CA2081307A1

CA2081307A1 - Method for producing homogeneous, fine, pulverulent solids dispersions optionally containing active substances

Info

Publication number: CA2081307A1
Application number: CA002081307A
Authority: CA
Inventors: Friedrich Boelsing
Original assignee: Individual
Current assignee: DCR INTERNATIONAL ENVIRONMENTAL SERVICES Inc
Priority date: 1991-03-01
Filing date: 1992-02-28
Publication date: 1992-09-02
Also published as: KR100220560B1; WO1992015539A1; NO924190L; AU648391B2; NO924190D0; AU1205592A; NO301222B1; JPH05507440A; EP0527984A1

Abstract

PROCESS FOR THE PRODUCTION OF HOMOGENEOUS, FINELY DISPERSED, PULVERULENT
SOLID DISPERSIONS, IF NECESSARY HOMOGENEOUSLY CHARGED WITH ACTIVE
COMPOUNDS, AND THE USE OF PRODUCTS THEREBY OBTAINED.

ABSTRACT:

In order to produce a homogeneous, finely dispersed, pulverulent solid dispersion an aqueous suspension of solids is being homoge-nized with the educt of a water-consuming reaction, e.g. calcium oxide, aluminium alcoholate or with an ester of silicic acid.
In order to homogeneously charge said homogeneous, finely disper-sed, pulverulent solid dispersion with active compounds a homo-geneous mix of an aqueous suspension of solids and a solution or suspension of said active compounds is being homogenized with the educt of a water-consuming reaction.
The homogeneous, finely dispersed, pulverulent solid dispersions, charged or not charged with active compounds, are versatile pro-ducts for agricultural and technical applications, particularly in the field of environmental remediation.

Description

2~ 3Q~

PROCESS FOR THE PRODUCTION OF HO~OGENEOUS, FINELY DISPERSED, PUL-VER~LENT SOLID DISPERSIONS, IF NECESSARY HOMOGENEOUSLY CHARGED WITH
ACTIVE COMPOUNDS, AND THE USE OF PROD~CTS THEREBY OBTAINED.

DESCRIPTION

Dispersions of solids play an important part in agriculture and in engineering. Examples include clay powders, which are im-portant both as soil conditioners and as adsorption agents in industrial processes. Producing finely dispersed solid disper-sions from finely dispersed aqueous intermediates such as natu-ral clay calls for drying processes requiring large amounts of heat, followed by mechanical homogenisation. Producing finely dispersed solid dispersions from coarse-particle solids or solid constituents calls for mechanically complex grinding or comminution operations, in order to obtain solid dispersions comprising more or less fine homogeneous particles; however, there are limits to these mechanical operations by virtue of the fact that the specific grain size attainable for each mate-rial is determined solely by the maximum shear forces that can be attained by engineering.
It is therefore the object of this invention to provide a proc-ess that allows extremely homogeneous finely dispersed solid dispersions to be produced without the need for complex engi-neering solutions.
To achieve this object, an aqueous, finely dispersed suspension is homogenized mechanically with an educt of a water-consuming chemical reaction, e.g. with an alkaline earth oxide or an aluminium alcoholate or a silicic acid ester or a mixture of these compounds, and the educt of a water-consuming chemical reaction in the homogeneous mix is then allowed to react with the stoichiometric amount of water.
The water-consuming reaction is selected from reactions in which finely dispersed solids are formed; said educts accord-ingly give rise to the formation of alkaline earth hydroxides, aluminium hydroxide and silica respectively.
The aqueous, finely dispersed suspensions suitabie for the purposes of the invention are suspensions of finely dispersed solids in water. Finely dispersed substances within the meaning of the invention are substances having particle sizes within the range from > 0 to < 250 micrometer, preferably within the range from 1 to 50 micrometer, whose structural characteristics give them a good adsorption capacity. Examples include laminated silicates, finely dispersed silica, aluminium oxides and aluminium hydroxides, precipitated chalk and iron oxides.
Paste-like mixtures of these with water are referred to here as finely dispersed suspensions.

