WO2017090057A1

WO2017090057A1 - Removal of inorganic pollutants using modified naturally available clay material

Info

Publication number: WO2017090057A1
Application number: PCT/IN2016/050350
Authority: WO
Inventors: Vivek Ramkrushna MATE; Amit Rajendra KALITA
Original assignee: Mate Vivek Ramkrushna
Priority date: 2015-11-23
Filing date: 2016-10-14
Publication date: 2017-06-01

Abstract

An inexpensive and sustainable process for both arsenic and iron removal simultaneously from any aqueous supply like ground water, surface waters, agricultural waters, wastewater from industrial processes, etc. using naturally available modified clay. Arsenic eliminated from both water and other aqueous supply after treatment with naturally modified clay (aluminosilicate) containing iron in +3 oxidation state, specially Fe₂O₃ and Fe₃O₄, to oxidize arsenic in soluble form (+3) into an insoluble form (+5). While, second inorganic pollutant iron is removed from water and other aqueous supply by treating with modified clay containing surface active sites (silanol, sodium aluminosilicate, etc.) and either forms iron-silanol or gets trapped/exchanged with sodium aluminosilicate layer. The excess amount of iron trapped inside the modified clay act as a precipitating agent for both arsenic and iron. In laboratory tests, a lab scale 10 grams of heat treated clay was sufficient to remove both arsenic and iron from 1 liters of 300 and 2000 ppb (parts per billion) arsenic and iron respectively below 1 ppb which is lower than the present WHO and United States Environmental Protection Agency (USEPA) limit set for drinking water norms. It is further expected that this invention supplies a very inexpensive and sustainable solutions to both arsenic and iron poisoning of water for large population segments.

Description

DESCRIPTION OF THE INVENTION:

Although the process/method of the invention is mainly developed for complete removal of soluble arsenic and iron from drinking water sources such as underground and surface water, the process can be effectively used to treat any aqueous liquid that contains objectionable quantity of arsenic and iron. Examples of such liquid supply comprise, among others, ground water, surface waters such as water from ponds, lakes, and wet-lands, agricultural waters, and industrial wastewater. The arsenic-containing source can additionally consist of other inorganic pollutants, such as lead, chrominum, mercury and cadmium, and certain organic pollutants. In general, the process/method of the invention can be utilized to effectively eliminate any aqueous liquid feedstock containing pollutants (arsenic and iron) more than 2.0 ppb and is effective for treating supply having about 300 and 2000 ppb arsenic and iron respectively. The proposed method is efficient in complete removal of the pollutants arsenic and iron levels to below 1 ppb in such feeds.

Initially the arsenic pollutant having the aqueous source material is generally soluble in the liquid medium and present in both +3 and +5 oxidation states, as arsenite (As0₂ ^1_) and arsenate (As0₄ ³ ) respectively. Technologies for removing soluble form of arsenic (arsenate) are moderately efficient, although removing arsenite at normal condition is a more complicated proposition for the reason that the current technologies for doing so are not significantly efficient.

The present description is directed to use of a special kind of modified natural clay (aluminosilicate) for removal of arsenic and iron impurities from the aqueous supply. The natural clay sample can be obtained from any component of tree (living or dead), cotton/jute fabrics, leaf (living or dead), dry wood, any processed wood like plywood, wooden furniture, carton products, etc. can also act as source for the clay material. XRF analysis of this sample reveals the following composition: Silica: 55-65%; Calcium oxide (CaO): 7-10%; Alumina (AI₂O₃): 4-7%; Iron oxide: 4%. The clay sample is then heat treated at a particular temperature.

In the method of the invention, the aqueous supply polluted with arsenic and iron is allowed to pass through an inlet into an oxidation vessel at ambient pressure and temperature conditions. If the supply is polluted with particulate solids, it is generally processed to remove the solids before it enter into the oxidation vessel. Any liquid-solids separation techniques can be implemented to eliminate the particulate solids.

