WO2007016100A1

WO2007016100A1 - System and method of removing heavy metals from waste streams

Info

Publication number: WO2007016100A1
Application number: PCT/US2006/028861
Authority: WO
Inventors: Michael F. Lally; Fan Maohong
Original assignee: Envirotech Systems, Inc.
Priority date: 2005-07-26
Filing date: 2006-07-26
Publication date: 2007-02-08

Abstract

A system and method of effectively removing heavy metal contaminants from waste water is provided with a concentration of rubber particles. The rubber particles may be comprised of waste rubber products or other rubber sources. The concentration of rubber particles may be provided in one or more various forms, including: fixed bed; moving bed; or soaked with the contaminated water and later separated by filtration. Waste water is directed through the concentration of rubber particles by various means including mechanical pumping or gravity-flow systems

Description

TITLE: ¹StSTEWAND METHOD OF REMOVING HEAVY METALS FROM

WASTE STREAMS

BACKGROUND OF THE INVENTION

Used tires accumulate in landfills in the United States at the rate of about 190 million per year, adding to an existing inventory of 2 billion to 3 billion discarded tires. This huge accumulation of waste tires represents an enormous repository of lost energy, materials, and money. Yet current methods for recycling or otherwise reusing tires barely put a dent in the waste tire inventory. Therefore, new methods for the cost-effective and environmentally friendly utilization of waste rubber material need to be explored.

Recently, much effort has been made on thermal degradation of waste rubber material to produce different substances including gaseous and liquid hydrocarbons and a solid char. The method provides an opportunity of using waste rubber as a material for developing different useful products. The generated hydrocarbonaceous substances can be used as raw materials for producing chemicals and fuels. The solid char residue has been tested either as a reinforcing filler or as a raw material for preparing activated carbon. Definitely, this method has its own advantages. However, the method consumes a lot of energy and generates air pollution during the thermal degradation process of rubber. Therefore, alternative approaches for the utilization of waste rubber materials need to be developed.

Lack of fresh water and environmental concerns caused by heavy metal contaminants in waste water have focused attention on the development of appropriate technologies for the treatment of waste water. Typical sources of heavy metals in waste water are mining, smelting, urban settlements and industrial complexes (such as coal-fired power plants, metallurgical processing, painting, pulp mills, chemical industries, docks, and shipyards). The major physical-chemical based technologies currently used in waste water treatment are coagulation, adsorption (filtration), oxidation and reduction. However, these methods have a number of shortcomings.

Coagulation has been widely used worldwide by waste water treatment plants. Typical coagulants used in waste water treatment plants include aluminum sulfate, aluminum chloride, polymeriq aluminum sulfate, polymeric aluminum chloride, polymeric aluminum silicate sulfate, ferric sulfate, ferric chloride, polymeric ferric sulfate and polymeric ferric chloride. The choice of coagulants depends on the price and the availability of coagulants in local markets. It also depends on the constituents of waste water. For example, if the turbidity and chemical oxygen demand (COD) are high, iron-based coagulants, especially polymeric ferric sulfate, work better than aluminum-based ones. One of the disadvantages of coagulation is the generation of a large quantity of additional solids. Another one is the high cost of the coagulants. In addition, coagulation is not effective in the removal of N-compounds in reduced state, such as ammonium-N. Adsorption is another major method currently used in many waste water treatment plants. Conventional adsorbents include ion exchange resins, activated carbon, activated alumina and different metal oxides. These adsorbents have been well characterized. Ion exchange resins pose some difficulties from an operational standpoint, such as the need for pH adjustment, frequent regeneration, and/or the production of a liquid stream that is considered to be hazardous under the Resource Conservation and Recovery Act (RCRA). Ion exchange method is very effective in many situations, but it is very expensive. Therefore, ion exchange is not appropriate for the removal of contaminants in many waste water treatment plants. Adsorption methods based on activated carbon, activated alumina and iron oxide are cheaper than ion exchange but still relatively expensive because those adsorbents are not cheap. Therefore, development of new and cheap adsorbents for waste water treatment plants has become increasingly important.

Accordingly, what is needed is a novel method for the cost-effective and environmentally friendly utilization of waste rubber material in the effective treatment of waste water containing heavy metals.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter.

