AU2021201922B2 - High capacity adsorbent for oxyanions and cations and method for making the same - Google Patents

Abstract

OF THE DISCLOSURE An alumina-based adsorbent and method of making exhibiting high affinity and capacity towards cations and oxyanions in a broad pH range and presence of large excess of competitive ions. Alumina based adsorbent is a mixed oxide of alumina existing in tetra-, penta-, and octahedral coordination at specific ratio, and oxides of polyvalent metals of elements titanium, zirconium, tin, cerium, lanthanum, iron, or combinations thereof. The alumina-based adsorbent may be used for selective removal of oxyanions of fluoride, phosphorus, arsenic, chromium, and/or selenium, and/or cations of lead, mercury, cadmium, copper, and/or zinc, from drinking water, industrial streams and wastes, in medicine and food industry.

Description

HIGH CAPACITY ADSORBENT FOR OXYANIONS AND CATIONS AND METHOD FOR MAKING THE SAME

Background Of The Invention

1. Field of the Invention

[0001] This invention relates to filtration media, and more specifically to a high capacity adsorbent and the fabrication thereof. The high capacity adsorbent includes enhanced performance towards fluoride ion and oxyanions of arsenic and phosphorus in a broad pH

range in the presence of high excess of competitive ions. A high capacity adsorbent is useful

for the selective removal of fluoride ion and oxyanions of phosphorus and arsenic from drinking water, industrial streams and wastes, in the medicine and food industries. Removal

of other types of oxyanions are possible, such as chromium (trivalent or hexavalent, as chromate or dichromate), and selenium (selenite and selenite). The invention further relates

to the use of mixed metal oxide (MOX) material to remove cations.

2. Description of Related Art

[0002] Ion exchange properties of insoluble polyvalent metal hydroxides have been studied since the 1950's [C.B. Amphlett, Inorganic Ion Exchangers, Elsevier, New York (1964)]. It was found that some of these hydroxides (aluminum hydroxide, ferric hydroxide, titanium

hydroxide, zirconium hydroxide, and the like) are amphoteric and behave as cation

exchangers or anion exchangers depending on pH.

[0003] Fluoride is considered an essential element for animals and humans because of the role it plays in bone and dentin mineralization. However, when fluoride is present in excess

of 1.5 mg/L it affects teeth, endocrine glands, liver and other organs. Presently, the World Health Organization recognizes activated alumina (AA) adsorption as one of the best

adsorbents for water defluorination. A number of studies on AA performance in water defluorination under varying process conditions have shown that the optimum pH for maximum adsorption is between 5 and 7. The capacity of the activated alumina on fluoride depends on the AA preparation route, crystalline form, and can vary from 1 to 20 mg/g, depending on the operating conditions [A. Bhatnagar et al, Fluoride removalfrom water by adsorption - A review, Chemical Engineering Journal, 171, p.811-840, (2011)]. Other types of polyvalent metal oxides also have ability to remove fluoride ion, but their efficiency typically is lower than that of AA. Granular ferric hydroxide (GFH) demonstrates capacity on fluoride of approximately 7 mg/g at a pH of approximately 6 - 7; hydrous titania and zirconia have similar poor performance (U.S. Patent 6,077,809, demonstrating capacity of approximately 5 mg F/g at a pH of approximately 3). Some binary polyvalent mixed oxides have been tested as potential adsorbents for fluoride. It was found that alumina-titania oxide has a capacity of approximately 3 mg F/g; zirconia-iron oxide having a capacity of approximately 10 mg F/g; and alumina-iron oxide having a capacity up to 4 mg F/g. (See, for example, U.S. Pat 6,599,429). Alumina-ceria oxide has high capacity on fluoride up to 90 mg/g at a pH of 6, but the high cost of cerium makes this material cost-prohibitive for water defluorination.

[0004] Polyvalent metal based hydrous oxides show high affinity towards oxyanions of phosphorus and arsenic. Zirconium hydrous oxide has been used for phosphate removal in

kidney dialysis. (See, e.g., U.S. Pat. Nos. 6,878,283; 7,033,498; 7,135,156; 8,002,726; and U.S.

Pat. Publication No. 20100078387). It has been shown that zirconium oxide capacity on phosphorus from blood dialysate can reach 90 - 120 mg P0 4/g. High affinity of iron oxides to

P04 allows their use for water treatment (Ref. U.S. Pat. No. 5,876,606), as well as for oral

administration in humans and animals for hyperphosphatemia prevention (Ref. Pat.

Publication Nos. 2009169645 and 2013316018).

[0005] Aluminum hydroxide was proposed as an adsorbent for arsenic (Ref. U.S. Pat. No. 6,030,537); however, alumina capacity on arsenic is significantly lower than that of hydrous titanium (see, e.g., U.S. Pat. Nos. 6,919,029; 7,473,369; and 7,497,952), zirconium (U.S. Pat. Nos. 6,383,395; 7,252,767; and 6,077,809) and iron oxides (U.S. Pat. Nos. 6,830,695;

7,625,487; and 8,404,210). Moreover, aluminum hydroxides are able to adsorb only arsenic(V) and have no affinity towards arsenic(III). Using polyvalent mixed oxides for

selective arsenic removal has been shown demonstrated: alumina-iron oxide (U.S. Pat. No.

6,599,429), manganese and iron-doped titania- and zirconium- oxides (U.S. Pat. No. 8,216,543).

[0006] Broad use of selective inorganic adsorbents for water defluorination and arsenic removal, eutrophication prevention, treatment of industrial streams, and in different

applications in the medicine and food industries is absent in the art, and requires further investigation for cost-efficient materials with enhanced adsorption performance.

Summary of the Invention

[0007] Bearing in mind the problems and deficiencies of the prior art, it is therefore an object at least in embodiments of the present invention to provide an adsorbent useable for selective removal of fluoride ions and oxyanions of phosphorus and arsenic from drinking

water, industrial streams and wastes, particularly in the medicine and food industries.

[0008] It is another object at least in embodiments of the present invention to provide an adsorbent having an affinity towards As(V) and As(III).

[0009] In a first aspect, the present invention is directed to an adsorbent for fluoride ion and oxyanions of arsenic and phosphorus, comprising mixed oxide containing alumina in tetra-,

penta-, and octahedral coordination or any combination thereof, and a polyvalent metal

oxide including titanium, zirconium, tin, cerium, lanthanum, iron, or any combination of thereof.