Inside the oxidation vessel the aqueous supply is in vicinity of the aluminosilicate (clay) material containing iron (III) oxide, which is a strong oxidizing agent and oxidize arsenic +3 into +5 oxidation state and simultaneously form insoluble iron arsenate compound. While, iron may be present in water in both +2 and +3 oxidation state, both being converted into either insoluble iron-silanol compound or trapped/exchanged in porous sodium aluminosilicate layer. All kind of arsenic species having arsenic in the +5 oxidation state and also trapped iron or insoluble iron- silanol are then precipitated from the aqueous phase by the active sites.

The excess of iron trapped inside the aluminosilicate matrix may also act as a precipitating agent by reacting with the soluble arsenic +3 converted into an insoluble +5 oxidation state. The iron silanol polymeric linkages are given below:

(a) (b) (c)

Schematic representation of bonding between Si(OH)₄ and Fe_(X)OH; (a) bonding with Si(OH)₄ monomer, (b) polymerization with silanol, and (c) polymerization with silanol and aluminate.

The active sites that reacts with both the arsenate and iron in higher oxidation state to convert into insoluble arsenic and iron-silanol compounds usually comprises of iron (III), iron hydroxide and porous aluminosilicate, siloxane, aluminium hydroxide, aluminosilicate, sodium aluminosilicate, iron siloxane. It is normally preferred that the iron (III) oxide composite and active sites both be water insoluble particulate solids.

Usually, an adequate quantity of the aluminosilicate is available in the oxidation vessel with the active sites such that the combination of the two contains from 0.2 to 80 weight percent of the iron (III) oxide compound. Conversely, in some cases, it may be expected for the combination to contain more than 40 to 45 weight percent of the iron (III) oxide.

When iron (III) oxide compound and active sites are available in the oxidation zone as a fixed bed, it is usually ideal that the particles be spherical in size so the stream of the aqueous liquid supply passing through the bed is systematically dispersed. Although, if preferred, the particles might acquire another shapes including that of extrudates. These extrudates would naturally have an extent of dimension in between about 0.1 and 2.0 millimeters.

Throughout the oxidation stage of the process/method of the invention, arsenite in the liquid aqueous supply is oxidized to arsenate according to the following reaction:

As the iron (III) oxide oxidizes the arsenite and subsequently reduced to iron in the +2 oxidation state, followed by reaction with the arsenate produced in the oxidation step to generate insoluble iron arsenate as given in the following reaction:

(Fe²⁺)_x + (0₂)_x + (As0₄ ³-)_x Fe₃(As0₄)₂

Even if in theory there is sufficient iron +2 generated by reduction of iron +3 to react with all form of arsenate generated in the oxidation reaction step to the arsenate, it is usually excepted that extra active sites be present. These active sites react with any unreacted arsenate to form an insoluble precipitate, which is eliminated from the aqueous liquid supply to generate the expected arsenic-deprived aqueous liquid.

Specially, if the liquid aqueous supply consists of different pollutants that must be eliminated in accumulation to both arsenic and iron to generate the desired purified liquid, the elimination of these pollutants is normally being carried either before or after the oxidation step. While, if the other pollutants will obstruct with the oxidation of arsenic or trapping of iron, they should be removed before the oxidation stage. In few cases the process/method of the invention is moreover efficient for eliminating other pollutants from the aqueous liquid supply in addition to arsenic and iron.

In a chosen embodiment of the invention, an arsenic and iron purification device/unit having a cartridge or filter is utilized to treat domestic drinking water. The processing device/unit usually is a free standing container with a filtering unit containing the mixture of the invention or a cartridge type device deliberate to fix under a sink. These units are positioned so that the water allowed entering home or business location/site passes from the filter or cartridge before it enters the sink faucet. These filter and cartridge units are relatively simple and consist of an inlet attached to the supply of the drinking water. A filter or cartridge having the aluminosilicate compound and an outlet to direct the arsenic and iron depleted drinking water to leave the cartridge or filter.

