METHOD FOR IRRIGATING A POROUS SUBSTRATE USING A FOAM, AND THE USES THEREOF

Abstract

The present invention relates to a method for irrigating a porous substrate comprising the steps of: preparing a foam consisting of a dispersion of air bubbles in a foaming aqueous solution, said foam comprising a liquid fraction of less than or equal to 15% by volume; spreading, over the surface of the porous substrate, a layer of the foam thus prepared, the thickness of the layer being greater than 5 cm, then maintaining the assembly long enough for at least a part of the liquid contained in the foam to infiltrate the porous substrate. The present invention also relates to the use of this method to recover an element of interest contained in a porous substrate and a particular aqueous foam.

Claims

1. A method for irrigating a porous substrate, the method comprising: preparing a foam consisting of a dispersion of air bubbles in a foaming aqueous solution, wherein the foam comprises 15% by volume or less of a liquid fraction, spreading, over the surface of the porous substrate, a layer of the prepared foam, wherein a thickness of the layer is greater than 5 cm, and then maintaining the porous substrate having the layer on the surface for a sufficient time such that at least a part of the liquid fraction contained in the foam to percolates in the porous substrate.

2. The method according to claim 1, wherein the porous substrate is selected from the group consisting of land, cultivated agricultural land, a green space, a stadium or terrain for sporting activity or a horticultural garden; sand; broken or fractured geological rocky formations; ore; ore concentrates; coal; mining residues; mining waste; slag; industrial, metallurgical and electronic waste; products containing strategic metals resulting from the recycling of lithium batteries, and a combination thereof.

3. The method according to claim 1, wherein the foam comprises from 5% to 15% by volume of the liquid fraction.

4. The method according to claim 1, wherein the spreading of the foam is repeated, wherein the foam is renewed by batches discontinuously or continuously at the surface of the porous substrate.

5. The method according to claim 1, wherein the foaming aqueous solution comprises at least one foaming organic surfactant.

6. The method according to claim 5, wherein the at least one foaming organic surfactant is at least one non-ionic foaming organic surfactant.

7. The method according to claim 5, wherein the at least one foaming organic surfactant is selected from the group consisting of alkylpolyglucosides, ethoxylated fatty alcohols and a combination thereof.

8. The method according to claim 5, wherein the at least one foaming organic surfactant is present, per litre of solution, in a quantity of from 0.1 g to 10 g.

9. The method according to claim 5, wherein the foaming aqueous solution further comprises at least one gelling or viscosifying organic agent.

10. The method according to claim 5, wherein the foaming aqueous solution further comprises at least one active ingredient.

11. The method according to claim 10, wherein the at least one active ingredient is selected from the group consisting of thiourea, a thiosulphate, a cyanide, a bicarbonate, an oxidant, an acid, and a combination thereof.

12. The method according to claim 10, wherein the at least one active ingredient is selected from the group consisting of a fertiliser, manure, urease, nitrification inhibitor, insecticide, repellent, herbicide, fungicide, bactericide, sporicide, algicide, germination inhibitor and chelating/complexing agent.

13. A method for recovering at least one element of interest contained in a porous substrate in the form of a heap, the method comprising: irrigating the porous substrate according to the method of claim 1, and recovering a permeation flow at a discharge from the heap and treating to recover the at least one element of interest.

14. The method according to claim 13, wherein the at least one element of interest is selected from the group consisting of gold, silver, uranium, platinum, palladium, lithium, nickel, cobalt, manganese, aluminum, zinc, copper, rare earths, niobium, tantalum, scandium and chromium.

15. A foam used in the method of claim 1, wherein the foam consisting of a dispersion of air bubbles in a foaming aqueous solution formed by: a foaming organic surfactant or a mixture of foaming organic surfactants, optionally an active ingredient or a mixture of active ingredients, and water, wherein the foam comprises less than 15% by volume of a liquid fraction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0124] FIG. 1 presents a diagrammatic representation of the assembly for studying infiltration, in the heap, of the drainage solution coming from a batch of foam.

[0125] FIG. 2 presents the influence over time of the height of foam on the flow.

[0126] FIG. 3 presents a test in successive batches with a foam with a liquid fraction of 5% and a height of 5 cm (4 batches) and of 10 cm (1 batch) in a column.

[0127] FIG. 4 presents the variation in the volume of permeate over time with 10 cm of ore and foams with a liquid fraction of 10% and a height of 10 to 30 cm.

