GB1602342A - Adsorber material for the adsorptive binding of uranium - Google Patents

Description

( 21) Application No 28222/80

( 62) Divided Out of No 1602341 ( 22) Filed 16 Mar 1978 ( 31) Convention Application No's 2711609 ( 32) Filed 17 Mar 1977 2711587 ( 33) Fed Rep of Germany (DE) ( 44) Complete Specification Published 11 Nov 1981 ( 51) INT CL 3 B Ol D 15/04 C Oi B 31/16 ( 52) Index at Acceptance C 1 A G 21 G 36 G 37 J 321 J 340 J 342 J 370 J 371 J 374 J 464 J 470 J 472 J 241 J 270 J 285 J 320 J 350 J 356 J 361 J 3 J 461 J 462 J 463 J 580 J 5 J 611 PD 2 A ( 54) IMPROVEMENTS IN OR RELATING TO AN ADSORBER MATERIAL FOR THE ADSORPTIVE BINDING OF URANIUM ( 71) We, KERNFORSCHUNGSANLAGE JULICH GESELLSCHAFT MIT BESCHRANKTER HAFTUNG, of Postfach 1913 5170 Julich Federal Republic of Germany a Body Corporate organised according to the Laws of the Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:

The present invention relates to an adsorber material capable of binding thereto uranium present in sea water.

Many attempts have been made to extract heavy metals contained in sea water, because there is a substantially unlimited supply of such metals therein However, so far as the hitherto-known processes for the extraction of heavy metals, more particularly uranium, are based upon such techniques as counter-current extraction, chemical precipitation and ion flotation in sea water it is necessary to use chemical substances This has the disadvantage that large quantities of chemicals must generally be employed, with the further disadvantage that the cost of the consumption of materials is relatively high.

In addition pollution of the environment by the chemicals employed can only be prevented, if at all, at great cost.

There is disclosed in German Patent Specification 2441,479 an adsorber material consisting of cultivable mutants of algae by which it is possible to extract uranium from sea water without chemical substances having to be employed, so that environmental pollution is avoided However, in order to obtain with this known adsorber material a sufficiently high daily production for economical operation, huge cultures would be necessary for growing the required quantity of algae, and this is not possible without high expenditure.

The present invention provides an adsorber material which can be produced at relatively low cost and which can be readily and economically used to concentrate uranium from sea water, without danger to the environment, while having high effectiveness and being available in sufficient quantities for economical operation The adsorber material can be used in an economic process for the extraction of uranium from sea water, which can be readily carried out without danger to the environment, as might be the case if a noxious chemical substance had to be used Such a process is disclosed and claimed in our co-pending Application No 10522/78 serial no 1602341.

According to the present invention there is provided adsorber material capable of binding thereto uranium from sea water, the adsorber material comprising humic acid or a carrier-supported source of humic acid which has been adhered to a carrier which is stable to sea water so as to leave a substantial proportion of said humic acid or carriersupported source thereof exposable to a flow of sea water The said stable carrier may comprise activated charcoal having an average particle size in a range of O 1 to 10 mm or brown coal having an average particle size in the range of O 1 to 10 mm The said stable carrier may comprise a natural fibrous substance, e g jute, cotton or coconut fibre The natural fibrous substance may be in the form of a gauze-like structure A desirable form of adsorber material comPATENT SPECIFICATION ( 11) 1 602 342 1 602 342 prises, as a carrier-supported source of humic acid, black peat, the peat being further supported by the said stable carrier which has been applied to the peat The black peat may be in granular form having an average particle size of from 0 1 to 10 mm, the granular black peat having been obtained by drying natural black peat and subsequent comminution The black peat may be adhered to a gauze of material, e g.

jute or nylon or like material, which constitutes said stable carrier.

The humic acid referred to in the present invention will generally be chosen from biologically recent humic acids, i e humic acids which have been produced from humification products formed in periods of up to several thousand years.

Humic acids are insoluble in water except for a minor proportion Therefore they can be used in an aqueous salt solution such as seawater for a long time, especially as they are biologically resistant to bacterial decay.

Their partition coefficient with respect to sea water and defined as the ratio of the uranium concentration in the humic acid adsorber material to the uranium concentration in sea water, under conditions of equilibrium, is surprisingly high.

In a particular convenient form of process employing an adsorber material embodying the invention, the adsorber material is disposed in an envelope in sea water and subjected to a relative movement with respect to the sea water, the envelope being impervious to the adsorber material and pervious to sea water, or the adsorber material may be whirled in a vessel containing sea water the whirling being caused by sea water flowing into the vessel.

