IT201600126508A1 - DEPURATING DEVICE OF HEAVY METALS IN WATERS AND POLLUTED TERRAIN AND METHOD OF MANUFACTURE - Google Patents

Description

DISPOSIT IV O DE PUR ANT E OF ME T AL L I PE SANT I IN WATERS

POLLUTED T E R E NI E ME T ODO OF MANUFACTURING

Summary of the invention

The present invention consists of devices, consisting of fibrous materials obtained from the grinding of bast plants. The device is based on the chemisorbent and physisorbent properties of the cellulosic fibers present in the bast plants, but also on the similar properties of the lignin that accompanies the cellulosic fibers, since lignin is the second most important component of the bast plants; and on the chemisorbent and or reactive properties of the substances fixed on the fibrous materials obtained from the bast plants. The devices object of the invention consist of: a) one or more layers of the aforementioned fibrous material which has the function of retaining pollutants; b) a confinement system for said material which gives shape stability to the layers of the fibrous material and is suitable not to release the material in the mobile phases in which the device can be inserted; c) a further container of the confined fibrous material, the shape of which can be diversified according to the type of purification to be implemented. The devices covered by the patent may constitute fixed Permeable Reactive Barriers (PRB) or fixed Biodreni, but also be made in the form of mobile vehicles, transportable on site if necessary. Through these devices, water polluted by heavy metals of any nature and origin can be circulated. Similar devices can be housed in soils polluted by heavy metals to obtain their purification by circulating a mobile phase.

State of the art

The problem of effectively removing heavy metals from aquifers, industrial and civil waste is today an urgent need in order to preserve the quality of the food environment and human health. In many industrial areas in Europe, inadequate placement of waste, accidental infiltrations and fallout from chimneys have led to the contamination of the soil surface and groundwater with various types of contaminants. Numerous contaminants are very persistent on the environmental surface, which means that they are still present in high concentrations even after tens of years from the moment in which the contamination has actually occurred.

In addition, there is often the malicious entry into the water courses of waste water

polluted by industrial processes, which contain metals extremely harmful to

the environment. An example of this is the residual polluted water of industrial treatments. For

with regard to polluted groundwater, according to the "2010 remediation report" of

Federambiente, in Italy alone there are over 12,600 polluted sites, with more than 1,350 municipalities

involved. Among these are also identified 57 Sites of Interest

National (SIN): strategic sites for the country that have been bounded by the ministry

of the Environment, which also controls the remediation procedure. The 57 Sites of Interest

National to be reclaimed

"They include the most polluted areas of Italy". These include the petrochemicals of Porto

Marghera, Brindisi, Priolo, Gela, Taranto, the industrial areas of Pioltello Rodano, Bagnoli-

Coroglio, Crotone, Trieste, Serravalle Scrivia, Sacco river basin, Domizio coast-

Flegreo and Agro Aversano.

The main pollutants found in the surveyed sites (FEDERAMBIENTE “Report

Remediation 2010 ") are shown in the following Table 1.

Number of times

Pollutant

found

Hydrocarbons alif. 1200

Aromatic 650

Heavy Metals 584

Inorganic 377

Chlorinated Phyathics 173

Other pollutants 455

Table 1

The presence of heavy metals in polluted sites is found with great frequency and is

secondary only to that of hydrocarbons and aromatic substances. That is

evidently due to the fact that most of the polluted sites have to do with the

processing or storage of petroleum products, or with industrial activities of

metallurgical type.

The most commonly used remediation techniques (FEDERAMBIENTE "Remediation Report 2010") are shown in Table 2.

Sites

T echnology

(no.)

Pump & treat 65

Excavation and disposal 39

Soil vapor extraction 21

A ir sparging 14

Capping 11

Hydraulic barrier 11

Bioventing 11 Unspecified Bioremediation 10

O ther techniques 20

Unknown data 12352

Table 2

As you can see, a predominance of the “pump & treat” technique emerges

however, it has the drawback of having long times and high management costs.

Soil decontamination is normally done by soil washing techniques.

The pollution in this case is generally moved into the water, washing the soil

with aqueous phases added with suitable surfactant complexing agents etc. Once the

pollutants, of whatever nature they are moved to the aqueous mobile phase

this water must in turn be purified of the pollutants moved into the aqueous phase

The realization of these operations, apparently very distant from each other, is based on the

development of low cost fixed phase filtering or chemisorbent systems that are in

able to retain the pollutants present in an aqueous phase, once that phase is

forced to cross them or in any case is put in contact with them.

