U.S. patent application number 13/046480 was filed with the patent office on 2011-09-15 for process for the removal of arsenic and chromium from water.
This patent application is currently assigned to Council of Scientific & Industrial Research. Invention is credited to Prabhat Kumar Gupta, Renu Pashricha, Rashmi, Nahar SINGH, Sukhvir Singh, Daya Soni.
Application Number | 20110220577 13/046480 |
Document ID | / |
Family ID | 44558953 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110220577 |
Kind Code |
A1 |
SINGH; Nahar ; et
al. |
September 15, 2011 |
PROCESS FOR THE REMOVAL OF ARSENIC AND CHROMIUM FROM WATER
Abstract
The present invention provides low cost and highly effective
method for the removal of arsenic and Cr(III&VI) from
contaminated water using zinc peroxide nanoparticles (20.+-.5 nm)
capped with glycerol/PVP/TEA upto the permissible range of drinking
water. As Arsenic and chromium occurs naturally in the earth's
crust. When rocks, minerals, and soil erode, they release arsenic
and chromium into groundwater. Arsenic and chromium occurs
naturally in varying amounts in groundwater in various parts of
country from ppb level to ppm level. The average concentration of
arsenic and chromium as per USEPA standard in drinking water it is
10 parts per billion and 0.05 ppm (50 ppb) respectively. In
drinking water the level of chromium is usually low as well, but
contaminated water may contain the dangerous Cr(III&VI).
Although Cr(III) is an essential nutrient for humans and shortages
may cause heart problems, disruptions of metabolisms and diabetes.
But the uptake of too much Cr(III) can cause health effects as
well, for instance skin rashes. Cr(VI) is known to cause various
health effects Skin rashes, upset stomachs, respiratory problems,
weakened immune systems, kidney and liver damage and lung cancer
The persons who are drinking water having upto 50 ppb of arsenic
and 0.05 ppm chromium over for many years could experience skin
damage or problems with their circulatory system, and may have an
increased risk of getting cancer. Keeping the above facts we
developed a cost effective nanoparticles for the removal of Arsenic
and Cr(III&VI) from potable water upto potable range.
Inventors: |
SINGH; Nahar; (New Delhi,
IN) ; Rashmi;; (New Delhi, IN) ; Singh;
Sukhvir; (New Delhi, IN) ; Pashricha; Renu;
(New Delhi, IN) ; Gupta; Prabhat Kumar; (New
Delhi, IN) ; Soni; Daya; (New Delhi, IN) |
Assignee: |
Council of Scientific &
Industrial Research
|
Family ID: |
44558953 |
Appl. No.: |
13/046480 |
Filed: |
March 11, 2011 |
Current U.S.
Class: |
210/688 |
Current CPC
Class: |
C02F 2101/103 20130101;
C02F 2305/08 20130101; B82Y 30/00 20130101; C02F 2103/06 20130101;
B01J 20/0244 20130101; B01J 20/3042 20130101; B01J 20/28007
20130101; B01J 20/3085 20130101; C02F 1/281 20130101; B82Y 40/00
20130101; C02F 2101/22 20130101; C02F 1/288 20130101 |
Class at
Publication: |
210/688 |
International
Class: |
C02F 1/62 20060101
C02F001/62; C02F 1/28 20060101 C02F001/28 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2010 |
IN |
0578/DEL/2010 |
Claims
1. A process for the removal of arsenic and Cr(III&VI) from
contaminated water using zinc peroxide nanoparticles comprising
treating the contaminated water containing arsenic and chromium
with the nanoparticles of zinc peroxide in a ratio (w/v) ranging
from 8:1 to 12:1 (mg/ml), having the concentration of arsenic,
Cr(III&VI) contamination below 50 ppm in water, at ambient
temperature, for a period of 5-10 min, followed by filtration to
obtain the desired low concentrated contamination permissible
drinking water.
2. A process as claimed in claim 1, wherein the zinc peroxide
nanoparticles used have size below 50 nm.
3. A process as claimed in claim 1, wherein the amount of zinc
peroxide used for the removal of arsenic and Cr(III &VI) is
preferably in the range of 225-250 mg per 25 ppm of arsenic and
Cr(III &VI) contaminated water.
4. A process as claimed in claim 1, wherein the zinc peroxide
nanoparticles are prepared by the process comprising the following
steps: a) dissolving zinc acetate in ammonium hydroxide to obtain a
solution mixture having pH in the range of 9-11; b) adding
glycerol/PVP/TEA to the solution mixture obtained in step (a) in a
ratio of zinc acetate to glycerol in the range of 2:0.5 to
6:1(w/w), PVP in the range of 10:0.25 to 10:1 (w/w) and TEA in the
range of 1:1 to 1:0.5 (w/w) with respect to zinc acetate
respectively; c) adding a polar organic solvent to the solution
Mixture obtained in step (b), under stirring, at ambient
temperature in the range of 25-30.degree. C., followed by adding
equimolar quantity of hydrogen peroxide with respect to zinc
acetate to obtain the desired nanoparticles of zinc peroxide.
5. A process as claimed in claim 4, wherein the weight ratio of
zinc acetate to glycerol used is preferably in the range of 2:0.5
to 3:1.
6. A process as claimed in claim 4, wherein the weight ratio of
zinc acetate to PVP used is preferably in the range of 10:0.5 to
10:1 (w/w).
7. A process as claimed in claim 4, wherein the weight ratio of
zinc acetate to TEA used is preferably in the range of 1:1 to 1:0.5
(w/w).
