GB2567695A

GB2567695A - Cobalt metal nanoparticles for heavy metal extraction from water

Info

Publication number: GB2567695A
Application number: GB1717391.5A
Authority: GB
Inventors: Rauwel Erwan; Rauwel Protima; Sóukand Ülis
Original assignee: Pro-1 Nanosolutions Ou; Tallinn University of Technology; Pro 1 Nanosolutions Ou
Current assignee: Pro-1 Nanosolutions Ou; Tallinn University of Technology; Pro 1 Nanosolutions Ou
Priority date: 2017-10-23
Filing date: 2017-10-23
Publication date: 2019-04-24
Also published as: GB201717391D0; WO2019081536A1

Abstract

A process for the extraction of heavy metal ions from water comprises the steps of: (i) mixing surfactant-free cobalt nanoparticles in contaminated water; (ii) waiting at least 5 seconds for heavy metal ions to agglomerate around the cobalt metal nanoparticles, and (iii) extracting the cobalt metal nanoparticles coated with the heavy metal ions in the metallic or metal oxide form from the contaminated water. Suitably, the cobalt metal nanoparticles are bonded on a support material, such as sand, wood, cellulose, metallic fibres, porous ceramic, a polymer support, or glass. The cobalt nanoparticles coated with heavy metal ions can be extracted using a magnetic field of up to 1 Tesla, and suitably of at least 0.2 Tesla. Preferably, the cobalt metal nanoparticles are agglomerated. The cobalt nanoparticles may be fixed on a substrate integrated in a filter. The cobalt nanoparticles can exhibit superparamagnetic properties. The cobalt metal nanoparticles may be coated with a layer of cobalt oxide. The cobalt metal nanoparticles may be stable under air and can be functionalised.

Description

Cobalt Metal Nanoparticles for heavy metal extraction from water

Technical field

This invention relates to a process in which cobalt metal nanoparticles and more particularly surfactant-free cobalt metal nanoparticles are used as medium for the extraction of heavy metal ions in solution and more particularly in water.

Background of invention

The described cobalt metal nanoparticles when introduced into heavy metal contaminated water, promote the agglomeration of heavy metal ions in the form of metallic cluster or metal oxide clusters. Metal nanoparticles are an increasingly emerging industrial material that is now integrated in multiple applications. Due to their high surface area and very high reactivity, metal nanoparticles are used in a variety of applications, many of which arise from the improved behaviour and properties of nanomaterials. In fact, metallic nanoparticles with diameter ranging from 2 to 100nm have received extensive attention in particular applications such as catalysis, biosensors, optical filters, biomedical applications, antibacterial coating, targeted drug delivery and cancer therapy. The synthesis of hybrid materials like carbon-based nanocomposite combining carbon nanotubes and nanoparticles or metal hydrides has spurred a lot of interest due to the synergetic effect of these nanocomposites.

By nanoparticles and nanomaterials one implies a size below 1 micrometer: typically below 500nm and generally above 3nm.

Due to the industrial development and human population growth, the natural resources are decreasing. In addition, the discharge of industrial effluents and generation of pollution caused by increase in human population further contaminates most of the water resources by organic pollutants, microorganisms and heavy metal ions release. Contaminated water regroups general water resources like lakes, rivers, ground water, phreatic zone, seas. The main issue is to clean that contaminated water, but some contamination remains and the contamination by heavy metal ions is one of the most difficult contamination to eliminate from water. This contamination can be found in tape water, well water, but can also be present in water after industrial catastrophes like Minamata and Bhopal for mercury contamination or Fukushima and Chernobyl for radioactive elements contamination.

Many processes already involve nanoparticles for water purification, for example carbon based nanomaterials, graphene nanocomposites combining inorganic and organic moieties, layered double hydroxide nanomaterials etc. Graphene nanocomposites have demonstrated superior performance in the removal of heavy metal. However, their performance at industrial scale limits their application due to the high cost of maintenance, energy consumption and high sludge generation. In addition, the utilization of graphene oxide requires toxicity tests before their application in real wastewater systems. Layered double hydroxide nanomaterials have also been studied for water remediation. These nanomaterials have an enormous potential and exhibit higher anion exchange capacity. However, due to structural unsteadiness under low pH and high cost for regeneration; high scale use appears difficult to apply in the case of these nanomaterials.