2 ~ ~ A. 3 ~ rl The proportion of water in the finely dispersed suspension may vary within broad limits, provided, on the one hand, that sufficient water is present for the subsequent chemical reac-tion of said water-consuming educts and, on the other hand, that no more than the permitted quantity of water for producing a pulverulent solid dispersion is present. The water content of the finely dispersed suspension is preferably adjusted to give a paste-like, kneadable material.
The aqueous, finely dispersed suspensions may be of natural or industrial origin. Clay, as extracted from pits for the pro-duction of earthenware, is a paste-like and kneadable, aqueous, finely dispersed suspension of natural origin, and can be employed wit`hout modification in accordance with the invention.
Bleaching earth and clay powders are industrial in origini mix-ing them with water into a paste produces aqueous, finely dispersed suspensions which are likewise suitable for use under the invention.
In addition to clay, clay-like and clayey materials can also be used to produce aqueous, finely dispersed suspensions.
The terms clay-like and clayey materials, as used here, refer solely to the adsorption capacity of such materials which is a result of their physical and structural characteristics, not to thelr chemical composition. Examples include clayey or clay-like flue-dusts, filter dusts, ashes and industrial residues and waste material, e.g. waste materials from the food industry in the form of spent bleaching earth, or, say, red mud from the Bayer process, a paste-like compound chiefly comprising iron oxides and iron hydroxides, which is a by-product of aluminium production.
It is an essential aspect of the invention that the water con-tained in the finely dispersed suspension is consumed uniformly in the chemical reaction with alkaline earth oxide or aluminium alcoholate or silicic acid esters, because only then can a homogeneous powdered solid dispersion be produced. For this reason the water-consuming reaction must not be allowed to begin until the educt of the water-consuming reaction has been uniformly distributed in the suspension. This can be achieved either by homogenizing the aqueous, finely dispersed suspension so quickly with the educt of the water-consuming reaction that said educt is uniformly distributed therein before the water-consuming chemical reaction has appreciably begun, or by adding conventional reaction retarders to the aqueous finely dispersed suspension, e.g. ammonia solution, alcohols, alkali sulfates and the like, or else by suitably pre-treating the educt of the water-consuming reaction, e.g. with alcohols or long-chain amines, fatty acids and the like. In place of the pure educts alkaline earth oxide or aluminium alcoholate or silicic acid ester, it is also possible to use mixtures thereof.
The clay products obtained in accordance with the invention can be used as soil conditioners or as earth construction material, e.g. to seal off waste dumps. This similarly applies to all 2~3~7 3 other suspensions designated. Solid dispersions with aluminium hydroxide or silica can be used as effective adsorption agents.
Numerous chemical and physical properties of active compounds on a solid carrier advantageously change in response to their degree of dispersion. Generally speaking, the chemical reactiv-ity of a solid or liquid substance acting as a reactant in-creases, the more finely dispersed it is on a carrier. One example of the physical effect is the change in the speed with which equilibrium states are reached, for instance in respect of adsorption or solution processes. When active compounds are finely dispersed on a solid carrier, chemical and physical processes become possible that would otherwise not, or only very slowly, take place.
It is known that solid and liquid active compounds can be put onto a solid carrier by mechanical means using comminution. It is also possible to impregnate a solid carrier with a solution of an active compound and then dry the suspension. Suitable active compounds can be put onto a solid carrier by vacuum deposition. Lastly it is possible to transfer active compounds homogeneously and in a finely dispersed form into a solid carrier in the course of a dispersing chemical reaction.
The foregoing processes are subject to certain limitations as to their applicability or else have other drawbacks. For in-stance, the comminution of active compounds is limited by the fact that the shear forces that can be achieved by mechanical means are not sufficient to produce as fine a dispersion as may be required of the active compounds in the material being ground. The production of homogeneously charged, powdered solid dispersions using a solution of an active compound or by vacuum deposition is restricted to soluble or volatile active com-pounds and, on account of the technical complexity required, is usually also costly. The option of very finely dispersing active compounds homogeneously in the course of dispersing chemical reactions is restricted to active compounds that can be dispersed beforehand in the educt of the dispersing chemical reaction. Added to this is the fact that these educts, notably alkaline earth oxides, aluminium alcoholates and silicic acid esters, are relatively expensive.
It is therefore the object of this invention to produce pow-dered solid dispersions charged homogeneously with active compounds by a method that is technically simple and hence also economic, at the same time largely avoiding limitations and drawbacks.
To achieve this object, an aqueous, finely dispersed suspension is homogenized by mechanical means with active compounds or mixtures of active compounds, and the resulting homogenized mix is then homogenized with an alkaline earth oxide or an aluminium alcoholate or a silicic acid ester or a mixture thereof.

