CA1079496A - Process for stabilizing and consolidating residues comprising metal compounds - Google Patents
Process for stabilizing and consolidating residues comprising metal compoundsInfo
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- CA1079496A CA1079496A CA266,132A CA266132A CA1079496A CA 1079496 A CA1079496 A CA 1079496A CA 266132 A CA266132 A CA 266132A CA 1079496 A CA1079496 A CA 1079496A
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- residues
- cao
- lumps
- grains
- active cao
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Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a process for stabi-lizing and consolidating residues based on metal compounds, in particular residues containing jarosites, goethites, iron oxides, iron hydroxides, iron sulfates, in order to allow to store these residues as piles which may be exposed to weather -ing agents, characterized in that said initially free flow-ing residues comprising at least 55% of solids are mixed with a stabilizing material containing active CaO, in a sufficient amount to form a solid product which is mechanically stable and substantially insensible to the solubilizing action of water, allowing without pollution risk to store this product as weathering exposed piles.
The present invention provides a process for stabi-lizing and consolidating residues based on metal compounds, in particular residues containing jarosites, goethites, iron oxides, iron hydroxides, iron sulfates, in order to allow to store these residues as piles which may be exposed to weather -ing agents, characterized in that said initially free flow-ing residues comprising at least 55% of solids are mixed with a stabilizing material containing active CaO, in a sufficient amount to form a solid product which is mechanically stable and substantially insensible to the solubilizing action of water, allowing without pollution risk to store this product as weathering exposed piles.
Description
~ - 2 - 10~79496 , 'rhis invention relates to a process for treating residues comprising metal compounds which are physically lnstable, particu~arly towards weathering agents, this process resulting in a restructuration of the residue materials by consolidating and stabilizing the latter, while making possible to store them as piles without any other protection against weathering a~ents.
In the known technique for preparing pure zinc sulfate soluti'ons,for example formed for the purpose of pro-ducing zinc by electrolysis, zinc ore, for example directly oxidised ores or ores sulfurized after roasting, is generally attacked under oxidising conditions by sulfuric acid in such a metered amount that, due to some ore excess, pH of the resulting solution is regulated to a va'lue between 4.0 and 4.5, iron being oxidised to the ferric state. By decantation and/or flltration, one separates a zinc sulfate solution which is very poor in iron, and a primary residue of undissolved solid . . ..
particles containing in particular almost all iron, silica, lead and silver, which were comprised in the ore used, this residue also possibly'~containing a large portion'of zinc for- - ~-mlng part'of the ore'initially. -In some known processes for traating zinc ores which are relatively rich in iron, for example in processes such as described in Austrian patent 279,188 and US patent 3,434,?98, this primary residue is again hot attacked with a . . .
sulfuric acid excess. From the so obtained slurry, a secondary residue which is rich in lead and silver is separated by decan-tation ancl/or filtration. The rcmainlrlg soIution compr'ises, in addition to the zinc sulfate corresponding to most of the zinc contalned in the primary residue and 1n the sulfuric acid used, mainly sulfuric acid in excess and substantially the whole iron -' .
~: . . .
. ' ' . .
i . .
3 -- .
essentially in the ferric state - which was comprised in the.
ore used. The solution is then hot treated with a metered and progressively added amount either of roasted zinc ore or zinc oxides or hydroxides, so as to bring pH of the li~uid to a value between 1 and 3, which causes iron in solution to be precipi-tated as basic sulfate, for example H30.Fe3.(SO4)2,(OH)6, jarrosite hydronium, or Fe4(SO4),(OH)10), glockerite, and, as far as K+, Na or NH4 ions are present, as jarosites :
3 4 2 )6 NaFe3(S4)2(H)6 NH4Fe3(so4) (OH) J
In the most recent industrial practice, iron is more particularly precipitated as mixed hydronium and.sodium.or ammonium jarosite (Nax.(oH3)l-x-Fe3-(so4)2~ ( 6 4 x (OH3)1 x.Fe3.(SO4)2.(0H)6 where O ~ x ~1), by maintaining concentration of Na or NH4 ions at an optimum value by adding metered amounts of suitable reactants.
; The so obtained precipitate of basic iron sulfates is separated from the.remaining solution by decantation and/or flltration and solubles materials are removed therefrom by water ~i wa~hing, leaving a tertiary residue containing almost all iron :~ and arsenic of the used zinciferous materials, as wall as other .; - .
elements, such as lead and-silica, and also some residual zinc ~ - .
~ amount.
:, . .
A typical analysis of the cake which is discharged after filtration of this latter ferriferous residue is for .
example as follows :
Humidity (on wet cake basis) : about 45 %
Elements (on dry residue basis) :
Fe : 2~ to 32% Pb : 0.5 to 1.5%
S(sulfate) : 10 to 13% Zn : 0.5 to 2 %
: Na : 3 to 4% Cd.: 0.01%
. . As : 0.2 to 0.5~ Cu : 0.01%
.
:. . .
- 4 ~ 1079496 Asimilar presently used process precipitates iron from the same impure solution of zinc and iron sulfates, mainly as hydrated iron hydroxides and/or oxides, such as goethite FeO.OH, in mixture with varying properties of basic sulfates, jarosites and other iron compounds. This precipitation is obtai-ned by means of a reduction of the iron to ferrous state, for example by addition of sulfurized ore or crude blende and then a neutralization by addition of zinc oxide, for example roasted blende, in combination with an oxidation by air or gaseous oxygen blowing.
- This precipitate is also separated, as in the case of the jarosite-based precipitate such as hereinabove described, by decantation and/or filtration, then substantially stripped of its soluble materials by water washing, leaving a tertiary residue having quite similar properties to those of the above jarosite-based tertiary residue, and having for example the approxlmate following analysis.
Humidity (on wet cake) : 4 to 4.5% by weight.
Elements (on dry residue : % by weight.
Fe :38 to 42% Cu :0.01 to o.i%
S(total) :2.5 to 5% As . ? to 0.6%
S(sulfate):2 to 4% SiO2; ~ :1.5 to 2.5%
Pb :0.5 to 2.5~ A123 :1 to 3%
zn :2 to 6~ CaO + MgO :1 to 4%
Cd :0.01 to 0.1%
In the common industrial practice, such tertiary re-sidues are resuspended in water and ~he suspension is drained to a decantation tank in which after solids have set~ed, the super-natant water is taken up in order to be reused for above-mentioned resuspension. The water involved in these operations is thus continuously recycled and is essentially used for hydraulic con-.
.. . .
, - . : :, . .-veying of tertiary ferriferous residue to the decantation and storage tank.
This residue separated from its dilution water is partlcularly difficult to handle, and store. At a 45% humidity, which is the normal mean humidity of the filtration cake, the residue has a semi-fluid consistency as a water-filled clay and it is very difficult or even impossible to handle this residue with usual mechanical devices.
-If the humidity increases, the residue quickly becomes more a~ more liquid and when retained between dikes or barriers, it forms more or less horizontal stratified decan-tation layers. , I by drying the-humidity of these layers substan-tially decresses below 45%, these layers crack as a clay in process of drying-up but the so "dried-up",solid has no consis-tency and under the action of any mechanical strain, compression, abrasion or erosion, it immediately disintegrates as an impalpa-ble dust which is blown off by the least wind. Any pile of such ,~, . . . .
, dried-up residue would be very quickly spreaded by the action of the wind and,of the water which would thln the humidified ~, - material to a flowing state.
s~ In decantation,tanks, deposits stratified in slightly ;
packed layers, which are formed by these residues and remain ; : , permeable, give rise to seepages of liqulds laden with soluble elements that pollute the water-bearing stratum in a non-, impermeable ground.
Thus, the use of decantation tanks does not complete-ly solve the problems of putting these ferriferous residues in ~':1 . . .
stock, and large areas of tanks made impervious, which are `~ necessary to this end generally constitute a not very economical solution.
. . .
, ,:`; , ' ' , . .
-.~ ' ..
- 6 ~ 79496 It is possible to find an use for t~ese residues after having converted them by hydrothermal way or by drying-calcina-tion, into more or less pure iron oxides. There are very exp~nsive treatments which in most cases do not solve the problem because, on the one hand, markets for such iron oxides are not wide enough to absorb large amounts of produced residues and, on the other hand, the so obtained iron oxides also form a material which is quite as difficult to store or warehouse.
Belgian patent 779,613 and the àrticle UTreatment of Iron Residue in the Electrolytic Zinc Process", pp.18-27 in TMS pages n. A73-11 of-The Metallurgical Society of AIME"
(New-York NY 10017, East 47th street) describe the problem of these ferriferous residues with more details.
Belgian patent 779,613 concerns a particular thermal process for treating said residues, this process also having the above-mentioned'drawbacks.
Said article more particularly mentions thermal and hydrothermal treatments and draws'the attention to the various condltions which are necessary in order that said process be commercially and economically appllcable.
-A first condition would be ~ find a 501ution for sto- ' ring said residues of basic iron sulfates. To thls end, an extensive was'hing of the residues before storage thereof has be'en mentioned but this washing, however, does not appear as techni-cally practicable according to said Article.
' Another solution proposed in this Article is to form with these residues a slurry at a pH'higher or equal to 10 by com-bining said washing with a precipitation of soluble metals by addi't~on of excess of lime.
The pH of the slurry sodbtained and so exposed to atmospheric conditions decreases due to the presence of C02 in ., ` , ' .
.
