NR 3/2016 INŻYNIERIA MATERIAŁOWA MATERIALS ENGINEERING 131

Influence of leather tanning waste addition and sintering parameters on physical and mechanical

properties of ceramic granulesMarcin Godzierz1*, Paweł Wilkołek1, Gözden Torun2, Tomasz Pawlik1,

Małgorzata Sopicka-Lizer1

1 Department of Material Science, Silesian University of Technology, Katowice, Poland, *godzierz@gmail.com 2Middle East Technical University, Ankara, Turkey

This paper presents results of manufacturing the ceramic porous granules made of the local waste materials. These granules were produced from the mixture of the car wind-shield glass contaminated by residuals of the PVB foil and aluminosilicate-based mine slates. Addition of the leather tanning wastes was used in order to increase granules porosity without significant decrease of mechanical properties. The paper shows the effect of tanning wastes addition and sintering parameters on the properties of the resultant granules in comparison to the leather-free product. Porosity, apparent density and water absorp-tion were examined according to EN 1097 standard, and compressive strength was examined according to UNE-EN 13055-1 standard. Differences in the microstructure of granules were examined using scanning electron microscope. Partial substitution of both starting materials by tanning wastes and/or the two-step sintering regime could significantly improve the physical properties, what has been shown in the present paper.

Key words: ceramic granules, leather tanning waste, recycling, waste management, windshield glass.

Inżynieria Materiałowa 3 (211) (2016) 131÷136DOI 10.15199/28.2016.3.7© Copyright SIGMA-NOT MATERIALS ENGINEERING

1. INTRODUCTION

Nowadays, there are several issues related to recycling the car windshield glass. One of these problem is related to the layered structure of a car windshield. Two layers of glass are separated by a polymer layer of polyvinyl butyral (mainly known as PVB), which improves mechanical properties of the laminated material but simultaneously it prevents the separation of layers in the waste glass during a mechanical treatment. Advanced technology allows to separate those layers during screening resulting in separation of PVB as a large-sized fraction from the fine glass powder. It is im-possible to produce the windshields again from these materials, but the PVB scraps can be used once more as an additive to different type of industrial glues. Recycled glass can be reused as well, for example in manufacturing fiber glass insulation or as an addition to concrete-based materials.

The general objective of the present research was to find a new way of recycling the windshield glass wastes. One of the solution could be mixing of the milled glass powder with aluminasilicate waste materials in order to produce the lightweight aggregates, which can be applied in many industrial areas (e.g. architecture, gardening). One of the most attractive solution is the local waste management, including mine slates or any other aluminosilicate-based mineral to produce ceramic granules intended for applica-tion in the concrete formulation. For this purpose they must fulfill a number of requirements, according to EN 1097, UNE-EN 13055 and many other standards [1÷5].

The third possible local waste material are the leather tanning wastes. Presently, they are utilized by thermal decomposition meth-od to obtain a post-process oil or a char [6]. Addition of tanning wastes to manufacturing ceramic granules could act as a porogen because of the glass powder presence and a carbon presence for CO2 gas evolution.

The purpose of this study is to examine the possibilities of the production of the environmentally friendly lightweight aggregates

from the local wastes of the mine slates, the windshield glass wastes and leather tanning wastes. The research aimed at the examination of the effects of the leather tanning waste addition, special prepara-tion of the leather wastes and various sintering regimes on the basic properties of ceramic aggregates.

2. EXPERIMENTAL

The mixtures of raw materials: windshield glass with residual PVB contamination, mine slates and leather tanning wastes were weighed out according to composition given in Table 1. The slates were derived from Krupiński mine (Suszec, Upper Silesia, Poland), the grinded windshield glass pieces and leather tanning wastes were delivered by Kapadora Company (Żory, Upper Silesia, Poland). As the reference a mixture without leather additive (G1) was pre-pared. Difference between G2 and G3 series is in the preparation of leather tanning wastes. In G2 specimens, leather was added in the as-received form after tanning, i.e. in the form of the tiny discs with a diameter of 1÷2 mm and thickness of 1 mm. In G3 series the tanning waste was milled in a small blade mill grinder and after that process, it looked like a cotton ball: soft and fluffy palpable gran-ules, permanently existing after grinding.

