ES2360785T3 - CONTACT GRANULES AND ADSORBENTS. - Google Patents

Abstract

Use of adsorption agents / reaction agents in the form of pieces consisting of α-FeOOH particles that are adhered together by (hydr) aluminum, magnesium or titanium oxides, for the purification of gases or liquids.

Description

The present invention relates to the use of adsorption agents / reaction agents in the form of pieces consisting of α-FeOOH particles that are adhered to each other by hydr (oxide) of aluminum, magnesium or titanium.

Contact granules and adsorbents, also those that are based on iron oxide and / or iron oxyhydroxide, have already been described. They are mainly used in continuous procedures, usually found in tower or column type apparatus through which the medium to be treated circulates, and chemical or physical reaction or adsorption processes take place on the inner and outer surface of the granules To this end, materials in powder form cannot be used, as they are compacted in the direction of flow of the medium and, thereby, increase the resistance to flow until the apparatus is locked. If a device is cleaned by backwashing (see below), large amounts of dust are discharged or lost, or cause an intolerable load of wastewater.

The circulating means also exert, however, forces on the granules, which can cause abrasion and / or movement until the agitation of the granules is intense. Therefore, the granules collide with each other and, as a consequence, unwanted abrasion wear is generated. This causes a loss of contact material or adsorbent and a contamination of the medium to be treated.

They are advantageously used, for example, in the field of water purification or gas purification, adsorption agents / reaction agents containing iron oxide and iron hydroxide. In the case of water purification, this agent is used in absorbent filters or columns with horizontal or vertical circulation or by adding to the water to be treated for the separation of compounds, organic or inorganic, dissolved, suspended or emulsified phosphorus , arsenic, antimony, sulfur, selenium, tellurium, beryllium, cyanocomposites and heavy metal compounds of drinking water, drinking water, industrial and domestic wastewater, mineral water, holy water and medicinal water, as well as garden pond water and water for agricultural use. It is also possible to use those known as reactive walls for the separation of contaminants from soils and infiltration water pipes from contaminated sites (landfills).

In the case of gas purification, the agent is used in adsorbers for binding to unwanted constituents such as sulfuric acid, mercaptans and cyanhydride acid, as well as phosphorus, arsenic, antimony, sulfur, selenium, tellurium compounds, as well as cyanocomposites and heavy metal compounds in exhaust gases. It is also possible to adsorb gases such as HF, HCl, H2S, SOx, NOx.

It is also possible to eliminate phosphorus, arsenic, antimony, selenium, tellurium compounds, as well as cyano compounds and heavy metal compounds from used oils and other contaminating organic solvents.

Contact granules and adsorbents based on iron oxides and / or iron oxyhydroxides are also used for catalysis of gas or liquid phase chemical reactions.

Methods of different types for removing trace elements and contaminants from aqueous systems using adsorption agents are also known.

Thus, in DE-A 3 120 891 a process is described in which, for the separation, particularly, of surface water phosphates, filtration is carried out through active alumina with a granulation of 1 to 3 mm.

DE-A 3 800 873 describes an adsorption agent based on porous materials such as, for example, hydrophobicized crete with a fine to medium granulation, for the removal of water contaminants.

In DE-A 3 703 169 a process for the manufacture of a granulated filter material for treating natural water is disclosed. The adsorbent is manufactured by granulating an aqueous kaolin suspension with the addition of dolomite in powder form in a fluidized bed. Next, the granules are calcined at 900 to 950 ° C.

From DE-A 40 34 417 a process is known for manufacturing and using reagents with high reactivity for the purification of exhaust gases and wastewater. This document describes mixtures of Ca (OH) 2 with clay additives, rocks in powder, volatile powder and volatile ash, which are manufactured with a porous shape and have an area of approximately 200 m2 / g.

The mentioned procedures or the contact agents used in said document have the general disadvantage that the corresponding components responsible for the selective adsorption of constituents of the media to be purified, that is, the true adsorbents, must be added with high amounts of aggregates, to allow a conformation to granules. This greatly reduces the ability to bond with aqueous contaminants that must be removed. In addition, subsequent processing or reuse of the material is problematic, since the foreign substance used as a binder must first be separated again.

In DE-A 4 214 487 a process and a reactor for removing contaminants from water are described. A funnel-shaped reactor, in which, as a sorbent for aqueous contaminants, iron hydroxide distributed in the form of flakes is used, has a horizontal circulation. The disadvantage in this process is the use of iron hydroxide in flakes, since due to the small difference in density between water and iron hydroxide, it results in a reactor of this type can only operate with flow rates very low and there is a risk that the sorbent, if already loaded with contaminant, is discharged from the reactor along with the water.