A new and innovative approach for the development of these purification systems a

low cost, is that relating to the present invention. This approach is based

on the use of fibrous materials obtained from bast plants, such as broom and hemp,

ramie, linen, through mechanical treatments, which expose to contact with the phases

aqueous large ligninocellulosic fibrous surfaces. The cellulose and lignins present

as major components in bast plants they have remarkable capabilities

complexing agents for heavy metals. The use of cellulosic fibers extracted from the broom

through chemical-physical processes it has already been taken into consideration in the past

patent application n. CS2013A000007 developed at the University of Calabria: "Biodreni for the remediation of contaminated sites made with natural bast fibers with high surface development produced with chemical-physical processes", by S. troisi et. to the.

The inventiveness relating to this patent represents an improvement on what was previously developed. The materials that have been taken into consideration by the patent can be obtained from the bast plants through an extremely simple and inexpensive process of an essentially mechanical nature. Furthermore, the simultaneous presence of cellulose and lignin leads to a much more effective chemisorption of heavy metals, compared to that obtainable in the presence of cellulose alone or lignin alone. This is due to the possibility of obtaining fibers with a wide surface development by means of a simple process of mechanical crushing of the vegetables. This characteristic is peculiar to the fibers obtained from bast plants such as broom (Spartium Jumceum and Citisus Scoparius), hemp, flax or ramie. The present invention also takes into consideration the possibility of using fibers obtained from the mechanical grinding of bast plants after a passage of said plants in aqueous solutions. A non-exhaustive example of washing that serves to purify the fibers of fungi or bacteria is their washing in a dilute aqueous solution of hydrogen peroxide (1-5%). A non-exhaustive example of washing that eliminates the waxy substances present in the bark and promotes the wettability of the fibers, obtained with mechanical grinding, improving the chemisorption capacity of heavy metals from aqueous phases, is that carried out using aqueous alkaline solutions followed by rinsing in drinking water.

Another innovative element is constituted by the fact that the material proposed as an absorbent active part of the device can be obtained from the plant material through inexpensive procedures. The material will therefore be available at very low costs of the order of a few hundred euros per ton and will therefore make it possible to reduce the costs of pump and treat and soil washing and of any type of filtering and purifying apparatus.

A further advantage of the proposed device compared to other devices for water purification based on the use of active materials consists in the fact of using lignin-cellulosic fibers having a density of the order of 0.1 g / ml and a high permeability to the aqueous phase. without undergoing packing phenomena which could limit its use in the presence of high aqueous flows. These characteristics make it possible to produce mobile devices that can be easily transported to the place of purification and replaced with the reduction of their purification efficiency.

The device object of the invention

A non-exhaustive diagram illustrating the operating principle of the device object of the invention is shown in the following fig. 1

The device consists of a removable central part C consisting of fibrous materials obtained from the grinding of bast plants such as broom (Spartium Junceum and Citisus Scoparius), hemp, flax, ramie. The active element C may be confined by plastic nets or metal light alloys or other suitable material, such as to give shape stability to the layers of the fibrous material and prevent it from being released in the mobile phases in which the device can be inserted

The central part C (confined fiber) could constitute the reacting core of a Reactive Permeable Barrier or be inserted in another container designed to convey the flows of water to be purified on the confined fiber. This confinement structure can be built according to different shapes and sizes according to the type of purification to be implemented, and will allow, if necessary, the replacement of the confined fibrous material to restore the absorption capacity of pollutants in cases where the material fibrous has become saturated and has lost its purifying properties. In this regard, it may be very useful to constitute this conveyor in two parts that can be separated and easily rejoined in order to ensure easy replacement of the central filtering / purifying apparatus. The water to be purified can be conveyed to the purification system also by means of circuits powered by pumps and the conveying structure can also be made in such a way that it can be hermetically closed.

In cases where you want to remove pollutants from surface water bodies with slow or even non-existent flows, you can simply place the active part C on the surface of the water and remove the pollutants by simply absorbing the fibrous material.

Simple application of the device

Example 1. Removal of Mercury in the static phase by means of broom fibers (Spartium J unceum). For this purpose, the plant has undergone a pre-treatment phase before being analyzed in the course of the experimental tests. In particular, a broom washed with a diluted solution of hydrogen peroxide was used in order to eliminate dust and any molds and bacteria from the plant. The worms were then dried in an oven at a temperature of 120 ° C for about 5 hours in order to allow the removal of much of its moisture. Subsequently they were shredded with an industrial mill up to a length of 3 ÷ 10 mm and diameters between 0.1 ÷ 1 mm.