An especially favoured process employing an adsorber material embodying the present invention comprises the following steps:

(a) treating the sea water with the said adsorber material by contacting the water with the said adsorber material for a sufficient time to adsorb onto the adsorber material as much uranium as possible; (b) separating the adsorber material from the treated sea water; (c) washing the resultant adsorber material with dilute acid having a p H value lower than 3 to elute the adsorbed uranium; and (d) separating the adsorber material from the acid containing the uranium.

Step (d) may be followed by steps comprising:

(e) adding an alkaline solution to the acid containing the uranium to form a solution having a p H value in the range of 4 to 8; and (f) contacting the resultant solution from step (e) with a second adsorber material capable of adsorbing the uranium thereon in order to further concentrate the uranium.

If desired the adsorbed uranium obtained from step (f) is further concentrated by the formation of metallic salt(s) thereof Preferably the dilute acid used for the elution of the uranium is employed for further elution of uranium until the uranium concentration reaches a value which is increased by a factor of 103 to 104 relative to the concentration in the sea water being treated with the first mentioned adsorber material, the p H value of the acid being kept below 2 by subsequent addition of concentrated acid.

The first-mentioned adsorber material containing the uranium may be washed out with hydrochloric acid which has been prepared by electrolytic decomposition of sodium chloride contained in the sea water being treated The said alkaline solution (step (e)) may be prepared by decomposition of the sodium chloride referred to above Preferably the second adsorber material comprises humic acid to bind the said uranium.

Of course, the process requires optimisation with a view to the most economical procedure It may therefore be desirable, in order to save time or by reason of the given adsorption kinetics, not to leave the adsorber material in the sea water until the maximum concentration of uranium has been obtained, but to remove it from the sea water before equilibrium is established and to replace it by fresh adsorber material On the other hand, the adsorptive charging will be made as high as possible in order that the quantity of adsorber necessary per unit weight of uranium and the acid consumption in a subsequent elution (which is preferably applied) may not become too high.

In a very advantageous process employing an adsorber material according to the invention uranium contained in sea water is concentrated on an adsorber material including natural black peat, the humic acid component of the black peat constituting the active adsorbing agent and the remainder of the black peat constituting a carrier therefor in situ The degree of decomposition of the black peat, which is a measure of the relative proportion of humification products in the total substance, is generally from 35 % to 55 % The partition coefficient of black peat for uranium in sea water is of the order of magnitude of 104 In this case, not only may uranium be accumulated on the peat but also one or more other heavy metals such as for example, vanadium and molybdenum The extraction of these other metals as by-products will increase the economy of the process and will therefore be a cost-saving factor Since the remaining constituents in the peat as well as the humic acid are resistant to bacterial decay in sea water, the black peat may be used in sea water over a long period of time for the 1 602 342 extraction of uranium For this reason, repeated re-use of the adsorber material after the elution of the heavy metals concentrated on the adsorber material may be envisaged Due to this fact, and owing to the ready availability of peat at reasonable price, the adsorber material can be used on a large scale, which in principle renders possible a daily production of 1 tonne of uranium, which is aimed at for an economical extraction of uranium The quantity of peat necessary for this purpose is less than about 5 x 10 tonnes per day with at least tenfold repeated use of the adsorber material.

A further advantage is that the peat can be used as peat coke after its usefulness as an adsorber is over.

In an adsorber material having a form especially suitable for use for the concentration of uranium, the black peat is present in the form of a granular mass having a grain size in the range from 0 1 to 10 mm, which has been produced, by drying natural black peat and subsequent comminution For the production of this form of construction of the adsorber material, there may be employed as starting material natural, black moist peat from which the greater part of the water content has been extracted by drying on large surfaces lying in the open air The dried peat sods, known as fuel peat, still have a residual water content of about 28 c to 30 % These sods are then comminuted into the form of fine-grained material.

Before the grains are employed as adsorber material, they are again wetted with water, whereby numerous fine channels and pores in the peat grains are filled with water and the grains are caused to swell This operation may be considerably accelerated by reducing the pressure over the wet peat by about 20 mm Hg, which expels the air from the channels and pores.

In one form of construction of the adsorber material comprising black peat which may be conveniently employed, the black peat is present as a layer which adheres to one or more gauzes consisting of material which is sufficiently stable in sea water, such as jute or nylon, the said layer having been formed by the application of natural black peat to the gauze(s) In this case the stability of the gauze material is sufficient if it remains stable during its wetting for the period of time for which it is proposed to use it, which may be about one month In the production of a preferred form of adsorber material natural, moist black peat is applied under sufficient pressure to both sides of suitable gauzes, which have a mesh width of a few mm so that the peat mass penetrates through the gauzes In the subsequent drying, the layers of peat on the two sides of the gauzes mat together through the meshes They are thereafter dimensionally stable when re-used with water, even in a strong current.