[0010] The content of the alumina in the mixed oxide is from about 20 wt% to about 80 wt%, or about 50 wt% to about 80 wt%. An amount of pentahedrally coordinated alumina is

preferably from about 10% to about 30% by weight, and an amount of tetrahedrally coordinated alumina is preferably from about 5% to about 15% by weight.

[0011] The mixed oxides may adsorb arsenic(V) and arsenic(Ill) species. The mixed oxide does not show phase segregation and remains amorphous up to 500°C. The mixed oxide shows adsorption capacity decrease less than 40% after calcination. The mixed oxide has

capacity on fluoride ion from about 40 mg F/g to about 80 mg F/g at pH range from 7 to 6, respectively.

[0012] The mixed oxide capacity on fluoride ion does not decrease more than 30% in the presence of competitive ions that are approximately 10 to 100 times in excess, the

competitive ions including HCO 3, Cl, NO3, SO4 , or any combination of thereof.

[0013] The mixed oxide capacity on fluoride ion does not decrease more than 40% in the presence of equimolar amounts of phosphate, silicate ions, or any combination of thereof.

[0014] The mixed oxide has a higher affinity towards phosphate ions than arsenic ions.

[0015] The mixed oxide has a separation factor ratio of phosphorus/arsenic from about 1.2 to about 2 in equimolar solutions. The mixed oxide may have an adsorption capacity on P0 4 ions from hemo-dialysate solution at a pH level of about 5 to 6 of at least 160 mg P0 4/g.

[0016] The mixed oxide may have an adsorption capacity on P04 ions from peritoneal dialysate solution at a pH level of about 7 to 8 of at least 100mg P0 4/g. The mixed oxide is thermally stable, and has an adsorption capacity decrease of less than 40% after calcination.

[0017] In a second aspect, the present invention is directed to a method of making an adsorbent comprising precipitation of mixed oxide by a reaction between a solution or a slurry including a water soluble compound, a polyvalent metal compound, and a base solution in the pH range from about 4 to about 10, ageing the precipitate in mother liquor at the pH level of precipitation, washing the precipitate with water, and drying the precipitate.

[0018] The adsorbent is preferably alumina-based, and the water soluble compound is preferably an aluminum compound comprising aluminum sulfate, aluminum chloride,

aluminum nitrate, or any combination thereof. The water soluble compound may further be comprised of an aluminum oxide pseudo-sol.

[0019] The polyvalent metal compound comprises water soluble nitrates, chlorides, sulfates of titanium, zirconium, tin, cerium, lanthanum, iron, or combinations thereof. The polyvalent

metal compound may comprise a sol of titanium, zirconium, tin, cerium, lanthanum, iron, or combinations thereof.

[0020] The polyvalent metal compound may comprise nano-sized titanium, zirconium, tin, cerium, lanthanum, iron oxides, or combinations thereof.

[0021] The precipitation is carried out at a constant pH level in the range 4-10 under batch or continuous flow conditions by using a base including alkali hydroxides, ammonium hydroxide, alkali carbonates, ammonium carbonate, or combinations thereof.

[0022] The precipitation may also be carried out at a pH level changing from acidic to about 4 -10 under batch conditions by addition of a base reagent including alkali hydroxides,

ammonium hydroxide, alkali carbonates, ammonium carbonate, or combinations thereof.

[0023] The precipitate is aged in mother liquor at a pH level of precipitation at ambient or elevated temperature for 1-3 hours.

[0024] The adsorbent may include combining 147 g of A(NO 3)3*9H 20, 10 g of anatase TiO 2 ,

and 400 g of deionized water, with NaOH at 25 wt % solution and water at the pH level of precipitation from about 4 to about 10, such that the adsorbent, when dried, contains approximately 66.6% A1 20 3 and 33.4% TiO 2

.

[0025] The adsorbent may include combining 100 g of 20% aluminum hydroxide pseudo solution, 10 g of rutile TiO2 and 300 g of deionized water, with 25 wt %solution and water at

the pH level of precipitation of about 7, such that the adsorbent contains approximately

66.6% A1 20 3 and 33.4% TiO 2 .

[0026] The adsorbent may include combining 130.6 g of A1 2 (SO 4 )3*18H 2 0, 100 g of a 20 wt

% ZrOCl2 solution on Zr 2, and 400 g of deionized water, with 25 wt %solution of NaOH and water at a constant pH level of 7, such that the adsorbent contains approximately 50% A1 2 0 3

and 50% ZrO 2 .

[0027] The adsorbent may include combining 130.6 g of A1 2 (SO 4 )3*18H 2 0, 100 g of a 20 wt

% La(NO 3)3 (on La 2 0 3 ) solution, and 400 g of deionized water, with 25 wt %solution of NaOH

and water at a constant pH level of 7, such that the adsorbent contains approximately 50% A120 3 and 50% La 2 0 3 .

[0028] The adsorbent may include combining 130.6 g of A 2 (SO 4 )3*18H 20, 67.5 g of FeC 3 *6H 20, and 400 g of deionized water, with 25 wt %solution of NaOH and water at a

constant pH level of 7, such that the adsorbent contains approximately 50% A1 20 3 and 50% Fe 20 3 .

[0029] In a third aspect, the present invention is directed to a method of making an alumina titania mixed oxide adsorbent comprising: forming a metal containing solution by mixing A12 (SO 4 )3*18H 2 0, 15.0 wt %titanyl sulfate solution on TiO2, and deionized water; adding

simultaneously the metal containing solution and 25 wt %solution of NaOH with water at a

predetermined flow rate, allowing for a constant pH level; aging a precipitate of the alumina titania mixed oxide in mother-liquor at ambient temperature; separating the precipitate from the mother-liquor by filtration; washing the precipitate with deionized water to form a wet cake; and drying the wet cake.

[0030] The step of forming a metal containing solution includes mixing 130.6 g of A12 (SO 4 )3*18H 2 0, 133 g of 15.0 wt %titanyl sulfate solution on TiO2, and 400 g of deionized water.

[0031] The step of adding simultaneously the metal containing solution and 25 wt % solution of NaOH with water includes adding 800 ml of the water.

[0032] The step of aging the precipitate includes exposing the precipitate to ambient temperature for one hour.