8. A process as claimed in claim 4, wherein yield of ZnO.sub.2
nanoparticles obtained is in the range of 98-99% with respect to
the starting material.
9. A process as claimed in claim 1, wherein the ZnO.sub.2
nanoparticles removes arsenic, Cr(III) and Cr(VI) each from 50 ppm
to 0.1, 0.14, and 0.18 ppm, respectively without disturbing the pH
of water.
10. A process as claimed in claim 1, wherein the ZnO.sub.2
nanoparticles removes arsenic, Cr(III) and Cr(VI) each from 30 ppm
to 0.03, 0.07 and 0.08 ppm, respectively without disturbing pH of
the water.
11. A process as claimed in claim 1, wherein the ZnO.sub.2
nanoparticles removes arsenic, Cr(III) and Cr(VI) each from 25 ppm
to less than the detection limit of AAS-HG in case of arsenic and
0.01 in case of Cr(III) and Cr(VI) without disturbing pH of the
water.
12. A process as claimed in claim 1, wherein the ZnO.sub.2
nanoparticles removes arsenic and Cr(III&VI) each from 20 ppm
to less than the detection limit of AAS-HG and FAAS/GFAAS
respectively without disturbing pH of the water.
13. A process as claimed in claim 1, wherein the ZnO.sub.2
nanoparticles removes arsenic and Cr(III&VI)each from 15 ppm to
less than the detection limit of AAS-HG and FAAS/GFAAS respectively
without disturbing pH of the water.
14. A process as claimed in claim 1, wherein the ZnO.sub.2
nanoparticles removes arsenic and Cr(III&VI) each from 10 ppm
to less than the detection limit of AAS-HG and FAAS/GFAAS
respectively without disturbing pH of the water.
15. A process as claimed in claim 1, wherein the ZnO.sub.2
nanoparticles removes arsenic and Cr(III&VI) each from 5 ppm to
less than the detection limit of AAS-HG and FAAS/GFAAS respectively
without disturbing pH of the water.
16. A process for the removal of arsenic and Cr(III&VI) from
contaminated water, substantially as herein described with
reference to the examples and drawings accompanying this
specification.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for the removal
of arsenic and Chromium [Cr(III) & Cr(VI)] from contaminated
water. Particularly, the present invention relates to a process for
the removal of arsenic and chromium from contaminated water using
nanoparticles of zinc peroxide (ZnO.sub.2) capped with
glycerol/triethylamine (TEA)/poly vinyl pyrrolidone (PVP). More
particularly, the present invention relates to a process for the
removal of arsenic and chromium from the contaminated water to a
level that is suitable for safe drinking.
BACKGROUND OF THE INVENTION
[0002] Presence of arsenic (As) and chromium metal ions in drinking
water has become the issue of global concern. Long-term exposure to
even low concentrations of arsenic in the drinking water may cause
skin, lung or prostrate cancer and cardiovascular, pulmonary,
immunological and neurological disorder [Environment Health
Criteria 224, Arsenic and Arsenic Compounds, Second edition, World
Health Organization 2001; S. Shevade and R. G. Ford. Use of
synthetic zeolites for arsenate removal from pollutant water. Water
Res. 38(14-15), 3197 (2004)].
[0003] At present there is no effective medicine available, which
can treat disease, causes by arsenic and chromium, so use of
arsenic and chromium free water can help the affected person to get
rid of the symptoms of arsenic and chromium toxicity. Hence, the
requirement of arsenic and chromium free water is urgently desired
to mitigate arsenic and chromium toxicity and protection of the
health of human beings living in the areas affected by arsenic and
chromium contamination.
[0004] World Health Organization (WHO) & Environment Protection
Agency (EPA) has established a level of 10 .mu.g/L arsenic and 50
.mu.g/L of chromium in drinking water from January 2006. But in
several countries like Bangladesh, India, arsenic and chromium
concentration in the drinking water can be as high as 500 .mu.g/L
or more. The reduction of arsenic and chromium from such high
concentrations and made it potable as per WHO prescribe limit is a
very challenging task.
[0005] Arsenic occurs in rocks, soil, water and air in -3, 0, +3
and +5 valence state. It is widely distributed having average
concentration of 2 mg/kg. The burning of fossil fuels, refining of
petroleum mining, smelting of metals like Zn, Cu, Ni, and Pb, are
major anthropogenic sources for arsenic contamination in air, water
and soil.
[0006] Therefore high toxicity and widespread occurrence created a
pressing need for effective monitoring, measurement and remediation
of arsenic in soil and groundwater. The effect and degree of
toxicity of arsenic depends on its inorganic or organic forms and
oxidation state. Inorganic arsenicals are more toxic than organic
arsenicals and in inorganic arsenicals trivalent form is more toxic
than the pentavalent form.
[0007] Reference may be made to Y. Lee, I. H. Um and J. Yoon,
Arsenic (III) oxidation by iron(VI) (ferrate) and subsequent
removal of arsenic (V) by iron (III) coagulation. Environ. Sci.
Technol. 37(24), 5750 (2003); B. Daus, R. Wennrich and H. Weiss,
Sorption materials for arsenic removal from water: a comparative
study. Water Res. 38(12), 2948 (2004); S. Bang, G. P. Korfiatis and
X. Meng, Removal of arsenic from water by zero-valent iron. J.
Hazard Mater. 121(1-3), 61 (2005); Y. S. Shen. Study of arsenic
removal from drinking water. J. American Water Works Association,
65(8), 543 (1973) and A. Joshi and M. Chaudhary. Removal of arsenic
from groundwater by iron-oxide-coated sand. ASCE J. Environ.