2 ~ rl ~ ' The idea underlying the invention exploits the latent adsorp-tion capacity of the solids present in a finely dispersed form in an aqueous suspension, said solids being completely coated with water in this environment and hence practically incapable of adsorption, if the water is chemically removed from the aqueous suspension in the presence of homogeneously dispersed active compounds capable of adsorption, and which may be in the form of a solution or in a finely dispersed suspension, by means of a reaction that consumes water, for example a hydra-tion reaction of an alkaline earth oxide or by hydrolysis of an aluminium alcoholate, with the result that the active compounds are adsorptively bound on the surface of the now largely anhy-drous solid. It is also an essential aspect of the invention that the finely dispersed solid reaction product simultaneously resulting from the educt of a water-consuming reaction, for example finely dispersed alkaline earth hydroxide or aluminium hydroxide from alkaline earth oxide and aluminium alcoholate respectively, likewise becomes adsorptively active.
The advantage of the invention lies in the fact that, unlike with mechanical distribution, it is also possible to disperse very small amounts of active compounds homogeneously onto a solid carrier, and that, unlike with a homogeneous very fine dispersion of active compounds achieved in the course of dispersing chemical reactions, the indispensable prerequisite for the latter, viz. the fact that it must be possible to disperse the active compounds for dispersion beforehand in the educt of the dispersing chemical reaction, e.g. in an alkaline earth oxide, aluminium alcoholate or silicic acid ester, is not necessary at all. Quite the contrary: under the invention to produce a pulverulent solid dispersion charged homogeneously with active compounds, the active compound is homogenized by mechanical means with an aqueous, finely dispersed suspension and the resulting homogenized mix only then homogenized with an alkaline earth oxide or aluminium alcoholate. This allows the proportion of alkaline earth oxide or aluminium alcoholate required to produce a powdered solid dispersion charged homoge-neously with active compounds to be substantially reduced, in favourable cases to around one-tenth the amount needed for a dispersing chemical reaction.
The term active compounds refers here to substances which, unlike the substances of the suspension regarded merely as the carrier substance, are particularly active chemically and physically in their finely dispersed state. Likewise in this connection, the physical and chemical properties of the com-pounds concerned are not important per se, but only in relation to the part that they will play in the particular application envisaged. This will be illustrated by means of two examples.
Natural clay is homogenized by kneading it with a concentrated aqueous solution of sodium sulphide; in the subsequent water-consuming chemical reaction with some 15~ hydrophobic calcium oxide, based on the amount of clay used, the resulting plastic material produces a pulverulent solid dispersion homogeneously charged with sulfide ions. As is known, the finely dispersed 2~.3~ 5 active compound, sulfide ions, is a highly reactive precipita-tion reagent, by means of which numerous toxic heave metals can be converted by precipitation into water-insoluble heavy metal sulphides and thus chemically fixed and immobilized. To this end, soils, fly ashes or slags contaminated with heavy metals are mixed with said solid dispersion and then compacted into a solid material. Large lumps of contamlnated materials, for example chimney linings, foundation sections, equipment and the like, are embedded in said solid dispersion either as such or in a mixture with other materials having advantages in terms of soil mechanics and the resulting mix is then compacted. The question of soil mechanics is of particularly great importance in the treatment of sludge from sewage-treatment plants con-taminated with heavy metals, in view of the gel structures of such sludge which are unstable in terms of soil mechanics, in order, after homogenizing them with said solid dispersion, to be able to dump them in the form of a material with a high bearing capacity which is stable from a soil-mechanical point of view. In this connection it is especially advantageous from an economic point of view to mix in suitable waste materials that have been contaminated with heavy metals, for example slags and ashes.
According to one especially effective variant of the process, one portion of the clay is first kneaded with an aqueous alkall sulphide solution and a second clay portior with a finely dispersed aqueous suspension of iron sulphate. When the two portions are subsequently homogenized, this gives rise in situ to very finely dispersed iron sulfide embedded in the clay structure. The compound, which is still paste-like, is now chemically reacted with around 20%, based on the total amount of clay, normal calcium oxide, i.e. not rendered water-repel-lent. The stoichiometric ratios are chosen to give a slight excess of iron ions, e.g. 10~. The active compound now consists of iron sulfide, which is considered insoluble in water.
However, the very much smaller solubility product of the sul-fides of toxic heavy metals means that a precipitation occurs after mixing in materials contaminated with heavy metals. This allows a particularly effective method of immobilizing heavy metals without risk to the ground water through direct use of mobile, i.e. water-soluble, alkali sulfides.
In the aforementioned example and in the associated variant of the process, substances, like said iron sulfide, are employed that are readily recognizable as active compounds on account of their chemical reactivity, notably as a precipitating reagent.
However, the invention also- allows substances regarded as chemically inert to be used as active substances.
For example, if hard bitumen is melted down and kneaded with clay, and this mix, once it has become homogeneous, is reacted with preferably hydrophobic calcium oxide and then kneaded again, after some time the water-consuming calcium oxide hydra-tion reaction will take place, and the originally paste-like material disintegrates into a pulverulent solid dispersion charged homogeneously with hard bitumen. As is known, the 2~3~ 6 calcium hydroxide contained in this solid dispersion is by no means inert chemically, but has highly basic properties and can therefore readily be reacted, e.g. with carbon dioxide, whereas the hard bitumen likewise contained in this solid dispersion is completely inert from a chemical viewpoint.
However, the mixture of clay particles and calcium hydroxide present in the solid dispersion is the carrier and the hard bitumen the active compound if the object is, say, to render harmless, by a process of irreversible immobilization, highly toxic organic substances such as polychlorinated biphenyls (PCB) or dioxins and dibenzofurans (PCDD/PCDF), e.g. as sub-stances contained in filter dusts from refuse incineration plants or as contamination in soils. To this end, such con-taminated flue dusts or soils are mixed with a powdered solid dispersion charged with a hard bitumen and produced using clay and calcium oxide, and the mixture is compacted to produce a soil. After a short time the finely dispersed hard bitumen in the solid matrix has incorporated the harmful organic sub-stances on account of their good solubility in the hard bitumen solid solvent. Leaching trials under long-term test conditions and applying trace analysis methods vouch for the fact that harmful organic substances treated in this way in accordance with the invention remain permanently and completely immobi-lized. Other high-boiling inert organic substances such as high melting point wax, vaseline or mineral oil may be used in place of the hard bitumen.
It is not possible to list the active compounds and mixtures thereof individually, because the choice thereof will automati-cally be decided on conventional criteria on the basis of the particular application envisaged. It is, for example, known that different concentrations and bioavailability of trace elements are needed when producing plant substrates. These include copper, iron, manganese, zinc, molybdenum and boron, the water-soluble compounds of which are mixed mechanically and used in the form of heterogeneous concentrates. The disadvan-tage of these preparations is that said plant trace elements are not uniformly available because they cannot be uniformly dispersed in the substrate. On the other hand, if the same compounds of the said trace elements are first kneaded into a clay matrix and uniformly distributed in this manner, after homogenizing this mixture with calcium oxide an extremely finely dispersed solid preparation is obtained in which the active ingredients are extremely uniformly dispersed. Simulta-neously dispersing tartaric and citric acid provides a way of determining the bioavailability of said trace elements in advance. If the trace element compounds, with or without tar-taric acid, are individually converted to a powdered solid dispersion and it is not desired to mix them in the particular proportions required for the application until later, it is also advisable to mix in a water repellent, for then no detri-mental interactions are possible between the compounds of the trace elements within the mixture of the individual powdered solid dispersions.