Many methods are presently available like coagulation, flocculation, ion exchange, membrane filtration, bioremediation, adsorption, oxidation (catalysis) etc. But the major disadvantages of these present methods are the handling and disposal problem due to the sludge production, the high cost for most of them and the technical constraints that have not yet been solved, more specifically in the case of heavy metal and radio elements removal. The continuous discharge of environmental pollutant is imposing to develop new and effective treatments and removal process and very recently many efforts have been made to develop magnetic nanosorbent for the separation of pollutants that can be easily recycled. However, most of these methods are not cost effective and scaling up these processes appears challenging. In addition, the absorption capacities of heavy metal for most of these methods are around 40 to 89mg/g, which remains a limitation to their efficiency.

In view of such problems as extracting heavy metal ions from liquid and more particularly from water, there is a need for the development of sustainable, simple, reliable and low cost methods. This method should enable the direct extraction of heavy metal from water with possibilities of recycling the extracted heavy metal without harming the environment.

Cost effective treatment poses a challenge for environmental engineers, in particular for highly toxic and persistent pollutants difficult to treat. New water treatment approaches that are more cost effective than available techniques are under investigation and from all these studies, technologies involving nanomaterials appear as the most promising solutions.

During the last decade, due to their magnetic properties, high chemical stability and low toxicity and recycling capability, hierarchically structured magnetic nanoparticles like Fe nanoparticles functionalized multi-walled carbon nanotubes or citric acid coated magnetic nanoparticles, have attracted a lot of attention. They have been more particularly studied for toxic metal ions and organic pollutant removal due to higher removal capacities with lower contact time than the bulk material. As mentioned before, the nanoparticle size should be below the critical limit to exhibit superparamagnetic properties. However, these magnetic nanoparticles are subjected to atmospheric conditions and are easily oxidized in open air and water: usually they need to be coated or functionalized in order to stabilize the magnetic nanoparticles in extreme environmental conditions. In addition, the synthesis of magnetic nanoparticles is a costly complex process due to their colloidal nature and high activity. One of the most popular example are SPIONs (superparamagnetic iron oxide (Fe3O4) nanoparticles) that exhibit very good magnetic saturation value (84 emu/g) demonstrating a strong magnetic responsivity easily separable from aqueous solutions using an external magnetic field. These superparamagnetic nanoparticles have, for example, been tested for Ni²⁺ ions extraction

Co element appears to be well tolerated in the human body and for example is administered in the supplementation of vitamin B12 and in the case of anemia. Contrary to iron element, the human body can easily eliminate the excess of cobalt element via urinals system and cobalt element is known as non-accumulating metal. In addition, cobalt levels go down once the source of cobalt is removed. A recent study has shown that cobalt concentration ranging between 9.4 and 117 pg/L in the blood system was not associated with clinically significant changes in basic hematologic and clinical variables (Tvermoes et al., Am. J. Clin. Nutr., Vol. 99(3), p632-646 (2014)), which makes cobalt element a possible suitable element for water purification.

Summary of invention

In one aspect, the present invention provides a process for the extraction of heavy metal ions that can be present in water and more particularly polluted water comprising:

i. mixing cobalt nanoparticles in water; and ii. waiting the necessary time for heavy metal ion agglomerating around the cobalt metal nanoparticles, and iii. Extracting the cobalt metal nanoparticles coated with the heavy metal ions in the metallic or metal oxide form from the water.

Preferably the process of the invention uses surfactant-free cobalt metal nanoparticles stable under air (figure 1). The cobalt metal nanoparticles preferably exhibit superparamagnetic properties to enable their extraction from the liquid medium using magnetic field.

After the reaction process between the cobalt metal nanoparticles and the heavy metal ions 50% of the quantity of the heavy metal ions have been extracted, preferably from 50 to 80%, more preferably 60 to 90% and most preferably 70 to 100%.

