WO2015122856A1

WO2015122856A1 - A process for preparation of composite sorbent for removal contaminants from water

Info

Publication number: WO2015122856A1
Application number: PCT/SK2015/050003
Authority: WO
Inventors: Dušan BEREK; Ivan NOVÁK; Karol MUNKA; Stanislav VARGA; Monika KARÁCSONYOVÁ
Original assignee: Ústav Polymérov Sav; Výskumný Ústav Vodného Hospodárstva; Centrum Vedecko-Technických Informácií Slovenskej Republiky
Priority date: 2014-02-13
Filing date: 2015-02-12
Publication date: 2015-08-20

Abstract

A process for the preparation of high performance composite sorbents suitable for the removal of contaminants namely harmful metals and natural radionuclides from water based on the nanoporous carbon fibers, on which the nano- and microparticles of iron hydrooxide is deposited, and which employs the synergistic effect of large surface of the nano- and microparticles of iron hydrooxide and the fibrous structure of the carrier, while the latter reduces the hydrodynamic resistance to the flow of water, whereas both the efficiency and the capacity of the sorbent in removing contaminants do not depend of the water pH within the practical applicability range.

Description

A process for preparation of composite sorbent for removal contaminants from water

Technical field

The invention relates to a process for the preparation of a sorbent for the efficient removal of contaminants from water, in particular toxic metals and radioactive substances, both in processes of water treatment and waste water purification, by depositing the nano- and microparticles of iron hydrooxide on the surface of the porous carbon fibers.

Current State of the Art

Presence of certain undesirable substances in water is a global problem. This mainly concerns the matter that threatens the health of the population and can be described as toxic contaminant, pollutant. The most attention is paid to the organic pollutants, toxic metals and to natural and synthetic radioactive substances. Among the frequently occurring pollutants in water are the heavy metals such as arsenic, As; antimony, Sb; cadmium, Cd; mercury, Hg; chromium, Cr; nickel, Ni; lead, Pb; selenium, Se, and others, and also waste products from the various industrial processes.

The specific problems are pollutants in drinking water. The allowable pollutant content in drinking water is governed by the laws of the particular country. In the European Union the limits set by the EU council are operative. Under the EU Council Directive 98/83/EC concerning water intended for human consumption, the antimony limit is 5.0 μg / L, for arsenic it is 10 μg / L, for cadmium 5.0 μg / L, for chrome 50 μg / L, for copper 2.0 mg / L, for Hg 1.0 μg / L, for nickel 20 μg / L, for lead, 10 μg / L, and for selenium 10 μg / L. The EU COUNCIL DIRECTIVE 2013/51/EURATOM of 22 October 2013 lays down requirements for the health protection of the general public with regard to the radioactivite substances in water intended for human consumption the gross alpha activity limit 0,1 Bq/ L.

The most frequently employed materials for removal of the above contaminants from water are solid sorbents, especially oxides and hydrated ferric oxides, both natural and synthetically produced, further both natural and surface modified zeolites, and different materials with a layer of TiO₂ and MnO₂ located on the surface of appropriate carrier, further activated carbon, activated alumina and limestone. The sorbents are usually porous substances in the particulate and sometimes in the fibrous shape. The efficiency of adsorption increases with the specific surface area of materials employed as sorbents. The disadvantage of porous sorbents is the limited accessibility of their inner surface because of the obstructed diffusion of sorbates. Large, easily accessible outer surface of the nano- and microparticles can not be directly used in practice because they exhibit high resistance against the flow of treated or purified medium.

Various sorbents are employed for removal of metal ions and radioactive substances from water, while the heavy metals are most often retained by the sorbents containing iron ions. A typical example is the sorbent GEH, which is widely used in technology. GEH is the granulated hydrated iron oxide, rich in crystalline β-FeOOH. A typical sorbent based on the activated alumina is produced by annealing the Al(OH)₃ at high temperature and consists of amorphous gamma- A1₂O₃. Activated carbon is a sorbent often employed in various technologies. In the water treatment and purification, it is used to remove organic matter and certain heavy metals. It is a highly porous particulate material with a large internal surface area (600-900 m²/g). The efficiency of heavy metals removal by the activated carbon depends on the process of its activation and may greatly vary with pH.

Among the disadvantages of the current methods of water treatment and purification is the relatively high cost of the commercially available sorbents. Therefore, the cheap particulate supports of active substances are developed such as silica gel, and porous carbon prepared from the waste materials such as fruit stones, agricultural scrap and the like.