Batches of the starting materials were then milled to 0.12 mm grain size using a cross beater mill (Retsch, SK 100). Subsequently, the powders were placed in the pelletizer (Eirich TR04) and were subjected to a granulation process with 15 wt % of water addition. Later, the mixture was transferred to the granulation plate to obtain the round granules. At the end, after drying, the granules were sin-tered with a heating rate of 600°C/h at temperature shown in Table 1. Two different sintering schemes were applied: the two-step sin-tering and a one-step sintering mode. The first step was applied in order to allow the evolving gases for bubbles formation for 15 min before the sintering at 950÷1000°C for 15 min took place. The one-step sintering regime employed a heating with a constant rate up to 950 or 1000°C and then isothermal holding for 30 min. Thus the

132 INŻYNIERIA MATERIAŁOWA MATERIALS ENGINEERING ROK XXXVII

total time at high temperature was the same in the all trials. The sintered granules were separated in a screen into 3 fractions: below 5 mm, between 5 and 10 mm and above 10 mm.

Water absorption (N), apparent density (ρa) and open porosity (Po) were examined using Archimedes method and the following formulas were applied:

N m m

mw= − ⋅100%

(1)

a

w h=

−⋅m

m md0

(2)

P m m

m mow

w h%= −

−⋅100

(3)

where: m is mass of dry material, mw is mass of wet material, mh is mass of material in water (hydrostatic mass), d0 is water density at measuring temperature (18.5°C).

Morphology and chemical composition of starting powders and morphology of the fractured granules were observed using a scan-ning electron microscope (SEM) (Hitachi S-3400N). EDS analysis was performed on the powdered samples in the four different mi-croareas of 0.25×1 mm (Fig. 1).

Compression tests of granules were performed according to UNE-EN 13055-1 standard. Compression strength was calculated from equation (4) [1, 5]:

C L F

Aa = +

(4)

where: Ca – compressive strength, N/mm2 or MPa, L – force exerted by the piston, N, F – force needed to the piston cavity, N, A – piston area, mm2.

All results were statistically verified with the Hampel’s test.

3. RESULTS AND DISCUSSION

Selected areas of EDS analysis of starting materials are shown in Figure 1. The chemical composition of examined powders is shown in Tables 2 and 3. The relatively high content of potassium in the mine slates suggests formation of a low eutectic melting at about 800°C. Some amount of titanium and iron in slates may cause for-mation of a brown color of the final product.

The chemical composition of slates indicates their aluminasili-cate origin with a quite stable composition in the microareas. Dif-ferences in a concentration of colouring cations (Fe, Ti) may pro-duce various coloration of the fired granules. Variation of the glass chemical composition seems to be slightly higher but it is expected to be on the acceptable level.

Relationship between sintering parameters and physical prop-erties (water absorption, apparent density and open porosity) of the examined granules are shown in Figures 2÷4. The leather-free

granules show lower density after the two-step sintering with the minimum value if the first step was carried out at 850°C. Direct sin-tering at 950 or 1000°C led to higher densities and lower porosity. Addition of the leather waste obviously reduced density and in-creased porosity of the resultant granules. The effect was more visi-ble if the leather waste was previously milled in the small blade mill grinder and the two-step sintering gave a density reduction of about 9% after first step sintering at 850°C. Some unexpected results were visible if the one-step sintering was applied to the granules with

Table 1. Composition (wt %) and sintering parameters of the exam-ined batchesTabela 1. Skład (% mas.) i parametry spiekania próbek

Batch number

Slate wt %

Windshield glass wt %

Leather tanning wastes wt %

Sintering parameters

G1 62.5 37.5 — 750°C/15 min + 1000°C/15 min 800°C/15 min + 1000°C/15 min 850°C/15 min + 1000°C/15 min

950°C/30 min 1000°C/30 min

G2 60 35 5 as-received

G3 60 35 5 milled

Slate Windshield glass

Fig. 1. Selected areas for EDS analysis of a slate and windshield glass powderRys. 1. Wybrane obszary do analizy EDS na próbkach łupka przywęglo-wego oraz szkła samochodowego

Table 2. Chemical composition in the selected areas of the slate sample, wt %Tabela 2. Skład chemiczny w wybranych obszarach próbki łupka przy-węglowego, % mas.

