EP0905265A1 - Method of reducing water quantity in slurries of oxidic nickel ores by injection of acrylic flocculant - Google Patents

Abstract

In this process to decrease the amount of water contained in the nickel ore pulps, dilute the pulp with water, inject a solution dilute aqueous flocculant based on a copolymer of acrylic acid, let settle, then separate the overflow from the overflow.

Description

The invention relates to a new method for eliminating maximum of water continues in the pulp of oxidized nickel ore.

It relates more particularly to the conditions of flocculation and settling of said minerals which may at one time or another of their treatment be partially or totally in the form of a pulp more or less diluted.

• qu'elles sont extrêmement diluées, puisque 70% du poids de la pulpe peut être constitué d'eau et 30 % seulement de solide,
• qu'elles ne peuvent pas naturellement sédimenter de manière à obtenir une phase aqueuse limpide et une pulpe très épaissie,
• qu'elles ne sont pas manipulées autrement que par pompage,
• qu'elles ne peuvent pas être, sans un séchage thermique préalable, fort coûteux, utilisées directement dans les fours permettant l'élaboration du métal.

These pulps are most often characterized by the fact:

• that they are extremely diluted, since 70% of the weight of the pulp can consist of water and only 30% of solid,
• that they cannot naturally sediment so as to obtain a clear aqueous phase and a very thickened pulp,
• that they are not handled other than by pumping,
• that they cannot be, without prior thermal drying, very expensive, used directly in the ovens allowing the production of the metal.

A considerable number of documents, theses, patents, concerning the flocculation and settling of the mineral pulps have been published both in the water treatment field than that of mineral treatment. However, the strict application of the processes thus described to ores oxidized nickel garnieritic is translated either by a total ineffectiveness, either by a prohibitive cost of implementation.

In US-A-4 110 401, pulp leached in an acid medium is treated and not in neutral medium at temperatures above 150 ° C and not at ambient temperature, while at SU 1 754 162, simultaneous use is proposed a flocculant and a coagulant without prior dilution of the pulp.

By way of example, we will cite the only known study on oxidized nickel ores and described in the French invention patent 2,320,781. This patent describes a flocculation method, which consists in adding 1500 g / Ts of flocculant, after having brought the pH to a value of 6.7. The pulp thus flocculated decant very slowly, since the necessary area of decantation calculated according to the Kynch method. Roberts is around 45 to 46 m ² / Ts / h, the concentration of the undersides, thickened pulp, then being doubled, since going from 10% dry matter to 20% dry matter per kilogram of pulp. A process of this kind is economically inapplicable and generates very high flocculant costs and huge decanter surfaces, since to treat 100 Ts / h would require 4,600m ² of decanter, ie a device of 77m in diameter.

Furthermore, the application of this process in an installation industrial, and in particular such considerable doses of flocculant organic, would result in great operating difficulties. Indeed, as already described in the literature (see book Mineral Processing Plant Design by Mular and Bhoppi. Society of Mining Engineers, 1978, p.570), la decanter operation would be disturbed by the formation of "islands", aggregates of viscous solid, preventing sedimentation of particles.

• à diluer la pulpe à l'eau à une concentration inférieure à 150g de solide par litre et, de préférence, inférieure à 80g de solide par litre,
• à injecter dans la pulpe diluée une solution aqueuse diluée à moins de 1g par litre et, de préférence, à moins de 0,5g par litre, d'un floculant organique à base d'un copolymère dérivé de l'acide acrylique faiblement anionique et de masse moléculaire moyenne en poids de 2.10⁶ à 3.10⁶, en une dose de 50 à 1000 g par tonne de matière sèche de la pulpe et à laisser la solution injectée en contact avec la pulpe diluée pendant une durée suffisante pour obtenir une surverse contenant moins de 100mg de solide par litre et une sousverse contenant entre 450 et 300g de solide par litre, et
• à séparer la sousverse de la surverse.

