FR2824003A1 - Valorization of coarse and porous industrial residues by mixing with insoluble residues from alkaline attack in the Bayer process for the fabrication of alumina - Google Patents

Abstract

A method allowing the valorization of coarse and porous industrial residues consists of mixing these residues with some insoluble residues from alkaline attack in the Bayer process for the fabrication of alumina. Independent claims are also included for: (a) a filler material incorporating a mixture of coarse and porous industrial residues and insoluble residues from alkaline attack in the Bayer process for the fabrication of alumina; (b) planting soil incorporating a mixture of coarse and porous industrial residues and insoluble residues from alkaline attack in the Bayer process for the fabrication of alumina .

Description

BR33568 / CR / FT / ml

  RECOVERY OF COARSE AND POROUS RESIDUES OF INDUSTRIAL ORIGIN

TECHNICAL AREA

  s The invention relates to a process for the recovery of porous residues of coarse particle size of industrial origin which are difficult to store due to their porosity, their poor mechanical characteristics and / or their low density and / or their toxicity, such as the final residues of everyday consumer goods made up of a tangle of metals, plastics, glasses, hydrocarbons and other organic compounds, each of these materials being in too small a quantity to be economically exploitable. This is in particular the ultimate shredding waste from motor vehicles, various metallic or electrical appliances (household goods, street furniture, electric vehicles, etc.) or even ashes from hearths of power plants

thermal electric.

STATE OF THE ART

  Ultimate waste is waste whether or not resulting from the treatment of waste, which is no longer likely to be treated under the technical and economic conditions of the moment, in particular by extracting the recoverable part of this waste or by reducing its polluting character or dangerous. Such waste is essentially mineral or organic solids more or less impregnated with industrial oils. They are generally not very recective, poorly evolving, poorly soluble but they have a polluting potential due to the presence of hydrocarbons and metallic compounds, the latter being, by percolation or leaching, susceptible

  to be dragged by rainwater.

  The ultimate grinding residues, which cannot be economically recovered, result, after o grinding of motor vehicles and other metallic or electrical devices - 2

  miscellaneous out of use, material recovery of separable metal fractions.

  These ultimate residues are characterized by a low density and a high porosity, which poses both problems of percolation in a natural environment and of mechanical strength in embankment. Even if they contain few toxic elements, their porosity is such that it favors percolation: rainwater can easily pass through them and, enriched on contact with heavy metals and organic matter,

  they risk polluting the water tables.

  Not very dense, with a coarse grain size, these wastes are very sensitive o to flight problems because they do not have sufficient consistency to be stored as is in natural sites. In addition, their mechanical characteristics being poor, this waste cannot be easily packed and compacted (compacting would significantly reduce the percolation speed). They cannot therefore be used either for backfilling

  s mines or quarries. All this puts a strain on the cost of their landfill.

  In the form of porous particles, with a heterogeneous particle size, the ashes of hearths of thermal power plants present less problems of instability but, by their porosity and their polluting potential, they present

  o comparable landfill problems.

PROBIEME POSE

  To facilitate disposal, such ultimate waste must be stabilized. A waste is considered to be stabilized not only when its water permeability and its leachable fraction have been reduced, but also when its mechanical strength has been improved. The plaintiff therefore sought to develop a treatment for

  stabilization of final waste which is economically satisfactory.

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OBJECT OF THE INVENTION

  The object according to the invention is a process allowing the recovery of coarse and porous residues of industrial origin characterized in that said residues are mixed with the insoluble residues resulting from the alkaline attack of the Bayer process.

manufacture of alumina.

  The coarse and porous residues are, for example, the ultimate residues from the treatment of household and industrial waste which, after grinding, are typically aggregates or not very dense consisting of a tangle of metals, plastics, glasses, hydrocarbons and d 'other organic compounds It can also be the ash from the hearths of thermal power stations which, although less prone to take-off than the previous residues, present comparable landfill problems. It can also be a mixture of ash from thermal power plant hearths and final residues of

  shredding of household electrical appliances and vehicles.

