Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2000-09-22
2003-12-09
Smith, Duane (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S748080
Reexamination Certificate
active
06660167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for precipitating or flocculating substances out of solutions.
2. Discussion of the Relevant Art
Undesirable ionic substances contained in water can be removed when they are transformed into the form of a sparingly soluble salt or mineral and are thus precipitated. Many metal ions, such as, for example, Ca
2+
, Mg
2+
, Fe
2+
, Me
2+
ions can be precipitated in the form of sparingly soluble hydroxides. Such reactions can be controlled via the pH value.
Ca
2+
ions in water are removed on a commercial scale in that they are precipitated as CaCO
3
(calcium carbonate) (decarbonization) This reaction is also controlled via the pH value.
Closely related to the precipitation of substances contained in water is the term of flocculation and sedimentation. This is so because the removal of (precipitated) substances contained in water requires:that they can also be separated from the water. In the context of flocculation and sedimentation it is important how the precipitated products grow further and/or can conglomerate. The addition of certain salts (aluminum salts, iron salt) can control this behavior.
In the conventional method technology it is difficult to avoid a local overdosage when introducing the flocculation agent (for example, when adding sodium hydroxide solution or when dissolving sodium hydroxide pellets). A local overdosage can result in the precipitation of inherently less soluble substances contained in the water which then cause, as an entrained solid particle, component hard-to-control conditions in the subsequent precipitation process.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved method for precipitation or flocculation of substances contained in solutions, especially water.
According to the invention, the method is characterized in that the solution is brought into contact with at least one ion exchange material which releases ions into the solution that effect precipitation or flocculation and/or has on its surface functional groups which catalytically effect flocculation or precipitation.
Ion exchange materials have been used in water or sewage treatment in order to exchange undesirable ions against desirable ions or ions that are less disruptive for the respective application purposes. Known are, for example, water softening devices which by means of ion exchangers bind Ca
2+
and/or Mg
2+
in exchange for Na
2+
or H
+
ions. Anionic exchangers (mostly in the Cl
−
or OH
−
form) allow the removal of undesirable anions (NO
3−
, HCO
3−
etc.) from the water. Known are also methods in which the Cu
2+
ion or heavy-metal ions are removed by means of ion exchangers from the water. All these methods have in common that the ions removed from the water are bonded to the resin; once the capacity of the resin is depleted, it must be regenerated. During the regeneration process, the metal ions which have been concentrated can be, for example, removed from the regenerated compound.
Novel is now the idea to employ an ion exchange material for inducing a precipitation or flocculation process.
According to a first aspect of the invention, ion exchange materials are used as supports for the ions which in solution make the precipitation reaction possible. The component required for transformation of the ionic species to be precipitated into a sparingly soluble salt/mineral is provided by the ion exchange material which has been conditioned for this purpose. For example, an ion exchange resin of the OH
−
form provides the required OH
−
ions for a hydroxide precipitation in order to, for example, precipitate Fe
2+
and Mn
2+
in the form of hydroxides but of the water. Ag
+
ions in the water can be precipitated as AgCl in the presence of an anionic exchange resin of the Cl
−
form.
When using specially conditioned ion exchange materials, the following advantages will result relative to the prior art in the field of water treatment:
The ion exchange material allows the directed addition of the components required alone for the precipitation reaction, for example, for the decarbonization of calcium carbonate-containing water. The principle of decarbonization of calcium carbonate-containing water is that the pH value is to be raised in order to shift the calcium carbonate/carbonic acid equilibrium such that the Ca
2+
ions will precipitate in the form of calcium carbonate. Conventionally, the pH value increase is achieved by adding Ca(OH)
2
NaOH and/or NaCO
3
. This addition has the disadvantage that with the OH
−
or CO
3
2−
ions acting as a base, additionally Ca
2+
or Na
30
ions are introduced into the water which partially counteract (additional Ca
2
+ ions which must be precipitated) or limit (sodium limit value in drinking water) the success of the method.
A weakly basic ion exchange resin of the OH
−
form only releases OH
−
ions; an ion exchange resin of the HCO
3−
/CO
3
2−
releases only CO
3
2−
and HCO
3−
ions.
Better control of the precipitation process by avoiding local overdosage, especially in combination with a fluidized bed variant.
The possibility of controlling the precipitation process by means of the contact time of the water to be treated with the ion exchange material.
The ion exchange is a surface process and depends on the degree of loading of the ion exchange material with the ions required for the reaction and the type and concentration of ions in the solution which can be exchanged for the ions on the resin.
The contact time can be adjusted simply and can be changed optionally (by the size of the ion exchange resin bed and the flow-through amount in continuous operation; via the residence time in the reaction vessel (tank) during batch operation).
The recyclability of the ion exchange material.
Depleted ion exchange material, especially resins, can be removed easily from the reaction vessel or tank and regenerated. The regenerated material can then be returned into the process.
Ion exchange materials can be used as carriers of ions which control the flocculation in solution. In analogy to the above described mechanism, ions which enhance the flocculation of substances contained in the water (for example, Al
3+
and Fe
3+
ions) can also be brought into the corresponding solution by ion exchange from an ion exchange material (it is then required to provide an ion exchange material that is at least partially loaded with Al
3+
and Fe
3+
ions). All advantages are also applicable here.
For certain processes, the combination of dosage of pH-controlling ions (for example, anionic exchangers of the OH
−
form) and flocculation agents (for example, cationic exchangers in the Fe
2+
form) is expedient.
According to a second aspect of the invention, a specially conditioned ion exchange material can be used as a catalyst for precipitation of substances contained in water. In many real solutions there is the situation that the solution, when considered thermodynamically, is oversaturated with respect to a dissolved phase. Despite this fact, within a finite time period no precipitation takes place which would bring the solution into equilibrium. Such meta-stable solutions lack suitable growth locations where the precipitation could take place. Suitable growth locations are crystal seeds of the phase to be precipitated or special heterogeneous surfaces which decrease considerably the seed formation work and thus make the formation of crystal seeds in the range of low saturations possible. An example for such a solution is water which is oversaturated with respect to calcium carbonate.
It is known that biological systems (muscles, algae etc.) are able to initiate a directed crystal seed formation by means of certain functional groups. In particular, it was found that the carboxyl group of certain carboxylic acids (stearic acid etc.) induc
Leiter Klaus
Walder Gerhard
Friedrich Kueffner
Greene Jason M.
Smith Duane
Watercryst chemiefreie Wasserbehandlung GmbH
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