[0033] In a fourth aspect, the present invention is directed to a method of making an adsorbent comprising: forming a metal containing solution by mixing AICl 3*6H 20, 15.0 wt

% titanyl sulfate solution on TiO 2, and deionized water; adding the metal containing solution

and 25 wt %solution of NaOH with water at a predetermined flow rate, allowing for a constant pH level in the reaction mixture; aging a precipitate of the alumina titania mixed

oxide in mother-liquor at ambient temperature; separating the precipitate from the mother liquor by filtration; washing the precipitate with deionized water to form a wet cake; and

drying the wet cake.

Brief Description of the Drawings

[0034] The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for

illustration purposes only and are not drawn to scale. The invention itself, however, both as

to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which:

[0035] Fig. 1 graphs P/A separation factors calculated from adsorption capacities on As and P as a function of equilibrium pH on hydrous titanium oxide, hydrated ferric oxide, aluminum

hydroxide, and the mixed oxide 33.4% TiO 2 - 66.6% A12 0 3 from Example 3; and

[0036] Fluoride breakthrough curves are presented in Figure 2 for the alumina based mixed oxide made in Example 3.

[0037] Fig. 3 depicts isotherm data comparing the metal oxide adsorbent of the present invention (MOX-Invention) against TiO2 and disodium titanate, measuring capacity removal

of Cr (mg/g) as a function of equilibrium concentration (ppm);

[0038] Fig. 4 depicts isotherm data comparing the metal oxide adsorbent of the present invention (MOX-Invention) against disodium titanate, measuring capacity removal of Pb

(mg/g) as a function of equilibrium concentration (ppm);

[0039] Fig. 5 depicts a graph charting kinetic data for one embodiment of the metal oxide adsorbent of the present invention (MOX-Invention) versus disodium titanate for the removal of lead (Pb);

[0040] Fig. 6 depicts a graph of Cd removal capacity for the metal oxide adsorbent developed pursuant to the present invention (MOX-Invention) versus titanium oxide (TiO 2 );

[0041] Fig. 7 depicts a graph of copper (Cu) removal capacity for the metal oxide adsorbent developed pursuant to the present invention (MOX-Invention) and titanium oxide (TiO 2); and

[0042] Fig. 8 depicts a graph of zinc removal capacity for metal oxide developed pursuant to the metal oxide adsorbent of the present invention (MOX-Invention) versus titanium oxide

(TiO 2).

Description of the Preferred Embodiment(s)

[0043] In describing the preferred embodiment of the present invention, reference will be made herein to Figs. 1- 8 of the drawings in which like numerals refer to like features of the invention.

[0044] The deficiencies of the prior art as discussed above can be alleviated or overcome by the adsorbent of the present invention. The present invention is directed to a high capacity mixed oxide adsorbent comprising alumina that exists in tetra-, penta-, and octahedral

coordination, and a polyvalent metal oxide selected from the group of titanium, zirconium, tin, cerium, lanthanum, iron, or any combination thereof, that can be used for simultaneous

selective removal of fluoride ion and oxyanions of phosphorus, arsenic(V) and arsenic(III)

from different aqueous streams. The present invention is applicable to other oxyanions as well. Utilizing the composition of the present invention, oxyanions may be removed in

varying degrees of efficiency. The mixed adsorbent of the present invention has been demonstrated to remove oxyanions such as chromium (trivalent or hexavalent, as chromate

or dichromate), and selenium, such as selenite or selenite.

[0045] Mixed oxide adsorbent is an amorphous material that contains from about 20 wt% up to about 80 wt% of alumina, or preferably from about 50% to about 80% of alumina, in

which aluminum exists in octahedral, pentahedral, and tetrahedral coordination, wherein

the amount of pentahedrally coordinated aluminum is from about 10% to about 30%, and tetrahedrally coordinated aluminum is from about 5% to about 15%.

[0046] The unexpected result of the present invention is a strong synergism between all elements in the mixed oxide composition resulting in a significant increase of media

adsorption capacity towards fluoride ion and oxyanions of phosphorus and arsenic in comparison with alumina hydroxide or activated alumina (on the order of twice to six times

greater), as well as with other individual polyvalent metal oxides tested under similar

conditions. Moreover, the applicability to oxyanions generally is realized.

[0047] In one embodiment, aluminum hydroxides are able to adsorb arsenic(V) and have no affinity towards arsenic(Ill), and alumina-based mixed oxides of present invention are able to remove both arsenic(V) and arsenic(Ill) species with a significant capacity increase only for

arsenic(V).

[0048] There appears to be less synergistic affect towards other oxyanions like silicate, chromate, sulfate, and the like. However, testing has provided an unexpected result in the

amount of removal of certain cations, that would otherwise not be considered candidates for the adsorbent of the present invention. In this regard, the removal of chromium

(chromate), and selenium, and other less responsive oxyanions, although less efficient than the removal of fluoride ion and oxyanions of phosphorus and arsenic, is still significant

enough to adopt the proposed mixed oxide adsorbent of the present invention for removal of these contaminants.

[0049] As an illustrative example, Table I depicts a comparison of the removal of chromium by various compositions. As depicted, the removal of chromium as demonstrated by the mixed oxide composition of the present invention was at least as effective as the other

compositions tested, and in most cases exceeded the removal amount.

TABLE I

Adsorbent Cr removed (mg) / dry media (g)

disodium titanate 0

Ti02 (50 rn) 0.051

Ti02 (1.0 pn) 0.377

EnviroScrub 0.7814

MOX-Invention 1 0.589

MOX - Invention 2 0.837

[0050] EnviroScrub is an aqueous amine mixture which irreversibly reacts with contaminants such as hydrogen sulfide and mercaptan. It is generally used to remove H 2 S from

hydrocarbon liquids, natural gas, gas streams, waste-water streams, and scrubber systems. MOX - Invention 1 and MOX - Invention 2 represent two separate trial runs in the test.

[0051] Fig. 3 depicts isotherm data comparing the metal oxide adsorbent of the present invention (MOX-Invention) against TiO2 and disodium titanate, measuring capacity removal

of Cr (mg/g) as a function of equilibrium concentration (ppm). As depicted, the isotherm

data indicates that the metal oxide adsorbent of the present invention is capable of a higher removal capacity at lower concentration levels, where the other adsorbents are unable to

challenge.

[0052] Table 11 depicts a comparison of the removal of selenium species (Se4 , Se) by various compositions. As depicted, the removal of selenium as demonstrated by the composition of the present invention was at least as effective as most other compositions

tested, save ETS-4, and in most cases, at least one test composition of the present invention

exceeded the removal amount of other tested compositions.