[0128] FIG. 5 presents the comparison of the extraction yield of uranium for foam tests (columns C1 to C5) in accordance with the method according to the invention and drip tests (columns C-1 and C-2) according to the prior art with C1: Glucopon 2 g/L, 5 batches of 30 cm of foam and 2 batches of 60 cm; C2: Glucopon 10 g/L, 5 batches of 30 cm of foam and 2 batches of 60 cm; C3: Glucopon 10 g/L, 4 batches of 10 cm; C4: Glucopon 10 g/L, 9 batches of 5 cm; C5: Glucopon 10 g/L, 2 batches of 10 cm and 2 batches of 5 cm; C-1 and C-2: conventional drip irrigation with distributing geotextile on the heap.

[0129] FIG. 6 presents the partial covering of the heap of sand NE 34 by the foam via an ejection point with an inside diameter of 8 mm.

[0130] FIG. 7 presents the covering, on real ore, of the foam via an ejection by pipe in flush contact with the heap.

[0131] FIG. 8 presents the covering of the heap by foam ejected at 4 points on the surface of the heap of sand distant by 50 cm.

[0132] FIG. 9 presents the change in the flow as a function of time for a continuous test on 2 hours of injection of foam on sand.

[0133] FIG. 10 presents a diagrammatic representation of the liquid fraction gradient within a dome of foam supplied continuously at the end of two hours.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0134] The following examples relate to: [0135] the irrigation, by a foam on a small heap surface, in a column 10 cm in diameter on sand, of models of ore heaps or on real uranium ore; [0136] the leaching of uranium via this foam method on real ore; and [0137] irrigation by covering a heap with a larger surface area: mason's sieve 45 cm or device of 2.25 m.sup.2.

[0138] In the following experimental part and in the corresponding figures, when reference is made to a foam with 5 cm in thickness, it must be understood that this foam has a thickness slightly greater than 5 cm, i.e. a thickness of the order of 5.2 cm, i.e. 5.2 cm0.1 cm.

Example 1: Irrigation, by an Acidic Leaching Foam, of a Sand and Kaolinite Model Heap Agglomerated in a Column, in Discontinuous Batches

[0139] The leaching foaming solution of the example (preferred solution) comprises Glucopon 215 CS marketed by the company BASF (hereinafter Glucopon), stable in a sulfuric acid medium (5 to 10 g/L) and the concentrations of acid and sulfate salts used are: [0140] Sulfuric acid at 10 g/L, [0141] Magnesium sulfate MgSO.sub.4 at 30 g/L (i.e. 6 g/L of Mg), [0142] Iron sulfate at 55 g/L (i.e. 20 g/L of Fe), and [0143] Aluminum sulfate at 190 g/L (i.e. 15 g/L of Al).

[0144] A given volume of leaching acidic foam containing air bubbles (batch of foam with a given height of 5 to 60 cm) is generated from this solution by a bead-type static generator that makes it possible to control the liquid fraction of the foam (usually 5 to 10%, i.e. 90 to 95% air).

[0145] The volume of foam is deposited directly on 12 cm of a model heap (mixture of sand and kaolinite) pre-agglomerated in sulfuric acid in a liquid/solid ratio of 8% by volume, contained in a glass column 10 cm in diameter (i.e. 7.810.sup.3 m.sup.2). The tests show that the foam deposited by a feed tube directly on the heap bears, under the effect of its own weight, on the heap and wets it homogeneously.

[0146] The experimental assembly shown schematically in FIG. 1 makes it possible to measure, by means of scales, the mass of solution that passes through the heap as a function of time, in order to calculate the permeation flow at each instant due to the irrigation by the foam (derived curves).

[0147] The tests on batches of foam with variable height and liquid fraction, implemented on a model heap of sand and kaolinite agglomerated in a column, made it possible to measure the maximum flow obtained in a batch of foam and the mean flow obtained during successive batches.

A. Example of Maximum Flow

[0148] The permeation flow caused by the batch of foam increases with time, and passes to a maximum (slope at the point of inflection of the curves FIG. 2).

[0149] A small fraction of liquid (i.e. 5%) with batches of foam with a height either of 52 cm or of 102 cm makes it possible for example to obtain maximum flows of the order of 198 L/h/m.sup.2 and of 296 L/h/m.sup.2. These maximum flows correspond to the maximum of each of the slopes in FIG. 3.

[0150] To within any experimental errors, the double-height foam generates a doubled hydraulic pressure at the interface that doubles the permeation flow (Darcy's law). A Glucopon foam with a height of 5 cm and 5% liquid makes it possible to obtain the smallest maximum flows. Other tests (not provided here) also show the proportionality of the permeation flow with the liquid fraction of the foam.