JP-A 55 132 633 describes granulated red sludge as a byproduct of aluminum production as an arsenic adsorbent. This is composed of Fe2O3, Al2O3 and SiO2. The stability of the granules and the granulation procedure is not reported in said document. Another disadvantage of these adsorbents is the lack of constancy of the composition of the product, the lack of security of availability.

A process for manufacturing an adsorption agent containing iron hydroxide is described in DE-A 19 826 186. A polymer dispersion is mixed with iron hydroxide in water in a dispersible form. This mixture dries well, obtaining a solid state, and the solid material is then mechanically ground into the desired shape and / or size or the mixture, if necessary after drying, is subjected to a shaping and, then, it has just dried obtaining a solid state. This results in a material in which iron hydroxide is solidly embedded in the polymer and must have a high binding capacity for contaminants included in wastewater or exhaust gas.

The disadvantage of this procedure is the use of organic binders, which additionally charge the water to be treated by erosion by washing and / or abrasion wear of organic substances. In addition, stability is not guaranteed with the long-term use of the combination of adsorbents. In addition, bacteria and other microorganisms can use an organic binder as a feeding medium, so that there is a risk of colonization of contact with microorganisms and contamination of the medium by them.

Basically, the presence of other organic auxiliary substances necessary for the manufacture of adsorbents in the processing, recycling or reuse of used adsorbents presents a disadvantage, since the use of pure substances is less problematic than the use of mixtures of substances as in this case. Thus, for example, polymeric binders, in the reuse of iron oxide-based adsorbent materials such as concrete coloring pigments, have the disadvantage that these binders can prevent the dispersion of the pigment in the liquid concrete.

In DE-A 4 320 003 a process for removing arsenic dissolved in groundwater by means of granulated or colloidal iron hydroxide is described. For the use of fine, suspended iron (II) hydroxide products, it is recommended in said document to introduce the iron hydroxide suspension in solid bed filters, which are filled with the granulated material or other vehicles with high external or internal porosity . This procedure also has the disadvantage that, due to the adsorbent "substrate + iron hydroxide", only reduced specific loading capacities can be achieved. In addition, there is only a weak bond between the substrate and iron hydroxide, so that in a subsequent treatment with arsenic-containing water there is a risk of discharging iron hydroxide

or iron arsenate. This publication also mentions the use of granulated iron hydroxide as an adsorbent material for a solid bed reactor. The manufacture of the granulated iron hydroxide is carried out by means of a freezing (lyophilization) conditioning of iron hydroxide obtained by neutralizing acidic solutions of iron (III) salts at temperatures below 5 ° C. This manufacturing process consumes a large amount of energy and generates a wastewater very charged with salts. In addition, as a result of this manufacturing process only very small particles with reduced mechanical stability are obtained. This causes, in the case of using a solid bed reactor, that the particle spectrum by mechanical abrasion of the particles is clearly reduced over the course of the operation, which again has the consequence that the finely dispersed particles are discharge from the reactor with the adsorption agent charged or not charged. Another disadvantage of this granulate is that the adsorption capacity against arsenic compounds is greatly reduced if the granulate, for example, due to a longer drying period, loses water.

For water treatment, adsorbents that operate continuously, which frequently operate in parallel oriented groups, are preferably used. For example, to release water from organic pollutants, adsorbent of this type is fed with activated carbon. At the time of maximum use, the adsorbents present operate in parallel, to allow the flow rate not to exceed the maximum allowed. During periods of reduced water use, the adsorbents are removed separately from the operation and can be kept on hold, meanwhile, for example, by fixing the adsorbent material at special loads, as explained in detail below.

GB 1568349 discloses a magnetic powder adsorbent for adsorption of dense suspensions containing magnetic iron oxide compounds and (hydr) titanium oxides

US 4,459,370 describes adsorbents in powder form composed of finely divided silicon oxide which are coated with finely divided-FeOOH.

The use of granules has also been considered, which can be generated by compacting, for example, iron oxide in powder form by using high linear forces. Granules of this type have already been described to homogeneously color liquid concrete. The use of high linear forces in compaction consumes a great deal of energy and is expensive and the stability of the compacting is insufficient in case of long-term use of the adsorbent. Therefore, the use of adsorbents of this type is considered, in particular in continuous operation, for example, for water purification, only to a limited extent. In particular, for the maintenance or purification of adsorbent installations by backwashing (see below), granules of this type lose, due to the agitation thereof associated with it, large amounts of substance. The backwash wastewater becomes heavily clouded due to abrasion. This is unacceptable for several reasons: First, adsorbent material is lost, which is heavily loaded with contaminants after a long period of operation and, therefore, is toxicologically worrying. In addition, the wastewater stream is loaded with the material produced by abrasion wear, which can sediment and thus cause a detrimental effect on the conduction system, and finally, the purification facility is physically and undesirably charged. Toxicologically, to mention just a few reasons.