TABLE II

Adsorbent Se 4 (mg) / dry media (g) Se" (mg) / dry media (g)

Ti02 (1.0 pm) 42.5 24.1

disodium titanate 18.3 0.0

EnviroScrub 47.1 5.7

ETS-4 7.8 62.1

ETS-10 4.1 27.9

MOX-Invention 1 56.2 9.5

MOX-Invention 2 57.0 35.5

[0053] Comparisons were made to titanium oxide, AMP-025, EnviroScrub, and Englehard Corporation titanosilicate ETS-4 and ETS-10. The capacities depicted in Table 11 are based on

selenium species, not on the full anion of selenite or selenite. Thus, the present invention is shown effectively capable of removing a plurality of oxyanions, inclusive of chromium and

selenium.

[0054] With respect to fluoride, the proposed mixed oxide has capacity on fluoride ion from about 40 mg F/g up to about 80 mg F/g at a pH range of approximately 7 to 6, respectively. Advantageously, the adsorbent's capacity on the fluoride ion does not decrease more than

% in the presence of competitive ions that are approximately 10 to approximately 100

times in excess. The competitive ions typically include HCO 3, Cl, NO 3, SO 4 , or any such combination, and do not decrease more than 40% in the presence of equimolar amounts of

phosphate, silicate ions, or their combination.

[0055] Alumina based mixed oxide has higher affinity towards phosphate ion over arsenic ions with a separation factor for phosphorus/arsenic from approximately 1.2 to about 2 in

equimolar solutions. Individual polyvalent metal oxides do not show preferences in uptake of these ions, and may preferably remove arsenic ions, like hydrous titanium oxide. The measured alumina based adsorbent capacity on the P04 ion from hemo-dialysate solution at a pH level of about 5 - 6 is at least 160 mg P0 4/g, and at least 100 mg P0 4/g from a peritoneal dialysate solution at a pH level of about 7 - 8, which makes it an efficient phosphate scavenger in such applications as, for example, artificial kidney devices.

[0056] Another advantage of the present invention is that mixed oxide is a thermally stable adsorbent and has an adsorption capacity decrease of less than 40% (after calcination at

450°C for 2 hours).

[0057] Some of the hydroxides (aluminum hydroxide, ferric hydroxide, zirconium hydroxide, and the like) are amphoteric and appear to behave as cation exchangers or anion exchangers depending upon the pH level. This unexpected result has been confirmed by the data taken

with respect to the composition of the present invention. In particular, testing has shown

the improved capacity of the composition of the present invention over standard oxides, such as TiO2 for contaminants such as Pb, Hg, Cu, Cd, and Zn, among others.

[0058] Table Ill depicts a comparison of the removal of mercury (Hg) by various adsorbent compositions. As depicted, the removal of Hg as demonstrated by the adsorbent

composition of the present invention was at least as effective as most other adsorbent compositions tested.

TABLE III

Adsorbent Hg removed (mg) / dry media (g)

Ti02 (1.0 pr) >0.326

Ti02 (50 pm) 0.326

Ti02 (different source) 0.326

Zeolite 0.166 titanosilicate 0.439

MOX-Invention 1 0.403

[0059] The adsorbent composition of MOX - Invention Test 1 indicates an appreciable removal amount of mercury with respect to the other compositions compared, fared better

than the others, and removal capacity was similar with that of the titanosilicate composition.

[0060] Similar comparative tests were performed for lead (Pb) removal. Table IV depicts the removal amount results of various compositions with respect to Pb. In this comparison, the adsorbent composition of Invention Test 1 was shown to be the most effective in removing

lead.

TABLE IV

Adsorbent Pb removed (mg) / dry media (g)

MOX-Invention 1 500

Ti02 (50 pm) 163

titanoaluminosilicate 171

Ti02 (1 pm) 227

disodium titanate 239

ETS-4 247

ATS1 280

ATS2 303

ETS-10 350

[0061] In the comparisons of Table IV, ATS was one of the compositions compared. ATS is a high capacity ceramic ion-exchanger with strong kinetics due to its formation, and is

selective predominantly for lead removal even in the presence of competing ions like

calcium and magnesium.

[0062] Fig. 4 depicts isotherm data comparing the metal oxide adsorbent of the present invention (MOX-Invention) against disodium titanate, measuring capacity removal of Pb

(mg/g) as a function of equilibrium concentration (ppm). As depicted, the isotherm data indicates how quickly the media of the present invention removes Pb. The metal oxide

adsorbent composition of the present invention has faster kinetics and a slightly higher

overall capacity for removal.

[0063] As demonstrated above, the synthesis of a mixed metal oxide (MOX) and its subsequent use to remove oxyanions is achieved by the mixed metal oxide adsorbent composition of the present invention.

[0064] Additionally, cations such as Pb2 +, Hg 2 , Cu 2, may also be removed by the composition of the present invention. The media of the present invention has demonstrated

a capacity of at least 385 mg/g for lead removal. This is significantly higher than the Pb

capacity of TiO2 alone, which suggests a reason for this unexpected result, that recombination of the metal oxides allow for sorption (adsorption or ion-exchange) of cations

simultaneously with anion removal.

[0065] Activated carbons are generally not successful in removing cations without additional additives. For example, Graver Technologies' Metsorb STP© can be added to an activated carbon component to remove Pb to a much higher capacity than activated carbon alone.

Activated carbon can remove Hg 2+, but usually only after treatment with a secondary

material, such as a thiol or sulfuric acid. The adsorbent of the present invention does not require this.

[0066] In general, ion-exchange properties, either cation or anion, of adsorbent composite materials depend on the type of impregnated oxide chosen, and as a rule capacity increases up to a certain point with an increase of inorganic oxide content; however, the correlation between the amount of dopant oxide and capacity is not universal, as in many cases capacity is a function of a specific metal oxide phase/structure formed in the pores, and it can vary significantly for similar loadings of the same polyvalent metal oxide. The synthetic method used to form such inorganic adsorbent and composite materials is unique. The compositions identified herein are essentially synthesized from a non-pure basis to provide a mixed oxide

(or hydroxide) to remove both cations and anions simultaneously. As an example, an embodiment of the present invention that forms cation/anion sorption media comprises: a

mixed metal oxide including alumina, titania, and other metals, for example, Fe, Mn, Mg, and such other metals prevalent in ores.

