Eggshells are among the emerging hazardous waste from the food processing industry. This work sought to valorize waste guinea fowl eggshells. Guinea fowl eggshells (GFEs) were evaluated in the production of CaO for chemical and industrial application. The functionality, thermal stability, elemental composition, phase distribution and surface morphology properties of uncalcined GFEs and GFEs calcined at 700°C, 800°C, 900°C, 1000°C and 1100°C were systematically studied by FTIR, TGA, XRF, XRD and SEM-EDX respectively. The elemental analysis revealed Ca as the main element in the GFEs. The uncalcined GFEs showed intense peaks that corresponded to calcite (CaCO 3) phases. These transformed into Ca(OH) 2 as the temperature of calcination increased and finally to CaO in the FTIR analysis. In the XRD diffractograms, the main peaks at 2 θ values were 29.466° for the uncalcined GFESs and at 37.377° for the sample treated at 1100°C. The phases were confirmed as CaO when compared with JCPDS files. Using the Scherer equation, the CaO crystallite size for the sample calcined at 1100°C was found to be 50.68 nm along the (2 0 0) orientation. All the samples showed multi-step decomposition patterns in the thermogravimetric analyses (TGA), with weight loss of up to 47% for the uncalcined GFEs sample, which was mainly due to the transformation of the calcite (CaCO 3) phase to CaO by removal of bound water, organic components, and CO 2. Samples calcined at 1100°C showed mainly CaO phases in XRD analyses and fairly stable with 7% loss in weight after treatment at 800°C. SEM images of samples calcined at 900°C were irregular compared to samples treated at 1100°C. EDX data revealed that the surface structure was 100% calcium and oxygen. GFEs are a potential source of pure calcium oxide for various industrial uses.
To guarantee sustainable development, there is the need to consider valorization of waste to ensure zero waste standards. Again, in the wake of “green chemistry” there is the need to develop new sustainable materials that are reusable, recyclable and green [
There has therefore been a shift in attention in research into developing new clean technology and more environmentally friendly compounds to substitute the use of harmful reagents and catalysts in the chemical industry [
The functional characteristics of eggshells are currently the object of intense research [
This study explored for the first time the synthesis and characterization of guinea fowl eggshells (GFEs) as an alternative source of CaO. The focus of the work was to thoroughly characterize and compare the functional and chemical properties of untreated GFEs, synthesized CaO (from the calcined GFEs) and commercially acquired CaO using Fourier Transform infra-red spectroscopy (FT IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and energy dispersive X-ray fluorescence spectroscopy (EDXRF).
Commercial CaCO3 and CaO (95%) of analytical grade were purchased from BDH, Labo Chemie (Mumbai, India). Waste guinea fowl eggs shells were collected from domestic waste, over a period of four weeks from the Sunbrungu area in the Upper East Region of Ghana.
The eggshells were washed with running water and rinsed in warm water to reduce organic materials. The sample was oven dried at 105˚C for 2 hours and crushed in a stainless steel grinder. The GFEs were calcined by heating at elevated temperatures in the range of 700˚C - 1100˚C with 2 hours hold time. The calcined samples were stored in capped glass vials to avoid reaction with air and moisture.
The functional groups of GFEs and calcined samples were identified by Fourier transform infrared (FTIR) analyses using a Perkin Elmer spectrum II (94133) in ATR mode, with NIOS2 at a resolution of 4 and 24 scans, at 400 - 4000 cm−1 and with a resolution of 1 cm−1. Background spectra were obtained before sampling. The crystalline phases and qualitative composition of the samples were studied by X-ray diffraction (XRD) using an X-ray tube with Cu kα radiation (Λ = 1.5412) source accelerated at 40 mA and 40 kV and a graphite secondary beam monochromator. The radiation was in the range of 10 - 80 2θ angle. The intensity was measured by continuous scanning with a step size of 0.033 and measuring time of 100 s. The phases were identified by comparing with Joint Committee on Powder Diffraction Standard (JCPDS) files. The thermal stability and weight loss of the uncalcined and calcined samples were evaluated by thermo-gravimetric analyses (TGA) (Mettler Toledo) in a temperature range of 30˚C - 1000˚C at a heating rate of 10˚C min−1 under nitrogen atmosphere and the samples held at 1000˚C for 10 minutes. Elemental composition analysis was investigated by using a hand held XRF instrument. Scanning electron microscopy (SEM) images were taken at 2000x and 10000x magnification. EDX was used to characterize the elemental composition of the surface structure of the GFESs samples. The loss in ignition of the GFEs samples was determined by calculation using the relationship:
The calcination process was accompanied by a series of colour changes, from light brown to grey and then white as the temperature increased from 700˚C to 1100˚C. The grey colour transformation observed at both 700˚C and 800˚C was due to the combustion of egg membranes and other organic components reducing the sample to mainly calcite (CaCO3). Formation of Lime (CaO), a white crystalline material produced from the decomposition of CaCO3 at elevated temperatures was confirmed above 800˚C with the formation of white samples. These transformations during calcination accounted for the corresponding weight loss in the samples (
Thermal decomposition of GFES-CaO was investigated by TGA (
Temperature treatment (˚C) | Loi (%) | Colour of sample |
---|---|---|
105 (Uncalcined GFESs) | 0.98 ± 0.05 | LB |
700 | 12.93 ± 0.67 | DG |
800 | 46.58 ± 0.15 | LG |
900 | 47.65 ± 0.01 | W |
1000 | 47.73 ± 0.19 | W |
1100 | 48.48 ± 0.24 | W |
Loi―weight loss on ignition, LB―light brown, DG―dark grey, LG―light grey, W―white.
