Scrambled Eggs or How Eggshells Become Phosphates | Journal of

Activity Cite This: J. Chem. Educ. 2019, 96, 1443−1448

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Scrambled Eggs or How Eggshells Become Phosphates Diana Potes Vecini,† Shirley C. Jofré,† Florencia B. Pereyra Ríos,† Javier Sartuqui,‡ Paula Messina,‡ M. Belén González,† Melisa Saugo,† Lorena Meier,† Mónica F. Díaz,† and Andrés E. Ciolino*,† †

Departamento de Ingeniería Química (DIQ), Universidad Nacional del Sur (UNS), Avenida Alem 1253, Cuerpo C′, 8000 Bahía Blanca, Argentina ‡ Departamento de Química, INQUISUR-CONICET, Universidad Nacional del Sur (UNS), Avenida Alem 1253, 8000 Bahía Blanca, Argentina Downloaded via UNIV AUTONOMA DE COAHUILA on July 23, 2019 at 07:08:43 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: As part of the training activities planned for the Chemical Engineering degree, in 2016, a group of students from the Chemical Engineering Laboratory course was challenged to face a plausible reuse of discarded eggshells. A straightforward methodology to synthesize phosphates such as calcium pyrophosphate or fluoroapatite among others was developed using commercial phosphoric acid and discarded eggshells as starting materials. Throughout the development of this activity, topics such as recycling and reuse of discarded materials, guided-inquiry instruction, self-learning, and soft-skills development were successfully covered. The strategy proposed in this work encourages students to make connections between science and life and provides an excellent linkage between chemical research and recycling without neglecting those basics required by the official curriculum. KEYWORDS: Upper-Division Undergraduate, Second-Year Undergraduate, Laboratory Instruction, Hands-On Learning/Manipulatives, Qualitative Analysis

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• Oral presentation of the research work: This complementary activity provides a good excuse to evaluate oral skills and learning outcomes. The general organization and some pedagogical aspects of the course are summarized in Figure 1, where the use of guided inquiry, self-learning, and soft-skills development are the goals of the assignment. Over the years, many research topics have been developed (e.g., recycling discarded materials, physicochemical analysis of different products, synthesis of thermoplastic biodegradable polymers, and chemical oscillating reactions), and some of them have already been published.6 This paper presents the results of one of these works as an example.

INTRODUCTION Chemical Engineering Laboratory is a second-year course in the Chemical Engineering degree at the Universidad Nacional del Sur (Argentina). In this course, after the basics of chemistry, undergraduate students are introduced to chemistry-laboratory activities by promoting their own research. This strategy based on self-learning activities is suggested by different pedagogical approaches.1−5 In this sense, throughout the course students must present research projects to be considered by professors. The main learning outcomes of this approach can be summarized as follows: • Development of feasible chemical research: From a topic of their own interest and considering the laboratory and university facilities, students must schedule laboratory activities to reach different goals. The promotion of creativity is the main purpose of this activity. • Establishment of correlations between experimental data and the data available from the scientific literature: Students have to correlate the data obtained in their own tests with those reported in the scientific literature (the Internet, books, and scientific papers). This goal justifies the activities proposed in their schedule and promotes research skills. • Production of a written report of activities, in which the subject under analysis is suitably presented and discussed: This activity promotes scientific communication skills, written production, and vocabulary. © 2019 American Chemical Society and Division of Chemical Education, Inc.