Inside the filter or cartridge, oxidation of arsenic +3 into +5 oxidation state occurs, and significantly all of the arsenic +5 present reacts with iron (III) oxide to form insoluble iron arsenate and get adsorbed over the active sites. Simultaneously, iron present in +2 and +3 oxidation state either gets trapped/exchanged in the aluminosilicate layered matrix or gets converted to iron-silanol compound. The precipitating agents (in situ generated) present in natural clay due to exchange/trap of excess iron in porous layers of clay are in the form of iron hydroxide, sodium aluminosilicate, Fe₂03, etc. The effluent exiting the outlet of the cartridge or filter device/unit will usually have an arsenic concentration below about 1 ppb. Next to the fixed bed in any one of the cartridge or filter devices/units becomes saturated with arsenic, the cartridge or filter is refurnished with a fresh cartridge or filter of original dimension. The used cartridge or filter is finally destroyed by following government norms.

In other embodiment, the process of the invention is implemented in municipal water purification facilities to eliminate both arsenic and iron from drinking water before is supplied for domestic or industrial purposes. For such use the aluminosilicate (modified clay) compound is typically available in huge tanks in a fixed bed so that comparatively enormous quantities of arsenic and iron containing pollutants in water can be treated either in a batch or continuous mode. The active sites as well as in situ generated precipitating agent can be available either in the tank (storage) with the aluminosilicate compound or in a different unit fed by the waste matter from the tank. The purified water has both arsenic and iron concentration less than about 1 ppb which is lower than the norms set for drinking water by WHO.

The behavior and objective of the invention are further highlighted by providing following example, which is established with the aim of clarification and not to restrict the invention as explained by claims. The example shows that both iron and arsenic can be completely removed from water using heat treated clay sample.

EXAMPLE

Standard solutions were prepared by mixing certified standard solutions of arsenic (300 ppb) and iron (2000 ppb) with natural water containing no arsenic and iron to the equivalent of these impurities present in groundwater. These solutions of arsenic were passed through 10 gm each of natural clay sample (VRM-1) and heat treated clay sample (VRM-2) (Table 1). The resultant water samples were collected in 100 ml plastic sample bottles. These bottles were then sent to a certified drinking water analysis laboratory where the quantification of both arsenic and iron in every sample were examined by ICP-OES coupled with mass spectroscopic technique. The results of these tests are given below in Table 1.

Table 1: Effect of VRM-1 and VRM-2 clay samples on removal of iron and arsenic from water

The result data for test 3 in the table shown that, as VRM-1 sample is used, 85 and 90 percent of iron and arsenic are removed respectively from water. The results of test 4, on the other hand, show that VRM-2 sample can completely remove both iron and arsenic simultaneously from water. The inconsistency in these results are attributed to the fact that with increase in heat treatment to clay sample, there is i) increase in strength of the bond of iron with aluminosilicate clay matrix, ii) appropriate combination of both strong and weak acid sites of clay, iii) porosity, iv) iron silanol, v) Fe₂03/Fe30₄ and vi) iron aluminate (spinel) structure thus resulting in increase in stability of the natural clay sample. Also with increase in rate of oxidation of arsenite to arsenate, ability of the natural clay sample to remove arsenic from water is increased. Tests 5-8 further shows the effectiveness of heat treated natural clay sample to remove iron and arsenic from water.

The explanation provided here, most excellent modes of operation of the invention, are not planned to limit the scope of the invention. Many modifications, alternative constructions, and equivalents may be employed without departing from the scope and spirit of the invention.

Claims

An efficient inexpensive, environment friendly method for removal of heavy metals preferably both arsenic and iron from any aqueous supply like ground water, surface waters, agricultural waters, wastewater from industrial processes, etc. using naturally available clay (VRM-1), wherein the process comprises of the following steps: i) Heat treatment of the natural clay material (VRM-2). ii) Allowing water containing inorganic impurities to pass over the natural and heat treated clay sample.

The clay material as claimed in claim 1 , can be obtained from any component of tree (living or dead), cotton/jute fabrics, leaf (living or dead), dry wood, any processed wood like plywood, wooden furniture, carton products, etc. can also act as a source for the natural clay material.

A method as claimed in claim 1 , wherein the clay sample has porous layered aluminosilicate matrix and active sites, wherein the active sites comprises of iron (III) oxide, iron siloxane, iron hydroxide, and the aluminosilicate matrix has significant quantity of iron, from about 0.2 to about 80 wt. %, bonded to the matrix in the form of iron (III) oxide and exhibits appropriate combination of both strong and weak acid sites of clay, and has porous structure. Heat treatment of the clay material results in the formation of strong bond between iron and aluminosilicate.

