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Instead of catastrophes…

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UTILIZATION OF THE RED MUD

Instead of

catastrophes…

2012.

UTILIZATION OF THE RED MUD MUD MUD

Utilization of red mud with the recovery of valuable metal contents

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Dr. Kozéky László Synpetrol Hungary Inc. 1

UTILIZATION OF THE RED MUD

with simultaneous production of masonry blocks, ferric chloride and with the recovery of titanium and rare earth metal contents

Budapest

2012

Dr. KOZÉKY LÁSZLÓ


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In Hungary presently about 50 million tons of red mud are stored, and multiples of this quantity all over the world.

The typical composition of red mud is as follows:

Components Typical composition

Al2O3 15 – 19 % Fe2O3 33 – 40 %

SiO2 10 – 15 % TiO2 4 – 6 %

CaO 3 – 9 % MgO 0,3 – 1,0 %

Na2O 7 – 11 % V2O5 0,2 – 0,4 %

P2O5 0,5 – 1,0 % CO2 2 – 3 %

Table 1 The very high iron content is conspicuous, moreover the scientists of the Hungarian Academy of Science estimate this amount to be about 15-18 million tons. The Hungarian Dobos-Bartha method is based on this, which produced iron form the red mud, while the intended use of the residue is in the cement industry. Obviously the iron produced form the red mud was not competitive with that produced form iron ore, but the high energy demand also made this idea of the 1970’s obsolete. Other Hungarian inventors wanted to utilize the red mud as artificial soil or as soil ameliorator, or at least wanted to utilize red mud to extract such components. These attempts did not achieve a breakthrough and remained at an experimental level.


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In China about 10% of the produced red mud is utilized for metal recovery or for brick production. In the latter case brick is baked from the clay-rich red mud with or without additives. In Australia ALCOA tried to utilize red mud in the building and construction industry and even dwelling houses were made of the bricks produced from it. The radioactive radiation of such bricks exceeded, however, the level permitted in dwelling houses in Australia; therefore this application was stopped by the local authorities. In Japan red mud was utilized as a secondary raw material in building and construction, as an additive in cement production. In India production of ceramic tiles was attempted, where the molten red mud provided nice enamel coating for the tile, but even in this case the industrial demand was not enough. At present the re-utilization of red mud, as a by-product of alum earth production is a problem all over the world and a satisfactory solution has not yet been found anywhere. Storage is also a problem everywhere, therefore elimination of dumps and industrial utilization of red mud is attempted all over the world. In Hungary no successful trials have been made to utilize this mineral waste economically, in industrial scale, and even now there are no noteworthy attempts to do so. As shown in Table1, red mud contains a considerable amount of titania. (According to the technical literature in older mud samples sometimes TiO2 contents exceeding 10% were indicated). Although this concentration is well below the economically utilizable level, it has to be taken into account that titanium is a metal and alloying ingredient of strategic importance in defense and in the aerospace industries. It is of similar importance in producing medical implants, as chemical catalyst etc. Therefore the titanium content of red mud is considered to be a registered strategic deposit for times when either the necessity will force us to utilize it or when the progress of science will make the recovery of titanium content economic. We will show that, if the red mud is processed by the method proposed by us, because of and simultaneously with the utilization of the silicate (SiO2) and iron (Fe2O3) contents the residue is enriched in TiO2 and in rare earth metals to a degree that their recovery will be relatively easy and economic. If the composition of the red mud is analyzed in more detail (see Table 2) it can be seen that it also exhibits a significant rare earth metal content:

Data are given in ppm or in g/t units

Beryllium 5 – 16

Gallium 33 – 40

Niobium 33 – 77

Molybdenum 19 – 32

Selenium about 11

Rutherfordium 80 – 100

Vanadium 490 – 730

Thorium 45 – 50

Uranium about 32

Zirconium 340 – 540


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Detailed composition of the red mud continuously produced even nowadays in the alum earth production factory of MAL in Ajka (Hungary) is shown in Tables 3 and 4.

