Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group vib metal
Reexamination Certificate
2000-12-13
2004-12-21
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group vib metal
C423S065000, C210S670000, C210S673000, C210S683000, C210S684000, C210S688000, C210S912000, C210S913000, C588S252000, C588S256000, C588S257000
Reexamination Certificate
active
06833123
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the removal and stabilization of chromate ions and other oxy-metal ions from liquid solution. Particularly, this invention relates to a method that makes use of barium compounds to remove chromate ions and other oxy-metal ions from liquid solutions.
For purposes of environmental protection, chromate ions are considered as very serious oxy-metal ions. Because of high toxicity, chromate ions can cause cancer or induce cell mutation in human as well as animal bodies. Chromate salts are widely used in electroplating, dye-works, chemical fertilizer production, petrochemical industry, tannery, textile industry, paper-mill, steel-works, and more. Therefore, research on the treatment and recycling of underground water, household waste water, or industrial liquid wastes containing chromate ions has received much attention all over the world. Presently, accepted methods for treating such liquid wastes involve methods such as: adsorption, reduction-precipitation, ion-exchange, solvent extraction, diaphragm electrolysis, inverse dialysis, etc.
U.S. Pat. No. 4,481,087 discloses an adsorption method, in which hydrous ferrous oxide (FeO(OH)) is used in processing to form a powdery, porous black material with high surface area, as adsorbent, whereby it adsorbs chromate ions or dichromate ions (Cr
2
O
7
−2
and HCr
2
O
7
−
). The method is far from satisfactory, in that one gram of the absorbent can at most absorb only 25 mg of hexavalent chromium ion Cr
+6
).
In U.S. Pat. Nos. 5,302,290 and No. 5,456,840, a complex salt agent, poly-di-methyl di-allyl ammonium chloride (i.e. PDMDAAC), is employed to react with the soluble Cr
+6
in an aqueous solution, thus forming a chromic complex. This aqueous solution is then made to pass through an ultra-filter. The concentrated chromic complex mud gathered after the filtration process is mixed with barium chloride (BaCl
2
) or lead chloride (PbCl
2
) to form the almost insoluble barium chromate (BaCrO
4
) or lead chromate (PbCrO
4
) precipitates; meanwhile, complex cations react with chlorine ions, turning into the original complex salt agent which is perfectly suitable for reuse. By applying this reduction-precipitation method to underground water purification, chromate ions' concentration can be reduced down to 42 ppm or below. However, because ultra-filtration is a time-consuming process, this method is of but very limited use.
U.S. Pat. No. 4,525,483 gives an example of ion-exchange resin technique, in which chlorine ion-exchange resin and hydrogen ion-exchange resin are mixed into a resin bed to remove CrO
4
−2
from the spent coolant discharged from a water cooling system, or from the sodium chloride solution used in an electrolysis process for the making of sodium chlorate (NaClO
3
). The method is still not exactly satisfactory, in that 1 mg of chlorine ion-exchange resin can absorb only about 0.01 g of CrO
4
−2
.
A method for stabilizing chromate ions within cement is disclosed in U.S. Pat. No. 4,572,739, where hydrated ferrous sulfate salt, FeSO
4
.7H
2
O, or ferrous sulfide, FeS, is mixed into cementing materials in the process of cement production, so as to reduce the solubility of the soluble chromate salts within said mixture. However, in practice, it was quickly found that, thanks to the high moisture and high temperature conditions inside the cement pulverizer, chromate salts were partially dissolved, which trickled down and left traces on the conveying belts, causing skin irritation and other more serious health problems among the cement workers. So this chromate-ion stabilization method fails to attain its goal.
U.S. Pat. No. 5,211,853 discloses a reduction-precipitation method using hydroxyl amine, NH
3
.OH, or hydroxyl amine sulfate, (NH
2
OH)
2
.H
2
SO
4
(i.e. HAS), for reduction agent. At controlled pH and temperature, said reduction agent reacts with potassium dichromate (K
2
Cr
2
O
7
) that has been used in the production of sodium chlorate, resulting in divalent and/or trivalent chromic hydroxide precipitates. After filtering out such chromate salts, residual Cr
+6
concentration in the filtrate is found to be between 2 and 10 ppm.