Eggshell Reuse: A Case Study

Discarded materials are an unavoidable consequence of human life and activities. During the last few decades, governments from all over the world have recognized the major consequences derived from deficient waste management, which leads to loss of millions of dollars and environmental and health issues.7−9 Industrial-waste management is a well-established and developed methodology; nowadays, there is a great variety of processes and procedures to deal with waste under government supervision.10−14 In contrast, mixed home garbage presents a Received: June 14, 2018 Revised: May 24, 2019 Published: June 12, 2019 1443

DOI: 10.1021/acs.jchemed.8b00451 J. Chem. Educ. 2019, 96, 1443−1448

Journal of Chemical Education

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Activity

EXPERIMENTAL SECTION

Material Source

White and brown chicken eggshells were used, either separate or mixed. Discarded eggshells were collected at students’ homes and used with or without prior cleaning, depending on the employed methodology (for further details, please refer to the Supporting Information, Synthetic Procedures). Reagents

Commercial phosphoric acid (H3PO4, Anedra, >85% purity) was used as received. Special safety care was taken to use this reagent (please refer to the Supporting Information, Chemical Hazards). Dilutions of this reagent in distilled water were prepared by measuring appropriate amounts of H3PO4 using pipettes and suitable volumetric flasks. Synthetic hydroxyapatite was obtained by a modification of a synthesis already reported,20 using 0.5 M calcium nitrate, 0.3 M phosphoric acid, and 14 M ammonia solutions (for further details, see the Supporting Information, Synthetic Procedures). Typical Synthetic Procedure for Obtaining Phosphates from Eggshells

Different methodologies were evaluated in order to test their efficiencies for yielding phosphate derivatives. The initial step involved crushing the eggshell waste to obtain samples for easy handling (powder form). A first “wet” pathway was tested in most cases, in which eggshells were reacted with H3PO4(aq) solutions; an alternative second “dry” step, in which the former product was heated in a muffle furnace at selected temperatures, was used to synthesize particular phosphates. The resulting products, in powder form, were then subjected to X-ray analysis. X-ray Diffraction

Powder samples were analyzed by X-ray diffraction (XRD) with a Rigaku D-Max III-C X-ray diffractometer with Cu Kα radiation and a graphite monochromator operated at 35 kV and 15 mA at the Departamento de Geologı ́a, Universidad Nacional del Sur.

Figure 1. Chemical Engineering Laboratory: outline of the pedagogical aspects of the course.

Scanning Electron Microscopy (SEM)

Samples were dispersed over 3 M aluminum conductive tape stuck onto stubs by using an air flow. Then, they were coated with gold in an SPI sputter coater and observed in an LEO 40XVP Scanning Electron Microscope (Jena) operated at 10 kV. The topographical characteristics of particles were obtained from a secondary electron signal. The analyses were performed at the Centro Cientı ́fico Tecnológico CONICET-Bahı ́a Blanca.

widespread variety of components (food wastes, metals, different kinds of papers and plastics, and even pharmacological or pathogenic residues), which hinders garbage management;15 thus, the three R’s rule (reduce, reuse, recycle) should be applied.16,17 Under this assumption, the term “waste” relies on the possibility or absence of further uses, depending on the potential value assigned to discarded materials. According to official statistics, 12,177 million eggs were produced in Argentina in 2015, giving an average consumption of 265 eggs per inhabitant.18 Surprisingly, there are neither procedures nor methodologies concerning eggshell management, and a reuse or recycling procedure for this discarded material is not planned. Considering that more than 95% of eggshell is calcium carbonate (CaCO3),19 alternative uses or applications regarding CaCO3 or its derivatives might be reasonably expected. This challenge really deserves pedagogical or learning activities. As part of the training activities planned for the Chemical Engineering degree, in 2016, a group of students from the Chemical Engineering Laboratory course was challenged to find a plausible reuse of discarded eggshells. They had to find an economically feasible potential use for this waste without using sophisticated experimental devices. The project results will be discussed as follows.

