EP0193109A2 - Method for beneficiating kaolinite by flotation - Google Patents

Abstract

Process for the selective separation of kaolinite and feldspar by flotation in aqueous pulp, wherein flotation is carried out at the pH-value of the pulp which is naturally obtained during suspension of the mixture of minerals in water using water-soluble salts with trivalent metal ions as activators and depressors, in the presence of cationic and/or anionic surfactants as collectors, and optionally in the presence of other standard flotation aids.

Description

The invention relates to a process for the preparation of kaolinite by flotation, in particular a process by which kaolin and feldspar can be separated in the finest grain area and both minerals can be obtained in high yield in pure form.

Kaolinite is a naturally occurring industrial mineral, for whose diverse and different applications as a filler in the paper and ceramic industry, in the plastics industry, in the manufacture of paints, varnishes, rubber and cables, there is a growing and increasing demand. Kaolinite arises from exogenous (weather, groundwater) and endogenous (hydrothermal hot solutions, deep vapors) influences with predominantly acidic pH values from feldspar (Ullmanns Encyclopedia of Technical Chemistry, Volume 13, page 509 (1977)). High quality demands on the kaolinite product in terms of purity are more difficult to meet, the higher in existing and new: _s chlossenen kaolinite deposits, the shares of not kaolinisiertem feldspar and quartz. Kaolinite _m ust be selectively separated from these accompanying rocks.

The processing of raw kaolin, which in addition to the main mineral kaolinite mostly also contains feldspar, quartz and various iron and titanium minerals, is usually carried out by wet processes in which the kaolinite-containing raw earth is suspended in water. The following separation process is based on a separation of the different mineral components according to the grain size and the specific weight. Since the minerals quartz and feldspar accompanying the kaolinite are generally coarser ("antiparallel grain distribution"), it is possible to satisfactorily separate the coarser quartz and feldspar from kaolinite down to grain sizes of 20 µm (cf. M. Clement and HM Tröndle; Erzmetall 22, H. 3, 131 (1969)).

In view of the fact that feldspar is a raw material that is sought after in the ceramic industry, the separation of kaolinite and feldspar from raw kaolin is aimed at obtaining a feldspar product in addition to the purest possible kaolinite, which meets the high demands for industrial use in glass and Ceramic industry is enough. As is known, mechanical separation processes in aqueous turbidity are used for this. However, the effectiveness of such separation processes reaches a limit if the grain sizes of kaolinite and feldspar are very close to each other in the fine grain range, since the specific weight of the two minerals (approx. 2.58 g / cm ³ ) is practical is equal to. In such a case, the requirement for high purity of both end products, kaolinite and feldspar, is associated with a loss in the inseparable grain classes (fine grain range), which is economically significant. The separation of kaolinite and feldspar in aqueous slurry is explained in detail in BM Coope, Industrial Minerals, 1979, 33 to 49 and HH Murray, Int. J. of Mineral Processing 7, 263 (1980).

Flotation processes are used in mineral purification practice to remove heavy metal oxides, e.g. Oxides of iron and titanium, removed from kaolinite and thus improve the whiteness of the product. Separate processes for the separation of kaolinite from quartz on the one hand and feldspar from quartz on the other hand by flotation of the minerals in the presence of an amine are also collectors from HM Trondle, M. Clement and B. Becher, Interceram 19, 185 and 268 (1970) according to Chemical Abstracts 74, 102589 u (1972). Hydrochlorides and hydroacetates of long-chain aliphatic amines were used as collectors in acidic turbidity.

Flotation experiments with kaolin-quartz or feldspar-quartz mixtures are also described in HM Trondle, M. Clement and B. Brehler, Ceramic Journal 21, 423 and 489 (1969), corresponding to Chemical Abstracts 72, 102251 m (1970). Hydrofluoric and hydrochloric acid aqueous slurries were mixed with long-chain aliphatic amines as collectors for the respective _T pension voltage kaolinite and feldspar minerals of Quarz.eingesetzt. In the process of separating the _K aolinites of quartz was also found that a sharp decrease in kaolinite output at alkaline pH values in the aqueous slurry is due to the fact that the undissociated amine molecules which are formed according to equation (1) below no longer adsorb on the negatively charged kaolin surface and thus preventing the discharge of the kaolinite portion of the slurry with the help of the ammonium salt.