.
~ 7 ~ 1079496 air and in rain-water, which again partially redissolves ini-tially precipitated metals.
In order to somewhat remedy these drawbacks, the above-mentioned Article proposes to create a vegetation on jarosite deposits, which would require very particular cautions against inc]uded toxic products, this Article drawing the attention to these cautions.
In titanium industry, titanium oxide which'is used as basic pigment for manufacturing paints is produced from ores, very often iron-laden (ilmenites), which are solubilized in sul-furic acid. Iron is dissolved with titanium and is by far the ' most important impurity of the soLution. ~t is eliminatedby a crystallization, for example a's mono- or heptahydrate ~errous sulfate, followed by a separation, decantation, filtration or centrifugation, leaving as a solid residue very large amounts (several hundred thousands of tons a year from only one produc-tion plant) of said sulfates which are very much soluble in water and very much laden with crystallization water and im-pregnation solution, these sulfates being left without any possible economical use'tilI now.
Due to the high solubility of said product, it can-not be stored as such in'the open air, due to quick pollution of surrounding grounds. The discharge into the high sea, which is the adopted solution till now, has a chance to be also prohibited nextly.
As a conclusion, sto'ring of these ~esidues suppose~
. , .
problems of occupied space and of water or air pollution, which have no valuable'solution till now.
'The present invention has more particularly for its ` object to propose a simple and economical solution'to this pro-blem.
' . .
To this end, according to the in~ention, said ini-tially free flowing residues comprising at least 55~ of solids are mixed with stabilizing material containing active CaO, in a sufficient amount to form a solid product which is mechanical-ly stable and substantially insenslble to the solubilizing action of water, allowing without pollution risk to store this product as weathering-exposed piles.
Advantageously, by agglomerating said residues by means of a stabilizing material, grains and lumps are produced which consist of a mass which is coated with a hardened protec-tive sheath based on substantially water insoluble reaction pro-ducts of active CaO with at least one of the constituents of said residues.
The invention also concerns the product obtained by carrying out said process, as well as use of this product as embanking material.
Other details and features of the invention will become apparent from the description given hereinafter, by way of a non-limitative example, of se-~eral particular embodiments of the invention.
Figure l shows a schematic block-diagram of a particular embodiment of the process according to the invention.
.. .. . . .
Figure 2 is a schematic and cross-sectional view .
of a lump or g~in obtained by carrying out the invention.
The invention concerns a process allowing to convert into products able to be stored by means of conventional . . .
mechanical means into stable piles which do not present any dis-integration risk or water or air pollution, (1) either free ` flowing residues containing at least 3% by weight of sulfur as sulfates, more paticularly as jarosites or various iron sulfates ` possibly mlxed with iron oxides or hydroxides, particularly as '`''' ' . , ,' ' ' : ' , ~ ' .
- . . . . . - . . . .
goethite, (2) or residues based on iron oxides or hydroxides, ...
such as goethite, having a sulfate sulfur content lower than 3~ by weight, (3) or still ferrous sulfates which are more or lessswollen with their impregnation solution.
These are more particularly either ferriferous tertiary residues, such as issuing from hereinbefore described separation by filtration or solid depositnesulting from decan-tation of these same residues after their hydraulic transfer or ferrous sulfates which are separated when purifying sulfuric titanium solutions.
According to the invention, from said residues which initially are quite free flowing, grains and lumps are produced which are of generally rounded varying forms and have a d.iameter ; ranging from 1 to 20 cm, by mixing with a stabilizing material : . containingjactive CaO, this mixing being carried out so as to restructure said residues into gr~ns and lumps, whlch are coated wlth a hardened protective sheath based on at least one of the :~. substantially water insoluble reaction products of active CaO
with at least one the constituents of said residues, and which .are internally consolidated by a s~eton also.based on at least one of these reaction products.
;.'~ . By one or more physico-chemical reactions,an agglo-meration of these initially powdered or free flowing residues ~` .is obtained into lumps and.grains, each formed of a mass which ? ..
is coated by a hardened protect.ive sheath and which is internally :? consolidated by a ~keleton, said sheath and skeleton being zones of materials where physico-chemical reactions were very.
.~ .
high, while these reactions were low or non-existent in the non-. .hardened or poorly hardened mass! these reactions being for ...example reactions.of sulfate radica]s and~or iron oxides of the .. . .
residues treated with active CaO, said reactions giving rise to ,` ''- ' . ' ' ' .
.
.... . .... . . . . . .
- 1()-107949~
a precipitation of a solid network of gypsum and/or ferro-cal-cium compounds, here conventionally referred to as'Yerro-lime".
Advantageously, said grains and lumps are obtained by an agglomerating treatment consisting of mixing residues with an amount of a stabilizing material containing active CaO, more particularly slaked line or quickline, lime milk or materials contain~ng lime, until hereinabove grains and lumps are obtained.
It is o be noted in this respect that quicklime is substantially more effective than slacked lime, and that the exact dosage value 1s a function of the content in-sulfate sul-fur and~or iron oxide of the residue and of its humidity con- ; .
tent .
- The advantage of.the quicklime resùlts from the fact that it improves the chemical~ stabilization reaction through a substantially more important heat output than in the case of slacked lime.
Advantageously, in the case of ferriferous residues of jarosite, goethite and other residues of precipitation of zinc sulfate solutions, a neutralizing material amount is used which carries into effect from 8 to 16~, preferably from 8 to 12~ by weight of active CaO with respect to the weight of the :, .
~, dry material of the treated residue.
-l . As a matter of fact, it is important to be noted that .~ according to the invention, it is more pa~ticularly aimed to carry out a stabilization reaction of only a portion of the resi-, ~ dues with ætive CaO giving use to gypsum or to said "ferro-lime"
. at the expense of sulfates and iron oxides.
The term "active CaO" in the above material means that portion of CaO taking part in said reactions; in the case of .;
commercial lime for example,the active.CaO content corresponds . ' .
.
''!' `'- - ~ ' '' , '' ' ': : ' - ~ ' '. , . ' ' . I
:: ' ' , . , '. ', ' ' ' . ' ` :.
-ll -1079496 to the total CaO content less CaO content as carbonate and sulfate.
In the application conditions of the invention to hereinabove considered residues of zinc industry, only a por-' tion of iron sulfates and oxides is converted into gypsum and/
or ferro-lime.
In the case of jarosites and other residues of relative "high" (5 to 13%) content in sulfate sulfur, the '-amount of active CaO which is used is generally comprised between 40 and 90~ of the amount which is necessary to convert the whole sulfate sulfur into gypsum.
In the case of goethites and analogues residues which are relatively poor in sulfate sulfur (2 to 3%), the amount of active CaO is generally equal to 100~ of that which is necessary for reaction with the whole sulfate sulfur, plus 10 to 30% of that necessary for reaction with'the whole contained iron oxide.
.. . .
. It is obviously permeable to use CaO amounts higher than those hereinabove indicated; the result of stabilization and consolidation of the lumps and'grains is still increased, -however at the expense of a higher cost.
~' During works having led to the concept of this ' invention, it has been searched to carry out the cristallization ' of gypsum resulting from'the reaction of lime with SO radicals of the treated materials,'and the lime amount has consequently ' been used in proportion of the content of sulfate sulfur.
The amount with respect to the treated dry material ' decreased with this content but more the content in sulfate sulfur decreased, more the ratio added in relation to the necessary amount for complete reaction of sulfate sulfur increa-sed. This corresponds to the purpose aiming to form a sh~eton .~ . .
: . . .
- 12 ~ 1079496 and sheath amount having a high enough mechanical strength.
For ferriferous residues which are poor in sulfur, about 3~ or less, the gypsum amount which can be so produced became insufficient to ensure this strength. Surprisingly, it has then however been found that by increasing the CaO amount well above that corresponding to the reaction with the whole sulfate sulfur, the consolidation and hardening effect became higher and higher, and it has been remarked that at this stage, in addition to gypsum,~one or more lime and iron compounds formed and precipitated similarly to gypsum, in the reaction zones having the best mixing and the best contact between reactants for forming the hardened sheath and skeleton.
On mixing with the material containing active CaO, the reaction medium being relatively poor in water, the intentionally imperfectly distributed CaO only partially reacts in a non-homogeneous way according to scores and zones in the material, and the reactions of calcium sulfation and iron calcification mainly develop on the surface of lumps and grans in ~urse of preparation, where the lime concentration is preci-sely higher.
The reaction products also form gypsum and/or ferro-lime sheathes and skeletons which contain masses of imperfectly reacted product and of unconsumed active CaO, the reactions then , . . . .
further proceeding slowly internally.
Under ~he application conditions according to the ~ . . . .
invention, as soon as physico-chemical reactions are sufficiently developped, the medium pH is higher than 8, above which val~e .
the compounds of zinc, cadmium, iron and other metals, which are then contained in the grains and lumps,are relatively s~ightly water soluble, the solubillties being low enough to effectively slow down any important diffusion of these elements inside the ~,` ' .
, ~
.':'' : . . . - , . . .
- 13 - 1~7949~
aggregated material of the lumps and grains, towards the sur-faces thereof, the formed skeleton and sheath opposing besides an effective barrier to such a migration.
Thus it results from the preceding, that the gene-ral increase of pH resulting from the mixing with lime is sufficient to make the various constituents of said residues, which are confined inside grains and lumps,substantially water 'insaluble.