The system and method of the present invention relates to methods of using rubber particles, derived from waste tires and other rubber materials, for the removal orneavy metais τronπ waste water. A preferred embodiment uses rubber particles as an adsorbent to adsorb heavy metals in different waste streams. A concentration of the rubber particles are provided in a media, which is applied to the waste stream. The rubber particles are allowed to adsorb heavy metals present in the waste stream. The invention provides several advantages over conventional waste rubber utilization procedures. First, the method is less expensive because it does not require the use of thermal degradation for processing rubber particles. It is also safer for the environment since it requires less energy. Further, the method has greater efficiencies of removal of heavy metals than previously available methods. It is therefore a principal object of the present invention to provide a system and method for a novel method for the cost-effective and environmentally friendly utilization of waste rubber materials.

A further object of the present invention is to provide a system and method for the cost-effective and environmentally friendly treatment of waste water containing heavy metals.

Still another object of the present invention is to provide a system and method for effectively removing heavy metals from waste water through the use of a concentration of rubber particles.

Yet another object of the present invention is to provide a system and method for effectively removing heavy metals from waste water in a cost-effective and environmentally benign manner.

A further object of the present invention is to provide a system and method for effectively removing heavy metals from waste water that is easily adapted for use in a variety of conditions. Still another object of the present invention is to provide a method for effectively removing heavy metals from waste water that is easily adapted for implementation through a nearly limitless number of different vehicles.

Yet another object of the present invention is to provide a system and method for effectively removing heavy metals from waste water and desorb the heavy metals from rubber particles through chemicals such as NaOH and/or Na₂Cθ₃ so that rubber particles can be used for many times.

These and other objects of the present invention will be apparent after consideration of the Detailed Description and Figures illustrated as follows. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments are described comprehensively below with reference to the accompanying figures, which form a part hereof and show, by way of illustration, specific exemplary embodiments. These embodiments are disclosed in sufficient detail to enable those skilled in the art to practice the invention. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense in that the scope of the present invention is defined only by the appended claims.

The system and method of the present invention adsorbs heavy metals in waste water on the surface of a concentration of rubber particles. The rubber particles are preferably derived from waste rubber materials and other rubber sources. However, favorable results have been derived from the use of rubber materials having the following major element concentrations: 2.56 wt-% O; 1.61 wt-% S; 84.42 wt-% C; 7.69 wt-% H; and 0.5 wt-% N.

By way of example and not for purposes of limitation, the following exemplary use demonstrates the manner and effectiveness of using rubber particles for the treatment of waste water. More, specifically, the following demonstrates one manner in which the present system and method may be used to remove heavy metal contaminants in waste water. While the following exemplary use is described as being in a controlled setting, the application of this and similar systems and methods will produce substantially similar results in less controlled, natural environments.

In one preferred embodiment, the rubber particles were provided with a surface area of approximately 0.3 m²/g. However, the particle size need not be uniform in size. The subject waste water solutions were comprised of analytical quality salts, deioned (Dl) water and the following heavy metals: Mn(II); Cr(III); Ni(II); Pb(II); Zn(II); and Cu(II). Specifically, CuSO₄ serves as source of Cu(II); ZnCI₂ for Zn(II); NiSO₄-6H₂O for Ni(II); Pb(CH₃COO)₄-H₂O for Pb(II); CrCI₃-6H₂O for Cr(III); and MnCI₂-4H₂O for Mn(II). The heavy metal concentration in tested solutions prepared was 10 ppm. Those of skill in the art will appreciate that the compounds used, and concentrations thereof, may be varied to a great degree without departing from the scope of the present invention. The waste water samples were subjected to jar tests to demonstrate and evaluate the adsorption efficiencies of heavy metals within rubber particles derived from waste rubber under different adsorption conditions that include pH, adsorption time and dosage of rubber particles. First, the solutions containing heavy metals were prepared by diluting the prepared stock solutions. Secondly, the pH values of the tested solution were adjusted with the prepared HCI solution measured by using and a pH meter. Rubber particles are then precisely weighed and added to water to make their dosages, ranging from 0 - 1g/L. A stirring rate of approximately 150 rpm was employed, and the top of all containers were sealed with stretchable plastic film to minimize possible evaporation and interference. In the present example, the tests were conducted at room temperature (-26.7⁰C). Samples were collected periodically and filtered with a 0.45//m membrane by using 10ml labeled vials. In an exemplary kinetics study, the dosage of waste rubber particles was applied at 0.1 g/L, and samples were retrieved at 0, 3 minutes, 5 minutes, 10 minutes, 20 minutes, 40 minutes and 60 minutes. In an exemplary isotherm study, the dosages of rubber particles applied were at 0 g/L, 0.1 g/L, 0.2 g/L, 0.3 g/L, 0.4 g/L and 0.5 g/L and the samples were retrieved after 60 minutes equilibration. The pHs of tested solutions during isothermal and kinetic studies were not justified. The effects of pH on the adsorption of heavy metals with rubber particles were also evaluated. It is noted that stirring time of 30 minutes was used to study the effect of pH on adsorption of heavy metals with rubber particles. The residual concentrations of heavy metals were measured by the ICP-MS (Inductively Coupled Plasma - Mass Spectrometry) technique using a Hewlett Packard 4500 programmable model. The minimum detection limit (MDL) of ICP-MS for each heavy metal is as low as 0.14ppb. Calibrations were conducted using the prepared standard solution of each heavy metal. The correlation coefficients (R²) between the counts and heavy metal solution concentrations were greater than 0.999 under all conditions suggesting a strictly linear relationship within the concentration range of each heavy metal. Adsorption efficiency (A.E.) of each heavy metal is defined as: A.E. (%) = (Co - C_r)/C₀ * 100, where C₀ and Cr are initial heavy metal concentration (Co) and residual heavy metal concentration (Cr), respectively. Results of Exemplary Kinetic Studies