2 ~7 ~ 3 ~
In the same way is possible to process the most diverse types of plant nutrients, provided they are stable in the resulting alkaline medium, into extremely homogeneous slow-release fer-tilizers.
The number of active compounds that can be used in the field of environmental protection is too great to list, because the number of harmful substances leading to problems is so great.
Thus, in theory, for each harmful substance, or at least for each class of harmful substances, there are active compounds within the meaning of the invention that can be employed as reagents, e.g. as precipitating, condensing or addition agents, for immobilization and detoxification, to name but a few exam-ples. In this connection high-boiling organic phases are of particularly great importance as active compounds for the adsorption or absorption of both harmful inorganic and organic substances, for this form of immobilization and physical fixa-tion is especially straightforward and thorough; one example among many is the absorptive removal of harmful substances from waste gases from refuse incineration plants with the help of long-chain amines as the active compound. Furthermore, still further active compounds may also be worked into the high-boiling organic phase that have the ability to interact chemi-cally with harmful substances and therefore shift the equilib-rium position in favour of complete absorption, for instance by means of long-chain amines in a bituminous phase. Anyone skilled in the art will be familiar with the relationship between choice of active compounds and the object that is to be achieved, and this therefore requires no further explanation here; for instance, any person skilled in the art will be aware that finely dispersed metals such as magnesium or aluminium can be used to dehalogenate aromatic compounds containing halides.
In the second example cited further above, in which the use of hard bitumen as active compound is illustrated, hydrophobic calcium oxide is preferably employed. It is an essential aspect of the invention that the water contained in the finely dis-persed suspension is consumed uniformly in the chemical reac-tion with alkaline earth oxide or aluminium alcoholate, because only on this condition can a homogeneously charged powdered solid dispersion be produced. For this reason the water-consum-ing reaction must not begin until the alkaline earth oxide or aluminium alcoholate has been uniformly dispersed in the homogenized mix from the active compound and the suspension.
This can be achieved either by homogenizing the homogenized mix comprising aqueous, finely dispersed suspension and active compounds so quickly with the alkaline earth oxide or aluminium alcoholate that the latter are uniformly dispersed in the homogenized mix before the water-consuming chemical reaction has begun to any appreciable extent, or by adding conventional reaction retarders to the aqueous finely dispersed suspension, e.g. ammonia solution, alcohols, alkali sulphates and the like, or else by pre-treating the alkaline earth oxide or aluminium alcoholate in the corresponding manner, e.g. with alcohol or long-chain amines, fatty acids or the like.