There may alternatively be employed a form of adsorber material in which there is employed as the carrier material a material which has a large surface having binding capacity, to which the humic acid material has been applied The material employed as carrier material for the humic acid material should be resistant to sea water and render possible re-use of the adsorber material.

There may with advantage be employed as such a material activated charcoal having a grain size in a range of 0 1 to 10 mm, which may be produced from fuel peat, for example, or brown coal having a similar granular structure Although activated charcoal has the larger surface having binding capacity, the use of brown coal as carrier material for the humic acid material would be preferable for reasons of cost However, it may be desirable for the material employed as carrier material to consist of fibrous natural substances such as jute, cotton and coconut fibres In this case, the carrier material may be present in the form of a conglomeration in which the fibres are loosely joined together However, in a preferred form of the carrier material, the fibrous natural substances are present in the form of a gauze-like structure to which the humic acid material has been applied.

An adsorber material supported on a carrier may be employed in various fashions, depending on its form of construction Thus, for example, it may be advantageous to subject the supported adsorber material to movement in relation to the sea water in an envelope which is impervious to the supported adsorber material and pervious to sea water Such procedures are recommended when the adsorber material is present in the form of a granular mass or as a kind of conglomeration of fibrous substances The adsorber material may then desirably be enclosed in gauzes of appropriate mesh width, which may consist, for example, of nylon fibres For the concentration of the heavy metal(s) comprising uranium, a multiplicity of filter bodies formed in this manner, and preferably having elongate form, which are preferably disposed parallel to one another and in line with one another, are introduced into the sea current in such manner that the current of sea water is directed along the filter bodies, but a sufficient exchange of sea water through the gauzes is nevertheless ensured.

The adsorber material may be employed in the same general way without any envelope being necessary, if it consists of a humic acid adsorber material layer on carrier gauzes The flow may then be directed along the gauzes, several of which are 1 602 342 disposed parallel to one another There may be a plurality of parallel gauzes disposed in layers, some of which are substantially in a line but offset from their neighbours In this way, the sea current, after having passed through the first layer, is split up by the succeeding layer, whereby a good intermixing of the water is obtained with comparatively low resistance to flow The distance between the gauzes and the number of layers are made such that, with velocities of flow of up to 5 m/s, the desired uranium depletion in the sea water is achieved.

Since acceleration of the sea water by pumping is unfavourable from the energy viewpoint, it is desirable for the necessary relative movement between the adsorber material of whatever form of construction, and the sea water to be produced by a travelling ship trailing the gauzes Taking as a basis, for example a daily production of 1 tonne of uranium about 109 m 3 of sea water must be passed through the adsorber material per day for an extraction of 1 ltg of uranium from 1 litre of sea water If the adsorber material is drawn through the sea at a speed of 20 km/h its total cross-section may be limited to about 2000 m 2 Also, when a ship is employed, the advantage is obtained that the adsorber material can be employed in waters which have low biological production The danger of any growth being formed on the adsorber material is thereby substantially avoided.

A further very desirable manner of using adsorber material according to the invention which is in the form of a granular mass involves whirling the adsorber material in a vessel containing sea water, the whirling being effected by means of sea water flowing into the vessel.

The whirling is preferably carried out with the aid of suitable deflecting devices provided in the vessel Loss of grains is prevented by the provision of fine-meshed gauzes at the outlet of the vessel When the adsorber material is used in this fashion, the desired charging thereof with uranium from the sea water is very rapidly achieved owing to the whirling.

After the concentration of the uranium.

the adsorber material containing it is normally taken from the sea water For this purpose, it is desirable for those parts of the adsorber material which are charged to the desired degree to be replaced as continuously as possible by fresh or eluted parts of the adsorber material In cases in which the adsorber material employed is situated in an envelope, or an adsorber material is situated on a gauze therein the adsorber material can be very simply removed from the sea water If the adsorber material in the form of a granular mass is whirled in an adsorber tank, the granular mass charged with uralium may be separated off, for example, by a centrifuge, which may take the simple form of a tubular coil having, for example, to 20 turns, through which the sea water containing the granular mass is pumped from the adsorber tank at a rate of, for example, 10 m/s The separated-off granular mass may be re-used a number of times, while the treated sea water is returned into the sea The capacity of the centrifuges must be made such that the whole adsorber material is eluted on average once per charging period in the adsorber tank.