The cobalt metal nanoparticles are preferably coated with one monolayer of cobalt oxide. The nanomaterials used for the extraction of heavy metal ions can be metal nanoparticles or a mixture of different metal nanoparticles decorating the surface of the superparamagnetic cobalt metal nanoparticles. The cobalt nanoparticles used for the extraction of heavy metal ions can be agglomerated which decreases possible toxicity and Co ion release in the treated solution. The cobalt metal nanoparticles can also be anchored or bonded via a chemical bonding on a support material or a substrate like sand (figure 2), activated carbon, metallic support, carbon nanotubes, graphene, alumina phases, glass, polymers but not limited to. In that case, the support material or substrate can be integrated in a filter.

The cobalt metal nanoparticles can also be integrated in a filter as active material. In that case, the polluted water flow goes through the filter and the process may further comprise:

i. Passing the polluted water on the support material I substrate covered by cobalt metal nanoparticles.

ii. Heavy metal ions are agglomerating around the cobalt metal nanoparticles anchored on the support material I substrate.

iii. Recuperation of the cleaned water at the exit of the filter iv. Removing from the filter when necessary, the support material I substrate covered by cobalt nanoparticles coated by heavy metal in the metallic form or oxide form.

In one embodiment of the invention the active material is cobalt metal nanoparticles that are stable under air. The process comprises two possible ways for extracting the heavy metal ions from polluted water. The first way consists in spreading the cobalt metal nanoparticles in the polluted water and waiting sufficiently long in order to agglomerate all the heavy ions on the surface of the cobalt metal nanoparticles and then proceed to the extraction of the superparamagnetic cobalt nanoparticles covered by heavy metals in the metallic form or oxide form. The second way consists of using a filter that comprises a material support covered by cobalt metal nanoparticles on its surface through which water is passed. The heavy metal ions present in the water interact with the cobalt metal nanoparticles and agglomerate on the surface of the cobalt metal nanoparticles in the metallic form or oxide form. Decontaminated water, without heavy metal is then obtained after the utilization of such a filter. After the reaction process between the cobalt metal nanoparticles and heavy metal ions, 50% of the quantity of the heavy metal ions have been extracted, preferably from 50 to 80%, more preferably 60 to 90% and most preferably 70 to 100%.

In another aspect, the invention provides water that does not contain heavy metal ions after having used cobalt metal nanoparticles for the extraction of heavy metal ions via their agglomeration on the surface of the cobalt nanoparticles. In any case, the quantity of heavy metals in the water after extraction using Co based composites respects the individual water norms. In a further aspect, the invention provides water that either does not contain heavy metal ions after having used the filter or contains heavy metals in acceptable amounts. The filter here integrates a support materials covered with cobalt metal nanoparticles for the extraction of heavy metal ions via their agglomeration on the surface of the cobalt nanoparticles.

In another aspect, the extracted cobalt metal nanoparticles covered by heavy metal in the metallic form or oxide form can be recycled in a high temperature oven to induce the separation of the different metals for reutilization.

Brief description of drawings

Figure 1 shows HRTEM images of surfactant-free cobalt metal nanoparticles that exhibit a cubic structure.

Figure 2 shows optical microscope image of sand covered with Co nanoparticles before reaction with water containing heavy metal ions.

Figure 3 shows X-ray diffraction (XRD) patterns show of Co metal nanoparticles with cubic structure.

Figure 4 shows SEM image of Co metal nanoparticles covered by metallic lead after reaction in a water solution containing lead ions.

Figure 5 shows SEM image of Co metal nanoparticles lead before reaction in a water solution containing heavy metal ions.

Figure 6 shows SEM image of Ag-Co nanocomposite before reaction in a water solution containing heavy metal ions.

Figure 7 shows SEM image of Ag-Co nanocomposite after reaction in a water solution containing lead ions.

Figure 8 shows SEM image of sand covered with Co metal nanoparticles covered by metallic iron after reaction in a water solution containing iron ions.

Figure 9 shows SEM image and Si, Fe and Co mapping of sand covered with Co metal nanoparticles after reaction in a water solution containing iron ions.