2 ~ , 8 In place of the pure alkaline earth oxides or aluminiu~ alcoho-lates it is also possible to use mixtures of alkaline earth oxides or aluminium alcoholates or mixtures of both classes of compounds.
Where these pulverulent suspensions charged homogeneously with active compounds are to be used for agricultural or engineering applications, more particularly in the field of environmental protection, it is advantageous to set an excess amount of calcium oxide, preferably hydrophobic calcium oxide, by use of a suitable procedure or subsequent mixing. This allows cohesive contaminated materials to be so broken down in one operation that the active compounds are dispersed uniformly in the medium and all the harmful substances are intercepted and rendered harmless.

Example 1 100 parts by weight of a natural plastic clay are homogenized in a compounder with 18 parts by weight of a calcium oxide rendered hydrophobic with 1% fatty acid. The hydration reac-tion, which begins after about 5 minutes, takes place outside the compounder; the result is an extremely homogeneous solid dispersion of calcium hydroxide in clay, which is so homogene-ous that the constituents are no longer visible even under a microscope.
Variant The plastic clay is first kneaded with 2% potassium sulfate as reaction retarder and then with calcium oxide that has not been rendered hydrophobic. The hydration reaction only begins after some 20 minutes have elapsed.
Variant In place of clay, red mud from the Bayer process is used, or a paste prepared from 70 parts by weight of dry, spent bleaching earth and 30 parts by weight of water.
Variant In place of calcium oxide, the stoichiometric equivalent of aluminium mixed alcoholate or silicic acid esters can be usedi in these cases the alcohol released during hydrolysis evapo-ratesi it can be recovered by condensation.

Example 2 70 parts by weight of clay, 7.6 parts by weight of iron sulfate FeSO4.7H20, 3 parts by weight of sodium sulfide Na2S (60%) and 4 parts by weight of water are homogenized in a compounder. The homogenized mix is homogenized with 15.4 parts by weight of calcium oxide. The result is 100 parts by weight of a pulveru-lent solid dispersion charged homogeneously with 2% iron sul-fide FeS, which can be used to precipitate heavy metals in contaminated materials. The proportion of iron sulfate is 2~3~ 9 chosen to give a 20~ excess relative to the amount required stoichiometrically; this prevents soluble alkali sulfide, for example in the treatment of contaminated soils or contaminated industrial wastes, from being able to pass into the ground water in the course of treatment in accordance with the inven-tion. The clay in this example can be replaced in full or in part by pastes mixed from dry, spent bleaching earth with water, for example 77 parts by weight of spent bleaching earth from the food industry with 23 parts by weight of water or with so-called red mud from the Bayer process, or else by mixing a fine-particle filter dust with enough water to produce a clay-like matrix. It is not necessary to add reaction retarders in this example, for the iron sulfate, like the alkali sulfates, already retards the chemical reaction of the calcium oxide such that complete homogenization is possible before the water-consuming reaction of the calcium oxide begins.