Main components (wt.%)

Fe2O3 33 – 40 Al2O3 15 – 19

SiO2 10 – 15 Na2O 7 – 11

TiO2 4 – 6 CaO 3 – 9

V2O5 0,2 – 0,4 P2O5 0,5 – 1,0

CO2 2 – 3 SO3 0,8 – 1,5

MgO 0,3 – 1,0 F 0,1-0,15

C 0,15 – 0,20 Table 3

Trace element contents, ppm

Gallium 20 – 30 Scandium 55

Yttrium 120 Lanthanum 240

Cerium 450 Praseodymium 10

Neodymium 190 Samarium 23

Gadolinium 160 Molybdenum 40

Zinc 410 Chromium 500 – 550

Cobalt 55 Uranium 42

Thorium 50 Manganese 1950

Table 4 For an easier understanding it should be stated that rare earth metals are trivalent elements of the 3rd column of the periodic table (with the exception of aluminum and boron, which do not belong to this group).


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Similarly scandium Sc, yttrium, Y, lanthanum La and the so-called lanthanides with properties similar to lanthanum (cerium Ce, praseodymium Pr, neodymium Nd, promethium Pm, samarium Sa, europium Eu, gadolinium Gd, terbium Tb, dysprosium Dy, Holmium Ho, Erbium Er, thulium Tm, ytterbium Yb, lutetium Lu). These elements are called “earth” metals, as they exhibit a high degree of chemical similarity to aluminum, hence the name rare “earth” metals similarly to alum “earth”. Chemical relatedness to aluminum, with special respect to chloride formation and the water solubility of aluminum chloride plays an important role in our process. Nevertheless the red mud is a hazardous waste as it should be classified as such due to its high sodium oxide (Na2O) and sodium hydroxide (NaOH) content and because of its corrosive, caustic properties. (EWC 010307* red mud, other wastes containing dangerous substances from physical and chemical processing of metalliferous minerals). The hazards of red mud come only from the corrosive sodium oxide content, practically from its sodium hydroxide content. If the caustic, corrosive effect is neutralized e.g. by adding acid so that the basic character is not more than pH=11, the waste is classified as EWC 010309 (red mud from alumina production other than the wastes mentioned in 01 03 07*). In our process neutralization by hydrogen chloride is suggested if the metal content of red mud is to be utilized and neutralization by sulfuric acid if only masonry blocks is to be produced from the mud (see later). Hydrogen chloride is also a hazardous substance because of its strong acidity and corrosive effect. Exactly this aggressive corrosivity is utilized in certain industrial processes where various metal parts are cleaned by hydrogen chloride. This results in the formation of a large amount of waste hydrogen chloride (e.g. in the preliminary cleaning of metal sheets to be plated before producing cans, or in other similar cleaning and/or pickling processes). Storage or disposal of hydrogen chloride waste, as a hazardous waste is an expensive process (although there are processes wherein it is transformed into ferric chloride by iron waste). The essence of the disposal processes is the elimination of the acidic corrosive property, which can be achieved by caustic neutralization in the simplest way, e.g.:

NaOH + HCl = NaCl + H2O Fe(OH)2 + 2HCl = FeCl2 + H2O

Under ambient conditions ferrous chloride (Fe(II)Cl2) is rapidly transformed into the industrially more important ferric chloride (Fe(III)Cl3) by oxidation. As hydrochloric acid waste needs caustic neutralization because of its acidity, it is suggested to use hydrochloric acid waste to neutralize the red mud. In case of proper dilution we dissolve about 3/4 of the total mass of the red mud into a ferric chloride based solution. This ferric chloride solution contains a mixture of other metal salts (chlorides) produced from the metal (oxides and hydroxides).


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One exception is titania TiO2, which remains precipitated in water, in caustic and in acidic solutions. Therefore the oxides of this industrially important metal remain among the silicate grains of red mud not dissolving in hydrochloric acid and sediment as a slurry from the mostly ferric chloride based solution together with the clay-like silicate (SiO2) slurry. The ferric chloride (salt) solution can be easily removed from the top of the deposited slurry by decantation (e.g. by means of filter press, centrifugal pumping etc.). The titania content of the residual SiO2/TiO2 slurry is around 25%, which is a concentration amenable to industrial utilization. The residual SiO2/TiO2 silicate slurry can be well used for building and construction purposes (and the potentially problematic radioactive components being present in minimal quantity are also removed). Although this slurry is the residue of a clay mineral (bauxite) therefore it is amenable to baked brick production by itself, we rather suggest its utilization as pressed masonry blocks. The essence of the masonry block production technology is based on US Patents 4,557,681 and 4,640,671 Assigned to John W. Wright which disclose the production of masonry blocks from clay mud or from mud-like materials by high pressure presses which meet the quality requirements of the building and construction industry.