Figure 10 shows a photograph of water containing 34 ppm of iron ions before (Erlenmeyer on left side) and after purification (Erlenmeyer right side).

Detailed Embodiment

The present invention provides a process for the extraction of heavy metal ions that can be present in water and more particularly polluted water. The process includes the utilization of cobalt metal nanoparticles (figure 1). Surfactant free cobalt metal nanoparticles are preferred. Cobalt metal nanoparticles stable under air are preferred. The structure of the cobalt metal nanoparticles is cubic (Figure 3), but it is also possible to use cobalt metal nanoparticles with a hexagonal crystal structure. These metal nanoparticles can be coated with a layer of cobalt oxide, and preferably one monolayer of cobalt oxide on their surface. The cobalt metal nanoparticles preferably exhibit superparamagnetic properties to enable their easy extraction from the liquid medium using magnetic field.

The invention provides a process for the extraction of heavy metal ions that can be present in water and more particularly polluted water comprising:

In that process, the cobalt metal nanoparticles preferably exhibit superparamagnetic properties to enable their extraction from the liquid medium using magnetic field.

The process of the invention can be applied essentially on water containing heavy metal ions. This process can also be applied to other liquid solution or gas medium that contains heavy metal ions.

In the process of the invention the heavy metal ions present in the solution or in the gas are interacting with the cobalt metal nanoparticles and attached on their surface of the nanoparticles. The interaction induces the growth of heavy metal structure on the surface of the cobalt metal nanoparticles. The heavy metal structure that grows on the surface of the cobalt metal nanoparticles can be in the metallic or oxide form. Figure 4 shows lead ions that grew in the metallic form on the surface of the cobalt metal nanoparticles after reaction in water.

The metal nanoparticles suitable for this process include cobalt metal nanoparticles. These cobalt nanoparticles can be used as sole active material for the extraction of heavy metal ions. The cobalt nanoparticles used for the extraction of heavy metal ions can be agglomerated which decreases possible toxicity and release in the treated solution (figure 5). Cobalt metal nanoparticles can also be combined with other metal nanoparticles. The other metal nanoparticles combined with the cobalt nanoparticles can be silver metal nanoparticles, copper metal nanoparticle, gold nanoparticle, platinum nanoparticles, but not limited to. Preferably the metal nanoparticles that will be combined with the cobalt metal nanoparticles are grown on the surface of the cobalt metal nanoparticles.

The cobalt metal nanoparticles can be spread on a material support (substrate) that will be used for filtering. The cobalt metal nanoparticles are then bonded on the support via a chemical bonding that anchored them on the surface of the materials support. The said substrate is covered by cobalt metal nanoparticles or by cobalt metal nanoparticles combined with other materials like other metal nanoparticles or polymer. The support material covered by the cobalt metal nanoparticles can be sand (figure 2), wood, cellulose, metallic fibres, porous ceramic, polymer, glass but not limited to.

The invention is a process that enables to extract heavy metal ions that contaminate a liquid like water or are present in gas like gas combustion exhaust. The process consists of introducing the metal nanoparticles in the liquid medium or gas and waiting sufficiently long to enable the heavy metal ions to react with the cobalt metal nanoparticles and form a metallic or oxide coating. The time necessary for the reaction is preferably 1-60 minutes, for example 4-50 minutes, 5-30 minutes, preferably at around 5 minutes in the case of a liquid medium. The reaction with a gas medium is faster and preferably 1-60 seconds, for example 4-50 seconds, 5-30 seconds, preferably at around 5 seconds.

The reaction process between the cobalt metal nanoparticles and the heavy metal ions occurs in the temperature range of 1 to 100 °C, preferably 10 to 80 °C, more preferably 15-40 °C and most preferably 15-30 °C.

The reaction process between the cobalt metal nanoparticles and the heavy metal ions occurs in a liquid medium at a pH range of 1 to 14, preferably 3 to 10, more preferably 4 to 9 and most preferably 6 to 8.