The clay material as claimed in claim 1 , wherein the material has at least single iron compound selected from the group consisting of iron-siloxane, iron oxide, iron hydroxide, Fe₂0₃, iron aluminate spinel, Fe₃0₄ spinel, and mixtures thereof..

The clay material as claimed in claim 1 , wherein the iron (III) oxide and active sites are supported on a substrate selected from the group consisting of clay, mesoporous material (MCM, MOF, etc.), alumina, gamma-alumina, activated alumina, acidified alumina, metal oxides comprising labile anions, crystalline aluminosilicates, amorphous silica alumina, ion exchange resins, ferric sulfate, porous ceramics, and mixtures thereof.

A method as claimed in claim 1 , wherein the VRM-1 sample is subjected to heat treatment at a particular temperature. Further there is increase in strength of strong and weak acid sites, porosity, and stable interaction of iron with aluminosilicate, which all in turn results in enhancement in its ability to remove inorganic impurities from water.

A method for arsenic removal, wherein arsenite (As³⁺) when passed over VRM samples, it gets oxidized to arsenate (As⁵⁺). The oxidized and initially present arsenate forms an iron arsenate [Ferrous arsenate (Fe₃(As0₄)₂)] insoluble complex with iron present in the aluminosilicate matrix. [Claim 8] A method for iron removal, wherein the excess iron as present in contaminated water either gets trapped inside the pores of aluminosilicate layers or adsorbed over silanol group of aluminosilicate and forms chemiadsorbed iron-silanol stable molecule which then act as a precipitating agent.

[Claim 9] The heat treated clay sample as claimed in claim 1 , can completely remove both iron and arsenic impurities simultaneously from all types of aqueous supply.

[Claim 10] The clay as claimed in claim 1 , can be used with different composite materials like cement, fiber-reinforced polymers, graphene, carbon, glass, ceramic, etc to produce hetero-structure, advanced functional material, engineering designed structural material, etc. which can then be used for water purification. The clay can be mold into different shapes and size for purification and filtration of water, further it can be used in a water purification device.

[Claim 11 ] An arsenic removal device, comprising:

One inlet to receive an arsenic-containing aqueous supply; one outlet to discharge an arsenic-depleted treated aqueous supply; and at least one of a filter and cartridge positioned so that the arsenic-containing aqueous supply passes from the inlet to generate the arsenic-depleted treated aqueous supply for discharge through the outlet, wherein the at least one of filter and cartridge comprises a iron (III) oxide or porous aluminosilicate (clay) to react with arsenic in the arsenic-containing aqueous supply and iron active sites/precipitating agent to form a precipitate with the arsenic.

[Claim 12] The device of claim 1 1 , wherein the at least one of a filter and cartridge is removable from the device and replaceable with a new at least one of a filter and cartridge, wherein the arsenic-containing aqueous supply is water, wherein the arsenic-containing water is contaminated with dissolved arsenic in the +3 oxidation state, wherein the iron (III) oxide or porous aluminosilicate (clay) oxidizes the arsenic to the +5 oxidation state, and wherein the arsenic-depleted treated aqueous supply comprises less than about 1 .0 ppb dissolved arsenic. The active sites comprise iron (III) and iron hydroxide and porous aluminosilicate.

[Claim 13] The device of claim 1 1 , wherein the aqueous supply further comprises of organic industrial contaminant and the organic industrial contaminant removal stage being positioned upstream of the at least one of a filter and cartridge.

[Claim 14] The device of claim 1 1 , wherein the aqueous supply further comprises living or biological microorganisms and biological impurities removal stage being positioned upstream of the at least one of a filter and cartridge.

[Claim 15] The device of claim 11 , wherein the arsenic-containing aqueous supply comprises a further contaminant selected from the group consisting of lead, chromium, selenium, cadmium, mercury, and mixtures thereof and the further contaminant removal stage being positioned upstream of the at least one of a filter and cartridge.