[0067] This sorption exchange material preferably includes metal oxide of aluminum oxides and titanium oxides, and doping polyvalent metal oxide including zirconium, tin, cerium,

lanthanum, iron, or manganese, or any combination thereof, where the mixed oxide or the

doping polyvalent metal oxide or both are configured to selectively adsorb organic molecules, fluoride ion, oxyanions of phosphorous and arsenic, or heavy metals such as Pb,

Hg, Cd, and the like. In yet another unexpected result, an adsorbent composition of the present invention has been shown to be capable of removing naturally occurring cations

from the alkali-metal, alkali-earth metals (Groups 1-2), including radioactive and non radioactive versions of Cs, Sr, Ba, Ra, and the like, under conditions where they are dissolved

ions in water.

[0068] In one embodiment, the mixed metal oxide is preferably formed from an aluminum sulfate component, a mixed-metal acid component, and a basic component. The mixed

metal acid component is comprised of a dissolved ore, such as ilmenite, rutile, or titanium slag. The ore is dissolved in hot sulfuric acid to make a mixture of sulfates (titanyl sulfate,

iron sulfate, etc.). After the dissolution of the ore, the remaining liquid (and solids) are

added to aluminum sulfate (or another aluminum salt).

[0069] Fig. 5 depicts a graph charting kinetic data for one embodiment of the metal oxide adsorbent of the present invention (MOX-Invention) versus disodium titanate for the

removal of lead (Pb). As depicted, the adsorbent of the present invention removes significantly more lead over a shorter period of time than the disodium titanate, showing a

considerable difference in the first 200 minutes.

[0070] With respect to the removal of oxyanions other than the aforementioned arsenic and phosphorus, Fig. 6 depicts a graph of Cd removal capacity for the metal oxide adsorbent

developed pursuant to the present invention (MOX-Invention) versus titanium oxide (Ti 2).

This data indicates that while the metal oxide adsorbent composition of the present

invention (MOX-Invention) does not have as high of a capacity, it does adsorb a measurable amount more cadmium in solution when compared to the TiO 2 adsorbent.

[0071] Similarly, Fig. 7 depicts a graph of copper (Cu) removal capacity for the metal oxide adsorbent developed pursuant to the present invention (MOX-Invention) and titanium oxide (Ti 2). Data shows that while the metal oxide adsorbent composition of the present

invention (MOX-Invention) does not have as high of a removal capacity, it does adsorb a measurable amount more copper in solution as a function of the concentration of copper

than that compared to the TiO 2 material.

[0072] Fig. 8 depicts a graph of zinc removal capacity for metal oxide developed pursuant to the metal oxide adsorbent of the present invention (MOX-Invention) versus titanium oxide

(Ti 2). Data shows that while the metal oxide adsorbent composition of the present invention (MOX-Invention) does not have as high of a capacity at lower concentrations, it

does adsorb a measurable amount more zinc in solution than that compared to the TiO 2

material at higher concentrations of zinc.

[0073] In another embodiment of the present invention, a method of making the aforementioned alumina-based mixed oxides is taught. The method requires a reaction

between a solution or a slurry containing an aluminum compound, a polyvalent metal compound, and a base solution in the pH range of approximately 4 to about 10, ageing

freshly formed precipitate in mother-liquor (a residual liquid resulting from the

crystallization and remaining after the substances that readily or regularly crystallize have been removed) at the pH level of precipitation, washing the precipitate with water, and

subsequently drying precipitate.

[0074] Specific to the method of forming the aluminum compound, a water soluble compound is chosen, preferably including aluminum sulfate, aluminum chloride, aluminum nitrate, and combinations thereof, or aluminum oxide pseudo-sol. The polyvalent metal

compound preferably comprises water soluble nitrates, chlorides, sulfates of titanium,

zirconium, tin, cerium, lanthanum, iron, or combinations thereof, or sol of titanium, zirconium, tin, cerium, lanthanum, iron, or combinations thereof. Additionally, polyvalent

metal compound may comprise nano sized titanium, zirconium, tin, cerium, lanthanum, iron oxides, or combinations thereof.

[0075] Another feature of the method of the present invention is that precipitation may be carried out at a constant pH level, which is kept in the range of 4 - 10 under batch or

continuous flow conditions by using base chosen from alkali hydroxides, ammonium

hydroxide, alkali carbonates, ammonium carbonate, and combinations thereof.

[0076] The precipitation may be carried at a pH level changing from acidic to about 4 - 10 under batch conditions by the addition of a base reagent chosen from alkali hydroxides,

ammonium hydroxide, alkali carbonates, ammonium carbonate, or combinations thereof.

[0077] On the final stage, freshly formed alumina based mixed oxide precipitate is aged in mother-liquor at the pH level of precipitation at ambient or elevated temperature for 1- 3

hours and then dried.

[0078] The present invention is described more specifically by reference to the following exemplary embodiments, which are not intended to limit the invention described in the

appended claims.

Example I

[0079] In a first exemplary embodiment, preparation of a metal containing solution of the present invention involves mixing 130.6 g of A1 2 (SO 4 )3*18H 2 0, 133 g of a 15.0 wt %titanyl

sulfate solution (on TiO2), and 400 g of deionized water. Metal containing solution and 25 wt %solution of NaOH are added simultaneously into a 2L glass beaker filled with 800 mL of

water with the use of a peristaltic pump at a predetermined flow rate which allows for a

constant pH level of 5 in the reaction mixture, the pH level being constant throughout the precipitation process. Next, the precipitate of alumina titania mixed oxide is aged in mother

liquor at ambient temperature for 1 hour, and then the aged precipitate is separated from mother-liquor by filtration and washed with deionized water. The wet cake is then dried at

100°C in air for approximately 18 hours. The dry adsorbent contains 50% A1 20 3 and 50% TiO 2 .