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They are strong, durable and exhibit acceptable hydrolytic resistance. Masonry blocks produced by the technology of AECT (Advanced Earthen Construction Technology) corresponding to the patents discussed above are durable, resistant and exhibit dimensional stability. Blocks do not emit dust and due to the hydrolytic resistance the compression molded components cannot be leached form the blocks. Therefore they are amenable to the environmentally friendly utilization of large amounts of mining wastes or mineral industrial wastes, which is made possible by the productivity of e.g. the AECT 5000 equipment (processing of 16 tons of material per hour into 20 kg masonry blocks, which are about 4 times stronger than the Ytong or gas concrete masonry blocks). Thermal properties of the masonry blocks are unique (heat insulation property, heat capacity), they are excellent sound insulators, their strength, water solubility properties can be further improved by additives such as calcium oxide, gypsum, Portland cement etc. Clay-like soils are the best raw materials.

Masonry blocks can be easily chiseled, formed and can be well plastered. They exhibit enough strength to build two level houses from them. The density is high therefore the masonry work requires much workforce. Due to their hydrolytic resistance they can be used to build linings for drainage constructions, to produce grass blocks or to build pavements and temporary roads in the countryside.

As the mold inserts are exchangeable shaped blocks can be also pressed. Therefore aesthetic tiles for outdoor use can also be produced form the red mud (with or without concrete reinforcement). In addition to dwelling houses these building blocks could be utilized in building agricultural buildings (such as swineries, barns, press houses, chemical stores, composting pits etc.), i.e. in various fields of the industry and agriculture, but they can be excellently utilized as waterproof bottom linings in hazardous waste dumps as well. Because of their high specific weight they can be well used for as heavy weight supports, for building, reinforcing or supporting flood preventing dams.


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From all written above it is clear that after disposal of red mud by hydrogen chloride and after removing the ferric chloride solution (containing other metal chlorides as well) it is possible to press mold good quality masonry blocks from the residual SiO2/TiO2 silicate slurry (containing titania as well), as its particle size and its particle size distribution is similar to those of clay minerals and is well compressible. Independently of this fact, because of economic reasons we suggest further processing. As indicated above titanium is an important metal demanded by the industry. In the residual slurry remaining after decantation the concentration of titania is about 25%. Therefore the separation of titania and its utilization for titanium metal production are suggested. Several physical and chemical separation methods are available. One of the best known ones is dissolution by hot sulfuric acid (H2SO4), as titania dissolves in hot sulfuric acid, while silica particles do not.

TiO2 + 2H2SO4 = Ti(SO4)2 + 2H2O Ti(SO4)2 titanium sulfate and TiO(SO4) titanium-oxi-sulfate dissolve well in water and titanium sulfate can be easily separeted for the residual silicate slurry of the red mud or removed by the decantation methods mentioned above (e.g. filter press, centrifugal pump etc.). Afterwards the acidity coming from the sulfuric acid adhering to the silicate particles can be neutralized by white lime Ca(OH)2, or by calcium oxide (CaO) so that the pH of the slurry is about 8-9.

H2SO4 + Ca(OH)2 = CaSO4 + 2H2O H2SO4 + CaO = CaSO4 + 2H2O

where the formation of gypsum CaSO4 makes the masonry block produced even more attractive. Calcium oxide is carbonated under the effect of ambien carbon dioxide (similarly to the caustic lime /i.e. calcium oxide/ content of cement) and improves the strength and adhesion strength of the masonry blocks.

CaO + H2O = Ca(OH)2 Ca(OH)2 + CO2 = CaCO3 + H2O

The recovered titanium sulfate content can be utilized for the chemical industry and metallurgy in several ways. One of these possibilities is to transform titanium sulfate into titanium chloride by adding hydrogen chloride, separating titanium chloride and, similarly to the the Kroll process (US Patent 1940. No: 2,205,854) titanium metal is produced. Separation of TiO2 titania and SiO2 silicate particles can be done relatively easily by a simple, cheap and effective physical method, as the densities of titianium dioxide and exhibit a significant difference.