The present invention is based, therefore, on the objective of providing an adsorption agent / reaction agent based on pieces of iron and oxygen in the form of pieces having a high mechanical stability together with a high binding capacity with the Contaminants included in liquids and gases without organic binders to be used to obtain sufficient mechanical stability or facilities that work with such media.

Contact or adsorption agents / reaction agents that consist of α-FeOOH particles, which are adhered together by (hydr) aluminum, magnesium or titanium oxides, solve this target complex.

In this regard, it is an adsorption agent / reaction agent that, as experiments have shown, has a high binding capacity with contaminants frequently present in wastewater or exhaust gases and without the addition of organic binders or other substances Inorganic type with binder function already has sufficient mechanical and hydraulic stability.

Because this material has only a low proportion of binders of another type, it also has the advantage of adsorbents of the prior art, in addition, the advantage that if necessary after separation or removal of adsorbed contaminants, it can be eliminated as a all or used for other applications, such as after crushing for the coloring of concrete and other building materials, as well as customary uses of pigments in paints, dyes and varnishes or for coloring other substrates such as crust padding or crushed wood , since the amount of additives does not represent a disadvantage for coloring.

The absorption agent / reaction agent according to the invention is obtained by mixing iron oxyhydroxide of the α-FeOOH phase in solid or suspended form by adding Fe (OH) 3 in suspension or in gel form with variable water contents and from this mixture, the water is then removed, totally or with maintenance of a certain amount of water, for example, by filtration or evaporation, and the solid or semi-solid material, then, is mechanically crushed in the form and / or desired size, or the dispersion is subjected, if necessary after a pre-drying to a semi-solid state, to a mechanical conformation and then (additionally) to drying to obtain a solid state. In this regard, iron oxyhydroxide is solidly embedded in the hydroxide or other oxide matrix.

The solidification of the α-FeOOH particles can also be carried out in situ: either a basic suspension of α-FeOOH is available, the aqueous salt of Al3 +, Mg2 +, Ti4 + or the mixture thereof is added, until a sufficiently insoluble precipitate of Al (OH) 3, MG (OH) 2, TiO (OH) 2 or sequential products of maturation or dehydration thereof precipitate on the α-FeOOH particles, or, conversely, the particles precipitate α-FeOOH suspended in the solutions of Al3 +, Mg2 +, Ti4 + when adding a base, such as, for example, NaOH, Ca (OH) 2, KOH, CaCO3, Na2CO3, K2CO3, NH4OH the insoluble precipitates such as Al (OH ) 3, MG (OH) 2, TiO (OH) 2 or its sequential products of maturation or dehydration. Aluminum oxide or (oxy) aluminum hydroxide can also precipitate from an aluminate suspension (for example NaAlOO2) on the α-FeOOH particles.

The elimination of water by evaporation is preferably carried out later, if the suspensions from which the water is to be removed are largely free of salt and / or less high demands on the mechanical stability in operation have been established on the final product obtained.

Alternatively, water is removed by filtration. In this regard, it is possible to improve the filtration behavior of the suspensions by applying measures that improve filtration, such as those described, for example in Solid-Liquid Filtration and Separation Technology, A. Rushton, AS, Ward RG., Holdich, 2nd. 2000 edition, Wiley-VCH, Weinheim and Handbuch der Industiellen Fest / Flüssig-Filtration, H. Gasper, D. Öchsle, E. Pongratz, 2nd edition 2000, Wiley-VCH Weinheim. In this way, flocculation agents are added to the suspensions, for example.

The adsorption agents / reaction agents according to the invention can be subjected to air and / or vacuum drying and / or in a drying cabinet and / or in a continuous-pass dryer or in a temperature-spray dryer which are in the range of 5 to 300 ° C. A lyophilization of the material is also possible.

The products preferably have a residual water content of less than 20% by weight.

The crushing of the material is preferably carried out by grinding to give particles of a size in the range of 0.5 to 20 mm. The mechanical conformation of the semi-solid material preferably takes place in a pelletizing or pelletizing installation or in an extruder, with molded bodies having a size in the range of 0.5 to 20 mm in diameter or length can be obtained.

It has been found that the fragments or granules obtained in this way have a binding capacity with contaminants present in water, liquids or gases and, in addition, have a sufficiently high stability against fluid media with respect to their mechanical or hydraulic stress.