  In general, said insoluble residues resulting from the alkaline attack of the o Bayer process for the manufacture of alumina, or "red mud", have, once removed from the last tank of the washing chain ("washer"), contain a humidity in the region of 8% (weight content) and, as solids, essentially iron oxide in the form of iron sesquloxide Fe203, hydrated natural aluminosilicates (zeolites) and titanium oxide TiO2. They have a fairly fine particle size with a D5û close to 5 and some coarser particles with a D5û which can reach 5ûû p. 'i At the outlet of the last scrubber, said red mud can be poured directly into the settling tanks, o by lagooning, the humidity is lowered o gradually up to around 3%. However, it is also possible to speed up the obtaining of - 4 sludge with a low moisture content by using specific devices called "thickeners" which, placed downstream of the last scrubber, make it possible to reduce the humidity of the red sludge to around 5% ( weight rate). Taking advantage of the fact that with such a moisture content the sludge exhibits a thixotropic behavior, if it is pumped to pour it on conical toas whose base has a diameter of several hundred meters and which have a slight slope (a few dogrés at most). With such a technique, called "drystacRing", the red mud spreads over these tos forming a thin layer, so that the water can evaporate quickly. The sludge thus poured can see their humidity o drop rapidly up to around 30% before the

  pouring of a new layer on said conical tos.

  With a humidity level of less than 30%, typically between 25 and 30%, the

  red mud is well suited to the mixture according to the invention.

  The waste materials can be mixed with the red mud without any special precautions. You just have to take, for example with a mechanical shovel, inert residues in the lagoon or the dry-stacking tos and then mix them, even

  roughly, with said porous residue using said mechanical shovel.

  It is not necessarily sought to obtain a particularly homogeneous mixture but it is preferable that at the time when the mixing is carried out, said red mud has a still fairly high residual humidity, typically greater than 25%, which is always the case. case when one uses without waiting too long the red mud sampled in the lagoon or on the tos of "dry-stacking". Such humidity facilitates the mixing conditions so that the ultimate residues, in the form of coarse aggregates, can be easily confined, i.e.

  coated with said red mud and their impregnation.

  The volume content of each constituent varies from 2% to 8%, preferably from% to 7%, or better still from 4% to 6%. The optimal content varies depending on the properties sought for the residue treated. The latter can advantageously be used as an inert material for backfilling mines and quarries and / or

  s as a soil suitable for planting plants.

  Until the present invention, none of the constituents taken in isolation could be recovered in significant quantities: the ultimate waste because it presents problems of take-off, is not compactable and is therefore likely to contain leachable pollutants , red mud because it forms a very soil

  heavy, not acrea, not conducive to plant growth.

  The Applicant has found that red mud, insoluble residues resulting from the alkaline attack on bauxites by the Bayer process, provide said mixture with three essential properties: - a significant adsorption of heavy metals and organic compounds; - a drastic reduction in percolation due to the confinement of porous residues;

  - an improvement in mechanical strength.

  The synergistic effect associated with the first two properties consists in an extremely strong reduction in the leachable fraction of the residues. The third property completes the conditions necessary to stabilize the tailings with a view to their landfill or their use for backfilling mines and quarries,

especially in the open.

  Conversely, the contribution of these porous and coarse residues aerates the red mud, the mixture becoming a soil completely suitable for planting or, simply, for a spontaneous resumption of vegetation. The use as a soil makes it possible to consume the red mud in significantly greater quantities than before the present invention, said quantities possibly reaching the order of - 6 magnitude of the quantities produced by alumina manufacturing plants, this which finally makes it possible to envisage an economically satisfactory alternative to dumping at sea, which is less and less accepted and whose ban, foreseen in the short term, is a constant threat of closure of existing industrial installations. This type of mixture can be used to backfill quarries or similar sites with, for positive results: - the re-stabilization of sites deteriorated by soil removal; o - Inexpensive disposal of solid effluents, for example by carrying out a coarse mixing with a backhoe during backfilling; - savings in landfill costs for each solid effluent taken separately

! 5 EXAMPLE 1

  A mixture according to the invention was claimed as follows.

  , 3kg of automobile grinding residue (RBA) were obtained by reconstituting the same proportion of the different fractions making up an industrial stock, which made it possible to precisely define the weight proportions of the constituents, namely: Foams 18.38% Paper and fabrics 20.37% Rubber and ferrous element (mainly tires) 8.22% Polymers (hard plastics, plastic films, various foams) 33.33% Wood 5.17% Rubber. 4.5% Polymers and non-ferrous elements (mainly electrical wires) 1.92% Ferrous elements 3.51% Non-ferrous elements 2.04% n / a. Fine minerals (glass, earth, sand, metallic particles) of diameter <5mm 12.56% By sieving, an approximate gravelometry has been determined: 2 to 4cm 19% there 2cm 28% To û, 5 to lcm 25% <O, Scm 28% The volume apparent RBA was 15 liters, an apparent density of 0.686 On the other hand, 45 kg of red mud at 28.5% humidity were taken from a o lagoon of an alumina plant. The overdry analysis gave: Al203 17.8% SiO2 12.64% Fe203 36.3% TiO2 6.1% s. CaO 7.69% Na20 6.96%

  This sludge had a very fine particle size centered on 4 micrometers.