d(SiO2) = 1.93 d(TiO2) = 3.84


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Therefore the slurry components can simply separated by a proper sedimantation technology, by centrifugation or other similar technologies. Similary flotation methods can also be used, moreover – if solutions or melts of proper density are used – silicium dioxide may float on the surface of of the solution (or the melt), while titania sinks to the bottom of the solution. When dipsoing of the red mud classified as hazardous waste by adding hydrogen chloride, in addition to the silicate slurry another typical product, ferric chloride solution is formed. Ferric chloride solution is utilized in large amounts in daily practice, as a flocculating agent in wastewater treatment, but it can also be used in drinking water technologies. Flocculation or coagulation is the agglomeration of mobile particles dipsersed in a liquid medium under the effect of additives. Agglomeration of particles dipersed in a colloidal solution is caused by the elimination of the electrokinetic potential, stated otherwise the electrokinetic properties are modified by proper additives. The essence of the process is that the repulsive charge condition maintaining the colloidal sol state is neutralized by the ions of a properly selected electrolyte, then the dispersed particles precipitate into a gel, agglomerates are formed. Under these conditons the agglomerates forme sediment easily from the solution or the flocculated coagulation products can be easily filtered. This is the basis of the coagulation filtering of wastewater, wherein trivalent metal salts (flocculating aids) are added to the water before entering the filter layer. This coagulation purpose is served by addig ferric chloride to the wastewater as flocculating aid. Accordingly wastewater treatment industry presents a continuous market demand for ferric chloride, where the ferric oxide content of red mud can be utilized by transforming it into ferric chloride. The ferric chloride made from red mud will contain a considerable amount of aluminum chloride, sodium chloride, and some calcium chloride and magnesium chloride as well, but these do not affect the usefulness of the ferric chloride solution for wastewater flocculation purposes. Similarly the few ppm of uranium and thorium causing the radioactivity of the red mud somewhat above the ambient level will be present in the chloride solution. This does not affect the use of the ferric chloride solution for flocculation purposes and even the high dilution notwithstanding (both in the chloride solution and both during dissolution in the wastewater to be flocculated) the activity level does not exceed even the values prescribed by the most stringent specification. In this way, however, the silicate slurry to be used for building and construction will not exhibit any activity (prescriptions are the most stringent


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for indoor activities pertinent to long term exposure in dwelling houses). This ferric chloride solution orginating from the red mud will contain – in addition to the aluminum chloride component already mentioned – the rare earth metal chlorides chemically very similar to aluminum chloride, which are the chlorides of the metals belonging to the lanthatnide group of the periodic system. As shown above the concentration of rare earth metals (in parts by weight) is very small in the red mud, consequently also in the ferric chloride solution made form it. Therefore they do not influence the flocculation use of the solution at all. Nevertheless it is mentioned that the hardly available rare earth metals are demanded more and more in modern industrial processes. Therefore it may hapaen that the market conditions render the recovery of these metals economic by separating the rare earth metals from the majority ferric chloride solution. There are well-known industrial processes for this, chlorides of rare earth metals can be precipitated by various physical or chemical methods and can be seaparated from the ferric chloride solution. These processes are sometimes very tedious, complicated and expensive methods, their necessity is backed only by the market demand and price conditions.Our proposed red mud recycling method is summarized in the following figure:

RED MUD

DISPOSAL, NEUTRALIZATION BY HYDROGEN CHLORIDE

SLURRY SOLUTION

SiO2 in silicate in Fe2Cl3 solution 25% TiO2 – aluminum chloride

– Ca, Mg Na chloride

– chlorides of rare earth metals

Separation of titania for metallurgical purposes

Aluminum chloride and rare earth chloride separation from the iron chloride solution if required compression molding of masonry blocks from silicate slurry

Silicate masonry blocks for building and construction or Use of the ferric chloride (based) for other purposes solutions for wastewater flocculation