[Claim 16] A system, comprising:

An inlet for an arsenic-containing aqueous supply, the aqueous supply containing particulate solids; A liquid-solids generator to generate particulate solids from the aqueous supply and form a liquid phase and solid phase, the liquid phase comprising the arsenic and the solid phase comprising the particulate solids; and

An oxidation vessel comprising iron (III) oxide and active sites/ in situ generated iron precipitating agent in the aluminosilicate, wherein iron (III) oxide reacts with the arsenic in lower oxidation state and convert it to a higher oxidation state and active sites/iron precipitating agent forms a precipitate with the arsenic in the higher oxidation state.

[Claim 17] The system of claim 16, wherein the active sites/precipitating agent comprises iron, wherein the aqueous supply is water, wherein the oxidation vessel outputs an arsenic-depleted water, wherein the arsenic-containing water is contaminated with more than about 300 ppb dissolved arsenic in the +3 oxidation state, wherein the iron (III) oxide oxidizes the arsenic to the +5 oxidation state, and wherein the arsenic-depleted water comprises less than about 1 ppb dissolved arsenic.

[Claim 18] A device, comprising:

One inlet to receive an iron-containing aqueous supply; one outlet to discharge an iron- depleted treated aqueous supply; and at least one of a filter and cartridge positioned so that the iron-containing aqueous supply passes from the inlet to generate the iron-depleted treated aqueous supply for discharge through the outlet, wherein the at least one of filter and cartridge comprises a porous aluminosilicate (clay) to react with iron in the iron-containing aqueous supply and active sites/ iron precipitating agent to form a precipitate with the iron.

[Claim 19] The device of claim 18, wherein the at least one of a filter and cartridge further comprises of the clay material as claimed in claim 1 , and the filter or cartridge is removable from the device and replaceable with a new at least one of a filter and cartridge, wherein the iron- containing aqueous supply is water, wherein the iron-containing water is contaminated with dissolved iron in the +2 and +3 oxidation state, wherein porous aluminosilicate (VRM-2) oxidizes the iron +2 to +3 oxidation state, which ultimately generate active sites/precipitating agent via formation of iron-silanol, Fe₂0₃, etc. inside the layer, wherein the active sites comprises iron (III), and wherein the iron-depleted treated aqueous supply comprises less than about 1 ppb dissolved iron.

[Claim 20] The device of claim 18, wherein the iron-containing aqueous supply comprises a further contaminant selected from the group consisting of lead, chromium, selenium, cadmium, mercury, and mixtures thereof and a further contaminant removal stage for removing the above contaminants, being positioned upstream of the at least one of a filter and cartridge.

[Claim 21 ] A system, comprising:

An inlet for an iron-containing aqueous supply, the aqueous supply containing particulate solids; A liquid-solids generator to generate particulate solids from the aqueous supply and form a liquid phase and solid phase, the liquid phase comprising the iron and the solid phase comprising the particulate solids; and

An oxidation vessel comprising iron (III) oxide and active sites/ precipitating agent, to form a precipitate with iron-silanol compound formed inside the porous aluminosilicate structure.

[Claim 22] The system of claim 21 , wherein the active sites/precipitating agent, comprises aluminosilicate, wherein the aqueous supply is water, wherein the oxidation vessel outputs an iron-depleted water, wherein the iron-containing water is contaminated with more than about 2000 ppb dissolved iron in the +2 and +3 oxidation state, wherein the both iron converted into either insoluble iron-silanol compound or trapped/exchanged in porous sodium aluminosilicate layer, and wherein the iron-depleted water comprises less than about 1 ppb dissolved iron.

[Claim 23] The system of claim 21 , wherein the excess of trapped/exchanged iron act as a precipitating agent and is partially dissolved in water and wherein the arsenic-containing aqueous supply comprises water.

