Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2001-08-24
2003-09-30
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S727000, C210S734000, C210S735000, C210S912000
Reexamination Certificate
active
06627087
ABSTRACT:
TECHNICAL FIELD
This invention concerns a method of removing lead from lead-containing water. More particularly, this invention is directed to a method of removing lead from near-neutral pH water using high molecular weight cationic dispersion polymers composed of (meth)acrylamide, a hydrophilic cationic monomer and a hydrophobic cationic monomer.
BACKGROUND OF THE INVENTION
Many industries, such as battery manufacture and electroplating, utilize lead in their manufacturing processes. Such use typically results in liquid (generally aqueous) effluent streams that contain residues of the lead utilized in the given manufacturing process.
Environmental compliance in removal of lead before discharge is now required in almost every country around the world. Typical permitted lead levels in the discharged water are <0.1 ppm. The traditional and commonly used techniques involving hydroxide, sulfide or carbonate precipitation are generally not effective in removing lead to this level.
Furthermore, traditional methods of removing lead from wastewater generate large sludge volumes. This sludge is generally landfilled or incinerated. The lead contained in the sludge, or ash generated as a result of incineration, can contaminate the landfill site, or vaporize and scatter into the air and cause environmental pollution. Accordingly, there is an ongoing need to develop new and effective methods of removing lead from water while simultaneously reducing the volume of sludge generated in the process.
U.S. Pat. Nos. 4,929,655, 5,006,590 and 6,171,505 B1 disclose dimethylaminoethylacrylate benzyl chloride quaternary salt/dimethylaminoethylacrylate methyl chloride quaternary salt/acrylamide dispersion polymer flocculants for waste water treatment.
U.S. Pat. No. 5,370,800 discloses a method of removing metals from wastewater comprising adding an unspecified anionic or cationic polymer flocculant to aerated, neutralized wastewater and separating the flocculated solids.
SUMMARY OF THE INVENTION
We have discovered that treatment of lead-containing water at near neutral pH with certain cationic dispersion polymers, alone or in combination with a water soluble ethylene dichloride ammonia polymer results in selective removal of lead to the sub ppb level, even in the presence of additional metals such as zinc and nickel. Use of these cationic dispersion polymers also results in accelerated solid-liquid separation and a reduction in the volume of sludge generated. Finally, because the process is effective at near neutral pH, there is lower chemical consumption for pH adjustment.
Accordingly, this invention is directed to a method of removing lead from water comprising
a) adjusting the pH of the water to about 7 to about 9; and
b) adding to the water an effective amount of a water soluble, high molecular weight cationic dispersion polymer composed of
i) (meth)acrylamide;
ii) a hydrophilic cationic monomer of formula
wherein A
1
is O or NH; B
1
is C
2
-C
4
alkylene or hydroxypropylene; R
1
is H or CH
3
, R
2
and R
4
are independently C
1
-C
2
alkyl; R
3
is H or C
1
-C
2
alkyl; and X
1
is an anionic counterion; and
iii) a hydrophobic cationic monomer of formula
wherein A
2
is O or NH; B
2
is C
2
-C
4
alkylene or hydroxypropylene; R
5
is H or CH
3
; R
6
and R
8
are C
1
-C
2
alkyl; R
7
is C
6
-C
20
alkyl or arylalkyl; and X
2
is an anionic counterion;
c) optionally adding a water soluble ethylene dichloride ammonia polymer to form a mixture of water and lead-containing flocculated solids; and
d) separating the lead-containing flocculated solids from the water.
DETAILED DESCRIPTION OF THE INVENTION
Definitions of Terms
“Dispersion polymer” means a fine dispersion of a water-soluble polymer in an aqueous continuous phase containing one or more inorganic salts and one or more particle stabilizing polymers. Representative examples of dispersion polymerization of water-soluble polymers in an aqueous continuous phase are found in U.S. Pat. Nos. 4,929,655, 5,006,590 and 6,171,505 B1.
Particle stabilizing polymers, also referred to as stabilizers or dispersants, facilitate the formation of fine particles and keep the formed polymer particles from becoming agglomerated and forming a gel rather than a fine dispersion of particles. Suitable particle stabilizing polymers include water-soluble cationic polymers that are soluble in the initial reaction mixture. Representative particle stabilizing polymers include homopolymers of cationic diallyl-N,N-disubstituted ammonium monomers or N,N-disubstituted-aminoethyl(meth)acrylate monomers and their quaternary salts, copolymers of diallyl-N,N-disubstituted ammonium monomers and N,N-disubstituted-aminoethyl(meth)acrylate monomers and their quaternary salts and cationic polymers comprising 20 mole percent or more of cationic diallyl-N,N-disubstituted ammonium monomers or N,N-disubstituted-aminoethyl(meth)acrylate monomers and their quaternary salts and one or more nonionic monomers, preferably acrylamide, methacrylamide or styrene. The molecular weight of the stabilizer is preferably in the range of about 10,000 to 10,000,000. Preferred particle stabilizing polymers include homopolymers of diallyldimethyl ammonium chloride, dimethylaminoethylacrylate methyl chloride quaternary salt and dimethylaminoethylmethacrylate methyl chloride quaternary salt. The particle stabilizing polymer(s) are used in an amount of from about 1 to about 10% by weight based on the total weight of the dispersion polymer.
Polyvalent anionic salts suitable for preparing the dispersion polymer include inorganic or organic sulfates, phosphates, chlorides or a mixture thereof. Preferred salts anionic salts include ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammonium hydrogen phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate and ammonium chloride. The salts are used in aqueous solution typically having a combined total concentration of 15 weight percent or above in the product mixture.
The cationic dispersion polymer of this invention is prepared by preparing a mixture of water, one or more polyvalent anionic salts, nonionic monomers, hydrophilic cationic monomers, hydrophobic cationic monomers, one or more particle stabilizing polymers, any polymerization additives such as chelants, pH buffers or chain transfer agents and charging the mixture to a reactor equipped with a mixer, a temperature regulating thermocouple, a nitrogen purging tube, and a water condenser.
A batch or semi-batch polymerization method can be employed to prepare the dispersion polymer of this invention. In a batch polymerization, the polymeric stabilizers, chain transfer agents, monomers, chelant, and water are initially added to the reactor. All or a portion of the formulation salt/salts are also added to the reactor at this time. Mechanical agitation is started and the reactor contents are heated to the desired polymerization temperature. When the set-point temperature is reached, the initiator is added and a nitrogen purge is started. The reaction is allowed to proceed at the desired temperature until completion and then the contents of the reactor are cooled. Additional inorganic salts may be added during the polymerization to maintain processability or influence final product quality. Moreover, additional initiator may be added during the reaction to achieve desired conversion rates and facilitate reaction completeness. Post polymerization additives such as additional salt, water, stabilizers for molecular weight and pH and anti-foaming and biocidal agents may also be added to the reaction mixture.
Use of a semi-batch polymerization method will vary from a batch polymerization method only in that one or more of the monomers used in the synthesis of the polymer are held out in part or whole at the beginning of the reaction. The withheld monomer is then added over the course of the polymerization. If acrylamide monomer is used as a semi-batch monomer, a chelant is often also added during the semi-batch period.
A multifunctional alcohol such as glycerin or pol
Bhaduri Manoj K.
Samaddar Ashis K.
Srivatsa Sanjay R.
Breininger Thomas M.
Hruskoci Peter A.
Martin Michael B.
Ondeo Nalco Company
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