In Vitro Degradability Tests under Acidic Conditions

The in vitro degradation behavior of synthesized phosphates under bone-resorption acidic conditions was evaluated by soaking them in an acetic acid/sodium acetate buffer solution (AcOH buffer) with a pH of 4.24.21 Phosphate particles (200 mg) were soaked in 100 mL of AcOH buffer solution at 25 and 36 °C for 3, 12, 16, and 25 days. The degradability of phosphates was estimated from the rate of weight loss (WL, %) according to eq 1:22 WL (%) =

W0 − Wt × 100% W0

(1)

where W0 and Wt are the dry weights of the initial and the degraded specimens at different immersion times, t, respectively. The same procedure was followed at pH 7.4 (phosphate-buffer solution, PBS) as a control. 1444



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Students’ Activities

Scheme 1. Synthetic Pathways Used To Obtain Ca2P2O7 and Ca3(PO4)2a

During the first month of the semester, students were trained in laboratory activities and safety. After this initial period, they started with their own research activities. These activities were scheduled twice a week, 4 h per meeting, according to the experimental advice given in the Supporting Information.

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RESULTS AND DISCUSSION Under a professor’s supervision, experimental activities designed and developed by students can make laboratory tests more attractive and motivational, becoming an excellent aid to stimulate curiosity. Teaching in-depth chemical concepts through learning experiences in which students interact with materials or data sources really helps them observe and understand the world and encourages self-studying and selflearning.23,24 In this sense, the reuse of discarded materials or the development of new ones from cheaper sources, such as domestic wastes or biomass, together with the basics associated with them (synthesis, analysis, and physicochemical properties) offers the possibility to develop chemical principles through an original approach. As was previously pointed out, in this work many phosphate derivatives were obtained by using discarded eggshells and simple synthetic pathways, which involved the reaction of crushed eggshells with commercial phosphoric acid with or without further thermal treatments. Basics from the curriculum, such as material balance, process-flow diagrams, in-excess and limiting reagents, and overall yield, can be easily introduced from these experiments. As an example, Scheme 1 displays the reaction pathways used to synthesize calcium pyrophosphate and tricalcium phosphate. Synthetic procedures are quite simple to apply; many phosphates derivatives, such as calcium pyrophosphate, whitlockite, monetite, tricalcium phosphate, and calcium dihydrogen phosphate monohydrated, were obtained by modifying suitable steps and reaction conditions, as is reported in the Supporting Information of this work. Regarding eggshell sources, students were able to demonstrate that origin (commercial or from family farms) and color (brown or white) did not exert any influence over yield or quality of synthesized phosphates. Consequently, eggshells were used mixed or separate, indistinctly. The X-ray-diffraction spectrum from synthesized calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2·H2O) is displayed in Figure 2. The synthesized phosphate (red line) is in good agreement with the reference spectrum from the software database (green line), although a low content of other impurities (mainly other calcium phosphates, calcite, and calcium hydroxide) can be observed. Similar results were obtained for other phosphate samples (please refer to the Supporting Information). Elemental principles such as chemical analysis, electromagnetic radiation and structure, chemical databases, and crystal-lattice structure were covered from this approach. Figure 3 displays SEM microphotographs from three selected samples: monetite, synthetic hydroxyapatite, and fluoroapatite. Whereas porous structures and coral-like appearances can be easily distinguished in the samples obtained from eggshells, flat surfaces are easily observed for synthetic hydroxyapatite. This fact might be attributable to the evolution of carbon dioxide when phosphoric acid reacts with eggshells, although further tests should be performed in order to check this assumption.

a Numbers inside the violet ellipses correspond to the Ca−P molar ratios.

Figure 2. X-ray-diffraction spectrum for Ca(H2PO4)2·H2O: synthetic phosphate (red line) and reference (green line). The dashed black lines correspond to matching peaks between samples. Note that the x-axis starts at 2θ = 3°.