Example 3 In a variant of Example 2, 35 parts by weight of clay are homogenized with a suspension of 7.6 parts by weight of iron sulfate and 2 parts by weight of water in a positive mixer.
35 parts by weight of clay are homogenized with an aqueous solution of 3 parts by weight of sodium sulfide (60%) in 2 parts by weight of water in a positive mixer.
Once homogenization has taken place, the two portions are homogenized in a positive mixer and then the resulting homoge-nized mix homogenized with 15.4 parts by weight of hydrophobic calcium oxide. The result is a pulverulent solid dispersion charged extremely homogeneously with 2% iron sulfide FeS, and said dispersion can be employed in the same way as that of Example 2.

Example 4 In a variant of Examples 2 and 3, the separately produced homogeneous mixes of clay and iron sulfate, and of clay and sodium sulfide, respectively, are homogenized with 7.7 parts by weight of calcium oxide and hydrophobic calcium oxide, respec-tively. By mixing the two pulverulent solid dispersions charged homogeneously with iron hydroxide and sodium sulfide, respec-tively, a preparation is obtained which can be used particu-larly effectively and at the same time in an environmentally safe manner in the presence of excess hydrophobic calcium hydroxide to treat cohesive materials containing heavy metals.
This is because on the one hand precipitation of the heavy metals takes place immediately with the help of the alkali sulfide, but on the other hand no trace of this sulfide is able to pass into the environment because it is intercepted by the iron hydroxide that is present, without thereby cancelling the precipitating action on heavy metals not yet reached.

2~.$~7 Example 5 56 parts by weight of clay are plasticized with 15 parts by weight of water and pre-heated to 70C. This aqueous, finely dispersed suspension is homogenized in a compounder with 35 parts by weight of melted bitumen B 80. The resulting homogene-ous m-ix is then homogenized with 56 parts by weight of calcium oxide which has been rendered water-repellent with 1~ fatty acid. The result is a pulverulent suspension homogeneously charged with bitumen which suspension can be used in the field of environmental protection both to isolate and protect land-fills and to immobilize non-ionic harmful inorganic and also organic substances. To this end, the suspension is mixed with a contaminated material, say in a ratio of 1:4, for example with a material containing halogenated dibenzodioxins or dibenzofu-rans in ppm range. The exact proportions required are deter-mined by simple routine tests to ascertain the pure bitumen's capacity for adsorbing the type and quantity of harmful sub-stance concerned. To absorb harmful substances with certain functional groups, the melted bitumen is for example mixed with the required amount of an active compound that contains a functional group capable of reacting with the harmful sub-stance, thereby shifting the adsorption equilibrium towards a complete adsorption. To treat harmful substances that cannot be immobilzed inside the alkaline range, rather than the calcium oxide a commercial mixed aluminium alcoholate is employed, e.g.
from aluminium isopropanolate and aluminium isobutanolate. The clay can at this point be replaced to particular advantage by red mud from the Bayer process, because this finely dispersed system is especially efficient in the dry state at adsorbing said dioxins and furans.

Example 6 150 parts by weight of clay with a 23~ water content are plas-ticized with 10 parts by weight of water in a compounder and homogenized with 1 part by weight of a water-soluble salt of copper, manganese, zinc, molybdenum, boron, and iron, respec-tively, e.g. in the form of the corresponding copper, iron, manganese and zinc sulfates, and respectively as ammonium molybdate and potassium metaborate. The resulting homogeneous mixes are then homogenized in a compounder with an alkaline earth mixture comprising 90% calcium oxide and 10~ magnesium oxide, rendered water-repellent with 0.2~ fatty acid. The individually obtained homogeneous pulverulent solid dispersions charged with the aforementioned trace elements are mixed in a vertical tube mixer in a required ratio corresponding to the envisaged application. The result is an additive for producing substrates for plants from peat or compost. The water-repellent properties of the additive bring about rapid mixing even with very moist peat or compost. The term mixing ratio corresponding to the envisaged application, as used here, denotes the differ-ent requirement which plants have in their various growth phases. ~hould an above-average increase in the bioavailability ~ 3 ~,~
of the individual constituents be desired, the clay is homoge-nized in the corresponding preparation with an additional 1 part by weight of tartaric acid or, to still further increase the bioavailability, with 1 part by weight of citric acid.

Example 7 100 parts by weight of clay or loam are plasticized with 10 parts by weight of water and homogenized with 20 parts by weight of calcium cyanamide; the resulting homogeneous mix is then homogenized with 10 parts by weight of hydrophobic calcium oxide. The solid dispersion thus obtained can be used as a nitrogenous agricultural slow-release fertilizer.