Example II

[0080] In a second exemplary embodiment, preparation of the metal containing solution comprises mixing 130.6 g of A1 2 (SO 4 )3*18H 2 0, 133 g of a 15.0 wt %titanyl sulfate solution

(on TiO2 ), and 400 g of deionized water. The metal containing solution and 25 wt %solution

of NaOH are then added simultaneously into a 2L glass beaker filled with 800 mL of water with the use of peristaltic pump at a predetermined flow rate that maintains a constant pH level at about 9 in the reaction mixture throughout precipitation process. Next, the precipitate of alumina titania mixed oxide is aged in mother-liquor at ambient temperature for 1 hour and then the aged precipitate is separated from mother-liquor by filtration and washed with deionized water. The wet cake is dried at 1000 C in air for 18 hours. The resultant dry adsorbent contains 50% A1 20 3 and 50%TiO 2

. Example III

[0081] In a third exemplary embodiment, preparation of a metal containing solution comprises mixing 94.5 g of AICl 3*6H20, 66.5 g of a 15.0 wt %titanyl sulfate solution (on TiO2 ), and 400 g of deionized water. NAOH at 25 wt % solution is slowly added to a beaker

with the metal containing solution until the pH level reaches 7. Next, the precipitate of alumina titania mixed oxide is aged in mother-liquor at ambient temperature for 3 hours and

then the aged precipitate is separated from mother-liquor by filtration and washed with

deionized water. The wet cake was dried at 1000 C in air for 18 hours. The dry adsorbent contains approximately 66.6% A1 20 3 and 33.4% TiO 2 .

Example 4

[0082] In a fourth exemplary embodiment, preparation of a metal containing solution comprises mixing 147 g of AI(NO 3)3*9H 2 0, 10 g of anatase TiO 2, and 400 g ofdeionized water. NaOH at 25 wt %solution is slowly added to a beaker with metal containing solution

until a pH level of approximately 7 is reached. Next, the precipitate of alumina titania mixed

oxide is aged in mother-liquor at ambient temperature for 3 hours, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water.

The wet cake is then dried at 1000 C in air for 18 hours. The dry adsorbent contains

approximately 66.6% A1 20 3 and 33.4%TiO 2 .

Example 5

[0083] In a fifth exemplary embodiment, the preparation of a metal containing solution comprises mixing 100 g of 20% aluminum hydroxide pseudo-solution, 10 g of rutile TiO 2 and 300 g of deionized water. A 25 wt %solution of NaOH is added slowly to a beaker with the

metal containing solution until the pH level reaches approximately 7. Next, the precipitate of

alumina titania mixed oxide is aged in mother-liquor at ambient temperature for 3 hours, and then the aged precipitate is separated from mother-liquor by filtration, and washed with

deionized water. The wet cake is dried at 100°C in air for 18 hours. The dry adsorbent contains 66.6% A1 20 3 and 33.4% TiO 2 .

Example 6

[0084] In a sixth exemplary embodiment, the preparation of a metal containing solution comprises mixing 130.6 g of A 2 (SO 4 )3*18H 2 0, 100 g of a 20 wt %ZrOCl2 solution (on Zr 2 ), and 400 g of deionized water. The metal containing solution and 25 wt %solution of NaOH are added simultaneously into a 2L glass beaker filled with 800 mL of water with the use of

peristaltic pump at a predetermined flow rate to maintain a constant pH level of 7 in the reaction mixture throughout precipitation process. Next, the precipitate of alumina zirconia

mixed oxide is aged in mother-liquor at ambient temperature for 1 hour, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water.

The wet cake is dried at 1000 C in air for 18 hours. The dry adsorbent contains 50% A1 20 3 and

% ZrO 2 .

Example 7

[0085] In a seventh exemplary embodiment, a preparation of metal containing solution comprises mixing 130.6 g of A 2 (SO 4 )3*18H 2 0, 100 g of a 20 wt %La(NO 3)3 (on La 2 0 3 )

solution, and 400 g of deionized water. The metal containing solution and 25 wt % solution of NaOH are added simultaneously into a 2L glass beaker filled with 800 mL of water with the use of peristaltic pump at a predetermined flow rate to maintain a constant pH level of 7 in the reaction mixture throughout precipitation process. Next, the precipitate of alumina lanthanum mixed oxide is aged in mother-liquor at ambient temperature for 1 hour, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water. The wet cake is dried at 100°C in air for 18 hours. The dry adsorbent contains 50% A1 20 3 and 50% La 2 0 3 .

Example 8

[0086] In an eighth exemplary embodiment, the preparation of a metal containing solution comprises mixing 130.6 g of A 2(SO 4)3*18H 2 0, 67.5 g of FeCI 3*6H 20, and 400 g of deionized water. The metal containing solution and 25 wt %solution of NaOH is added simultaneously

into a 2L glass beaker filled with 800 mL of water with the use of peristaltic pump at a

predetermined flow rate maintaining a constant pH level of approximately 7 in the reaction mixture throughout precipitation process. Next, the precipitate of alumina iron mixed oxide

is aged in mother-liquor at ambient temperature for 1 hour, and then the aged precipitate is separated from mother-liquor by filtration, and washed with deionized water. The wet cake

is dried at 100°C in air for 18 hours. The dry adsorbent contains 50% A1 20 3 and 50% Fe 2 0 3 . Example 9

[0087] The Al-27 MAS NMR spectra of freshly prepared alumina hydroxide and alumina based mixed oxides have been recorded on a Bruker Avance Ill400 MHz spectrometer.

Sample Octahedral Al % Pentahedral Al % Tetrahedral Al

% AI(OH)3 100 0 0

50% Al203 - 50% Ti02 80 15 5

Example 2

50% A1203 - 50% ZrO2 60 25 15

Example 6

50% A1203 - 50% Fe203 80 15 5

Example 8

67% A1203 - 33% Ti02 70 70 10

Example 3

Example10

[0088] Adsorption experiments have been carried out under batch conditions with a contact time 18 hours. The following test solutions were used in the adsorption experiments:

a) Fluoride ion - 10 ppm F + 2mM NaHCO 3 + 2 mM Na 2 SO 4 , pH = 6;

b) Phosphate ion- 0.83 ppm P+2 mM NaHCO 3, pH =8; and

c) Arsenateion-2ppmAs+2mMNaHCO 3,pH=8.

[0089] Commercial adsorbents, such as those from GFO (Bayer), MetSorb (Graver Technologies) and activated alumina AA400, have been used for a comparison study.