Inside a 2-liter beaker, 800 mL of an aqueous solution having a concentration of Hg2 + equal to 100 mg / L (100 ppm) was inserted. A purifying element consisting of 40 g of the fiber prepared as described above and contained in a highly permeable nylon mesh bag with a discoidal geometry was inserted into the solution. The purifying element was left to infuse for a time that made it possible to measure the concentration of mercury remaining in the aqueous solution for a period of a few hours. Residual mercury in solution was measured with an inductively coupled plasma (ICP / MS, ICapQ Thermofischer) using the atomic emission spectroscopy method. The reduction of mercury present in the aqueous solution was equal to 80% after a contact time of less than one hour. The removal rate is close to 90% after about three hours. The kinetics of mercury removal were found to be of the first order with respect to its concentration.

Example 2. Mercury removal in the dynamic phase by broom fibers (Spartium J unceum).

The fiber was prepared as in example 1. Inside a flow cell with a diameter of 6.7 cm and a length of 15 cm, 80 g of fiber were inserted. The flow cell consists of a plexiglass cylinder closed at the ends by two perforated plates designed to contain the fiber inside the cylinder and to allow the inlet and outlet of the solution to be purified. These end plates were secured to the central body of the cylinder by means of suitable flanges. The purifying device was completed by a supply tank, a recirculation pump and solution adduction and recovery pipes. Two liters of a solution containing 100 ppm of divalent mercury were circulated through the purifying element for times of the order of a few hours. Small amounts of solution were withdrawn at various time intervals to analyze the amount of mercury remaining in the aqueous phase. 80% of the amount of mercury was found to be removed from the aqueous phase in about 90 minutes.

Example 3. Removal of Mercury in the static phase by broom fibers (Cytisus Scoparius).

This example was carried out as in the case of example 1, using the Cytisus Scoparius type broom as a source of purifying fibers. The purifying capacity of the system, in one hour of contact, was approximately 75%.

Example 4. Mercury removal in the dynamic phase by broom fibers (Cytisus Scoparius).

This example was carried out as in the case of example 2, using the Cytisus Scoparius type broom as a source of purifying fibers. The purifying capacity of the system, in one hour of recirculation, was approximately 68%.

Example 5. Cadmium removal in the static phase using broom fibers (Spartium J unceum).

This example was carried out as in the case of example 1, except for the use of a Cadmium solution containing a concentration equal to 10 ppm of the metal. The purifying capacity of the system, in one hour of contact, was approximately 90%.

Example 6. Cadmium removal in the dynamic phase by means of broom fibers (Spartium J unceum).

This example was carried out as in the case of example 2, except for the use of a Cadmium solution containing a concentration equal to 10 ppm of the metal. The purifying capacity of the system, in one hour of contact, was approximately 84%.

Example 7. Removal of lead in the static phase by means of broom fibers (Spartium J unceum).

This example was carried out as in the case of example 1, except for the use of a Lead solution containing a concentration equal to 100 ppm of the metal. The purifying capacity of the system, in one hour of contact, was approximately 83%.

Example 8. Lead removal in the dynamic phase using broom fibers (Spartium J unceum).

This example was carried out as in the case of example 2, except for the use of a Lead solution containing a concentration equal to 100 ppm of the metal. The purifying capacity of the system, in one hour of contact, was approximately 78%.

Example 9. Zinc removal in the static phase by means of broom fibers (Spartium J unceum).

This example was carried out as in the case of example 1, except for the use of a zinc solution containing a concentration equal to 100 ppm of the metal. The purifying capacity of the system, in one hour of contact, was approximately 79%.

Example 10. Zinc removal in the dynamic phase by means of broom fibers (Spartium J unceum).

This example was carried out as in the case of example 2, except for the use of a zinc solution containing a concentration equal to 100 ppm of the metal. The purifying capacity of the system, in one hour of contact, was approximately 77%.

Example 11. Removal of Mercury in the static phase by means of hemp fibers.

The hemp fibers were prepared from the vegetable in the same way in which the broom fibers were treated in example 1. The remaining experiment was also conducted as in example 1. The purifying capacity of the system, in one hour of contact , was equal to approximately 73%.

Example 12. Removal of Mercury in the dynamic phase by means of hemp fibers.

This example was carried out as in the case of example 2, except for the use of hemp fiber of the same type as in example 11. The purifying capacity of the system, in one hour of contact, was approximately 67% .

