FR2932470A1 - PROCESS FOR TREATING MINERAL SLUDES AND EQUIPMENT FOR IMPLEMENTING THE METHOD - Google Patents

Abstract

Process for treating sludge from the mining or mineral industry according to which, before spreading above ground, the mud is subjected to an upward movement during which it is brought into contact with a flocculation agent.

Description

PROCESS FOR TREATING MINERAL SLUDGE AND EOUPMENT FOR THE IMPLEMENTATION OF THE PROCESS

The present invention relates to a mineral sludge treatment process and equipment for carrying out the method. It applies, inter alia, to the treatment of effluents from the mining or mineral industry, dredging processes or public works operations producing large quantities of mineral sludge for dehydration and solidification above ground.

Because of their large volume, these sludges present a significant storage problem insofar as they are not destructible.

Traditionally, their storage was mainly carried out by spreading sludge in closed areas where sludge decanted and then abandoned: - construction of dam on recessed valleys, - use of excavations produced by the removal of materials, - lagoons (basins) more or less natural, - construction of lockers with levees ...

While some coarse sludge (sand, gravel ...) can dry and reconstitute a soil usable for example in agriculture, most of the effluents, containing large quantities of suspended matter in colloidal form (clays, silts ...), are particularly stable and difficult to decant and do not dehydrate.

It should be noted that the terms sand, gravel, clay and silt refer to the size of the grain rather than its composition. Sand is a material passing through No. 4 sieve (4.76 mm), but not into No. 200 sieve (0.074 mm). Gravel is a granular material that does not cross a No. 4 sieve and reaches up to 9 cm. The finer, colloidal material, which passes through a No. 200 sieve, is called clay or silt.

These sludge thus stored then constitute in the long term risk areas, especially said mud pools in case of breakage of dikes. In addition, with a superficial crust more or less dry covering a soft colloidal layer, these storage areas do not support the weight of animals, pedestrians, or vehicles.

As traditional storage solutions prove unsuitable or even dangerous, more and more national regulations have been published prohibiting the abandonment of

these areas with an obligation of restoration, namely treatment and consolidation.

To do this, various techniques have been tested to facilitate the removal of trapped water: vibration, porous wicks, drains, trees with high evaporation but the thickness of the layers is such (3 to 150 meters) and the amount of imprisoned water so important that these treatments have been doomed to failure.

A first improvement was obtained by thickening the effluents before sending them to these basins. The thickening (or conditioning) consists of a flocculation of the sludge which aims to promote, with the help of a slow mixture, the contact between the colloidal particles which will gather to form larger conglomerates (flocs) .

By the implementation of this technique, it has been possible to double the dry matter concentration of the treated sludge but in most cases (colloidal clay, red sludge, oil sand sludge, dredging with large silts ...). result was insufficient. In particular, it has been found that the transport of these sludges by pipeline before storage results in the destruction of the flocs rendering the sludge, at least partially, its original colloidal structure.

In 1979-1980 Alsthom Atlantique and SNF (US 4347140) developed a multi-step flocculation system to specifically treat clay lagoons from phosphate production in Florida. The process used consisted in a first step, to condition with the aid of flocculants the sludge (from - either phosphate washing - or dredged lagoons where they had been stored) in a decanter or in a decanter then a thickener. The thickened sludge was then pumped to an above-ground area where it was subsequently deposited after a piping addition at one or more points of an additional quantity of flocculant. This over-flocculation in the pipe had the effect of allowing the sludge to constitute a flow slope thus allowing storage above ground and not in a bin. The water escaping from the overflowing mud was recycled through a peripheral ditch and pumped back to the phosphate launderette and / or a flocculant dilution unit to increase its effectiveness. It had also been shown that a bed of stone, lying below

under the storage area, allowed to drain the interstitial water and greatly reduce the drying time. Similarly, the addition of the flocculant at several points had the effect of improving its efficiency and allowing a partial reduction of its consumption. At the same time, some tests with flocculant injection from a pressurized capacity incorporated in the piping have allowed a significant but very limited improvement of the system.

