FR2477427A1 - Filtration of liq. contg. solids in suspension - where sandy material is added so high filtration speeds are obtd. with suspensions normally very difficult to filter (BR 15.9.81) - Google Patents

Abstract

The suspensions can only be filtered with difficulty, so a chemically-inert, sandy material with a min. grain size of 0.1 mm is added. Thr result is eay filtration and simple washing of the filter cake. The amt. of sandy material added pref. has a wt. equal to 20-90% of the initial solid matter in the suspension. The sandy material is pref. recovered from the filter cake by physical or chemical washing, and is then re-used for the filtration of more suspensions. Alternatively, part of the filter cake contg. the sandy material may be recycled. Very high filtration speeds can be obtd., which are faster than when synthetic flocculants are used.

Description

 IMPROVED PROCESS FOR SEPARATION BY FILTRATION OF.

PHASES SOLID AND LIOUID DIFFICILE # # FILTRABLES
The present invention relates to a novel method of separation by filtration of solid and liquid phases difficult to filter.

For a long time now, those skilled in the art have been confronted with the obligation of separating, by filtration, two distinct solid and liquid phases resulting from an industrial cycle, such as, for example, the attack of ore by a liquor. Aqueous, and leading to collect separately these two phases for later recovery by extracting the elements that are of interest. Generally, this separation is followed by a washing of the solid phase in order to recover the impregnation liquor of the solid phase, so that a purified solid phase can be obtained or the all the interesting elements solubilized in the liquid phase.

 Among all the means of separation and lavae made available to those skilled in the art, such as decanters, clarifiers, cyclones, etc., it is well known that filtration has many advantages. Indeed, in the case of an attack of an ore for example, the suspension resulting from the attack must be separated from the solid phase formed of unexpected materials and the liquid phase containing in solution the In this case, the filtration of the aqueous suspension resulting from the attack of the ore makes it possible to reduce the quantity of the liquid phase retained by the solid phase during the separation and makes it possible to limit the volume of washing. necessary to entrain the liquor impregnation of this solid phase. Therefore, the liquid phase obtained by filtration of the attack suspension, to which is joined the washing volume of the separated solid phase, constitutes a much higher concentration aqueous solution, resulting in an improvement of the subsequent recovery treatments and a reduction of the technology used downstream of the separation. In addition, it quickly became apparent to those skilled in the art that the filtration practiced in industrial operation, brings great operating facilities because it can be easily made available. the stop, as opposed to the decanter for example.

Apart from these facts, filtration requires smaller investments than other technologies, less occupied areas, much smaller fixed assets, etc. All these reasons have particularly encouraged manufacturers to produce high filtration capacity equipment, such as automated filter presses that have replaced old hand-held frame machines, belt filters and rotary or bucket filters.

However, despite the technological improvements made to filtration equipment, despite the use of new materials, such as plastics, synthetic fibers of filter media, despite the use of chemical resources such as natural flocculants improved, various synthetic polyelectrolytes ... it turns out, in certain cases, that the properties of the solid phase to be filtered considerably hinder the filtration, or even exclude this means of separation, as is the case, for example, for precipitated hydroxides or for minerals too finely ground before the attack.

In this case, the productivity is so low that it leads to too large filtration surfaces and too expensive to implement.

To avoid the aforementioned phenomena, which are manifested by the clogging of the cake or the filtering medium, a person skilled in the art has resorted to the so-called 'recoat' device which consists in placing on the filtering medium an intermediate cake of fine materials and calibrated does not cause the aforementioned drawbacks and constantly renew the filter layer of the cake by peeling gradually by means of a suitable tool called "costa #".

Although this means proves to be a significant improvement, however, there are drawbacks that make its use unacceptable in some cases, such as for example when the fine and calibrated materials constituting the intermediate cake which mix with the product to be filtered, are pollutants for the filtered solid.

In view of the above-mentioned major drawbacks, the Applicant, in pursuing his research in this field, has found and developed an improved method of separation by filtration of liquid and solid phases which are difficult to filter.

