DOI:10.14311/APP.2021.30.0063 Acta Polytechnica CTU Proceedings 30:63–68, 2021 © Czech Technical University in Prague, 2021 available online at http://ojs.cvut.cz/ojs/index.php/app INFLUENCE OF EARTH COMPOSITION ON ADSORPTION CAPACITY OF METHYLENE BLUE DYE Tereza Plaček Otcovská∗, Barbora Mužíková, Pavel Padevět Czech Technical University in Prague, Faculty of Civil Engineering, Department of Mechanics, Thákurova 7, 166 29 Prague 6, Czech Republic ∗ corresponding author: tereza.otcovska@fsv.cvut.cz Abstract. Final properties of unfired earth are influenced by composition of earth mixtures. Methy- lene blue test could be useful method for analysis of earth composition. This would facilitate of de- signing unfired earth building structures because composition of natural earth is various. Principle of methylene blue test is measure of amount of adsorbed methylene blue dye by clay. The essential component of earth mixtures is clay because clay fulfils a function of binder. Experimental measure of adsorption capacity of individual kind of clay is described in this paper. Adsorption capacity was investigated in montmorillonite, kaolinite, illite-kaolinite and illite clays. The obtained results show that the adsorption capacity of clays is significantly different. Keywords: Adsorption capacity, clay, methylene blue dye, methylene blue test. 1. Introduction Unfired earth is a building material which had be- come minor in 2nd half of 20th century because of modern building materials such as steel or concrete have have become readily available. Nowadays, the unfired earth is getting back to forefront of interest for its properties that fit into principles of a sustainable building and improving microclimate in interiors [1– 4]. Earth mixture is a basic material for production of unfired earth constructions. Uncertain composi- tion of natural earth is the main reason why using of unfired earth in construction is complicated. It is be- cause of final properties of unfired earth constructions are greatly influenced by the earth composition [4, 5]. Methylene blue test is described in standard ČSN EN 933-9. Methylene blue test could be a good method for analysis of the earth composition. Basic idea of this research is that every kind of clay (main com- ponent of earth mixture) has different adsorption ca- pacity of methylene blue dye. If adsorption capacity of individual clay is known, this test could be a good method for analysing earth composition [5–8]. This paper is focused on experimental determina- tion of adsorption capacity of clay by methylene blue test. Four kinds of clay were investigated (montmo- rillonite, kaolinite, illite-kaolinite, illite). Minimum number of measurements for each investigated ma- terial was 3. The result of this research is the de- termination of the adsorption capacity of mentioned clay and determination of dependence between the amount of adsorbed dye and amount of clay in earth. 2. Description of Experimental Measurement A burette, a beaker, a filter paper, a magnetic stirrer and a glass rod are basic equipment for methylene blue test. Solution of methylene blue dye (methylth- ioninium chloride - C16H18ClN3S) by concentration 10 g/l is used. Earth samples are produced from earth and distilled water. Methylene blue solution is inserted into earth sample by a burette (Fig. 1). Figure 1. An earth sample with methylene blue so- lution. Earth sample with the solution is stirred on a mag- netic stirrer 1 minute for each 1 millilitre of solution. After that a drop of the mixture is placed on a fil- ter paper. This process is repeated and each sample drop with increasing amount of methylene blue solu- tion is marked (Fig. 2). Methylene blue test is fin- ished when a blue ring spreads around a drop sample (Fig. 3) because clay has already adsorbed the max- imum amount of methylene blue dye. Amount of dye adsorbed depends on a kind and amount of clay. Amount of dye adsorbed is deter- mined by the Eq. 1. Amount of dye adsorbed is defined as the weight amount of dye in grams that is adsorbed by 1 kilogram of test material. 63 http://dx.doi.org/10.14311/APP.2021.30.0063 http://ojs.cvut.cz/ojs/index.php/app T. Plaček Otcovská, B. Mužíková, P. Padevět Acta Polytechnica CTU Proceedings Figure 2. A drop of the mixture is placed on a filter paper. Figure 3. A result of methylene blue test. MM B = ms.mM B,1ml.1000 MES (1) 3. Investigated Material Earth samples are produced in laboratory from sand, clay powder (Fig. 5) and distilled water. A grain curve of sand is shown in Fig. 4. 