For the treatment of kaolinite- and feldspar-containing aqueous turbidity, the area of fine grain size of both mineral particles is of particular interest; So far, it has not been possible to separate the two minerals in this grain range on an industrial scale. However, this area plays an outstanding role in practice in that mineral mixtures with a particle size distribution of 90% less than 30 µm for kaolinite and 10% less than 30 µm for feldspar are obtained in the washing out of the deposits containing kaolinite and feldspar. Kaolins suitable for use in ceramics even have a fine grain fraction (less than 2 µm) of 50% and more. In the range of these grain sizes, selective flotation in aqueous turbidity causes great problems. The direct flotation for the separation of kaolinite and feldspar in this grain area has not yet been described.

It is known that polyvalent cations are adsorbed on the surfaces of the mineral particles which are suspended in the aqueous slurry and the flo can affect the minerality of these mineral particles within wide limits (B. Dobias, 6th International Congress for Surfactants, Zurich 1972, page 563 (1973)). In addition, polyvalent cations are able to react with the collector surfactant to form complex compounds or poorly soluble precipitates, and in this way remove the surfactant from the desired adsorption process on the surface of the mineral particles. Experience has shown that this reduces the flotation yield unless increased amounts of the collector surfactant are used.

Depending on the composition of the system to be processed by flotation, one and the same multivalent cation can have both activating and deactivating effects in the flotation of mineral particles for the selected collector (surfactant). When which of the two properties dominates can only be determined empirically. As a rule, these effects, whose mechanisms of action are not fully known in detail, are more disruptive than beneficial in the flotation process itself. Preventing the undesired effect of polyvalent cations in the flotation process is therefore a special problem in the preparation of the respective minerals.

The activating or deactivating ("pressing") effect of polyvalent metal cations on silicate minerals is known in part from the literature. Chemical Abstracts 68, 116 041a (1968) reports that aluminum, iron and calcium ions have an activating effect in the flotation of quartz, Have feldspar and sillimanite. Is in this case the concen- _t ration of iron (III) - and aluminum (III) salts to values above 300 mg per liter is increased, a significant decrease of the activating effect in the silicate flotation occurs in acidic and alkaline pH ranges.

The use of cationic collectors in acidic media for the flotation separation of quartz-feldspar sands in the presence of copper (II), calcium, iron (III) and aluminum (III) ions is described in Chemical Abstracts 71, 5014h (1969) described. In strongly sulfuric acid or hydrochloric acid media, the cations mentioned have an activating effect on feldspar and pressing on quartz.

Chemical Abstracts 79, 147 840p (1973) describes the feldspar separation of accompanying materials by flotation in the presence of aliphatic amines or petroleum sulfonates in strongly sulfuric acid solutions. SiO ₂ , Al ₂ O 3 and Fe ₂ O _{3 are} added to the aqueous slurries as activators, the output of feldspar from the slurries increasing with increasing concentrations of collectors.

In Neue Bergbautechnik 9, 349 (1979), corresponding to Chemical Abstracts 92, 150 570 (1980), it is described that aluminum trichloride has an activating effect on feldspar and a pressing effect on the aqueous flotation of feldspar-quartz mixtures in the presence of long-chain aliphatic amines Quartz shares in the cloudiness. However, the problem of separating kaolinite and feldspar in aqueous slurries is not addressed in any of the references mentioned.

It has now been found that for the separation of kaolinite and feldspar by flotation it is in no way necessary to adjust the aqueous turbidity to strongly acidic pH values with the aid of hydrohalic acids or sulfuric acid. Rather, a selective separation of kaolinite and feldspar is also possible at a natural pH, which is 5 to 8 when the minerals are suspended in water. It was also found that, in the natural pH range, the addition of trivalent metal ions, for example Al ³⁺ or Fe ³⁺ , in the form of corresponding salts, significantly improves the selectivity in the flotation separation of kaolinite and feldspar in the fine grain range. It has also been found that when the aqueous slurry is adjusted to natural pH values and the use of trivalent metal ions, flotation with anionic surfactants as collectors is advantageous over cationic flotation.

The invention therefore relates to a process for the selective separation of kaolinite and feldspar by flotation in aqueous slurry, which is characterized in that the flotation is carried out at a pH of the slurry, which occurs naturally when the mineral mixture is slurried in water water-soluble salts with trivalent metal ions as activators and depressors and in the presence of cationic or anionic surfactants as collectors and, if appropriate, with the addition of other auxiliaries customary in flotation.

The pH at which the process is carried out according to the invention is generally in the range between 5 and 8. This pH then results if the solid mineral mixtures are slurried in tap water or fully demineralized water or the mineral mixture is washed out of the rock under high pressure with water jet and brought to light. The addition of large amounts of activating acids, for example hydrohalic acid or sulfuric acid, to set a strongly acidic pH, as was mandatory in the prior art for such flotation processes, is necessary to achieve an effective and selective separation of kaolinite and feldspar Invention no longer required.