- The mixture of residues and stabiliæing material containing quicklime , and the agglomeration thereof as ' grains or lumps, such as hereinbefore defined, can be obtained with various apparatus such as- particularly : blenders, granulators, extruders, drum grinders and the like, optionally followed by granulation drums or tables.
The product resulting from this treatment is shaped as grains or lumps which are coated'with hardened surface sheathes, shells or layers of gypsum and/or ferro-lime, and which are consolidated ln their mass by skeletons based on same materials.
, ' According to a more elaborate'and more expensive embodiment of the invention, but ~iving higher results, said . .
'~ ' coated and internally consolidated grains and lumps are subjected .
to'an addit'ional treatment during which said grains and lumps are made more compact through a moisture expu~ion to the surface thereof. Said additional treatment forms a particular compression treatment whlch will be more precisely named compaction treatment hereinafter. Moisture sweating causes a more pronounced reinforcement and hardening of the sheath.
This effect is still reinforced if an additional amount of material containing active CaO is added during said Gompaction treatment.
' ;, . . .
, . .
. ~ .
~.. .
: ?i: ' ' . " ~
- 14 ~ 1 0 79 49 6 This compaction treatment takes advantageously place in a granulator wherein grains and lumps turn over and over while materials containing active CaO and also advantageously other materials allowing to more completely seal the grain and lump surfaces are added,such as for example bentonites, clays, silicas, silicate solutions, ores and the like.
Relating to the moisture content of the residues to be mixed with the stabilizing material, which is an important ' factor, it has been found that favourable results are obtained with moisture contents of 5 to 45%, preferably from 15 to 40%, namely residues containing from 55 to 95% of solides, preferably from 60 to 85%.
As already mentioned before, the initial moisture content of the residue to be traated, obtained after a normal filtration, rangesabout 45% in most cases.
Such a residue is advantageously subjected to a pretreatmenti~ as to reduce moisture down to 40%.
To this end, according to the invention, sald residue is suspended in water, this suspension is filtered and moisture of the so obtained cake is reduced till a level lower than 40% by possibly using in addition to the "normal drainage", mechanical ,: . . .
means such as a pressure on the cakes, or pneumatical means '~
such as air blowing or suction through this cake. ' ' Then, tl-is cake is mlxed as hereinbefore described ' with the stabilizing material containing active'CaO.
~i ~' Although various filters'-able to produce a "very ~' dry" cake may be suitable'to this pretreatment, the filter-press is particularly adapted. The above-~entioned suspension is fil-tered through this filter-press until the filter is packed at the ' maximum with the cake produced, then compressed air is blown through this cake.
.. . .
: ~ ~.- , .
- 15 ~ l 079 49 6 According to the invention, any kind of filter having similar performances may be used, particularly some types of pressure or vacuum filters and inter alia those which are equipped with mechanical compression systems for the cakes.
The filtered liquid is recycled to a decantation tank or to a process step for suspending the tertiary residue.
If the ferriferous tertiary residue, such as issu-ing from this initial filtration, has alre~dy a moisture lower to 40%, this pretreatment of resuspension and second filtration is obvlously unuseful.
Said residues containing less than 40% of moisture, optionally after pretreatment, are mixed with the stabilizing material containi.ng active CaO, preferably at a rate of 60 to 160 kg, preferably 80 to 120 kg of active CaO to 1000 kg of dry material in the residues. .
In particular concerning ferriferous residues essen-.
tially formed of ferrous sulfate, for example heptahydrate, as ~ that which is precipitated and separated in *itanium industry ~ as hereinabove mentioned, said residues are particularly suitable to the stabilizing and aggregating treatment according to the invention. The stro~gheat output of the reactions promotes formation of specially hard and strong grains and lumps and it is genera~y possible to limit to 20 to 50% of the stoichimetrical amount of CaO, such as determined by the following basic reaction:
FeS04 + CaO --~ CaS04 + FeO
Being given the known properties of various iron .~ oxides, the formed and ~r exposed FeO oxidises very quickly, more particularly at the surface of grains and lumps such as . obtained , producing in addition an impervious blackish brown ..
layer of basic iron sulfate which reinforces the gypsum barrier.
of the sheath.
'.~ , ' ~079496 Advantageously, in order to make maximum the effect of used CaO and thus to reduce the amount thereof as much as possible, one provides during the treatment a surface dusting of grains and lumps which are formed or in process to be formed by the stabilizing material, in order to reinforce the effects in surface films by a relative excess of active CaO.
Being given the distinctly crystalline character 7 thereof, residual ferrous sulfates of the titanium industry can be directly treated at the outlet of the drying machine with their usual moisture of 5 to 8~. It is also possible to success-fully treat such very moist residues, up to 45% of moisture.
In the case when lime mil~ is used as stabilizing material, it is obviously necessary to take care that the residue to be treated will be relatively dry so that the total moisture content is not too high and allows to obtain a product which, on the one hand, is mechanically stable and which is, on the other hand, substantially insensible to the solubilizing ~
action of water, so as to allow storing thereof as piles exposed ~ -to weathering agents, without any pollution risk for surrounding ; -areas.
It is to be noted in this connection that, in some cases, the necessary amount of stabilizing material can exceed that which is sufficient to obtain the simple mechanical stabi-lization. This more particularly depends on the distribution of lime with respect to the residue, as it results from the prece-ding.
Following examples give additional details on several particular embodiments of the process according to the invention, ; with reference to Figure 1.
Fxample l Mixed ammonium and hydronium jarosite with a moisture , :: : . . . . - :
- 17 - 10794~6 of 45%, issuing from the outlet of a rocking cell filter l with horizontal filtration surface was resuspended in a vat 2 provi-ded with a stirrer (not shown), with recycled l~quid so as to form a 10% solid suspension, which was pumped to filter-presses 3, the filtered liquid having been returned to the vat 2, as indica-ted by reference numeral 4.
; The feeding to filter-presses 3 was stopped at the ; time when the pressure therein exceeded 5 kg/cm ,which is an indication of the complete filling of the filter w~th formed cakes. At that time, compressed air at 6 kg/cm2 was blown according to the arrow 5 through cakes, in the same sense as the filtration, until the filtrate ~ischarge does no longer show any important flow.
Cakes were then discharged from the filter 3 and sent into the storage hopper 6. Their moisture content was about 38% with respect to the total weight, while the sulur content as sulfate was about 12% on dry material basis.
Said cakes desintegrated in numerous pieces when falling into said hopper. From the latter, pieces were sent to a screw conveyor 7 to a continuous mixer 8 of conventional type, comprising in a double trough, two parallel shafts with lnclined blades rotating in opposite directions and which interpenetrate , constituent parts of the mixer being not shown. At the same time, according to the arrow 9, quicklime containing 92% active CaO
is added at the rate of 80 kg to 1000 kg of residues having a .j . .
38% moisture content.
In this mixer, the cake was divided and mixed with said lime and temperature rose to 30C, following partial ~1 ,ij . .
neutralization of basic iron sulfates.
The mixing time was about l minute.
The material from the mixer was as generally rounded .; ' .. ..
--- -- ., ,' : ` - ' :
- 18 ~ l 07 9 49 6 grains and lumps with a diameter varying from l to 20 cm.
This material was then sto~ed in a pile 10 having a slope of about 45.
Example 2 Mixed ammonium and hydronium jarosite was pretreated in an identical way as in Example l, by resuspending and fil-tration on a filter-press. The so obtained cake had a 36%
moisture content and a sulfur content as su~ate of 12~, on dry material basis.
In mixer 8, commercial hydrated Iime containing 68%
of active CaO was added at a rate of 80 kg of lime to 1000 kg of 36% moisture cake. The mixing duration was of 80 sec. and material temperature rose by 10C from inlet to outlet of the mixer.
The material from mixer was as grains and lumps of sa-~me sizes asin the preceding example, but much less hard with a less crushing strength.
After storage for l to 2 hours, it was howeYer possible to take up these grains and lumps with a mechanical shovel, to discharge them on a truck and to pile them.
Example 3 Same jarosite, pretreated as in both preceding .
examples, was mixed in mixer 8 with commercial quicklime contai-ning 92~ active CaO , at a rate of loO kg of lime to 1000 kg of cake. The latter had a 86% moisture content and comprised 12%
of sulfur as sulfates as dry material.
The mixing duration was of 1 minute and material ~ temperature rose to 40C.
`;~ The material left the mixer as grains and lumps of 1 : to 5 cm in diameter, which were much smaller, harder and having a higher crushing strength. This materiale~lved water and .. , _ . :
.
.~ ~ . . .
.,:
ammoniac vap~urs. It could be piled immediately.
Example 4 Mixed ammonium and hydronium jarosite, identical to that of example 1, was pretreated, then mixed in mixer 8, as in example 2, with a reduced amount of active CaO (that is to say 80 kg of hydrated lime with 68% of active CaO to 1000 kg of dry material in the cake).
The material from mixer 8 was sent to a drum granula-tor (not shown) in which 20 kg of pulverised and dry hydrated lime with 68~ of active CaO was added.
The material left this drum granulator as very dry and quite hard grains of 1 to 10 cm in diameter, having substan-tially rounder shapes.
Grains could be conveyed and piled up immediately.
Example 5 Mixed sodium and hydronium jarosite also containing iron as goethite ~FeO.(OH)7 was pretreated as in example 1 by resuspending and flltration on filter-press. The cake discharged from the latter had a 32% moisture content and its sulfur content as sulfate was 6% on dry material basis.