Because the mineralized phase of bone tissue is made of calcium phosphates, many of its derivatives have been tested as possible substitutes for hard-tissue repair.25 Considering this fact, the in vitro degradability under acidic conditions of selected samples was investigated. Tests were performed in order to verify if synthesized phosphates from eggshells might display potential uses as biodegradable cell-growth scaffolds. In this sense, their stabilities in simulated body fluid (SBF) and under acidic conditions were analyzed. Results from this study are shown in Figure 4. Experimental data were fitted to an asymptotic model: y = a − bcx, where y is WL (%); x is the incubation time; and a, b, and c are constants. The asymptote value (y = a) represents the 1445



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Figure 3. SEM microphotographs for selected phosphate samples: monetite (a), synthetic hydroxyapatite (b) and fluoroapatite (c). The scale bars correspond to 20 μm.

biological units (i.e., enzymes or cells) and consequently did not allow prediction of resorption times in vivo, essential conclusions could be drawn from the in vitro result: calcium phosphate materials do not dissolve under physiological pH fluid conditions, but they are resorbable by osteoclasts in acidic environments.26 Curriculum basics such as pH, solubility and stability, degradation, and kinetics were used to perform these experiments and explain the results. Finally, Table 1 shows a comparison of the costs of some commercial phosphates (suggested prices for Argentina) and the hypothetical prices for the phosphates obtained in this paper. Table 1. Comparative Prices for Commercial and Synthesized Phosphates Cost in 2018 U.S. Dollars for 100 g

Figure 4. Sample stabilities as weight-loss percentage (WL, %) vs time (days) in simulated body fluid (SBF, pH 7.4) and under acidic conditions (pH 4.2). The continuous lines corresponds to the fitting model.

Phosphate

Commerciala

Experimentalb

Ca2P2O7 Ca(H2PO4)2·H2O Ca3(PO4)2

580.80 136.73 36.54

33.04 63.26 32.04

a

Current cost data obtained from the Sigma-Aldrich website for Argentina. bCost calculated considering egg prices, electricity costs, reagents quantities, etc. in 2018.

maximum WL (%) attained at the end of the incubation time. The colored curves correspond to the obtained fitted equations. In acidic conditions, phosphates from eggshells display a higher weight loss at the beginning of the test when compared with that of synthetic hydroxyapatite. After 10 days, fluoroapatite from eggshells exhibits higher stability (lower weight loss). In SBF, phosphates from eggshells seem to be more stable at the beginning. Nevertheless, after 7 days monetite from eggshells starts degrading faster. However, as in the previous case, fluoroapatite from eggshells displays the highest stability. Although a degradation test was carried out in the absence of

As one can clearly observe, costs fall noticeable for the synthesized phosphates obtained from eggshells. As an initial approach, it can be concluded that the procedure involved in this activity might be considered as a real alternative, allowing the reuse of discarded eggshells in the production of phosphate derivatives for commercial purposes. 1446



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Concluding Remarks

The research activities proposed at the Chemical Engineering Laboratory course from the second year of the Chemical Engineering degree at the Universidad Nacional del Sur (Argentina) lay on the basis that challenges will always improve students’ abilities. Consequently, different research projects leading to original achievements were developed throughout the years. Regarding self-learning experiences, students concluded that these activities gave them the opportunity to face different challenges. According to their own experiences, we summarize here some of the collected conclusions:

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Paula Messina: 0000-0001-7533-453X Mónica F. Díaz: 0000-0002-6680-8067 Andrés E. Ciolino: 0000-0002-9482-3889

• “I think that the free atmosphere in which we developed our own research is the most valuable result from this course.”

Notes

The authors declare no competing financial interest.

• “I did really appreciate the nice atmosphere in the laboratory. It was a great pleasure to share this semester with professors and classmates.”

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ACKNOWLEDGMENTS The authors thank the Departamento de Ingenierı ́a Quı ́mica (DIQ) and the Universidad Nacional del Sur (UNS, Bahı ́a Blanca, Argentina) for their financial support. The authors also thank Gabriela Martı ́nez Ipucha and Miguel Nievas for their technical assistance and aid in laboratory tests, Ana Julia Avila for her assistance in the SEM analysis, Leticia Lescano for her assistance in the X-ray analysis, and Alicia Comelli for her assistance in English grammar.