According to the invention, salts of trivalent metal ions are also added to the aqueous slurries as activators or depressors. Salts or polysalts of aluminum and iron (III) salts are used. In practice, the sulfuric salts of trivalent metals are used with advantage. The concentration of the salts is in the range from 50 to 2000 g / t, preferably 100 to 1000 g / t, based on the anhydrous metal salt.

Aluminum salts, for example aluminum sulfate, are particularly preferably used according to the present invention. It has been found that the Al (III) ion in aqueous slurries at pH values in the _Be - rich to 8 activating effect on kaolinite and deactivating, ie pressing, acts from 5 to feldspar. By adding aluminum salts to the aqueous slurry, concentrates with a higher kaolinite concentration are obtained during flotation. At the same time, the kaolinite output is increased, so that feldspar in a higher purity is also obtained as a flotation residue.

Cationic or anionic surfactants can be used as collectors in the process according to the invention. Compounds from the group of monoalkyltrimethylammonium compounds, dialkyldimethylammonium compounds, alkylarylammonium compounds, alkylamines, hydroxylamines and / or hydroxyalkylamine polyglycol ethers are used as cationic surfactants, the compounds mentioned preferably containing alkyl groups having 12 to 18 carbon atoms. Preferred aryl radicals are phenyl and / or benzyl radicals.

However, the use of aluminum ions in the separation of kaolinite and feldspar achieved by flotation in particular enables a process to be carried out with the addition of anionic surfactants as collectors. The flotation with anionic collectors has surprisingly been found to be particularly advantageous over the flotation with cationic surfactants in that heavy mineral components present in the ore can be separated from the kaolinite before the flotation, which leads to a higher degree of whiteness of the kaolinite concentrate and also an improved quality of the feldspar residue. In addition, the subsequent processing of the kaolinite is facilitated in that anionic surfactants can be more easily desorbed from the surface of the kaolinite particles than cationic surfactants. It should also be borne in mind that anionic surfactants should be preferred over cationic surfactants due to their environmental behavior alone.

Compounds from the group consisting of fatty acids, alkyl sulfates, alkyl ether sulfates, alkyl benzene sulfonates, petroleum sulfonates, ester sulfonates, alkyl sulfosuccinates, alkyl sulfosuccinamides, alkyl phosphates and / or alkyl ether phosphates are preferably used as anionic surfactants. Alkylbenzenesulfonates, _P etrolsulfonate, fatty alcohol sulfates, ester sulfonates and / or alkyl sulfosuccinates having the above chain length of the alkyl use.

According to the method of the present invention, it is also possible to use mixtures of cationic and anionic surfactants with nonionic additives, for example fatty alcohol, alkyl polyglycol ethers and / or alkylphenol polyglycol ethers.

The concentration of surfactants used as collectors according to the invention is in the range from 50 to 2000 g / t, preferably from 100 to 1000 g / t.

According to the invention, additional auxiliaries known to be used in flotation can be added for the separation of kaolinite and feldspar from the aqueous slurry caused by flotation. Examples of such auxiliaries are foaming agents on the one hand or anti-foaming agents on the other hand, which, in contrast to methods known from the prior art, are not absolutely necessary.

When the constituents provided according to the invention are used, the first component is floated in the mineral mixture of kaolinite and feldspar, while feldspar with surprisingly high purity is obtained as a flotation residue in comparison with processes from the prior art. The respective flotation steps are repeated, depending on the quality requirements for the products, a selective separation of the two components being achieved, particularly in the fine grain area. According to the invention, a further post-cleaning step is sufficient to obtain concentrates with a kaolinite content between 93 and 97%.

The kaolinite fraction obtained by flotation is worked up in subsequent process steps. The surfactants adsorbed on the surface are desorbed. In the anionic surfactants used with preference, the binding of the surfactant molecule to the negatively charged surface of the kaolinite particles takes place via the ion bridges consisting of trivalent metal ions, so that the anionic surfactants can be desorbed more easily from the surface of the kaolinite than cationic surfactant molecules.

Another advantage of the process according to the invention can be seen in the fact that the flotation of kaolinite caused by anionic or cationic surfactants in the presence of trivalent metal ions, preferably aluminum (III) ions, is largely independent of the water hardness and of the turbidity content of indifferent electrolytes . Divalent ions, such as Cal _- cium- or magnesium ions, improve likewise the selectivity in the flotation of kaolinite / feldspar mineral mixture, however, this effect occurs only at very high ion concentrations that would make the addition of these ions uneconomical for flotation pulp.