The material discharged from filter-press was mixed in mixer 8, with 50 kg of quicklime compising 92% of active CaO
to 1000 kg of treated dry material. The mixing duration was 2 ; minutes, during which period the temperature rose to 30C.
The product leaving the mixer was as grains and lumps of 1 to 6 cm in diameter, which were quite dry and hard, and it ~ could be piled up immediately.
: , ;`- Example 6 .
.,~
~ Heptahydrate ferrous sulfate issuing from the tita-~ ,. . .
nium industry and leaving the drying machine contained about 8% of mother-waters. It was mixed in a continuous mixer with _~ .
fine quicklime at a rate of 14 parts by weight of CaO to 100 :, .
parts of sulfate. The products got warm and quickly granulated, forming granules of 1 to 20 mm, which brownished in the cpen air The granules ~ere then dusted with 0.2 parts of CaO in the granu-lator drum. A brownish ferric hydroxide layer formed on the exter-nal surface of the g ains. At the ou~let of the drum, grains were dry and dld not stick together. They were~immediately taken up by a track and piled up.
Example 7 , Residual goethite from electrolytic zinc industry ~nd containing about 40% of total iron and 3.0% of sulfate sulfur (dry material), and leavlng a filter-press as a cake with 40~ of moisture was treated in the continuous mixer of ' Example 1 with fine quicklime in the ratio of 3.5 parts of lime to 100 parts of wet goethite, namely a li~le more than the stoichrometrical amount which is needed to convert the comprised sulfate lnto gypsum. When mixed, the product became warm and .
granulation occurred very imperfectly. The product passed as very heavy sticky lumps ~ the drum where a portion o fine quicklime for coating was added. The coated lumps remained plastic and hardened only progressively, and several hours were'necessary, before it was possible to handle them without rupturing. Such .
process conditions cannot be practical'ly used commercially~due "
~' ' to the time needed to obtaln valuable results.
' In a parallel test, the amount of quickLime added ... . ~ .
~ ~ to the mixer was increased from 3.5 to 8 parts.'In such'a case, '`' the product became warm and granulated quickly. The addition of coating lime was not necessary and the ohtained product was `` immedia~ely transportable. The gra'ins such as obtained sized '` 5 to 50 mm and were very much resistent to crushing. The lime ~ dosage being in excess, the insolubilization of water soluble ,~ , .
materials i9 complete, even inside the grains. This material ' when piled up and subjected to weatherings did not cause dust ,.~, ~ .
,, .
' ' .
.
formation or pollution due to s~lubilized elements.
Figure 2 schematically shows a cross séction of a grain or lump resulting from use of the process according to thls inventi~n. Reference numeral 11 corresponds to internal gy~sum skeleton, 13 designates mass of resi'due and unconsumed CaO, and 12 designates hardened sheath, the latter as well as the skeleton being formed of gypsum and~or ferro-lime essentially.
The product according to the invention is as grains and lumps of dry appearance, in contrast with the slurry form of untreated tertiary residues, and this product can be transported and handled without any particular drawbacks with conventional handling apparatus. This product can also be stored on a storage ' piece of ground as a' pile af large heigh~t, similar to spoil-banks resulting from mining or metallurgical exploitations and on which usual transport and handling utensils with wheels and caterpillars ' can move, particularly on sloping approach arranged in the stored materlal itself. '' The posslb~ity of making high piles allows to cover to this end very reduced ground areas only with respect to areas r'equired for large decantation tanks which have been used for .
storing such residues of hydrometallurgical zinc induetry till now.
.
Moreover, these grains and lumps form a valuable emba~king material, which can be an importa~t opening in many cases.
Residues such as treated according to the invention , ' remarkably behave under atmaspheric conditions, particularly ; under rain. As a matter of fact, lumps and grains of the exter-nal layer of the pile,which are reached by rain-are wettedi '~ without however losing neither their shape nor their strength.
Most o~ rain flows between lumps and grains, mainly on the sides .
.
` .
- 22 - 1079~96 of the pile without deeply entering therein. Under these condi-tions, pile mass retains a little water only, the latter very quickly evaporating after rain, as soon as allowed by the atmos-phere, this evaporation being promoted by the large developped area of grains and lumps.
Washing by rain water flow only acts on the substan-tially waterproofed surface of grains and lumps, while internal mass of the latter is not badly affected. Accordingly, losses of solubilised materlals from residue piles due to rain waters susceptible to be drained into water-bearing stratum are extremely reduced, even insignificant. It results thereform that there are no risks of pollution of this stratum. In this r~spect, it is also to be noted that C02 Present ln the atmosphere has a favourable influence on the stabilization of the grain and lump sheathes by reinforcing them more completely due to a carbonation of active CaO which is in excess in this location.
The process according to the invention thus converts substantially non-storable, non-free flowing, powdered, slurried and muddy ferriferous residues, which are air and water pollution sources, lnto hard, non-stic~y grains and lumps which are of suitable mechanical strength and physical properties~j~to ..
' ~ ' allow stable piles of large height to be formed, by means of ' con~entional handling means; these piles may be exposed to - weatherings without any pollution or spreading risk, for example . . . . .
`' by sliding, running or 10wing.
... i . .
Although the process according to the invention was originally studied for ferriferous residues such as produced by iron precipitation from mixed solutions of iron and zinc sulfate ' in zinc hydrometallurgy and althou'gh this process was then ,. . . . . .
`~ ' successfully'applied on f~rrous sulfate residues, it is quite ~ obvious that this' invention can also be applied on other ferri-... .
. ~ , .
: .
.. . .
. . . - . .. .. . .
ferous residues, and other nletal residues containiing in general iron sulfates, various iron oxides and hydroxides, or compounds of other metals having similar properties with respect to reactiOn with lime, all said residues resulting from any indus-try, namely from zinc or any other industry.
It also appears as being evident that lime, as stabilizing element, may be replaced by metal oxides having si-milar properties, such as barium, strontium, and the like.
. With respect to MgO which generally is present with active CaO in numerous stabilizing materials, it does not.
produce any insoIuble material but however it takes part in the neutralising action of lime by precipitating iron hydroxides for example, which contrlbute to the waterproofing of the pro- :
tective sheath, particularly in the case of jarosite and goethite, so fixing polluting metals, as insoluble compounds by increase of the medium pH.
, ~ . , , . ' , ~
r, ! - - ~ ` ~
.
i`. .
.
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..
, . .
. . . . . .
... . - . . ~ . .
`- . .
In the known technique for preparing pure zinc sulfate soluti'ons,for example formed for the purpose of pro-ducing zinc by electrolysis, zinc ore, for example directly oxidised ores or ores sulfurized after roasting, is generally attacked under oxidising conditions by sulfuric acid in such a metered amount that, due to some ore excess, pH of the resulting solution is regulated to a va'lue between 4.0 and 4.5, iron being oxidised to the ferric state. By decantation and/or flltration, one separates a zinc sulfate solution which is very poor in iron, and a primary residue of undissolved solid . . ..
particles containing in particular almost all iron, silica, lead and silver, which were comprised in the ore used, this residue also possibly'~containing a large portion'of zinc for- - ~-mlng part'of the ore'initially. -In some known processes for traating zinc ores which are relatively rich in iron, for example in processes such as described in Austrian patent 279,188 and US patent 3,434,?98, this primary residue is again hot attacked with a . . .
sulfuric acid excess. From the so obtained slurry, a secondary residue which is rich in lead and silver is separated by decan-tation ancl/or filtration. The rcmainlrlg soIution compr'ises, in addition to the zinc sulfate corresponding to most of the zinc contalned in the primary residue and 1n the sulfuric acid used, mainly sulfuric acid in excess and substantially the whole iron -' .
~: . . .
. ' ' . .
i . .
3 -- .
essentially in the ferric state - which was comprised in the.
ore used. The solution is then hot treated with a metered and progressively added amount either of roasted zinc ore or zinc oxides or hydroxides, so as to bring pH of the li~uid to a value between 1 and 3, which causes iron in solution to be precipi-tated as basic sulfate, for example H30.Fe3.(SO4)2,(OH)6, jarrosite hydronium, or Fe4(SO4),(OH)10), glockerite, and, as far as K+, Na or NH4 ions are present, as jarosites :
3 4 2 )6 NaFe3(S4)2(H)6 NH4Fe3(so4) (OH) J
In the most recent industrial practice, iron is more particularly precipitated as mixed hydronium and.sodium.or ammonium jarosite (Nax.(oH3)l-x-Fe3-(so4)2~ ( 6 4 x (OH3)1 x.Fe3.(SO4)2.(0H)6 where O ~ x ~1), by maintaining concentration of Na or NH4 ions at an optimum value by adding metered amounts of suitable reactants.
; The so obtained precipitate of basic iron sulfates is separated from the.remaining solution by decantation and/or flltration and solubles materials are removed therefrom by water ~i wa~hing, leaving a tertiary residue containing almost all iron :~ and arsenic of the used zinciferous materials, as wall as other .; - .
elements, such as lead and-silica, and also some residual zinc ~ - .
~ amount.
:, . .
A typical analysis of the cake which is discharged after filtration of this latter ferriferous residue is for .
example as follows :
Humidity (on wet cake basis) : about 45 %
Elements (on dry residue basis) :
Fe : 2~ to 32% Pb : 0.5 to 1.5%
S(sulfate) : 10 to 13% Zn : 0.5 to 2 %
: Na : 3 to 4% Cd.: 0.01%
. . As : 0.2 to 0.5~ Cu : 0.01%
.