Mg Al Si K Ti Fe

Slate_1 1.0 20.9 54.2 9.6 2.4 11.9

Slate_2 0.9 20.9 54.5 9.1 2.5 12.1

Table 3. Chemical composition in the selected areas of the windshield glass sample, wt %Tabela 3. Skład chemiczny w wybranych obszarach próbki szkła samo-chodowego, % mas.

Mg Al Si K Ca Fe

Glass_1 2.3 2.8 66.7 1.9 19.8 6.1

Glass_2 2.3 3.1 67.1 1.4 20.0 6.1

1,901,88 1,88

1,91

1,96

1,6

1,65

1,7

1,75

1,8

1,85

1,9

1,95

2

2,05

2,1

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5

750/15+1000/15 800/15+1000/15 850/15+1000/15 950/30 1000/30

Dens

ity, g

/cm

3

Ope

n po

rosit

y, %

Sintering parameters - temperature/time, oC/min

Open porosity Apparent density

Fig. 2. Open porosity and density depending on sintering parameters of G1 series without leather waste additionRys. 2. Porowatość otwarta i gęstość w zależności od parametrów spieka-nia próbki G1 bez dodatku odpadów garbowniczych

NR 3/2016 INŻYNIERIA MATERIAŁOWA MATERIALS ENGINEERING 133

the leather waste addition: increase of density in the granules with as-received leather addition and the opposite effect, if leather was previously milled after sintering at 950°C.

Deviation from the trend points of apparent density of 950°C/30 min specimen in G2 series may indicate one thing — studied samples were not homogenous. Also, these results (ap-parent density of 950°C/30 min specimen in G2 series) is beyond standard deviation and Hampel test have revealed that these result is the outlier.

As the results at 950°C/30 min in G2 series should be rejected, the lowest density in G1 and G3 series was found after sintering at the two-step regime: 850°C/15 min + 1000°C/15 min. In G2 se-ries the lowest density was found after sintering at one-step scheme 1000°C/30 min thus those samples were chosen for SEM examina-tion (Fig. 5.). Taking into account the economical aspect and good results of G2 and G3 series after the two-step sintering scheme, it has been decided to examine the morphology of the samples (Fig. 6.)

Smooth areas could be identified as a glassy phase and in those areas may be closed porosity in the spheroidal form, shown on G1/1000°C/30 min. There is no visible explanation of low apparent density of G2 granules sintered at 1000°C/30 min (Fig. 5. middle right).

A higher amount of porosity and formation of glassy bubbles is visible on the each picture thus it could be the result of the two-step sintering program (Fig. 6). The traces of leather burnout (only in G2 and G3 series) are not clearly visible.

The summary results of the compression test are shown in Fig-ure 7. The largest differences of the compression strength are re-lated to the presence of leather waste addition and the form of it. The lowest values are observed for the granules with addition of the milled leather waste and the values are quite independent on the sintering scheme: less than 6% change of compression strength for various ways of sintering while those variation are close to 15% in case of the leather-free granules. Decrease of the compressive strength was obviously related to the variation of the porosity and

1,86 1,86 1,87

2,09

1,85

1,6

1,65

1,7

1,75

1,8

1,85

1,9

1,95

2

2,05

2,1

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5

750/15+1000/15 800/15+1000/15 850/15+1000/15 950/30 1000/30

Dens

ity, g

/cm

3

Ope

n po

rosit

y, %

Sintering parameters - temperature/time, oC/min

Open porosity Apparent density

Fig. 3. Open porosity and density depending on sintering parameters of G2 seriesRys. 3. Porowatość otwarta i gęstość w zależności od parametrów spie-kania próbki G2

