Preparation of filter aids based on diatomites

Int. J. Miner. Process. 80 (2006) 255 – 260 www.elsevier.com/locate/ijminpro

Preparation of filter aids based on diatomites Sanja Martinovic ⁎, Milica Vlahovic, Tamara Boljanac, Ljubica Pavlovic Institute for Technology of Nuclear and Other Mineral Raw Materials, 86 Franchet d'Esperey St, 11 000 Belgrade, Serbia and Montenegro Received 28 July 2005; received in revised form 17 May 2006; accepted 23 May 2006 Available online 11 July 2006

Abstract Two major deposits of diatomaceous earth (diatomite) in the region of the Balkan Peninsula, the Kolubara basin (Serbia and Montenegro) and the Vesje deposit (Former Yugoslav Republic of Macedonia), were selected for detailed investigation of their possible application in preparation of beer filter aids. Chemical, mineralogical and structural properties of diatomite samples were analyzed with the aim of predicting the filtration efficiency. Results of beer filtering compounds preparation are presented in this paper. The parameters of crushing, drying, calcination and classification are also defined. Beer filtration tests proved diatomites to be satisfactory and not causing any degradation of filtration process or beer quality. Technological flow scheme for obtaining the beer filter aids is proposed in the paper. © 2006 Elsevier B.V. All rights reserved. Keywords: diatomite; XRD; TEM; processing; filtration

1. Introduction Diatomaceous earth is a non-metallic mineral raw material composed of skeletal remains of single-cell water plants (algae), known as diatomite. The skeletal diatomite, microscopically viewed, have quite complex structure with numerous fine microscopic pores, cavities and channels and, therefore, large specific surface area and high adsorption capacity. Owing to these characteristics, diatomaceous earth can be used as adsorption auxiliary material for filtration. In some regions, deposits of diatomaceous earth are suffi-

⁎ Corresponding author. Tel.: +381 63 451 190; fax: +381 11 3691 583. E-mail addresses: [email protected] (S. Martinovic), [email protected] (M. Vlahovic). 0301-7516/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.minpro.2006.05.006

ciently thick and pure to be exploited and processed for certain purposes. Diatomaceous earth is suitable for production of filtering compounds used in breweries. The annual production of beer in Serbia and Montenegro is about 4.6 million hl (Serbian Chamber of Commerce, 2004). Serbia and Montenegro has sufficient resources of diatomaceous earth to meet the needs of domestic breweries, but there is no organized production of beer filter aids. According to market analysis, the annual consumption of diatomaceous earth filter aids by breweries in Serbia and Montenegro is about 862 t and it is completely covered by imports from the USA and European countries. Diatomaceous earth can be found at several localities on the Balkan Peninsula. Two of these deposits, the Kolubara deposit in Serbia and Montenegro, located 60 km south of Belgrade and the Vesje deposit in the Former Yugoslav Republic of Macedonia located near

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Negotino, were selected for the purpose of this investigation. 2. Materials and methods 2.1. Geological characteristics of deposits The Kolubara deposit of diatomaceous earth is located within surface layers of lignite and belongs to marine lake sedimentary type of deposits (Jankovic and Vakanjac, 1969). The mineral appears in the upper layers of lignite that are actively exploited, so it is characterized by insignificant presence of carbon. Different levels of coal contamination result in existence of two basic qualities: white and gray diatomaceous earth. In case of higher contamination level, the thickness of the gray earth layer is in the range of 0.8–3.5 m and it is found close to the upper layers of coal. The thickness of the white diatomaceous earth bed is in the range of 0.2–2 m and it is found above upper coal layers. White diatomaceous earth is considered to be the raw material of the highest quality. Resources of white diatomaceous earth are almost negligible in comparison to those of the gray one, so the investigation was focused on gray diatomaceous earth of the Kolubara deposit. The Vesje deposit of diatomaceous earth is situated within the Tikves Basin in the Former Yugoslav Republic of Macedonia. Deposit is located in broad area along the Vardar River, at 730 m a.s.l. The deposit of Vesje locality is geologically associated with preexistence of the fresh-water lake. The layers are found between sandy-clay tuffs and andesite conglomerates. Direction of layers is horizontal with a slight slope of 3.5° towards southwest. Diatomaceous earth from this deposit is considered to be the raw material of the highest quality. 2.2. Sample preparation The tests were performed with 2000 kg of diatomaceous earth obtained from the Kolubara and Vesje deposits. The method of mechanical and thermal sample preparation consisted of the following phases: natural draught drying, ore crushing and cutting, plant drying, flux calcinations, disintegration process and air classification (Verzele, 1979; Rose, 1970). Samples from the Kolubara deposit containing high amount of carbon i.e. coal (up to 20%) were fired prior to chemical characterization. On the other hand, the Vesje diatomaceous earth did not contain organic impurities and was therefore only dried.