Preferred heavy metal ions that will be extracted by the invention are:

V, Or, Mn, Fe, Ni, Cu, Zn, As, Mo, Rh, Pd, Ag, Cd, In, Sn, Sb, lr, Pt, Au, Hg, Tl, Pb, Bi, Po, Ra, U, Pu

Heavy metal ions that will be extracted by the invention:

Ti, Ga, Ge, As, Y, Zr, Nb, To, Ru, Te, La, Hf, Ta, W, Re, Os, At, Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Me, Lv, Ts, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, Pa, Np, Am, Cm, Bk

The cobalt metal nanoparticles can also be integrated in a filter as the active material. In that case, the polluted water flow or contaminated gas goes through the filter and the said method comprises:

i. Passing the polluted water or polluted gas on the support material or substrate covered by cobalt metal nanoparticles.

ii. Heavy metal ions are agglomerating around the cobalt metal nanoparticles anchored on the support material or substrate.

iii. Recuperation of the cleaned water or gas at the exit of the filter or exhaust.

iv. Removing from the filter when necessary, the support material or substrate covered by cobalt nanoparticles coated by heavy metal in the metallic or oxide form.

The cobalt metal nanoparticles coating may cover at least 50% of the surface of the substrate, for example at least 60%, 70%, 80% of the surface of the substrate. Preferably the coating will cover at least 90% of the surface of the substrate, for example at least 95%, 98% or 100% of the substrate surface.

In another aspect the coating of cobalt metal nanoparticles may consist of discrete metal nanoparticles or aggregates of metal nanoparticles. The nanoparticles typically have diameters in the range of 1-4000 nm, preferably 2-500 nm, more preferably 3200 nanometers. The metal nanoparticle aggregates typically have an overall diameter in the range 50-500 nm, for example they may be approximately 100, 200, 300 or 400 nm in diameter.

After the reaction, the materials support decorated with cobalt metal nanoparticles coated with heavy metal in the form of metallic of oxide film or coating (figure 4) oxide is removed from the filter for recycling via high temperature gradient treatment.

The active material, said cobalt metal nanoparticles can be coated with a polymer shell that acts as stabilisers to control the agglomeration/coalescence of the nanoparticles, thus the formed nanoparticles have a coating of stabiliser on their surface.

Extraction of heavy metal from polluted water has been performed using both methods. The direct introduction of surfactant-free cobalt metal nanoparticles in a solution containing lead ions (Pb²⁺) during 5 minutes and the extraction of the superparamagnetic cobalt nanoparticles coated with lead in metallic form using a magnetic field of at least 0.2 Tesla, preferably ranging from 0.5 to 1 Tesla (Example 1). The filtration of a solution containing copper ions (Cu²⁺) using sand coated with surfactant-free cobalt metal nanoparticles has been performed. The filter consisted of one essay tube of 15ml cut at its extremity and filled with active materials (sand decorated with surfactant-free cobalt metal nanoparticles) and to avoid the escape from the sand, net in polyethylene has been stretched at the bottom of the tube and glued with silicon (example).

All XRD patterns were produced using Cu-alpha radiation.

Examples

The ions contents in examples 1-4 have been measured by inductively coupled plasma mass spectrometer Agilent Technologies 7700x. The ions content in examples 5-8 have been measured by a multiparameter photometer Hanna Instruments HI83300 capable of providing Cu concentration in ppm.

Example 1

A solution of water contaminated with lead ions has been prepared. 1.0031 g of Pb(NO3) has been dissolved in 100 ml of distilled water to obtain a concentration of 6500 ppm of lead ion (Pb²⁺) in the water solution. The pH of the solution after preparation is pH = 4.24. 15ml of contaminated water has been transferred in one essay tube of 15ml and 6mg of surfactant-free Co metal nanoparticles have been added to the water containing lead ion. The solution has been shaked manually for 5 minutes. A magnet has been used to fix the superparamagnetic cobalt nanoparticles on the surface of the tube and the purified solution has been transferred in another essay tube of 15ml. A lead content of 6500ppm has then been measured. After the purification 5300ppm of lead ions has been measured indicating a decrease of 1200ppm of lead ions with the introduction of 536ppm of Co nanoparticles. The ratio of extraction is 2.24 ppm of Pb²⁺ for 1 ppm of Co metal nanoparticles. An increase of the pH of the solution after purification has been observed. The pH before extraction was 4.24 and after extraction the pH value is 6.02. Figure 5 is a SEM image of the cobalt nanoparticles before being used for lead extraction. Figure 4 is a SEM image of the cobalt nanoparticles after being used for lead extraction showing a modification of the surface morphology and the growth of Pb microsheets on the surface of the agglomerated Co nanoparticles.