1,72 1,72 1,71

1,65

1,73

1,6

1,65

1,7

1,75

1,8

1,85

1,9

1,95

2

2,05

2,1

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5

750/15+1000/15 800/15+1000/15 850/15+1000/15 950/30 1000/30

Dens

ity, g

/cm

3

Ope

n po

rosit

y, %

Sintering parameters - temperature/time, oC/min

Open porosity Apparent density

Fig. 4. Open porosity and density depending on sintering parameters of G3 seriesRys. 4. Porowatość otwarta i gęstość w zależności od parametrów spie-kania próbki G3

G1 G2 G3

Fig. 5. Morphology of the fractured granules with the lowest apparent density: 850°C/15 min + 1000°C/15 min and 1000°C/30 minRys. 5. Morfologia przełomu granuli o najmniejszej gęstości pozornej: 850°C/15 min + 1000°C/15 min i 1000°C/30 min

850°

C/1

5 m

in +

100

0°C

/15

min

1000

°C/3

0 m

in

134 INŻYNIERIA MATERIAŁOWA MATERIALS ENGINEERING ROK XXXVII

G1 G2 G3

Fig. 6. Morphology of the fractured granules with the lowest density after the two-step sintering: the first step of sintering at 750°C and at 800°CRys. 6. Morfologia przełomów granul o najmniejszej gęstości po dwustopniowym spiekaniu: pierwszy etap spiekania w 750°C i w 800°C

750°

C/1

5 m

in +

100

0°C

/15

min

800°

C/1

5 m

in +

100

0°C

/15

min

33,02 32,89

32,00

28,22

30,20

29,3128,91

27,48

26,55

28,24

27,32 27,4527,95

26,22

27,46

25

26

27

28

29

30

31

32

33

34

750/15+1000/15 800/15+1000/15 850/15+1000/15 950/30 1000/30Com

pres

sive

stre

ngth

, MPa

Sintering parameters, oC/min

G1 G2 G3

Fig. 7. Compresive strength of ceramic granules as a function of sintering parameters of G1, G2, and G3 series with various tanning waste ad-ditionRys. 7. Wytrzymałość na ściskanie ceramicznych granul w funkcji parametrów spiekania próbek G1, G2, G3 o różnej zawartości odpadu garbowni-czego

consequently to the addition of the leather wastes, however some impact on the resultant microstructure is also visible. All the batch-es show the lowest value of the mechanical strength after the one-step sintering schedule at 950°C/30 min but they do not correspond to the highest porosity of the leather-free granules (G1). The results show that addition of the milled leather waste is an effective way in the porosity enlargement (10%) but it is accompanied by the reduc-

tion of the compaction strength in comparison to leather-free prod-uct. The alternative way of the porosity increase, it is to apply the two-step scheme of sintering instead of the leather waste addition. If the leather-free granules were sintered with the two-step regime 850°C/15 + 1000°C/15 min in comparison to the one-step sintering at 1000°C/30 min then 4% improvement of density was observed with only 5% reduction of the compressive strength.

NR 3/2016 INŻYNIERIA MATERIAŁOWA MATERIALS ENGINEERING 135

4. CONCLUSIONTaking into account the fact that the main task of the presented research was to examine the influence of tanning wastes on the physical and mechanical properties of ceramic granules, it could be seen that these wastes could be used as blowing agent. They do not decrease mechanical properties significantly, but they simulta-neously improve physical properties in the meaning of the porosity increase. The very important aspect is a method of the introduction of waste into the mixture, because better physical properties (espe-cially apparent density) is obtained if the milled, cotton-like waste was used. Application of the two-step sintering\\\\ (850°C/15 min + 1000°C/15 min), gives higher compressive strength than in the series with addition of unmilled tanning wastes. The alternative op-tion of the improvement of ceramic granule properties is to apply the two-step sintering way since a rise of porosity does not involve a significant reduction of the compressive strength.