Although novel, the Alsthom process has several drawbacks: the need to dilute the flocculant (usually less than 1 g / l) so that the mixture with the sludge flow can be done in a few seconds, which increases the mud volume of 30 to 40% - moreover, by the pumping speed usually applied in the piping (of the order of 2 to 3 m / sec), a strong overdose of the flocculant is necessary so that the flocs are not destroyed as they are formed.

The invention overcomes all the disadvantages described above. Description of the invention

The present invention therefore aims to develop a process and equipment for treating effluents from the mining or mineral industry for their subsequent dehydration and solidification above ground so that the storage location become usable again.

According to the invention, it has surprisingly been found that the upward movement of a sludge from the mining or mineral industry into a vertical tank serving as a flocculator, placed at the outlet of the pipe just before the spreading operation. and in which a flocculation agent is introduced by one or more telescopic injection rods significantly improved the settling of the fine solid particles contained in the sludge during their storage above ground for the rehabilitation of the surfaces used. The invention therefore firstly relates to a process for treating sludges from the mining or mineral industry according to which, before spreading above ground, it is subjected to 20

mud an upward movement during which it is brought into contact with a flocculation agent.

In the rest of the description and in the claims, the term sludge, an effluent from the mining or mineral industry, dredging processes or public works operations. The method of the invention therefore consists in interposing before the spreading step, a specific flocculation step during which the sludge undergoes an upward movement.

According to a first characteristic, the upward speed of the sludge is greater than its settling speed. The climbing speed is in practice between 0.1 and 0.5 mis.

Advantageously, the upward movement is doubled by a centrifugal movement causing the sludge to be mixed with the flocculation agent at a speed of between 0.2 and 0.8 μm. This gives a homogeneous mixture. It is also possible to accelerate the sludge in the tank by the presence of baffles obscuring part of the surface and changing the direction of the currents thus improving mixing and flocculation. According to the invention, the flocculation agent is introduced into the sludge at a concentration of between 50 and 500 g per tonne of solid depending on the nature and composition of the sludge to be treated.

In practice, the contact time between the sludge and the flocculation agent is between 1 and 10 minutes, advantageously between 2 and 5 minutes. According to another characteristic, the flow angle of the sludge at the time of spreading is preferably between 2 and 20% (i.e .: unevenness per 100 meters horizontally).

The present invention also relates to an installation for carrying out the method.

This installation is characterized in that it comprises a vertical tank fed at its base by a sludge feed pipe. According to another characteristic, the tank is preferably provided in the upper part with an inclined plane intended for the evacuation of the sludge. In practice:

a / the tank: - has a diameter making it possible to maintain a climbing speed greater than the settling speed of the flocculated sludge, - has a mud inlet pipe to be treated, either by a dip tube or by a pipe, located in the lower part of the tank and shaped so as to create a centrifugal effect allowing mixing at low speed (0.2 to 0.8 m / sec), and is dimensioned so that the sludge has a residence time included between 1 and 10 minutes, preferably between 2 and 5 minutes, b / the flocculation agent: - is introduced by one or more injection rods - telescopic - or distributed over the height of the tank allowing the control of the time of flocculation. For example, with a tank with a residence time of 4 minutes, the mixing can be carried out according to the injection height of the flocculant in the mud for 1 to 4 minutes, and is preferably injected in diluted form, occurring in solution in water or in dispersion in a solvent medium (or brine) in which the flocculant is not or not totally soluble, c / the flocculated sludge: - evacuates from the top of the tank, because of the ascending speed, or it is deposited on its storage place above ground through an inclined plane consisting: - by one or chutes, possibly perforated (curved grids), preferably steel or wood or - by a armourstone under the flocculation tank or - by large pipes at low speed (less than 0.2 m / sec).

This method makes it possible both to significantly reduce the consumption of flocculant compared to a direct addition of the same flocculant in the pipeline and also to greatly increase the mud flow angle, which is usually 2 to 7% and can go up to 8 to 20%.