The selective separation of kaolinite and feldspar caused by flotation according to the invention in the range of small grain sizes of the minerals involved, i.e. especially when conventional separation processes have caused major problems. Grain sizes in the range from 30 to 2 μm are preferred for the application of the method according to the invention.

Normally, the quartz content of the raw products in question for the flotative separation of kaolinite and feldspar is due to a previously current separation process extremely low, so that quartz does not have to be separated. However, it is also possible to float feldspar to separate quartz if the raw product has a high quartz content after the flotation of kaolinite by reactivation with aluminum ions and addition of a collector. This is then done practically by methods known from the prior art.

The invention is illustrated by the examples below.

The flotation experiments were carried out in a Humboldt-Wedag laboratory flotation cell of 1 1 or 2 1 content with a kaolinite / feldspar / quartz fraction with a particle size of 90% less than 20 µm. This fraction was taken from the intermediate stage of a conventional kaolinite processing plant.

The selectivity of the flotation, i.e. The content of kaolinite and feldspar in the concentrate or in the flotation residue was determined using the known method of loss on ignition (DIN 51 081 for testing ceramic raw materials through change in weight during annealing (July 1979)).

Examples 1 to 4

The minerals mixture was treated 5 min in the flotation cell, wherein, in the examples 2 to ₄ activating additives (sulfuric acid and / or _aluminum-m i niumsulfat) were added. The aqueous solution of a cationic collector Araphen ^R G2D was then added. The flotation was carried out with the addition of a commercially available foamer (Araphen ^R G2 _D 1 ₅ ).

The results are shown in Table 1 below.

Result:

While, according to Example 1 (without activating additives), an extremely poor separation performance of the flotation was achieved both with regard to the kaolinite output in the concentrate and with regard to the kaolinite content in the flotation residue, the selectivity could be improved by the addition of sulfuric acid (Example 2). The addition of aluminum sulfate significantly improved the selectivity in the flotation, so that concentrates with a high kaolinite content were obtained in a single post-cleaning step.

Examples 5 to 7

Instead of the cationic collector of Examples 1 to 4, cetylpyridinium chloride was used as the cationic collector. The results are shown in Table 2 below.

Result:

Even when using cetylpyridinium chloride as a cationic collector, a significant increase in the selectivity of the separation and an increase in the amount applied were measured when aluminum sulfate was added.

Examples 8 to 11

In contrast to Examples 1 to 7, the flotation was carried out with an anionic collector (sodium alkylbenzenesulfonate) in the absence (Example 8) or in the presence (Examples 9 to 11) of activating additives. The results are shown in Table 3 below.

Result:

While the use of an anionic collector in the absence of activating additives gave relatively poor results with regard to the kaolinite yield and the residual kaolinite content in the flotation residue, selective addition of kaolinite and feldspar was achieved when Al (III) ions were added to the flotation solution the yield of kaolinite and the kaolinite content in the flotation residue were significantly more favorable than when using sulfuric acid as an activator.

Claims (11)

1. A process for the selective separation of kaolinite and feldspar by flotation in aqueous cloudy, characterized in that the flotation a) at the pH of the slurry, which naturally occurs when the mineral mixture is slurried in water, b) using water-soluble salts with trivalent metal ions as activators and depressors and c) in the presence of cationic and / or anionic surfactants as collectors and d) optionally with the addition of other auxiliaries customary in flotation
carries out. 2. The method according to claim 1, characterized in that one carries out the flotation at a pH in the range from 5 to 8. 3. Process according to claims 1 and 2, characterized in that chlorides and / or sulfates of trivalent metal ions are used as water-soluble salts. 4. Process according to Claims 1 to 3, characterized in that aluminum and / or iron (III) salts are used as salts of trivalent metal ions. 5. Process according to Claims 1 to 4, characterized in that aluminum sulfate is used as an activator. 6. Process according to Claims 1 to 5, characterized in that the activator concentration is set to a range from 50 to 2000 g / t, preferably to 100 to 1000 g / t, based on the anhydrous salt. 7. The method according to claims 1 to 6, characterized in that anionic surfactants are used as collectors. 8. Process according to Claims 1 to 7, characterized in that the collector concentration is set to a range from 50 to 2000 g / t, preferably to a range from 100 to 1000 g / t. 9. The method according to claims 1 to 8, characterized in that alkylbenzenesulfonates, petroleum sulfonates, fatty alcohol sulfates, ester sulfonates and / or alkyl sulfosuccinates are used as anionic collectors in which the alkyl radicals have 12 to 18 carbon atoms. 10. The method according to claims 1 to 9, characterized in that adding a foamer to the flotation slurry. 11. The method according to claims 1 to 10, characterized in that an anti-foaming agent is added for foam regulation.