ACKNOWLEDGEMENTS

The study was financially supported under the GEKON2/O5/267917/14/2015 project.

REFERENCES

[1] Franus M., Barnat-Hunek D., Wdowin M.: Utilization of sewage sludge in the manufacture of lightweight aggregate. Environ Monit Assess 10 (2016) 188.

[2] Volland S., Brötz J.: Lightweight aggregates produced from san sludge and zeolitic rocks. Construction and Building Materials 85 (2015) 22÷29.

[3] Yiu Lo T., Cui H., Ali Memon S., Noguchi T.: Manufacturing of sintered lightweight aggregate using high-carbon fly ash and its effect on the me-chanical properties and microstructure of concrete. Journal of Cleaner Pro-duction 112 (2016) 753÷762.

[4] UNE-EN 13055 standard — part 1: Lightweight aggregates for concrete, mortar and grout.

[5] EN 1097 standard — part 6: Tests for mechanical and physical properties of aggregates. Determination of particle density and water absorption.

[6] http://www.teraz-srodowisko.pl/aktualnosci/Polski-sposob-na-re-cykling-470.html.

[7] De’ Gennaro R., Graziano S. F., Cappelletti P., Colella A., Dondi M., Langella A., De’ Gennaro M.: Structural concretes with waste-based light-weight aggregates: From landfill to engineered materials. Environmental Science & Technology 43 (2009) 7123÷7129.

[8] Spratt B. H.: The structural use of lightweight aggregate concrete. Cement And Concrete Association, United Kingdom (1974).

136 INŻYNIERIA MATERIAŁOWA MATERIALS ENGINEERING ROK XXXVII

Wpływ dodatku odpadów garbowniczych oraz parametrów spiekania na fizyczne i mechaniczne

własności ceramicznych granulMarcin Godzierz1*, Paweł Wilkołek1, Gözden Torun2, Tomasz Pawlik1,

Małgorzata Sopicka-Lizer1

1Department of Material Science, Silesian University of Technology, Katowice, Poland 2Middle East Technical University, Ankara, Turkey, *godzierz@gmail.com

Inżynieria Materiałowa 3 (211) (2016) 131÷136DOI 10.15199/28.2016.3.7© Copyright SIGMA-NOT MATERIALS ENGINEERING

Słowa kluczowe: odpady garbownicze, recykling, zarządzanie odpadami, szkło samochodowe, keramzyt.

1. CEL PRACYGłównym celem pracy było zbadanie możliwości zagospodarowa-nia lokalnych odpadów do produkcji lekkich kruszyw. W badaniach uwzględniono odpady takie jak łupek przywęglowy, szkło samo-chodowe zanieczyszczone folią PVB oraz odpady z garbowania skór. Głównym problemem ponownego przetwarzania szkła samo-chodowego jest jego warstwowa struktura — dwie warstwy szkła są przedzielone warstwą polimeru poliwinylobutyralowego, PVB. Mechaniczna separacja pozwala na rozdzielenie materiałów, lecz zanieczyszczenie polimerem dyskwalifikuje szkło do ponownego wytworzenia z nich szyb samochodowych. Wykorzystywane jest obecnie w produkcji waty szklanej, jak również jako wypełniacz do betonu.

Jednym z możliwych rozwiązań zagospodarowania tych od-padów jest produkcja lekkich kruszyw zawierających w składzie recyklat szkła oraz łupek przywęglowy bądź inny materiał glino-krzemianowy. Granule takie mogą być zastosowane w wielu dzie-dzinach, jak architektura, ogrodnictwo czy jako wypełniacz do betonu. Najbardziej restrykcyjnym obszarem zastosowań jest bu-downictwo dróg, co jest związane ze spełnieniem przez granulat szeregu norm.

W pracy autorzy przedstawili wyniki badań wpływu dodatków garbowniczych, sposobu wprowadzenia do mieszanki oraz para-metrów ich spiekania na podstawowe właściwości ceramicznych kruszyw lekkich.