It is also noted that the higher the slope, the lower the pore water and the faster its drainage, despite the pressure exerted by the height of the sludge.

According to the invention, in order to obtain large storage volumes, it is necessary to construct flocculation tank supports of relatively high height (10, 5).

20 to 50 meters). Similarly, once the treated and dumped sludge reaches the bottom of the tank, it is necessary to move it or to rebuild one when it is positioned in central pivot and impossible to recover.

In addition to the preceding arrangements, the invention also comprises other variant embodiments. Among these, there will be mentioned in a non-limiting way: - the addition of sand, lime and / or calcium sulphate in the sludge, - the introduction of flocculant at 2 points in the tank see at a point in the channeling and the second in the tank according to the invention, see the use of 2 types of flocculants according to the 2 aforementioned introduction modes, - the presence of a cleaning opening at the bottom of the tank to remove gravel or sand heavy vehicles that can accumulate there, - the use of a tank on wheels or on a rail allowing it to move on the ground, - the use, as inclined plane, of the angle constituted by the lifting of Earth...

The main advantages of the invention are: - strong reduction in flocculant consumption, - significant improvement in the dewatering and solidification of the sludge, - and great adaptability to the constraints related to both the nature of the mud to treat (in terms of composition: quantities of fines / sands, specific surface area, etc.) at the flow rate and the conditions linked to the storage site itself (no electricity, difficult access, etc.).

Typically and without limitation, the muddy effluents from industry and treated according to the invention come from dredging processes, public works operations, effluents from the extraction of ores (coal, alumina, platinum, phosphate , iron, diamonds, gold, copper ...), oil sands, or any type of aqueous sludge made of clay or silt.

According to the invention, the flocculating agents used include all types of water-soluble organic polymers, including cationic, anionic, nonionic or amphoteric (co) polymers. The most suitable flocculation agent for sludge is first selected in the laboratory using routine tests. Preferably, it is selected from the group consisting of: anionic (co) polymers,

cationic or amphoteric (co) polymers, generally for the most organic sludges, such as channel dredges, polyacrylates, polyhydroxamates or natural polymers of the dextran type, generally for red alumina sludge, polyamines or polydiallyldimethylammonium chloride ( polydadmac). generally for drilling muds.

In practice, the polymer used is preferably composed of at least one monomer chosen from: a / anionic monomers having a carboxylic function (eg acrylic acid, methacrylic acid, and their salts, etc.), having a function sulfonic acid (eg 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and their salts ...) ... b / and / or the nonionic monomers: acrylamide, methacrylamide, N-vinyl pyrrolidone, vinylacetate, alcohol vinylic acid, acrylate esters, allyl alcohol, N-vinyl acetamide, N-vinylformamide, etc. and / or cationic monomers: mention may be made in particular and in a nonlimiting manner of dimethylaminoethyl acrylate (ADAME) and and / or quaternized or salified dimethylaminoethyl methacrylate (MADAME), dimethyldiallylammonium chloride (DADMAC), acrylamido propyltrimethylammonium chloride (APTAC) and / or methacrylamido propyltrimethylammonium chloride (MAPTAC).

In combination with these monomers, it is also possible to use water insoluble monomers such as acrylic, allylic or vinyl monomers having a hydrophobic group. When used, these monomers will be employed in very small amounts, less than 20 mole%, preferably less than 10 mole%, and they will be chosen preferentially from the group comprising dacrylamide derivatives such as N-alkylacrylamide for example N-tert-butylacrylamide, octylacrylamide and N, N-dialkylacrylamides such as N, N-dihexylacrylamide ... acrylic acid derivatives such as alkyl acrylates and methacrylates ...