Engineering. 122(8), 769 (1996), which discloses several methods
for the removal of arsenic from contaminated water to the
consumable limit.
[0008] In U.S. Pat. No. 4,566,975, heavy metals such as arsenic are
removed in a two step process which involves an alkaline
precipitation carried out at a pH of at least about 8 and using
ferrous sulfate as an additive.
[0009] In U.S. Pat. No. 4,880,510, the electrolytic cell has been
used to remove color impurities such as dyes from wastewater
solution. The ferrous iron generated at the anode reacts with
hydroxide ion to form an iron complex or compound, which further
was found to react with or otherwise remove the color bodies from
aqueous media as an insoluble precipitate.
[0010] In U.S. Pat. No. 4,490,257, contaminants are removed by
electrolysis process. The electrodes are resistant to
corrosion.
[0011] In U.S. Pat. No. 5,043,080, contaminated groundwater is
treated with hydrogen peroxide and transition metal ions at an acid
pH in the presence of ultraviolet light. The main object, however,
is the removal of organic contaminants rather than heavy
metals.
[0012] In U.S. Pat. No. 4,163,716, it was recognized that heavy
metals and color bodies from dye house affluent could be removed
with ferrous ions supplied by iron electrodes with the ferrous ion
oxidizing to the ferric state by use of an oxidizing agent such as
hydrogen peroxide. At a pH of between 7 and 9, heavy metals and
traces of color adhere to the ferric hydroxide floc, which then may
be removed. This process also involves a pH adjustment from a
reaction pH of below 6.5 to a pH of from 7 to 9 to achieve removal
of color particles.
[0013] The common technologies used for removal of arsenic are
oxidation, co-precipitation, adsorption onto sorptive media, ion
exchange resin and membrane techniques etc. Presently, various
materials like activated carbon (AC), zirconium coated activated
carbon (Zr-AC) [B. Daus, R. Wennrich and H. Weiss, Sorption
materials for arsenic removal from water: a comparative study.
Water Res. 38(12), 2948 (2004)]; iron hydroxide [W. Wang, D. Bejan
and N. J. Bunce, Removal of arsenic from synthetic acid mine
drainage by electrochemical pH adjustment and co-precipitation with
iron hydroxide. Environ. Sci. Technol. 37(19), 4500 (2003)]; iron
(II) and iron (III) oxides [L.C. Roberts, S. J. Hug, T. Ruettimann,
M. Billah, A. W. Khan and M. T. Rahman; Arsenic removal with iron
(II) and iron (III) in waters with high silicate and phosphate
concentrations, Environ. Sci. Technol. 38(1), 307 (2004)], sand and
zero-valent iron [O. X. Leupin and S. J. Hug. Oxidation and removal
of arsenic(III) from aerated groundwater by filtration through sand
and zero-valent iron; Water Res. 39(9), 1729 (2005)], hardened
paste of Portland cement [Kundu, S. S. Kavalakatt, A. Pal, S. K.
Ghosh, M. Mandal and T. Pal; Removal of arsenic using hardened
paste of Portland cement: batch adsorption and column study. Water
Res. 38(17), 3780 (2004)]; iron oxide coated polymers [A.
Katasoyiannis and A. I. Zouboulis, Removal of arsenic from
contaminated water sources by sorption onto iron-oxide-coated
polymeric materials, Water Res. 36(20), 5141 (2002)]; biological
systems (bacteria) [A. Katasoyiannis and A. I. Zouboulis;
[Application of biological processes for the removal of arsenic
from groundwater] Water Res. 38(1), 17 (2004)] has been removed
arsenic from contaminated water through biological process and
could be used for drinking and other household utilities.
[0014] The above materials and methods are effective and reduce
arsenic concentration in the potable water upto acceptable limits.
But these materials and methods have their own advantages and
disadvantages like, oxidation process is very simple and low cost
but it is very slow and removes only a part of the arsenic,
co-precipitation by alum or iron is again simple and low capital
arrangement but it produces toxic sludge's and pre-oxidation is
required to start the reaction.
[0015] The use of iron or iron oxide for removing arsenic is
dominative as it is very cheap, highly effective and can purify
large volume of water. In this process, arsenite (As.sup.3+)
species is first oxidized to arsenate (As.sup.5+) in the presence
of atmospheric oxygen, or Ozone or free chlorine. Reference may be
made to G. Hering, P. Y. Chen. J. A. Wilkie, M. Elimelech and S.
Liang. Arsenic removal by ferric chloride. J. American Water Works
Association; 88(4), 155 (1996). Wherein the arsenate species got
adsorbed over the surface of iron oxide during filtration and are
removed from the contaminated water. Roberts L.C. et al. have used
Fe (II) and Fe (III) to remove arsenic from water with high
silicate and phosphate concentrations.
[0016] Reference may be made to Daus B. et al. Water Res. 2004 Jul;
38-(12): 2948-54 that has proved that arsenite and arsenate can be
removed from water using Activated carbon (AC), zirconium loaded
Activated carbon with other materials successfully.
[0017] Reference may be made to Water Res. 2003 May; 37(10):
2478-88, wherein the arsenic was effectively removed by steel
manufacturing byproducts like evaporation cooler dust (ECD), oxygen
gas sludge (OGS), and basic oxygen furnace slag (BOFS).
[0018] Reference may be made to Bang S. et al. J. Hazard Mater.