2. MATERIAŁ I METODYKA BADAŃ

Materiały w postaci proszków o średniej średnicy ziarna 0,12 mm zostały odważone w proporcjach masowych określonych w tabeli 1. Próbki łupka przywęglowego pochodziły z kopalni Krupiński (Suszec, Polska), a próbki mielonego szkła oraz odpady garbow-nicze z firmy Kapadora (Żory, Polska). Mieszaniny homogenizo-wano w mieszalniku (Eirich, TR04) i poddano granulacji na talerzu granulacyjnym, w celu uzyskania sferoidalnych granul z dodatkiem 15% masowych wody. Następnie wytworzone agregaty poddano suszeniu i spiekaniu zgodnie z parametrami zamieszczonymi w ta-beli 1, z szybkością nagrzewania 600°C/h.

Właściwości fizyczne, tj.: gęstość pozorną, nasiąkliwość i poro-watość otwartą, wytworzonych granul oznaczono metodą Archime-desa, korzystając ze wzorów (1)÷(3). Morfologię i skład chemiczny bazowych proszków oraz morfologię przełomów granul zbadano za pomocą skaningowego mikroskopu elektronowego (Hitachi S-3400N) z detektorem EDS. Odporność na ściskanie oznaczono

zgodnie z normą UNE-EN 13055-1, korzystając z wzoru (4). Wy-niki odstające zweryfikowano statystycznie za pomocą testu Ham-pela.

3. WYNIKI I ICH DYSKUSJA

Skład chemiczny bazowych proszków łupka przywęglowego (tab. 2) był podobny. Niewielkie odchylenie obserwowane w składzie szkła samochodowego (tab. 3) było na dopuszczalnym poziomie. Obecność pierwiastków takich jak tytan czy żelazo może powodo-wać zmiany koloru granul po spiekaniu.

Związek pomiędzy parametrami spiekania a właściwościami fizycznymi wytworzonych granul przedstawiono na rysunkach 2÷4. Próbka referencyjna uzyskała najmniejszą gęstość pozorną po dwuetapowym spiekaniu, w którym pierwszy etap prowadzo-no w 850°C. Dodatek odpadów garbowniczych zmniejsza gęstość otrzymanych granul. Wpływ ten jest bardziej widoczny, gdy odpa-dy zostały wcześniej przetworzone (rys. 4).

Morfologię przełomów granul pokazano na rysunkach 5 i 6. Gładkie obszary mogą być zidentyfikowane jako faza szklista, w której może występować porowatość zamknięta (rys. 5). Brak jest widocznych śladów spowodowanych wypaleniem skóry obec-nej w odpadach garbownicznych (rys. 6).

Wprowadzenie dodatku odpadów garbowniczych zmniejsza wy-trzymałość na ściskanie granul (rys. 7). Zmniejszenie wytrzymało-ści na ściskanie sięga nawet 21%. Zastosowanie dwustopniowego spiekania zwiększa porowatość granul bez dodatku odpadów gar-bowniczych i nie zmnieszja ich wytrzymałości na ściskanie.

4. PODSUMOWANIE

Wprowadzenie dodatku odpadów garbowniczych poprawia wła-ściwości fizyczne granul (zwłaszcza porowatość). Ważnym czyn-nikiem jest sposób wprowadzenia tych odpadów do mieszanki, po-nieważ zmielone odpady w większym stopniu poprawiają gęstość pozorną granul.

Zastosowanie dwustopniowego spiekania (850°C/15 min + 1000°C/15 min) i zmielonych odpadów garbowniczych daje lepszą wytrzymałość na ściskanie niż w przypadku tych samych parame-trów i odpadów w formie wyjściowej.

Inną możliwością poprawy właściwości granul ceramicznych jest zastosowanie dwustopniowego spiekania, ponieważ zauwa-żalne jest zwiększenie porowatości bez znaczącego zmniejszenia wytrzymałości na ściskanie.