• “It was really amazing to have the opportunity to develop our own research assisted by professors. In addition, it was really exciting to use devices and techniques that are not available at the laboratory and to have the opportunity to collect data from them.” • “Although we chose the research topic, it was really valuable to have always the professor’s assistance. I did really appreciate the freedom to work and the aid given at any moment.”

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REFERENCES

(1) Viera, L.; Ramı ́rez, S.; Fleisner, A. El laboratorio en Quı ́mica Orgánica: una propuesta para la promoción de competencias cientı ́ficotecnológicas. Educ. Quim. 2017, 28, 262−268. (2) Muñ oz-Osuna, F.; Medina-Rivilla, A.; Guillén-Lúgigo, M. Jerarquización de competencias genéricas basadas en las percepciones de docentes universitarios. Educ. Quim. 2016, 27, 126−132. (3) Sella, A. Rethinking practical clases. Nat. Rev. Chem. 2017, 1, 0090. (4) Golde, M. F.; McCreary, C. L.; Koeske, R. Peer Instruction in the General Chemistry Laboratory: Assessment of Student Learning. J. Chem. Educ. 2006, 83, 804−810. (5) Whelan, R.; Zare, R. Teaching Effective Communication in a Writing-Intensive Analytical Chemistry Course. J. Chem. Educ. 2003, 80, 904−906. (6) (a) Caucino, F.; Calderón, R.; Montes Spinsanti, G.; Ciolino, A. Available chlorine in household bleaches by using a new and easy spectrophotometric method. Chem. Educ. 2014, 19, 236−240. (b) Hernando, F.; Laperuta, S.; Van Kuijl, J.; Laurin, N.; Sacks, F.; Ciolino, A. Another Twist of the Foam: An Effective Test Considering a Quantitative Approach to “Elephant’s Toothpaste. J. Chem. Educ. 2017, 94, 907−910. (7) Ikhlayel, M. An integrated approach to establish e-waste management systems for developing countries. J. Cleaner Prod. 2018, 170, 119−130. (8) La basura: consecuencias ambientales y desafı ́os, 2016. Facultad de Ciencias Económicas y Sociales, Universidad Nacional de Mar del Plata. https://eco.mdp.edu.ar/institucional/eco-enlaces/1611-la-basuraconsecuencias-ambientales-y-desafios (accessed May 5, 2019). (9) Singh-Ackbarali, D.; Maharaj, R.; Mohamed, R.; Ramjattan-Harry, V. Potential of used frying oil in paving material: solution to environmental pollution problem. Environ. Sci. Pollut. Res. 2017, 24, 12220−12226. (10) U.S. Environmental Protection Agency Home Page. https:// www.epa.gov/ (accessed May 7, 2019). (11) United Nations Department of Economic and Social Affairs Division for Sustainable Development Goals. https:// sustainabledevelopment.un.org/ (accessed April 22, 2019). (12) Aleluia, J.; Ferrão, P. Characterization of urban waste management practices in developing Asian countries: A new analytical

From the professor’s point of view, the methodology offers the opportunity to explore a nonconventional teaching activity. Advice and recommendations given by professors are relevant, but it is clear that students play the key roles in the project. This activity based on challenges promotes their independence and contributes to the development of many soft skills scarcely considered in current programs, such as cooperation, scheduling of activities, communication strategies, dialogue, and empathy. Furthermore, in the particular case of this paper, the methodology proposed for reusing discarded eggshells offers a true alternative to be considered and explored in order to minimize the environmental impact of eggshells as waste.

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CONCLUSIONS Teaching in-depth chemical concepts through learning experiences in which students interact with materials or data sources helps students observe and understand the world and encourages self-studying and self-learning. In this sense, a laboratory activity focused on minimizing the environmental impact of discarded eggshells was developed. Many phosphate derivatives were obtained through a simple and straightforward method that involves the use of the above-mentioned wastes and commercial phosphoric acid solutions. The chemical natures of the phosphate derivatives were confirmed by X-ray-diffraction, SEM, and biodegradability analyses. Besides the valuable pedagogical aspects of this approach, the strategy employed here might be considered as a useful methodology to minimize the total amount of discarded eggshells.