Table V Ion Exchange Capacities (IEC) of test ions on alumina based mixed oxides Sorbent IEC-F, mg/g IEC-P04, mg/g IEC-AsO4, mg/g

Example 1 75 55 65

Example 2 70 55 70

Example 3 70 50 60

Example 4 65 50 60

Example 5 65 50 60

Example 6 75 55 70

Example 7 80 60 65

Example 8 65 50 65

GFO, Granular Ferric Oxide 10 12 20

MetSorb TiO2 12 10.5 17

Activated Alumina AA400 15 7 7

Example11

[0090] Adsorption experiments have been carried out under batch conditions with a contact time 18 hours. The following equimolar test solutions were used in adsorption experiments:

a) Phosphate ion- 0.83 ppm P + 2 mM NaHCO 3, pH=8; and

b) Arsenate ion - 2 ppm As + 2 mM NaHCO 3, pH=8

[0091] Adsorption capacities on As and P as a function of equilibrium pH on hydrous titanium oxide, hydrated ferric oxide, aluminum hydroxide, and mixed oxide 33.4% TiO 2 -

66.6% A12 0 3 from Example 3 have been determined and P/As separation factors have been calculated from experimental data according to formula:

SF = IEC - P/IEC-As (at fixed pH),

and presented in Figure 1. As seen Fe 203 and A1 20 3 do not show selectivity to AsO 4 or P04 in

the pH range 6 - 10, whereas anatase TiO 2 exhibits affinity towards AsO4 at a pH level of

greater than or equal to 7. Alumina based mixed TiO 2 - A12 0 3 shows distinct affinity towards phosphate ion over arsenate ion in the tested pH range. The separation factor P/As for this

media increases with an increase of equilibrium pH reaching a value of 1.5 at a pH = 8, and 1.9 at a pH = 9.7.

Example12

[0092] The alumina based mixed oxide made in Example 3 (66.6% A1 2 0 3 - 33.4% TiO 2

, particle size 45-75 pm) and activated alumina 400G (particle size 45-75 pm) were tested for

fluoride ion removal from tap water spiked with 6.2 ppm F and pH = 7.5 under column conditions. In both cases two grams of adsorbent were placed in a glass column with inner

diameter 8 mm and test solution was passed through an adsorbent bed with flow rate 80 BV/hr. Fluoride breakthrough curves are presented in Figure 2. As seen, alumina-based

adsorbent from Example 3 (purifies ~3,300 BV) outperform the benchmark activated alumina 400G (purifies ~500 BV) before breakthrough (1.5 ppm F) more than 6 times.

Example13

[0093] The effect of competitive ions on fluoride ion sorption on mixed oxide of Example 1 is shown in the Table VI. Initial concentration of fluoride ion in all test solutions was 10 ppm

and contact time was 18 hours.

Table VI

Effect of competitive ions on fluoride ion sorption on alumina-titania mixed oxide Competitive ion Ion Excess, times IEC-F, mg/g

- 75

HCO 3 5 65

CI 50 70

S04 25 65

Si03 4 45

P0 4 1 45

Example14

[0094] Effect of thermal treatment on AsO 4 ion sorption on mixed oxide of Example 1 is shown in the Table VII. The arsenic test solution contained 2 ppm As(V), pH = 8. The fluoride

test solution contained 10 ppm F in tap water, pH = 7.5. The contact time was 18 hours.

Table VII Effect of thermal treatment on AsO4 and F ion uptake by alumina-titania adsorbent Ion IEC 100 0C, mg/g IEC 250 0C, mg/g IEC 350 0C, mg/g I EC 450 0C, mg/g

As04 75 65 60 50

F 25 21 19 18

[0095] While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and

variations will be apparent to those skilled in the art in light of the foregoing description. It

is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.

[0096] In one aspect there is provided an adsorbent for removal of fluoride ion and oxyanions of fluoride, phosphorus, arsenic, chromium, and/or selenium, said adsorbent comprising mixed oxide

containing alumina in tetra-, penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide including titanium, zirconium, tin, iron, or any combination of thereof,

wherein said mixed oxide contains 50% A1 O 3 and 50% TiO 2, having 80% Octahedral Al, 10%-30% 2

Pentahedral Al, and 5%-15% Tetrahedral Al, and wherein said mixed oxide does not show phase

segregation and remains amorphous up to 500°C.

[0097] In a second aspect there is provided an adsorbent for removal of cations of lead, mercury, cadmium, copper, and/or zinc, said adsorbent comprising mixed oxide containing alumina in tetra-,

penta-, and octahedral coordination or any combination thereof, wherein content of said alumina in

said mixed oxide is from about 20 wt% to about 80 wt%, wherein an amount of pentahedrally

coordinated alumina is from about 10% to about 30% by weight, and an amount of tetrahedrally

coordinated alumina is from about 5% to about 15% by weight, and a polyvalent metal oxide

including titanium, zirconium, tin, iron, or any combination of thereof.

[0098] In a third aspect there is provided an adsorbent for removal of fluoride ion and oxyanions of fluoride, phosphorus, arsenic, chromium, and/or selenium, said adsorbent comprising mixed oxide

containing alumina in tetra-, penta-, and octahedral coordination or any combination thereof, and a

polyvalent metal oxide including titanium, zirconium, tin, iron, or any combination of thereof,

wherein said mixed oxide contains 50% A1 O 3 and 50% Fe 2O 3, having 80% Octahedral Al, 15% 2

Pentahedral Al, and 5% Tetrahedral Al, and wherein said mixed oxide does not show phase

segregation and remains amorphous up to 500°C.

[0099] In a fourth aspect there is provided an adsorbent for removal of fluoride ion and oxyanions of fluoride, phosphorus, arsenic, chromium, and/or selenium, said adsorbent comprising mixed oxide

containing alumina in tetra-, penta-, and octahedral coordination or any combination thereof, and a

polyvalent metal oxide including titanium, zirconium, tin, iron, or any combination of thereof,

wherein said mixed oxide contains 67% A1 O 3 and 33% TiO 2, having 70% Octahedral Al, 20%

Pentahedral Al, and 10% Tetrahedral Al, and wherein said mixed oxide does not show phase

segregation and remains amorphous up to 500°C.

[00100] In a fifth aspect there is provided an adsorbent for removal of fluoride ion and oxyanions of fluoride, phosphorus, arsenic, chromium, and/or selenium, said adsorbent comprising mixed oxide containing alumina in tetra-, penta-, and octahedral coordination or any combination

thereof, and a polyvalent metal oxide including titanium, zirconium, tin, iron, or any combination of

thereof, wherein said mixed oxide contains 50% A1 20 3 and 50% ZrO 2, having 60% Octahedral Al, 25%

Pentahedral Al, and 15% Tetrahedral Al, and wherein said mixed oxide does not show phase

segregation and remains amorphous up to 500°C.