4 kinds of clay are tested (montmorillonite, kaolinite, illite-kaolinite, illite). Industrial marking which is used in this paper too and chemical composition are shown in Table 1. Earth samples are suspension of clay and sand in distilled water. Clay and sand are mixed in pre- scribed ratio (Table 2) and it is solid part of earth Figure 4. Grain curve of sand. Figure 5. Clay powder. samples. This solid part is always 15 g. Distilled wa- ter is always 75 g. Distilled water serves as a medium for adsorption. 4 clay/sand ratios are used for each kind of clay. 54 measurements are performed on 16 types of samples. The minimum number of measurements for each sam- ple type was 3. Table 2 shows composition of sam- ples, amount of components and a number of mea- surements. Mark of a sample contains mark of clay and per- centage number of clay in a sample. Table 2 shows mark of samples. 4. Adsorption Capacity of Clay Adsorption capacity is very different for each kind of clay. The highest adsorption capacity is found for montmorillonite clay (GEM), lower for kaolinite clay (B4), even lower for illite-kaolinite clay (KR) and the lowest for illite clay (AGL). Table 3 and Figure 6 shown results from methylene blue test. Maximum average amount of adsorbed dye 88 g/kg (σ = 3.8 g/kg) is calculated for GEM-100. The clay 64 vol. 30/2021 Earth Composition and MBD adsorption capacity Kind of Mark of AMM SIO2 AL2O3 FE2O3 TIO2 CAO MGO NA2O K2O clay clay [ml/g] [%] [%] [%] [%] [%] [%] [%] [%] Montmorillonite GEM 17 50.51 31.2 3.37 0.86 0.4 0.42 0.08 1.62 Kaolinite B4 4.5 58.13 24.29 4.7 1.21 0.13 0.5 0.5 3.96 Illite-kaolinite KR 8.4 59.31 24.71 3.37 1.09 0.19 0.4 0.3 2.82 Illite AGL 29.4 56.57 18.4 9.72 1.16 1.12 2.54 0.18 2.91 Table 1. Chemical composition of used clays. Clay Mark of sample Clay/sand ratio Amount of distilled water Amount of clay Amount of sand Number of measurements [−] [g] [g] [g] [−] Montmorillonite GEM-100 100/0 75 15 0 3 GEM-75 75/25 75 11.25 3.75 4 GEM-50 50/50 75 7.5 7.5 3 GEM-25 25/75 75 3.75 11.25 5 Kaolinite B4-100 100/0 75 15 0 3 B4-75 75/25 75 11.25 3.75 3 B4-50 50/50 75 7.5 7.5 3 B4-25 25/75 75 3.75 11.25 3 Illite- KR-100 100/0 75 15 0 3 kaolinite KR-75 75/25 75 11.25 3.75 3 KR-50 50/50 75 7.5 7.5 4 KR-25 25/75 75 3.75 11.25 5 Illite AGL-100 100/0 75 15 0 3 AGL-75 75/25 75 11.25 3.75 3 AGL-50 50/50 75 7.5 7.5 3 AGL-25 25/75 75 3.75 11.25 3 Table 2. Clays used for experimental measurements, their designation and composition. Figure 6. Amount of adsorbed methylene blue dye by clays. contained in a sample is montmorillonite and clay is 100 % of the solid part of a sample. On the contrary, the lower value of adsorbed dye 4.6 g/kg (σ = 0 g/kg) is determined for AGL-25 sample. The clay contained in AGL-25 sample is illite and clay is 25 % of the solid part of a sample. Compared to montmorillonite clay, the adsorp- tion capacity of kaolinitic clay is 34.3 % lower (e.i. 65.7 %), illite-kaolinite is 63.5 % lower(e.i. 36.5), il- lite is 78.2 % lower (e.i. 21.8 %). Figure 6 shows that the same trend was also observed for the sam- ples with a clay content of 75 %, 50 % and 25 %. The percentage difference in adsorption capacity for all clays is given in Table 4. Obtained values of adsorbed dye by individual sam- ples are interpolated by a linear regression curve. It can be seen from Figure 7 that dependence of ad- sorption on amount of clay is linear for all kinds of clays. 4.1. Confidence Intervals From the obtained adsorption values, limits of the confidence interval L1 and L2 were calculated by Eq. 2 (α = 0.05). Calculated confidence interval limits are given in Table 5. L1,2 = x ± σ · tk√ n (2) Confidence interval is calculated for all measure- ment values of adsorption dye. Figure 8 shows depen- dence between amount of adsorbed dye and amount 65 T. Plaček Otcovská, B. Mužíková, P. Padevět Acta Polytechnica CTU Proceedings Clay Mark of sample Average amount of adsorbed dye Standard deviation Relative standard deviation [g/kg] [g/kg] [%] Montmorillonite GEM-100 88.0 3.8 4.3 GEM-75 65.3 5.6 8.6 GEM-50 41.8 6.9 16.4 GEM-25 17.3 3.5 20.1 Kaolinite B4-100 57.9 2.0 3.5 B4-75 44.5 1.7 3.7 B4-50 