The flocculation agents may optionally branched with a branching / crosslinking agent in the presence or absence of a transfer agent. The following is a nonlimiting list of branching / crosslinking agents: methylene bisacrylamide (MBA), ethylene glycol di-acrylate, polyethylene glycol dimethacrylate, diacrylamide, cyanomethylacrylate, vinyloxyethylacrylate or methacrylate,

triallylamine, formaldehyde, glyoxal, glycidyl ether compounds such as ethylene glycol diglycidyl ether, or epoxy or any other means well known to those skilled in the art for crosslinking.

Similarly, the (co) polymers may also: - be from the family of polycondensates: epichlorohydrin resin, dicyandiamide resin ... - or have undergone reaction (s) of post-modification (hydrolysis, degradation of Hoffman, Mannich product, hydroxamation reaction ...) The present invention is aimed particularly at the equipment for treating mineral or mineral sludges suitable for carrying out the invention, but also for the implementation and the treatment processes in this invention. which are included these devices.

Of course, the examples which follow are given solely by way of illustration of the subject of the invention, of which they do not in any way constitute a limitation.

Figure 1 is a schematic representation of the installation of the invention according to a first embodiment. Figure 2 is an alternative of Figure 1. Figure 3 is a schematic representation of the vessel in a first embodiment. Figure 4 is a schematic representation of the vessel in a second embodiment. Figure 5 is a schematic representation of the installation of the invention according to a third embodiment. Figure 6 is a schematic representation of the installation of the invention applied to dredging. Example 1 (counterexample)

The effluents of a phosphate launderette, after separation of the sand, are flocculated in a decanter with an anionic flocculant (acrylamide / sodium acrylate 70/30, molecular weight 18 million) allowing the mud thus treated to reach a concentration. 150g / liter of dry matter.

The sludge is then pumped at a flow rate of 300m3 / h through a pipeline to a 20-meter-high earthquake constructed on a bed of drained sand. The same flocculant used in the decanter is introduced into the pipe after dilution at a concentration of 0.05 g / liter: at a first point 100 meters from the end of the pipe and at a second point at 15 meters from the pipe. end of the pipeline

The quantities of flocculant required are then varied so as to create the maximum slope of the sludge thus flocculated (value which is 5.5%).

The required quantities of flocculating agent are: - about 200g / ton of sludge at the first injection point, - and 300g / ton of sludge at the second point, ie a total of 500 g / ton.

A sample of spread sludge taken two days after the end of pumping. It contains 480g / liter of solid matter. After 12 months of storage the surface of the spreading site is cracked and sufficiently consolidated to allow a passage of light vehicle. Example 2

Example 1 is reproduced above. The effluents of a phosphate launderette, after separation of the sand, are flocculated in a decanter (1) with an anionic flocculant (acrylamide / sodium acrylate 70/30, molecular weight 18 million) allowing the sludge thus treated to be treated. reach a concentration of 150g / liter of dry matter.

The sludge is then pumped at a flow rate of 300m3 / h through a pipe (3) to a 20m high earth (2) constructed on a bed of drained sand. Following the pipe (3) is installed a vertical cylindrical tank (4) of 6m3 useful with a diameter of 1 meter 20. A flocculation rod (5.1) (Figure 2) is lowered into the tank to obtain visually the best flocculation at both the overflow and bottom of the inclined plane (6). The flocculation rod 35 must be plunged by about 4 meters. In an alternative represented in FIG. 3, three lateral flocculation rods (5.2) are used. The optimum amount required for flocculation agent is 320 g / tonne of sludge. The inclined plane has an angle of 20 ° to the ground. The flow slope (7) obtained is 9%. After two days, the concentration of the spread sludge is 640 g / liter of solid material. Surface cracking is very important after one month of storage with very deep cracks. After 7 months, the mud supports a light vehicle. In the embodiment shown in Figure 4, the slope (2) is used as inclined plane (6).

Example 3 A suction dredge (8) is used for the construction of a harbor in low level dunes consisting of about: 85% very fine sand with a maximum particle size of 1 mm. and silts consisting of very fine clays and a small amount of organic matter.

The pumping is done on a dike 12 meters high through a pipe of 60cm diameter at an average flow of 1500m3 / h.