2.3. Material characterization Characterization of the samples was made by chemical and mineralogical analyses, determination of physical and thermal properties, microstructure analysis, filtration efficiency and their influence on beer quality. Content of silica was determined by conventional gravimetric analysis, while contents of aluminium, iron, sodium and potassium were determined by atomic absorption spectroscopy (AAS 703-Perkin Elmer and AANALYST 300, USA). Particle size distribution was performed by sedimentation method using Sartorius balance. X-ray diffraction analysis was carried out in a Philips X-ray diffractometer type Philips PW-1820/00 using monochromatic CuKα radiation. Transmission electron microscope (TEM) observations were made using a microscope of the type JSM T20, JEOL Japan, equipped with an energy dispersive Xray analyser (EDAX). Bulk density, moisture content, loss of ignition and influence of diatomaceous earth on organoleptic characteristics of beer were determined according to the recommended method for inspection of the filter aids used in breweries (Briggs et al., 1982; Nykänen and Suomalainen, 1983). Membrane filtration test, also called the Esser test (standard filterability test), was used for determination of beer filtration rate. Industrial filtration tests were performed with SEITZ frame filter having 10 m3/hl capacity, 50 filter plates and effective filter surface of 33 m2. 3. Results and discussion 3.1. Characterization of samples Chemical compositions of initial diatomite are presented in Table 1. Table 1 Chemical composition of diatomaceous earth from the Kolubara (fired) and Vesje (dried) deposits Component

Kolubara-fired (%)

Vesje-dried (%)

SiO2 Al2O3 Fe2O3 CaO MgO TiO2 K2O Na2O LOI

82.0 11.0 2.5 1.7 0.8 0.6 0.4 0.3 0.3

90.0 2.9 1.5 0.8 0.1 – 0.1 0.2 4.4

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Based on chemical analyses data it could be concluded that there are certain differences in chemical compositions of deposits depending on their origin. The Vesje sample has higher content of SiO2 than the sample from the Kolubara deposit and therefore lower contents of other present oxides. Hence, diatomaceous earth from the Vesje deposit is considered as raw material of the highest quality with the content of SiO2 about 90%. On the other side, the Kolubara deposit shows better mineral and physical properties. It is also evident that Fe2O3 content in the Kolubara sample is higher than in the Vesje sample, but it has no effects on beer quality. Loss of ignition (LOI) is considerable in the Kolubara sample due to high content of coal. The diffractograms of diatomaceous earth samples from the Kolubara and Vesje deposits are presented in Fig. 1. X-ray diffraction analyses show that the samples mostly consist of amorphous phases with traces of quartz, feldspar, cristobalite, and tridimite. Mineralogical analyses show that content of skeletons and shells is approximately 80% while the rest are impurities of organic and inorganic origin. Microstructure analysis provides reliable information about shape, structure, porosity and size of diatomaceous earth particles. Transmission electron micropho-