The product has a BET area of 50 to 500 m2 / g, preferably 80 to 200 m2 / g.

The primary particle size was determined by measurements by scanning with the scanning electron microscope, for example, with an increase of 60000: 1 (apparatus: XL30 ESEM FEG, Philips company). If the primary particles are needle-shaped, such as, for example, in the α-FeOOH phase, the width of the needle can be indicated as a measure of particle size. A needle width of 100 nm is observed for α-FeOOH nanoparticles, however, mainly between 4 and 50 nm. The α-FeOOH primary particles usually have a length: width ratio of 5: 1 to 50: 1, typically 5: 1 to 20: 1. By endowment or a special embodiment of the reaction, however, the length: width ratio of the needle shapes can be varied.

By mixing Fe (OH) 3 with iron hydroxides, the existence of the crystalline pigment or germ particles in their known particle morphology, which are held together with each other or is observed in the scanning electron microscope. they are adhered to each other by means of the amorphous Fe (OH) 3 polymer.

Yellow iron oxyhydroxide pigments are generally synthesized by precipitation of hydroxides

or iron (II) carbonates from the corresponding iron (II) salt solutions such as, for example, FeSO4, FeCI2, in pure form or as pickling solutions, in an acidic or basic pH range, and thereafter oxidation in iron (III) oxyhydroxides (see, among others, G. Buxbaum, Industrial Inorganic Pigments, VCH Weinheim, 2nd edition, 1998, page 231 et seq.). The oxidation of bivalent or trivalent iron is preferably carried out with air; In this regard, intensive gasification is an advantage. Also oxidation with H2O2 results in iron oxyhydroxides. As the precipitation agent, preferably, NaOH is used. However, other precipitation agents, such as KOH, Na2CO3, K2CO3, CaO, Ca (OH) 2, CaCO3, NH3, NH4OH, MgO and / or MgCO3, can also be used.

Against the state of the art, in the case of the described use, it is an improvement. The granules according to the invention can be loaded much more than those of the prior art and therefore have superior abrasion stability against mechanical and hydraulic stresses. They can be used directly as such. In the crushing or grinding of the pure dry substances obtained below, from filter cakes or extruders, a purification of water can be avoided, for example, in the use of adsorbent plants, since the thick pieces are broken down by themselves in case of contact with water. In this case a statistical distribution of grain size appears; however, no particle of a size that is discharged in considerable quantities through the medium in circulation from the adsorbent.

In a separate granulation, as would be necessary in the use of conventional oxyhydroxides in the form of (loose) powder, either by using binders other than the substance or high lienal forces in compaction, it can be totally avoided.

As another procedure for obtaining a granulate, the effectiveness of granulation of a semi-liquid paste has been tested. In this respect, pellets or rods are formed from a semi-solid paste, for example using a simple perforated sheet, a roller press or an extruder and these are dried either similarly or this extrudate is carried by means of a spheronizer. , additionally, to a ball or granule shape. The still wet pellets or pellets can be subsequently dried to a discretionary moisture content. With this, the granules do not agglutinate, with a residual moisture content <50% being recommended. Such a ball shape may be advantageous for the use of solid bed adsorbents due to the improved loading in this way in adsorbent containers against crushed granules or stick-shaped pellets.

Particularly preferably, the granules according to the invention are used for the purification of liquids, in particular for the removal of heavy metals. A preferred application in this technical field is the decontamination of water, in particular drinking water. Some time ago, the removal of arsenic from drinking water gave special attention. The granules according to the invention are very suitable for this, because the limit values established by the United States EPA administration by using the granules according to the invention are not only respected, but can even be lowered.

For this purpose, the granules can be used in conventional adsorption apparatus, as currently used, for example, fed with activated carbon, for the removal of contaminants of another type. A batch operation is also certainly possible, for example in tanks or similar containers, which if necessary are equipped with stirrers. However, use in continuous operating facilities such as step adsorbers is preferred.

Because the water treated for drinking water usually also contains organic pollutants such as algae and similar organisms, the surface of the adsorbents is covered, in particular the outer surface of adsorbents in the form of granules, during use, with sediments in mostly viscous, which hinder or completely prevent the entry of water and, with it, the adsorption of the components to be removed. For this reason, the adsorber devices are washed countercurrently from time to time with water, which is preferably carried out during periods with reduced water consumption (see above), individually, in the appliances removed from service. In this regard, the adsorbent according to the invention swirls, and by the mechanical stress of the implicit surface, the unwanted coating is removed and discharged against the direction of the fluid in useful operation. Washing water is usually fed to a purification facility. In this regard, the adsorbents according to the invention are preserved in a particularly good way, since their high stability allows a purification in a short period, without significant losses of adsorbent material being recorded or the backwashing water fed to the Waste water is enriched with expelled adsorbent material, if necessary, already heavily loaded with heavy metals.