20 The tank which is placed on a raised earth (2), with a diameter of 2 meters and a height of 6 meters. The inclined plane (6) has an angle of 20 ° with respect to the ground.

The flocculant cane (5) is introduced into the bottom of the tank (4) and the flocculant content (as in Example 1) is visually determined to obtain good flocculation and a perfectly clear interstitial water.

The amount of flocculant required is about 90 g / tonne of dry matter. Given the variations in flow rate and composition, the permanent average consumption obtained amounts to about 110 g / tonne of treated sludge.

The slope obtained is very important, on average 16%. It is therefore necessary to move the tank very often. The sand-silt mixture obtained is totally homogeneous. After one month it is possible to bulldoze the surfaces thus treated and to build the storage buildings of the port under 6 months.

By way of comparison, when the same flocculant is introduced in the pipeline 10 meters before the exit, an average of 180 g / ton is required to obtain a flocculation which is partially broken by the height of the drop. Likewise, with an introduction in

points (at 100 meters and 10 meters from the exit) consumption remains high at around 150g / ton. In this case, due to a partial rupture of the flocs, a portion of the silts disperses in the recovery water, requiring then to pass into a settling lagoon before being discharged into the sea.

In this embodiment, the tank (4) is mounted on a support (9) at a height of about 20 meters. The tank is provided on its entire periphery with an inclined plane (6). It follows that the treated sludge is discharged on both sides of the tank, above ground. When the level of the treated sludge reaches the base of the tank, it is changed or buried.

The invention and the advantages thereof are well within the scope of the foregoing description. In particular, the decantation of the fine solid particles contained in the sludge during their storage above ground for the rehabilitation of the surfaces used is significantly improved.

Claims (1)

CLAIMS1 / Process for treating sludges from the mining or mineral industry according to which, before spreading above ground, the sludge is subjected to an upward movement during which it is brought into contact with a flocculation agent. 2 / A method according to claim 1, characterized in that the upward speed of the sludge is greater than its decantation rate. 3 / A method according to one of the preceding claims characterized in that the upward movement is doubled by a centrifugal movement causing mixing of the sludge with the flocculation agent at a speed between 0.2 and 0.8 m / s. 4 / A method according to one of the preceding claims characterized in that the contact time 15 between the sludge and the flocculation agent is between 1 and 10 minutes, preferably between 2 and 5 minutes. 5 / A method according to one of the preceding claims, characterized in that the flocculating agent is introduced into the sludge at a concentration of between 50 and 500g per ton of sludge. 6. The process as claimed in one of the preceding claims, characterized in that the flocculating agent is selected from the group comprising: anionic monomers having a carboxylic function or a sulphonic acid function; b / and / or nonionic monomers: acrylamide, methacrylamide, N-vinylpyrrolidone, vinylacetate, vinyl alcohol, acrylate esters, allyl alcohol, N-vinylacetamide, N-vinylformamide; c / and / or the cationic monomers: quaternized or salified dimethylaminoethyl acrylate (ADAME) and / or dimethylaminoethyl methacrylate (MADAME), dimethyldiallylammonium chloride (DADMAC), acrylamido propyltrimethylammonium chloride (APTAC) and / or methacrylamido propyltrimethylammonium chloride (MAPTAC). d) copolymers derived from the family of polycondensates: epichlorohydrin resin, dicyandiamide resin ... e) anionic or cationic (co) polymers derived from a (or) post-modification reaction (s) such as hydrolysis, Hoffman degradation, Mannich product, hydroxamation reaction ... f) or natural polymers such as dextran. 7 / A method according to one of the preceding claims, characterized in that the flow angle of the sludge at the time of spreading is between 2 and 20%. 8 / Installation for the implementation of the method according to one of claims 1 to 7. 9 / Installation according to claim 8, characterized in that it comprises a vertical tank 10 fed at its base by a supply line mud. 10 / Apparatus according to claim 9, characterized in that the tank is provided in the upper part, an inclined plane for the evacuation of the sludge. 15