U.S. Pat. No. 5,326,439 makes use of Andco electrolytic method to remove such soluble toxic elements as chromium (Cr), arsenic (As) and lead (Pb) from underground water. According to this disclosure, ferrous ions are formed at the iron-alloy anodes under suitable conditions, while in the electrolyte Cr
+6
is reduced to Cr
+3
, and at the same time the barely soluble chromium trioxide (CrO
3
) precipitates are coming out. Thereafter, the precipitates are separated from the water by means of filtration. This is doubtless a very effective method for small-scale water purification, as residual Cr
+6
concentration of such treated water is lower than 0.05 ppm.
Canadian Patents No. 1, 119, 772 and No. 1, 139, 080 disclose a reduction-precipitation method to reduce Cr
+6
to Cr
+2
and C
+3
, where hydroxylamine (NH
3
OH) or hydrazine (NH
2
.NH
2
) is the reduction agent which reacts with dichromate salts present in a chlorate solution, resulting in a blue-green hydrated chromium oxide precipitate (Cr
3
O
4
.xH
2
O). A distinct drawback of this method is that such reduction agents are as toxic as they are expensive.
Still one more reduction-precipitation method is found in U.S. Pat. No. 3,616,344, where sodium sulphite Na
2
SO
3
), or ammonium sulphite ((NH
4
)
2
SO
3
), or tin diethyl-oxide (Sn(C
2
H
5
)
2
O), being the Cr
+6
reduction agent of choice, is added into a chlorate solution, causing the precipitation of a trivalent chromium hydroxide. The precipitates are then separated from the solution by means of filtration or centrifugation. Furthermore, the patent discloses that the addition of soluble metal salts (e.g. zinc, cobalt, lead and copper salts) into chromate ions' solution can cause the formation of insoluble chromate salts (e.g. PbCrO
4
) which are subsequently filtered out, resulting in the removal of chromate ions.
A similar reduction-precipitation method for removing chromate salts from sodium chlorate solution is disclosed in U.S. Pat. No. 4,086,150, where soluble sulphides and then ferrous salts are added into the solution to convert chromate ions into trivalent chromium compounds which afterwards are filtered out.
In Taiwan Patent Application No. 6211803 a unique approach to chromate ions' removal and recycling is made public. Here a pipe is filled up with porous leech stones which are spread over with almost insoluble lead compounds such as lead hydroxide (Pb(OH)
2
) and lead carbonate (PbCO
3
). Then the two ends of the pipe are sealed off with cotton fibers. By putting through the pipe a waste water known to be containing chromate ions, chromate ions react with aforesaid lead compounds, resulting in insoluble lead chromate (PbCr)
4
). Since by this method some lead ions are present in the treated water, the water is conducted to pass through a cation-exchange resin to absorb and detain the lead ions. And finally, the lead chromate is retrieved from the pipe for use in painting.
Taiwan Patent Application No. 77106237 discloses a method to remove Cr
+6
from a chlorate-salt aqueous solution which contains chlorite ions and dichromate ions. Said chlorate salts solution is obtained from electrolytic salt water. At pH 10.0 and temperature 80° C., chlorine water and alkaline buffers are added into the solution, converting dichromate ions into divalent or trivalent chromium compounds which gradually become precipitates of a blue-green color. Thereafter, said precipitates are removed from the solution by means of filtration.
Taiwan Patent Application No. 78102127 discloses a solvent-extraction method for removing heavy metal ions anions or cations of chromium, nickel, lead and copper, from waste water, where organic phosphinic acid, or 2,2-diethyl hexethyl phosphoric acid (D2EBPA), or one of aliphatic ammonium group is employed as extraction agen
Huang Ching-Tsuen
Lai Wen-Chao
Lee Tsye-Shing
Liu Tzeng-Ming
Bos Steven
Burns Doane Swecker & Mathis L.L.P.
Institute of Nuclear Energy Research
LandOfFree
Method for liquid chromate ion and oxy-metal ions removal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for liquid chromate ion and oxy-metal ions removal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for liquid chromate ion and oxy-metal ions removal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3296188