2005 May 20, 121(1-3): 61-67, who has reported effect of dissolved
oxygen and pH on the removal of Arsenic from water and concluded
that at pH 6 that arsenate removal (99.8%) was faster than arsenite
(82.6%) and more dissolved oxygen and low pH increases the rate of
iron corrosion and leads to the formation of iron hydroxide, which
ultimately adsorbs arsenic from the solution.
[0019] Reference may be made to S. Kundu, S. S. Kavalakatt, A. Pal,
S. K. Ghosh, M. Mandal, and T. Pal, Water Res. 2004 Oct; 38(17):
3780-90 wherein Portland cement (HPPC) paste has been used as
adsorbent for the removal of arsenic from water and have shown that
95% arsenate and 88% Arsenite can be removed easily.
[0020] Reference may be made to Sarkar, A. et al. Water Res. 2005
May; 39(10): 2196-206 wherein activated alumina has been used as
adsorbent for arsenic removal from drinking water.
[0021] Reference may be made to Bang S. et al. Chemosphere. (2005)
Jul; 60(3): 389-97 wherein granular titanium dioxide (TiO.sub.2)
has been used for the removal of arsenic from groundwater.
[0022] Reference may be made to Oklahoma State University, USA,
Advanced ceramic reports; Issue: August 2004, page: 6 wherein
Porous Zinc oxide beads has been used to remove arsenic from the
contaminated water.
[0023] Chromium is a common heavy metal contaminant of water
supplies, largely arising from the textile, leather and wood
production industries. The metal industry mainly discharged
trivalent chromium. Hexavalent chromium in industrial wastewater
mainly originates from tanning and painting. Chromium may be
applied as a catalyser, in wood impregnation, in audio and video
production and in lasers. Chromite is the starting product for
inflammable material and chemical production. Levels of chromium in
drinking water have been controlled in the past by expensive, often
toxic chemical based cleansing procedures. Trivalent chromium is a
dietary requirement for a number of organisms as trivalent chromium
is an essential trace element for humans and with insulin it
removes glucose from blood and also plays a vital role in fat
metabolism.
[0024] But hexavalent chromium is very toxic to flora and fauna.
The human body contains approximately 0.03 ppm of chromium. Daily
intake of chromium depends upon feed and levels, and is usually
approximately 15-200 but may be as high as 1 mg. The Placenta is
the organ having highest chromium amounts. Chromium deficits may
enhance diabetes symptoms. Chromium can also be found in RNA.
Chromium deficits are very rare, and chromium feed supplements is
not often applied. Chromium (III) toxicity is unlikely, at least
when it is taken up through food and drinking water. It may even
improve health, and cure neuropathy and encephalopathy. Hexavalent
chromium is known for its negative health and environmental impact.
It causes allergic and asthmatic reactions and it is 1000 times
more toxic than trivalent chromium. Exposure to hexavalent chromium
causes diarrhoea, stomach and intestinal bleeding, cramps,
paralysis and liver and kidney damage. The hexavalent chromium is
mutagenic and carcinogenic in nature. Toxic effects may be passed
on to children through the placenta. Chromium oxide is a strong
oxidant and after dissolution it forms chromium acid, which
corrodes the organs. The lethal dose is approximately 1-2 gm. Most
countries apply a legal limit of 50 ppb chromium in drinking water.
A professional illness in chromium industries is chromium sores
upon skin contact with chromates. . Chromium trioxide dust uptake
in the workplace may cause cancer, and damage the respiration
tract.
[0025] Common Cr(VI) removal technologies for drinking water
applications are ion exchange, membranes, reduction/ precipitation/
coagulation/ filtration, sorptive media etc. The trivalent chromium
can be removed by contacting the solution with a weak acid cation
exchange resin. The chromate can be removed by a weak base anion
exchange resin in the presence of acid [Chopra, Randhir C, "Removal
of chromium, chromate, molybdate and zinc" U.S. Pat. 3,972,810
(1976)]. Each of the resins requires different regenerate so that
the process will require bulky equipment due to the requirement for
separate sites for the regeneration of the two resins. Thus the
chromium can be removed but the other pollutant is added to its
solution. The most common industrial chromium treatment methods are
reduction/ precipitation/filtration. In this process, the Cr(VI) is
reduced to Cr(III) typically by some reductant and chromium
precipitated out as Cr(OH).sub.3 and further coagulation were
carried out with ferric salt and filtered.[Besselievre, E. B.
(1969); The treatment of industrial wastes, McGraw-Hill, New
York].
[0026] Reference may be made to Several U.S. Pat. Nos. 3,926,754;
4,036,726; and 4,123,339, which claims removal of hexa or trivalent
chromium from wastewater electrochemically. In these patents, a
process is described wherein wastewater containing hexavalent
chromium ions is caused to flow between a plurality of electrodes.
When the anode has a surface of iron/iron alloy/insoluble iron
compound, an iron hydroxide derivative will be produced
electrochemically. In this process, hexavalent chromium undergoes
cathodic reduction to form trivalent chromium as insoluble chromic
hydroxide, which complexes with iron at the anode The trivalent
chromium compound, physically or chemically combine with the
insoluble iron derivative to thereby permit removal from solution.
The precipitate is then removed from aqueous by any conventional
techniques.
[0027] Reference may be made to Jakobsen, K. and Laska, R. (1977)
Advanced treatment methods for electroplating wasters, Pollution
Engineering, 8:42-46] wherein aspearin as resin have been used in
ion exchange for removal of chromium.