beyond 1000˚C it increases sintering effect. This phenomenon reduces the catalytic activity of CaO due to reduced surface area. This could have accounted for the slight increase in masses observed in the TGA analysis of the samples after 900˚C. Optimum temperature for calcination of was chosen above 800˚C in earlier works reported by Birla et al., [
XRD patterns gave information on the crystalline phases in the samples. The XRD patterns of the calcined and untreated GFEs are presented in
to phase transformation of calcite to lime. However, lime could have absorbed atmospheric moisture resulting in the formation of Ca(OH)2. The major peaks associated with CaCO3 reduced in intensity at elevated temperatures from 800˚C to 1000˚C. At 1100˚C calcite peaks were absent; sharp peaks of CaO phases were visible at 2θ values of 32.23˚C, 37.37˚C, 53.87˚C, 64.37˚C and 67.60˚C, which corresponded to the (111), (200), (220), (311) and (222) planes. In previous studies by Cree and Rutter [
Fourier transform spectra were used to confirm the functional groups present in the GFE-CaO (
that less intense peaks of -C-O groups were observed as temperature increased. Also similar trends were reported in previous studies by Cree and Rutter [
The elemental composition of the samples was determined by XRF data in
The morphology of the GFE-CaO particles was observed by Scanning Electron Microscopy (SEM).
The images showed irregular clusters of spherical particles for both samples calcined at 900˚C and 1100˚C at high magnification (10,000×) (
SAMPLE | Ba (% w/w) | Ca (% w/w) | Fe (% w/w) | K (% w/w) | S (% w/w) | Sr (% w/w) |
---|---|---|---|---|---|---|
Commercial CaO | 60.35 ± 0.38 | 0.07 ± 0.04 | 0.02 ± 0.00 | |||
UGFEs | 0.10 ± 0.00 | 47.91 ± 1.91 | 0.04 ± 0.01 | 0.18 ± 0.01 | 0.76 ± 0.03 | 0.13 ± 0.01 |
700˚C | 0.12 ± 0.01 | 61.86 ± 1.32 | 0.05 ± 0.01 | 0.10 ± 0.01 | 0.15 ± 0.01 | 0.21 ± 0.00 |
800˚C | 0.19 ± 0.01 | 70.83 ± 1.86 | 0.05 ± 0.02 | 0.11 ± 0.02 | 0.15 ± 0.02 | 0.32 ± 0.02 |
900˚C | 0.19 ± 0.02 | 71.04 ± 0.96 | 0.06 ± 0.02 | 0.08 ± 0.02 | 0.15 ± 0.03 | 0.31 ± 0.01 |
1000˚C | 0.19 ± 0.00 | 73.70 ± 0.73 | 0.04 ± 0.02 | 0.06 ± 0.02 | 0.14 ± 0.05 | 0.34 ± 0.01 |
1100˚C | 0.20 ± 0.00 | 71.65 ± 0.67 | 0.06 ± 0.03 | 0.06 ± 0.03 | 0.16 ± 0.02 | 0.34 ± 0.01 |
Commercial CaCO3 | 55.48 ± 0.96 | 0.07 ± 0.04 | 0.04 ± 0.00 | 0.15 ± 0.02 | 0.03 ± 0.00 |
UGFEs: unclaimed guinea fowl egg shells, LOD: lower than detectable concentration.
Sample | Element | Weight (%) |
---|---|---|
900˚C | calcium | 55.50 |
900˚C | oxygen | 44.50 |
Total | 100 | |
1100˚C | calcium | 58.64 |
1100˚C | oxygen | 41.36 |
Total | 100 |
In this study, the most suitable temperature for the conversion of waste guinea fowl eggshells (GFEs) to calcium oxide (CaO) was investigated. The characterization techniques employed confirmed that GFEs were mainly calcite. Both FTIR and XRF data indicated the presence of CaO in all the calcined GFE samples. However, CaO crystallite phases were more prominent in the XRD analysis of the sample calcined at 1100˚C. SEM showed bulky particles, which were more regular in the sample calcined at 1100˚C. EDX data also confirmed the surface elemental composition of the calcined GFE samples at 900˚C and 1100˚C to be 100% calcium and oxygen. Therefore, at temperatures above 900˚C and a hold time of 2 hours GFEs were successfully converted to pure CaO. The results suggest that GFEs are promising sources of pure bio-based CaCO3 for CaO production with potential chemical and industrial applications.
M-M. Pedavoah is grateful for the support of Michael B. Mensah, Selina A. Saah and the Schools of Materials and Chemistry, University of Manchester for the assistance during the characterization of the synthesized CaO.
Pedavoah, M.-M., Badu, M., Boadi, N.O. and Awudza, J.A.M. (2018) Green Bio-Based CaO from Guinea Fowl Eggshells. Green and Sustainable Chemistry, 8, 208-219. https://doi.org/10.4236/gsc.2018.82015