The invention overcomes these drawbacks by a process which successively consists

• diluting the pulp with water to a concentration of less than 150 g of solid per liter and, preferably, less than 80 g of solid per liter,
• injecting into the diluted pulp an aqueous solution diluted to less than 1 g per liter and, preferably, to less than 0.5 g per liter, of an organic flocculant based on a copolymer derived from weakly anionic acrylic acid and weight average molecular weight of 2.10 ⁶ to 3.10 ⁶ , in a dose of 50 to 1000 g per tonne of dry matter of the pulp and to leave the solution injected in contact with the diluted pulp for a sufficient time to obtain an overflow containing less than 100 mg of solid per liter and an underflow containing between 450 and 300 g of solid per liter, and
• to separate the underflow from the overflow.

Paradoxically, the pulp is deliberately diluted before flocculation to finally better remove the water by flocculation.

The whole process can be carried out at room temperature (5 to 35 ° C).

The first stage of the process consists in diluting the pulp with water to a concentration less than 150 g of solid per liter and, preferably, less 80 g of solid per liter. Preferably, a mineral of particle size less than 500 microns.

The second stage of the process according to the invention consists in injecting into the diluted pulp a dilute aqueous solution of an organic flocculant based on a copolymer derived from acrylic acid. The flocculant may be an acrylic acid salt of the family of polyacrylamides having a weight average molecular weight of 2.10 ⁶ to 3.10 ⁶ and of which 40% at most and, preferably, 30% at most of the number of units of the copolymer carry a negative surface charge as it can be measured by potentiometry. Flocculants of this kind are available, for example, under the name AF 400 from the company BASF or AN 934 from the company Floerger.

The dose of flocculant is greater as the particle size of the solid pulp is smaller. The dose ranges from 300 to 1000g and, from preferably 300 to 500 g per tonne of pulp dry matter for a particle size of the solids thereof less than 15 microns. The dose ranges from 60 160 g per tonne of dry matter for a particle size less than 200 microns. The duration of contact between the pulp and the flocculant solution is less than 2 minutes and preferably less than 1 minute when the flocculation takes place in a stirred tank. Too long a contact time can destroy the flocs already formed.

Preferably, the flocculant is injected in several places in the diluted pulp. This injection can be done in a stirred tank with moderation or, and the result is even more effective, in the tank of flocculation and in the pulp inlet piping in the decanter, or even even in the decanter injection well.

When the flocculation takes place in a stirred tank, the residence time pulp in the reactor should not exceed 2 minutes and, preferably, 1 minute, too long residence times that can destroy the flocs already trained.

When the flocculation is carried out in several places of the circuit, we can advantageously use the following distribution: one third of the quantity total flocculant in the flocculation reactor, a third in the piping supply of the pulp to the decanter and the remaining third in the well decanter supply. This distribution can be modified according to the type of ore to be processed.

If the total dose of flocculant is insufficient, flocculation will be incomplete and the decanter underflow will be very loaded with solid, which is contrary to the desired effect. At the same time, and this may be important if the solids must undergo a subsequent mechanical filtration, the undersides of the decanter will not be thickened enough, which will require surfaces of important filtration.

If the total dose of flocculant is too large, it will not improve in no way the characteristics of overflows and overflows while exposing himself to the "island" phenomenon mentioned above.

The flocculated pulp then settles quickly so as to obtain a clear overflow containing very little suspended solid (less than 100mg / l and a concentrated overflow included, depending on the size of the treated pulps, between 450 and 300 g / l. This underflow is then able to be pumped to facilities that will continue to remove water residual, such as mechanical filtration or drying thermal.

The pH of the pulp to be flocculated is not checked or regulated, the operation generally scrolling down for pH values between 6 and 8.

Depending on the treatment you want to subject to decanter underpasses, and in particular in the case where these underpasses are intended to be filtered by mechanical processes such as filters presses a number of additives can be added before the flocculant have virtually no effect on decantation performance, but greatly improve filtration speeds.

la chaux à des doses comprises entre 1 et 3% en poids par rapport à la matière solide contenue dans la pulpe,

les coagulants de la famille des polyamines fortement cationiques dont au moins 50% des motifs portent une charge positive et ayant une masse moléculaire moyenne en poids inférieure à 3.10⁶, tels que le produit vendu sous la marque FL 28 P2 par la Société Floerger.