29.3 3.4 11.6 B4-25 14.5 0.7 4.5 Illite- KR-100 32.1 2.1 6.6 kaolinite KR-75 25.5 3.6 14.2 KR-50 18.0 1.4 7.6 KR-25 8.7 1.1 12.4 Illite AGL-100 19.2 0.6 3.3 AGL-75 13.9 1.3 9.5 AGL-50 9.5 1.0 10.7 AGL-25 4.6 0.0 0.0 Table 3. Results obtained by methylene blue test. Amount of adsorbed dye GEM B4 KR AGL Amount of clay [g/kg] [g/kg] [g/kg] [g/kg] in a sample [%] [%] [%] [%] 15.00 g / 100 % 88.0 57.9 32.1 19.2100 65.7 36.5 21.8 11.25 g / 75 % 65.3 44.5 25.5 13.9100 68.1 39.1 21.2 7.50 g / 50 % 41.8 29.3 18.0 9.5100 70.0 43.0 22.6 3.75 g / 25 % 17.3 14.5 8.7 4.6100 84.0 50.4 26.7 Table 4. Comparison of the amount of adsorbed dye. of clay in sample with confidence interval area for each clay. The curves of adsorption are created by combining the calculated values of adsorption for amount of clay in samples 25 %, 50 %, 75 % and 100 %. Extreme values of confidence interval area are join between the calculated values of the confidence interval limits L1, L2. It can be seen from Figure 8, that illitic clay (AGL) and illitic-kaolinitic clay (KR) can be well distin- guished from each other in an amount of clay in solid part at least 25 %. Confidence intervals of montmorillonite (GEM) and kaolinite (B4) clay overlap when clay content is 25-50 %. Based on Figure 8, it can be assumed that the methylene blue test is applicable for amounts of 75 % and higher in the case of montmorillonite and kaolinitic clays. 5. Conclusions Methylene blue test is applicable to diagnose compo- sition of earth. Each of the investigated clays (mont- morillonite, kaolinite, illite-kaolinite, illite) adsorbs a different amount of methylene blue dye. Montmoril- lonite is characterized by the largest adsorption ca- pacity. The adsorption capacity of methylene blue dye decreases for clays in the order: kaolinite, illite- kaolinite and illite (Fig. 6). Furthermore, it was experimentally determined that the amount of adsorbed dye is directly depen- dent on the amount of clay in earth (Fig. 7). Using confidence intervals, it was determined that illitic and illitic-kaolinitic clays can be determined by methylene blue test in earth in quantities from 25 %. Montmorillonite and kaolinite clay can be determined by methylene blue test in earth in amounts from 75 % (Fig. 8). 66 vol. 30/2021 Earth Composition and MBD adsorption capacity Figure 7. Amount of adsorbed methylene blue dye by clay. Figure 8. Confidence intervals of clays. 67 T. Plaček Otcovská, B. Mužíková, P. Padevět Acta Polytechnica CTU Proceedings Clay Mark of sample Confidence interval [g/kg] L1 L2 G E M GEM-25 13.31 21.29 GEM-50 29.18 54.43 GEM-75 57.54 73.16 GEM-100 81.01 95.01 B 4 B4-25 13.31 15.73 B4-50 23.04 35.49 B4-75 41.45 47.53 B4-100 54.16 61.57 K R KR-25 7.49 9.96 KR-50 16.10 19.88 KR-75 18.84 32.20 KR-100 28.23 36.02 A G L AGL-25 4.62 4.62 AGL-50 7.61 11.31 AGL-75 11.44 16.29 AGL-100 18.01 20.32 Table 5. Calculated confidence interval limits of ad- sorption for clays (α = 0.05). List of symbols M B Methylene blue MM B Amount of MB dye absorbed [g/kg] ms Amount of methylene blue solution [g] mM B,1ml Amount of methylene blue in 1 g of methylene blue solution [g/g] MES Amount of tested material [g] L1,2 Limits of the confidence interval [g/kg] x Arithmetic mean [g/kg] σ Standard deviation [g/kg] tk Student’s T critical values n Number of measurement Acknowledgements The financial support of this experiment by the Czech Science Foundation (GAČR project NO. 18-10884S) and Faculty of Civil Engineering, Czech Technical University in Prague (SGS project No. SGS19/148/OHK1/3T/11) is gratefully acknowledged. References [1] P. Jaquin, C. Augarde. Earth building : History, science and conservation. Report, Bracknell : IHS BRE Press, 2012. [2] Agenda 21 - United Nations Environment Programme (UNEP). http://www.unep.org. [3] ČSN. ČSN 1168-1939 - PODMÍNKY PRO ZEDNICKÉ A PŘIDRUŽENÉ PRÁCE POZEMNÍCH STAVEB, 1951. [4] G. Minke. Building With Earth. Ökobuch Verlag, Staufen, 2006. [5] I. Žabičková. Hliněné stavby. Era 21, Brno, 2002. [6] P. Walker. Rammed Earth: Design and Construction Guidelines. IHS BRE Press, Watford, 2010. [7] Z. Weiss. Jílové minerály : jejich nanostruktura a využití. Karolinum,, vyd. 1. edn., 2005. [8] Evropský výbor pro normalizaci. ČSN EN 933-9, Tests for geometrical properties of aggregates – Part 9: Assessment of fines – Methylene blue test 2013. 68