:. . .
- 4 ~ 1079496 Asimilar presently used process precipitates iron from the same impure solution of zinc and iron sulfates, mainly as hydrated iron hydroxides and/or oxides, such as goethite FeO.OH, in mixture with varying properties of basic sulfates, jarosites and other iron compounds. This precipitation is obtai-ned by means of a reduction of the iron to ferrous state, for example by addition of sulfurized ore or crude blende and then a neutralization by addition of zinc oxide, for example roasted blende, in combination with an oxidation by air or gaseous oxygen blowing.
- This precipitate is also separated, as in the case of the jarosite-based precipitate such as hereinabove described, by decantation and/or filtration, then substantially stripped of its soluble materials by water washing, leaving a tertiary residue having quite similar properties to those of the above jarosite-based tertiary residue, and having for example the approxlmate following analysis.
Humidity (on wet cake) : 4 to 4.5% by weight.
Elements (on dry residue : % by weight.
Fe :38 to 42% Cu :0.01 to o.i%
S(total) :2.5 to 5% As . ? to 0.6%
S(sulfate):2 to 4% SiO2; ~ :1.5 to 2.5%
Pb :0.5 to 2.5~ A123 :1 to 3%
zn :2 to 6~ CaO + MgO :1 to 4%
Cd :0.01 to 0.1%
In the common industrial practice, such tertiary re-sidues are resuspended in water and ~he suspension is drained to a decantation tank in which after solids have set~ed, the super-natant water is taken up in order to be reused for above-mentioned resuspension. The water involved in these operations is thus continuously recycled and is essentially used for hydraulic con-.
.. . .
, - . : :, . .-veying of tertiary ferriferous residue to the decantation and storage tank.
This residue separated from its dilution water is partlcularly difficult to handle, and store. At a 45% humidity, which is the normal mean humidity of the filtration cake, the residue has a semi-fluid consistency as a water-filled clay and it is very difficult or even impossible to handle this residue with usual mechanical devices.
-If the humidity increases, the residue quickly becomes more a~ more liquid and when retained between dikes or barriers, it forms more or less horizontal stratified decan-tation layers. , I by drying the-humidity of these layers substan-tially decresses below 45%, these layers crack as a clay in process of drying-up but the so "dried-up",solid has no consis-tency and under the action of any mechanical strain, compression, abrasion or erosion, it immediately disintegrates as an impalpa-ble dust which is blown off by the least wind. Any pile of such ,~, . . . .
, dried-up residue would be very quickly spreaded by the action of the wind and,of the water which would thln the humidified ~, - material to a flowing state.
s~ In decantation,tanks, deposits stratified in slightly ;
packed layers, which are formed by these residues and remain ; : , permeable, give rise to seepages of liqulds laden with soluble elements that pollute the water-bearing stratum in a non-, impermeable ground.
Thus, the use of decantation tanks does not complete-ly solve the problems of putting these ferriferous residues in ~':1 . . .
stock, and large areas of tanks made impervious, which are `~ necessary to this end generally constitute a not very economical solution.
. . .
, ,:`; , ' ' , . .
-.~ ' ..
- 6 ~ 79496 It is possible to find an use for t~ese residues after having converted them by hydrothermal way or by drying-calcina-tion, into more or less pure iron oxides. There are very exp~nsive treatments which in most cases do not solve the problem because, on the one hand, markets for such iron oxides are not wide enough to absorb large amounts of produced residues and, on the other hand, the so obtained iron oxides also form a material which is quite as difficult to store or warehouse.
Belgian patent 779,613 and the àrticle UTreatment of Iron Residue in the Electrolytic Zinc Process", pp.18-27 in TMS pages n. A73-11 of-The Metallurgical Society of AIME"
(New-York NY 10017, East 47th street) describe the problem of these ferriferous residues with more details.
Belgian patent 779,613 concerns a particular thermal process for treating said residues, this process also having the above-mentioned'drawbacks.
Said article more particularly mentions thermal and hydrothermal treatments and draws'the attention to the various condltions which are necessary in order that said process be commercially and economically appllcable.
-A first condition would be ~ find a 501ution for sto- ' ring said residues of basic iron sulfates. To thls end, an extensive was'hing of the residues before storage thereof has be'en mentioned but this washing, however, does not appear as techni-cally practicable according to said Article.
' Another solution proposed in this Article is to form with these residues a slurry at a pH'higher or equal to 10 by com-bining said washing with a precipitation of soluble metals by addi't~on of excess of lime.
The pH of the slurry sodbtained and so exposed to atmospheric conditions decreases due to the presence of C02 in ., ` , ' .
.
.
~ 7 ~ 1079496 air and in rain-water, which again partially redissolves ini-tially precipitated metals.
In order to somewhat remedy these drawbacks, the above-mentioned Article proposes to create a vegetation on jarosite deposits, which would require very particular cautions against inc]uded toxic products, this Article drawing the attention to these cautions.
In titanium industry, titanium oxide which'is used as basic pigment for manufacturing paints is produced from ores, very often iron-laden (ilmenites), which are solubilized in sul-furic acid. Iron is dissolved with titanium and is by far the ' most important impurity of the soLution. ~t is eliminatedby a crystallization, for example a's mono- or heptahydrate ~errous sulfate, followed by a separation, decantation, filtration or centrifugation, leaving as a solid residue very large amounts (several hundred thousands of tons a year from only one produc-tion plant) of said sulfates which are very much soluble in water and very much laden with crystallization water and im-pregnation solution, these sulfates being left without any possible economical use'tilI now.
Due to the high solubility of said product, it can-not be stored as such in'the open air, due to quick pollution of surrounding grounds. The discharge into the high sea, which is the adopted solution till now, has a chance to be also prohibited nextly.
As a conclusion, sto'ring of these ~esidues suppose~
. , .
problems of occupied space and of water or air pollution, which have no valuable'solution till now.
'The present invention has more particularly for its ` object to propose a simple and economical solution'to this pro-blem.
' . .
To this end, according to the in~ention, said ini-tially free flowing residues comprising at least 55~ of solids are mixed with stabilizing material containing active CaO, in a sufficient amount to form a solid product which is mechanical-ly stable and substantially insenslble to the solubilizing action of water, allowing without pollution risk to store this product as weathering-exposed piles.
Advantageously, by agglomerating said residues by means of a stabilizing material, grains and lumps are produced which consist of a mass which is coated with a hardened protec-tive sheath based on substantially water insoluble reaction pro-ducts of active CaO with at least one of the constituents of said residues.
The invention also concerns the product obtained by carrying out said process, as well as use of this product as embanking material.
Other details and features of the invention will become apparent from the description given hereinafter, by way of a non-limitative example, of se-~eral particular embodiments of the invention.
Figure l shows a schematic block-diagram of a particular embodiment of the process according to the invention.
.. .. . . .
Figure 2 is a schematic and cross-sectional view .
of a lump or g~in obtained by carrying out the invention.
The invention concerns a process allowing to convert into products able to be stored by means of conventional . . .
mechanical means into stable piles which do not present any dis-integration risk or water or air pollution, (1) either free ` flowing residues containing at least 3% by weight of sulfur as sulfates, more paticularly as jarosites or various iron sulfates ` possibly mlxed with iron oxides or hydroxides, particularly as '`''' ' . , ,' ' ' : ' , ~ ' .
- . . . . . - . . . .
goethite, (2) or residues based on iron oxides or hydroxides, ...
such as goethite, having a sulfate sulfur content lower than 3~ by weight, (3) or still ferrous sulfates which are more or lessswollen with their impregnation solution.
These are more particularly either ferriferous tertiary residues, such as issuing from hereinbefore described separation by filtration or solid depositnesulting from decan-tation of these same residues after their hydraulic transfer or ferrous sulfates which are separated when purifying sulfuric titanium solutions.
According to the invention, from said residues which initially are quite free flowing, grains and lumps are produced which are of generally rounded varying forms and have a d.iameter ; ranging from 1 to 20 cm, by mixing with a stabilizing material : . containingjactive CaO, this mixing being carried out so as to restructure said residues into gr~ns and lumps, whlch are coated wlth a hardened protective sheath based on at least one of the :~. substantially water insoluble reaction products of active CaO
with at least one the constituents of said residues, and which .are internally consolidated by a s~eton also.based on at least one of these reaction products.
;.'~ . By one or more physico-chemical reactions,an agglo-meration of these initially powdered or free flowing residues ~` .is obtained into lumps and.grains, each formed of a mass which ? ..
is coated by a hardened protect.ive sheath and which is internally :? consolidated by a ~keleton, said sheath and skeleton being zones of materials where physico-chemical reactions were very.
.~ .
high, while these reactions were low or non-existent in the non-. .hardened or poorly hardened mass! these reactions being for ...example reactions.of sulfate radica]s and~or iron oxides of the .. . .
residues treated with active CaO, said reactions giving rise to ,` ''- ' . ' ' ' .
.
.... . .... . . . . . .
- 1()-107949~
a precipitation of a solid network of gypsum and/or ferro-cal-cium compounds, here conventionally referred to as'Yerro-lime".
Advantageously, said grains and lumps are obtained by an agglomerating treatment consisting of mixing residues with an amount of a stabilizing material containing active CaO, more particularly slaked line or quickline, lime milk or materials contain~ng lime, until hereinabove grains and lumps are obtained.