[0028] Another way of removing Cr(VI) from drinking water is to
reduce the Cr(VI) to Cr(III) and precipitate it as chromium
hydroxide. Reference may be made to El-Shafey. J. Phys. IV France,
107(2003) 419 wherein carbon sorbent has been used to remove Cr
(VI) from aqueous solutions in the pH range 2.2-2.6.
[0029] Reference may be made to A. Li Bojic, M Purenovic and D
Bojic, Water SA, 30(3), 2004, wherein micro-alloyed aluminium
composite (MAIC) has been used as reducing agent for Cr(VI) removal
from water. The mechanism of action is based on processes of
reduction and co-precipitation by Al(OH).sub.3, because Cr(VI) is
removed from the water phase as metal chromium and insoluble
Cr(OH).sub.3 .
[0030] Reference may be made to Liora Rosenthal-Toib et al.,
Synthesis of stabilized nanoparticles of zinc peroxide, Chemical
Engineering Journal Vol 136, March 2008, wherein stabilized
nanoparticles of zinc peroxide were prepared by an
oxidation-hydrolysis-precipitation procedure. However the surface
modifiers used in the present invention are different from the one
reported in prior art.
OBJECTIVE OF THE INVENTION
[0031] The main objective of the present invention is to provide a
process for the removal of arsenic and Cr(III&VI) from the
contaminated water.
[0032] Another objective of the present invention is to reduce the
size of the zinc peroxide nanoparticles suitable for the removal of
arsenic and Cr(III&VI) from the contaminated water Another
object of the present invention is to provide a low cost, high
yield and simple process for the removal of arsenic and
Cr(III&VI) from the contaminated water by using nanoparticles
of zinc peroxide.
[0033] Yet another object is to provide a process for the removal
of arsenic and Cr(III&VI) from the contaminated water without
getting any change in the pH of water after treatment.
[0034] Yet another object is to provide low cost ZnO.sub.2
nanoparticles capped with glycerol /PVP/TEA having size 20.+-.5 nm
for the removal of arsenic and chromium from the contaminated
water.
SUMMARY OF THE INVENTION
[0035] Accordingly, the present invention provides a process for
the removal of arsenic and chromium from contaminated water using
zinc peroxide nanoparticles comprising treating the contaminated
water containing arsenic and chromium with the nanoparticles of
zinc peroxide in a ratio (w/v) ranging from 8:1 to 12:1 (mg/ml),
having the concentration of arsenic, Cr(III&VI) contamination
below 50 ppm in water, at a temperature of 25-30.degree. C., for a
period of 5-10 min, followed by filtration to obtain the desired
low concentrated contamination permissible drinking water.
[0036] In an embodiment of the present invention, the zinc peroxide
nanoparticles used have size below 50 nm.
[0037] In another embodiment of the present invention, the amount
of zinc peroxide used for the removal of arsenic and chromium is
preferably in the range of 225-250 mg per 25 ppm of arsenic and
chromium contaminated water.
[0038] In another embodiment of the present invention, the zinc
peroxide nanoparticles are prepared by the process comprising the
following steps:
[0039] a) dissolving zinc acetate in ammonium hydroxide to obtain a
solution mixture having pH in the range of 9-11;
[0040] b) adding glycerol/PVP/TEA to the solution mixture obtained
in step (a) in a ratio of zinc acetate to glycerol in the range of
2:0.5 to 6:1(w/w), PVP in the range of 10:0.25 to 10:1 (w/w) and
TEA in the range of 1:1 to 1:0.5 (w/w) with respect to zinc acetate
respectively;
[0041] c) adding a polar organic solvent to the solution mixture
obtained in step (b), under stirring, at ambient temperature in the
range of 25-30.degree. C., followed by adding equimolar quantity of
hydrogen peroxide with respect to zinc acetate to obtain the
desired nanoparticles of zinc peroxide.
[0042] In another embodiment of the present invention, the weight
ratio of zinc acetate to glycerol used is preferably in the range
of 2:0.5 to 3:1.
[0043] In another embodiment of the present invention, the weight
ratio of zinc acetate to PVP used is preferably in the range of
10:0.5 to 10:1 (w/w).
[0044] In another embodiment of the present invention, the weight
ratio of zinc acetate to TEA used is preferably in the range of 1:1
to 1:0.5 (w/w).
[0045] In another embodiment of the present invention, yield of
ZnO.sub.2 nanoparticles obtained is in the range of 98-99% with
respect to the starting material.
[0046] In another embodiment of the present invention, the
ZnO.sub.2 nanoparticles removes arsenic, Cr(III&VI) each from
50 ppm to 0.1, 0.14, and 0.18 ppm, respectively without disturbing
the pH of water.
[0047] In another embodiment of the present invention, the
ZnO.sub.2 nanoparticles removes arsenic, Cr(III&VI) each from
30 ppm to 0.03, 0.07 and 0.08 ppm, respectively without disturbing
pH of the water.
[0048] In yet another embodiment of the present invention, the
ZnO.sub.2 nanoparticles removes arsenic, Cr(III&VI) each from
25 ppm to less than the detection limit of AAS-HG in case of
arsenic and 0.01 in case of Cr(III&VI) without disturbing pH of
the water.
[0049] In yet another embodiment of the present invention, the
ZnO.sub.2 nanoparticles removes arsenic, Cr(III&VI) each from
20 ppm to less than the detection limit of AAS-HG and FAAS/GFAAS
respectively without disturbing pH of the water.