B. Examples of Mean Flows

[0151] Three successive batches of 5 to 10 cm of foam with 5% liquid fraction were implemented over several hours under conditions of leaching on agglomerated heap, after a first foam batch with a height of 30 cm called saturation batch, which makes it possible to completely saturate the heap and to obtain a percolating heap (height of 30 cm to provide enough liquid in a batch).

[0152] The graph in FIG. 3 presents a succession of four batches of 5 cm and one batch of 10 cm. The mean flows are calculated over a mean period of 45 min, for each of the 5 batches, which represents the time where the foam remains stable.

[0153] First a similar behaviour of the batches is noted over time when they follow each other on the same heap; around 20 L/(h.Math.m.sup.2) for the maximum flow without the appearance of puddles. The mean permeation flow obtained semi-continuously is 4.4 L/(h.Math.m.sup.2) over three times 45 min for 3 batches of foam with a height of 5 cm and a liquid fraction of 5%. These mean permeation flows are compatible with the industrial flows obtained in drip mode of the order of 5 L/(h.Math.m.sup.2).

Example 2: Leaching of Real Uranium Ore in Column Method (Effect of the Surfactant Content and Foam Height)

[0154] A test campaign with the leaching foams was implemented on an agglomerated uranium ore (500 ppm U). Five leaching columns with a diameter of 10 cm contain approximately 1 kg of ore each, i.e. 12 cm in height. The leaching foaming solution comprises Glucopon stable in a sulfuric acid medium (2 or 10 g/L) and the concentrations of acid and sulfate salts used are: [0155] Sulfuric acid at 10 g/L, [0156] Magnesium sulfate MgSO.sub.4 at 30 g/L (i.e. 6 g/L of Mg), [0157] Iron sulfate at 55 g/L (20 g/L of Fe), [0158] Aluminum sulfate at 190 g/L (15 g/L of Al).

[0159] The measurements of uranium concentration in the permeates were made by x-ray fluorescence and by inductively coupled plasma atomic emission spectroscopy (ICP/AES).

[0160] The protocol used is as follows: upstream of the irrigation test, the ore is pre-agglomerated by a 3M sulfuric acid solution in a liquid/solid ratio of 8% (non-saturated ore) and then introduced into the column. The foam is then generated directly on the surface of the heap by means of an air-type foam generator via bead tube of 2-2.3 mm (flow rate of 1 to 2 L/min) connected to the compressed air system. This method makes it possible to control the liquid fraction (5 to 10%) and the height (5 to 60 cm) of the foam on the surface of the heap.

[0161] The leaching by layer of foam directly deposited on the heap of uranium is implemented discontinuously by replacing, every 45 to 60 min, the layer of foam with a previous given height and having drained, by a fresh layer of foam.

[0162] For several experiments implemented for example at 10 g/L of Glucopon and a foam with a fixed expansion F equal to 10 (i.e. 10% liquid fraction, the expansion being equal to the inverse of the volume liquid fraction) with heights varying from 10 to 30 cm and on a heap of real ore with a thickness of 122 cm (approximately 1.5 kg of ore) made it possible to evaluate the permeation flow of a method according to the invention (FIG. 4).

[0163] The mean flows calculated over one hour per batch are in the range from 7 to 28 L/(h.Math.m.sup.2) and the maximum flows vary between 33 and 90 L/(h.Math.m.sup.2).

[0164] A reduction in the concentration to 2 g/L of Glucopon was also able to be implemented in order to reduce the cost of the method associated with the use of surfactant. The behaviour of the foam at 2 g/L of Glucopon is similar to that of the foam at 10 g/L with a mean flow of 31 L/(h.Math.m.sup.2) and a maximum flow of 86 L/(h.Math.m.sup.2).

[0165] Finally, tests on reducing the permeation flow were implemented with a smaller foam height (5 cm) and greater swelling of 20. These conditions made it possible to obtain, in a very satisfactory manner, a mean flow of 4.3 L/(h.Math.m.sup.2) and a maximum flow of 9-12 L/(h.Math.m.sup.2). These results are entirely comparable to the permeation flows obtained industrially in drip mode (4 to 6 L/(h.Math.m.sup.2).

Leaching of Uranium

[0166] The leaching yield of uranium by foam at 10% liquid fraction was in particular measured for the 2 concentrations of surfactant (2 and 10 g/L) after 5 batches of foam 30 cm high and two batches 60 cm high (column 1 and 2 respectively) making it possible to achieve a quantity of liquid with respect to the ore greater than 1 (FIG. 5).