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Of course high quality masonry blocks may be produced from the slurry obtained from the red mud without seperating titania, neither does the utility of the ferric chloride solution as a flocculating agent change if the chlorides of the other metals are not separated from it. Both processes may become feasible, however, if the actual economic and profitability considerations make the reasonable. Both the market conditions and the budget of the alum earth production factory may be such that it is not worth to invest into the processes mentioned above or there is no financial bacground fo them. In this case the production of masonry blocks directly from the red mud is suggested, using the AECT technology. This is still cheaper solution than building and maintaining proper hzrdous waste dumps. Moreover the red mud ceases to be a hazardous waste and is utilized in the masonry blocks producing value. In our direct masonry block producing technology from the red mud we suggest using H2SO4 sulfuric acid to neutralize the basicity. Partly because this proved to be acceptable in our pilot plant scale trials, secondly because sulfate salt dissociate less and their presence is more advantageous in the building and construction industry (see e.g. CaSO4 gypsum). In our pilot plant scale trial we utilized a red mud produced 5 years ago. The water content of the red mud was around 10 %. Its strong basicity caused by caustic soda was neutralized by sulfuric acid and a pH of 8.5 was set (the level of neutralization sugggested by us is in the 7.5-9 range). Production was performed using AECT 5000 CSB (compressed soil block) machinery. (The equipment is capable of compression molding clays of much higher water content.) The applied pressure used in compression molding was around 20-25 MPa. (The hydraulic press can of the equipment can apply a pressure of 14 – 35 MPa on the compressed specimen.) The size of the masonry blocks produced according to an US standard was 25,4 cm x 35,6 cm x 9,26 cm. (Mold inserts are variable, therefore masonry blocks of other size can also be produced as well as other shaped products.) The compression (breaking) strength of the masonry blocks produced was 10 MPa (typically it scattered in the 9 – 11 MPa range). For comparison the compression strength of the Ytong (cellular light concrete) masonry blocks is 1.5 – 5 MPa, while the relevant US standards prescribe a compression strength above 1000 psi (pound per sq inch), corresponding to about 7 MPa. It means that the masonry blocks made of red mud slurry itself meet by far the requirements, they include the silicate slurry waste of alum erath production without leaching and dust formation, thus eliminating all hazardous effects (and the necessity of storing it in hazardous waste dumps). Moreover both the strength and hydrolytic resistance (leaching) properties of the masonry block porduced can be further improved by using additives (e.g. Portlan cement). As their thermal and acoustic properties are uniquely excellent and can be easily machined and shaped, they can be well utilized by the building and construction industry. Because of their high specific weight they recommend themselves as heavy weight supports in flood protection, for supporting dams.


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In the wide range utilization it is a great advantage that the 50 million tons “deposit” of red mud (which is increasing further continuously) provides a large amount of homogeneoous raw material and makes possible a production of constant quality. Our process technology patent differs essentially form earlier attempts in that we produce the masonry blocks from the red mud not by baking but by high pressure compression for the building and construction industry. Under the effect of high pressure the silicate microcrystallites of the slurry fragment and the fresh cleavage surfaces are pressed together by the high compression pressure. The diffusion initiated at such freshly formed cleavage surfaces provides the same strength which would be provided by thermal diffusion in the case of baking. The specific first production cost (per unit volume of the masonry block) is many times smaller for block produced by the comporesion technology in comparison to those produced by baking. Therefore a competitive industrial product can be produced from the red mud economically. This allows not only the elimination of very expensive hazardous red mud dumping sites together with all their risk factors, but a profitable product is made of the waste.

(It is noted that the masonry blocks can also be fired – if needed.)


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TECHNICAL SUMMARY

This process technological invention provides possible ways of utilizing red mud, thus solving the notorious problems related to the mass storage of red mud wastes. The description of the invention provides two processes wherein the red mud is utilized in masonry blocks used by the building and construction industry. In one of these processes the basicity of the red mud residue coming from the cuastic soda content is neutralized by an acid (typically by sulfuric acid) and masory blocks are produced from the neutralized red mud by high pressure compression. In the other, more complicated process the residual basicity is neutralized by hydrochloric acid and simultaneously other metal (oxides) of the red mud are also dissolved. This solution (consisting mainly of ferric chloride) is separated from the silicate slurry (and from the residual titania in it) and is treated separately. The ferric chloride solution can be utilized e.g. in wastewater flocculation, but the rare earth metal content of the red mud can also be recovered from it. The silicate slurry separated from the (mainly) ferric chloride based solution (which exhibits considerable titania content) can be compression molded into masonry blocks after neutralization- with or without additives. It is possible to separate the titania content as well. In this case only the residual silicate sllurry is comporession molded into Masonry blocks after enutralization and after the eventual admixtrue of additives. If one has choice …

One should choose the “greener” solution!

utilization of the red mudusers.atw.hu/poszttrauma/06/munkahely1.pdfutilization of red mud with the...

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