The process according to the invention, the purpose of which is to make general the use of filtration for the separation of liquid and solid phases difficult to filter, is characterized in that, in order to create with the solid phase to separate a permeable cake easy to wash and to filter, is introduced into the mixture difficult to filter a sandy material chemically inert with respect to the liquid phase whose particle size is at least equal to 0.1 mm, then the separation of the two phases by filtration is carried out .

The material added for filtration may be independent of the solid phase to be filtered, such as, for example, calibrated natural sand, ground ceramic or glass, synthetic polymer in granular form. This material may also be constituted by a calibrated fraction, selected from the filtered solid phase and recycled after its selective separation of the materials constituting the cake, by well known means, such as cyclones, classifiers, sieves, etc. .

In practice, the added filtration material is intimately melted, by any known means, with the mixture of difficult to filter phases before distributing it on the filter and after possibly incorporating conventional flocculants.

According to a first variant, if the solid phase to be separated does not contain particles of particle size at least equal to 0.1 millimeter, then a sandy material, external to the mixture to be filtered, is added in an amount such that the mixture of 20 t to 90% by weight of said material relative to the mass of fine solid to be filtered. In this case, to avoid excessive consumption of said sandy material, it is possible, after the filtration has been carried out, to wash it by a physical means such as backwash> or by a chemical means such as an acidic liquor for solubilizing the elements constituting the initial solid phase, and thus to separate the sandy material, to wash it and finally to recycle it.

According to another variant, if the initial solid phase, after separation of the difficultly filterable mixture, contains particle size of at least 0.1 mm, the sandy material added to the difficultly filterable mixture is constituted by a recycled fraction of the filtered solid, the particle size of which is at least 0.1 μm and in the amount of 50% to 90% by weight of said material having a size greater than 0.1 mm, relative to the mass of fine solid to be filtered.

The invention will be better understood thanks to the examples given by way of illustration.

 EXAMPLE 1 A liquid effluent from a chemical plant containing solution of sodium fluoaluminate and sodium fluosilicate in solution was treated with sufficient lime to give a suspension containing 15 g of a mixture of calcium fluoaluminate and of calcium fluosilicate forming a solid phase difficult to filter.

The pH of the aqueous phase was 7.9 after introduction of the lime. The aqueous phase could be released into the environment provided the suspended solids were removed.

Using the only known means of the prior art to facilitate filtration, a synthetic flocculant was introduced into the above-mentioned suspension (non-ionic polyacrylamide) at a rate of 3 milligrams per liter of said suspension. A much higher suspension was then obtained. comprising 100 g / l of solids, this suspension filtering at a rate of 200 kg per square meter per hour (m2 / h) while the cake obtained was rendered non-manipulable due to the 80% moisture content it contained.

According to the process of the invention, the above-mentioned suspension, containing calcium fluoaluminate and calcium fluosilicate, was treated by addition of ground limestone to the size of 0.6 mm in the proportion of 25 g / l of suspension to be filtered. Then, 3 mg / l of the same synthetic flocculant was added, giving a suspension comprising 220 g / l of solids.

The filtration was then carried out at the rate of 800 kg / m 2 / h, giving a cake of solid material manipulable, having only 55 t of moisture.

Thus, according to the process of the invention, the filtration capacity for the same filter surface was multiplied by 4 for the total mass and by 2 for the precipitate to be removed.

EXAMPLE 2
In a hydrogen gas purification cycle containing carbon monoxide, a liquor charged with ammoniacal cuprous complex was to be periodically removed from the purification circuit.

This liquor was treated with sodium hydroxide, thus causing the precipitation of copper hydroxide very difficult to filter. it was not possible to use a flocculant to facilitate filtration because the cupric precipitate separated from the liquor had to be reintroduced into the gas purification cycle after resolubilization in concentrated form.

It turned out that the separation of copper hydroxide was very difficult to achieve, if not impossible. It clogged the filter media used and led to prohibitive filtration surfaces.