Example 13. Removal of Mercury from a phreatic aquifer, simulated on a laboratory scale, by means of a Permeable Reactive Barrier of broom fibers (Spartium J unceum).

A physical model (Sandbox) has been created which reproduces, on a reduced scale, the behavior of a groundwater aquifer that flows within the ground. The model has dimensions (H × S × L) 40 × 40 × 150 cm and is divided, by means of two perforated walls, into three sectors. The central one, of larger dimensions (130 cm in length), contains the ground crossed by the aquifer, the two sides, each 10 cm long, act respectively as inlet and outlet water basins. To keep the underground water flow constant, the two side tanks have been connected to two loading tanks which, positioned at different heights, ensure the establishment of a constant hydraulic gradient. In particular, the aforementioned tanks have been arranged in such a way as to create a difference in hydraulic load of 5 cm between upstream and downstream, and an average hydraulic load, within the ground, of 25 cm. In the central sector of the model, containing the ground, a permeable barrier in broom fiber has been inserted with a width equal to the size of the sandbox (40 cm), a height greater than the average hydraulic load of the pitch (30 cm) and a thickness of 10 cm. The barrier contains about 1.3 kg of ground broom fiber as in example 1. The contact surfaces between the fiber and the ground were made of fine-meshed wire mesh in order to contain the fibers and ensure the passage of water. The density of the broom fiber was graduated so that the barrier had a permeability similar to that of the surrounding soil. After reaching the stationarity of the underground water flow, 10 liters of divalent mercury solution with a concentration of 100 ppm were introduced through the upstream tank. In the solution that emerged downstream and flowed in about three hours, a residual Mercury percentage equal to 15% of the initial one was found.

Example 14. Removal of Mercury in the static phase by means of broom fibers (Spartium J unceum).

The example follows the procedure of example 1 apart from the fact that the washing of the fiber was obtained by digesting the ground fiber in a 1% sodium hydrate solution, followed by two rinses in drinking water free of heavy metals. The removal rate was close to 92% after about two hours.

Example 15. Mercury removal in the dynamic phase by means of a broom fiber filter (Spartium J unceum).

320 g of fiber were used, prepared as in example 1. The fiber was packed (packing with an average density of about 0.21 g / cc.) In a flow cell consisting of a transparent cylinder of methacrylic polymer, having a length of 60 cm and an internal diameter of 6 cm, so as to create a fibro-porous filter. The ends of the cylinder were closed by suitable permeable membranes which allowed the fibers to be kept in place and at the same time to ensure the establishment of a hydraulic flow through the filter itself. The filter was inserted, by means of suitable flanges, in a hydraulic circuit in which a peristaltic pump (model PD 5101, Heidolf) was used to circulate an aqueous solution containing the Mercury ion Hg + 2. The flow rate of the solution circulating in the circuit containing the filter has been set at 19 ml / minute. A total volume of 11.8 liters of solution with an inlet mercury concentration of 100 mg / l was circulated through the filter. The mercury ion concentration exiting the filter was measured for 600 minutes with a sampling interval of 30 minutes. From the measured data it was possible to evaluate the following purifying parameters. The mercury ion was retained in the filter up to about 93% of the amount initially present in all the solution that passed through the system. The saturation level of the filter was estimated at 47% of its purifying capacity.

Claims (6)

Claims 1. Purifying device of heavy metals, in polluted waters and soils, in which the purifying element consists of materials consisting of vegetable fibers of bast plants such as broom, hemp, flax, ramie, jute, kenaf, characterized in that said materials are ground vegetable fibers with a maximum length of 1 cm and a maximum diameter of 1 mm. 2. Heavy metal purifying device according to claim 1, characterized in that the vegetable fibers are confined by permeable walls. 3. Heavy metal purifying device according to claim 2, characterized in that the permeable walls consist of meshes, fabrics, membranes, perforated septa. 4. Method for manufacturing purifying devices according to any preceding claim characterized in that the vegetable fibers of bast plants are previously washed with aqueous solutions of hydrogen peroxide and / or aqueous solutions of alkali and are subsequently ground to maximum lengths of 1 cm and maximum diameters of 1 mm. 5. Use of purifying devices according to claims 1-3 characterized in that they are used in hydraulic circuits of any type in which water polluted by heavy metals is circulating. 6. Use of purifying devices according to claim 5 characterized in that the hydraulic circuits in which water polluted by heavy metals circulate are groundwater.