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tographs (TEM) of diatomaceous earth are presented in Fig. 2. Microphotographs of diatomaceous earth from the Kolubara deposit are presented in Fig. 2a–b. In Fig. 2a, broken pieces of diatomaceous earth having cylindrical and plateaus shapes are present. There are also fine plates and shells of accompanying impurities, probably coal and alumosilicates. Fig. 2b shows undamaged forms of diatomaceous earth with extremely clean pores. On the surface of diatomaceous earth insignificant content of the impurities originating from coal can be noticed. The impurities are outside pores, so during the calcination, complete combustion of coal is obtained. Microphotographs presented in Fig. 2c–d show the morphological shape and size of diatomaceous earth particles of the Vesje deposit. The presence of various shapes of diatomaceous earth (cylindrical and plateaus particles) together with small particles of impurities (small shales and plates) and broken diatomites, too, could be noticed in Fig. 2c. Considerable content of small crystals (impurities) such as quartz, feldspar and cristobalite are detected on the surface of diatomaceous earth and this sample belongs to gray diatomaceous earth. In Fig. 2d diatomaceous earth particle of cylindrical shape with all accompanying ingredients on its surface could be noticed.

Fig. 1. X-ray diffraction (XRD) patterns of the diatomaceous earth: (a) Kolubara deposit; (b) Vesje deposit.

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Fig. 2. Transmission Electron Micrographs of diatomaceous earth: (a–b) Kolubara deposit (a – magnification of 1800×; b – magnification of 4000×); (c–d) Vesje deposit (c – magnification of 4000×; d – magnification of 800×).

3.2. Preparation of filtration aids The experimental processing of beer filter aids was performed in the following way: • • • • •

Natural draught of crude raw materials; Primary crushing of dried raw materials; Drying and calcination; Disintegration of calcined materials; Air classification of calcined materials.

Natural draught of raw materials was simulated in laboratory under the conditions normally applied in industry. Crushing of raw materials air-dried to the moisture content of 30–50% was performed in a laboratory mill with cutters. During the crushing, cuts sized 0–16 mm were obtained. The main goal of primary processing is to avoid sticking of ore to the parts of mill if moisture exceeds 30%. For this reason, it is necessary to dry the Vesje ore to the moisture level lower than in the Kolubara ore. Drying was

monitored through the experiments performed in a laboratory drum drier. Calcination was performed according to the flux calcination regime. During calcination, the additives supporting the formation of agglomerated diatomite particles were applied. The experiments of the calcination process were performed in electric laboratory drum furnace. Technological parameters of drying and calcinations are presented in Table 2. Drying and calcination are the most important phases of the process. Powder with maximum moisture content of 7% is obtained after drying process. The agglomerates are always present in dried powder. During the Table 2 Technological parameters of drying and calcination Parameter

Drying

Calcination

Revolution (rpm) Temperature (°C) Moisture (input)

5 180–250 30–35

3 900–950

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calcination, these agglomerates tend to slow down the combustion of coal present in dried diatomaceous earth samples. Therefore, it is necessary to disintegrate the agglomerates prior to calcination. The method of moving layer flux calcination of real powders is applied. This method was selected due to high ratio of very fine primary diatomite particles (1–5 μm) in dried semiproduct. The fine particles decrease the flux because of high resistance to flow. Hence, it is necessary to provide size distribution of the filter aids particles that have its maximum in the range of 5–40 μm. Size distributions of particles of tested materials, before and after calcination, are presented in Table 3. Particles of diatomaceous earth of the Vesje deposit are characterized by a high proportion of particles smaller then 5 μm or bigger then 30 μm. On the other side, particles of diatomaceous earth of the Kolubara deposit are characterized by high ratio of particles in the range of 5–10 μm and 25–30 μm. According to the results of diatomaceous earth investigation from the Kolubara and Vesje deposits, general processing flow scheme of beer filter aids preparation is developed, Fig. 3. 3.3. Beer filtration test Based on the laboratory tests, influence of diatomaceous earth on beer quality is presented in Table 4. Laboratory tests proved the absence of adverse effects of diatomaceous earth on the beer characteristics. According to both the data on filtration times and particle size-distribution, it could be concluded that the particles of diatomaceous earth from the Kolubara deposit are coarser and therefore provide shorter filtration time and larger capacity of filtration. On the other hand, the smaller size and shape (cylindrical and plateaus) of diatomaceous earth particles from the Vesje deposit result in longer filtration time and consequently lower capacity of the filtration. Table 3 Size distribution of particles of diatomaceous earth of the Kolubara and Vesje deposits Particle size (μm)