Example 8 In a combination of Examples 2 and 5, 100 parts by weight of clay are homogenized in turn with a suspension of 32 parts by weight of iron sulfate in 7 parts by weight of water, with 8 parts by weight of sodium sulfide and with 30 parts by weight of melted bitumen in a positive mixer; the resulting homogene-ous mix is then homogenized with 28 parts by weight of a cal-cium oxide rendered water-repellent with 0.5% fatty acid. The resulting pulverulent solid dispersion, charged homogeneously with the active compounds iron sulfide and bitumen, can be used for simultaneous irreversible immobilization of heavy metals and high-toxicity compounds, e.g. PCDD/DF in correspondingly contaminated filter dusts and ashes from refuse incineration plants.

Example 9 Respective double excesses of the stoichiometrical amounts of dipotassium hydrogen phosphate, iron sulfide and calcium car-bonate are separately converted to homogeneous solid disper-sions as in the method in Example 2, using calcium oxide that has been rendered water-repellent with 1~ fatty acid. The mixture of the various solid dispersions is eminently suited to irreversibly immobilizing heavy metal ions in sewage sludge, composts, river and harbour sediments, by precipitating the individual heavy metals as carbonates, sulfides and phosphates.
Arsenic and antimony can also be chemically fixed in this way.
To this end, said solid dispersions are mixed simultaneously with additional, slightly water-repellent calcium oxide into the waste matters that are to be treated, e.g. by feeding them synchronously into a vertical tube mixer. For the first time this enables large quantities of these waste matters to be stored without further safety measures in an environmentally neutral fashion or used as landfill, e.g. for landscaping purposes. The necessary proportions are determined by the requirements of soil mechanics; they can be ascertained in conventional suitability tests, e.g. by determining Proctor density.

2 ~ 12 Example 10 100 parts by weight of clay, or a paste mixed from finely dispersed aluminiu~ hydroxide or zeolith or bentonite with water, or spent, moist bleaching earth, or 100 parts by weight of a mixture of said suspensions, are homogenized in a com-pounder with 50 parts by weight of a long-chain amine, e.g.
stearylamine, and 10 parts by weight of an aminosilane, e.g. a trialkoxyaminosilane, and then homogenized with 500 parts by weight of hydrophobic calcium oxide. The resulting dry, pul-verulent and homogeneous solid dispersion, containing excess calcium oxide, can be used as such or else, after the hydration reaction with not quite the stoichiometric amount of water in relation to the calcium oxide excess has been carried out, in the form of this reaction product, i.e. with calcium hydroxide as the chief component in terms of quantity, for very extensive adsorption or chemisorption of harmful substances in the off-gases of refuse incinerator plants, especially of halogenated dibenzodioxins and dibenzofurans.

Example 11 100 parts by weight, or a paste mixed from finely dispersed aluminium hydroxide or zeolith or bentonite with water, or spent, moist bleaching earth, or 100 parts by weight of a mixture of said suspensions, are homogenized in a compounder with 50 parts by weight of an alkali sulfide or alkaline earth sulfide and the resulting homogeneous mix then homogenized with 150 parts by weight of hydrophobic calcium oxide. Thanks to its hydrophobic nature, the resulting dry, pulverulent and homoge-neous solid dispersion, containing excess calcium oxide, can readily be worked into the surface of industrial waste tips containing heavy metals. This produces, over a large area, a deposit with precipitating reagents which, on account of slow-acting desorption processes (sulfide ions) or else on account of their poor solubility (calcium hydroxide and calcium carbon-ate obtained from calcium hydroxide), are only incorporated very slowly into the tip along with rainwater as the vehicle, and there bring about precipitation reactions in situ. The absolute quantity of precipitating reagents required for this, and thus the thickness of the deposited layer, can be ascer-tained from the height of the tip and the average concentration of precipitable heavy metals in the tip. A similar procedure is adopted for immobilizing harmful substances in other accumu-lated deposits and waste dumps.

Claims

PROCESS FOR THE PRODUCTION OF HOMOGENEOUS, FINELY DISPERSED, PUL-VERULENT SOLID DISPERSIONS, IF NECESSARY HOMOGENEOUSLY CHARGED WITH
ACTIVE COMPOUNDS, AND THE USE OF PRODUCTS THEREBY OBTAINED.

1.
Process for producing homogeneous, finely dispersed, pulveru-lent solid dispersions, consisting essentially of a) mechanically homogenizing an aqueous, finely dispersed sus-pension with an alkaline earth oxide or an aluminium alcoholate or a silicic acid ester or with a mixture of these compounds, and b) allowing the alkaline earth oxide or the aluminium alcoholate or the silicic acid ester or the mixture of these compounds in the homogeneous mix to react with the stoichiometric quantity of water.