[0050] In yet another embodiment of the present invention, the
ZnO.sub.2 nanoparticles removes arsenic, Cr(III&VI) each from
15 ppm to less than the detection limit of AAS-HG and FAAS/GFAAS
respectively without disturbing pH of the water.
[0051] In yet another embodiment of the present invention, the
ZnO.sub.2 nanoparticles removes arsenic, Cr(III&VI) each from
10 ppm to less than the detection limit of AAS-HG and FAAS/GFAAS
respectively without disturbing pH of the water.
[0052] In still another embodiment of the present invention, the
ZnO.sub.2 nanoparticles removes arsenic, Cr(III&VI) each from 5
ppm to less than the detection limit of AAS-HG and FAAS/GFAAS
respectively without disturbing pH of the water
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0053] FIG. 1 XRD Pattern of ZnO.sub.2 powder
[0054] FIG. 2 TEM of ZnO.sub.2 powder as synthesized
[0055] FIG. 3 TEM and EDS of ZnO.sub.2 powder after reacting with
arsenic (showing adsorption of arsenic on the surface of zinc
peroxide)
[0056] FIG. 4 TEM of ZnO.sub.2 powder after removing Arsenic
[0057] FIG. 5 TEM and EDS of ZnO.sub.2 powder after reacting with
chromium (showing adsorption of chromium on the surface of zinc
peroxide)
[0058] FIG. 6 TEM of ZnO.sub.2 powder after removing chromium
[0059] FIG. 7 FTIR of ZnO.sub.2 powder after arsenic removing
[0060] FIG. 8 FTIR of ZnO.sub.2 powder after Cr(III&VI)
removal
DETAILED DESCRIPTION OF THE INVENTION
[0061] The present invention demonstrates the use of chemically
prepared ZnO.sub.2 nanoparticles capped with glycerol and PVP for
removal of arsenic and chromium metal ion from the contaminated
water. The synthesized ZnO.sub.2 nanoparticles remove arsenic and
chromium from the contaminated water from the level of 25 ppm to
less than the detection limits of the AAS-HG and FAAS/GFAAS
instruments used respectively, which is less than the USEPA
prescribed limit 10 ppb for arsenic and 50 ppb for chromium for
drinking water.
[0062] Synthesis of zinc peroxide nanoparticles
[0063] In the present invention ZnO.sub.2 nanoparticles, used for
arsenic and chromium removal, were synthesized using zinc acetate
di-hydrate as precursors in ammonical water medium at room
temperature. For the synthesis of ZnO.sub.2, 10 gm of zinc acetate
was dissolved in minimum quantity of ammonia solution and it was
diluted to 200 ml by acetone/methanol/ ethanol water mixture
(Water: solvent: 4:1). 0.5 gm PVP or 2.5 gm of glycerol or 1:1
quantity of TEA of with respect to zinc acetate were added to
reduce the size of particles of the zinc peroxide. Further, 65 ml
of hydrogen peroxide was added in above solution at pH 9-11 at room
temperature. The maximum quantity of zinc peroxide nanoparticles of
20.+-.5 nm were synthesized by varying quantity of the capping
agent, pH and by varying solvent to water ratio. The solution was
stirred on magnetic stirrer for 1 hour after adding hydrogen
peroxide solution. The precipitate was centrifuged washed several
times with 1:1 water-solvent mixture and then with de-ionized water
several times. Finally the precipitate was dried at 105.degree. C.
in an oven upto complete dryness. XRD of synthesized zinc peroxide
nanoparticles shows pure phase of zinc peroxide and HRTEM
micrograph shows spherical nature of the nanoparticles. We have
also synthesized particles of sizes 10.+-.5 and 45.+-.5 by varying
the solvent and capping agent concentration. The efficiency
increases as the particles sizes reduces. But at the same time it
is not possible for us to separate the nanoparticles of zinc
peroxide without centrifuge because particles of lower sizes float
in the water and without centrifuge does not settled down. The
particles of bigger sizes as claimed gets settled down and water
can be separate easily. However we are in the process to make some
device, which can filter the particles of low size.
[0064] Arsenic/ Chromium metal ion removal using ZnO.sub.2
nanoparticles:
[0065] Standard arsenic and Cr(III) solutions of 1000-ppm
concentration (SCP science USA) were used after desired dilutions,
while 1000-ppm of Cr(VI) was prepared from high purity potassium
dichromate following primary method and it was further diluted to
desired range by proper dilution.
[0066] For each experiment known quantity (by weight) of ZnO.sub.2
nanoparticles powder was mixed in 25 ml of standard arsenic/
Cr(III) and Cr(VI) solution in an ultrasonic cleaner (5-10 min).
The mixture was then subjected to 2-3 minutes of centrifugation
process to remove the ZnO.sub.2 nanoparticles. The remaining
solution was filtered by any known method to remove the residual
ZnO.sub.2 nanoparticles like Buckner funnel. The filtered water was
then tested for the left over arsenic, Cr(III) and Cr(VI)
content.
[0067] In the present invention a highly sensitive hydride
generation atomic absorption spectroscopy (HGAAS) was used in which
arsenic in presence of hydrochloric acid and sodium borohydride
forms arsenic hydride (AsH.sub.3), which atomizes at 900.degree. C.
and produces the spectra. This technique is highly sensitive and
arsenic can be detected upto 0.03 ppb.
[0068] The determination of Cr(III&VI) was carried out by Flame
atomic absorption spectrometer at the optimize conditions for
chromium, while the lower concentration less than 0.1 ppm were
analyzed by graphite furnace atomic absorption spectrometer.