  24 kilograms of this sludge (approximately 13 liters) were removed to carry out a

  summary mixing with the 15 liters of RBA. This was shoveled on a

  concrete area. The composite thus obtained was loaded into a glass column

  of diameter û, 2 m on a height of û, 90 m.

  The lower support consisted of a metal grid surmounted by a canvas, and

  opening out through a hose flowing into a container.

  Water was supplied to the top of the column, and an overflow device maintained a constant height of 10 cm of water above the bed of solids. - 8 The percolation speed (calculated in empty barrel) was measured by the volume collected in the container under the column. The values were as follows: Zero time: û.û39 m / h 1 û days: û.ûl 2 m / h s. 1.5 months: û.ûûû9 m / h The chemical analyzes of the last percolate showed that this water respected the

environmental release standards.

EXAMPLE 2

  To evaluate the percolation through the RBAs alone compared to the mixture of Example 1, the previous column was loaded to the same height with 20 kg

  of RBA, and the water was supplied.

  s It was not possible to keep the lû cm of water above the bed, because the maximum flow of the supply circuit was lower than the percolation flow. The corresponding speed was at least several meters per hour, or at least a thousand times

  more than in the example according to the invention.

  We can see that the red mud, whose intrinsic percolation speed is less than a tenth of a millimeter per hour, allows, by their presence in the mixture and due to the confinement of the ultimate residues that it causes, decrease the percolation speed very strongly. The risks of

  pollution by leaching of rainwater is greatly reduced here.

EXAMPLE 3

  Pilot experiments with planting Mediterranean species were

  Réclisoes on an experimental site located in the south of France.

  For this, test boards were created by mixing with the mechanical shovel a stock of RBA with red mud coming from the lagoon of Example 1, respecting substantially equal volume proportions, such as those

  exposoes in Example 1 (13 liters of red mud for 15 liters of RBA).

  After 4 years of experimentation, it was found that out of 24 different species resisted and had normal growth compared to control plantations. s The growth co mu lated for plants on the mix with red / waste mud was, over a period of 4 years, of 1 12 cm while for the controls we measured a

average growth of 12 cm.

  To control the behavior of plants with regard to their water supply, o irrigation has been cut on certain rows of plantations. If the results mark overall the normal positive effect of irrigation, we find that 3 years

  after planting, watering can be eliminated without major inconvenience.

  In comparison, a planting test on a board containing only RBA s ended in failure. This medium, not retaining water, was unfit for recovery

Plant.

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BENEFITS

  Due to the humidity contained in the red mud and the wettability of porous and coarse waste, it is not necessary to carry out an intimate and costly mixing of the constituents A There is thus an important synergistic effect in the recovery of these two types of residue previously considered separately as particularly

  aggressive towards the environment.

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Claims (7)

  1) Process allowing the valuation of coarse and porous residues of industrial origin characterized in that the said residues are mixed with the insoluble residues resulting from the alkaline attack of the Bayer process for the manufacture of alumina. 2) The method of claim 1 wherein said insoluble residues from the alkaline attack of the Bayer process are removed when their humidity is   ro less than 3%, preferably between 25% and 3%.   3) Method according to claim 1 or 2 wherein the coarse and porous residues are ultimate residues from the treatment of waste, such as the ultimate grinding residues of household appliances, electrical appliances or motor vehicles. 4) Method according to claim 1 or 2 wherein the ultimate residues are   ashes from hearths of power stations.   o 5) Method according to any one of claims 2 to 4 wherein the content   the volume of each constituent varies from 2% to 8%, preferably from 30% to %, or better still from 4% to 60%.   6) Backfill material characterized in that it comprises a mixture of coarse and porous residues of industrial origin and insoluble residues from   the alkaline attack of the Bayer process for manufacturing alumina.   7) Soil suitable for planting, characterized in that it comprises a mixture of coarse and porous residues of industrial origin and insoluble residues resulting from the attack