[00101] In another aspect there is provided A method of making an adsorbent comprising precipitation of mixed oxide by a reaction between a solution or a slurry including combining:

a water soluble compound consisting essentially of aluminum hydroxide, ferric hydroxide,

zirconium hydroxide, or combinations thereof; and

a polyvalent metal compound consisting essentially of water soluble nitrates, water soluble

chlorides, sulfates of titanium, zirconium, tin, iron, or combinations thereof, or a sol of titanium,

zirconium, tin, iron, or combinations thereof; and adding a base solution or base reagent during

precipitation consisting essentially of alkali hydroxides, ammonium hydroxide, alkali carbonates,

ammonium carbonate, or combinations thereof;

adjusting said precipitate for a constant pH in the range from about 4 to about 10;

ageing said precipitate in mother liquor at the pH level of precipitation;

washing the precipitate with water; and

drying said precipitate.

[001021 The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

[001031 In the present specification and claims, the word 'comprising' and its derivatives including 'comprises' and 'comprise' include each of the stated integers but does not exclude the

inclusion of one or more further integers.

Claims (21)

Claims

1. An adsorbent for removal of fluoride ion and oxyanions of fluoride, phosphorus, arsenic,

chromium, and/or selenium, said adsorbent comprising mixed oxide containing alumina in tetra-,

penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide

including titanium, zirconium, tin, iron, or any combination of thereof, wherein said mixed oxide

contains 50% A12 03 and 50% TiO2, having 80% Octahedral Al, 10%-30% Pentahedral Al, and 5%-15%

Tetrahedral Al, and wherein said mixed oxide does not show phase segregation and remains

amorphous up to 500°C.

2. The adsorbent of the claim 1 wherein said mixed oxide shows adsorption capacity decrease less than 40% after calcination.

3. The adsorbent of claim 1, wherein said adsorbent is capable of removing radioactive or non

radioactive versions of cesium, strontium, and/or barium.

4. The adsorbent of the claim 1 wherein said adsorbent is capable of removing naturally occurring

alkali-metals and alkali-earth metals Groups 1 and 2.

5. The adsorbent of the claim 1 wherein said mixed oxide is formed from an aluminum sulfate

component, a mixed-metal acid component, and a basic component.

6. The adsorbent of claim 5 wherein said mixed metal acid component is comprised of an ore

dissolved in hot sulfuric acid, to form a mixture of sulfates, such that once dissolved, remaining liquid

is added to said aluminum sulfate component.

7. The adsorbent of claim 6 wherein said mixture of sulfates includes titanyl sulfate or iron sulfate.

8. The adsorbent of claim 7 wherein said titanyl sulfate is used to form said mixed metal oxide, said

titanyl sulfate being combined with an aluminum sulfate salt and/or an iron salt.

9. The adsorbent of claim 1 wherein said mixed oxide is thermally stable, and has an adsorption

capacity for fluoride ions and oxyanions of arsenic and phosphorous decrease of less than 40% after

calcination up to 500°C.

10. An adsorbent for removal of cations of lead, mercury, cadmium, copper, and/or zinc, said

adsorbent comprising mixed oxide containing alumina in tetra-, penta-, and octahedral coordination

or any combination thereof, wherein content of said alumina in said mixed oxide is from about 20

wt% to about 80 wt%, wherein an amount of pentahedrally coordinated alumina is from about 10%

to about 30% by weight, and an amount of tetrahedrally coordinated alumina is from about 5% to

about 15% by weight, and a polyvalent metal oxide including titanium, zirconium, tin, iron, or any

combination of thereof.

11. The adsorbent of claim 10 wherein content of said alumina in said mixed oxide is from about 50

wt% to about 80 wt%.

12. The adsorbent of claim 10 wherein said mixed oxides includes titanium, iron, or manganese.

13. The adsorbent of claim 10 wherein said mixed oxide does not show phase segregation and

remains amorphous up to 5000 C.

14. The adsorbent of claim 10 wherein said mixed oxide shows adsorption capacity decrease less

than 40% after calcination.

15. The adsorbent of claim 10 wherein said mixed oxide is formed from an aluminum sulfate

component, a mixed-metal acid component, and a basic component.

16. The adsorbent of claim 15 wherein said mixed metal acid component is comprised of an ore

dissolved in hot sulfuric acid, to form a mixture of sulfates, such that once dissolved, remaining liquid

is added to said aluminum sulfate component.

17. The adsorbent of claim 16 wherein said mixture of sulfates includes titanyl sulfate or iron sulfate.

18. The adsorbent of claim 17 wherein said titanyl sulfate is used to form said mixed metal oxide,

said titanyl sulfate being combined with an aluminum sulfate salt and/or an iron salt.

19. An adsorbent for removal of fluoride ion and oxyanions of fluoride, phosphorus, arsenic,

chromium, and/or selenium, said adsorbent comprising mixed oxide containing alumina in tetra-,

penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide

including titanium, zirconium, tin, iron, or any combination of thereof, wherein said mixed oxide

contains 50% A12 O3 and 50% Fe 2 3, having 80% Octahedral Al, 15% Pentahedral Al, and 5%

Tetrahedral Al, and wherein said mixed oxide does not show phase segregation and remains

amorphous up to 500°C.

20. An adsorbent for removal of fluoride ion and oxyanions of fluoride, phosphorus, arsenic,

chromium, and/or selenium, said adsorbent comprising mixed oxide containing alumina in tetra-,

penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide

including titanium, zirconium, tin, iron, or any combination of thereof, wherein said mixed oxide

contains 67% A12 O3 and 33% TiO2, having 70% Octahedral Al, 20% Pentahedral Al, and 10% Tetrahedral Al, and wherein said mixed oxide does not show phase segregation and remains

amorphous up to 500°C.

21. An adsorbent for removal of fluoride ion and oxyanions of fluoride, phosphorus, arsenic,

chromium, and/or selenium, said adsorbent comprising mixed oxide containing alumina in tetra-,

penta-, and octahedral coordination or any combination thereof, and a polyvalent metal oxide

including titanium, zirconium, tin, iron, or any combination of thereof, wherein said mixed oxide contains 50% A12 03 and 50% ZrO2, having 60% Octahedral Al, 25% Pentahedral Al, and 15% Tetrahedral Al, and wherein said mixed oxide does not show phase segregation and remains amorphous up to 500°C.