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Additional material for instructors and students regarding the synthesis of phosphates derived from eggshells (PDF, DOCX)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00451. 1447



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framework based on waste characteristics and urban dimension. Waste Manage. 2016, 58, 415−429. (13) Gestión de Residuos Domiciliarios. Información Legislativa, Ley 25.916, 2004. http://servicios.infoleg.gob.ar/infolegInternet/anexos/ 95000-99999/98327/norma.htm (accessed April 26, 2019). (14) El Senado y Cámara de Diputados de la Provincia de Buenos Aires. Gestión Integral de Residuos Solidos Urbanos, Ley 13592; Ministerio de Gobierno de la Provincia de Buenos Aires. http:// www.gob.gba.gov.ar/legislacion/legislacion/l-13592.html, 2006 (accessed April 29, 2019). (15) Study on hazardous household waste with a main emphasis on hazardous chemicals; European Commission, 2002. http://ec.europa. eu/environment/waste/studies/household.htm (accessed May 10, 2019). (16) Household Hazardous Waste (HHW). U.S. Environmental Protection Agency. https://www.epa.gov/hw/household-hazardouswaste-hhw (accessed May 12, 2019). (17) Rinkesh. The ‘Reduce, Reuse, Recycle’ Waste Hierarchy, 2014. Conserve Energy Future. https://www.conserve-energy-future.com/ reduce-reuse-recycle.php (accessed May 20, 2019). (18) Estadı ́sticas. CAPIA. http://capia.com.ar/estadisticas (accessed May 16, 2019). (19) Valdés Figueroa, J.; Valdés, E. J.; Valdés, M. A. La cáscara de huevo: Desecho o valor agregado para la salud humana y la producción avı ́cola? Proceedings of the Seminario Internacional sobre Nutrición del huevo, La Habana, Cuba, May 23−25, 2007. (20) Koutsopoulos, S. Synthesis and characterization of hydroxyapatite crystals: a review on the analytical methods. J. Biomed. Mater. Res. 2002, 62 (4), 600−612. (21) Matsumoto, T.; Okazaki, M.; Inoue, M.; Yamaguchi, S.; Kusunose, T.; Toyonaga, T.; Hamada, Y.; Takahashi, J. Hydroxyapatite particles as a controlled release carrier of protein. Biomaterials 2004, 25, 3807−3812. (22) Tampieri, A.; Iafisco, M.; Sandri, M.; Panseri, S.; Cunha, C.; Sprio, S.; Savini, E.; Uhlarz, M.; Herrmannsdörfer, T. Magnetic Bioinspired Hybrid Nanostructured Collagen−Hydroxyapatite Scaffolds Supporting Cell Proliferation and Tuning Regenerative Process. ACS Appl. Mater. Interfaces 2014, 6, 15697−15707. (23) Lunetta, V.; Hofstein, A.; Clough, M. Learning and teaching in the school science laboratory: An analysis of research, theory, and practice. In Handbook of research on science education; Lederman, N., Abel, S., Eds.; Routledge: New York, NY, 2007; pp 393−441. (24) Abrahams, I.; Millar, R. Does Practical Work Really Work? A study of the effectiveness of practical work as a teaching and learning method in school science. Int. J. of Sci. Educ. 2008, 30, 1945−1969. (25) Dorozhkin, S. V. Bioceramics of Calcium Orthophosphates. Biomaterials 2010, 31, 1465−1485. (26) Baron, R.; Neff, L.; Louvard, D.; Courtoy, P. J. Cell-mediated Extracellular Acidification and Bone Resorption: Evidence for a Low pH in Resorbing Lacunae and Localization of a 100-kD Lysosomal Membrane Protein at the Osteoclast Ruffled Border. J. Cell Biol. 1985, 101, 2210−2222.

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Scrambled Eggs or How Eggshells Become Phosphates | Journal of

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