Among these adjuvants, there may be mentioned:

lime in doses of between 1 and 3% by weight relative to the solid matter contained in the pulp,

coagulants of the family of highly cationic polyamines, at least 50% of the units of which carry a positive charge and having a weight-average molecular mass of less than 3.10 ⁶ , such as the product sold under the brand FL 28 P2 by the company Floerger.

Polyamine is generally used in an amount of 1 to 50 to ppm by weight compared to the pulp solids.

The following examples illustrate the invention.

All tests were carried out in a laboratory settling tank sold by the company ENVIROCLEAR, characterized by the fact that the flocculation and settling takes place dynamically, not statically, like this is the case in the case of test tubes known to those skilled in the art under the name of JARTEST.

The Enviro-Clear laboratory decanter is a diameter decanter internal 10 cm, continuous and which allows the flocculation-settling of the pulp dynamically.

• il y a emprisonnement des flocs dans le lit de boue, ce qui limite la présence de flocs dans la surverse;
• dans la partie supérieure du lit de boue (au-dessus de l'alimentation), des remous permanents permettent une poursuite de la floculation et une croissances des flocs.

The pulp to be flocculated is fed through the middle of the decanter. The height of the pulp inlet pipe is adjustable and allows the decanter to be fed into the mud bed. This has several advantages:

• there is trapping of the flocs in the mud bed, which limits the presence of flocs in the overflow;
• in the upper part of the mud bed (above the feed), permanent eddies allow further flocculation and growth of the flocs.

The flocculant is injected into the pulp supply pipe. before arrival in the decanter. This allows good dispersion of the flocculating in the pulp.

A deflector, placed above the arrival of the pulp, ensures a good distribution and homogenization of the pulp. The gap between the feed pipe deflector is adjustable.

A stirring system with offset pulps allows better dispersion of the pulp on arrival in the bed and ensures more decantation homogeneous.

A mud level sensor, based on the reflection of the signal emitted by infrared lamps, is placed on the side of the decanter. Its height, by level of arrival of the pulp, is adjustable and therefore governs the height of the level of mud above the feed. The withdrawal pump is slaved to this level sensor.

The pulp supply, flocculation and withdrawal pumps are peristaltic pumps.

After adjusting the geometric characteristics of the device (mud height - pulp injection level), a solution is injected diluted with flocculant (dilution 0.1 g / l) in the pulp before feeding the device.

In the same way the pulp flow is ensured by a pump variable speed for sweeping a wide range of flow rates.

concentration en % ms ou en g/l pour la sousverse,

taux de matières en suspension en mg/l pour la surverse.

After reaching equilibrium, the overflow and underflow are sampled in order to measure the main characteristics, namely:

concentration in% ms or in g / l for the underflow,

suspended matter rate in mg / l for overflow.

Example 1 (comparative)

A nickel ore pulp with a grain size of 0 / 250µ is diluted to 68.8 g / l.

This pulp is pumped to the decanter at a flow rate of 10 l / h, which corresponds to a volumetric flow rate of 1.27 m ³ / m ² / h of decanter and to a solid flow rate of 0.087 Ts / m ² / h , which corresponds to a decanter surface of 11.44 m ² / Ts / h of solid to be decanted.

No flocculant is added to the pulp.

After 1 hour of continuous operation it does not appear sedimentation and the concentration of the underflow and overflow are practically identical to that of food, i.e. 68.8 g / l. At most we can note that particles larger than 100 microns sediment in the device.

Example 2

A pulp from the aliquot of that used in Example 1 is injected under the same flow conditions in the laboratory decanter.

A solution diluted to 0.1 g / l of SEDIPUR AF 403 flocculant is added so as to use an amount of active flocculant of 150 g / Ts to flocculate.

After 1 hour of continuous operation, the overflow is sampled and the underflow and we obtain an overflow with a concentration of 112 mg / l and a subflow having a concentration of 531 g / l.