It is o be noted in this respect that quicklime is substantially more effective than slacked lime, and that the exact dosage value 1s a function of the content in-sulfate sul-fur and~or iron oxide of the residue and of its humidity con- ; .
tent .
- The advantage of.the quicklime resùlts from the fact that it improves the chemical~ stabilization reaction through a substantially more important heat output than in the case of slacked lime.
Advantageously, in the case of ferriferous residues of jarosite, goethite and other residues of precipitation of zinc sulfate solutions, a neutralizing material amount is used which carries into effect from 8 to 16~, preferably from 8 to 12~ by weight of active CaO with respect to the weight of the :, .
~, dry material of the treated residue.
-l . As a matter of fact, it is important to be noted that .~ according to the invention, it is more pa~ticularly aimed to carry out a stabilization reaction of only a portion of the resi-, ~ dues with ætive CaO giving use to gypsum or to said "ferro-lime"
. at the expense of sulfates and iron oxides.
The term "active CaO" in the above material means that portion of CaO taking part in said reactions; in the case of .;
commercial lime for example,the active.CaO content corresponds . ' .
.
''!' `'- - ~ ' '' , '' ' ': : ' - ~ ' '. , . ' ' . I
:: ' ' , . , '. ', ' ' ' . ' ` :.
-ll -1079496 to the total CaO content less CaO content as carbonate and sulfate.
In the application conditions of the invention to hereinabove considered residues of zinc industry, only a por-' tion of iron sulfates and oxides is converted into gypsum and/
or ferro-lime.
In the case of jarosites and other residues of relative "high" (5 to 13%) content in sulfate sulfur, the '-amount of active CaO which is used is generally comprised between 40 and 90~ of the amount which is necessary to convert the whole sulfate sulfur into gypsum.
In the case of goethites and analogues residues which are relatively poor in sulfate sulfur (2 to 3%), the amount of active CaO is generally equal to 100~ of that which is necessary for reaction with the whole sulfate sulfur, plus 10 to 30% of that necessary for reaction with'the whole contained iron oxide.
.. . .
. It is obviously permeable to use CaO amounts higher than those hereinabove indicated; the result of stabilization and consolidation of the lumps and'grains is still increased, -however at the expense of a higher cost.
~' During works having led to the concept of this ' invention, it has been searched to carry out the cristallization ' of gypsum resulting from'the reaction of lime with SO radicals of the treated materials,'and the lime amount has consequently ' been used in proportion of the content of sulfate sulfur.
The amount with respect to the treated dry material ' decreased with this content but more the content in sulfate sulfur decreased, more the ratio added in relation to the necessary amount for complete reaction of sulfate sulfur increa-sed. This corresponds to the purpose aiming to form a sh~eton .~ . .
: . . .
- 12 ~ 1079496 and sheath amount having a high enough mechanical strength.
For ferriferous residues which are poor in sulfur, about 3~ or less, the gypsum amount which can be so produced became insufficient to ensure this strength. Surprisingly, it has then however been found that by increasing the CaO amount well above that corresponding to the reaction with the whole sulfate sulfur, the consolidation and hardening effect became higher and higher, and it has been remarked that at this stage, in addition to gypsum,~one or more lime and iron compounds formed and precipitated similarly to gypsum, in the reaction zones having the best mixing and the best contact between reactants for forming the hardened sheath and skeleton.
On mixing with the material containing active CaO, the reaction medium being relatively poor in water, the intentionally imperfectly distributed CaO only partially reacts in a non-homogeneous way according to scores and zones in the material, and the reactions of calcium sulfation and iron calcification mainly develop on the surface of lumps and grans in ~urse of preparation, where the lime concentration is preci-sely higher.
The reaction products also form gypsum and/or ferro-lime sheathes and skeletons which contain masses of imperfectly reacted product and of unconsumed active CaO, the reactions then , . . . .
further proceeding slowly internally.
Under ~he application conditions according to the ~ . . . .
invention, as soon as physico-chemical reactions are sufficiently developped, the medium pH is higher than 8, above which val~e .
the compounds of zinc, cadmium, iron and other metals, which are then contained in the grains and lumps,are relatively s~ightly water soluble, the solubillties being low enough to effectively slow down any important diffusion of these elements inside the ~,` ' .
, ~
.':'' : . . . - , . . .
- 13 - 1~7949~
aggregated material of the lumps and grains, towards the sur-faces thereof, the formed skeleton and sheath opposing besides an effective barrier to such a migration.
Thus it results from the preceding, that the gene-ral increase of pH resulting from the mixing with lime is sufficient to make the various constituents of said residues, which are confined inside grains and lumps,substantially water 'insaluble.
- The mixture of residues and stabiliæing material containing quicklime , and the agglomeration thereof as ' grains or lumps, such as hereinbefore defined, can be obtained with various apparatus such as- particularly : blenders, granulators, extruders, drum grinders and the like, optionally followed by granulation drums or tables.
The product resulting from this treatment is shaped as grains or lumps which are coated'with hardened surface sheathes, shells or layers of gypsum and/or ferro-lime, and which are consolidated ln their mass by skeletons based on same materials.
, ' According to a more elaborate'and more expensive embodiment of the invention, but ~iving higher results, said . .
'~ ' coated and internally consolidated grains and lumps are subjected .
to'an addit'ional treatment during which said grains and lumps are made more compact through a moisture expu~ion to the surface thereof. Said additional treatment forms a particular compression treatment whlch will be more precisely named compaction treatment hereinafter. Moisture sweating causes a more pronounced reinforcement and hardening of the sheath.
This effect is still reinforced if an additional amount of material containing active CaO is added during said Gompaction treatment.
' ;, . . .
, . .
. ~ .
~.. .
: ?i: ' ' . " ~
- 14 ~ 1 0 79 49 6 This compaction treatment takes advantageously place in a granulator wherein grains and lumps turn over and over while materials containing active CaO and also advantageously other materials allowing to more completely seal the grain and lump surfaces are added,such as for example bentonites, clays, silicas, silicate solutions, ores and the like.
Relating to the moisture content of the residues to be mixed with the stabilizing material, which is an important ' factor, it has been found that favourable results are obtained with moisture contents of 5 to 45%, preferably from 15 to 40%, namely residues containing from 55 to 95% of solides, preferably from 60 to 85%.
As already mentioned before, the initial moisture content of the residue to be traated, obtained after a normal filtration, rangesabout 45% in most cases.
Such a residue is advantageously subjected to a pretreatmenti~ as to reduce moisture down to 40%.
To this end, according to the invention, sald residue is suspended in water, this suspension is filtered and moisture of the so obtained cake is reduced till a level lower than 40% by possibly using in addition to the "normal drainage", mechanical ,: . . .
means such as a pressure on the cakes, or pneumatical means '~
such as air blowing or suction through this cake. ' ' Then, tl-is cake is mlxed as hereinbefore described ' with the stabilizing material containing active'CaO.
~i ~' Although various filters'-able to produce a "very ~' dry" cake may be suitable'to this pretreatment, the filter-press is particularly adapted. The above-~entioned suspension is fil-tered through this filter-press until the filter is packed at the ' maximum with the cake produced, then compressed air is blown through this cake.
.. . .
: ~ ~.- , .
- 15 ~ l 079 49 6 According to the invention, any kind of filter having similar performances may be used, particularly some types of pressure or vacuum filters and inter alia those which are equipped with mechanical compression systems for the cakes.
The filtered liquid is recycled to a decantation tank or to a process step for suspending the tertiary residue.
If the ferriferous tertiary residue, such as issu-ing from this initial filtration, has alre~dy a moisture lower to 40%, this pretreatment of resuspension and second filtration is obvlously unuseful.
Said residues containing less than 40% of moisture, optionally after pretreatment, are mixed with the stabilizing material containi.ng active CaO, preferably at a rate of 60 to 160 kg, preferably 80 to 120 kg of active CaO to 1000 kg of dry material in the residues. .
In particular concerning ferriferous residues essen-.
tially formed of ferrous sulfate, for example heptahydrate, as ~ that which is precipitated and separated in *itanium industry ~ as hereinabove mentioned, said residues are particularly suitable to the stabilizing and aggregating treatment according to the invention. The stro~gheat output of the reactions promotes formation of specially hard and strong grains and lumps and it is genera~y possible to limit to 20 to 50% of the stoichimetrical amount of CaO, such as determined by the following basic reaction:
FeS04 + CaO --~ CaS04 + FeO
Being given the known properties of various iron .~ oxides, the formed and ~r exposed FeO oxidises very quickly, more particularly at the surface of grains and lumps such as . obtained , producing in addition an impervious blackish brown ..
layer of basic iron sulfate which reinforces the gypsum barrier.
of the sheath.
'.~ , ' ~079496 Advantageously, in order to make maximum the effect of used CaO and thus to reduce the amount thereof as much as possible, one provides during the treatment a surface dusting of grains and lumps which are formed or in process to be formed by the stabilizing material, in order to reinforce the effects in surface films by a relative excess of active CaO.
Being given the distinctly crystalline character 7 thereof, residual ferrous sulfates of the titanium industry can be directly treated at the outlet of the drying machine with their usual moisture of 5 to 8~. It is also possible to success-fully treat such very moist residues, up to 45% of moisture.