Before calcination

After calcination

Kolubara

Vesje

Kolubara

Vesje

>30 25–30 20–25 15–20 10–15 5–10 <5

9.0 5.0 6.0 2.0 18.0 25.0 35.0

12.8 2.0 2.6 4.8 9.1 18.1 50.1

6.2 21.0 13.4 6.4 21.2 23.0 8.8

31.6 3.2 6.9 1.1 6.4 15.9 30.9

Fig. 3. General processing flow scheme for preparation of filter aids.

The industrial tests of beer filtration using the filter aids proposed in this study were performed at BIP– Belgrade Brewery Plant. The final goal of these tests Table 4 Results of laboratory filtration test Parameter

pH Beer colour (EBC) Beer turbidity (EBC) Beer taste and flavour Fe2O3 (mg/dm3) Filtration time (s) Bulk density (g/dm3)

Test beer before filtration

4.42 9.0 8.6 Normal 0.06 – –

Test beer after filtration Kolubara

Vesje

4.47 9.0 3.2 Normal 0.361 94 240

4.45 9.0 2.6 Normal 0.362 112 210

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Table 5 Results of industrial filtration test Parameter

Kolubara

Vesje

pH Beer colour (EBC) Beer turbidity after filtration (EBC) Fe2O3 in beer after filtration (mg/dm3) Filtration time (h) Beer filterability (ml)

4.52 10.0 0.35 0.232 8.5 90.0

4.66 10.0 0.30 0.313 11.5 90.0

was to determine the filtration efficiency of the tested filter aids. Results of these tests are presented in Table 5. Certain differences could be registered during the investigation and design of processing procedure of filter aids preparation causing the corresponding differences in filtration parameter values, as well as in beer quality. Size distribution of calcined particles shows influence on filtration rate. Namely, it is noticed that high content of fine particles (smaller then 5 μm) in the Vesje samples decreases filtration rate and increases filtration time. 4. Conclusion There are certain differences in processing technology of two investigated qualities and the following conclusions could be derived: Microstructure analysis shows that all impurities of either organic or inorganic origin are outside diatomite pores, which had significant influence on technological process design.

The proposed technological processing procedure provides complete combustion of finely dispersed particles of coal present in the Kolubara deposit. Fine and coarse beer filter aids can be produced from both types of diatomaceous earth. The laboratory and industrial tests of filtration proved that there is a possibility to replace the currently imported beer filter aids with domestic product, which causes no degradation of filtration process or beer quality. Further research will be occupied with determination of appropriate conditions for removal of quartz, feldspar and cristobalite traces (crystal phases) from the Vesje diatomaceous earth. References Briggs, D.E., Young, T.W., Stevens, R., Hough, J.S., 1982. Malting and Brewing Science: Hopped Wort and Beer, second ed. Chapman and Hall, New York. Jankovic, S., Vakanjac, B., 1969. Lezista Nemetalicnih Mineralnih Sirovina. GK, Belgrade. Nykänen, I., Suomalainen, H., 1983. Aroma of Beer, Wine and Distilled Alcoholic Beverages. Reidel Publishing Company, Dordrecht, Netherlands. Rose, A.H., 1970. The Yeasts, Volume 2 and 3, Yeast Technology. Academic Press, New York. Serbian Chamber of Commerce, http://news.suc.org/bydate/2004/ December_02/13.html. Verzele, M., 1979. In: Pollack, J.R.A. (Ed.), Brewing Science, vol. 1. Academic Press, London, p. 311.