Because the granules are free of binders of a different type, the material is easily removed similarly after use. Thus, the adsorbed arsenic can, for example, in special apparatus, be removed thermally or chemically, obtaining an iron oxide pigment as pure material, which is either recycled for similar application purposes or can be supplied for conventional pigment applications. Depending on the application and legal determinations, the content of the adsorber can also be used without prior removal of heavy metals, for example, as a pigment for coloring long-lasting building materials such as concrete, because the heavy metals extracted from it Drinking water mode are immobilized in the long term and extracted from the water cycle. The determination of the specific surface of the products according to the invention according to BET is carried out by means of carrier gas processes (He: N2 = 90: 10) according to the one-point procedure, in accordance with DIN 66131 (1993). For measurement, the sample is heated 1 hour at 140 ° C in a stream of dry nitrogen.

To measure the adsorption of arsenic (II) and arsenic (V), a 5-liter PE bottle is treated for a given period of 3 l of an aqueous solution of NaAsO2 or Na2HAsO4 with the corresponding initial indicated concentrations of 2-3 mg / 1 arsenic with 3 g of the sample to be analyzed and, in this regard, the bottle is added to a rotating roller. The adsorption rate of As ions on iron hydroxide during this given period, for example one hour, is indicated with mg (As3 + / 5 +) / g (FeOOH) · from the difference with As3 + / 5 + ions Remnants in solution.

The amounts of Hg or Pb absorbed are determined in a similar way.

The As, Hg or Pb contents of the charged iron hydroxide or solutions are determined by mass spectroscopy (ICP-EM) according to DIN 38406-29 (1999) or by optical emission spectroscopy (ICP-OES) according to EN-ISO 11885 (1998) with the corresponding inductive coupled plasma as an activation unit.

The mechanical and hydraulic abrasion resistance is evaluated according to the following procedure: 10 g of the granulate to be analyzed were introduced, with a grain size> 0.1 mm in a 500 ml Erlenmeyer flask with 150 ml of demineralized water in a LabShaker shaker (Modell Kühner, Braun company) for a period of 30 minutes with a rotation of 250 revolutions per minute. Next, the portion> 0.1 mm is isolated from the suspension by means of a sieve, dried and weighed. The weight ratio between the weighing out and the weighing determines the value of abrasion wear in%.

The invention will be explained in detail below by an example. The example should serve as an illustration of the procedure and does not represent any limitation

To a liter of Bayferrox® 920 suspension with a solid content of 50 g / l FeOOH 569 ml of a MgSO4 solution (100 g / l) was added, then with stirring 173 g of a NaOH solution was added to the 24% and stirred for 15 min. The yellow suspension was washed on a filter until a residual conductivity of the filtrate of 1 mS / cm was washed and the cake of the filtrate was then dried in a drying cabin at 75 ° C to a humidity

5 residual <2%. The product was granulated to a grain size between 0.5 and 2 mm and the granulate was used for arsenic adsorption.

The product was constituted, according to X-ray diffractogram, by α-FeOOH and Mg (OH) 2. By scanning with the scanning electron microscope, for example with an increase of 60000: 1, it was observed that the needles of the α-FeOOH type of amorphous layers are adhered together or agglomerated. The specific surface area according to BET gave 43 m2 / g and

10 was compared with Bayferrox® 920 (BET of approximately 15 m2 / g). The value of abrasion wear after 30 minutes amounted to only 11%

The adsorption rate with respect to an aqueous solution of NaAsO2 with an initial concentration of 2.6 mg / l (As3 +) 1.2 mg (As3 + / g (FeOOH) · h, relative to a solution of Na2HAsO4 with a concentration initial 2.7 mg / l (As5 +) 1.5 mg (As5 +) / g (FeOOH) · h.

fifteen

Claims (4)

one.

Use of adsorption agents / reaction agents in the form of pieces consisting of α-FeOOH particles that are adhered together by (hydr) aluminum, magnesium or titanium oxides, for the purification of gases or liquids.

2.

Use according to claim 1, characterized in that the purification of gases or liquids is a water treatment.

Use according to claim 2, characterized in that the water treatment is carried out in a water supply plant 4. Use according to claim 2 or 3, characterized in that the water treatment comprises the removal of heavy metals, as well as phosphorus, antimony, beryllium, selenium, tellurium and cyanocomposite compounds. 5. Use according to claim 2 or 3, characterized in that the water treatment comprises the removal of 10 arsenic compounds from the water.