In the case when lime mil~ is used as stabilizing material, it is obviously necessary to take care that the residue to be treated will be relatively dry so that the total moisture content is not too high and allows to obtain a product which, on the one hand, is mechanically stable and which is, on the other hand, substantially insensible to the solubilizing ~
action of water, so as to allow storing thereof as piles exposed ~ -to weathering agents, without any pollution risk for surrounding ; -areas.
It is to be noted in this connection that, in some cases, the necessary amount of stabilizing material can exceed that which is sufficient to obtain the simple mechanical stabi-lization. This more particularly depends on the distribution of lime with respect to the residue, as it results from the prece-ding.
Following examples give additional details on several particular embodiments of the process according to the invention, ; with reference to Figure 1.
Fxample l Mixed ammonium and hydronium jarosite with a moisture , :: : . . . . - :
- 17 - 10794~6 of 45%, issuing from the outlet of a rocking cell filter l with horizontal filtration surface was resuspended in a vat 2 provi-ded with a stirrer (not shown), with recycled l~quid so as to form a 10% solid suspension, which was pumped to filter-presses 3, the filtered liquid having been returned to the vat 2, as indica-ted by reference numeral 4.
; The feeding to filter-presses 3 was stopped at the ; time when the pressure therein exceeded 5 kg/cm ,which is an indication of the complete filling of the filter w~th formed cakes. At that time, compressed air at 6 kg/cm2 was blown according to the arrow 5 through cakes, in the same sense as the filtration, until the filtrate ~ischarge does no longer show any important flow.
Cakes were then discharged from the filter 3 and sent into the storage hopper 6. Their moisture content was about 38% with respect to the total weight, while the sulur content as sulfate was about 12% on dry material basis.
Said cakes desintegrated in numerous pieces when falling into said hopper. From the latter, pieces were sent to a screw conveyor 7 to a continuous mixer 8 of conventional type, comprising in a double trough, two parallel shafts with lnclined blades rotating in opposite directions and which interpenetrate , constituent parts of the mixer being not shown. At the same time, according to the arrow 9, quicklime containing 92% active CaO
is added at the rate of 80 kg to 1000 kg of residues having a .j . .
38% moisture content.
In this mixer, the cake was divided and mixed with said lime and temperature rose to 30C, following partial ~1 ,ij . .
neutralization of basic iron sulfates.
The mixing time was about l minute.
The material from the mixer was as generally rounded .; ' .. ..
--- -- ., ,' : ` - ' :
- 18 ~ l 07 9 49 6 grains and lumps with a diameter varying from l to 20 cm.
This material was then sto~ed in a pile 10 having a slope of about 45.
Example 2 Mixed ammonium and hydronium jarosite was pretreated in an identical way as in Example l, by resuspending and fil-tration on a filter-press. The so obtained cake had a 36%
moisture content and a sulfur content as su~ate of 12~, on dry material basis.
In mixer 8, commercial hydrated Iime containing 68%
of active CaO was added at a rate of 80 kg of lime to 1000 kg of 36% moisture cake. The mixing duration was of 80 sec. and material temperature rose by 10C from inlet to outlet of the mixer.
The material from mixer was as grains and lumps of sa-~me sizes asin the preceding example, but much less hard with a less crushing strength.
After storage for l to 2 hours, it was howeYer possible to take up these grains and lumps with a mechanical shovel, to discharge them on a truck and to pile them.
Example 3 Same jarosite, pretreated as in both preceding .
examples, was mixed in mixer 8 with commercial quicklime contai-ning 92~ active CaO , at a rate of loO kg of lime to 1000 kg of cake. The latter had a 86% moisture content and comprised 12%
of sulfur as sulfates as dry material.
The mixing duration was of 1 minute and material ~ temperature rose to 40C.
`;~ The material left the mixer as grains and lumps of 1 : to 5 cm in diameter, which were much smaller, harder and having a higher crushing strength. This materiale~lved water and .. , _ . :
.
.~ ~ . . .
.,:
ammoniac vap~urs. It could be piled immediately.
Example 4 Mixed ammonium and hydronium jarosite, identical to that of example 1, was pretreated, then mixed in mixer 8, as in example 2, with a reduced amount of active CaO (that is to say 80 kg of hydrated lime with 68% of active CaO to 1000 kg of dry material in the cake).
The material from mixer 8 was sent to a drum granula-tor (not shown) in which 20 kg of pulverised and dry hydrated lime with 68~ of active CaO was added.
The material left this drum granulator as very dry and quite hard grains of 1 to 10 cm in diameter, having substan-tially rounder shapes.
Grains could be conveyed and piled up immediately.
Example 5 Mixed sodium and hydronium jarosite also containing iron as goethite ~FeO.(OH)7 was pretreated as in example 1 by resuspending and flltration on filter-press. The cake discharged from the latter had a 32% moisture content and its sulfur content as sulfate was 6% on dry material basis.
The material discharged from filter-press was mixed in mixer 8, with 50 kg of quicklime compising 92% of active CaO
to 1000 kg of treated dry material. The mixing duration was 2 ; minutes, during which period the temperature rose to 30C.
The product leaving the mixer was as grains and lumps of 1 to 6 cm in diameter, which were quite dry and hard, and it ~ could be piled up immediately.
: , ;`- Example 6 .
.,~
~ Heptahydrate ferrous sulfate issuing from the tita-~ ,. . .
nium industry and leaving the drying machine contained about 8% of mother-waters. It was mixed in a continuous mixer with _~ .
fine quicklime at a rate of 14 parts by weight of CaO to 100 :, .
parts of sulfate. The products got warm and quickly granulated, forming granules of 1 to 20 mm, which brownished in the cpen air The granules ~ere then dusted with 0.2 parts of CaO in the granu-lator drum. A brownish ferric hydroxide layer formed on the exter-nal surface of the g ains. At the ou~let of the drum, grains were dry and dld not stick together. They were~immediately taken up by a track and piled up.
Example 7 , Residual goethite from electrolytic zinc industry ~nd containing about 40% of total iron and 3.0% of sulfate sulfur (dry material), and leavlng a filter-press as a cake with 40~ of moisture was treated in the continuous mixer of ' Example 1 with fine quicklime in the ratio of 3.5 parts of lime to 100 parts of wet goethite, namely a li~le more than the stoichrometrical amount which is needed to convert the comprised sulfate lnto gypsum. When mixed, the product became warm and .
granulation occurred very imperfectly. The product passed as very heavy sticky lumps ~ the drum where a portion o fine quicklime for coating was added. The coated lumps remained plastic and hardened only progressively, and several hours were'necessary, before it was possible to handle them without rupturing. Such .
process conditions cannot be practical'ly used commercially~due "
~' ' to the time needed to obtaln valuable results.
' In a parallel test, the amount of quickLime added ... . ~ .
~ ~ to the mixer was increased from 3.5 to 8 parts.'In such'a case, '`' the product became warm and granulated quickly. The addition of coating lime was not necessary and the ohtained product was `` immedia~ely transportable. The gra'ins such as obtained sized '` 5 to 50 mm and were very much resistent to crushing. The lime ~ dosage being in excess, the insolubilization of water soluble ,~ , .
materials i9 complete, even inside the grains. This material ' when piled up and subjected to weatherings did not cause dust ,.~, ~ .
,, .
' ' .
.
formation or pollution due to s~lubilized elements.
Figure 2 schematically shows a cross séction of a grain or lump resulting from use of the process according to thls inventi~n. Reference numeral 11 corresponds to internal gy~sum skeleton, 13 designates mass of resi'due and unconsumed CaO, and 12 designates hardened sheath, the latter as well as the skeleton being formed of gypsum and~or ferro-lime essentially.
The product according to the invention is as grains and lumps of dry appearance, in contrast with the slurry form of untreated tertiary residues, and this product can be transported and handled without any particular drawbacks with conventional handling apparatus. This product can also be stored on a storage ' piece of ground as a' pile af large heigh~t, similar to spoil-banks resulting from mining or metallurgical exploitations and on which usual transport and handling utensils with wheels and caterpillars ' can move, particularly on sloping approach arranged in the stored materlal itself. '' The posslb~ity of making high piles allows to cover to this end very reduced ground areas only with respect to areas r'equired for large decantation tanks which have been used for .
storing such residues of hydrometallurgical zinc induetry till now.
.
Moreover, these grains and lumps form a valuable emba~king material, which can be an importa~t opening in many cases.
Residues such as treated according to the invention , ' remarkably behave under atmaspheric conditions, particularly ; under rain. As a matter of fact, lumps and grains of the exter-nal layer of the pile,which are reached by rain-are wettedi '~ without however losing neither their shape nor their strength.
Most o~ rain flows between lumps and grains, mainly on the sides .
.
` .
- 22 - 1079~96 of the pile without deeply entering therein. Under these condi-tions, pile mass retains a little water only, the latter very quickly evaporating after rain, as soon as allowed by the atmos-phere, this evaporation being promoted by the large developped area of grains and lumps.
Washing by rain water flow only acts on the substan-tially waterproofed surface of grains and lumps, while internal mass of the latter is not badly affected. Accordingly, losses of solubilised materlals from residue piles due to rain waters susceptible to be drained into water-bearing stratum are extremely reduced, even insignificant. It results thereform that there are no risks of pollution of this stratum. In this r~spect, it is also to be noted that C02 Present ln the atmosphere has a favourable influence on the stabilization of the grain and lump sheathes by reinforcing them more completely due to a carbonation of active CaO which is in excess in this location.