[0167] Uranium extraction yields in foam are greater than 50% for an addition of liquid greater than the initial quantity of solid (L/S >1) (FIG. 5), and can even achieve 65% for foam with 10 g/L of surfactant.

[0168] These two yields are compared with the yields obtained by drip mode of the industrial type on the same ore that do not exceed 30% (conventional irrigation on C-1 and C-2).

[0169] These results show the advantage of the method according to the invention: the foam extracts the uranium rapidly over the first centimetres of the heap (10 to 14 cm) by means of a homogeneous irrigation of the heap over the first centimetres.

Example 3: Covering of a Foam on a Sand Heap by a Vertical Ejection Tube

[0170] Tests on the deposition/covering of a Glucopon leaching acidic foam with a 10% liquid fraction were implemented on a sand heap.

[0171] Three kilograms of NE 34 sand are deposited on an absorbent paper at the bottom of a mason's sieve 45 cm in diameter in order to form a heap of 0.16 m.sup.2 over a thickness of 3-4 cm. A neutral Glucopon foam with 10% liquid fraction is deposited by means of a flexible tube of 8 mm inside diameter secured above the centre of the sieve at a height of 10 cm (FIG. 6).

[0172] The foam-generation rate is 2 L/min for 2 min and makes it possible to generate 4 litres of foam, which flows and gradually covers the heap, without touching the edges of the sieve. In the end of 2 min, the final disc of foam forms a radius of 20 cm and the foam therefore does not bear on the edges of the sieve. The mean thickness of foam deposited is approximately 61 cm. This result shows the possibility of easily covering the heap with a thickness of foam of 5 cm.

Example 4: Covering of a Foam on Real Ore by Ejection by a Pipe in Flush Contact with the Heap

[0173] FIG. 7 illustrates the addition of the sulfate acid foam of example 2 with swelling 10 and a thickness of 5 cm on a heap of real uranium ore 40 cm in diameter by means of the horizontal flush tube in contact with the heap.

[0174] The covering forms a disc of foam the radius of which increases with time at a speed of approximately 7 cm/minute. The layer of foam easily repairs on the surface to eliminate the hollows and any air pockets.

Example 5: Covering of a Foam on the Surface of a Heap with Surface Area Greater than 2 m.SUP.2

[0175] A neutral foam (Glucopon 10 g/L) with liquid fraction of 10% is used on a surface of 1.51.5 m.sup.2 of white-sand heap with granulometry of less than 2 mm. The experiments are conducted in a dedicated stainless-steel tank with a frame and grille supporting the heap of sand (5 to 10 cm).

[0176] The foam is ejected from the generator onto the heap at 4 points distant by 50 cm (FIG. 8, spacing representative of pipes for industrial drip mode).

[0177] With the continuous injection of the foam, the four domes of foam formed end up by completely covering the surface of 2 m.sup.2 with a 5 to 15 cm layer of foam according to the conditions of flow rate and liquid fraction of the foam.

[0178] The tests on continuous supply of foam are implemented with an ejection rate of 1 L/min per supply point in order to reduce the mean height of the foam with 3.5% liquid fraction (FIG. 9).

[0179] In the end of one hour, the maximum flow reaches a flat level and the dimensions of the foam scarcely change further. The flow of 8 L/(h.Math.m.sup.2) is here calculated with the total visual surface of the dome. The final dome measures approximately 120 cm resulting from the junction of 4 domes 60 cm in diameter with a mean maximum height of 25 cm by simple geometric measurement. In reality, the dome consists of the wettest layer of foam on the surface of the heap and then a liquid-fraction gradient over the thickness of the layer where the driest foam is located at the periphery (FIG. 10).

[0180] Under dynamic conditions, the real dimensions of the wetting of the final dome are obtained by destroying the dry foam on the surface of the dome by compressed air. The wetted core for its part remains stable under air flow. The parameters of the stabilised foam are a mean height of fresh foam of around 10 cm with a wetting diameter of 45 cm with an injection of 1 L/min per injector. Under these conditions, the stabilised maximum flow changes from 8 L/(h.Math.m.sup.2) to 14 L/(h.Math.m.sup.2). The continuous-supply tests (spacing 50 cm) show that a flow rate of 2 L/min of foam with 3.5% liquid fraction affords total coverage with the most complete wetting of the surface, with a flow of 10 L/(h.Math.m.sup.2). Adjustments to the liquid fraction, to the injection rate and to the arrangement of the injectors thus make it possible to manage both the coverage and the height of foam on the surface of the heap as well as the permeation flow at the discharge from the heap.

BIBLIOGRAPHIC REFERENCES

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