1. Ni(II)

Time (min) Removal Efficiency (%)

0 0

3 45.8

5 48.5

10 50.7

20 56.1

40 57.3

60 59.4

2. Cr(III)

Time (min) Removal Efficiency (%)

0 0

3 7.8

5 17.4

10 40.1

20 55.3

40 63.7

60 67.2

3. Pb(II)

Time (min) Removal Efficiency (%)

0 0

3 17.2

5 26.6

10 52.2

20 64.7

40 71.9

60 72.8

4. Cu(II) Time (min) Removal Efficiency (%)

0 0

3 45.3

5 53.7

10 68.1

20 72.5

40 74.7

60 81.6 5. Zn(II) Time (min) Removal Efficiency (%)

0 0

3 33.9

5 46.7

10 53.6

20 62.1

40 66.9

60 68.4

6. Mn(II)

Time (min) Removal Efficiency (%)

0 0

3 15.5

5 24.9

10 29.1

20 35.6

40 36.9

60 37.7

The studies demonstrate the rapid adsorption of Ni(II) and Zn(II) with rubber particles during the first three minutes. The adsorptions of Cr(III), Pb(II), Cu(II) and

Mn(II) with rubber particles occurred during the first ten minutes. The adsorption rate of each metal decreased gradually with time after certain period of time, which varies from metal to metal. After 60 minutes adsorption, the adsorption of each heavy metal with rubber particles reached near pseudo-equilibrium. Accordingly, 60 minutes was used as the adsorption equilibrium time in the subsequent isotherm tests.

Results of Isothermal Studies

1. Ni(II) Removal

Dosage Efficiency (%) (QlL)

0 0

0.1 59.4

0.2 83.9

0.3 95.6

0.4 98.7

0.5 99.5

3. Pb(II)

Removal Dosage(g/L) Efficiency (%)

0 0

0.1 72.9 0.2 84.5

0.3 92.7

0.4 96.9 0.5 99.4

4. Cu(II)

Removal Dosage(g/L) Efficiency (%)

0 0

0.1 81.6

0.2 87.4

0.3 92.9

0.4 93.5

0.5 93.7

5. Zn(II)

Removal

Dosage(g/L) Efficiency (%) 0 0

0.1 67.5

0.2 75.8 0.3 79.9

0.4 83.2

0.5 84.6 6. Mh(If)

Removal

Dosage(g/L) Efficiency (%)

0 0

0.1. 36.4

0.2 50.1

0.3 63.2

0.4 69.8

0.5 72.3

The aforementioned data clearly demonstrates that the rubber particles provide a superior sorbent for the removal of heavy metals from waste water

Effect of PH

1. Ni(II)

PH Removal Efficiency (%)

4 55.2

5 57.2

6 68.8

2. Cr(III)

PH Removal Efficiency (%)

4 54.3

5 65.7

6 79.3

3. Pb(II) pH Removal Efficiency (%)

4 60.4

5 67.2

6 72.1

4. Cu(II)

PH Removal Efficiency (%)

4 71.3

5 73.8

6 77.4 5. Zn(II) pH Removal Efficiency (%)

4 59.2

5 63.3

6 67.1

6. Zn(II) PH Removal Efficiency (%)

4 33.5

5 38.7

6 41.2

As-received rubber particles are efficient in the removal of heavy metals, even when their surface area is only -0.3 m²/g. The heavy metal adsorption capacity of raw rubber particles can be improved, however, as their surface area increases, which can be realized by mechanical methods.