[0069] The novelty of the invention lies in the use of ZnO.sub.2
nanoparticles as the adsorbent for arsenic/Cr(III&VI) metal
ions and the level up to which it removes the
arsenic/Cr(III&VI) concentration from 25 ppm to the potable
limits (less than 0.01 ppm in case of arsenic and 0.01 in case of
Cr(III&VI)).
[0070] Several experiment were carried out for varying quantity of
arsenic, Cr(III&VI) with fixed quantity of ZnO.sub.2
nanoparticles.
[0071] The following examples are given by the way of illustration
and therefore should not be construed to limit the scope of the
invention.
Example 1
Methods for the preparation of ZnO2 nanoparticles using glycerol as
surface modifier
[0072] (i) 10 gm of zinc acetate was dissolved in 15 mL of ammonia
solution and it was diluted to 200 ml of aqueous acetone (Water to
solvent: 4:1). 2.5 gm of glycerol was added to the above solution
mixture at pH 9.5 followed by adding 65 ml of hydrogen peroxide to
obtain the nanoparticles of the zinc peroxide having average
particle size distribution of 20.+-.5 nm.
[0073] (ii) 10 gm of zinc acetate was dissolved in 15 mL of ammonia
solution and it was diluted to 200 ml of aqueous acetone (Water to
solvent: 4:1). 5 gm of glycerol was added to the above solution
mixture at pH 9.5 followed by adding 65 ml of hydrogen peroxide to
obtain the nanoparticles of the zinc peroxide having average
particle size distribution of 10.+-.5 nm.
[0074] (iii) 10 gm of zinc acetate was dissolved in 15 mL of
ammonia solution and it was diluted to 200 ml of aqueous acetone
(Water to solvent: 4:1). 0.5 gm of glycerol was added to the above
solution mixture at pH 9.5 followed by adding 65 ml of hydrogen
peroxide to obtain the nanoparticles of the zinc peroxide having
average particle size distribution of 45.+-.5 nm.
Example 2
Preparation of ZnO2 nanoparticles using PVP as surface modifier
[0075] (i) 10 gm of zinc acetate was dissolved in 15 mL of ammonia
solution and it was diluted to 200 ml of aqueous methanol (Water to
solvent: 4:1). 0.5 gm of PVP was added to the above solution
mixture at pH 10, followed by adding 65 ml of hydrogen peroxide to
obtain the nanoparticles of the zinc peroxide having average
particle size distribution of 20.+-.5 nm.
[0076] (ii) 10 gm of zinc acetate was dissolved in 15 mL of ammonia
solution and it was diluted to 200 ml of aqueous methanol (Water to
solvent: 4:1). 1 gm of PVP was added to the above solution mixture
at pH 10, followed by adding 65 ml of hydrogen peroxide to obtain
the nanoparticles of the zinc peroxide having average particle size
distribution of 10.+-.5 nm.
[0077] (iii) 10 gm of zinc acetate was dissolved in 15 mL of
ammonia solution and it was diluted to 200 ml of aqueous methanol
(Water to solvent: 4:1). 0.15 gm of PVP was added to the above
solution mixture at pH 10, followed by adding 65 ml of hydrogen
peroxide to obtain the nanoparticles of the zinc peroxide having
average particle size distribution of 45.+-.5 nm.
Example 3
Preparation of ZnO2 nanoparticles using TEA as surface modifier
[0078] (i) 10 gm of zinc acetate was dissolved in 15 mL of ammonia
solution and it was diluted to 200 ml of aqueous ethanol (Water to
solvent: 4:1). 5gm of TEA was added to the above solution mixture
at pH 11, followed by adding 65 ml of hydrogen peroxide to obtain
the nanoparticles of the zinc peroxide having average particle size
distribution of 20.+-.5 nm.
[0079] (ii) 10 gm of zinc acetate was dissolved in 15 mL of ammonia
solution and it was diluted to 200 ml of aqueous ethanol (Water to
solvent: 4:1). 10 gm of TEA was added to the above solution mixture
at pH 11, followed by adding 65 ml of hydrogen peroxide to obtain
the nanoparticles of the zinc peroxide having average particle size
distribution of 10.+-.5 nm.
[0080] (iii) 10 gm of zinc acetate was dissolved in 15 mL of
ammonia solution and it was diluted to 200 ml of aqueous ethanol
(Water to solvent: 4:1). 1.5gm of TEA was added to the above
solution mixture at pH 11, followed by adding 65 ml of hydrogen
peroxide to obtain the nanoparticles of the zinc peroxide having
average particle size distribution of 45.+-.5 nm.
Example 4
Removal of Arsenic and chromium from water using zinc peroxide
nanoparticles
[0081] Three different ranges nonmaterial i.e. 10.+-.5, 45.+-.5 and
20.+-.5 nm sizes have been used for the removal of arsenic and
Cr(III&VI). All the three ranges of ZnO.sub.2 nanoparticles
remove arsenic and Cr(III&VI) effectively. The particles of
10.+-.5 nm sizes requires centrifuge after process to separate out
from the water because the small particles get filtered through
Buckner funnel. The arsenic and Cr(III&VI) efficiency of
nanoparticles reduces as the size of nanoparticles increases
(>50 nm). The following example has been given for the 20.+-.5
nm size nanoparticles.