After the adsorber material having heavy metal(s) comprising uranium concentrated thereon has been removed from the sea water, it may be washed out with dilute acid, preferably hydrochloric acid or nitric acid, at a p H value of less than 3 for the elution of the adsorbed heavy metal(s) The acid may here serve as a heavy metal store provided that its p H value is kept low For this purpose, the dilute acid used for the elution of the heavy metal(s) may be employed for the further elution of heavy metals until the heavy metal concentration therein has reached a value which is greater by a factor of the order of magnitude of 103 or 104 in relation to the sea water, the p H value of the acid being kept below 2 by further addition of concentrated acid In this way, the volume throughput of solution in the further course of the process can be kept low.

In a particularly advantageous form of a process using the adsorber material according to the invention, the adsorber material containing the uranium (and other heavy metals) is washed out by hydrochloric acid produced by electrolytic decomposition of sodium chloride contained in the sea water.

The electrolytic decomposition of sodium chloride is known as alkali-metal chloride electrolysis and is already employed on a large scale For the production of the hydrochloric acid required for the process described, there is employed a method in which sea water is concentrated by known means to form brine, and then hydrogen, sodium hydroxide solution and chlorine are produced therefrom in accordance with the reaction equation of the alkali-metal chloride electrolysis process Energy + 2 H 20 + 2 Na Cl H, + 2 Na OH + Clh.

In accordance with the reaction equation H 2 + Cl 2 2 HCI + 43 8 kcal chlorine may then be burnt in hydrogen to form hydrogen chloride with the release of energy and the HCQ formed introduced into water for the production of hydrochloric 1 602 342 acid.

In this case, it is also desirable to add to the hydrochloric acid containing the heavy metal(s) sodium hydroxide solution produced by decomposition of sodium chloride contained in the sea water, because sodium hydroxide solution is in any case formed in the performance of the alkali-metal chloride electrolysis.

By the application of the alkali-metal chloride process for producing from sea water the hydrochloric acid required for the performance of the preferred form of process, no additional cost for transport and the provision of the necessary working means is incurred This is especially advantageous when the process of the invention is carried out, for example, on a ship at sea In this case, there may be used as starting material for producing the hydrochloric acid and sodium hvdroxide solution inspissated sea water produced directly at the site of the heavy metal extraction installation by evaporation of sea water by known processes.

For the evaporation of the water, there is advantageously employed the waste heat of a nuclear reactor which may be situated, like the other parts of the installation required, on the ship or on a corresponding floating body provided for this purpose.

In a very advantageous form of the process using the adsorber material of the invention, elution solution containing the heavy metal(s) comprising uranium is again brought into contact, for the futher concentration of the heavy metal(s), with a second adsorber material which contains biologically recent humic acid and in which there is present a proportion of at most 99 % by weight of material serving as carrier material for the humic acid In order to achieve maximum concentration of the uranium, the p H value of the solution may be adjusted to an appropriate level for this purpose (preferably minimum 4 and maximum 8) Since the partition coefficient of the uranium also has substantially the same value in this relatively high concentration range as in the concentration range of the sea water, the uranium concentration in the elution solution may be reduced to about 1/10 of its initial value by introducing the adsorber material into an exchanger column In this way, there is achieved a further concentration in the adsorber material by a factor of 103 to 1 ( 4 calculated on the dry substance of the adsorber material, so that the uranium concentration is increased in all by a factor of about 1 ( 7 in relation to the sea water.

Other heavy metals may be concentrated comparably at the same time.

The adsorber material employed for increasing the concentration of the heavy metal(s) may also be burnt after the adsorption of the heavy metal(s) Since the ash residues of the adsorber material generally amount to less than 5 % by weight of the unburnt dry substance, a further concentration of the heavy metal(s) by a factor of about 20 may be achieved by the burning.

This means that the heavy metal(s) is/are then generally present in the ash residue in a concentration which is higher by substantially a factor of 108 in relation to the sea water, and constitute in respect of weight the main components of the ash residue The heavy metal(s) can be readily isolated from the ash residue by known methods.

Example 1

Natural muddy black peat (as adsorber material) was applied under pressure to both sides of jute gauzes (mesh widths about 2 mm) and nylon gauzes (mesh width 1 mm) held in plastics frames in such manner that the peat slurry penetrated through all the meshes After subsequent drying in air and the accompanying interlinking, the layers on the two sides of the gauzes became mutually stabilised through the many unions existing through the meshes Peat of a total dry weight of 3 g was applied to 1 g of jute gauze and 1 g of nylon gauze in this manner so as to adhere firmly thereto After re-wetting with water, the layers of peat on the gauzes again swelled up somewhat In a stability test, these matrices were exposed for 4 days to sea water flowing along them at a relative speed of about 2 m/sec The layers of peat remained dimensionally stable and did not become detached from the gauzes.