The general disadvantage of particulate sorbents is their high resistance to water flow and usually pressure is to be applied in the filtration. Their sedimentation is slow. Moreover, the efficiency of numerous sorbents employed in technology is highly dependent on the pH of treated and purified water. As it is known, fibrous materials exhibit generally lower resistance against the flow of liquids compared with particulate materials with the identical effective diameter.

Summary of the Invention

The above drawbacks of the currently employed sorbents removes the invention, based on the Slovak patent applications 50017-2014 and 50077-2014 of 13 February, 2014 and 12 December 2014, respectively, which is based on the deposition of nano- and microparticles of iron hydrooxide in an amount from 5% to 40 wt.% on the nanoporous fibrous carbon support, prepared by carbonization of carbon precursors, fibrous de-lignified cellulose and or natural cellulose containing materials at a temperature from 450 ° C to 1000 ° C in absence of oxygen. Nano- and microparticles of iron hydrooxide are formed by controlled precipitation of water-soluble ferric salts from their solution at a concentration from the saturated one down to the diluted to 1 wt.% in presence of carbon fibers employing alkali metal hydroxides, namely natrium and potasium, as well as ammonium hydroxide, added in the amount equivalent to the precipitation of present dissolved ferric salt, to form the composite sorbent with the original structure.

The precursor for the preparation of porous carbon fiber is selected from cellulose fiber- containing material comprising the paper furnish, pulp, wood chips, woven and nonwoven fabrics based on cellulose, various natural materials such as crushed bamboo, hemp, sisal, jute, oil palm fiber.

Of the ferric salts particularly preferable are ferric sulfate, ferric chloride, and ferric nitrate, either as a single-component solutions or as a combination of several solutions of water- soluble ferric salts. The invention preferably makes use of the micro-fibrous structure of the nanoporous carbon fibers prepared by controlled carbonization of the delignified cellulose fibers and various natural cellulosic fibrous materials, and the synergistic effect of a large efficient surface of nano- and microparticles of the iron hydrooxide deposited in the pores and on the surface of the fibrous carbon support.

A two-step coverage process may be with advantage employed to increase amount of deposited iron hydrooxide on the nanoporous fibrous carbon support. After primary coagulation, a new portion of the ferric salt solution is added to the substrate and the precipitation process is repeated.

The structure of composite sorbent, which contains nano- and micro particles of iron hydrooxide, is shown in Figure 1 (micrograph of the carbon fiber with deposited nanoparticles of iron hydroxide).

The advantage of the invention is that it employs the cheap and available nanoporous carbon microfibers as a carrier of the nano- and microparticles of active substance, iron hydrooxide. The large outer surface of nano- and micro particles of the iron hydrooxide can be efficiently employed in a technologically feasible arrangement, which enables performing filtration and sedimentation under well manageable conditions because the fibrous structure of the composite sorbent reduces the flow resistance of water. The efficiency of resulting composite sorbent in the removal of the contaminants is in the practical application range independent of the pH of the water.

The resulting composite sorbents can be employed

- in the flow-through mode, i.e. by its application into water within the suitable site of the process line, in the amount which depends on the quality of the raw water. After appropriate time of its action, the sorbent is removed either by filtration or by sedimentation followed by filtration

- in the flow-through mode as a filling of the open filters, operated either at atmospheric- or under low hydrostatic pressure

- in the flow-through mode as a filling of the pressure filters, where the water is transported by pressure generated by a pump

- in a batch mode, i.e., dosing sorbent into the tank with the raw water in an amount that depends on the water quality. After mixing and a suitable time of contact the sorbent is separated by filtration or sedimentation.

The best mode for carrying out the invention

Carbonization of cellulose precursors were performed in absence of air oxygen.

Content of iron hydrooxide is related to the weigth of carbon present in the composite sorbent. Example 1

100 g of porous carbon microfibers prepared from the delignified cellulose, product of SCP Papier, Joint-Stock Comp., Ruzomberok, SK, by carbonization at 550 °C, was added under stirring to a solution of 30 g FeCl₃ in 500 mL of water. 80 ml of 25 wt.% NH₄OH was poured into this suspension under intensive stirring. The resulting material was filtrated, washed out with water to remove all soluble reaction products, and dried. It contained about 19 wt.% of iron hydrooxide.

Example 2

200 g of porous carbon microfibers prepared by the carbonization of cellulosic precursor FABOCEL (product of Bukocel, Joint-Stock Comp., SK) at 600°C, was added to 2000 mL of 6 wt.% of FeCl₃. Next, 340 mL of 25 wt.% NH₄OH was added under intensive stirring. Suspension was filtrated, washed with water and dried. Content of iron hydrooxide in the resulting material was 39 wt.%.