Example 3

A nickel ore pulp with a grain size of 0/63 µ is diluted to 69.6 g / l.

This pulp is pumped to the decanter at a flow rate of 10 l / h, either in the same conditions as in examples 1 and 2.

The AF 403 flocculant is added under the same conditions as in Example 2, but at an amount of active material of 200 g / Ts.

After one hour of continuous operation, the overflow and underflow. We then obtain an overflow having a concentration of 102 mg / l and an underflow of 470 g / l.

Example 4

A nickel ore pulp with a particle size of 0/15 µ is diluted to 73.6 g / l.

The operating conditions are the same as in Example 3, except for the flocculant which is injected at an amount of active material of 450 g / Ts.

After one hour of continuous operation, the overflow and underflow.

We then obtain an overflow having a concentration of 112 mg / l and an underflow of 354 g / l.

Example 5

Take the pulp from Example 2, but this pulp is not diluted before treatment and it is at a concentration of 215 g / l.

This pulp is injected under the conditions of Example 2 and the flocculation is also practiced in the same way.

We then see that the flocculation is very bad and after 1 h of operation the overflow is very loaded with 5g of solid per liter.

The dosage of flocculant is then modified to inject a dose corresponding to 280 g / Ts.

Under these conditions and after one hour of operation we find results close to those of Example 2.

Example 6

Take the pulp of Example 2 diluted to 70 g / l and, before injection into the decanter, condition the pulp by adding 125 ppm (parts per million) by volume of a Floeger FL 28 PE brand coagulant diluted to 1g / l. This conditioning is carried out in a stirred reactor under conditions 100 l normal.

The pulp is injected at a flow rate of 10 l / h after adding flocculant (type SEDIPUR AF 403) at a dose of 150 g / l.

After one hour of continuous operation, the overflow and underflow.

We then obtain an overflow having a concentration of 4 mg / l and a underflow of 470 g / l.

Claims (13)

Process for reducing the quantity of water contained in the pulp of oxidized nickel-bearing ore, comprising the following successive stages: diluting the pulp with water to a concentration of less than 150 g of solid per liter, to inject into the diluted pulp an aqueous solution diluted to less than 1 g per liter of an organic flocculant based on a copolymer derived from weakly anionic acrylic acid and of average molecular weight by weight from 2.10 ⁶ to 3.10 ⁶ , a dose of 50 to 1000 g per tonne of dry matter of the pulp and to leave the injected solution in contact with the diluted pulp for a sufficient time to obtain an overflow containing less than 100 mg of solid per liter and an underflow containing between 450 and 300g of solid per liter, and to separate the underflow from the overflow The method of claim 1, wherein at most 40% at most more than the number of units of the flocculant copolymer carry a charge negative. The method of claim 1 wherein the dose is as much larger than the particle size of the pulp solid is smaller. The method of claim 3, wherein the dose ranges from 300 to 1000g per tonne of pulp dry matter for grain size less than 15 microns. Method according to claim 3, characterized in that the dose ranges from 60 to 160 g per tonne of dry matter for a grain size less than 200 microns. Method according to claim 1, characterized in that the duration contact between the pulp and the flocculant solution is less than 2 minutes. The method of claim 1, wherein the flocculant solution in several different places. The method of claim 1, wherein the pulp, before injecting the flocculant solution, a coagulant or lime. Process according to Claim 8, in which the coagulant is a strongly cationic polyamine, at least 50% of the number of the units of which carries a positive charge and which has a weight-average molecular mass of less than 3.10 ⁶ , the coagulant being added in an amount 10 to 50 ppm by weight relative to the volume of the pulp. The method of claim 8, wherein the lime is added at a rate of 1 to 3% by weight relative to the solid of the pulp. The method of claim 1, wherein the pulp is diluted to water at a concentration of less than 80g of solid per liter. Process according to Claim 1, in which the following is injected into the diluted pulp an aqueous solution diluted to less than 0.5 g per liter of organic flocculant. The method of claim 1 which is carried out at a temperature between 5 and 35 ° C.