The present invention differs from conventional techniques, such as activated carbon, that operate through surface sorption. Rather, the rubber particles used according to this invention operate under a bulk adsorption mode. This provides flexibility in the shape and size of the rubber particles, which may be determined by availability of product or the treatment conditions presented. Accordingly, the rubber particles can be used in a granular or pelletized form or as integrated powders.

The present invention easily lends itself to various treatment techniques, including: fixed bed; moving bed; or soaked with the contaminated water and later separated by filtration. In one preferred embodiment, however, a fixed bed of granular rubber particles is provided in the path of moving waste water. It is contemplated that multiple beds may be provided in series or parallel relation with one another. Either such arrangement could, for example, be used in the form of a permeable adsorption barrier for treating contaminated groundwater. It will be understood that, depending upon the conditions of the site to be used, impermeable wall sections may be provided in order to direct the groundwater flow through the treatment area. Other materials, such as gravel may be used as a border adjacent the treatment area in order to maintain uniform flow therethrough. The rubber particles may be placed within containers formed from permeable materials to create one or more removable cartridges or packets that comprise the treatment area. The permeable materials may be'"trex!Die or πgrα m nature, as the circumstances deem appropriate. Such an arrangement is provided for the easy removal of the rubber particles for processing and/or removal of the heavy metals therefrom.

In another preferred embodiment, the rubber particles may be disposed within one or more canisters of varying shapes and sizes. The waste water may then be directed through the canisters, either through mechanical pumping or gravity-flow systems, to capture and remove the heavy metals from the waste water. Removable engagement of the canisters with a system for directing the water flow (enclosed or open channels, and the like) provide for easy removal and replacement of the canisters for processing of the rubber particles and/or removal of the heavy metals therefrom.

Although the invention has been described in language that is specific to certain structures and methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific structures and/or steps described. Rather, the specific aspects and steps are described as forms of implementing the claimed invention. Since many embodiments of the invention can be practiced without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Claims

CL1AHWS"What is claimed is:

1. A method of removing heavy metals from waste water, the method comprising: providing a concentration of rubber particles comprising an adsorbent for heavy metals; positioning the concentration of rubber particles in a treatment area; introducing the waste water to said concentration of rubber particles within the treatment area; said rubber particles adsorbing heavy metals present in the waste water on the surface area thereof.

2. The method of claim 1 wherein said rubber particles are comprised of waste rubber.

3. The method of claim 2 wherein said rubber particles being comprised of at least the following approximate major element concentrations: 2.56 wt-% O; 1.61 wt-% S; 84.42 wt-% C; 7.69 wt-% H; and 0.5 wt-% N.

4. The method of claim 1 wherein the waste water is comprised of at least one of the following heavy metals: Mn(II); Cr(III); Ni(II); Pb(II); Zn(II); and Cu(II).

5. The method of claim 1 wherein said treatment area is positioned at least partially beneath ground level.

6. The method of claim 5 wherein said treatment area is provided as a part of a permeable adsorptive barrier for treating contaminated groundwater.

7. The method of claim 6 wherein said rubber particles are disposed within at least one permeable cartridge that comprises the treatment area.

8 The method of claim 7 wherein said cartridge is comprised of a flexible material and is removably associated with said permeable adsorptive barrier.

91 Trie" method of claim 8 wherein said waste water is introduced to said concentration of rubber particles by positioning said concentration of rubber particles in the path of a waste water stream.

10. The method of claim 1 wherein said rubber particles are disposed within at least one canister that comprises the treatment area.

11. The method of claim 10 wherein said waste water is introduced to said rubber particles by directing said waste water through said at least one canister using a mechanical pumping system.

12. The method of claim 10 wherein said waste water is introduced to said rubber particles by directing said waste water through said at least one canister using a gravity-flow systems.

13. The method of claim 10 wherein said at least one cartridge is removably associated with said treatment area.

14. The method of claim 1 wherein said rubber particles are provided with a surface area of approximately 0.3 m²/g or higher.