Example 2

The solution of water contaminated with lead ions prepared in example 1 that contains 6500ppm of Pb²⁺ has been treated with 6mg of Ag-Co nanocomposite. 15ml of contaminated water has been transferred in one essay tube of 15ml and 6mg of surfactant-free Ag-Co nanocomposite have been added to the water containing lead ion. The solution has been shaken manually for 5 minutes. A magnet has been used to fix the superparamagnetic Ag-Co nanocomposite on the surface of the tube and the purified solution has been transferred in another essay tube of 15ml. The lead content has then been measured. After the purification 5700ppm of lead ions has been measured indicating a decrease of 800ppm of lead ions. An increase of the pH of the solution after purification has been observed. The pH before extraction was 4.24 and after extraction the pH is 5.27. Figure 6 is a SEM image of the Ag-Co nanocomposite before being used for lead extraction.

Example 3:

The solution containing 6500 ppm of lead ions (Pb²⁺) prepared in example 1 has been used and diluted lOOtimes. 1ml of water containing 6500ppm of Pb²⁺ has been mixed with 99mL of distilled water to prepare a solution containing 65ppm of lead ions. 15ml of contaminated water has been transferred in one essay tube of 15mI and 6mg of AgCo nanocomposite (Figure 6) have been added to the water containing 65ppm of lead ions. The solution has been shaken manually for 5 minutes. A magnet has been used to fix the superparamagnetic Ag-Co nanocomposite on the surface of the tube and the purified solution has been transferred in another essay tube of 15ml. The lead content has then been measured. After the purification, 28ppb of lead ions has been measured indicating a decrease of 99,95% of lead content with the introduction of 560ppm of AgCo nanocomposite. Figure 7 is a SEM image of the Ag-Co nanocomposite after being used for lead extraction showing a modification of the surface morphology and the growth of Pb microsheets on the surface ofthe agglomerated nanocomposite.

Example 4:

15ml of tap water from our laboratory containing heavy metal ions like Mn, Ni, Pb, V and Cu has been transferred in a 15ml essay tube. 3.5mg of cobalt metal nanoparticles have been added to the water containing and then the tube has been shaken manually for 5 minutes. A magnet has been used to fix the superparamagnetic cobalt nanoparticles on the surface of the tube and the purified solution has been transferred in another essay tube of 15ml. The pH before extraction was 7.07 and after extraction the pH is 7.58. The heavy metal ions have been measured before and after the purification process and a clear decrease of heavy metal ion concentration in the water has been observed:

	Cu (ppb)	Mn (ppb)	Ni (ppb)	U (ppb)	Zn (ppb)
Ions content before extraction	110	3.7	4.4	4.5	570
Ions content after extraction	1	0.22	3.6	3.2	47

Example 5:

15ml of well water from Estonia countryside and containing manganese (Mn) has been transferred in a 15ml essay tube. 2.3mg of cobalt metal nanoparticles have been added to the water containing and then the tube has been shaken manually for 5 minutes. A magnet has been used to fix the superparamagnetic cobalt nanoparticles on the surface of the tube and the purified solution has been transferred in another essay tube of 15ml. The manganese has been measured before and after the purification process and a clear decrease of Mn content has been observed. The Mn content decreased from 210ppb before extraction to 5.9ppb after the purification process. The pH before extraction was 7.47 and after extraction the pH is 8.00.