Example 2 g of naturally moist black peat having a water content of around 80 % by weight was shaken for about 15 hours in 120 cc of 0.5-normal sodium hydroxide solution and then centrifuged There were first added to the centrifuged-off solution 3 6 g of finegrained activated charcoal (mean grain size um) and then adjusted to a p H of 1 with 32 % hydrochloric acid The humic acid fraction thus precipitated (adsorber material) adhered to the activated charcoal, which acted as carrier The dry weight of the humic acid-activated charcoal thus produced was 4 8 g, the humic acid being in a weight ratio of 1:3 to the active charcoal.

This humic acid-activated charcoal was stirred for 2 hours with 10 litres of natural sea water having a p H of 8 3 and a uranium content of 3 3 Rg per litre, at 20 WC The uranium content of the sea water was thus reduced from 3 3 fig per litre to 0 8 tg per litre when the humic acid-activated charcoal had been air-dried before the contacting with the sea water, and to 0 6 Rg per litre when the prior air drying was omitted The corresponding partition coefficients, calculated on the respective dry weight quantities 1 602 342 of the humic acid, were 2 6 x 104 and 3 7 x 104 respectively.

The uranium adsorbed on this humic acid-activated charcoal was completely eluted by stirring with 1 % hydrochloric acid (p H = 0 6) The concentration and the elution were repeated 8 times on the same humic acid-activated charcoal without detriment to the partition coefficients.

Example 3 g of naturally moist black peat having a water content of about 80 % by weight, which had been taken from the upland moor at Gross Hesepe in Emsland, was shaken for about 15 hours in 120 cc of 0 5-molar sodium hydroxide solution and then centrifuged The solution centrifuged off was added to 32 % hydrochloric acid until a p H value of I was reached The humic acid fraction thus precipitated was centrifugedoff and washed to neutrality with distilled water The dry weight of the humic acid thus obtained was 1 2 g The freshly precipitated humic acid was left in neutral suspension and brought into contact with 8 g of jute gauze for a number of days until the suspension had dried upon the jute in uniform distribution Thereafter, the adsorber material was again wetted with sea water, and 5 % of the humic acid applied to the jute again went into solution The residual adsorber material remained substantially water-insoluble and the further loss of solution of the humic acid in dayslong contact with flowing sea water remained below 1 %.

Claims (9)

WHAT WE CLAIM IS:-

1 An adsorber material capable of binding thereto uranium from sea water, the adsorber material comprising humic acid or a carrier-supported source of humic acid which has been adhered to a carrier which is stable to sea water so as to leave a substantial proportion of said humic acid or carriersupported source thereof exposable to a flow of sea water.

2 An adsorber material according to claim 1, wherein the said stable carrier comprises activated charcoal having an average particle size in a range of 0 1 to 10 mm.

3 An adsorber material according to claim 1, wherein the said stable carrier comprises brown coal having an average particle size in a range of 0 1 to 10 mm.

4 An adsorber material according to claim 1 wherein the said stable carrier comprises a natural fibrous substance.

5 An adsorber material according to claim 4 wherein the natural fibrous substance comprises jute, cotton or coconut fibre.

6 An adsorber material according to claim 4 or claim 5 wherein the natural fibrous substance is in the form of a gauzelike structure.

7 An adsorber material according to any one of claims 1 to 6, comprising, as a carrier-supported source of humic acid, 70 black peat, the peat being further supported by the said carrier which is stable to sea water and to which the peat has been adhered.

8 An adsorber material according to 75 claim 7, wherein the black peat is in granular form having an average particle size of from 0 1 to 10 mm.

9 An adsorber material according to claim 7 or claim 8, wherein the black peat 80 has been adhered to a gauze of material as said stable carrier.

An adsorber material according to claim 9, wherein the gauze is made of jute or nylon 85 11 An adsorber material according to claim 1 substantially as herein described and exemplified.

MEWBURN ELLIS & CO, 90 Chartered Patent Agents, 70-72, Chancery Lane, London WC 2 A 1 AD.

Agents for the Applicants.

Printed for Her Majesty's Stationery Office.

by Croydon Printing Company Limited Croydon, Surrey 1981.

Published by The Patent Office 25 Southampton Buildings.

London, WC 2 A l AY, from which copies may be obtained.