The process according to the invention thus converts substantially non-storable, non-free flowing, powdered, slurried and muddy ferriferous residues, which are air and water pollution sources, lnto hard, non-stic~y grains and lumps which are of suitable mechanical strength and physical properties~j~to ..
' ~ ' allow stable piles of large height to be formed, by means of ' con~entional handling means; these piles may be exposed to - weatherings without any pollution or spreading risk, for example . . . . .
`' by sliding, running or 10wing.
... i . .
Although the process according to the invention was originally studied for ferriferous residues such as produced by iron precipitation from mixed solutions of iron and zinc sulfate ' in zinc hydrometallurgy and althou'gh this process was then ,. . . . . .
`~ ' successfully'applied on f~rrous sulfate residues, it is quite ~ obvious that this' invention can also be applied on other ferri-... .
. ~ , .
: .
.. . .
. . . - . .. .. . .
ferous residues, and other nletal residues containiing in general iron sulfates, various iron oxides and hydroxides, or compounds of other metals having similar properties with respect to reactiOn with lime, all said residues resulting from any indus-try, namely from zinc or any other industry.
It also appears as being evident that lime, as stabilizing element, may be replaced by metal oxides having si-milar properties, such as barium, strontium, and the like.
. With respect to MgO which generally is present with active CaO in numerous stabilizing materials, it does not.
produce any insoIuble material but however it takes part in the neutralising action of lime by precipitating iron hydroxides for example, which contrlbute to the waterproofing of the pro- :
tective sheath, particularly in the case of jarosite and goethite, so fixing polluting metals, as insoluble compounds by increase of the medium pH.
, ~ . , , . ' , ~
r, ! - - ~ ` ~
.
i`. .
.
`
..
, . .
. . . . . .
... . - . . ~ . .
`- . .
Claims (21)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for stabilizing and consolidating residues comprising metal compounds reactive with active CaO
to form a solid water-insoluble material, said residues having a consistency such that they are free flowing or non-coherent and cannot be piled up for storage, wherein these residues are provided in a form in which they contain at least 55% by weight of solids, and are mixed with a stabilizing material containing an amount of active CaO which is less than the stoichiometric amount for reaction with those constituents of the residues which are reactive with CaO, the mixing being carried out such that a heterogeneous mixture is obtained which is in the form of grains and lumps comprising a firm and hard shell portion with a relatively high content of material derived from active CaO, in which the extent of the reaction with active CaO has been substantial, and a softer and less firm core portion with a relatively low content of material derived from active CaO, in which the extent of the reaction with active CaO has been relatively low whereby the consolidated grain and lump product obtained is mechanically stable when piled up in heaps, and is also substantially insensitive to weathering when exposed to the ambient atmosphere in heaps, the shells forming an impervious layer which substantially prevents the extraction of any pollut-ing compounds of the softer portion inside the shells as a result of weathering and thus avoids the risk of pollution from them.
to form a solid water-insoluble material, said residues having a consistency such that they are free flowing or non-coherent and cannot be piled up for storage, wherein these residues are provided in a form in which they contain at least 55% by weight of solids, and are mixed with a stabilizing material containing an amount of active CaO which is less than the stoichiometric amount for reaction with those constituents of the residues which are reactive with CaO, the mixing being carried out such that a heterogeneous mixture is obtained which is in the form of grains and lumps comprising a firm and hard shell portion with a relatively high content of material derived from active CaO, in which the extent of the reaction with active CaO has been substantial, and a softer and less firm core portion with a relatively low content of material derived from active CaO, in which the extent of the reaction with active CaO has been relatively low whereby the consolidated grain and lump product obtained is mechanically stable when piled up in heaps, and is also substantially insensitive to weathering when exposed to the ambient atmosphere in heaps, the shells forming an impervious layer which substantially prevents the extraction of any pollut-ing compounds of the softer portion inside the shells as a result of weathering and thus avoids the risk of pollution from them.
2. A process as claimed in claim 1, in which grains and lumps are produced, which are internally consolidated by a skeleton which is also formed from the water insoluble material having said relatively high content of material derived from active CaO.
3. A process as claimed in claim 2 in which the grains and lumps so formed are rounded and have a diameter ranging from 1-20 cm.
4. A process as claimed in claims 1, 2 or 3 in which the metal compound is selected from jarosite , goethite , iron oxide, iron hydroxide and iron sulfate.
5. A process as claimed in claim 1, in which said grains and lumps are subjected to an additional compaction treat-ment accompanied with moisture expulsion to the surface of said grains and lumps, this moisture so causing a reinforcing action on the shell portion thereof.
6. A process as claimed in claim 5, in which an additional amount of stabilizing material as a powder is added for the treatment of compaction.
7. A process as claimed in claim 5 or 6, in which a material susceptible to waterproofing the surfaces of treated grains and lumps more completely is added for the compaction treatment.
8. A process as claimed in claim 1, 2 or 3, in which the residues comprise 55 to 95% of solids.
9. A process as claimed in claim 1, 2 or 3, in which the residues comprise 60 to 85% of solids.
10. A process as claimed in claim 1, in which the res-idues essentially contain jarosite and an amount of said material is used, the active CaO content of which forms 6 to 16% by weight of the dry material of the so treated residues.
11. A process as claimed in claim 10, in which an amount of said material is used, the active CaO content of which forms 8 to 12% by weight of the dry material of the treated residues.
12. A process as claimed in claim 1 in which the residues essentially contain goethite, and an amount of said material is added, the active CaO content of which is higher to the stoichiometric amount as determined by the reaction CaO +
SO3 ? CaSO4.
SO3 ? CaSO4.
13. A process as claimed in claim 12, in which an amount of said material is used, the active CaO content of which is 3.5 to 8 parts to 100 parts of goethite.
14. A process as claimed in claim 1 in which the residues essentially contain ferrous sulfate, and from 30 to 100% of the stoichiometric amount of said active compounds, which is determined by the reaction FeSO4 + CaO ? CaSO4 + FeO are used.
15. A process as claimed in claim 1, in which ferriferous residues having a moisture content higher than 45 are suspended in water, the suspension is filtered, and moisture of cakes so obtained is reduced, either due to conditions of the filtration, or by mechanical or pneumatic means, until the moisture content is lower than 45%, these cakes being then mixed with an amount of stabilizing material containing active CaO until grains and lumps are obtained, which are coated with said shell portion and internally consoli-dated by a skeleton based on said material with a high content of material derived from CaO.
16. A process as claimed in claim 15 in which said suspension is passed into a filter-press and after the latter is filled with cake, compressed air is blown through said cake until the moisture content thereof is reduced to 45%.
17. A process as claimed in claim 1, 2 or 3 in which quicklime, hydrated lime or lime milk is used as the material containing active CaO.
18. A residue based on metal compounds consisting of lumps or grains comprising a firm hard shell portion of a solid water insoluble material which is the reaction product of said metal com-pounds with material containing active CaO, said shell portion having a relatively high content of material derived from active CaO in which the extent of reaction has been substantial and a softer and less firm core portion of said reaction product with a relatively low content of material derived from active CaO in which the extent of the reaction with active CaO has been relatively low.
19. A residue as claimed in claim 18 in which the grains and lumps are rounded and have a diameter thereof from 1-20 cm.
20. A residue as claimed in claim 19 in which the grains and lumps are internally consolidated by a skeleton which is also formed from said water soluble material of said shell portion.
21. A residue as claimed in claim 18 which is based on jarosite, goethite, iron oxide, iron hydroxide or iron sulfate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BE162044A BE835777A (en) | 1975-11-20 | 1975-11-20 | PROCESS FOR TREATING WASTE CONTAINING AT LEAST 3% SULFUR IN THE FORM OF BASIC IRON SULPHATES |
| BE172325A BE848299R (en) | 1976-11-12 | 1976-11-12 | PROCESS FOR TREATING WASTE CONTAINING AT LEAST 3% SULFUR IN THE FORM OF BASIC IRON SULPHATES, |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1079496A true CA1079496A (en) | 1980-06-17 |
Family
ID=25648964
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA266,132A Expired CA1079496A (en) | 1975-11-20 | 1976-11-19 | Process for stabilizing and consolidating residues comprising metal compounds |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1079496A (en) |
| ES (1) | ES453462A1 (en) |
| IT (1) | IT1123931B (en) |
| NO (1) | NO763961L (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011151521A1 (en) | 2010-06-04 | 2011-12-08 | Outotec Oyj | Method and apparatus for homogenising and stabilising an iron-bearing residue |
-
1976
- 1976-11-19 IT IT2959876A patent/IT1123931B/en active
- 1976-11-19 ES ES453462A patent/ES453462A1/en not_active Expired
- 1976-11-19 CA CA266,132A patent/CA1079496A/en not_active Expired
- 1976-11-19 NO NO76763961A patent/NO763961L/no unknown
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011151521A1 (en) | 2010-06-04 | 2011-12-08 | Outotec Oyj | Method and apparatus for homogenising and stabilising an iron-bearing residue |
| US9085020B2 (en) | 2010-06-04 | 2015-07-21 | Outotec Oyj | Method and apparatus for homogenizing and stabilizing an iron-bearing residue |
Also Published As
| Publication number | Publication date |
|---|---|
| IT1123931B (en) | 1986-04-30 |
| ES453462A1 (en) | 1978-03-01 |
| NO763961L (en) | 1977-05-23 |
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