Example 6:

Cobalt metal nanoparticles have been spread on the surface of cleaned sand (Trixie Basissand Art. Nr. 76131) that has been used as material support (figure 2). The sand has been transferred in an essay tube of 15ml cut at its extremity and sealed with polyester net to allow the water to go through the sand in the tube and is then collected in a beaker. A 200 ml_ solution containing 22 ppm of Copper ions has been passed through the system containing sand coated with cobalt metal nanoparticles. The copper content in the water collected after the filtering process was 7.3ppm. The colour of the solution changed from translucent blue to a more translucent blue

Example 7:

Cobalt metal nanoparticles have been spread on the surface of cleaned sand (Trixie Basissand Art. Nr. 76131) that has been used as material support (figure 2). The sand has been transferred in an essay tube of 15ml cut at its extremity and sealed with polyester net to let the water going through the sand in the tube and being collected in a beaker. A 1 L solution containing 7.32 ppm of Zn ions has been passed through the system containing sand coated with cobalt metal nanoparticles. The zinc content in the water collected after the filtering process was 2.66 ppm. The colour of the solution changed from translucent to colourless-translucent.

Example 8:

Cobalt metal nanoparticles have been spread on the surface of sand (Trixie Basissand Art. Nr. 76131) that has been used as material support (figure 2). The sand has been transferred in an essay tube of 15ml cut at its extremity and sealed with polyester net to let the water going through the sand in the tube and being collected in a beaker. A 300 mL solution containing 34 ppm of Fe ions has been passed through the system containing sand coated with cobalt metal nanoparticles. The Fe content in the water collected after the filtering process was 0.8 ppm. After reaction, the iron ions have reacted and agglomerated on the surface of the sand coated with Co metal nanoparticles (Figure 8 and 9). The colour of the solution changed from yellow to colourless (figure 10). The pH before extraction was 2 and after extraction the pH is 5.9.

Example 9:

Cobalt metal nanoparticles have been spread on the surface of sand (Trixie Basissand Art. Nr. 76131) that has been used as material support (figure 2). The sand has been transferred in an essay tube of 20 mL cut at its extremity and sealed with polyester net to let the water going through the sand in the tube and being collected in a beaker. A 15 mL solution containing 65 ppm of Pb ions has been passed through the system containing sand coated with cobalt metal nanoparticles. The Pb content in the water collected after the filtering process was 1.2ppb. After reaction, the lead ions have reacted and agglomerated on the surface of the sand coated with Co metal nanoparticles. The pH before extraction was 4.24 and after extraction the pH is 6.2.

Claims

1. A process for the extraction of heavy metal ions from water where the process for the extraction is based on cobalt metal nanoparticles introduced into contaminated water comprising steps of:

i. mixing surfactant-free cobalt metal nanoparticles in contaminated water; and ii. waiting at least 5 seconds for heavy metal ion agglomerating around the cobalt metal nanoparticles, and iii. extracting the cobalt metal nanoparticles coated with the heavy metal ions in the metallic or metal oxide form from the contaminated water

2. The process according to claim 1 wherein said cobalt metal nanoparticles are bonded on sand.

3. The process according to claim 1 and 2 wherein cobalt metal nanoparticles coated with heavy metal ions in the metallic or metal oxide form are extracted by using magnetic field of up to 1 Tesla.

4. The process according to any one of the preceding claims wherein said cobalt metal nanoparticles are agglomerated.

5. The process according to claim 1 wherein said cobalt metal nanoparticles are fixed on a substrate integrated in a filter.

6. The process according to any one of the preceding claims wherein said cobalt metal nanoparticles exhibit surperparamagnetic properties.

7. The process according to any one of the preceding claims wherein the cobalt metal nanoparticles are coated with a layer of cobalt oxide.

8. The process according to any one of the preceding claims wherein the cobalt metal nanoparticles are stable under air.

9. The process according to any one of the preceding claims wherein the cobalt metal nanoparticles are functionalized.

10. The process according to any one of the preceding claims wherein the cobalt metal nanoparticles are extracted using a magnetic field of at least 0.2 Tesla.

11. The process according to claim 9 wherein the magnetic field is produced by a permanent magnet or an electromagnet.

12. The process according to claim 2 wherein said cobalt metal nanoparticles are bonded on a substrate, a carbon based support, a glass support, a metal support or a polymer support.