2.
Process of claim 1 wherein said aqueous, finely dispersed sus-pension comprises a material of natural or industrial origin.

3.
Process of claim 1 wherein said aqueous, finely dispersed sus-pension has been obtained from finely dispersed dry materials of natural or industrial origin through the addition of water.

4.
Process according to claims 1 to 3 wherein said aqueous, finely dispersed suspension of natural origin comprises pulverulent natural clay, natural clay and clay-like or clay-containing ma-terials.

5.
Process according to claims 1 to 4 wherein said aqueous, finely dispersed suspension of industrial origin comprises production residues, such as used bleaching earth and red mud in the form of a residue of the Bayer Process.

6.
Process according to one of claims 1 to 5 wherein calcium oxide is employed as the alkaline earth oxide.

7.
Process according to one of claims 1 to 6 wherein the alkaline earth oxide has been pre-treated with reaction retarders.

8.
Process according to claim 7 wherein the reaction retarder comprises a hydrophobizing agent.

9.
Process according to one of claims 1 to 8 wherein the reaction retarders are added to said aqueous, finely dispersed suspen-sion.

10.
Process according to one of foregoing claims wherein said alu-minium alcoholate comprises a commercial liquid mix of alu-minium alcoholates.

11.
Process according to one of foregoing claims wherein said silicic acid ester comprises a commercial mix of silicic acid esters.

12.
Process according to claim 1 for producing pulverulent solid dispersions, homogeneously charged with active compounds, con-sisting essentially of a) mechanically homogenizing an aqueous, finely dispersed sus-pension with active compounds, b) homogenizing the resulting homogenized mix with an alkaline earth oxide or an aluminium alcoholate or a silicic acid ester or with a mixture of these compounds, and c) allowing the alkaline earth oxide or the aluminium alcoholate or the silicic acid ester or the mixture of these compounds in the homogeneous mix to react with the stoichiometric quantity of water.

13.
Process according to claim 12 wherein the active compounds are formed in situ within an aqueous finely dispersed suspension by mixing appropriate proportions of aqueous, finely dispersed suspensions mechanically homogenized with the stoichiometrical quantity of the corresponding chemical components of the active compounds to be formed.

14.
Process according to on of the claims 12 and 13 wherein said active compounds comprise substances and mixes of substances utilizable in agriculture.

15.
Process according to claim 14 wherein said substances and mixes of substances utilizable in agriculture comprise fertilizers and/or trace elements and/or plant protection agents or mixes thereof.

16.
Process according to on of the claims 12 and 13 wherein said active compounds comprise inorganic or organic reaction partners for the detoxification, immobilization and chemical fixation of harmful substances.

17.
Process according to claim 16 wherein said active compounds comprise reducing metals like magnesium and aluminium or pre-cipitating agents like sulfides, carbonates and phosphates.

18.
Process according to on of the claims 12 and 13 wherein said active compounds comprise inorganic and/or organic adsorption and absorption agents for the immobilization and adsorptive or absorptive fixation of harmful substances.

19.
Process according to claim 18, wherein said inorganic and/or organic adsorption and absorption agents comprise high-boiling inert substances.
20.
Process according to claim 19, wherein said high-boiling inert substances comprise paraffin wax, vaseline, bitumen and bitumi-nous substances.
21.
Method for the improvement of agricultural and technical proc-esses consisting of employing said pulverulent finely dispersed solid dispersions produced according to one of the claims 1 to 20.
22.
Method for the improvement of agricultural and technical proc-esses consisting of employing said pulverulent finely dispersed solid dispersions produced according to one of the claims 1 to

20 along with an excess of calcium oxide and/or aluminium alco-holate.
23.
Method for the immobilization, fixation, insulation, encapsula-tion and detoxification of harmful substances consisting of em-ploying said pulverulent finely dispersed solid dispersions produced according to one of the claims 1 to 20.
24.
Method for the immobilization, fixation and detoxification of harmful substances in off-gases consisting of employing said pulverulent finely dispersed solid dispersions produced accord-ing to one of the claims 1 to 20.
25.
Method for the dehalogenation of halogenated organics consist-ing of employing said pulverulent finely dispersed solid dis-persions produced according to one of the claims 1 to 20.