficiently. Because
manganese dioxide is deposited on the surface of zeolite, the dioxide
may readily fall off and be lost with the deposited zeolite deteriorating
It is generally accepted that manganese dioxide itself has the
effect of removing manganese, iron and coloring matters from water.
For use as a water purifier, manganese dioxide has to be reduced
into pieces having a suitable range of size. For instance, chips
of electrolytic manganese dioxide removed from the electrode or
natural manganese dioxide may be crushed to have a desired particle
size. Alternately, manganese dioxide powder may be bonded with use
of an inorganic binder such as alumina cement and shaped to have
a suitable particle size. However, the former manganese dioxide
particles are disadvantageous in that a reactive area is relatively
small. On the other hand, the particles obtained by using inorganic
binder have the drawback that active surfaces of the manganese dioxide
are covered with the inorganic binder added and the purification
effect is lower than the one achieved by the starting manganese
dioxide material itself.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide
water purifiers useful for purifying water which overcome the drawbacks
of the prior art.
It is another object of the invention to provide water purifiers
which are useful in efficiently, economically removing manganese
and iron components and coloring matters from raw water such as
from lakes, rivers and the like.
It is a further object of the invention to provide a method for
making the water purifiers of the above-mentioned type.
The above objects can be achieved, according to the invention,
by a water purifier for use in the purification of water which consists
essentially of discrete particles of manganese dioxide having a
20 to 48 mesh size, the particles having macroscopic pores through
which water is able to pass. Preferably, the particles should have
active sites on the surfaces in the form of needle-like or columnar
The particles of manganese dioxide having such large-size pores
are obtained by a method which comprises immersing starting manganese
dioxide powder in an acidic solution comprising from 5 to 80 g/liter
of divalent manganese ions and from 5 to 100 g/l of an acid for
a term of from 2 to 7 days at a temperature of from 80.degree. to
100.degree. C., reducing the resulting manganese dioxide mass into
pieces, classifying the pieces to have a size of from 20 to 48 mesh,
and neutralizing the pieces with an alkali whereby manganese dioxide
particles having macroscopic pores through which water is able to
pass are obtained. Preferably, magnesium ions may be further added
to the acidic solution. By the immersion in the acidic solution
containing manganese and/or magnesium ions, the starting manganese
dioxide powder which may be microscopically porous is bonded without
any binder and converted into a macroscopically porous mass. In
a preferred embodiment of the invention, manganese dioxide of the
gamma type is used and immersed in such acidic solution as defined
above under such conditions that part or all of the manganese dioxide
is converted into beta-type manganese dioxide while forming a macroscopically
porous mass with surface activity. The present invention also provides
a method for making a water purifier of the type described above.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) and 1(b) are, respectively, microphotographs by electron
microscope showing the surface state of a manganese dioxide water
purifier according to the invention;
FIG. 2 is a graph showing the relation between chromaticity of
water treated in Example 2 and Comparative Examples 1 through 3
and time after the treatment;
FIG. 3 is a graph showing the relation between chromaticity of
water treated in Examples 2 and 3 using one type of manganese dioxide
water purifier according to the invention and time by days after
FIG. 4 is a graph showing the relation between chromaticity of
water treated in Examples 6 and 7 using another type of manganese
dioxide water purifier according to the invention and time by days
after the treatment; and
FIGS. 5(a) through 5(f) are, respectively, X-ray diffraction patterns
of ordinary gamma-manganese dioxide, beta-manganese dioxide obtained
in Examples 1 4 6 and 8 and a mixture of beta- and gamma-manganese
dioxide substances obtained in Examples 5 and 7.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
As described before, the manganese dioxide particles of the present
invention should be macroscopically porous and have a mesh size
of 20 to 48. The term `macroscopically porous particles` used herein
is intended to mean particles having pores which permit free passage
of water through the pores. Ordinary particles of manganese dioxide
are microscopically very porous but have not such macroscopic pores.
Macroscopically porous particles of manganese dioxide according
to the invention are readily obtained by immersing manganese dioxide
powder in an acidic solution containing divalent manganese ions
preferably along with magnesium ions for a time sufficient to convert
the powder into a macroscopically porous mass of the dioxide. The
acidic solution is prepared to have a concentration of an acid of
from 5 to 100 g per liter of the solution. A typical example of
the acid is sulfuric acid though other mineral acids such as (nitric
acid, hydrochloric acid, phosphoric acid and the like) may be used.