Example 3

60 g of porous carbon microfibers prepared from defibrilatad sisal fibers by carbonization at 980°C was mixed with a solution of 10 g of iron (III) sulphate cryst. in 50 mL of water. To this mixture, 10 g KOH in 80 mL of water was added under intensive stirring. After 5 min., solution of 10 g iron (III) sulphate cryst. in 80 mL of water was added. The suspension was stirred for 10 min., filtered, washed with water and dried. The product contained about 12.5 wt.% of iron hydrooxide.

Example 4

150 g of porous carbon microfibers prepared from crushed waste newspaper named S-cel 7 (product of CIUR, Joint-Stock Comp., CZ) by carbonization at 550°C, was added to a solution of 90 g Fe(N0₃)₃.9 H₂0 in 320 mL of water. Solution of 270 mL of 10 wt.% NaOH was slowly added upon stirring. Suspension was washed out, filtered and the remaining alkali was washed and dried. The resulting product contained 1 .7 wt.% of iron hydrooxide.

Example 5

To 1000 mL of solution containing 27 g of FeCl₃, 90 g of porous carbon microfibers was added, which was prepared from crushed waste newspaper named S-cel 7 (product of CIUR, Joint-Stock Comp., CZ) by carbonization at 900 °C. Under stirring, 900 mL of 2.5 wt.% solution of NH₄OH was added. Resulting suspension was filtered, washed with water and dried. The resultong product containedl9.6 wt.% of iron hydrooxide. Example 6

10 g of ZnCl₂ as a porogen was added to 50 g of delignified cellulose FABOCEL (product of Bukocel, Joint-Stock Comp., SK) and carbonized at 560°C. Next the porogen was washed-out with water on a filter and dried. 50 g of resulting carbon fibers was added to a solution of 30 g of FeCl₃ in 500 mL of water and under stirring a 80 mL of solution 25 wt.% NH OH was poured. The resulting suspension was filtrated, the soluble substances were washed-out with water and dried. The resulting product contained 39.6 wt.% of iron hydrooxide.

Example 7

60 g of FeCl₃ was dissolved in 1000 mL of water and 100 g of porous carbon fibers prepared from crushed waste newspaper named S-cel 7 (product of CIUR, Joint-Stock Comp., CZ) by carbonization at 800 °C was added into the solution. Under stirring, 2200 mL of 2.5 wt.% NH₄OH solution was added. The resulting suspension was filtered, washed with water and dried. The resulting product contained 39.2 wt.% of iron hydrooxide.

Example 8

Solution of 100 g NH₄Fe(S0₄)₂.12 H₂0 in 500 mL of water was added under stirring to 100 g of porous carbon fibers prepared by the carbonization of delignified cellulose Greencel (BUKOZA INVEST, Ltd., SR) at 480 °C. Then a solution of 24 g NaOH in 100 mL of water was added to the resulting suspension under stirring. Next the solution of 10 g FeCl₃ in 170 mL of water was added under stirring, followed with a solution of 8 g NaOH in 100 mL of water. The resulting suspension was filtered, washed out to remove the alkali and dried. The content of iron hydrooxide in the resulting material was 28.5 wt.%.

Example 9

40 g of the porous carbon fibers prepared from the defibrilated jute by carboniztion at 460°C, was poured by the solution of 20 g FeCl₃ in 100 mL of water. Then a solution of 15 g NaOH in 120 mL of water was added under intensive stirring and after filtration the material was dried and then washed with water and all soluble products were removed. The resulting material contained 32.7 wt.% of iron hydrooxide;

Example 10

Processes as in Example 9 with the exception that as the carbon material the cellulose based fabric carbonized at 750 °C was employed.

Example 11

Processes as in Example 9 with the exemption that as the carbon material the defibrilated hemp carbonized at 550 °C was used. Example 12

100 g of carbon fibers prepared by carbonization of cellulosic precursor FABOCEL (Bukocel, Joint-Stock Comp., SR) at 600°C was poured with the solution of 30 g FeCl₃ in 1000 mL of water. Next, 80 mL of 25 wt.% NH₄OH was added under stirring. The suspension was filtered, washed with water to neutral reaction and dried. The content of iron hydrooxide in the resulting material was 19.6 wt.%.

Example 13

60 g of the fibrous carbon material prepared from crushed bamboo cane by the carbonization at 700 °C was poured with the solution of 20 g of FeCl₃ in 120 mL of water. Next, 52 mL of 25 wt.% NH OH was added under stirring. The suspension was filtered, washed till neutral reaction and dried. The resulting product contained 21.6 wt.% of iron hydrooxide.