By applying the process of the invention, 50 g / l of sand suspension calibrated between 0.15 and 1.0 mm, of which 50% greater than 80%, were introduced into the suspension containing the copper hydroxide, 5 mm for a quantity of 5 g / l of copper hydroxide present in the suspension.

Without any prior concentration, the suspension thus obtained was filtered on an industrial suction beaker giving a ~ reduced filtration area corresponding to 1 m 2 of filter surface per 10 kg of solids to be recovered.

A perfectly clear filtration solution was then obtained, without the occurrence of clogging phenomena.

The recovered solids cake was treated on the filter, stopping the suction, with an ammonia liquor which caused the solubilization of the cupric compound in less than one hour. It was then possible, with great facility, to wring and wash the cake.

This gave a concentrated, directly recyclable cupric solution and purified sand available for a new filtration operation.

EXAMPLE 3
A highly clayey uraniferous ore milled to 0.5 mm was processed, the composition of which was as follows
Uranium: 0.17%
Slolybdenum: 0.22%
Vanadium: 0.05%
Fe203 soluble: 0.35%
AI 203 soluble: 0.25 Oc
Soluble MgO: 0.10%
Soluble CaO: 0.36 t
insoluble matter: 98,5%
Of which gold materials: 0.12 90 After this ore was attacked with a sulfuric solution, according to a well-known process, the solid phase consisting of the uninvolved materials, which was 98.5% of the solid, was separated off. initial.

Using the only means known to those skilled in the art, for
To achieve the separation of the solid and liquid phases, 0.125 kg per ton of guar flocculant ore was introduced into the suspension resulting from the attack. A much more concentrated suspension was then obtained, which it tried to filter. The result was quite disappointing since we could not separate and wash more than 175 m2 / h.

 By a substantial increase of flocculant introduced into the suspension, at a rate of 0.5 kg / t of ore, it was possible to increase the filtration productivity by increasing it to 300 kg / m2 / h but undergoing multiple washing problems, due to excess flocculant.

By applying the process of the invention to the above suspension-suspension of the sulfuric attack of the clayey uranium ore, the suspension of the unattacked materials was treated by cycloning, which was treated with water at the end of filtration to allow its evacuation. hydraulic.

 Sands with a size greater than 0.2 mm were separated and mixed with the slurry arriving at filtration so that 0.750 tons of sands per tonne of ore were introduced into the attack and filtration cycle.

Since the clay ores are poor in sand, it was necessary to establish a recirculation equilibrium so that the necessary quantity of sand was available.

It was thus possible to obtain a productivity of 875 kg / m 2 / h with a quantity of flocculant equal to 0.2 kA per ton of ore with a washing efficiency of 99.5%.
By relating the values to the mass of ore entering the attack and filtration cycle, 500 kg / m2 / h could be filtered with 0.35 kg of flocculant per ton of ore, with a washing efficiency of 99> 10 t.

Claims (4)

REVENDIGATI0NS 10 / - Improved method for separation by liquid and solid phase filtration of a suspension which is difficult to filter, characterized in that, in order to create, with the solid phase to be separated, a permeable cake which is easy to wash and to filter, it is introduced in the mixture difficult to filter a sandy material chemically inert with respect to the liquid phase, whose particle size is at least equal to 0.1 millimeter, and then the separation of the two phases by filtration.  20 / - improved method of filtration separation according to claim 1, characterized in that the amount of sandy material added to the suspension is 20 to 90% by weight of the initial solid mass to be filtered. 30 / - improved filtration separation method according to claim 1, characterized in that the sandy material introduced into the suspension to be filtered is recovered by physical or chemical washing after filtration of the mixture, and recycled in preparation of the suspension to be filtered. 40 / - Improved filtration separation method according to claim 1, characterized in that the sandy material used is a sandy fraction of the suspension to be filtered which is separated after the f tration to be recycled in preparation for the suspension to be filtered.