In the acidic solution, it is essential that divalent manganese
ions be present in an amount of from 5 to 80 g per liter of the
solution. Preferably, divalent magnesium ions should be further
added in an amount up to 50 g per liter of the solution. If magnesium
ions are used singly instead of the divalent manganese ions, the
conversion velocity unfavorably becomes very low. The reason why
magnesium ions are used is that the apparent specific gravity of
the resulting particles becomes smaller than in the case where magnesium
ions are used singly upon comparing at the same level of particle
size, thus leading to an increase of porosity. The divalent manganese
and magnesium ions may be derived from various sources. Such sources
include inorganic salts such as (nitrates, sulfates, phosphates
and the like of these metals).
In order to ensure high mechanical strength of the macroscopically
porous mass, the temperature of the acidic solution should preferably
be as high as possible but below a boiling point of the solution.
Moreover, the immersion time is preferred to be as long as possible.
The macroscopically porous mass is subsequently reduced into pieces
having a 20 to 48 mesh size (U.S. mesh) for use as a water purifier.
The reduction into pieces may be carried out by any known means
and the pieces may be classified to have a defined range of size
Next, the pieces are washed with water until the washing has a
hydrogen ion concentration within the regulated standard for city
water, followed by neutralizing with an alkaline substance such
as caustic soda. The manganese dioxide particles obtained by the
above sequence of treatment steps have the high ability of removing
manganese and iron components from water and also coloring matters
therefrom. By the neutralization, the pH of water purified by passage
through the water purifier of the invention is in the range of about
5.8 to 8.6 at the initial stage of the water passage, which is within
the standard for city water.
In the above embodiment, starting manganese dioxide powder may
have any crystal forms such as alpha, beta, gamma and delta forms.
In accordance with another embodiment of the invention, the macroscopically
porous manganese dioxide particles are of the beta form or the beta
and gamma-mixed form in crystal structure. In order to obtain these
types of manganese dioxide, the starting manganese dioxide powder
should be of the gamma form and is subjected to the same procedure
as described with regard to the first embodiment. As a result, macroscopically
porous manganese dioxide particles of the beta form or the beta
and gamma-mixed form are obtained.
In general, manganese dioxide of the beta form may be prepared
by several methods including, for example, heating of gamma-manganese
dioxide at about 400.degree. C., treatment of gamma-manganese dioxide
in an autoclave containing an aqueous solution of an oxidative salt,
and electrolysis of manganese dioxide under elevated current density
conditions. However, water purifiers of beta-manganese dioxide obtained
by these methods are much poorer in water purification performance
and bleaching ability than the manganese dioxide of the beta form
or the beta and gamma-mixed form of the invention. From this, it
will be appreciated that manganese dioxide useful as a water purifier
should have not only the beta form or beta and gamma-mixed form
in crystal structure, but also possess macroscopic pores through
which water is able to pass freely and the form of needle-like or
columnar crystals on the surfaces thereof.
As described before, gamma-manganese dioxide powder is converted
into the macroscopically porous manganese dioxide mass of the beta
or beta and gamma-mixed form under conditions defined with reference
to the first embodiment. Higher concentrations of manganese and
magnesium ions and an acid result in a higher velocity of conversion
of from the gamma form to the beta form. It is favorable that the
conversion velocity is relatively low from the standpoint of mechanical
strength of the mass.
A mixing ratio of the beta to gamma form may be arbitrarily varied
by changing the immersion conditions.
In order to ensure good water purification performance, the mixing
ratio should preferably be in the range of ##EQU1##
The starting gamma-manganese dioxide is not necessarily pure gamma-manganese
dioxide but may contain, aside from gamma-manganese dioxide, several
to some dozen percent of manganese dioxide of other crystal forms.
Electrolytic manganese dioxide is made of the gamma form alone or
the gamma form with several percent of beta form. Thus, this dioxide
is suitable as a starting material of this embodiment.
Although electrolytic manganese dioxide of the gamma form is very
microscopically porous, manganese dioxide particles of the invention
having macroscopic pores through which water is able to pass are
very advantageous for use as a water purifier.
When the water purifiers of the invention are practically applied,
it is convenient to add, to raw water being treated, oxidizing agents
such as sodium hypochlorite in order to further improve the removability
of coloring matters, whereby the service life of the water purifiers
would be prolonged several years.