Example 14

75 g of fiber-like spruce saw dust with the size below 2 mm, carbonized at 650 °C was mixed with the solution containing 30 g of FeCl₃ in 400 mL of water and 80 mL of 25 wt.% of NH₄OH was added. The mixture was dried, the reaction products were washed-out with water and dried again. The content of iron hydrooxide in the resulting product was 26 wt.%.

Both the efficiency and the capacity of the composite sorbent in removing antimony, Sb, arsenic, As, cadmium, Cd, chromium, Cr, nickel Ni, lead Pb and selenium Se from the spiked water is documented in Tables 1 to 4 and in Table 6. The determination of metal concentration was carried out by atomic absorption spectrometry by hydride generation on the Solar 939 instrument.

Both the efficiency and the capacity of the composite sorbent in removing gross alpha activity of the water is documented in Table 5. Determination of the gross alpha activity was carried out according to the EU COUNCIL DIRECTIVE 2013/51/EURATOM.

The efficiency of contaminant removal was calculated according to the formula:

U (%) = [( c_s - c_u) / c_s)]. 100% where

U (%) - efficiency of contaminant removal

c_s - concentration of contaminants in the raw water

c_u - concentration of the contaminant in the treated water (residual concentration)

The adsorption capacity was calculated as the amount of captured contaminant per weight unit of adsorbent relative to the experimental conditions (concentration of contaminant in the raw water, pH and temperature of water, contact time of water with sorbent). Table 1. Adsorption efficiency and capacity of sorbents in removal of As and Sb. The concentrations in the raw water were 914 μ^Ι, and 65 μg/L for As and Sb, respectively.

Table 2. Effect of water pH on the concentration of Sb in water treated by sorbent prepared according to Example 12. Concentration of Sb in the raw water was 49,9 μg/L.

Table 3. Adsorption efficiency and capacity of sorbents in removal of Cd and Cr. The concentrations in the raw water were 110,6 μg/L and 100,0 μg/L for Cd and Cr, respectively.

Table 4. Adsorption efficiency and capacity of sorbents in removal of Ni and Pb. The concentrations in the raw water were 101,9 μg/L and 208,8 μg/L for Ni and Pb, respectively

Table 5. Adsorption efficiency and capacity of sorbent in removal of gross alpha activity. The activity in the raw water gross alpha activity was 0,28 Bq/L

Table 6. Adsorption efficiency and capacity of sorbent in removal of Se. Concentration of Se in the raw water was 92,5 μq/L

Industrial applicability

Composite sorbents prepared according to the invention find wide use in removing contaminants, especially toxic metals and natural radionuclides from both groundwater and surface water intended for the production of drinking water and in the purification of industrial waste water produced in many plants, for example by rinsing the products of electroplating and by the chemical surface treatment of metals.

Claims

1. A process for preparing a composite sorbent for removal of contaminants from water that employs the sorption effects of iron hydrooxide particles deposited on the porous carbon fiber material

w h e r e i n

on the nanoporous support of carbon fibers, prepared by carbonization of cellulosic carbon precursors at a temperature from 450 °C to 1000 °C in absence of atmospheric oxygen, nano and micro particles of iron hydrooxide are deposited in an amount from 5 to 40 wt.% relative to the amount of nanoporous fibrous carbon support with help of controlled precipitation from solutions of water-soluble ferric salt in a concentration from the saturated one down to diluted to 1 wt.% by alkali metal hydroxides, in an amount equivalent to the added ferric salt.

2. The process according to claim 1,

w h e r e i n the carbon precursor is selected from the delignified and natural fibrous cellulosic materials, including wood pulp, papermaking stock, paper furnish, as well as saw dust and wood chips, woven and nonwoven fabrics based on cellulose, crushed bamboo, hemp, sisal, jute, palm oil fibers.

3. The process according to claims 1 and 2,

w h e r e i n for the deposition of hydrooxide on the support of porous carbon, water-soluble ferric salts are primarily employed, including ferric sulfate, ferric chloride, ferric nitrate, ferric sulfate, as solutions and / or a combination of solutions of water-soluble ferric salts.

4. The process according to claims 1 to 3,

w h e r e i n for the deposition of nano- and microparticles of hydrated iron oxides in the pores and on the surface of the fibrous nanoporous carbon support the hydroxides of sodium or potassium or ammonium are employed.

5. The process according to claims 1 to 4,

w h e r e i n for the deposition of nano and microparticles of iron hydrooxides on the nanoporous carbon fibers a two-step deposition process induced by precipitation of the hydrated iron oxides is employed so that after the first stage, additional solution of the ferric salt is added and the precipitation process is repeated.