[0082] Quantity of ZnO.sub.2 having average particle size
distribution of 20.+-.5 nm taken for process=0.25 g
[0083] Water taken=25 ml
[0084] Concentration of Arsenic and Cr(III&VI) taken=50 ppm
[0085] Concentration of Arsenic after treatment with ZnO.sub.2=0.1
ppm
[0086] Concentration of Cr(III) after treatment with ZnO.sub.2=0.14
ppm
[0087] Concentration of Cr(VI) after treatment with ZnO.sub.2=0.18
ppm
Example 5
[0088] Quantity of ZnO.sub.2 having average particle size
distribution of 20.+-.5 nm taken for process=0.25 g
[0089] Water taken=25 ml
[0090] Concentration of Arsenic and Cr(III&VI) taken=30 ppm
Concentration of Arsenic after treatment with ZnO.sub.2=0.03 ppm
Concentration of Cr(III) after treatment with ZnO.sub.2=0.07
ppm
[0091] Concentration of Cr(VI) after treatment with ZnO.sub.2=0.08
ppm
Example 6
[0092] Quantity of ZnO.sub.2 having average particle size
distribution of 20.+-.5 nm taken for process=0.25 g
[0093] Water taken=25 ml
[0094] Concentration of Arsenic and Cr(III&VI) taken=25 ppm
[0095] Concentration of Arsenic after treatment with
ZnO.sub.2=below detection limit of AAS-HG instrument
[0096] Concentration of Cr(III) after treatment with ZnO.sub.2=less
than 0.01 ppm by GFAAS instrument Concentration of Cr(VI) after
treatment with ZnO.sub.2=0.01 ppm by GFAAS instrument
Example 7
[0097] Quantity of ZnO.sub.2 having average particle size
distribution of 20.+-.5 nm taken for process=0.25 g
[0098] Water taken=25 ml
[0099] Concentration of Arsenic and Cr(III&VI) taken=20 ppm
[0100] Concentration of Arsenic after treatment with
ZnO.sub.2=below detection limit of AAS-HG instrument
[0101] Concentration of Cr(III) after treatment with
ZnO.sub.2=below detection limit of FAAS/GFAAS instrument
[0102] Concentration of Cr(VI) after treatment with ZnO.sub.2=below
detection limit of FAAS/GFAAS instrument
Example 8
[0103] Quantity of ZnO.sub.2 having average particle size
distribution of 20.+-.5 nm taken for process=0.25 g
[0104] Water taken=25 ml
[0105] Concentration of Arsenic and Cr(III&VI) taken=15 ppm
[0106] Concentration of Arsenic after treatment with
ZnO.sub.2=below detection limit of AAS-HG instrument
[0107] Concentration of Cr(III) after treatment with
ZnO.sub.2=below detection limit FAAS/GFAAS of instrument
[0108] Concentration of Cr(VI) after treatment with ZnO.sub.2=below
detection limit FAAS/GFAAS of instrument.
Example
9
[0109] Quantity of ZnO.sub.2 having average particle size
distribution of 20.+-.5 nm taken for process=0.25 g
[0110] Water taken=25 ml
[0111] Concentration of Arsenic and Cr(III&VI) taken =10
ppm
[0112] Concentration of Arsenic after treatment with
ZnO.sub.2=below detection limit of AAS-HG instrument
[0113] Concentration of Cr(III) after treatment with
ZnO.sub.2=below detection limit FAAS/GFAAS of instrument
[0114] Concentration of Cr(VI) after treatment with ZnO.sub.2=below
detection limit FAAS/GFAAS of instrument
Example 10
[0115] Quantity of ZnO.sub.2 having average particle size
distribution of 20.+-.5 nm taken for process=0.25 g
[0116] Water taken=25 ml
[0117] Concentration of Arsenic, Cr(III&VI)taken=5 ppm
[0118] Concentration of Arsenic after treatment with
ZnO.sub.2=below detection limit of AAS-HG instrument
[0119] Concentration, of Cr(III) after treatment with
ZnO.sub.2=below detection limit FAAS/GFAAS of instrument
[0120] Concentration of Cr(VI) after treatment with ZnO.sub.2=below
detection limit FAAS/GFAAS of instrument
[0121] Advantages of the present invention:
[0122] 1. This invention makes the contaminated water almost free
of arsenic and Cr(III&VI) after filtration that could be use
for drinking and various household utilities.
[0123] 2. Treatment with ZnO.sub.2 nanoparticles maintains the pH
of the water to the permissible limit.
[0124] 3. The proposed method for the synthesis of zinc peroxide is
eco-friendly and there is no generation of any toxic gases during
synthesis.
[0125] 4. The material was synthesized at low temperature and there
is no requirement of any specific instruments.
[0126] 5. The method gives more than 98% yield, which is an added
advantage of the process.
[0127] 6. The proposed material is low cost in comparison to other
materials available for the removal of arsenic.
[0128] 7. The solvent used in the synthesis process can be
recovered by distillation, which is further added advantages of the
process for reduction of the cost of the process.
[0129] 8. The process does not add any impurities in the water as
it is insoluble in water and can be separated by any known
method.
[0130] 9. The synthesis method is so simple and fast and within 2-3
hours on can get synthesized nanoparticles of zinc peroxide with
more than 98% yield.
[0131] 10. The particles of 10.+-.5 are more efficiently removes
arsenic and Cr(III&VI) from contaminated water but in this
process centrifugation is essential to separate zinc peroxide from
the water. The particles of 10.+-.5 nm sizes can be synthesized by
varying the concentration of solvent and capping agent.
* * * * *