[Claim 24] A system, comprising:

An input for an aqueous supply contaminated with both arsenic and iron and a further contaminant that is at least one of lead, chromium, selenium, cadmium, mercury, living/biological pollutants and an organic industrial/domestic contaminant. At least one of a filter and cartridge positioned so that the arsenic and iron containing aqueous supply passes from the inlet to generate arsenic and iron containing aqueous supply passes from the inlet to generate arsenic and iron depleted aqueous supply for discharge through the outlet, wherein the at least one of filter and cartridge comprises iron (III) oxide or porous aluminosilicate (clay) to react with arsenic (+3 and +5) and iron (+2 and +3) in the aqueous supply and active sites/precipitating agent to form precipitate with arsenic and iron in higher oxidation state. A contaminant removal stage, positioned upstream of the at least one of a bed, filter, and cartridge, for removing the at least one of lead, chromium, selenium, cadmium, mercury, living/biological pollutants and an organic industrial/domestic contaminant.

[Claim 25] The system of claim 24, wherein the at least one of a filter and cartridge comprises of the clay material as claimed in claim 1 , and the filter and cartridge is removable from the system and replaceable with a new at least one of a bed, filter, and cartridge, and wherein the precipitating agent/active sites is at least one of iron (III) oxide, iron silanol, aluminosilicate and sodium aluminosilicate compounds.

[Claim 26] The system of claim 24, wherein the system outputs a purified water stream, and wherein the purified water stream comprises less than about 1 .0 ppb dissolved total arsenic and iron.

[Claim 27] A device/system for removing arsenic and iron from drinking water comprising:

a. an inlet communicating with a source of said drinking water having arsenic (+3 and +5) and iron (+2 and +3). b. a vessel containing aluminosilicate (clay) compound and a particulate arsenic active sites/precipitating agent, said aluminosilicate containing compound comprises sodium aluminosilicate, porous aluminosilicate, iron silanol, iron hydroxide, iron oxide (in a +2 and +3 oxidation state), siloxane, reaction/exchange/trapping leads to conversion of both arsenic and iron into insoluble iron arsenate and iron-silanol compounds.wherein said vessel having an entry portion and an exit portion, wherein said entry portion communicates with the inlet; and

c. an outlet communicating with said exit portion of the vessel, wherein said drinking water leaves said vessel through said exit portion and wherein said drinking water exiting said exit portion has low arsenic and iron concentration.

[Claim 28] The device of claim 27, wherein said vessel comprises a tank containing said naturally modified aluminosilicate (VRM-2) as claimed in claim 1.

[Claim 29] The device of claim 27, wherein said aluminosilicate material as claimed in claim 1 , is a water-insoluble solid and is present as a fixed bed, wherein the excess of iron present in contaminated water act as a precipitating agent and active sites are comprised within the solid, wherein said iron-containing compound is supported on or in pores of said active sites and wherein said purified aqueous liquid has arsenic content of less than 1 ppb when allowed to pass through the particulate solids.

[Claim 30] The device of claim 27, wherein said aqueous supply containing arsenic and iron has another contaminant that interferes with said reaction of said aluminosilicate compound with said arsenic, wherein said another contaminant is removed upstream of said vessel, wherein said another contaminant comprises one or more of lead, chromium, selenium, cadmium, mercury or an organic contaminant, and wherein said another pollutants is removed in addition to arsenic.

[Claim 31] The device of claim 27, wherein said vessel comprises a cartridge or filter containing said particulate arsenic precipitating agent/active sites comprising iron in +2 and +3 oxidation state. [Claim 32] The device of claim 27, wherein said vessel comprises clay material as claimed in claim 1 , and surface active sites modified by making composite with charcoal (made from rice husk, ashoka leaf, etc.).

[Claim 33] The device of claim 27, wherein said oxidation vessel comprises clay material as claimed in claim 1 , designed by providing external supply of air/oxygen along with aqueous supply for regeneration of material.

[Claim 34] The device of claim 27, wherein said vessel comprises clay material as claimed in claim 1 , surface properties like surface area, porosity, adsorption/absorption property, adsorbents, etc. can be enhanced by use of 1 to 50% synthetic aluminosilicate clay material.

[Claim 35] A layer of the clay material as claimed in claim 1 , can be sandwiched in between two layers of porous concrete such that contaminated water when allowed to pass through it, can incur removal of inorganic impurities like arsenic and iron.

[Claim 36] The clay material of claim 1 , can be mixed in fixed proportion with other fine aggregates like sand, gravels, glass waste, polymeric waste etc. and can be used in any filter media for removal of inorganic impurities like arsenic and iron.